Appendix: Flow rules for 1999-2000

Integrated monitoring of environmental flows State summary report 1998-2000

Compiled by: Bruce Chessman Principal contributors: Estelle Avery, Chris Burton, Patrick Driver, Sean Dwyer, Tracy Fulford, Sean Grimes, Ivor Growns, Lorraine Hardwick, David Hohnberg, Chris Howden, Renée Kidson, Peter Lloyd-Jones, James Maguire, Warwick Mawhinney, Lisa Thurtell, Suzanne Unthank and Doug Westhorpe.

NSW Department of Infrastructure, Planning and Natural Resources

Further information about the IMEF program is available on the Internet and can be located by using the terms ‘IMEF’ and ‘NSW’ in a search engine.

© Crown Copyright 2003 Printed December 2003 NSW Department of Infrastructure, Planning and Natural Resources www.dipnr.nsw.gov.au ISBN 0734 754 06X (print version) ISBN 0734 754 078 (web version) ISBN 0734 754 094 (compact disc version) Disclaimer While every reasonable effort has been made to ensure that this document is correct at the time of publication, the State of New South Wales, its agents and employees, disclaim any and all liability to any person in respect of anything or the consequences of anything done or omitted to be done in reliance upon the whole or any part of this document.

Contents 1.

OVERVIEW AND PRINCIPAL FINDINGS .............................................................................................1 1.1. 1.2. 1.3. 1.4. 1.5. 1.6. 1.7.

2.

BACKGROUND TO THE PROGRAM .....................................................................................................7 2.1. 2.2. 2.3. 2.4.

3.

CONTEXT AND OBJECTIVES ...........................................................................................................7 SCOPE AND LIMITATIONS .............................................................................................................10 PROGRAM DESIGN ..........................................................................................................................10 PROGRAM IMPLEMENTATION .....................................................................................................14

STUDY AREAS ..........................................................................................................................................15 3.1. 3.2. 3.3. 3.4. 3.5. 3.6. 3.7.

4.

IMEF: INTEGRATED MONITORING OF ENVIRONMENTAL FLOWS ........................................1 ALGAL AND CYANOBACTERIAL BLOOMS ..................................................................................2 RIVER BIOFILMS ................................................................................................................................3 RIVER ORGANIC CARBON ...............................................................................................................3 WETLAND BIODIVERSITY ...............................................................................................................4 RIVER FISH ..........................................................................................................................................4 CONCLUSIONS AND FUTURE DIRECTIONS .................................................................................5

BARWON-DARLING VALLEY ........................................................................................................15 GWYDIR VALLEY ............................................................................................................................15 HUNTER VALLEY.............................................................................................................................16 LACHLAN VALLEY ..........................................................................................................................17 MACQUARIE VALLEY.....................................................................................................................18 MURRUMBIDGEE VALLEY ............................................................................................................18 NAMOI VALLEY ...............................................................................................................................19

WATER REGIMES....................................................................................................................................21 4.1. INTRODUCTION ...............................................................................................................................21 4.2. METHODS ..........................................................................................................................................21 4.3. RESULTS ............................................................................................................................................23 4.3.1. Rainfall ............................................................................................................................................23 4.3.2. Barwon-Darling River system..........................................................................................................25 4.3.3. Gwydir River system ........................................................................................................................25 4.3.4. Hunter River system (including Glennies Creek system) .................................................................25 4.3.5. Lachlan River system .......................................................................................................................26 4.3.6. Macquarie River system...................................................................................................................26 4.3.7. Murrumbidgee River system ............................................................................................................27 4.3.8. Namoi River system .........................................................................................................................27 4.4. DISCUSSION ......................................................................................................................................27

5.

RIVER PHYTOPLANKTON ....................................................................................................................47 5.1. INTRODUCTION ...............................................................................................................................47 5.2. BARWON-DARLING VALLEY ........................................................................................................48 5.2.1. Sites and methods ............................................................................................................................48 5.2.2. Results..............................................................................................................................................48 5.3. HUNTER VALLEY.............................................................................................................................51 5.3.1. Sites and methods ............................................................................................................................51 5.3.2. Results..............................................................................................................................................51 5.4. LACHLAN VALLEY ..........................................................................................................................53 5.4.1. Sites and methods ............................................................................................................................53 5.4.2. Results..............................................................................................................................................54 5.5. NAMOI VALLEY ...............................................................................................................................57 5.5.1 Sites and methods ............................................................................................................................57 5.5.2. Results..............................................................................................................................................58 5.6. DISCUSSION ......................................................................................................................................58

6.

RIVER BIOFILMS AND MACROINVERTEBRATES.........................................................................63 6.1.

INTRODUCTION ...............................................................................................................................63

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6.2. HUNTER VALLEY.............................................................................................................................64 6.2.1. Sites and methods ............................................................................................................................64 6.2.2. Results..............................................................................................................................................66 6.3. MURRUMBIDGEE VALLEY ............................................................................................................69 6.3.1. Sites and methods ............................................................................................................................69 6.3.2. Results..............................................................................................................................................72 6.4. DISCUSSION ......................................................................................................................................76 7.

RIVER ORGANIC CARBON AND ZOOPLANKTON..........................................................................81 7.1. 7.2 7.3.

8.

INTRODUCTION ...............................................................................................................................81 SITES AND METHODS .....................................................................................................................81 RESULTS AND DISCUSSION...........................................................................................................82

WETLAND BIODIVERSITY....................................................................................................................85 8.1. INTRODUCTION ...............................................................................................................................85 8.2. GWYDIR VALLEY ............................................................................................................................85 8.2.1. Sites and methods ............................................................................................................................85 8.2.2. Results..............................................................................................................................................87 8.3. LACHLAN VALLEY ..........................................................................................................................92 8.3.1. Sites and methods ............................................................................................................................92 8.3.2. Results..............................................................................................................................................93 8.4. MACQUARIE VALLEY...................................................................................................................101 8.4.1. Sites and methods ..........................................................................................................................101 8.4.2. Results............................................................................................................................................102 8.5. MURRUMBIDGEE VALLEY ..........................................................................................................106 8.5.1. Sites and methods ..........................................................................................................................106 8.5.2. Results............................................................................................................................................107 8.6. NAMOI VALLEY .............................................................................................................................110 8.6.1. Sites and methods ..........................................................................................................................110 8.6.2. Results............................................................................................................................................110 8.7. DISCUSSION ....................................................................................................................................113

9.

RIVER FISH .............................................................................................................................................117 9.1. 9.2. 9.3. 9.4.

10.

INTRODUCTION .............................................................................................................................117 SITES AND METHODS ...................................................................................................................117 RESULTS ..........................................................................................................................................119 DISCUSSION ....................................................................................................................................123 REFERENCES .....................................................................................................................................125

APPENDIX: FLOW RULES FOR 1999-2000 ................................................................................................135 BARWON-DARLING VALLEY ............................................................................................................................135 GWYDIR VALLEY .............................................................................................................................................135 HUNTER VALLEY .............................................................................................................................................135 LACHLAN VALLEY ...........................................................................................................................................136 MACQUARIE VALLEY .......................................................................................................................................136 MURRUMBIDGEE VALLEY ................................................................................................................................137 NAMOI VALLEY................................................................................................................................................138 MAPS

foldouts facing page 140

MAP 1: STUDY AREAS 1998–2000 MAP 2: BARWON–DARLING STUDY SITES 1998–2000 MAP 3: GWYDIR STUDY SITES 1998–2000 MAP 4: HUNTER STUDY SITES 1998–2000 MAP 5: LACHLAN STUDY SITES 1998–2000 MAP 6: MACQUARIE STUDY SITES 1998–2000 MAP 7: MURRUMBIDGEE STUDY SITES 1998–2000 MAP 8: NAMOI STUDY SITES 1998–2000

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Acknowledgments Compiled by: Bruce Chessman Principal contributors: Estelle Avery, Chris Burton, Patrick Driver, Sean Dwyer, Tracy Fulford, Sean Grimes, Ivor Growns, Lorraine Hardwick, David Hohnberg, Chris Howden, Renée Kidson, Peter Lloyd-Jones, James Maguire, Warwick Mawhinney, Lisa Thurtell, Suzanne Unthank and Doug Westhorpe. In addition to the compiler and principal contributors, many people and organisations were involved in the IMEF program and production of this report, often in more than one capacity. They are gratefully acknowledged below, and listed according to their principal roles. Program coordinators: Marie Egerrup, Simon Mitrovic, Sarah Rish. Landholders who provided site access and, in some cases, undertook voluntary data collection: Howard Blackburn, Sandra and Will Boede, George Boland, David Cattanach, Eric and Megan Coates, Eric Coates Jnr, Horry Cox, Neville Crisp, Peter Fawcett, Charlie and Michelle Franks, Phillip Lenehan, Simon Matear, David and Meg Merrylees, Gary and Samantha Mooring, Terry Murphy, Gavin Offerman, Alan and Gwen Percival, Mark Rowe, Bruce and Jen Southeron, Jenny and Robert Taylor, Myra and Phil Tolhurst, Joyce and Tony Toscan, Bill Wilks, Tara Wilks. DIPNR contributors to field studies: Allan Amos, Alastair Buchan, Simon Catzikiris, Marcus Finn, Neal Foster, Liz Gardiner, Rod Gleeson, Clare Hamill, Michael Healey, Maren Heckel, Chris Higgins, Gordon Honeyman, Natasha Kelley, Helen Keenan, Steve Lewer, Michael Longhurst, Debbie Love, Alastair Mackenzie-McHarg, Sheridan Maher, Paul McInerney, Adam McLean, Sandra Mitchell, John Palmer, Sue Powell, Allan Raine, Greg Raisin, Ken Reynolds, Shane Rose, Darren Shelley, Mathew Silver, John Temple, David Thomas, Kerrie Tomkins, Paul Wettin, Marita Woods. NSW Fisheries contributors to field studies: Karen Astles, Andrew Bruce, Bob Creese, Peter Gehrke, Dean Gilligan, Simon Hartley, Michael Rodgers, Ian Wooden. DIPNR sample analysts: Joann Bethune, Nada Bozinovski, John Brayan, Youmin Chen, Adam Crawford, Huong Crawford, Jon Holliday, Frances Laurenson, Lisa Meldrum, Isabel Montecinos, Marina Stepluyk, Elionora Zelenkova, other staff of the Water Environment Laboratory, Wolli Creek. Other contributors to field studies and sample analysis: Australian Water Quality Centre, Adelaide (identification of aquatic macroinvertebrates and biofilm algae), Central Darling Shire Council (assistance with Barwon-Darling algal sampling program), Centre for Catchment and Instream Research, Griffith University (stable isotope analyses), NSW Herbarium, Sydney (identification of wetland plant specimens), Mike Shultz, Leeton (Murrumbidgee Valley bird surveying), Walgett Shire Council (assistance with Barwon-Darling algal sampling program), WSL Consultants, Melbourne (identification of aquatic macroinvertebrates). Hydrological modellers and contributors to flow rule information: Andrew Brown, Kerrie Burns, Shahadat Chowdhury, Richard Cooke, Mark Foreman, Mark Harris, Paul Keyte, Chris Ribbons, Stephen Roberts, Sam Samarawickrama, Jon Sayers, Mark Simons, Marina Sivkova, other staff of State Water and DIPNR Surface and Groundwater Processes Unit. Report production staff: Julito Briones, Justine Moore. Advisors on methods: Andrew Boulton, Stuart Bunn, Tony Church, Tsuyoshi Kobayashi, Simon Treadwell, Michelle Winning. Draft report reviewers: Andrew Boulton, Lee Bowling, Margaret Brock, Bob Creese, David Crook, Brian Finlayson, Gary Hamer, Hugh Jones, Richard Kingsford, Rod Oliver, Peter Scanes, Paul Simpson. Where time and space did not permit suggested changes or additions to be included in this interim report, they will be considered further in relation to future reporting.

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1.

Overview and principal findings

1.1.

IMEF: INTEGRATED MONITORING OF ENVIRONMENTAL FLOWS

As environmental knowledge and awareness have grown, it has increasingly been recognised that toxic blue-green algal blooms, loss of native fish and waterbird populations, rising salinity and other adverse environmental outcomes will become more prevalent in New South Wales (NSW) unless water is shared in an equitable manner between extractive users and the environment. Governments have responded with various initiatives that allocate water for environmental purposes. But until recently, no systematic program was in place to assess the diversity of ecosystem responses to the provision of environmental water across the State. Without such feedback, efficient sharing of water is impossible. The Integrated Monitoring of Environmental Flows – IMEF – was designed to assist in filling this gap. IMEF is a scientific program managed by the NSW Department of Infrastructure, Planning and Natural Resources (DIPNR) with support from NSW Fisheries, university researchers and both government and private analytical laboratories. It has provided ecological monitoring in relation to environmental flow rules that were developed by community-based river management committees. These rules now form the basis of environmental water provisions within statutory water sharing plans, prepared under the Water Management Act 2000. IMEF also contributes to knowledge of biodiversity and ecological processes in NSW rivers and wetlands. The program was established in 1998 and has developed and expanded since that time. IMEF has three formal objectives: 1. to investigate relationships between water regimes, biodiversity and ecosystem processes in the major regulated river systems of NSW (and the Barwon-Darling River) 2. to assess responses in hydrology, habitats, biota and ecological processes associated with specific flow events targeted by environmental flow rules 3. to use the resulting knowledge to estimate likely long-term effects of environmental flow rules and provide information to assist in future adjustment of rules. The river systems currently covered by IMEF are the Barwon-Darling, Gwydir, Hunter, Lachlan, Macquarie, Murrumbidgee and Namoi systems. The approach developed in IMEF has been applied to the Snowy River in a separate project. The environmental flow rules that were developed for these river systems are varied. However, they can be grouped into six main categories: 1. embargos and diversion limits, which precluded increases in the total volume of water extracted 2. pumping thresholds, which prohibited water extraction when a river was below a particular level 3. end-of-system rules, which required a certain minimum flow to be retained at the downstream end of rivers, below the areas where major extraction occurs 4. transparent and translucent dam rules, which required some reservoir inflows to be passed immediately downstream, either in whole (transparency, as though no dam was present) or in part (translucency) 5. ‘off-allocation’, and other high-flow access rules, which limited pumping when reservoirs spilled or high flows entered flow-regulated rivers from unregulated tributaries 6. environmental allocations, which created a ‘bank’ of reservoir water to be used for specific environmental purposes, such as flushing blue-green algal blooms, reducing salinity or supporting bird-breeding events. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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The rules that operated in 1999-2000 are described in detail in the appendix to this report. In order to assess the performance of these rules, the IMEF project team created a series of predictions (expressed as 16 scientific hypotheses) about possible environmental benefits these types of rules may produce. Scientific studies were designed and implemented to test the most important of these predictions in individual river valleys. The full set of hypotheses is listed in Chapter 2. This interim report provides technical information, at a statewide level, on study methods and the results and interpretation arising from investigations of six hypotheses during the first two years of the program (July 1998-June 2000). Most of the studies initiated in this period have continued since, and will be reported further in the future. The priority hypotheses, the studies designed to test them and the principal findings of these studies to June 2000 are summarised in a less technical manner in the following sections. 1.2.

ALGAL AND CYANOBACTERIAL BLOOMS

Blooms of algae and cyanobacteria (so-called ‘blue-green algae’) in NSW rivers can render waters unsuitable for recreation or consumption by humans or livestock, especially if toxins are produced. IMEF has two hypotheses concerned with nuisance blooms. IMEF hypothesis No. 1 proposes that: •

protecting natural low flows, for example by raising pumping thresholds, will reduce the frequency and severity of algal and cyanobacterial blooms by making conditions less favourable for bloom development (more turbulence; less stratification).

IMEF hypothesis No. 3 is similar, but is concerned with flushing blooms that have already developed, rather than stopping blooms from developing in the first place. It proposes that: •

protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability, through off-allocation use restrictions and dam releases, will flush algal and cyanobacterial blooms from the water column, making blooms less prevalent.

These hypotheses are based on previous research, which has indicated that algal and cyanobacterial blooms in large NSW rivers develop mainly under conditions of warm, still weather and low river flows. Warm weather and a lack of turbulent flow often result in vertical stratification, whereby a layer of warm surface water lies over a layer of cooler bottom water. Some cyanobacteria can migrate to the top layer, where abundant sunlight enables them to photosynthesise and multiply rapidly. A lack of flow also means that algae and cyanobacteria accumulate rather than being washed rapidly downstream. These observations suggest that environmental flows that maintain river currents, and prevent stratification, could reduce the chance of blooms developing or persisting. Studies to test these hypotheses were developed in the Barwon-Darling, Hunter, Lachlan and Namoi valleys. In the Barwon-Darling River, dense cyanobacterial blooms were recorded only rarely, and generally briefly, during the first two years of monitoring. Although flow rules were not yet in operation during this time, a strong negative relationship between cyanobacterial abundance and river flow suggested a potential for local flow rules to reduce the frequency and intensity of blooms. However, flows below the thresholds for bloom development are likely to occur periodically as a result of natural droughts and upstream water extraction, regardless of local pumping restrictions. In the Hunter River, diatom blooms, which can cause discoloration and interfere with water supplies, were recorded intermittently in summer downstream of Denman and in some tributaries. These blooms were clearly flow-related. Restrictions on high-flow extraction (Hunter flow rule 2) did not entirely protect the flows that prevent bloom development. An environmental contingency allocation was available but was not used to flush blooms in 1998-2000.

Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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In the Lachlan River, a dense cyanobacterial bloom developed in the summer and autumn of 1998-99. This bloom was not caused by low river flow, but rather by the discharge of cyanobacteria-laden water from Lake Brewster, a large off-river storage. It was controlled by changing the source of river water from Lake Brewster to Wyangala Dam, and did not recur the following summer. In the Namoi River, cyanobacterial blooms occurred only sporadically, and could not be readily related to flow or other environmental factors such as nutrients. Rainfall during the 1998-2000 period was generally above average, and a greater incidence and severity of blooms is likely when drier conditions occur in the study valleys. This is being assessed through ongoing monitoring. 1.3.

RIVER BIOFILMS

Biofilms are mixtures of algae, fungi and other organisms that coat submerged surfaces such as rocks and logs in many rivers. Past research indicates that biofilms can be an important base of food webs in Australian rivers, but that excessive algal growths and silt layers that can develop under unnatural low-flow conditions may interfere with normal ecosystem processes. IMEF hypothesis No. 4 proposes that flow events may act as a resetting mechanism for river biofilms, removing excessive algae and silt and stimulating new growth that is more palatable to grazing invertebrates. These invertebrates are in turn food for fish and other animals. Scouring of biofilms and silt may also make river-bed gravels more suitable as spawning sites for some native fish species. The hypothesis proposes that: •

protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability, through off-allocation use restrictions and dam releases, will induce scouring of silt and sloughing of biofilms from stony substrata, resetting biofilm development and improving habitat quality for some invertebrate scrapers and their predators, and spawning conditions for gravel-spawning fishes.

IMEF studies to test hypothesis No. 4 were developed in the Hunter and Murrumbidgee valleys. In the Hunter Valley, sites were sampled on Glennies Creek, downstream of Glennies Creek Dam, and on unregulated tributaries for comparison. During 1998-2000, initial baseline data were obtained, in order to establish conditions prior to environmental releases from the dam. Although the density of biofilm was very high immediately downstream of the dam, suggesting a lack of flushing, the numbers of grazing invertebrates (‘scrapers’) were not consistently lower below the dam than in the unregulated tributaries. In the Murrumbidgee Valley, sites were sampled on the Murrumbidgee River a short distance downstream of Burrinjuck Dam, which provided a series of ‘translucent’ environmental releases in winter and spring. Comparison sites were sampled on the regulated Tumut River, which does not have translucent releases, and on two unregulated tributaries. Despite the presence of environmental flows, biofilms and grazing invertebrates in the Murrumbidgee River were always quite different from those in the unregulated rivers. This contrast was probably related to differences in catchment development and consequently water quality (forested catchments of the unregulated tributaries compared with large agricultural and urban areas in the Murrumbidgee River catchment), as well as to differences in flow regime. Water quality factors and high-volume summer irrigation flows may constrain the capacity of environmental releases to engender natural biofilm characteristics in the Murrumbidgee River. Future analysis of data collected since June 2000 will provide greater insights into this question. 1.4.

RIVER ORGANIC CARBON

The leaves and other organic material that fall, blow or wash into rivers from the riparian zone and floodplains can be another important carbon and energy source at the base of river food webs. Sometimes this material is eaten directly by aquatic invertebrates and other animals in the river. In other cases, it releases dissolved organic chemicals, which are used as a food source by natural Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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populations of bacteria in the water. These bacteria may be eaten by zooplankton, which are in turn consumed by small fish and the larvae of larger fish species. Environmental flows may assist in these processes, by wetting leaf litter on river banks and floodplains, making it available to aquatic organisms. IMEF hypothesis No. 5 suggests that: •

protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability, through off-allocation use restrictions and dam releases, will increase the wetting of coarse terrestrial organic matter on river banks, benches and floodplains, and consequently increase microbial activity and the populations of animals that feed on detritus or on the microbes that use dissolved organic matter.

Testing this hypothesis is complex, and accordingly it is being trialed initially in a single valley, the Namoi. Only preliminary work was done in 1998-2000, as resources were limited and study methods were still being developed. Three sites along the course of the lower Namoi River were sampled at a range of river flows. Initial data from these sites did not show a strong relationship between river flow and either the concentration of dissolved organic carbon or zooplankton density. However, far more detailed assessment is needed and the study is continuing. 1.5.

WETLAND BIODIVERSITY

The regulation and extraction of river flows have greatly reduced the frequency and extent of flooding of many NSW riverine wetlands. This in turn has reduced the abundance and diversity of wetland plants and animals. In other cases, temporary wetlands have been made permanent by their use as water storages and conduits. This can also be ecologically detrimental through the loss of the natural drying and flooding cycle, which stimulates productivity. It is possible that environmental flow rules will help to rehabilitate these wetlands by creating a more natural wetting and drying regime. IMEF hypothesis No. 7 proposes that: •

protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability, through off-allocation use restrictions and dam releases, will replenish anabranches and riverine wetlands, restoring their biodiversity.

IMEF wetland studies have been initiated in the Gwydir, Lachlan, Macquarie, Murrumbidgee and Namoi valleys. Initial sampling at numerous sites has shown that the richness or composition of vegetation, invertebrate and bird communities is frequently related to the long-term water regime in individual wetlands. Therefore, protection of the array of natural flooding and drying patterns is critical to sustaining wetland biodiversity and ecosystem processes. In 1998-2000, sampling of wetland fish communities was confined to 10 sites in the Gwydir Valley. These wetlands were dominated by alien fish species – gambusia (‘plague minnow’), carp and goldfish – although native bony herring were abundant and several other native species were present in smaller numbers. Hydrological modelling suggested that wetland flooding frequencies in the lower Lachlan Valley, around Booligal, were moderately close to natural in 1998-2000. An environmental allocation in the spring and summer of 1998-99 helped to sustain a large waterbird breeding event in these wetlands. In the Murrumbidgee Valley, wetland flooding frequencies were typically far below natural in 1998-2000. Similar analyses have not yet been completed for other valleys. Environmental releases supported a large bird breeding event in the Gwydir wetlands in 1998-99. 1.6.

RIVER FISH

Several native freshwater fish species have suffered major population declines across much of NSW during the last century. This has been attributed to a combination of over-harvesting, interference with migration through the construction of dams, weirs and levees, and disruption of environmental cues for spawning through cold-water releases from reservoirs and reduced flooding frequencies. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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Competition with, and predation by, alien fish species may also be a factor. Previous research indicates that the abundance and recruitment of several native fish species are adversely affected by river regulation in NSW. It is therefore possible that environmental flow rules could assist in the recovery of native fish populations. IMEF hypothesis No. 8 suggests that: •

protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability, through off-allocation use restrictions and dam releases, will increase the abundance and dominance of native fish to rehabilitate fish communities, by creating conditions more favourable for native fish recruitment and less favourable for carp.

IMEF hypothesis No. 4, which deals mainly with biofilms, is also concerned with riverine fish. It proposes that: •

protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability, through off-allocation use restrictions and dam releases, will induce scouring of silt and sloughing of biofilms from stony substrata, resetting biofilm development and improving habitat quality for some invertebrate scrapers and their predators, and spawning conditions for gravel-spawning fishes.

Annual sampling of fish communities began in all IMEF study valleys in the summer of 1999-2000. Although most specimens recorded in each IMEF river belonged to native species, the great majority of native river fish were from just four species: bony herring in the western valleys, striped mullet and freshwater herring in the Hunter Valley and Australian smelt in both eastern and western valleys. None of the popular native angling species of inland rivers – such as golden perch and Murray cod – was recorded in large numbers. Although freshwater catfish were reasonably common in the Hunter River system, only seven specimens of this formerly abundant species were recorded from all of the IMEF sites on western rivers. A lack of diversity and abundance of native fish was particularly evident in the Lachlan and Macquarie rivers. Very few specimens were recorded for species listed as vulnerable or endangered. Common carp were the most abundant alien fish, and were present in all valleys. With the exception of the Hunter Valley, very young fish made up only a very small proportion of the catch at IMEF river sites. Therefore, there was no evidence that environmental flow rules facilitated major recruitment of native fish in the western rivers in 1999. This could be because environmental allocations did not create conditions conducive to either spawning or post-spawning recruitment, or because recruitment was constrained by other aspects of the flow regime, or by other factors such as migration barriers, cold water or a scarcity of adult fish. Further surveys at the IMEF fish study sites, under a range of annual flow patterns, should establish the hydrological conditions that lead to successful recruitment. 1.7.

CONCLUSIONS AND FUTURE DIRECTIONS

As yet, only a few environmental benefits can be clearly ascribed to the operation of environmental flow rules during 1998-2000. However, a much longer period of investigation, covering a broader range of climatic conditions, is necessary for the implications of environmental water provisions to be adequately understood. Many studies were still at an early stage of development by mid 2000, and some possible responses to environmental flows, such as changes in adult fish populations, can be assessed only in the long term. In addition, some rules were not operational during the 1998-2000 period, in part because of the generally wet conditions experienced. Evidence was obtained that environmental releases supported bird breeding events in wetland areas. However, initial hydrological modelling indicated that despite the existence of environmental flow rules, inundation of wetlands remained far below natural levels in the Murrumbidgee Valley, and somewhat below natural in the lower Lachlan Valley. Similar analyses are needed for other areas and valleys. This will require further development of hydrological modelling capabilities, which is Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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currently in progress. Once wetland inundation can be adequately modelled, ecosystem models can be built to link hydrological and biological information. In-stream benefits of environmental flow rules are yet to be clearly demonstrated. Cyanobacterial and algal blooms were not major issues in most valleys during 1998-2000, and the dense bloom in the Lachlan River was managed by changing the source of river water. The capacity of environmental flows for suppressing and flushing blooms will be more apparent in drier periods when the potential for bloom development is greater. The studies of river food webs (biofilms and terrestrial organic matter) did not reveal clear benefits of environmental flows, but were only at an early stage of implementation by mid 2000. The recovery of native fish stocks remains a major challenge for river management in NSW. The initial year of IMEF monitoring indicated that the collapse of populations of many native species in the western rivers has not been reversed. Rehabilitation of fish communities will require a greater understanding of fish biology, as well as concerted and sustained action to address the whole range of impediments to native fish breeding and survival (altered flow regimes, cold water pollution, barriers to migration, degraded habitat and competition and predation by alien fish). It is important to recognise that despite environmental water provisions in 1998-2000, the flow regimes of the IMEF study rivers remained heavily modified by winter and spring impoundment in large reservoirs and summer and autumn releases for irrigation supply, with consequent damping of natural flow variability and reversal of seasonal flow patterns. Some environmental flow rules also embodied unnatural flow patterns, such as those that required fixed minimum flows even when natural flows would have been lower or even zero. In the ongoing refinement of environmental water provision, through the development and review of water sharing plans and through other processes, the challenge is to direct the environmental water that is available to where it can produce the greatest benefit, consistent with the environmental objectives of legislation and planning instruments.


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2.

Background to the program

2.1.

CONTEXT AND OBJECTIVES

The Department of Land and Water Conservation (DLWC), the predecessor to the current Department of Infrastructure, Planning and Natural Resources (DIPNR), established the Integrated Monitoring of Environmental Flows (IMEF) as a scientific assessment of the response of major rivers and associated wetlands to environmental water allocations in NSW. IMEF has been progressively developed and implemented since 1998. Provisions have been in place for many years to maintain particular quantities of water within some NSW rivers for environmental purposes. However, a systematic approach to environmental water allocation across the State was first developed as part of the water reform process instigated by the NSW Government in 1997 (DLWC 1998; Thoms and Swirepik 1998). As part of this process, the government adopted twelve broad river flow objectives (RFOs: Box 1). These embody key attributes of flow regimes and flow management that affect the condition of aquatic ecosystems. They are strongly oriented toward the partial restoration of the natural flow regime, a strategy advocated by many river ecologists (e.g. Power et al. 1996; Poff et al. 1997).

Box 1. NSW river flow objectives 1.

Protect natural water levels in river pools and wetlands during periods of no flow

2.

Protect natural low flows

3.

Protect or restore a portion of freshes and high flows

4.

Maintain or restore the natural inundation patterns and distribution of floodwaters supporting natural wetland and floodplain ecosystems

5.

Mimic the natural frequency, duration and seasonal nature of drying periods in naturally temporary streams

6.

Maintain or mimic natural flow variability in all streams

7.

Maintain the rates of rise and fall of river heights within natural bounds

8.

Maintain groundwater within natural levels and variability, critical to surface flows or ecosystems

9.

Minimise the impact of in-stream structures

10. Minimise downstream water quality impacts of storage releases 11. Ensure that the management of river flows provides the necessary means to address contingent environmental and water quality events 12. Maintain or rehabilitate estuarine processes and habitats

Relevant river flow objectives have been addressed in individual valleys by a combination of: •

extraction limits such as the cap on diversions in the Murray-Darling Basin (Murray Darling Basin Agreement, schedule F)

•

environmental flow rules, which target specific aspects of flow regimes at various points in each river system

•

other river and groundwater management activities such as water management plans, weir reviews and measures to mitigate the thermal impact of storage releases.

Environmental flow rules were developed in 1998 by community-based river management committees (RMCs) in each of six valleys that have major rivers regulated by large storages operated by NSW State Water: the Gwydir, Hunter, Lachlan, Macquarie, Murrumbidgee and Namoi valleys. Rules were also formed for the Barwon-Darling River which, although not formally regulated, has flows that are greatly affected by storages and water extraction on its major tributaries in both NSW and Queensland. Rules were approved by the NSW Government and progressively implemented through Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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the operating and licensing procedures of the former DLWC. They have been reviewed annually since their implementation in the six regulated rivers in 1998-99 and in the Barwon-Darling River in 2000-01. Different combinations of flow rules were applied to each river system (see Appendix), but they can mostly be grouped into six categories. Category 1: embargos and diversion limits In the Hunter Valley, rules were established to restrict the issuing of new licences for high-yield groundwater bores and extraction from the regulated section of the Hunter River. Category 2: pumping thresholds Τhreshold rules prohibited water extraction if river levels were below a particular stage height. In the Barwon-Darling River, a complex series of thresholds was defined for different classes of licences. Class A licences, which are generally issued to provide small amounts of water for stock and farmstead use, had lower thresholds than the large Class C irrigation licences, with Class B licences falling in between. Category 3: end-of-system flows End-of-system rules required a certain minimum flow to be retained at the downstream end of rivers, below the areas where major extraction occurs. Category 4: transparent and translucent dam rules Some rules required variable releases from dams during the non-irrigation season, instead of the small and stable releases that were generally made previously. The terms ‘transparency’ and ‘translucency’ have been used to refer to the release of the whole or a proportion of reservoir inflows respectively. Upper limits on such releases may be imposed by the capacity of dam outlet works, the impact on the volume of water stored for later use, or the need to avoid downstream flood damage. Category 5: off-allocation access rules and high-flow rules ‘Off-allocation’ periods were declared on inland rivers when reservoirs spilled or high flows entered from unregulated tributaries. During such periods, irrigators could pump water without the quantity being debited from their annual entitlement. Off-allocation rules set flow thresholds for off-allocation access and restricted the amount of water permitted for extraction during such periods, or limited its timing. They applied mainly in the northern river systems (i.e., the Gwydir, Namoi and Macquarie rivers), since water use in the south is generally from regulated flows. ‘High-flow’ rules in the Hunter Valley were analogous to off-allocation rules. Category 6: environmental allocations These rules created a ‘bank’ of reservoir water for specific environmental purposes, variously referred to as an environmental contingency allowance (ECA) or wild life allocation (WLA). These allocations were generally developed for uses such as flushing of cyanobacterial blooms or sustaining waterfowl breeding events. The Water Management Act 2000 (NSW) provided a new legislative basis for environmental water allocations. The objects of the Act include the intention ‘to protect, enhance and restore water sources, their associated ecosystems, ecological processes and biodiversity and their water quality’. The water management principles on which the Act is based include a requirement that ‘sharing of water from a water source must protect the water source and its dependent ecosystems’.


8

The Act defines three classes of environmental water: •

environmental health water (committed for environmental purposes at all times, and not available for other purposes)

•

supplementary environmental water (committed for environmental purposes at specified times or under specified circumstances, but otherwise available for other purposes)

•

adaptive environmental water (water committed for specified environmental purposes under an access licence).

Water sharing plans are progressively being prepared for all water sources in NSW – regulated rivers, unregulated rivers and groundwater. Thirty-five water sharing plans were gazetted by late February 2003 for implementation in 2003-04, including plans for the regulated Gwydir, Lachlan, Macquarie, Murrumbidgee and Namoi rivers. The water sharing plans build on the previous environmental flow rules and establish environmental water provisions for one or more classes of environmental water, as well as basic landholder rights to water, various provisions for water extraction under access licences, system operating rules and monitoring and reporting requirements. IMEF was instigated in order to provide RMCs, natural resource management agencies and the broader community with sound scientific feedback on the effects of environmental flow rules. This was intended to inform reviews of water allocation, and to enable an adaptive approach in which management strategies are adjusted in the light of experience. Such an approach is necessary because the complexity and variability of river ecosystems prevents the effects of environmental allocations from being predicted precisely at the present state of knowledge. Water sharing plans will be subject to mid-term reviews, which will benefit from IMEF findings. IMEF covers the seven valleys for which flow rules were formulated, and may be extended to other valleys in the future. Its objectives are: •

to investigate relationships between water regimes, biodiversity and ecosystem processes in the major regulated river systems (and the Barwon-Darling River)

•

to assess responses in hydrology, habitats, biota and ecological processes associated with specific flow events targeted by environmental flow rules

•

to use the resulting knowledge to estimate likely long-term effects of environmental flow rules and provide information to assist in future adjustment of rules.

The intended outcomes of the project are: • a better understanding of the relationships between hydrology, morphology and ecology in the major regulated river systems (and the Barwon-Darling river), and their trends over time • an evaluation of whether flow events targeted by the rules produce the expected short-term environmental responses • an estimation of the likely longer-term effects of environmental flow rules • an informed environmental flow review process. The outputs of the project include: • information brochures and fact sheets • presentations to river management committees and scientific conferences • scientific journal papers • regional reports presenting detailed project results • State-wide reports providing summaries of findings. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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2.2.

SCOPE AND LIMITATIONS

The focus of IMEF is the effects of environmental flow rules on the ecology of major regulated rivers, the Barwon-Darling River, and associated wetlands (Map 1, located in the map section at the back of this report). It is also concerned with factors closely associated with the delivery of environmental allocations, such as changes in water quality (e.g. temperature) associated with reservoir management (e.g. offtake levels). While IMEF is a large project using up-to-date scientific methods, there are practical limitations to what any such project can achieve in a complex and dynamic natural environment. These limitations are specified below so that the expectations of the project are not unrealistic. 1. Since environmental flow rules can affect innumerable aspects of river and wetland ecology, it was necessary to make judgements about which organisms and processes were most likely to be influenced. This was difficult because while much research has addressed the general effects of flow on Australian rivers and wetlands (Lake 1995), little has been done on flow rules such as those implemented in NSW. 2. The implementation of environmental flow rules is not a controlled scientific experiment like an agricultural plot trial. Ideally, each river with environmental flow rules would be assessed by comparison with a control group of large, regulated rivers without those rules but otherwise very similar. Such control groups do not exist. Nor is there a stable control period before the start of environmental flow rules, because flow regimes have been continually changing over recent decades as the degree of regulation and diversion have increased. Some environmental water provisions, such as the Macquarie Marshes Water Management Plan (DWR/NPWS 1986; DLWC/NPWS 1996) have also been in operation for several years. These constraints make it more difficult to determine whether observed changes are caused by environmental allocations or other factors. 3. For most ecosystem attributes, few or no relevant data were collected before environmental flow rules were established. This makes it difficult to identify trends that may be due to the rules. 4. The changes in flow patterns induced by environmental flow rules are often much smaller than the effects of water extraction and natural climatic shifts (e.g. droughts and floods). Many responses to the rules are therefore subtle and difficult to distinguish from responses to other aspects of the total flow regime. 5. Some environmental flow rules take effect only under specific climatic and hydrological conditions (e.g. after prolonged dry spells) and it may be several years before these circumstances arise. 6. Some responses to environmental flows may be indirect and take years or even decades to develop. It is hard to link particular flow changes to their specific effects over such long periods, because many other factors may also have changed in the meantime. 7. River ecosystems are affected by many other factors than flow – for example, wastewater discharges, catchment and riparian conditions, in-stream barriers and biological interactions. Many of these factors will be changing at the same time as environmental allocations are provided. In some cases, river ecosystems may still be adjusting to past changes such as catchment clearing or the spread of alien pest species. These confounding factors can make it difficult to attribute particular ecological changes specifically to environmental flow rules. 8. The numbers of sites studied, variables measured and frequency of measurement must be realistic given the project budget. 2.3.

PROGRAM DESIGN

The first step in the design of IMEF was a review of the scientific literature in order to formulate a series of predictions about the ecological responses that might be expected as a result of flow rules. This has been termed a hypothesis-based approach (Chessman and Jones 2001). Hypothesis testing is Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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a fundamental component of the scientific method, but it is more commonly incorporated in controlled experiments than in monitoring programs (e.g. Havens and Aumen 2000). IMEF hypotheses were structured to link four components: •

a type of flow rule or rules

•

the RFO or RFOs that the flow rule was designed to address

•

an expected and beneficial environmental outcome of the rule

•

the biophysical mechanism by which application of the rule was expected to lead to the outcome.

The advantages of this option were seen as follows. 1. Anchoring IMEF to hypotheses would ensure that the program had clear aims, direction and focus, by stating, unequivocally and at the outset, the expected types of ecosystem responses to the flow rules. 2. The formulation of hypotheses incorporating objectives, rules, outcomes and mechanisms would set the direction for charting structural links between these four critical components of environmental water management, and thus provide a firm basis for detailed study design. 3. Acquisition of evidence either supporting or contradicting the hypotheses would enable the expected links between flow regimes and ecology to be either confirmed or reformulated, regardless of whether or not a long-term ecological improvement was recorded. The hypothesis-based approach was developed and progressed into the IMEF study design in the following sequence of steps (Chessman and Jones 2001). 1. The proposed RFOs were examined in order to identify the environmental outcomes that they were intended to achieve. 2. The changes in the regulated flow regime that were likely to result from implementation of flow rules were considered. 3. Existing information was reviewed to determine which plants, animals and ecological processes were likely to be sensitive to these changes. 4. Hypotheses were developed about the responses of these components. 5. The hypotheses were prioritised according to their relevance to the intended environmental outcomes and on other appropriate criteria in each valley. 6. Study designs were devised to test the priority hypotheses. These designs incorporated selection of study sites, variables and sampling strategies and approaches to data analysis. At first, more than 40 hypotheses were formulated. This large set was culled after considering the views of scientific experts and the following criteria: •

relevance to intended environmental benefits of RFOs

•

strength of a priori support for the hypothesis from previous scientific studies and expert opinion

•

practicality of testing the hypothesis (including cost)

•

temporal and spatial applicability of the hypothesis (giving preferences to hypotheses that apply widely rather than at particular times and places)

•

strength of the expected response to flow rule implementation

•

sensitivity to confounding factors

•

community perception of the importance of the hypothesis

•

availability of relevant historical data.


11

This process produced a short-list of generic (State-wide) hypotheses. The applicability of this generic set to each river system was then assessed through a series of regional workshops with local agency staff and RMC representatives, and by reviewing existing information. Some of the generic hypotheses were not relevant to a particular river because of its biophysical features or the nature of the local flow rules. In some cases minor modification of a hypothesis was needed to suit local circumstances. A few additional hypotheses relevant to individual river valleys were added as a consequence of the regional workshops. The hypotheses are listed in Box 2. They do not address the effects of environmental contingency allocations (RFO 11), because the purposes to which such allocations were to be put had not been fully defined at the time.

Box 2. Generic and valley-specific response hypotheses Hypothesis 1 (generic). Suppressing blooms Protecting natural low flows (RFO 2), for example by raising pumping thresholds, will reduce the frequency and severity of algal and cyanobacterial blooms by making conditions less favourable for bloom development (more turbulence; less stratification) Hypothesis 2 (generic). Improving low-flow habitat Protecting natural low flows (RFO 2), for example by raising pumping thresholds, will promote the recovery of water plants, native fish and invertebrates, by maintaining wetted physical habitat and reducing the frequency and severity of stratification, thereby increasing dissolved oxygen levels and reducing salinity Hypothesis 3 (generic). Flushing blooms Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will flush algal and cyanobacterial blooms from the water column, making blooms less prevalent Hypothesis 4 (generic). Conditioning stony beds Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will induce scouring of silt and sloughing of biofilms from stony substrata, resetting biofilm development and improving habitat quality for some invertebrate scrapers and their predators, and spawning conditions for gravel-spawning fishes Hypothesis 5 (generic). Wetting terrestrial organic matter Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will increase the wetting of coarse terrestrial organic matter on river banks, benches and floodplains, and consequently increase microbial activity and the populations of animals that feed on detritus or on the microbes that use dissolved organic matter Hypothesis 6 (generic). Resetting lowland biofilms Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will cause scouring and level changes that will shift the species composition of river biofilms on snags and in the littoral zone towards a greater representation of pioneering taxa such as diatoms, heterotrophic bacteria and fungi relative to filamentous algae and cyanobacteria, and consequently increase macroinvertebrate diversity Hypothesis 7 (generic). Replenishing wetlands Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3, 4 and 6), through off-allocation use restrictions and dam releases will replenish anabranches and riverine wetlands, restoring their biodiversity Hypothesis 8 (generic). Rehabilitating fish communities Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will increase the abundance and dominance of native fish to rehabilitate fish communities, by creating conditions more favourable for native fish recruitment and less favourable for carp


12

Box 2 (continued). Generic and valley-specific response hypotheses Hypothesis 9 (generic). Restoring natural drying Mimicking the natural frequency, duration and seasonal nature of drying periods in naturally temporary anabranches (RFO 5), by restricting diversions, will cause shifts towards more diverse biota by creating an intermediate level of disturbance Hypothesis 10 (generic). Reducing bank erosion Maintaining the rates of rise and fall of river heights within natural bounds (RFO 7) will reduce bank slumping and scouring, and consequently reduce losses of riparian vegetation Hypothesis 11 (specific to the Hunter Valley). Maintaining estuarine productivity Protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will maintain the supply of nutrients and organic carbon to the estuary, thereby sustaining production of organisms such as prawns and fish Hypothesis 12 (specific to the Hunter Valley). Restructuring habitat Protecting or restoring a portion of freshes and high flows, and thereby mimicking natural flow variability (RFOs 3 and 6), through off-allocation use restrictions and dam releases, will cause scouring and level changes that will improve habitat structure and diversity in morphologically unstable sections of the river Hypothesis 13 (specific to the Lachlan Valley). Regenerating riparian vegetation Protecting or restoring a portion of freshes and high flows, and thereby mimicking natural flow variability (RFOs 3 and 6), through dam releases and off-allocation restrictions, will result in increased wetting of riparian zones, and thereby promote the regeneration of native riparian vegetation Hypothesis 14 (specific to the Hunter Valley). Phasing in temperature changes Minimising the downstream water quality impacts of storage releases (RFO 10), by gradually increasing and reducing release volumes, will reduce the risk of thermal shock in summer when reservoir water temperatures are lower than tributary water temperatures, thereby fostering more natural fish and macroinvertebrate communities Hypothesis 15 (specific to the Lachlan Valley). Increasing light for water plants Improving water quality (RFO 10), by winter and spring releases of clear reservoir water, will increase light penetration to the river bed, thereby fostering the recovery of water plants Hypothesis 16 (specific to the Murrumbidgee Valley). Reducing temperature depression Minimising the downstream water quality impacts of storage releases (RFO 10), by the use of the stony sluice at Burrinjuck Dam, will reduce downstream temperature depression, thereby fostering more natural fish and macroinvertebrate communities

A series of river inspections by DLWC staff was then used to further refine and prioritise the hypotheses relevant to each river valley. Priorities (Table 2.1) were set according to several criteria: • the likelihood that a measurable response of the type described by the hypothesis would occur, given the magnitude of environmental allocations in relation to other flow variation • the practicality of testing the hypothesis with techniques that could be implemented in a routine monitoring program at a large spatial scale • the feasibility of developing an effective sampling and statistical design to test the hypothesis, bearing in mind likely confounding factors • the length of river to which the hypothesis might apply (giving lower priority to hypotheses with only localised applicability) • the lack of existing studies already producing information relevant to the hypothesis.


13

Table 2.1. Priority of testing hypotheses in each valley. -, not applicable Hypothesis

Hunter

Gwydir

Namoi

Macquarie

Lachlan

Murrumbidgee

Barwon-Darling

1.

Suppressing blooms

-

-

-

-

-

=4th

=1st

2.

Improving low-flow habitat

-

3rd

-

5th

-

8th

3rd

3.

Flushing blooms

5th

-

4th

-

3rd

=4th

=1st

4.

Conditioning stony beds

3rd

4th

-

3rd

7th

3rd

-

5.

Wetting terrestrial organic matter

6th

5th

3rd

6th

5th

6th

4th

6.

Resetting lowland biofilms

-

6th

5th

4th

6th

7th

6th

7.

Replenishing wetlands

-

1st

1st

1st

1st

1st

5th

8.

Rehabilitating fish communities

2nd

2nd

2nd

2nd

2nd

2nd

2nd

9.

Restoring natural drying

-

-

-

-

8th

-

-

-

-

-

-

9th

-

-

11. Maintaining estuarine productivity

1st

-

-

-

-

-

-

12. Restructuring habitat

7th

-

-

-

-

-

-

13. Regenerating riparian vegetation

-

-

-

-

10th

-

-

4th

-

-

-

-

-

-

15. Increasing light for water plants

-

-

-

-

4th

-

-

16. Reducing temperature depression

-

-

-

-

-

5th

-

10. Reducing bank erosion

14. Phasing in temperature changes

Study designs were developed to test hypotheses 1-5, 7, 8 and 11, which were of sufficient priority to be developed into studies in at least one valley. Designs incorporate the elements of statistical (or numerical) framework, site and variable selection and sampling protocols. The resulting methods are described later in this report for individual studies and valleys. 2.4.

PROGRAM IMPLEMENTATION

Twenty-two IMEF studies have been implemented progressively since 1998. A study refers to the testing of a particular hypothesis (or two closely related hypotheses) in a particular valley. Implementation has been dependent on availability of physical resources and of staff, many of whom were recruited specifically to work on the program. In many cases it was necessary to invest considerable effort in the development, review and testing of methods, because of a lack of similar projects in the past from which to derive precedents. A staged approach was therefore adopted in which individual studies began as resources became available and methods were finalised. In some cases, IMEF studies built upon existing programs such as the Key Sites network of water quality monitoring stations (Preece 1998) and the community-based Barwon-Darling Riverwatch program (Mitrovic and Gordon 1998). This report describes interim results up to June 2000 for 19 studies. Three studies are not yet sufficiently advanced to warrant reporting. These will be included in future reports.


14

3.

Study areas

3.1.

BARWON-DARLING VALLEY

The Darling River is formed by the junction of the Barwon and Culgoa rivers, upstream of Bourke, whence it flows in a broadly south-westerly direction to its confluence with the Murray River near Wentworth (Map 2). The length of the Darling River is 1390 km. The Macintyre-Barwon River, which rises along the NSW-Queensland border, has an additional length of 1140 km and the Condamine-Balonne-Culgoa River, which rises in southern Queensland, measures 1350 km. The Barwon-Darling River and its many tributaries drain a total area of 650 000 km2, mostly of low relief. The river has generally low bed slope, high sinuosity, low stream power and highly cohesive bank materials (Thoms et al. 1996). Its floodplain contains numerous anabranches and shallow lakes. Land use in the catchment includes grazing, dryland cropping and irrigation. Because of the semi-arid nature of the western catchment, the more intensive land uses are concentrated in the eastern tributary valleys. Nevertheless, substantial areas of irrigated cotton occur along the Barwon-Darling River around Bourke and upstream. Annual rainfall declines across the catchment from about 960 mm at Toowoomba (Queensland) in the north-east to around 260 mm at Broken Hill and Wilcannia in the south-west. The proportion of summer rainfall increases to the north, where decaying tropical cyclones can generate intense falls. Most flow in the river is generated by these and other large rain events in southern Queensland and north-eastern NSW. Upstream of the Menindee Lakes water storage scheme the Barwon-Darling River is defined as unregulated. However, flows in the river are greatly affected by several dams on the river’s NSW and Queensland tributaries (especially the Border, Gwydir, Namoi and Macquarie rivers: Table 3.1) and by water extraction in both States. Within NSW, most extraction occurs between Brewarrina and Wilcannia (Map 2). About one third of the average annual flow is diverted from the river and its tributaries and the median monthly flow at Menindee is now less than 50% of its natural value (Thoms et al. 1996; Thoms and Sheldon 2000). Ninety percent of diversions are in tributary streams. Flow patterns are also affected by 17 weirs along the river, including 15 in the IMEF study region between Mungindi and Wilcannia (Thoms et al. 1996). For the remainder of this report, the term ‘Barwon-Darling Valley’ refers to the western part of the total catchment within NSW, excluding the Gwydir, Namoi and Macquarie-Castlereagh-Bogan valleys. These valleys are treated separately. 3.2.

GWYDIR VALLEY

The Gwydir River (Map 3) rises on the New England Tableland and flows westward for about 310 km to the Barwon River. The major tributary is the Horton River. The eastern portion of the 26 000 km2 catchment comprises mountainous terrain where streams have moderate or rapid currents over stony and sandy beds. Downstream of Copeton Dam the Gwydir is less constrained by valley margins and has more gentle flows on a bed of sand and silt. On the western alluvial plains, the river disperses into a system of braided distributaries and feeds the extensive Gwydir wetlands, located on the lower Gwydir River and Gingham Watercourse (Keyte 1994). The ‘Gwydir raft’, a mass of sediment and woody debris about 35 km long, blocks the river channel west of Moree and has a major influence on local flood behaviour. Land use in the catchment is dominated by pasture grazing and cropping. Cotton production is by far the largest agricultural industry in economic terms (DWR undated). Annual rainfall decreases from east to west across the Gwydir Valley, from around 880 mm at Guyra to 510 mm at Collarenebri. The only major storage is Copeton Reservoir on the upper Gwydir River near Inverell (Table 3.1). Flows released from Copeton Dam are apportioned among the various distributary streams by a complex series of regulating weirs. Tareelaroi Weir, on the Gwydir River east of Moree, regulates flow in the Mehi River. Boolooroo Weir, on the Gwydir River north of Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

15

Moree, allows delivery of water into Carole Creek, whence it flows into Gil Gil Creek, part of the adjacent Border Rivers system, to the north. Tyreel Weir and Tyreel Regulator, on the Gwydir River west of Moree, distribute water between the lower Gwydir River and the Gingham Watercourse. Combadello Weir diverts from the Mehi River to Moomin Creek and Gundare Regulator diverts from the Mehi River into Mallowa Creek. Most water extraction in the valley occurs downstream of Moree (Map 3). Table 3.1. Major water storages (capacity > 100 000 ML) on IMEF study rivers and their tributaries in the Murray-Darling Basin. Ranges of year completed indicate initial construction and final enlargement. Source: Crabb (1997)

3.3.

Valley

River

Storage

Year completed

Capacity (ML)

Barwon-Darling

Darling River

Menindee Lakes

1960

2 285 000

Border Rivers

Pike Creek (Qld)

Glenlyon

1976

261 000

Border Rivers

Severn River

Pindari

1962-96

312 000

Gwydir

Gwydir River

Copeton

1976

1 364 000

Intersecting streams

Balonne River (Qld)

Beardmore

1972

101 000

Intersecting streams

Sandy Creek (Qld)

Leslie

1985

108 000

Lachlan

Lachlan River

Lake Brewster

1952

150 000

Lachlan

Lachlan River

Wyangala

1936-71

1 220 000

Macquarie

Cudgegong River

Windamere

1984

368 000

Macquarie

Macquarie River

Burrendong

1967

1 678 000

Murrumbidgee

Murrumbidgee River

Burrinjuck

1927-95

1 026 000

Murrumbidgee

Murrumbidgee River

Tantangara

1960

254 000

Murrumbidgee

Queanbeyan River

Googong

1978

125 000

Murrumbidgee

Tumut River

Blowering

1968

1 628 000

Murrumbidgee

Tumut River

Talbingo

1971

921 000

Namoi

Manilla River

Split Rock

1987

397 000

Namoi

Namoi River

Keepit

1960

423 000

HUNTER VALLEY

The Hunter River (Map 4) rises on the Liverpool Range and flows for 470 km to the Pacific Ocean. Its major tributaries are the Goulburn River in the west, which drains almost half of the catchment but contributes only 23% of river flow, the Paterson and Williams rivers, which drain the wetter northeast of the catchment, and Wollombi Brook, which drains the south-eastern segment of the catchment. The Hunter Valley covers an area of 22 000 km2. The terrain ranges from steep and dissected in some headwater areas to relatively flat along the lower Hunter River where the floodplain is up to 40 km wide. Native vegetation has been removed from most of the valley floor but some large areas, mostly in rugged landscapes, have been retained as national parks and state forests. The major industries are coal mining, power generation, heavy industry, grazing and cropping (mostly cereals, grapes, legumes and vegetables) (DLWC 2000a). The valley includes large urban areas, particularly Newcastle. Rainfall averages are highest in the Barrington Tops (over 1600 mm/year) and on the coast (about 1140 mm/year at Newcastle), decreasing with distance inland to around 620 mm/year at Cassilis. Eight major impoundments occur in the valley (Table 3.2). Three provide regulated flow for downstream irrigation, urban and industrial supply: Glenbawn Dam, Glennies Creek Dam and Lostock Dam. Two off-river storages supply water to power stations: Lake Liddell on Gardiners Creek (a tributary of Bayswater Creek) and Plashett Dam on Saltwater Creek. The catchment areas of Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

16

these two storages are small and most of the water stored in them is pumped from the Hunter River at Jerrys Plains. Chichester Dam, Seaham Weir and Grahamstown Dam (an off-river storage) are operated by the Hunter Water Corporation to provide water supplies for urban areas. Most extractive use on the Hunter River main stream occurs between Muswellbrook and Liddell (Map 4). Table 3.2. Major water storages (capacity > 10 000 ML) on the Hunter River and its tributaries. Ranges of year completed indicate initial construction and final enlargement. The capacity figure for Glenbawn Dam includes 120 000 ML set aside for flood mitigation. Sources: ANCOLD (1990); Jeffcoat (undated) River

Storage

Year completed

Capacity (ML)

Chichester River

Chichester

1923

17 740

Gardiners Creek

Liddell Cooling Water

1968

148 000

Glennies Creek

Glennies Creek

1983

283 000

Hunter River

Glenbawn

1958-87

870 000

Offstream

Grahamstown

1969

152 597

Paterson River

Lostock

1971

20 200

Saltwater Creek

Plashett

1987

65 000

Williams River

Seaham

1978

16 090

Glenbawn Dam captures high flows entering the storage, as 120 000 ML of capacity has been reserved for flood mitigation. As a consequence, the dam has never spilled and downstream flows above about 9000 ML/day have been eliminated. Water captured in the flood mitigation zone of the dam during floods is released after downstream flooding subsides, reducing the occurrence of flood flows and extending periods of moderately high flows after a flood event. During drier periods, water is released to satisfy downstream requirements, increasing flows above natural levels. The effect of Glenbawn Dam is progressively moderated by downstream inflows from unregulated tributaries, but upstream of Muswellbrook the natural seasonal pattern of high winter flows and lower summer flows has been reversed (DLWC 2000a). Below Liddell, flows tend to be less than natural in both winter and summer because of extraction, except in very dry periods when minimum flows are maintained above natural levels. Glennies Creek Dam has altered the seasonality of downstream flows to the confluence with Goorangoola Creek. High flows have been removed from this reach because the dam has never spilled, and the maintenance of a minimum flow of about 20 ML/day below the dam has eliminated natural periods of zero flow. Flows in the section of Glennies Creek downstream of the confluence with Goorangoola Creek are more similar to natural, as Goorangoola Creek is unimpounded. 3.4.

LACHLAN VALLEY

The Lachlan River (Map 5) has a length of around 1450 km, commencing near Gunning and terminating in the Great Cumbung Swamp near Oxley. Outflow from the Cumbung Swamp to the Murrumbidgee River occurs only during major floods. The major tributaries of the Lachlan River are the Abercrombie, Boorowa, Belubula and Crookwell rivers. The Lachlan catchment covers approximately 85 000 km2 and varies markedly from east to west. The eastern headwaters are characterised by fast to moderately flowing streams with sandy and stony beds, steep vegetated ranges and cleared grazing lands. From Wyangala Dam to Forbes, the land is mostly undulating to hilly and cleared apart from patchy remnant vegetation. The streams are gently flowing with muddy to sandy beds and some terraces formed by floods. The middle reaches of the Lachlan feature extensive plains and the occasional rocky outcrop. Further west the land is entirely flat and wetlands are abundant. Vegetation is sparse as a result of clearing and a dry climate. The drainage network in this part of the catchment includes many paleochannels, anabranches and distributaries Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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such as Merrowie, Middle and Willandra creeks. The predominant land uses are grazing and both dryland and irrigated cropping (cereals, cotton, grapes, wheat and vegetables). Average annual rainfall varies from 1200 mm along the eastern fringe of the catchment to 250 mm in the west. Summer rainfall is more variable than that in winter. The major storage is Wyangala Dam (Table 3.1) at the junction of the Lachlan and Abercrombie rivers. Most of the regulated flow in the Lachlan River is provided by Wyangala Dam. Carcoar Dam, on the Belubula River, has a capacity of 36 000 ML and provides supplementary irrigation flows. Lake Brewster (153 000 ML) and Lake Cargelligo (36 000 ML), off-river storages situated in the middle of the valley, are used to maintain flows in the lower Lachlan River. Summer flows downstream of Wyangala Dam are now generally greater than those that would have occurred under natural conditions, and winter flows are lower (DLWC 1997). Lengthy periods of zero flow, which occurred periodically before regulation, have now been eliminated, and floods and freshes have been reduced. Water extraction is fairly evenly distributed along the valley downstream of Cowra (Map 5). 3.5.

MACQUARIE VALLEY

The Macquarie River (Map 6) is formed near Bathurst by the junction of the Fish and Campbells rivers and flows in a north-westerly direction to the Barwon River between Walgett and Brewarrina. The Bogan River forms a parallel system to the west, and receives flow from the Macquarie via distributary streams. The Castlereagh River to the north-east joins the Macquarie just above the latter’s confluence with the Barwon. The Macquarie-Bogan catchment, excluding the Castlereagh system, covers 73 000 km2. The upper catchment above Dubbo is mountainous to hilly terrain where the Macquarie is joined by several major rivers: the Turon, Cudgegong, Bell, Little and Talbragar. Downstream of Dubbo the valley opens onto flat plains, where numerous anabranches and distributary channels diverge from the main river. The Macquarie Marshes, a 2200 km2 wetland complex, are a dominant feature of the lower valley. Most of the marshes are freehold land, but the Macquarie Marshes Nature Reserve of 181 km2 is managed by the National Parks and Wildlife Service. This portion of the Marshes and a small area of private property are covered by national and international agreements protecting waterbirds (e.g. the Ramsar Convention). The dominant land uses in the Macquarie Valley are sheep and cattle grazing, irrigated cropping for cotton and production of a wide variety of other crops, particularly wheat and cereals (DWR 1991). Average annual rainfall ranges from over 900 mm in the headwaters near Oberon to 450 mm at Quambone in the north. The lower Macquarie River is regulated by two major structures: Burrendong Dam on the Macquarie River and Windamere Dam on the Cudgegong River (Table 3.1). Other water control works on the Macquarie River include ponding weirs at Dubbo, Narromine and Gin Gin, and diversion weirs at Warren and Marebone that control diversions to distributary creeks. Regulatory structures within the marshes comprise Marebone Weir, which can regulate flow down the Macquarie River and the Bulgeraga and Marra channels, a regulator on the bifurcation of Bulgeraga Creek, and the Northern By-Pass Channel, which diverges downstream of Pillicawarrina and rejoins the Macquarie River upstream of Miltara. Water extraction occurs mainly between Narromine and Warren (Map 6). 3.6.

MURRUMBIDGEE VALLEY

The Murrumbidgee River (Map 7) rises in the South East Alps at Long Plain, north of Kiandra and flows generally west for over 1600 km to join the Murray River at Boundary Bend. Numerous tributaries enter the upper Murrumbidgee, including the Bredbo, Cotter, Goobarragandra, Goodradigbee, Molonglo, Numeralla, Tumut and Yass rivers. The area of the catchment is 84 000 km2. In the upper catchment the river and its tributaries lie mostly within forested terrain, and have been influenced by past glacial processes. These have left a series of Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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well defined pool and riffle sequences set within broad valleys, alternating with bedrock gorges. West of Wagga Wagga, large scale floodplain features develop, leading into the extensive riverine plain at Narrandera. High rates of sediment deposition, as a result of high discharges and sediment scouring from the upper catchment during the past 120 000 years (Page et al. 1996), have had the effect of reducing channel capacity downstream. Numerous anabranches and palaeochannels occur on the riverine plain, and a major distributary, the Yanco Creek system, leaves the river downstream of Narrandera, eventually flowing to the Murray River. At the downstream end of the valley, the Lowbidgee floodplain supports extensive wetlands. In the upper catchment, the predominant land uses are sheep and cattle grazing, nature conservation and growing urbanisation, particularly in the ACT. The middle and lower catchment areas support forestry, horticulture, cropping, irrigated agriculture and grazing. Average annual rainfall ranges from over 1400 mm in the headwaters of the Tumut River to about 320 mm at Balranald in the west. Several large reservoirs occur in the upper Murrumbidgee catchment (Table 3.1). The headwaters of the Murrumbidgee River flow into Tantangara Reservoir, whence the majority of flow is diverted via the Snowy Mountains Hydroelectric Scheme into Lake Eucumbene. This water plus inter-basin diversions from the Snowy River system are transferred to Talbingo and Blowering storages on the Tumut River. Googong Reservoir on the Queanbeyan River supplies urban water in the Canberra-Queanbeyan region, as do other smaller storages on the Cotter River. Burrinjuck Dam on the Murrumbidgee River, together with Blowering Dam, regulates irrigation flows for the lower Murrumbidgee River. A series of weirs along the course of the lower Murrumbidgee River (Berembed, Yanco, Gogeldrie, Hay, Maude, Redbank and Balranald), and a small off-river storage (Tombullen Reservoir), provide further regulation and divert water to irrigation areas. Regulation has changed the seasonal pattern of flows, and has reduced river flooding, and consequently the frequency, extent and duration of wetland inundation (DLWC 1995a). Water extraction is strongly concentrated in the mid-lower part of the valley, between Narrandera and Hay (Map 7). 3.7.

NAMOI VALLEY

The Namoi River (Map 8) has its headwaters (as the Cobrabald and Macdonald rivers) in the Great Dividing Range at altitudes of about 1200 m. Its principal tributaries are the Peel, Manilla and Mooki rivers and Coxs Creek. The river flows generally westward to join the Barwon River at Walgett. The Namoi catchment covers an area of approximately 42 000 km2. The upper river system is heavily constrained with sandy and stony beds. Below a gorge zone in the vicinity of Manilla, the valley slope decreases dramatically and the valley floor widens. The river is more gently flowing with muddy and sandy beds. Downstream of Narrabri, the extensive floodplain contains numerous small wetlands and several anabranches, particularly the extensive Pian Creek system. Several minor tributaries enter this section of river from the Pilliga region to the south. Grazing of sheep and cattle dominates catchment land use in terms of area, but cotton production is most important economically (DLWC 2000b). Cereal cropping is also common and timbered areas cover 25% of the valley. Urban development is not extensive. Annual average rainfall in the Namoi catchment varies from more than 1000 mm on the high parts of the Great Dividing Range to about 480 mm at Walgett. The catchment has two major dams, Keepit on the Namoi River and Split Rock on the Manilla River (Table 3.1), as well as the smaller Chaffey Dam on the Peel River. Downstream of Keepit Dam, the river is further regulated by a series of weirs: Mollee, Gunidgera and Weeta. Gunidgera Weir raises water levels to enable regulated flows to be diverted to Gunidgera and Pian creeks. Four privately owned weirs have been built on the GunidgeraPian system. Water extraction in the Namoi Valley is concentrated downstream of Narrabri (Map 8).


19


20

4.

Water regimes

4.1.

INTRODUCTION

The effects of environmental flow rules on regimes of river discharge and wetland inundation sit within a broader hydrological context, formed by climatic patterns and those actions taken to support consumptive uses of water, such as impoundment, regulated release, extraction and irrigation tailwater discharge. The hydrological effects of the flow rules were assessed by documenting the application of the rules during the two-year reporting period, and by comparing flows measured at river gauging stations with simulated flows produced by hydrological modelling. Since the NSW river flow objectives (p. 7) mostly relate to protection of components of the natural flow regime, an ideal reference point for measured flows would be modelled natural flows. However, the hydrological models currently available for the IMEF study rivers are not able to simulate the absence of all human influences. In general, these models can mimic the removal of major water infrastructure such as dams, large weirs and the principal irrigation pumps and town water supply offtakes. However, they generally do not take account of the smaller water extraction activities, or of human impacts on channel and floodplain morphology, such as channel excavation and filling, construction of levee banks and the accelerated erosion and sedimentation engendered by human activity. These morphological changes can greatly affect the pathways and distribution of water, particularly in flat landscapes. In addition, the models do not account for human impacts on catchment vegetation, which can affect surface runoff and rainfall infiltration to groundwater. 4.2.

METHODS

The environmental flow rules recommended by RMCs for each river for the 1999-2000 water year are listed in the appendix to this report. Rules recommended for the 1998-1999 water year were very similar. In the Barwon-Darling River system and regulated parts of the Hunter, Lachlan, Macquarie and Murrumbidgee rivers, the water year runs from 1 July to 30 June. For regulated sections of the Gwydir and Namoi rivers, the water year runs from 1 October to 30 September. Information on the implementation of rules for the 1998-2000 reporting period was compiled from unpublished audit reports produced by DLWC for use by RMCs and in the former Department's river operations. Relevant information included the timing, volume and purpose of releases from storages and the declaration of off-allocation and high-flow extraction periods. Rainfall data for the reporting period were obtained from the Bureau of Meteorology (Figure 4.1) and daily river flows for representative stations, derived from routine hydrographic monitoring, were extracted from the HydSys data base. Generally, one station was selected in the upper part of the regulated system (downstream of the principal dam but upstream of major extraction points), one near the middle of the regulated system, and one near the end of the river system (downstream of major extraction areas). The selected stations are listed in Table 4.1. The Integrated Quality and Quantity Model (IQQM: DLWC 1995b) was used to simulate the daily flows that would have occurred at each station, over the reporting period, in the absence of major impoundment, river regulation and water extraction (hereafter called low-development flows). This set of models simulates the major hydrological processes in each river system via a set of nodes and links. The nodes are significant points such as dams, gauging stations, tributary junctions and extraction points, whereas the links describe flow routes. The reliability of the models is affected by many factors, including the availability and accuracy of information on water extraction, stream flow and interactions between surface water and groundwater. Stream-flow data are limited by the distribution of gauging stations, which often do not cover all relevant tributaries, the number and frequency of gaugings and the stability of the flow control at each gauging station. (The flow control is the natural or artificial feature, such as a bar or weir, that determines the relationship between flow volume and river level.) In addition, gauging of flood flows is often difficult on alluvial rivers because Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

21

these flows can disperse widely on the floodplain. The modelling of low-development flows in distributary systems is especially problematic because the points at which effluent streams diverge from river channels have often been modified by excavation, filling and the construction of weirs. Moreover, information on the pre-European morphology of these points is often lacking. Modelling results are therefore not provided for distributary systems. Table 4.1. Gauging stations selected for flow modelling River system

Upper system

Mid system

Lower system

Barwon-Darling

422001 Barwon River at Walgett

425003 Darling River at Bourke

425002 Darling River at Wilcannia

Gwydir

418012 Gwydir River at Pinegrove

418063 Gwydir River downstream Tyreel

418066 Gwydir River at Millewa

Hunter (mainstream)

210002 Hunter River at Muswellbrook

210083 Hunter River at Liddell

210001 Hunter River at Singleton

Hunter (Glennies Creek)

210084 Glennies Creek at the Rocks

Not applicable

210044 Glennies Creek at Middle Falbrook

Lachlan

412002 Lachlan River at Cowra

412038 Lachlan River at Willandra Weir

412005 Lachlan River at Booligal Weir

Macquarie

421001 Macquarie River at Dubbo

421090 Macquarie River downstream Marebone Weir

421012 Macquarie River at Carinda

Murrumbidgee

410001 Murrumbidgee River 410021 Murrumbidgee River at Wagga Wagga at Darlington Point

Namoi

419001 Namoi River at Gunnedah

410130 Murrumbidgee River downstream Balranald Weir

419059 Namoi River 419026 Namoi River at downstream Gunidgera Weir Goangra

Measured flows and modelled low-development flows were summarised in several ways. As a simple summary statistic, total flow was calculated from measured data for each station over the two-year period, and expressed as a percentage of the modelled equivalent. In addition, time series plots were generated to show the seasonal patterns of measured and modelled daily flows at each station (Figures 4.2–4.9). Modelled daily flows for each station were also plotted against corresponding measured flows, expressed as percentages of modelled flows (Figures 4.10–4.13). These plots indicate the extent to which natural high, medium and low flows have been increased or reduced as a result of river regulation and water extraction during the two-year reporting period. In addition, flow-duration curves for each station were generated from measured and modelled daily flows for the period over which data were available in 1998-2000 (Figures 4.14–4.17). These plots show the proportion of time for which particular flows were exceeded under observed and modelled scenarios during the two-year period. All flow plots are grouped at the end of this chapter for ease of reference. River discharges sufficient to produce inflow (commence-to-flood flows) to individual, discrete wetlands (swamps and billabongs) were estimated in the Lachlan, Murrumbidgee and Namoi valleys by a combination of remote sensing, topographic surveys, information from wetland water level gauges, observations during flooding periods and consultation with local landowners (Tables 4.2-4.4). Methods are described for the Murrumbidgee River by Maguire (1998) and Hardwick et al. (2001), and for the Namoi River by Foster (1999). Daily flow data for hydrographic stations were used to calculate the frequency with which commence-to-flood thresholds for nearby wetlands were exceeded during the reporting period. Modelled low-development flows for the same stations were used to approximate natural flooding frequencies (Figure 4.18).


22

Table 4.2. Summary of commence-to-flood (CTF) flows for assessed wetlands in the Lachlan Valley. The river gauges used as benchmarks for commence-to-flood flows are arranged in sequence from upstream to downstream River gauge

Number of wetlands

Flow at gauge (ML/day)

412004 Lachlan River at Forbes

2

12 000–13 000

412006 Lachlan River at Condobolin Bridge

3

5 100–12 000

412039 Lachlan River at Hillston Weir

2

2 700–3 600

412005 Lachlan River at Booligal Weir

8

240–3 300

412122 Merrimajeel Creek at Cobb Highway

1

30

Table 4.3. Summary of commence-to-flood (CTF) flows for assessed wetlands in the Murrumbidgee Valley. The river gauges used as benchmarks for commence-to-flood flows are arranged in sequence from upstream to downstream River gauge

Number of wetlands

410004 Murrumbidgee River at Gundagai


3

29 000

30

17 000–61 000

1

23 000

410005 Murrumbidgee River at Narrandera

12

22 000–260 000

410021 Murrumbidgee River at Darlington Point

19

16 000–49 000

410078 Murrumbidgee River at Carrathool

10

10 000–20 000

410136 Murrumbidgee River downstream Hay Weir

14

13 000–38 000

8

4 600–7 800

410001 Murrumbidgee River at Wagga Wagga 410023 Murrumbidgee River downstream Berembed Weir

410130 Murrumbidgee River downstream Balranald Weir

Table 4.4. Summary of commence-to-flood (CTF) flows for assessed wetlands in the Namoi Valley. The river gauges used as benchmarks for commence-to-flood flows are arranged in sequence from upstream to downstream River gauge

Number of wetlands


419012 Namoi River at Boggabri

1

4 600

419082 Namoi River upstream Duncans Junction

3

1 700–3 300

419021 Namoi River at Bugilbone

4

1 800–4 500

419026 Namoi River at Goangra

4

1 900–14 000

4.3.

RESULTS

4.3.1.

Rainfall

Annual rainfall exceeded the long-term average across most of NSW in both 1998-99 and 1999-2000 (Figure 4.1). In the north and north-west of the State, including much of the Barwon-Darling, Gwydir, Macquarie and Namoi valleys, falls in both years were in the top 10% of all records. Extensive flooding occurred in this region during the reporting period. Rainfall was less extreme across the Hunter, Lachlan and Murrumbidgee valleys, though still generally well above average and sufficient to produce widespread inundation of flood plains.


23

Figure 4.1. Distribution of annual rainfall across NSW during 1998-99 and 1999-2000. Reproduced with permission


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4.3.2. Barwon-Darling River system Environmental flow rules were not implemented in the Barwon-Darling River during the reporting period because of delays in the installation of new flow gauging stations. Modelling of lowdevelopment flows was particularly difficult for the Barwon-Darling River because of the large number and diversity of tributaries and the limited information available on their flows and on water extraction in Queensland. The model tends to underestimate flood flows. Flow statistics (Table 4.5) suggest a reduction of total flow to about 60-75% of natural levels during the reporting period. However, the natural temporal pattern seemed to be largely preserved (Figure 4.2). Mid-range flows (around 10 000 ML/day) appeared to be the ones most reduced below natural levels, with very high and very low flows little altered (Figures 4.10 and 4.14). Table 4.5. Measured total flow (% modelled low-development flow) for the period July 1998-June 2000 for stations listed in Table 4.1. Asterisks indicate up to 120 days of missing data River system

Mid system

Lower system

Barwon-Darling

58

74

64

Gwydir

73

140

74*

120

69

70

Hunter (mainstream) Hunter (Glennies Creek)

22*

Not applicable

68

Lachlan

72

83

77

Macquarie

62*

86

68

110

46

22

95

89

69

Murrumbidgee Namoi

4.3.3.

Upper system

Gwydir River system

Environmental flow rule 1 for the Gwydir River required tributary inflows downstream of Copeton Dam to be passed to the wetlands when they were less than 500 ML/day. Such inflows occurred over long periods: on 260 days in 1998-99 and 302 days in 1999-2000 (Figure 4.3). Rule 2 limited offallocation extractions. Off-allocation was declared in parts of the Gwydir regulated system on 147 days in 1998-99 but only 44 days in 1999-2000 (Figure 4.3). A dam release (rule 3) of 9000 ML was made over 71 days from early November 1998 to early January 1999 in order to maintain bird breeding in the wetlands (Figure 4.3). No such release was made in 1999-2000. Modelling of low-development flows suggested that total flows were not greatly reduced below natural levels in the Gwydir River (Table 4.5). However, the midddle and lower Gwydir system is extremely difficult to model because of the flat terrain, great complexity of the channel network and presence of numerous structural modifications. The modelling suggested that winter-spring flows were artificially reduced in the upper part of the regulated system, whereas summer-autumn flows were elevated in the upper and middle parts (Figure 4.3). Consequently, natural flow variation tended to be damped (Figure 4.14). Very high flows were sometimes reduced to below 10% of modelled lowdevelopment values, whereas low flows were often increased to over ten times modelled levels (Figure 4.10). 4.3.4.

Hunter River system (including Glennies Creek system)

Environmental flow rule 1 in the Hunter Valley created an annual environmental contingency allowance of 22 000 ML, shared among Lostock, Glenbawn and Glennies Creek reservoirs. Although this water was reserved, contingencies requiring release did not occur in either 1998-99 or 1999-2000. Rule 2 established conditions under which off-allocation access to high flows was permitted. Such access was available in parts of the Hunter regulated system on 180 days in 1998-99 and 187 days in 1999-2000 (Figure 4.4). Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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At the modelling stations on the Hunter main stream, measured total flows ranged from above simulated low-development flows at Muswellbrook to about 70% of simulated flows near the end of the system (Table 4.5). Compared to the modelled flows, measured mid-range and high-range daily flows were reduced in volume at the mid-system and lower-system stations, and low-range flows were increased in volume throughout the regulated system (Figure 4.11). Total flow in Glennies Creek downstream of Glennies Creek Dam was greatly reduced from modelled levels (Table 4.5). At Middle Falbrook, downstream of the unregulated inflow from Goorangoola Creek, total flow was more similar to modelled flow. Both stations showed a marked artificial diminution of high-range daily flows and converse augmentation of low-range flows (Figure 4.11), suggesting that natural flow variation was greatly suppressed (Figure 4.15). Below the dam, simulated minimum flows were zero, but actual flows did not fall to this level during the reporting period (Figure 4.5). 4.3.5.

Lachlan River system

In the Lachlan River, environmental flow rule 1 required translucent releases from Wyangala Dam to achieve flows below Lake Brewster of 3500 ML/day between 1 June and 30 October. Such releases were made on 95 days in 1998-99 and 39 days in 1999-2000 (Figure 4.6). Rule 2 provided an environmental contingency allocation of 20 000 ML/year. Four ECA events were provided during the reporting period (Figure 4.6). From December 1998 to February 1999, 2600 ML were released from Toriganny Weir to maintain a naturally-triggered bird breeding event in the Booligal wetlands complex (see Chapter 8). In 1999 and 2000, 4600 ML were released from Wyangala Dam to suppress high river salinities measured at Cowra. Lachlan rule 3 limited off-allocation diversions to 30 000 ML annually. Off-allocation was declared in parts of the Lachlan valley on 98 days in 1998-99 and 26 days in 1999-2000 (Figure 4.6). Rule 4 provides for a minimum flow of 100 ML/day at Booligal to achieve a visible flow at ‘Geramy’, near the end of the system. Actual flows were above 100 ML/day at Booligal Weir for 326 days in 1998-99 and 260 days in 1999-2000 (Figure 4.6). Total flows in the Lachlan River were around 70-80% of modelled low-development flows during the reporting period (Table 4.5). Flows were generally below modelled levels during the late winter and spring periods and above modelled values during summer and autumn (Figure 4.6), signifying considerable suppression of natural flow variability (Figures 4.12 and 4.16). Modelling suggested that flows in the lower Lachlan River would naturally have fallen to zero during some parts of the reporting period, but zero flows never actually occurred. In wetlands near Booligal, analysis based on commence-to-flood levels implied that the natural range of flooding frequencies had been fairly well preserved, although low flooding frequencies were more common, and high flooding frequencies less common, than under modelled low-development conditions (Figure 4.18). 4.3.6.

Macquarie River system

Environmental flow rules in the Macquarie Valley included a Wild Life Allocation of up to 125 000 ML each year. Releases from Burrendong Dam under this rule occurred over four intervals during the reporting period (Figure 4.7), and totalled 13 300 ML in 1998-99 and 137 000 ML in 19992000. Water was also released from Burrendong Dam to maintain storage capacity for flood mitigation, over 164 days in 1998-99 and 113 days in 1999-2000 (Figure 4.7). The Macquarie rules limited off-allocation extraction to 50 000 ML annually. Off-allocation was declared in parts of the Macquarie regulated system on 98 days in 1998-99 and 29 days in 1999-2000 (Figure 4.7). The rules also included a provision to direct tributary flows and unused storage releases to the Macquarie Marshes for a period of 45 days when water was necessary for the successful completion of waterbird breeding. However, circumstances requiring this rule to be activated did not arise in either 1998-99 or 1999-2000. Total flows in the lower Macquarie River over the reporting period were about 60-90% of simulated low-development levels (Table 4.5). The overall pattern of measured flows at Dubbo was one of Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

26

curtailed flow variability, with suppressed winter and spring flow peaks and flows far above natural levels in summer and autumn (Figure 4.7). Further downstream the annual rhythm appeared more natural (Figure 4.7), although the tendency for suppression of natural high flows was evident throughout the system (Figures 4.12 and 4.16). The tendency for low flows to be boosted in natural low-flow periods was less evident in the Macquarie than in most other rivers. 4.3.7.

Murrumbidgee River system

The requirements of the Murrumbidgee Valley environmental flow rule 1 for minimum releases from Blowering and Burrinjuck dams were met throughout the reporting period, as were rule 2 requirements for minimum flow in the lower system at Balranald. Translucent releases from Burrinjuck Dam, under rule 3, occurred for intermittent short periods totalling 24 days in 1998-1999 and 46 days in 1999-2000 (Figure 4.8). No ECA releases were made under rule 4, which allocated up to 25 000 ML annually to support water quality, algal bloom suppression, fish breeding and forest and wetland watering. Total river flows over the reporting period were close to simulated low-development flows at Wagga Wagga, but only about 20% near the end of the system (Table 4.5). At Wagga Wagga, the daily pattern of measured flows had a reversed seasonality, with unnaturally high flows in summer and autumn and suppressed flow peaks in winter and spring (Figure 4.8). Further downstream the natural seasonal pattern was replaced by erratic fluctuations with no seasonal cycle. Plots of actual flows against modelled flows (Figure 4.13) and flow-duration curves (Figure 4.17) clearly show the longitudinal shift from high-flow suppression and low-flow augmentation in the upper regulated system, through to reduction throughout the flow range in the lower Murrumbidgee River. Analysis based on commence-to-flood levels indicated that flooding frequencies of wetlands near Wagga Wagga, Darlington Point and Balranald were drastically reduced below natural frequencies over the reporting period (Figure 4.18). Many wetlands did not flood at all under the regulated regime. The major exception is Berryjerry Lagoon near Wagga Wagga, which appeared to be flooded more often than under natural conditions. 4.3.8.

Namoi River system

The Namoi Valley environmental flow rules principally concerned off-allocation extraction. During the reporting period, off-allocation was declared in parts of the Namoi regulated system on 31 days in 1998-99 and 20 days in 1999-2000 (Figure 4.9). Modelling of the Namoi River suggested that total flows were only slightly reduced by regulation and extraction, except near the end of the system (Table 4.5). However, as in most other valleys, peak flows were suppressed and low flows boosted, particularly in the upper regulated system (Figures 4.13 and 4.17). The temporal pattern showed considerable damping of natural seasonal cycles at Gunnedah, with increased summer and autumn flows. Further downstream the regulated pattern appeared more erratic than the modelled low-development pattern (Figure 4.9). 4.4.

DISCUSSION

Flow regulation to support irrigated agriculture generally involves the capture of winter and spring runoff in reservoirs and its release during summer and autumn. Where regulation is intense and precise, natural seasonal and short-term variability is greatly damped. Natural flow peaks, mostly in spring and summer but sometimes at other times of the year, are typically removed or suppressed. Conversely, flows are consistently boosted at times, usually in summer and autumn, when they would naturally be low or even zero. This pattern can be seen clearly in the plots of simulated lowdevelopment versus measured flows for many stations on the Gwydir River, Glennies Creek in the Hunter Valley, the Macquarie River, the Murrumbidgee River and the Namoi River, especially in the upper regulated sections immediately below the major dams, where the capacity for tight flow regulation is greatest (Figures 4.10–4.13). Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

27

A less regulated pattern, with more erratic deviation between measured and modelled lowdevelopment flows, was indicated by plots for stations on the Barwon-Darling River (Figure 4.10), the Hunter River (Figure 4.11), and those stations near the end of the system on the Macquarie and Namoi rivers (Figures 4.12–4.13). There are probably several reasons for this. In the case of the Hunter River, unregulated tributaries entering downstream of Glenbawn Dam carry large volumes of water, and restore a more natural flow pattern. In the case of the Darling River and end-of-system stations, the great distance from the regulating storages, the contribution of unregulated tributary inflows, the variable extraction of water upstream and the dispersal of water by distributary channels probably all contribute to less precise regulation. The greater difficulty of modelling low-development flows at these stations may also be a contributor to the observed pattern. Most of the environmental flow rules that operated during the 1998-2000 reporting period were designed to engender higher river flows, over varying periods, than might otherwise have been the case. They did this either by requiring reservoir releases in addition to those made to supply extractive water requirements, or by limiting permissible extraction from rivers. The rules did not address the issue of reservoir releases producing sustained higher-than-natural flows, especially during the irrigation season, though in some cases environmental releases from reservoirs are likely to have resulted in slightly reduced irrigation flows because of their effect on volumes in storage. Some environmental flow rules that specified fixed minimum flows probably contributed to higher-thannatural flows at times. The partial retention of medium flow events downstream of the major dams can be seen in the timeseries plots for the Gwydir River (Figure 4.3), the Lachlan River (Figure 4.6) and the Namoi River (Figure 4.9), and to a lesser extent the Macquarie River (Figure 4.7) and the Murrumbidgee River (Figure 4.8). In contrast, the largest flows were never passed undiminished down the Gwydir, Lachlan, Macquarie, Murrumbidgee and Namoi river systems. In summer and autumn, flows in at least the upper and middle regulated parts of these river systems were often maintained far above natural levels for weeks or months at a time. In parts of the river systems where floodplain swamps and billabongs are inundated at relatively low river flows, such as the bottom end of the Lachlan River, the preservation of medium flow events apparently resulted in flooding frequency being only moderately diminished below natural levels during the reporting period (Figure 4.18). However, where high flows are generally needed to inundate such wetlands, as in much of the Murrumbidgee River, the medium flow events remained mainly within the channel, so that inundation seldom occurred. The ecological implications of wetland water regimes are explored in chapter 8. The possibility of in-channel environmental benefits of medium flow events is addressed in chapters 5, 6, 7 and 9. Since the reporting period was one of high rainfall and extensive flooding, flow patterns, their differences from natural patterns, and the ecological responses to them, are likely to be substantially different in drought years. The findings presented in this interim report should be considered in this context. IMEF was designed as a long-term project in recognition of the need for studies to extend across the full spectrum of climatic conditions.


28

Barwon River at Walgett 1 000 000

Daily flow (ML)

100 000

10 000

1 000

100 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

1-Jan-00

1-Jul-00

Darling River at Bourke 1 000 000

Daily flow (ML)

100 000

10 000

1 000

100 1-Jul-98

1-Jan-99

1-Jul-99

Darling River at Wilcannia 1 000 000

Daily flow (ML)

100 000

10 000

1 000

100 1-Jul-98

1-Jan-99 M e a s u r e d flo w

1-Jul-99

1-Jan-00

1-Jul-00

M o d e lle d l o w - d e v e l o p m e n t f lo w

Figure 4.2. Measured flow and modelled low-development flow for stations on the Barwon-Darling River (logarithmic scale)


29

Gwydir River at Pinegrove 1 000 000

Tributaries low Off allocation Bird release

Daily flow (ML)

100 000

10 000

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Gwydir River downstream Tyreel 10 000


Daily flow (ML)

1 000

100

10

1 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Gwydir River at Millewa 10 000


Daily flow (ML)

1 000

100

10

1 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.3. Measured flow and modelled low-development flow for stations on the Gwydir River (logarithmic scale). Symbols at top of each plot indicate periods when tributary flows were less than 500 ML/day, when off-allocation extraction was permitted in parts of the Gwydir regulated system and when releases were made to support bird breeding. Measured flow data are not available for 66 days at Millewa Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

30

Hunter River at Muswellbrook 1 000 000

Off allocation

Daily flow (ML)

100 000

10 000

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Hunter River at Liddell 1 000 000

Off allocation

Daily flow (ML)

100 000

10 000

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Hunter River at Singleton 1 000 000

Off allocation

Daily flow (ML)

100 000

10 000

1 000

100

10 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.4. Measured flow and modelled low-development flow for stations on the Hunter River (logarithmic scale). Symbols at top of each plot indicate periods when off-allocation extraction was permitted in parts of the Hunter regulated system


31

Glennies Creek at The Rocks 10 000

Daily flow (ML)

1 000

100

10

1 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Glennies Creek at Middle Falbrook 100 000

Daily flow (ML)

10 000

1 000

100

10

1 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.5. Measured flow and modelled low-development flow for stations on Glennies Creek (logarithmic scale). Measured flow data are not available for 120 days at The Rocks


32

Lachlan River at Cowra Translucency ECA Off allocation

1 000 000

100 000

Daily flow (ML)

10 000

1 000

100

10

1 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Lachlan River at Willandra Weir Translucency ECA Off allocation

100 000

Daily flow (ML)

10 000

1 000

100

10

1 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Lachlan River at Booligal Weir Translucency ECA Off allocation

10 000

Daily flow (ML)

1 000

100

10

1 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.6. Measured flow and modelled low-development flow for stations on the Lachlan River (logarithmic scale). Symbols at top of each plot indicate periods when translucency releases occurred, when Environmental Contigency Allowance [ECA] flows were provided and when off-allocation extraction was permitted in parts of the Lachlan regulated system Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

33

Macquarie River at Dubbo WLA Flood mitigation Off allocation

1 000 000

Daily flow (ML)

100 000

10 000

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Macquarie River at Marebone Weir WLA Flood mitigation Off allocation

10 000

Daily flow (ML)

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Macquarie River at Carinda WLA Flood mitigation Off allocation

100 000

Daily flow (ML)

10 000

1 000

100

10 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.7. Measured flow and modelled low-development flow for stations on the Macquarie River (logarithmic scale). Symbols at top of each plot indicate periods when Wild Life Allocation [WLA] releases occurred, when releases were made from Burrendong Dam for flood mitigation and when off-allocation extraction was permitted in parts of the Macquarie regulated system. Measured flow data are not available for 15 days at Dubbo


34

Murrumbidgee River at Wagga Wagga 100 000

Translucency

Daily flow (ML)

10 000

1 000

100 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Murrumbidgee River at Darlington Point 100 000

Translucency

Daily flow (ML)

10 000

1 000

100 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Murrumbidgee River downstream Balranald Weir 100 000

Translucency

Daily flow (ML)

10 000

1 000

100 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.8. Measured flow and modelled low-development flow for stations on the Murrumbidgee River (logarithmic scale). Symbols at top of each plot indicate periods when translucency releases were made from Burrinjuck Dam


35

Namoi River at Gunnedah 1 000 000

Off allocation

Daily flow (ML)

100 000

10 000

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Namoi River downstream Gunidgera Weir 100 000

Off allocation

Daily flow (ML)

10 000

1 000

100

10 1-Jul-98

1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Namoi River at Goangra 1 000 000

Off allocation

100 000

Daily flow (ML)

10 000

1 000

100

10

1 1-Jul-98


1-Jul-99

1-Jan-00

1-Jul-00


Figure 4.9. Measured flow and modelled low-development flow for stations on the Namoi River (logarithmic scale). Symbols at top of each plot indicate periods when off-allocation extraction was permitted in parts of the Namoi regulated system


36

Barwon River at Walgett

Gwydir River at Pinegrove

100 100

10000

1000

10000

100000

Measured daily flow (% LDDF)


1000

1000000

10

1

1000

100 10

100

1000

1000000

1

LDDF (ML)

Darling River at Bourke

Gwydir River downstream Tyreel

1000

100000

100 100

1000

10000

100000



100000

10

LDDF (ML)

1000000

10

10000

1000

100 1

10

100

1000

10000

10

1

LDDF (ML)

LDDF (ML)

Darling River at Wilcannia

Gwydir River at Millewa 10000

100 100

1000

10000

100000


1000


10000

1000000

10

1

1000

100 1

10

100

1000

10000

10

1

LDDF (ML)

LDDF (ML)

Figure 4.10. Relationships between modelled low-development daily flows (LDDF) and measured daily flows (expressed as a percent of LDDF) from 1 July 1998 to 30 June 2000 for the Barwon-Darling River (left) and Gwydir River (right). Data are plotted on logarithmic scales and exclude periods of zero LDDF and missing measured data


37

Hunter River at Muswellbrook

Glennies Creek at The Rocks 10000



10000

1000

100 10

100

1000

10000

100000

1000000

10

1

1000

100 1

10

1000

10000

10

1

0.1

LDDF (ML)

LDDF (ML)

Hunter River at Liddell

Glennies Creek at Middle Falbrook 100000


1000


100

100 10

100

1000

10000

100000

1000000

10

1

10000

1000

100 0.1

1

10

100

1000

10000

10

1

0.1

LDDF (ML)

LDDF (ML)

Hunter River at Singleton Measured daily flow (% LDDF)

1000

100 10

100

1000

10000

100000

1000000

10

1

LDDF (ML)

Figure 4.11. Relationships between modelled low-development daily flows (LDDF) and measured daily flows (expressed as a percent of LDDF) from 1 July 1998 to 30 June 2000 for the Hunter River (left) and Glennies Creek (right). Data are plotted on logarithmic scales and exclude periods of zero LDDF and missing measured data


38

Lachlan River at Cowra

Macquarie River at Dubbo 10000



100000

10000

1000

100 1

10

100

1000

10000

100000 1000000

10

1

1000

100 10

100

1000

1000000

1

LDDF (ML)

Lachlan River at Willandra Weir

Macquarie River at Marebone Weir 10000


10000


100000

10

LDDF (ML)

1000

100 1

10

100

1000

10000

100000

10

1

1000

100 10

100

1000

10000

10

1

0.1

LDDF (ML)

LDDF (ML)

Lachlan River at Booligal Weir

Macquarie River at Carinda

100000

1000



10000

10000

1000

100 1

10

100

1000

10000

10

100 10

100

1000

10000

10

1

1

LDDF (ML)

LDDF (ML)

Figure 4.12. Relationships between modelled low-development daily flows (LDDF) and measured daily flows (expressed as a percent of LDDF) from 1 July 1998 to 30 June 2000 for the Lachlan River (left) and Macquarie River (right). Data are plotted on logarithmic scales and exclude periods of zero LDDF and missing measured data


39

Murrumbidgee River at Wagga

Namoi River at Gunnedah 10000



10000

1000

100 100

1000

10000

100000

10

1000

100 10

100

Murrumbidgee River at Darlington Pt

Namoi River at Gunidgera Weir Measured daily flow (% LDDF)


1000000

10000

1000

1000

10000

100000

10

1000

100 10

100

1000

10000

100000

10

1

1

LDDF (ML)

LDDF (ML)

Murrumbidgee River d/s Balranald Weir

Namoi River at Goangra 1000

1000

10000


1000


100000

LDDF (ML)

10000

100 100

10000

10

LDDF (ML)

100 100

1000

100000

10

1

100 100

1000

10000

100000

1000000

10

1

LDDF (ML)

LDDF (ML)

Figure 4.13. Relationships between modelled low-development daily flows (LDDF) and measured daily flows (expressed as a percent of LDDF) from 1 July 1998 to 30 June 2000 for the Murrumbidgee River (left) and Namoi River (right). Data are plotted on logarithmic scales and exclude periods of zero LDDF


40


Gwydir River at Pinegrove

1 000 000

1 000 000

100 000

Daily flow (ML)

Daily flow (ML)

100 000

10 000

10 000

1 000

1 000 100

100

10 0

20

40

60

80

100

0

20

Percent of time exceeded

60

80

100

Gwydir River downstream Tyreel

1 000 000

10 000

100 000

1 000

Daily flow (ML)

Daily flow (ML)


10 000

1 000

100

10

100

1 0

20

40

60

80

100

0

20


40

60

80

100



Gwydir River at Millewa

1 000 000

10 000

100 000

1 000

Daily flow (ML)

Daily flow (ML)

40


10 000

1 000

100

10

100

1 0

20

40

60

80

100

0

20


M e a s u r e d flo w

40

60

80

100



Figure 4.14. Flow-duration curves for measured flow and modelled low-development flow (logarithmic scale) from 1 July 1998 to 30 June 2000, excluding periods with missing measured data, for the Barwon-Darling River (left) and Gwydir River (right)


41


Glennies Creek at The Rocks 10 000

1 000 000

100 000

Daily flow (ML)

Daily flow (ML)

1 000

10 000

1 000

100

10 100

10

1 0

20

40

60

80

100

0

20

40

60

80

100


Glennies Creek at Middle Falbrook

1 000 000

100 000

100 000

10 000

Daily flow (ML)

Daily flow (ML)

Hunter River at Liddell

10 000

1 000

100

1 000

100

10

10

1 0

20

40

60

80

100

0

20


40

60

80

100


Hunter River at Singleton 1 000 000

Daily flow (ML)

100 000

10 000

1 000

100

10 0

20

40

60

80

100




Figure 4.15. Flow-duration curves for measured flow and modelled low-development flow (logarithmic scale) from 1 July 1998 to 30 June 2000, excluding periods with missing measured data, for the Hunter River (left) and Glennies Creek (right) Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

42

Lachlan River at Cowra

Macquarie River at Dubbo

1 000 000

1 000 000

100 000

100 000

Daily flow (ML)

Daily flow (ML)

10 000

1 000

10 000

1 000

100

100

10

1

10 0

20

40

60

80

100

0

20


40

60

80

100



Macquarie River at Marebone Weir

100 000

10 000

10 000

Daily flow (ML)

Daily flow (ML)

1 000 1 000

100

100

10

1

10 0

20

40

60

80

100

0

20


40

60

80

100



Macquarie River at Carinda

10 000

10 000

1 000

Daily flow (ML)

Daily flow (ML)

1 000

100

100 10

1

10 0

20

40

60

80

100

0

20



40

60

80

100



Figure 4.16. Flow-duration curves for measured flow and modelled low-development flow (logarithmic scale) from 1 July 1998 to 30 June 2000, excluding periods with missing measured data, for the Lachlan River (left) and Macquarie River (right) Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

43

Murrumbidgee River at Wagga Wagga

Namoi River at Gunnedah

100 000

1 000 000

100 000

Daily flow (ML)

Daily flow (ML)

10 000 10 000

1 000

1 000

100

100

10 0

20

40

60

80

100

0

20


40

60

80

100


Murrumbidgee River at Darlington Point

Namoi River downstream Gunidgera Weir 100 000

100 000

10 000

Daily flow (ML)

Daily flow (ML)

10 000

1 000

1 000 100

100

10 0

20

40

60

80

0

100

20

40

60

80

100



Murrumbidgee River downstream Balranald Weir

Namoi River at Goangra

100 000

1 000 000

100 000

Daily flow (ML)

10 000

Daily flow (ML)

10 000

1 000

1 000

100

10

100

1 0

20

40

60

80

100

0

20



40

60

80

100



Figure 4.17. Flow-duration curves for measured flow and modelled low-development flow (logarithmic scale) from 1 July 1998 to 30 June 2000 for the Murrumbidgee River (left) and Namoi River (right) Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

44

Booligal

No. of wetlands

3

2

1

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

19

20

12

13

14

15

16

17

18

19

20

12

13

14

15

16

17

18

19

20

12

13

14

15

16

17

18

19

20

Flooding frequency

Wagga Wagga 25

No. of wetlands

20 15 10 5

0

1

2

3

4

5

6

7

8

9

10

11

Flooding frequency

Darlington Point 12

No. of wetlands

10 8 6 4 2

0

1

2

3

4

5

6

7

8

9

10

11

Flooding frequency

Balranald 7

No. of wetlands

6 5 4 3 2 1

0

1

2

3

4

5

6

7

8

9

10

11

Flooding frequency A ctual

M o de lled lo w -d eve lo pm ent

Figure 4.18. Calculated actual and modelled low-development flooding frequencies in 1998-2000 of swamps and billabongs in the Booligal region (Lachlan Valley) and three regions of the Murrumbidgee Valley. Data are based on local river flows known to reach wetland commence-to-flood heights, hydrographic monitoring of river flows during the reporting period, and hydrological modelling of lowdevelopment river flows


45


46

5.

River phytoplankton

5.1.

INTRODUCTION

Phytoplankton communities in rivers are dynamic because the constituent species have short life cycles and are governed by complex and often rapidly-changing interactions between turbulence, light regimes, temperature, nutrients, competition and grazing (Sullivan et al. 1988; Sullivan 1990). Although phytoplankton can play a major role in the carbon dynamics of lowland rivers (Robertson et al. 1999), much of the focus on phytoplankton in Australian lowland rivers relates to the development of blooms, particularly of cyanobacteria, that are hazardous to recreational uses of water, and water consumption by humans and livestock (Wasson et al. 1996). Nuisance blooms of cyanobacteria are common in the western rivers of NSW, the most spectacular being the bloom dominated by Anabaena circinalis that affected almost 1000 km of the Barwon-Darling River in the early summer of 1991 (Bowling and Baker 1996). Blooms of planktonic diatoms have been reported periodically in summer in the Hunter River from about the Dart Brook confluence to the Glennies Creek junction. These blooms cause clogging of water filters and sedimentation in water tanks. Under the NSW Algal Management Strategy, a high-level alert is issued for waters used for town, stock and domestic supply when the concentration of cyanobacteria exceeds 15 000 cells/mL. For recreational waters, a high alert is issued if more than 15 000 cells/mL of Anabaena circinalis or Microcystis aeruginosa are present, or if the count of potentially toxic species is below 15 000 cells/mL but the total cyanobacterial biovolume exceeds 2 mm3/L. If biovolume data are not available, local authorities can take a precautionary approach and issue an alert nevertheless. Several studies, mostly of riverine weir pools, have demonstrated that flow plays an important role in bloom development in the Murray-Darling Basin, in interaction with other factors such as turbidity, nutrients and weather (Burch et al. 1994; Hötzel and Croome 1994; Bormans et al. 1997; Donnelly et al. 1997; Oliver et al. 1999). Oliver et al. (1998) and Mitrovic et al. (2003) found that the dominance and growth of A. circinalis in the far-western rivers of NSW was strongly associated with pronounced and persistent vertical thermal stratification. This stratification occurred in the hotter months from October to April when river flows were less than 450 ML/day in the Darling River at Bourke or 100 ML/day in the Namoi River at Walgett. Stratification resulted in reduced turbidity, and consequent increased light penetration of the water column. It also enabled A. circinalis to take advantage of its ability to regulate buoyancy, migrating to surface waters where photosynthesis is enhanced (Mitrovic et al. 2001). Similarly, Webster et al. (1997) found that flows below 1000 ML/day in the lower Murrumbidgee River allowed persistent stratification to develop in the Hay and Maude weir pools. Under these conditions, A. circinalis became dominant over the diatom Aulacoseira granulata. IMEF hypotheses 1 and 3 postulate that environmental flow rules can influence the development and persistence of blooms in the study rivers. Hypothesis 1 proposes that rules protecting natural low flows (i.e., rules that restrict extraction when flow is naturally low) may make stratification less frequent and persistent than it would otherwise be. Hypothesis 3 is similar to hypothesis 1 but is concerned with rules that protect freshes and high flows. At times when thermal stratification and associated blooms have developed, natural freshes may flush the blooms by disrupting stratification and by diluting phytoplankton cells and washing them downstream. Protecting these freshes from extraction could be important in maintaining these removal mechanisms. These hypotheses are being tested in four valleys where nuisance cyanobacterial and algal blooms have periodically been reported: the Barwon-Darling, Hunter, Lachlan and Namoi valleys. Phytoplankton communities have been sampled at key sites (e.g. in weir pools and below tributary junctions), mostly close to locations where flows are continuously gauged. Other factors that may influence phytoplankton growth, such as temperature and nutrients, have also been recorded. In some cases, the development and breakdown of thermal stratification were measured. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

47

5.2.

BARWON-DARLING VALLEY

5.2.1.

Sites and methods

Data were obtained from the Barwon-Darling ‘Riverwatch’ program, which has been running since 1992 and includes 12 sites on the Barwon-Darling River (Map 2; Table 5.1). This program was established to provide an early warning of bloom development to residents and water managers along the river (Mitrovic and Gordon 1998). Samples are taken by community volunteers. Table 5.1. ‘Riverwatch’ sampling sites on the Barwon-Darling River, arranged in sequence from upstream to downstream Site number

Site name

No. of samples July Maximum cyanobacterial 1998 - June 2000 concentration (cells/mL)

416001

Barwon River at Mungindi

5

900

422003

Barwon River at Collarenebri

11

120

422001


13

1400

422002

Barwon River at Brewarrina

11

120

425003


61

13 940

42510044

Darling River at ‘Rose Isle’

51

24 358

425004

Darling River at Louth

26

8 840

425900

Darling River at Tilpa

30

4 760

42510046

Darling River at ‘Trevallyn’

27

12 680

42510047

Darling River at ‘Atley’

34

30 920

425008


33

7 640

42510048

Darling River at ‘Culpaulin’

29

31 840

Sampling frequency varied among sites (Table 5.1) and over time; the maximum was weekly and more samples were taken in the warmer months. Water samples for phytoplankton analysis were taken in a 1 L polyethylene bottle attached to a sampling pole, from 0.25 m below the surface and approximately 2 m from the river bank. They were preserved using Lugol's iodine solution and kept in the dark in transit to the laboratory, where cells were counted with a Lund cell by APHA (1998) method 10200-F. 5.2.2.

Results

Cyanobacterial counts exceeding 15 000 cells/mL were recorded at only three sites during the study period (Table 5.1). Such blooms were short lived, but at ‘Rose Isle’ a bloom lasted for four weeks during the summer of 1998-99 while flows remained low, and collapsed before the onset of higher flows (Figure 5.1). Relatively high cell counts were recorded at other sites during the same period (Figure 5.1). Blooms were mostly dominated by Anabaena sp., although counts above 1000 cells/mL were recorded for six other genera (Anabaenopsis, Aphanizomenon, Merismopedia, Microcystis, Oscillatoria and Pseudanabaena).


48

15 000

200 000

10 000

100 000

5 000

0 1-Jul-98

Cyanobacteria (cells/mL)

Daily flow (ML)

Darling River at Bourke 300 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

30 000

200 000

20 000

100 000

10 000

0 1-Jul-98


Daily flow (ML)

Darling River at 'Rose Isle' 300 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00


Daily flow (ML)

40 000 4 000 30 000

20 000 2 000


6 000

50 000

10 000

0 1-Jul-98

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00


40 000 Daily flow (ML)

6 000 30 000 4 000 20 000 2 000


8 000

50 000

10 000

0 1-Jul-98

0 1-Jan-99

1-Jul-99 F lo w

1-Jan-00

1-Jul-00

C y a n o b a c te ria

Figure 5.1. Daily flow and spot cyanobacterial cell concentrations in the Darling River at four sites, July 1998 - June 2000. Flow is not measured at 'Rose Isle', but has been estimated as flow at Bourke three days earlier


49

When flows in the river were high, cyanobacterial cell concentrations were always low, but when flows were low, cyanobacterial numbers were sometimes low and sometimes high (Figures 5.1 and 5.2), even in summer. Thus, factors other than flow controlled cyanobacterial numbers when flows were low. Plotting cyanobacterial numbers against nutrient concentrations (from the Riverwatch data set) did not reveal patterns suggesting that nutrients were the controlling factor. However, data were available only on total nutrients, not bioavailable nutrients. Darling River at Bourke

Darling River at 'Rose Isle' 30000



30000

20000

10000

0 100

1000

10000

100000

20000

10000

0 100

1000000

1000

Daily flow (ML)


1000000

Darling River at Wilcannia 30000



100000

Daily flow (ML)

30000

20000

10000

0 100

10000

1000

10000

100000

20000

10000

0 100

1000000

Daily flow (ML)

1000

10000

100000

1000000

Daily flow (ML)

Figure 5.2. Relationships between daily flow (logarithmic scale) and cyanobaterial cell concentration in the Darling River at four sites, July 1998 - June 2000. Flow is not measured at ‘Rose Isle’, but has been estimated as flow at Bourke three days earlier. All relationships are statistically significant (Spearman rank correlation: P < 0.05 for Bourke and Wilcannia; P < 0.01 for Tilpa; P < 0.001 for ‘Rose Isle’)


50

5.3.

HUNTER VALLEY

5.3.1.

Sites and methods

Eleven sites were sampled on the Hunter River downstream of Glenbawn Dam and on major tributaries (Map 4; Table 5.2). Sites were chosen to assess changes downstream of tributary inputs and along reaches without major tributaries. Sites were sampled weekly from October to March and fortnightly from April to September. Sampling started in August 1998 at all study sites with the exception of Glenbawn, Tyrrells and Broad Crossing, where sampling began in February 1999. On each occasion, the temperature of the stream was measured with a Hydrolab QuantaG probe and a single water sample for algal and nutrient analysis was obtained at each site. These samples were taken from the edges of fast-flowing sections of river with a 1 L polyethylene terephthalate (PET) bottle attached to a sampling pole. The pole was extended as far from shore as practical and the bottle was immersed upside down at 0.25 m depth. The bottle was then inverted, partly filled and rinsed. This procedure was repeated, filling the bottle. Two 250 mL PET bottles were rinsed with sampled water, then filled. One was preserved with Lugol’s iodine (2 mL) for algal analysis, and placed in the dark for transport to the laboratory. The second was retained for analysis of silica. A sterile 0.45 µm filter (Sartorius Minisart), attached to a rinsed 60 mL plastic syringe, was used to filter sampled water into a third 250 mL bottle for analysis of soluble nitrogen and phosphorus. The initial 20 mL of filtrate was used to rinse the bottle. Both nutrient subsamples were immediately frozen. In the laboratory, samples were analysed for oxidised and ammoniacal nitrogen, filterable phosphorus and reactive silica by APHA (1998) methods 4500-NO3-F, 4500-NH3, 4500-P and 4500-Si respectively. Analysis for phytoplankton was as for the Barwon-Darling Valley. Table 5.2. Phytoplankton sampling sites on the Hunter River and tributaries. Hunter River sites are arranged in sequence from upstream to downstream

5.3.2.

Site No.

Site name

No. of samples July Maximum diatom 1998 - June 2000 concentration (cells/mL)

210015

Hunter River at Glenbawn Dam

40

472

21010088

Hunter River at Tyrrells vineyard

43

476

21010089

Hunter River at Broad Crossing

43

813

210056

Hunter River at Aberdeen

61

2294

210002


61

1980

210055

Hunter River at Denman

59

6424

21010091

Hunter River at Bowmans Crossing

60

19 242

21010092

Hunter River at Moses Crossing

61

33 077

21010093

Hunter River at Maison Dieu

61

19 874

21010090

Dart Brook at Macintyre Bridge

45

27 538

210031

Goulburn River at Sandy Hollow

41

5364

Results

The phytoplankton of the Hunter River below Glenbawn Dam was dominated by green algae and cyanobacteria, though cyanobacterial counts did not exceed 4000 cells/mL. Flows and diatom counts at this site were low (Figure 5.3) and uncorrelated (Figure 5.4). High diatom cell counts were recorded at Denman and all Hunter River sites farther downstream, and in Dart Brook and the Goulburn River (Table 5.2). Peaks in diatom abundance occurred in both summers (Figure 5.3), under low-flow conditions (Figure 5.4). The dominant genera were Cyclotella and Nitzschia. Diatom blooms were associated with high temperatures, but cell counts showed no correlation with concentrations of dissolved phosphorus, oxidised nitrogen, ammonia or reactive silica.


51

Hunter River at Glenbawn Dam 800

500

400

300 400 200

Diatoms (cells/mL)

Daily flow (ML)

600

200 100

0 1-Jul-98

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Hunter River at Moses Crossing 150 000

40 000

20 000

50 000

Diatoms (cells/mL)

Daily flow (ML)

30 000 100 000

10 000

0 1-Jul-98

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Hunter River at Maison Dieu 20 000

100 000

80 000

60 000 10 000 40 000

Diatoms (cells/mL)

Daily flow (ML)

15 000

5 000 20 000

0 1-Jul-98

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

30 000

10 000

20 000

5 000

10 000

0 1-Jul-98

Diatoms (cells/mL)

Daily flow (ML)

Dart Brook at Macintyre Bridge 15 000

0 1-Jan-99

1-Jul-99

F lo w

1-Jan-00

1-Jul-00

D ia to m s

Figure 5.3. Daily flow and spot diatom cell concentrations in the Hunter River at three sites, and in Dart Brook, July 1998 - June 2000. Flow in Dart Brook is not measured at Macintyre Bridge; flow at Yarrandi Bridge is shown (with gaps where data are unavailable)


52

Hunter River at Glenbawn Dam

Hunter River at Moses Crossing

500

40000

Diatoms (cells/mL)

Diatoms (cells/mL)

400

300

200

30000

20000

10000 100

0

0 1

10

100

10

1000

100

1000

10000

Daily flow (ML)

Daily flow (ML)

Hunter River at Maison Dieu

Diatoms (cells/mL)

20000

15000

10000

5000

0 100

1000

10000

100000

Daily flow (ML)

Figure 5.4. Relationship between daily flow (logarithmic scale) and diatom cell concentrations in the Hunter River at three sites, July 1998 - June 2000. Relationships are statistically significant at Moses Crossing (Spearman rank correlation: P < 0.001) and Maison Dieu (P < 0.01) but not Glenbawn Dam (P > 0.05)

5.4.

LACHLAN VALLEY

5.4.1.

Sites and methods

Five weir pools were sampled on the Lachlan River (Map 5; Table 5.3). These sites were selected to include weirs that were known to be susceptible to cyanobacterial blooms. Samples were taken weekly during the warmer parts of the year when blooms are more likely: from January to May 1999 and November 1999 to April 2000. The frequency was reduced to fortnightly between mid April and mid June 2000. Forbes Weir was not sampled in the summer of 1999-2000 because it was found to have little ponding effect, being small and readily submerged by irrigation releases. Samples were taken from a boat at three to five randomly allocated locations in each weir pool. These locations had a minimum spacing of 100 m and were at mid stream. In 1999-2000 three points were sampled at all sites. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

53

Table 5.3. Phytoplankton sampling sites on the Lachlan River, arranged in sequence from upstream to downstream Site No.

Site name

No. of sampling No. of samples July Maximum cyanobacterial points 1998 - June 2000 concentration (cells/mL)

41210153

Lachlan River at Forbes Weir (town water supply)

3

17

3 040

412048

Lachlan River at Lake Brewster Weir

5

43

14 040

412038


3

45

287 700

412039

Lachlan River at Hillston Weir

5

45

127 060

412005


3

44

144 620

In 1998-99, surface and bottom water temperatures were measured with a WTW LF320 meter and in 1999-2000, a Hydrolab MiniSonde 4a multiprobe was used. A depth-integrated sample was collected at each point for phytoplankton and nutrient analysis. A 2 m flexible pipe, 25 mm in diameter with a one-way valve, was lowered vertically into the water, then removed and its contents deposited into a bucket. A composite sample from all points was stirred and a portion transferred to a 250 mL polyethylene bottle, preserved with Lugol’s iodine and stored in the dark. A further aliquot of the composite sample was filtered through a GFC 0.45 µm filter into a 100 mL polyethylene bottle for analysis of oxidised and ammoniacal nitrogen and filterable phosphorus. Analytical methods were as previously described for other valleys. 5.4.2.

Results

Cyanobacterial concentrations above 15 000 cells/mL were not observed at the two upstream sites at Forbes Weir and Lake Brewster Weir (Table 5.3). However, extremely high counts were recorded at the three downstream sites in the summer of 1998-99 (Table 5.3; Figure 5.5). In Willandra Weir pool, the genera Anabaena, Microcystis and Oscillatoria were present in roughly equal numbers in January 1999. As the bloom developed, Microcystis assumed dominance, though the other taxa were still common. By mid February 1999, Anabaena became dominant, and it remained so until the end of the bloom. As well as Microcystis and Oscillatoria, Aphanizomenon, Anabaenopsis, Cylindrospermopsis, Dactylococcopsis and Pseudanabaena were present in small numbers. At Hillston, Microcystis and Oscillatoria were dominant from January to March 1999, and Anabaena was also abundant in January. At the end of the bloom, Aphanizomenon, Cylindrospermopsis, Dactylococcopsis and Pseudanabaena were also present, but in low numbers. In Booligal Weir pool Microcystis attained large numbers in February 1999 and remained dominant until May. Oscillatoria, Anabaena and Aphanizomenon were present in low numbers. In late March, when total cyanobacterial numbers dropped, other genera such as Dactylococcopsis and Pseudanabaena were also present in low numbers. The cause of the high cyanobacterial concentrations in the lower Lachlan in the summer of 1998-1999 was clearly the outflow of cyanobacterial-laden water from Lake Brewster, which discharges to the Lachlan River between Lake Brewster Weir and Willandra Weir (Map 5). Peak cyanobacterial concentrations in the river during this period increased about 20-fold between the two weir pools (Figure 5.5). The lake was discharging between 800 and 1200 ML/day from late July 1998, contributing the bulk of downstream river flow from late December 1998 until the end of February 1999, when outflow ceased. Grab samples taken from the centre and outlet of the lake, as part of the Regional Algal Coordinating Committee monitoring program, showed cyanobacterial concentrations above 10 000 cells/mL during summer. The March decline in cyanobacterial populations in the riverine weir pools closely followed the cessation of this discharge. As a consequence of the role of Lake Brewster outflows, cyanobacterial cell counts in the weir pools of the lower river did not show a negative relationship with river flow (Figure 5.6). Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

54

Lachlan River at Lake Brewster Weir

Daily flow (ML)

10 000

5 000

0 1-Jul-98


15 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

300 000

10 000

200 000

5 000

100 000

0 1-Jul-98


Daily flow (ML)

Lachlan River at Willandra Weir 15 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Lachlan River at Hillston Weir 150 000

Daily flow (ML)

6 000 100 000

4 000

50 000 2 000

0 1-Jul-98


8 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Lachlan River at Booligal Weir 150 000

Daily flow (ML)

3 000 100 000

2 000

50 000 1 000

0 1-Jul-98


4 000

0 1-Jan-99

1-Jul-99 F lo w

1-Jan-00

1-Jul-00


Figure 5.5. Daily flow and spot cyanobacterial cell concentrations in the Lachlan River at four sites, July 1998 - June 2000. Flow data are not available for Lake Brewster Weir


55

Lachlan River at Forbes Weir

Lachlan River at Willandra Weir 300000



4000

3000

2000

1000

0

200000

100000

0

100

1000

10000

10

Daily flow (ML)

1000

10000

Daily flow (ML)

Lachlan River at Hillston Weir

Lachlan River at Booligal Weir 150000


150000


100

100000

50000

100000

50000

0

0 10

100

1000

10

10000

100

1000

Daily flow (ML)

Daily flow (ML)

Figure 5.6. Relationship between daily flow (logarithmic scale) and cyanobacterial cell concentrations in the Lachlan River at four sites, July 1998 - June 2000. Relationships are not statistically significant at any site (Spearman rank correlation: P > 0.05)

The massive blooms in the lower river did not recur during the summer of 1999-2000, which was wetter and cooler than the previous summer. Measurements of surface and bottom water temperatures showed that although all four weir pools stratified at some time during the summer, the vertical temperature differences were not great (maximum of 4.7 °C in Lake Brewster Weir pool, 2.2 °C in Willandra Weir pool, 2.2 °C in Hillston Weir pool and 3.4 °C in Booligal Weir pool) and pronounced stratification did not persist for long periods. Vertical temperature differences were inversely correlated with flow (Spearman rank correlation: P < 0.05; see Figure 5.7).


56


Lachlan River at Hillston Weir 3

Temperature difference (C)

Temperature difference (C)

3

2

1

2

1

0

0 10

100

1000

10

10000

100

1000

10000

Daily flow (ML)

Daily flow (ML)

Figure 5.7. Relationship between daily flow (logarithmic scale) and the vertical temperature difference in the Lachlan River at two sites, July 1998 - June 2000. Both relationships are statistically significant (Spearman rank correlation: P < 0.05)

5.5.

NAMOI VALLEY

5.5.1

Sites and methods

Four sites were selected for sampling in 1998-99: the Namoi River at Gunidgera Weir, the Namoi River at Mollee Weir, Pian Creek at Greylands Weir and Pian Creek at Dundee Weir. These weirpool sites were chosen because they were considered likely to be prone to cyanobacterial blooms and were sampled in pre-existing sampling programs, or were close to sites sampled in those programs. This approach minimised resource requirements and enabled IMEF data to be linked to other data, including historical data. In 1999-2000, a site on Narrabri Creek (an anabranch of the Namoi River that carries most of the flow) and two extra sites on the Namoi River were added to assess cyanobacterial transport between weir pools. The two Pian Creek sites were omitted because of the lower priority attached to this system. Thus nine sites were sampled in total over the two years (Map 8; Table 5.4). Table 5.4. Phytoplankton sampling sites on the Namoi River, Narrabri Creek and Pian Creek. Namoi River sites are arranged in sequence from upstream to downstream Site No.

Site name

No. of samples July Maximum cyanobacterial 1998 - June 2000 concentration (cells/mL)

419001


21

26 896

419062

Namoi River at Mollee Weir

45

9 005

419039

Namoi River at Mollee

28

1 087

419060

Namoi River at Gunidgera Weir

46

6 829

419068

Namoi River at downstream Weeta Weir

20

715

419021

Namoi River at Bugilbone

21

210

419003

Narrabri Creek at Narrabri

19

1 371

41910201 Pian Creek at Greylands Weir

25

7 825

41910202 Pian Creek at Dundee Weir

25

17 227


57

Sites were generally sampled weekly in summer and fortnightly or monthly at other times. In 1998-99 samples were taken by boat, 100 m upstream of the weir at each site. Water temperature and turbidity were measured at the thalweg, near the surface (0.25 m depth) and at depth intervals of 1.5 m, with a Horiba U 10 Water Checker. Nutrient and phytoplankton samples were collected at three points across the weir pool (between left bank and midstream, midstream and between right bank and midstream) in an integrated tube sampler, 1.5 m long with an internal diameter of 25 mm. The three samples were pooled and processed for analysis of oxidised and ammoniacal nitrogen, filterable phosphorus and phytoplankton cell counts in the same manner as for the Lachlan Valley, except that 0.45 µm cellulose acetate filters were used for filtration and samples were stored in PVC bottles. Because of resource constraints, in 1999-2000 surface grab samples were collected from the bank at each site, in the same manner as for the Hunter Valley except that no sample was taken for analysis of reactive silica. Water temperature and turbidity were measured at the same points with a Horiba U 10 Water Checker. Laboratory methods were as previously described for other valleys. 5.5.2.

Results

Cyanobacterial cell counts above 15 000 cells/mL were recorded at only two sites (Table 5.4) and there only rarely (Fig. 5.8). A bloom dominated by the genera Anabaena and Planktothrix occurred in Pian Creek at Dundee Weir in December 1998, when flows were low. A bloom dominated by Planktolyngbya sp. was recorded in the Namoi River at Gunnedah on one day in January 2000. Flow on this day was among the highest flows on days when cyanobacteria were sampled at this site. Overall, there was no clear relationship between cells counts and coincident flow (Fig. 5.9), nutrients or turbidity. Vertical temperature differences in the weir pools ranged up to 6 °C and showed only weak correlation with flow. 5.6.

DISCUSSION

Cyanobacterial and algal blooms were not especially prevalent in the study rivers during the reporting period. However, cyanobacterial cell densities above the nominal high alert level of 15 000 cells/mL were recorded periodically at some sites in each of the Barwon-Darling, Lachlan and Namoi valleys. No alert level exists for diatoms, but concentrations of these algae above 15 000 cells/mL were found at some sites in the Hunter River. Temperature, light availability or both appeared to limit phytoplankton cell concentrations in all valleys, since in every case, blooms were confined to the summer and autumn months. This may not always be so, however, since Hötzel and Croome (1994) recorded cyanobacterial peaks in the lower Darling River at Burtundy at temperatures as low as 10 °C. The role of flow appeared to be more variable. In the Barwon-Darling and Hunter valleys there was a strong inverse relationship between flow volume and cyanobacterial and diatom cell concentrations respectively (Figures 5.2 and 5.4). However, no such association was observed in the Lachlan and Namoi valleys (Figures 5.6 and 5.9). There was no evidence that nutrients played a major role in bloom limitation, probably because nutrients were seldom in short supply. Vertical thermal and chemical stratification, particularly in weir pools, is often considered to be the mechanism by which low flows mediate cyanobacterial blooms in the Murray-Darling Basin (Burch et al. 1994; Sherman et al. 1994; Bormans et al. 1997; Bormans and Condie 1998; Sherman et al. 1998; Webster et al. 2000). Stratification, or at least a lack of vertical mixing, leads to flocculation and settling of suspended sediment, with consequent increases in light penetration, and enables buoyant cyanobacteria to remain in the photic zone (Sherman and Webster 1994; Bormans et al. 1997; Donnelly et al. 1997; Mitrovic et al. 2001). Vertical mixing is promoted by greater flow volume, but can also be effected by wind action (Bormans et al. 1997).


58

Namoi River at Gunnedah 30 000

Daily flow (ML)

150 000 20 000

100 000

10 000 50 000

0 1-Jul-98


200 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

Namoi River at Mollee Weir 10 000

Daily flow (ML)

150 000

100 000

5 000

50 000

0 1-Jul-98


200 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

8 000

30 000

6 000

20 000

4 000

10 000

2 000

0 1-Jul-98


Daily flow (ML)

Namoi River at Gunidgera Weir 40 000

0 1-Jan-99

1-Jul-99

1-Jan-00

1-Jul-00

20 000

1 500

15 000

1 000

10 000

500

5 000

0 1-Jul-98


Daily flow (ML)

Pian Creek at Dundee Weir 2 000

0 1-Jan-99

1-Jul-99 F lo w

1-Jan-00

1-Jul-00


Figure 5.8. Daily flow and spot cyanobacterial cell concentrations in the Namoi River at three sites and at one site on Pian Creek. For Mollee Weir flow data are for Mollee (station 419039); for Gunidgera Weir flow data are for immediately below the weir (419059); for Dundee Weir, flows are at Dempsey Bridge (419089) (with gaps where data are unvailable)


59


Namoi River at Mollee Weir 10000



30000

20000

10000

0

8000

6000

4000

2000

0 10

100

1000

10000

10

Daily flow (ML)

100

1000

10000

Daily flow (ML)

Figure 5.9. Relationship between daily flow (logarithmic scale) and cyanobacterial cell concentrations in the Namoi River at two sites, July 1998 - June 2000. Relationships are not statistically significant at either site (Spearman rank correlation: P > 0.05)

In the Barwon-Darling River, blooms were never associated with flows above about 1000 ML/day (Figure 5.2), as previously observed by Oliver et al. (1999). This threshold is roughly comparable to the flow of 450 ML/day that Mitrovic et al. (2003) considered to be the maximum that would permit the development of persistent vertical stratification in the Darling River at Bourke between October and April. However, blooms often failed to develop at flows below this threshold, even in summer, suggesting the presence of other controlling factors. Donnelly et al. (1997) suggested that a lack of dissolved iron might often limit cyanobacterial nitrogen fixation in the Darling River, because inflows of sulphate-rich saline groundwater may precipitate dissolved iron when river flows are low. In the Hunter River, diatom blooms were restricted to low-flow conditions, the flow threshold for bloom suppression varying with site (Figure 5.4). Low diatom concentrations were recorded downstream of Glenbawn Dam (Figure 5.3), indicating that the dam was not the source of the blooms. This contrasts to the situation in the La Trobe River, Victoria, where an on-stream impoundment was considered to initiate diatom blooms that proliferated downstream (Chessman 1985a). In the Hunter River, the blooms appeared to develop progressively with distance downstream (Table 5.2). In the Lachlan River the outflow of cyanobacteria-rich water from Lake Brewster was the source of the major bloom in early 1999, and consequently river flow volume was largely irrelevant. In addition, stratification in the Lachlan River weir pools was not pronounced (Figure 5.7). Apart from the normal seasonal pattern, the factors controlling cyanobacterial blooms in the Namoi River are unclear. The brief peak at Gunnedah corresponded with a small flow peak and the cyanobacteria may have originated with the source of the water. Lake Keepit is a possible source since a bloom was present in the reservoir at the time. However, the reservoir was not spilling and was releasing bottom water only. In Pian Creek at Dundee Weir, high temperatures, persistent low flows and associated stratification appeared responsible for the bloom in December 1998. The lack of a strong correlation between flow and stratification in Gunidgera and Mollee weirs may be because these are ‘undershot’ weirs, with bottom releases that allow the warmer water above the thermocline to remain as a ‘dead zone’, regardless of the rate of flow-through of colder bottom water released from Keepit Dam. Nevertheless, these weirs did not develop cyanobacterial populations in excess of 15 000 cells/mL during the study period. Environmental water allocations are likely to reduce the frequency and duration of cyanobacterial blooms in those rivers where the occurrence of blooms seems to strongly relate to flow. For example, the Barwon-Darling pumping thresholds for B and C class licences (Appendix: Table A1; not yet Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

60

implemented during the 1998-2000 reporting period) generally protect flows in the range below which blooms can develop (500–1000 ML/day). However, the frequency of flows below this level appears to be substantially greater than natural. For example, simulation modelling suggested that flows below 1000 ML/day would have naturally occurred on only about 9% of days at Bourke during the reporting period, whereas such flows actually occurred on 26% of days (Chapter 4: Figure 4.14). Of course, the occurrence of such flows is affected by extraction on all upstream river systems, and not just by local pumping. In the Hunter River the apparent threshold for potential development of diatom blooms (around 300–1000 ML/day, depending on site) exceeds the minimum flows protected by rule 2. At Liddell, flows below 300 ML/day occurred on 40% of days during the reporting period and flows below 1000 ML/day on 70% of days (Chapter 4: Figure 4.15). By contrast, modelling suggested that flows under 300 ML/day would have naturally occurred on only about 14% of days and flows under 1000 ML/day on about 56% during this period. In those systems where bloom development did not appear to be closely associated with river flow (the Lachlan and Namoi rivers), the place of environmental flows in management of blooms is less certain. However, analysis of data collected over a longer period, and perhaps modelling of cyanobacterial populations, are needed before confident answers to this question can be formulated.


61


62

6.

River biofilms and macroinvertebrates

6.1.

INTRODUCTION

The complex biogenic film that coats the surface of submerged rocks, logs and other substrata can be an important component of the food webs in Australian rivers (Walker et al. 1995; Bunn and Davies 1999; Burns and Ryder 2001). This biofilm, also known as periphyton or Aufwuchs (German for ‘growth upon’) comprises algae, fungi, bacteria and detritus, often embedded in a polysaccharide matrix (Geesey et al. 1978; Lock et al. 1984). Biofilms in Australian rivers are grazed by many aquatic invertebrates, and some fish and turtles (e.g. Chessman 1986a, 1986b; McDowall 1996; Burns and Walker 2000). River biofilms are prone to scouring during high flows (Biggs et al. 1999a). Scouring resistance and post-spate biomass are governed by interactions among water velocity, light, nutrient availability, recolonisation mechanisms and macroinvertebrate grazing (Horner and Welch 1981; Stevenson 1990; DeNicola et al. 1992; Biggs 1995; Peterson et al. 1994; Poff and Ward 1995; Peterson 1996; Biggs et al. 1998a, 1999b). Different algal groups are best adapted to particular frequencies of resource supply and physical disturbance (Biggs et al. 1998b), and an intermediate level of flood disturbance can maintain high diversity of periphytic algal species (Ács and Kiss 1993; Fayolle et al. 1998). The effects of flow alteration on the biofilms in Australian rivers are poorly known. Chessman (1985b) found that periphyton biomass in the La Trobe River, Victoria, was related to annual cycles in both flow and nutrient concentrations. Robson (2000) showed that residual biofilm on dry rocks in intermittent streams influenced algal regrowth when the rocks were wetted. Growns and Growns (2001) reported differences in genus composition between the periphytic diatom assemblages of regulated and unregulated streams in the Hawkesbury-Nepean River system, NSW. Burns et al. (1994) compared biofilm algal assemblages upstream of Lock 1 on the lower Murray River (with relatively stable water levels) and at a site below the lock (with fluctuating levels). Biomass peaked at shallow depths above the lock where water levels were relatively stable and in deeper water below, where levels fluctuated. Community composition varied more with depth at the downstream site. Burns and Walker (2000) suggested that river levels could be managed to maintain diverse successional stages of biofilms as resources for grazing macroinvertebrates. It has been hypothesised that anthropogenic flow alteration can affect the palatability of biofilms to grazing invertebrates in Australian rivers. Historically the inland river systems of south-eastern Australia supported rich assemblages of aquatic snails. In the River Murray in South Australia, a marked decline in populations of most species, and local extinctions of some, have paralleled increasing flow regulation over the past half century (Sheldon and Walker 1993). The viviparids Notopala sublineata and N. hanleyi and the thiarid Thiara balonnensis have been particularly affected. Sheldon and Walker (1997) have speculated that the loss of detritivorous snails is related to a shift from bacterial to algal-dominated littoral biofilms occasioned by stabilisation of river levels following the construction of dams and weirs. Extensive surveys of the western rivers of NSW have failed to locate any extant populations of Notopala, and have found Thiara at only a few localities (DIPNR unpublished data). Notopala sublineata has been listed as an endangered species under the Fisheries Management Act 1994. IMEF hypothesis 4 proposes that protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (to meet RFOs 3 and 6), through off-allocation use restrictions and dam releases, will induce scouring of silt and sloughing of biofilms from stony substrata, resetting biofilm development and improving habitat quality for some invertebrate scrapers and their predators, and spawning conditions for gravel-spawning fishes. The issue of fish spawning is considered as part of the native fish studies (Chapter 9). The present chapter deals with changes in biofilms and the macroinvertebrate assemblages feeding on them. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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It is hypothesised that the maintenance of a low and steady flow over long periods, such as has often occurred below major storages during the non-irrigation season, has allowed the build-up and persistence of mature biofilms. These biofilms may have a different structure from those that dominate under natural flow regimes, when periodic freshes and floods reset biofilm development to early successional stages. Restoring a proportion of freshes and floods under environmental flow rules may partly reverse this change, and make biofilms and the invertebrates that graze on them more natural and more diverse. The hypothesis is being tested by sampling biofilms and invertebrates from stones on the bed of regulated rivers before and after environmental flow events. Sampling of nearby unregulated rivers (reference rivers) provides a benchmark, so that the communities of regulated rivers with environmental flows (test rivers) can be compared to those occurring under natural flow regimes. If environmental flows are beneficial to biofilm quantity and quality, the biofilms and associated invertebrates of test rivers should become more similar to those of reference rivers when environmental flows are in operation. Sampling of control sites (regulated rivers without environmental flow provisions) is also desirable, in order to make inferences about whether changes observed in test rivers would have occurred without environmental flow provisions. However, suitable controls are seldom available. Biofilms are being studied in Glennies Creek and its tributaries in the Hunter Valley, and in the Murrumbidgee River and its tributaries. Various structural and functional attributes of the biofilm, and the invertebrates that graze on it, are being studied. These include the total organic and inorganic mass of the biofilm and its chlorophyll a concentration as a measure of algal content. In the Murrumbidgee region only, additional studies are being done on the rate of primary production (photosynthesis) and community respiration of the biofilm, and on stable isotopes. Dual isotope analysis (13C and 15N) is being used with the aim of determining whether the macroinvertebrate primary consumers found on and around the biofilm are using it as a food source. This involves comparison of isotope signatures in biofilms and macroinvertebrates collected at the same time (Peterson and Fry 1987). Nitrogen isotope measurements function as trophic level indicators, while carbon isotope measurements can indicate which primary producers (e.g. C3 or C4 plants) are important sources of nutrition for consumers (Fry 1991). 6.2.

HUNTER VALLEY

6.2.1.

Sites and methods

Regular sampling at six sites on the Glennies Creek system (Map 4; Table 6.1) began in February 2000. The sampling design involved three rivers with a pair of sites on each river. Two sites are located on Glennies Creek downstream of Glennies Creek Dam and upstream of the unregulated inflow from Goorangoola Creek. These are treatment sites and will be exposed to a scouring flow from Glennies Creek Dam after baseline data collection for over two years. Four reference sites with near-natural flow regimes are located on two unregulated tributaries (Carrow Brook and Goorangoola Creek). No control sites (regulated but without environmental releases) are available for this system. During the period covered by this report, sampling occurred in February and May 2000. May samples have not yet been fully processed, and only February results are reported here. Flows during the February sampling period were low in both Carrow Brook and Glennies Creek (Figure 6.1). Flows in Goorangoola Creek are not gauged, but probably follow a similar pattern to those in Carrow Brook.


64

Table 6.1. Biofilm study sites on Glennies Creek and its tributaries in the Hunter Valley Site number

Site name

Site type

21010183

Carrow Brook (1) near Balmoral

Reference

21010182

Carrow Brook (2) near Balmoral

Reference

21010184

Glennies Creek (1) below Glennies Creek Dam

Treatment

21010187

Glennies Creek (2) at Mount Olive

Treatment

21010186

Goorangoola Creek (1) near Murulla

Reference

21010185

Goorangoola Creek (2) near Greylands

Reference

Glennies Creek at The Rocks 1400

1200

1200

1000

1000

Daily flow (ML)

Daily flow (ML)

Carrow Brook at Carrowbrook 1400

800 600

800 600

400

400

200

200

0 01-Jul-99

0 01-Oct-99

01-Jan-00

01-Apr-00

01-Jul-00

01-Jul-99

01-Oct-99

Date

01-Jan-00

01-Apr-00

01-Jul-00

Date

Figure 6.1. Daily flows during 1999-2000 for Carrow Brook (upstream of Glennies Creek Dam) and Glennies Creek at the Rocks (downstream of dam). Data for Carrow Brook are not available for much of 1999

For macroinvertebrate sampling, five points within a riffle at each site were defined at random coordinates and located with tape measures. Sampling proceeded from downstream to upstream. At each random point a large stone (120–250 mm diameter) was located and a dip net (350 x 250 mm opening and 0.25 mm mesh) was lowered to the stone’s downstream edge. The stone was lifted, without disturbing the surrounding stream sediments, and transferred to a bucket with the net beneath it; any matter washed from the stone was caught in the net. The net was inverted and its contents were washed into the bucket with the stone. The stone was cleaned with a paintbrush and forceps were used to pick invertebrates out of any crevices. The contents of the bucket were then transferred to a 500 mL PET container, which was refrigerated in transit to the laboratory. Each stone was allowed to dry, labelled and returned to the laboratory. In the laboratory, the contents of the container were transferred to a large white tray and all macroinvertebrates were picked under a magnifying lamp into a glass jar containing a mixture of ethanol (90%) and glycerol (10%). Invertebrates were subsequently identified to genus or, where this was not possible, to the lowest practicable taxonomic level. Each stone was wrapped in pieces of aluminium foil so that the whole surface was covered by a single layer. The foil was removed and weighed using a top-loading laboratory balance. Its mass was converted to stone surface area by comparison with the mass of a known area of the same foil. Stone surface areas were used to convert counts of invertebrate taxa to densities per unit area of stone surface. For sampling of biofilms, five random stones were removed individually from the stream as described previously, except that no dip net was used. The biofilm was removed from the surface of each stone Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

65

with a stiff brush, after which the brush and stone were rinsed and the biofilm and washings were placed in a PET container and returned to the laboratory under refrigeration. In the laboratory, the contents of the container were transferred to a mechanical blender, the volume was made up to 1 L using deionised water, and the mixture was homogenised for 1 minute. At the end of this interval, a 10 mL aliquot of the blended material was quickly removed with a syringe and passed through a GFC filter. The filter was folded using forceps, wrapped in aluminium foil, placed in a small plastic ziplock bag and frozen with dry ice. Subsequently, these samples were analysed for chlorophyll a (and phaeophytin a) by the Lorenzen and UNESCO methods (APHA 1998). Chlorophyll and phaeophytin concentrations in the subsample were used to calculate mass per unit area of stone surface. A further 50 mL subsample was removed in the same manner, transferred into a glass jar and fixed with Lugol’s iodine. These preserved subsamples were used for algal counts in a Sedgwick-Rafter counting chamber under a compound microscope at magnifications of 100–400×. A total cell count was performed as well as individual counts for abundant genera. These counts were based on 5–10 random transects, up to a maximum of 100 cells, filaments or colonies per genus. In the case of cyanobacterial filaments, individual cells were often hard to distinguish and counts were recorded as filaments per mL. Cell concentrations were converted to densities per unit area of stone surface. Nested analysis of variance (ANOVA) was used to test for significant differences in various biofilm properties. Site was nested within river. The properties considered were mass per unit area of stone surface of chlorophyll a, phaeophytin a, the major algal and cyanobacterial groups (cyanobacterial filaments, centric diatoms, pennate diatoms and filamentous green algae) and macroinvertebrate functional feeding groups. Feeding groups considered were those defined on the basis of mechanisms of food acquisition by Merritt and Cummins (1996): engulfing predators, filtering collectors, gathering collectors, piercers, scrapers and shredders. Individual taxa were assigned to feeding groups from information in Chessman (1986a) and Merritt and Cummins (1996). All data were transformed to the fourth root before analysis. The ordination method of non-metric multidimensional scaling (NMS), in the PC-ORD software package (McCune and Mefford 1999), was used to examine spatial patterns in algal-cyanobacterial and macroinvertebrate assemblages. Taxa density data for individual samples (rocks) were transformed to the fourth root for analysis and dissimilarity was expressed as the Bray-Curtis coefficient. Differences in assemblages among sites were tested for statistical significance by the multi-response permutation procedure (MRPP) in PC-ORD. 6.2.2.

Results

Nested ANOVA showed that most biofilm properties differed significantly both among rivers and between sites (Table 6.2). Phytopigment densities (chlorophyll a and phaeophytin a) were particularly high in Glennies Creek immediately downstream of the dam, but were also high at the downstream site on Goorangoola Creek (Figure 6.2). Filamentous cyanobacteria and centric and pennate diatoms were also most abundant immediately below the dam, whereas filamentous green algae (mostly Cladophora sp.) were scarce in Glennies Creek but abundant in the unregulated tributaries (Figure 6.3). Invertebrate scrapers were the dominant macroinvertebrate functional feeding group (Figure 6.4). Their density in Glennies Creek was intermediate between the densities in the two unregulated tributaries. Two-dimensional NMS showed a clear separation both among rivers and between sites within rivers for both algal-cyanobacterial assemblages (Figure 6.5, left) and macroinvertebrate assemblages (Figure 6.5, right). The differences among sites were highly statistically significant (MRPP: P < 0.001). The patterns were different for the two groups of biota, since for algae the two reference rivers overlapped, whereas for macroinvertebrates they did not. However, the site on Glennies Creek immediately downstream of the dam was the most distinctive for both groups.


66

Table 6.2. F-values from nested ANOVA of differences among rivers and between sites within rivers for various properites of stone-surface biofilms and associated macroinvertebrates in the Glennies Creek system, February 2000. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, not significant Property

Rivers

Sites

2

8.1 **

15.9 ***

2

8.2 **

16.8 ***

5.5 *

9.2 ***

8.5 **

5.7 **

25.3 ***

36.6 ***

32.8 ***

19.1 ***

16.6 ***

1.1 ns

15.8 ***

3.1 *

1.1 ns

5.4 **

5.2 *

2.3 ns

0.6 ns

3.1 *

2.5 ns

1.0 ns

20.8 ***

0.6 ns

Chlorophyll a (Lorenzen) (mg/m ) Chlorophyll a (UNESCO) (mg/m ) 2

Phaeophytin a (mg/m ) 2

Cyanobacteria (filaments/mm ) 2

Centric diatoms (cells/mm ) 2

Pennate diatoms (cells/mm ) 2

Filamentous green algae (cells/mm ) 2

Engulfing invertebrates (No./m ) 2

Filtering invertebrates (No./m ) 2

Gathering invertebrates (No./m ) 2

Piercing invertebrates (No./m ) 2

Scraping invertebrates (No./m ) 2

Shredding invertebrates (No./m )

Chlorophyll a (Lorenzen)

Chlorophyll a (UNESCO)

Phaeophytin a

30

2

Density (mg/m )

40

20

10

Carrow 1

Carrow 2

Glennies 1

Glennies 2

Goorangoola 1

Goorangoola 2

Figure 6.2. Densities of phytopigments on rocks at sites in the Glennies Creek system, February 2000 (mean ± standard error of untransformed data)


67


68

0

1 000

2 000

3 000

4 000

5 000

2

100

200

300

400

500

600

Carrow 1

Cyanobacterial filaments

Carrow 2

Glennies 1

Centric diatoms

Glennies 2

Goorangoola 1

Filamentous green algal cells

Goorangoola 2

Pennate diatoms

Filterers

Carrow 1

Carrow 2

Glennies 1

Gatherers

Glennies 2

Goorangoola 1

Piercers

Goorangoola 2

Scrapers

Shredders

Figure 6.4. Densities of macroinvertebrate functional feeding groups on rocks at sites in the Glennies Creek system, February 2000 (mean ± standard error of untransformed data)

Engulfers

Figure 6.3. Densities of major algal and cyanobacterial groups on rocks at sites in the Glennies Creek system, February 2000 (mean ± standard error of untransformed data)

Density (units/mm )

Density (No./m )

2

Algae

Macroinvertebrates

2.0

1.5

1.5

1.0

1.0 0.5 0.5 0.0 0.0 -0.5 -0.5 -1.0

-1.0 -1.5 -1.5

-1.0

-0.5

0.0

Carrow 1

0.5

1.0

Carrow 2

1.5

-1.5 -2.0

2.0

Glennies 1

Glennies 2

-1.5

-1.0

-0.5

Goorangoola 1

0.0

0.5

1.0

1.5

2.0

Goorangoola 2

Figure 6.5. NMS ordination of density data for biofilm algae and cyanobacteria (left) and associated macroinvertebrates (right) at sites in the Glennies Creek system, February 2000. Stress = 0.12 and 0.14 respectively

6.3.

MURRUMBIDGEE VALLEY

6.3.1.

Sites and methods

Preliminary sampling of macroinvertebrates at eight sites on the Murrumbidgee River and tributaries (Map 7; Table 6.3) occurred in July 1999, but detailed work began in October. Two treatment sites, located on the Murrumbidgee River downstream of Burrinjuck Dam, receive periodic environmental releases, as well as irrigation flows and uncontrolled spills. Both heavy grazing and recreational use are present along the margins of the river, though some remnant native riparian vegetation remains. Four reference sites are located on the Goobarragandra and Goodradigbee rivers. Both rivers are unregulated, although a small, fixed-crest weir in the headwaters of the Goodradigbee River diverts a small proportion of the river’s total flow to Tantangara Reservoir on the upper Murrumbidgee River. Both flow mainly through native forest, with some grazing in their lower reaches. Two control sites were chosen on the Tumut River, which is regulated by Blowering Dam but unlike the Murrumbidgee River was not expected to receive translucent environmental releases in late winter and early spring. This river carries an annual flow volume that is substantially greater than natural because of interbasin transfers in the Snowy Mountains Hydro-electric Scheme. It has been highly modified by rock walling, straightening of the channel and removal of woody debris and cobble beds. Adjacent land is grazed but some remnant riparian vegetation remains. All sites have a substratum of boulders and cobbles. All eight sites were sampled in late October-early November 1999, but because of resource constraints and high flows only three sites were sampled in February 2000 and four in May 2000 (Table 6.3). The October-November sampling period was characterised by stable low flows in the Murrumbidgee River downstream of Burrinjuck Dam following environmental releases in early spring (Figure 6.6). The February sampling occurred during the period of high-volume irrigation releases from Burrinjuck Dam and the May sampling followed these releases. High summer flows also occurred in the other rivers, as a result of rainfall events for the Goobarragandra and Goodradigbee Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

69

rivers and irrigation releases for the Tumut River (Figure 6.6). The pattern of flows was similar in the two reference rivers, but quite different in each of the regulated rivers. Table 6.3. Biofilm study sites on the Murrumbidgee River and tributaries Site number

Site name

Site type

Months sampled

41010312

Goobarragandra River (1) at Lacmalac

Reference

Oct.-Nov. 99, Feb 00, May 00

41010173

Goobarragandra River (2) at Flat Rock Reserve

Reference

Oct.-Nov. 99

41010351

Goodradigbee River (1) at Swinging Bridge

Reference


41010166

Goodradigbee River (2) at Swinging Bridge

Reference

Oct.-Nov. 99

41010313

Murrumbidgee River (1) at Illawong

Treatment

Oct.-Nov. 99

41010314

Murrumbidgee River (2) at Riverview

Treatment


41010311

Tumut River (1) at Jones Bridge Reserve

Control

Oct.-Nov. 99

41010988

Tumut River (2) at Green Hills Forestry Nursery

Control

Oct.-Nov. 99, May 00

Goodradigbee River at Wee Jasper 12000

10000

10000

8000

8000

Daily flow (ML)

Daily flow (ML)

Goobarragandra River at Lacmalac 12000

6000

4000

2000

6000

4000

2000

0 01-Jul-99

01-Oct-99

01-Jan-00

01-Apr-00

0 01-Jul-99

01-Jul-00

01-Oct-99

Date

Murrumbidgee River at Burrinjuck

01-Jul-00

Tumut River at Brungle Bridge 12000

10000

10000

8000

8000

Daily flow (ML)

Daily flow (ML)

01-Apr-00

Date

12000

6000

4000

2000

0 01-Jul-99

01-Jan-00

6000

4000

2000

01-Oct-99

01-Jan-00

01-Apr-00

0 01-Jul-99

01-Jul-00

01-Oct-99

Date

01-Jan-00

01-Apr-00

Date

Figure 6.6. Daily flows during 1999-2000 for biofilm study rivers in the Murrumbidgee Valley Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

70

01-Jul-00

Sampling and sample processing methods were the same as in the Hunter Valley with the following exceptions. In the Murrumbidgee, six macroinvertebrate samples were taken and they were washed on a 0.25 mm mesh sieve before transport to the laboratory. Biofilm samples were blended at medium speed for 1-2 minutes, depending on the quantity of filaments, and for chlorophyll determination a 20 mL subsample was filtered through 47 mm glass fibre filter (Advantec GC50), unless the sample was very turbid in which case only 10 or 15 mL was filtered. In addition, Murrumbidgee Valley biofilms were analysed for organic and inorganic mass. A further 430 mL aliquot of blended material was quickly removed into a measuring cylinder, transferred into a PET bottle and frozen for later laboratory determination of organic and inorganic matter by potassium dichromate reduction (Australian Standard AS1289.4.1.1-1997). In February and May 2000, both biofilms and macroinvertebrates were analysed for stable isotopes. Blended biofilm material remaining after removal of subsamples for other analyses was allowed to settle under refrigeration for 24 hours. The supernatant water was siphoned off and the residual slurry was transferred to a zip-lock bag and frozen for later analysis. Common non-predatory macroinvertebrates were collected at each site for isotope analysis by the riffle kick method described by Chessman (1995). Live macroinvertebrates were sorted in the field to the level of family or order and kept in chilled (ca 4 °C) water for a minimum of 8 hours to allow them to void their guts. The macroinvertebrates (excluding associated material such as caddisfly larval cases) were then removed to labelled zip-lock bags and frozen for transport to the laboratory. In the laboratory, biofilm samples were thawed and after removal of sand particles were dried in an oven at 60 °C for 24 hours or until all moisture had been removed. After drying, any non-biofilm material was removed and the residue was ground to a fine powder using a ring mill or mortar and pestle. The grinding apparatus was rinsed with distilled water between samples and dried with compressed air. Aquatic insects were thawed, dried at 60 °C for 24 hours and ground with a mortar and pestle. Replicate analyses were run for each insect family if the collected biomass was sufficient. Samples were oxidised at high temperatures in a EuroEA 2000 elemental analyser and the resulting N2 and CO2 gas analysed with an IsoPrime continuous-flow isotope ratio mass spectrometer. Ratios of heavy and light isotopes were expressed in δ notation as δ = (Rsample/Rstandard - 1), where Rsample and Rstandard are the isotope ratios of the sample and standard respectively. Standards used in this study were referenced to PeeDee Belemnite (PDB) for carbon and atmospheric air for nitrogen (Peterson and Fry 1987). The average analytical variability of the mass spectrometer was 0.2 ‰. Estimates of gross primary production and community respiration were made for individual stones from riffles at the Murrumbidgee Valley sites sampled in February and May 2000. Net oxygen production or consumption was measured within sealed perspex chambers. At each site, six stones were removed from the stream at random and each was placed right-side-up on a clear perspex base plate (68 x 80 mm) in the river at a similar depth to that at which it was found. A clear perspex dome of known volume (approx. 11 L) with a rubber seal around its base was fastened over each; a plug and valve atop each dome allowed any air bubbles to be purged. Each chamber was equipped with a small water pump to circulate water internally. A calibrated Hydrolab Minisonde probe fitted into a hole on the side of each chamber through a rubber seal allowed internal dissolved oxygen concentration and temperature to be logged every 5 minutes. In February 2000, measurements were made over two periods of 2.25 hours between 11:00 and 16:00 hours. Three of the six chambers were covered with black covers and all chambers were purged with fresh river water between the two periods. In May 2000, meaurements were made continuously from 17:00 hours on one day to 17:00 hours on the next. Chambers were purged between 09:00 and 09:30 hours. At the end of the incubation each stone was scrubbed and the removed material was processed for analysis of chlorophyll and biofilm composition as described above. Stone surface area was also estimated as explained previously. The volume of each stone was measured by water displacement in order to estimate the water volume in each chamber during incubation (chamber volume minus stone Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

71

volume). Community respiration (for incubation periods when black covers were in place, or at night) and net primary production (for periods without covers) were calculated from changes in dissolved oxygen concentration within the known water volume, and expressed per unit area of stone surface. Gross primary production was estimated from the difference between net primary production and community respiration. Analysis of variance (ANOVA) was used to test for significant differences in various biofilm properties (Table 6.4), in a similar fashion to the Glennies Creek analysis. However, nested ANOVA (with site nested within river) was not possible for the February and May sampling occasions because only one site per river was sampled. For these months, ANOVA simply compared sites. Because each site was on a different river, the analysis was referred to as analysis of sites across rivers (to distinguish it from the comparison of sites within rivers within the nested ANOVA of October-November data). NMS and MRPP were used for multivariate analysis in the same manner as for Glennies Creek. 6.3.2.

Results

ANOVA showed that differences in biofilm properties occurred primarily among rivers (OctoberNovember 1999), or among sites across rivers (February and May 2000), rather than between sites within rivers (Table 6.4). All variables showed significant differences across the four rivers on at least one occasion. However, spatial patterns were quite variable from one sampling period to the next (Figures 6.7–6.9). Organic and inorganic mass per unit area, and chlorophyll a density, were often highest in the Murrumbidgee River (Figure 6.7) and were typically, but not invariably, low in the two reference rivers. In the Murrumbidgee River, biofilms tended to be dominated by centric and pennate diatoms (Figure 6.8), whereas filamentous algae were most abundant in the reference rivers and the Tumut River (Figure 6.8). Scraping macroinvertebrates were most common in the Murrumbidgee River, whereas filter feeders were often dominant in both the reference rivers and the Tumut River (Figure 6.9). Table 6.4. F-values from ANOVA of various properties of stone-surface biofilms and associated macroinvertebrates in the Murrumbidgee River system, October-November 1999, February 2000 and May 2000. For October-November, nested ANOVA was used to test differences both among rivers and between sites within rivers. In February and May, only one site per river was sampled, and therefore only differences among sites across rivers could be tested. *, P < 0.05; **, P < 0.01; ***, P < 0.001; ns, not significant Property

2

Organic mass (g/m ) 2

Inorganic mass (g/m ) 2

Chlorophyll a (mg/m ) 2

Cyanobacteria (filaments/mm ) 2

Centric diatoms (cells/mm ) 2

Pennate diatoms (cells/mm ) 2

Filamentous green algae (cells/mm ) 2

Engulfing invertebrates (No./m ) 2

Filtering invertebrates (No./m ) 2

Gathering invertebrates (No./m ) 2

Piercing invertebrates (No./m ) 2

Scraping invertebrates (No./m ) 2

Shredding invertebrates (No./m )

Rivers (Oct.Nov.)

Sites within rivers (Oct.Nov.)

Sites across rivers (Feb.)

Sites across rivers (May)

5.8 **

0.1 ns

1.9 ns

13.3 ***

12.4 ***

0.5 ns

2.8 ns

26.9 ***

6.4 **

0.6 ns

5.0 *

15.9 ***

27.2 ***

0.6 ns

2.1 ns

1.3 ns

39.6 ***

1.1 ns

49.7 ***

57.1 ***

7.5 ***

0.6 ns

11.5 ***

17. 3 ***

7.7 ***

1.5 ns

27.9 ***

10.6 ***

2.7 ns

0.5 ns

2.6 ns

5.0 *

5.6 **

5.1 **

65.2 ***

3.2 *

11.6 ***

0.8 ns

11.4 **

15.3 ***

30.2 ***

2.7 *

6.4 *

109.8 ***

19.5 ***

0.7 ns

0.2 ns

9.0 **

2.0 ns

0.3 ns

13.7 ***

5.0 **


72


2

2

Oct.-Nov. 1999

G oobarragandra 2

0

10

20

30

0

10

20

30

0

10

20

30

G oodradigbee 1

Organic mass

G oodradigbee 2

M urrum bidgee 1

Inorganic mass

M urrum bidgee 2

T um ut 1

Chlorophyll a

T um ut 2

Figure 6.7. Densities of chlorophyll a and total organic and inorganic matter on rocks at sites in the Murrumbidgee River system, October-November 1999, February 2000 and May 2000 (mean ± standard error of untransformed data)

G oobarragandra 1

2

February 2000

May 2000

Organic and inorganic density (g/m ) 2 Chlorophyll density (mg/m )



73


Oct.-Nov. 1999

Goobarragandra 1

0

200

400

600

800

0

200

400

600

800

0

200

400

600

800

Goobarragandra 2

Cyanobacterial filaments

Goodradigbee 1

Goodradigbee 2

Centric diatoms

Murrumbidgee 1

Murrumbidgee 2

Pennate diatoms

Tumut 1

Tumut 2

Filamentous green algal cells

Figure 6.8. Densities of major algal and cyanobacterial groups on rocks at sites in the Murrumbidgee River system, October-November 1999, February 2000 and May 2000 (mean ± standard error of untransformed data)

2

February 2000

May 2000

2

2

Density (units/mm )

Density (units/mm )

Density (units/mm )

74

75

2

Density (No./mm )

Density (No./mm )

Density (No./mm )

October-November 1999

Feburary 2000

May 2000

2

0

2 000

4 000

6 000

8 000

10 000

12 000

0

2 000

4 000

6 000

8 000

10 000

12 000

0

2 000

4 000

6 000

8 000

10 000

12 000

Goobarragandra 1

Engulfers

Goobarragandra 2

Filterers

Goodradigbee 1

Goodradigbee 2

Gatherers

Murrumbidgee 1

Piercers

Murrumbidgee 2

Tumut 1

Scrapers

Tumut 2

Shredders

Figure 6.9. Densities of macroinvertebrate functional feeding groups on rocks at sites in the Murrumbidgee River system, October-November 1999, February 2000 and May 2000 (mean ± standard error)

2


Two-dimensional NMS of both biofilm algae-cyanobacteria and stone-surface macroinvertebrate assemblages showed a clear separation of the four rivers on all three sampling occasions, with the exception of macroinvertebrates in the two unregulated rivers in February (Figure 6.10). Differences among sites were highly statistically significant when tested by MRPP (P < 0.001). However, the two sites sampled within each river were not well separated in ordination space in October-November 1999 (Figure 6.10). In most cases the two reference rivers were proximate or overlapped, and the Murrumbidgee River was most distinctive. The Tumut River appeared more similar to the reference rivers than to the Murrumbidgee River. Stable isotope analysis also showed a strong distinction between the Murrumbidgee River and the reference rivers, with the Tumut somewhere in between (Figures 6.11 and 6.12). Macroinvertebrate isotope signatures tended to track those of the biofilms in each river, but in the reference rivers the macroinvertebrates tended to be enriched in 13C, whereas in the Murrumbidgee they were depleted. Daytime net primary production estimates in February 2000 averaged 19 mg O2/m2/hour for the Goobarragandra River, 4 mg O2/m2/hour for the Goodradigbee River and 30 mg O2/m2/hour for the Murrumbidgee River. Community respiration estimates averaged 31, 5 and 26 mg O2/m2/hour respectively. In May 2000, averages for the Goobarragandra River over 24 hours were net primary production of 48 mg O2/m2/day and community respiration of 138 mg O2/m2/day. No data were obtained from the other three sites because of technical difficulties. Because of various technical problems and limited numbers of measurements, no statistical analysis was performed on these data. 6.4.

DISCUSSION

Both the Hunter and Murrumbidgee Valley studies were at an early stage of implementation by June 2000, and therefore only preliminary inferences can be drawn for this report. In general, while the analysis showed clear differences between the regulated rivers and unregulated streams, the nature of these differences did not always lend support to the IMEF hypothesis. In the Glennies Creek system in the Hunter Valley, the February 2000 sampling occurred prior to any environmental flow releases. An accumulation of stone-surface biofilm material downstream of Glennies Creek Dam was indicated by high phytopigment densities (Figure 6.2). This biofilm was clearly of a different composition from that in the two unregulated tributaries (Figure 6.5), being dominated by pennate diatoms rather than filamentous algae (Figure 6.3). The stone-surface macroinvertebrate fauna of Glennies Creek was also clearly different from that of the unregulated tributaries. However, in this case, the two tributaries were also different from one another (Figure 6.5). The density of macroinvertebrate scrapers in Glennies Creek fell between densities in the reference creeks (Figure 6.4), suggesting that the Glennies Creek biofilm was palatable to at least some grazing invertebrates. Further sampling, both before and after environmental releases, will enable the IMEF hypothesis to be tested thoroughly in this system. In the Murrumbidgee Valley, the October-November 1999 sampling followed the late winter-early spring period of translucent releases from Burrinjuck Dam to the Murrumbidgee River, and natural spring freshes in the unregulated reference rivers. The February 2000 sampling occurred in the midst of high-volume irrigation releases down the Murrumbidgee and Tumut rivers and after high natural flow pulses in the unregulated tributaries. By the May 2000 sampling, flows had returned to a low and stable level in the Murrumbidgee River, and to a lesser extent in the other study rivers.


76

Algae

Macroinvertebrates

October-November 1999

2

1.5 1.0

1

0.5 0

0.0 -0.5

-1

-1.0 -2

-1.5 -2

February 2000

Goobarragandra 1

-1.5

-1

-0.5

0

Goobarragandra 2

0.5

1

Goodradigbee 1

1.5

2

Goodradigbee 2

1.5

1.5

1.0

1.0

0.5

0.5

0.0

0.0

-0.5

-0.5

-1.0

-1.0

-1.5 -2

-1.5

-1

-0.5

0

0.5

Goobarragandra 1

1

1.5

1.5

0.6

1.0

0.4

-2

-1

Murrumbidgee 1

-1.5 -1.5

Goodradigbee 1

-1

0

1

2

Murrumbidgee 2

-0.5

0

0.5

Tumut 1

1

Tumut 2

1.5

Murrumbidgee 2

0.2

0.5

May 2000

-3

0.0

0.0

-0.2 -0.5

-0.4 -1.0

-0.6

-1.5

-0.8

-2.0

-1.0 -2

-1.5

-1

-0.5

0

0.5

Goobarragandra 1

1

1.5

2

Goodradigbee 1

-2

-1.5

Murrumbidgee 2

-1

-0.5

0

0.5

1

1.5

Tumut 2

Figure 6.10. NMS ordination of density data for biofilm algae and cyanobacteria (left) and associated macroinvertebrates (right) at sites in the Murrumbidgee River system, October-November 1999 (top), February 2000 (centre) and May 2000 (bottom). Stress = 0.16, 0.14 and 0.15 (left, top to bottom) and 0.20, 0.13 and 0.14 (right, top to bottom)


77

Goodradigbee 1 18

16

16

14

14

12

12 10 8

15

10

N

18

Delta

Delta

15

N

Goobarragandra 1

8 6

6

4

4

2

2

0 -30

-28

-26

-24 Delta

-22

-20

0

-18

-30

-28

-26

13

C

-24

-22

-20

Delta 13C Biofilm

Diptera

Diptera (Chironomidae)

Diptera (Simuliidae)

Ephemeroptera

Plecoptera

Trichoptera

Murrumbidgee 2 18 16 14

Delta

15

N

12 10 8 6 4 2 0 -30

-28

-26

-24 Delta

-22

-20

-18

13

C

Figure 6.11. Scatterplot of δ135C and δ15N values for biofilm and macroinvertebrate samples from three sites in the Murrumbidgee River system, February 2000. All data are plotted on the same scales to facilitate comparisons of sites


78

-18

Goodradigbee 1 18

16

16

14

14

12

12 N

18

15

10

Delta

Delta

15

N

Goobarragandra 1

8

10 8

6

6

4

4

2

2

0

0 -30

-28

-26

-24 Delta

-22

-20

-18

-30

-28

-26

13

-24 Delta

C

-22

-20

-18

-22

-20

-18

13

C

Biofilm Diptera (Simuliidae) Ephemeroptera (Baetidae) Ephemeroptera (Coloburiscidae) Ephemeroptera (Leptophlebiidae) Plecoptera Plecoptera (Gripopterygidae) Trichoptera (Calamoceratidae) Trichoptera (Hydropsychidae)

Tumut 2 18

16

16

14

14

12

12 N

18

15

10

Delta

Delta

15

N

Murrumbidgee 2

8

10 8

6

6

4

4

2

2

0

0 -30

-28

-26

-24 Delta

-22

-20

-18

-30

-28

-26

13

-24 Delta

C

13

C

Figure 6.12. Scatterplot of δ13C and δ15N values for biofilm and macroinvertebrate samples from four sites in the Murrumbidgee River system, May 2000. All data are plotted on the same scales to facilitate comparisons of sites


79

All biofilm attributes studied differed substantially among the four rivers, and in both cases the Murrumbidgee River was clearly distinct from the reference rivers (e.g. Figure 6.10). The two reference rivers diverged to a small degree, but were generally much more similar to one another than they were to either of the regulated rivers. The Murrumbidgee River appeared more similar to the reference rivers, in both biofilm algae and macroinvertebrates, after the spring period of environmental releases than it did during the summer period of irrigation releases (Figure 6.10), lending support to the hypothesis. However, it also appeared more similar in the stable low-flow autumn period after irrigation flows. In addition, the Murrumbidgee River in spring was no more similar to the reference rivers than was the control river, the Tumut (Figure 6.10). Furthermore, the Murrumbidgee River supported large populations of macroinvertebrate scrapers (Figure 6.9), and of pennate diatoms which should be readily consumed by them (Figure 6.8). In contrast, the reference rivers and the Tumut River contained large quantities of filamentous algae, which are generally considered less palatable. Biofilm δ13C values were generally in the range from -28 to -24 in all four study rivers (Figures 6.11 and 6.12). This suggests a mix of riparian and algal material, since riparian C3 plants usually have δ13C values in the range from -30 to -27, whereas the range for benthic algae is -25 to -15 (Peterson and Fry 1987; Peterson and Howarth 1987; Bunn and Boon 1993; Thorp et al. 1998; Beaudoin et al. 2001). However, average C:N ratios obtained during the course of isotope analysis suggest that the biofilms are largely autochthonous material (i.e., of in-stream origin). These averages were very low in the Murrumbidgee River (2:1 and 3:1) and somewhat higher in the reference rivers (range from 8:1 to 19:1). Wetzel (1975) reported that autochthonous organic matter has a C:N ratio of about 12:1, while allochthonous organic matter (derived from the riparian zone) has a ratio of 45:1 to 50:1. The δ15N values for biofilms from the reference rivers were much lower than those from the Murrumbidgee River (Figures 6.11 and 6.12). The δ15N value for riparian atmospheric nitrogen is 0, and values for riparian vegetation are also close to zero (e.g. Peterson and Fry 1987; Peterson and Howarth 1987). Biofilms in the reference rivers may therefore have been using riparian nitrogen sources or fixing atmospheric nitrogen. The much greater degree of native vegetation cover in the catchments of the reference rivers, and the lower intensity of stock grazing and human settlement, may be responsible for differences from the Murrumbidgee River with its more developed catchment. Bunn and Boon (1993) found differences in δ15N values of primary producers in billabongs with and without cow manure as a potential nitrogen source. The presence of Burrinjuck Reservoir upstream of the Murrumbidgee River site, and the greater width and less shaded nature of the Murrumbidgee River, may also be influential. Macroinvertebrates from the Murrumbidgee were generally 13C depleted compared with the biofilm (had more negative δ13C values), while invertebrates from the reference sites were 13C enriched. Enrichment of 13C in invertebrates may reflect preferential feeding on microbes within biofilms (Hershey and Peterson 1996). Sheldon and Walker (1997) found higher δ13C values in grazing snails than in their detrital food source. They suggested that heterotrophic microorganisms using the detritus as their primary carbon source were becoming 13C enriched by about 1 unit. The snails then fed on the microbes, becoming enriched by an additional 1 unit. This level of enrichment is similar to that seen in the Goobarragandra and Goodradigbee rivers for several invertebrate groups (Figures 6.11 and 6.12). The depletion of 13C in macroinvertebrates from the Murrumbidgee River, relative to the biofilm, suggests that it was not a favoured food source. It is possible that invertebrates in the Murrumbidgee River, especially filterers such as simuliid fly larvae, were taking advantage of suspended food material passed downstream from Burrinjuck Reservoir rather than in situ biofilm growth. Alternatively, the macroinvertebrates may have been grazing selectively on certain components of the biofilm. Sampling and analysis subsequent to that reported here will provide further insights into these matters. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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7.

River organic carbon and zooplankton

7.1.

INTRODUCTION

The principal sources of the organic carbon and associated energy that fuel the food webs of large rivers are much debated in the ecological literature. The River Continuum Concept (RCC), developed primarily from studies in temperate North America, proposes that the majority of the carbon supply to large rivers arrives with upstream water in the form of dissolved and fine particulate non-living matter, the product of upstream processing of inputs from the riparian zones of small streams (Vannote et al. 1980). In contrast, the Flood Pulse Concept (FPC) of Junk et al. (1989) emphasises the exchanges between large, lowland rivers and their floodplains that occur during annual seasonal inundation. The Riverine Productivity Model (RPM) of Thorp and Delong (1994) maintains that instream photosynthesis and local riparian inputs are often important in large rivers, particularly those with constricted channels. Recently, Thorp and Delong (2002) have expanded on this model, suggesting that multicellular animals in most large rivers rely mainly on carbon sourced from algal photosynthesis. They contend that terrestrial carbon inputs are processed mainly by a ‘microbial loop’ involving bacteria and fungi. Limited transfers can occur from this loop to the algal-grazer pathway, for example planktonic fishes feeding on rotifers, which in turn feed on heterotrophic microbes. Studies to track carbon flow through the food webs of large Australian rivers have barely begun. However, it is clear that riparian trees such as Eucalyptus camaldulensis contribute large quantities of litter to large rivers and associated floodplains in south-eastern Australia (Briggs and Maher 1983). Some of this litter falls directly into water bodies at times of low flow, but much of it remains on dry floodplains (Robertson et al. 1999) and in-channel surfaces (Thoms and Sheldon 1996, 1997) until inundated by rises in river levels. Opinions on the extent to which shredding macroinvertebrates process this litter vary (Schulze and Walker 1997; Francis and Sheldon 2002). Dissolved organic matter (DOM) is readily leached from wetted leaves (Baldwin 1999; Glazebrook and Robertson 1999; Francis and Sheldon 2002), and subsequently used as a food source by bacteria (Baldwin 1999) and probably fungi (cf. Findlay and Sinsabaugh 1999). Microbes feeding on DOM may be one of the primary food sources for zooplankton (Boon and Shiel 1990). However, evidence from stable isotope studies (Bunn and Davies 1999) suggests that algal production may be a more important source of carbon for higher trophic levels, at least in some situations. IMEF hypothesis 5 focuses on the role that wetting of riparian litter may play in stimulating riverine food webs. It proposes that those flow rules that protect a proportion of freshes and high flows will result in more frequent wetting of river banks, benches and in some cases floodplains than would otherwise occur. This wetting should make terrestrial carbon sources more accessible to leafshredding aquatic invertebrates, if they are present. It should also result in leaching of dissolved organic matter, which will then pass up the planktonic food chain. While any fallen leaves will inevitably be wetted eventually (i.e., by major floods), leaching may be greater from freshly fallen leaves than from those that have been in a terrestrial setting for some time (Baldwin 1999). In addition, frequent wetting may be important in ensuring continuity of terrestrial carbon supply. This study has been confined to a single river, the Namoi, in order to develop methods. Initial attention has been directed to testing whether a pulse of dissolved organic carbon and a subsequent increase in zooplankton numbers follows flows that wet the river banks. If the expected pulses occur, the mechanisms involved and their ecological implications can be explored in more detail. 7.2

SITES AND METHODS

Three sites were selected along the middle and lower reaches of the Namoi River (Map 8; Table 7.1), at Boggabri, Bugilbone and Goangra. The cover of native riparian woody vegetation at the Boggabri site is less than 25%, whereas at both Bugilbone and Goangra it is approximately 50% with a depleted


81

understorey (DLWC, 2000). The dominant tree species are river red gums (Eucalyptus camaldulensis) at Boggabri and Goangra and weeping willows (Salix babylonica) at Bugilbone. Table 7.1. Terrestrial organic matter study sites in the Namoi Valley Site number

Site name

419012

Namoi River at Boggabri

419021

Namoi River at Bugilbone (‘Riverview’)

419026


Each site is a reach of river about 10 km long. Fifteen cross sections have been selected (via stereo imaging) at each site to represent the various geomorphological features present (e.g. sweeping bend, slumping bank and sand bar). During the reporting period, two sections at Boggabri and Bugilbone and three sections at Goangra were sampled. Each section was sampled once per month from September to November 1999, except that in November only two sections were sampled at Goangra. The September sampling followed a long period of low flow, whereas the other two sampling occasions followed small flow peaks in early October and early-mid November. For dissolved organic carbon (DOC), one midstream sample was collected at a depth of 250 mm on each section. Pilot sampling showed that the concentration at this point was generally within 10% of the average of up to five samples spread over a cross section. Sampling equipment was rinsed thrice with reverse osmosis water between sections. Each sample was passed through a 0.45 µm nylon membrane and the first 10–20 mL of filtrate were discarded. Approximately 100 mL of subsequent filtrate was placed in a 200 mL acid-washed amber glass bottle. After addition of 1 mL of concentrated HCl, the sample was chilled at about 4 °C prior to analysis (APHA 1998). Zooplankton samples were taken midstream in a 4.2 L perspex Schindler trap. One sample was taken at 1 m depth, and if the stream was more than 2 m deep, an additional sample was taken at 2 m. A pilot study showed that such sampling provided concentration values within 10% of the average of up to 11 samples spread over a cross section. Each sample was filtered through a 38 µm mesh sieve, and material retained on the sieve was rinsed into a jar of 70% ethanol. When two samples were collected they were pooled. In the laboratory, each sample was mixed and a 1 mL subsample was removed with an automatic pipette to a Sedgewick-Rafter counting cell. The first 200–300 zooplankters observed in this cell, or the total content if fewer than 200 were present, were identified to major taxonomic groups under a compound microscope. Counts were converted to total concentration per litre of river water. 7.3.

RESULTS AND DISCUSSION

Flows at times of sampling were confined within the banks. Although data are not sufficient to merit statistical analysis, DOC concentrations showed no obvious strong relationship with flow on the day of sampling (Figure 7.1). The lowest average of the recorded DOC concentrations was at Boggabri (Figure 7.1), which may have been a result of the scarcity of riparian woody vegetation, and consequently litter inputs, around this site.


82

Namoi River at Boggabri 10

DOC (mg/L)

8 50 6 4 25 2 0 1500

0 0

500

Zooplankton (organisms/L)

75

1000 Daily flow (ML)

Namoi River at Bugilbone 15

DOC (mg/L)

75 10 50 5 25

0 0

500

1000

1500


100

0 2000

Daily flow (ML)


200

DOC (mg/L)

75

150 50 100 25

50


250

100

0

0 0

500

1000

1500

Daily flow (ML)

DOC

Zooplankton

Figure 7.1. Relationship between daily flow and dissolved organic carbon concentration and zooplankton abundance in the Namoi River at three sites, September - November 1999

Recorded zooplankton concentrations were highest at Goangra in September, when flows were low. Other studies (Bottrell et al. 1976; Thorp et al. 1994) have shown zooplankton density to be negatively correlated with river velocity. Periods of low flow offer favourable conditions for reproduction of zooplankton, resulting in increased abundance, whereas high current velocities tend to inhibit reproduction (Saunders and Lewis 1989). Low flows have also been shown to increase algal productivity (Shiel et al. 1982), thus providing a more abundant food source for zooplankton. As in Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

83

other zooplankton studies of Australian rivers (e.g. Shiel et al. 1982; Kobayashi et al. 1996), samples from the Namoi were dominated by smaller zooplankton such as rotifers, which constituted an average of 90% (range 68-100 %) of the number of individuals per sample. Cladocerans and copepods made up the remainder. Results from different cross sections sampled at the same site on the same day were generally similar, with the exception of an anomalously high DOC concentration of 61 mg/L in section 2 at Goangra when flow was 1478 ML/day in November. The concentration in section 1 at this site at the same time was only 10 mg/L (Figure 7.1). The high concentration could have been the result of a sample processing or analytical error, or could have reflected a transient pulse of DOC that was missed at section 1 (since at least 80 minutes elapsed between the sampling of sections 1 and 2). Much more intensive sampling will be needed to track changes in DOC and zooplankton abundances and relate them to flow sequences. Bottrell et al. (1976) suggested that sampling intervals for zooplankton should be less than their generation time, which would require rotifers and protozoans to be sampled every few days, as their life cycles are often shorter than one week. Changes in DOC concentration are likely to occur over very short time intervals, particularly during and after flow events. Intensive short-term studies have been planned and will be described in future reports.


84

8.

Wetland biodiversity

8.1.

INTRODUCTION

The regulation and extraction of river flows have greatly diminished the frequency and extent of inundation of floodplain wetlands in the Murray-Darling Basin (Kingsford 2000). In consequence, wetland vegetation associations have contracted (Brock 1998) and habitat and breeding opportunities for water birds have been impaired (Kingsford and Thomas 1995, 2001; Kingsford and Johnson 1999; Leslie 2001). Effects on other organisms are less well understood, although it is known that a lower flooding frequency is associated with a reduced biomass and diversity of invertebrates that emerge from dormant eggs and other resting stages when dry floodplain soils are wetted (Boulton and Lloyd 1992; Jenkins and Boulton 1998). It is likely that populations of wetland fish, frogs and turtles have also declined as a result of reduced flooding. Unnatural permanent wetting, which occurs in some wetlands as a result of their use as water storages or conduits, can also be ecologically detrimental. Although some native wetland species can thrive in permanently wetted habitats, flooding of previously dry habitats is a major stimulus to production of water plants and macroinvertebrates, which are important food sources for some waterbird species (Maher and Carpenter 1984; Briggs and Maher 1985). Mesocosm research also suggests that permanent wetting is associated with lower plant biomass and diversity than intermittent wetting (Casanova and Brock 2000). Since floodplain wetlands are major repositories of biodiversity (Kingsford 2000) and support distinct biological communities from those of the associated rivers (Hillman 1986), wetlands are a major target for ecological rehabilitation driven, at least in part, by environmental water allocations. IMEF hypothesis 7 proposes that protecting or restoring a portion of freshes and high flows, and otherwise maintaining natural flow variability (to address RFOs 3, 4 and 6), through off-allocation use restrictions and dam releases, will replenish anabranches and riverine wetlands, restoring their biodiversity. The critical questions are whether environmental flow rules can achieve some approximation of the natural spectrum of wetland flooding and drying regimes, and whether this will sustain the variety of native biota adapted to these natural water regimes. Testing the hypothesis requires establishing relationships between environmental flows and wetland inundation patterns, and between wetland water regimes and ecological responses. IMEF wetland studies have been established in five valleys: the Gwydir, Lachlan, Macquarie, Murrumbidgee and Namoi. Floodplain wetlands of diverse form occur among these valleys. The studies focus on vegetation and macroinvertebrates as recommended by Reid and Brooks (2000), but also include fish, frogs and birds in some valleys. Not all of these groups of biota could be assessed in all valleys during 1998-2000 because of resource constraints. The studies involve the statistical testing of relationships between water regimes and biological community composition and structure, while recognising other sources of variation such as the physical forms of water bodies. For this report, detailed information on water regimes was not available for all valleys. In some cases, simple interim classifications are used, pending more detailed hydrological analysis. 8.2.

GWYDIR VALLEY

8.2.1.

Sites and methods

Sites for vegetation assessment and macroinvertebrate sampling were chosen by generation of random map coordinates within the range across which the wetlands extend. Each random location was checked for accessibility, after which seven locations were retained as sampling sites (Map 3; Table 8.1). Sites were classified from local knowledge as having wet, dry or intermediate long-term water regimes. On each wetland visit where water was present, water temperature, electrical conductivity, pH and dissolved oxygen were measured with a Horiba U10 Water Checker and turbidity with a Hach 2100P turbidimeter. Vegetation was assessed along three 100 m transects at each of five sites in June 2000. Transects were located to maximise variation in water level and the number of vegetation associations traversed. Vegetation and water depth were recorded for 1 m square quadrats positioned Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

85

at 10 m intervals along each transect. Percentage cover of each plant species was visually estimated in Braun-Blanquet (1932) categories of 75%. Table 8.1. Wetland study sites and timing of vegetation and macroinvertebrate assessment in the Gwydir Valley. Sites are arranged in sequence from east to west Site number

Site name

Water regime

Vegetation

Macroinvertebrates

418073

Gwydir North at Baroona Waterhole

Wet

Nov. 99

418076

Gingham Channel at Tillaloo Bridge

Intermediate

Dec. 99; Feb. 00

41810035

Gingham Channel at Rookery

Wet

Jun. 00

Nov. 99; Feb. 00

418077

Gingham Channel at The Waterhole

Dry

Jun. 00

Nov. 99; Feb. 00

41810034

Big Leather at Old Dromana

Intermediate

Jun. 00

Nov. 99; Feb. 00

41810036

Big Leather at Troy Wet Patch

Wet

Jun. 00

Dec. 99; Feb. 00

41810038

Gingham Channel at Crinolyn

Intermediate

Jun. 00

Macroinvertebrates were sampled in two periods (Table 8.1). The first was five weeks after a flow peak of 4500 ML/day passed Brageen Crossing, on the Gwydir River upstream of the wetlands, in October 1999. This delay was chosen to allow macroinvertebrate assemblages time to respond to inundation. The second sampling period was three months after the first. Baroona Waterhole was not sampled in the second period because it transpired that it is connected to the river system only in major floods. In each period, 2-6 macroinvertebrate samples were taken per wetland with a sweep net with 350 by 250 mm opening and 0.5 mm mesh. The samples were distributed among habitat types in proportion to their areal coverage of the wetland; habitats included beds of various aquatic macrophyte species, inundated roots of terrestrial plants, submerged woody debris and unvegetated sediment. To take each sample the net was swept for 1 minute in a forward direction, away from the centre of the wetland and toward the shore, in a 1 m wide path. Sequential short movements were used to alternately lift the net above the substratum and up to the water surface while it was pushed forward and then drop it vertically onto the substratum. After sampling, net contents were separated into three size fractions by washing on a series of sieves (8 mm, 2 mm and 0.5 mm mesh). The fraction retained on each sieve was washed into a large white sorting tray, and macroinvertebrates were picked by eye with forceps into a jar of 70% ethanol for 10 minutes per fraction. Picking was selective with the aim of maximising the number of species retrieved. Picked specimens were sent to a laboratory for identification to the lowest practical taxonomic level (usually genus or species). Ten sites were chosen for fish sampling (Map 3; Table 8.2), primarily for accessibility and proximity to river sites (see Chapter 9). Artificial water bodies and those without sufficient water to maintain viable populations of fish were excluded from consideration. All of these sites were classed as having a wet long-term water regime. Fish were sampled in January, February and June 2000, mainly by boat electrofishing. This has proved a cost-effective technique for sampling fish of a wide range of species and body sizes (Growns et al. 1996; Harris and Gehrke 1997). Boat sizes ranged from 3.5 to 5 m, depending on water body size and access. Generators of 5-7.5 KW capacity were used to produce a pulsed DC waveform (60-120/s), at 2-25 A and 170-1000 V, with a duty cycle range of 10-100%. Settings were adjusted according to the electrical conductivity of the water body. As the boat traversed navigable parts of the water body, fish were immobilised with large electrodes, netted and placed in a live well in the boat prior to examination and release. Backpack electrofishing was sometimes used in shallow waters. Each sampling event comprised a maximum of 15 ‘shots’ per wetland, each lasting 2 minutes. Access at some sites did not allow 15 shots, in which case at least eight shots were completed. All fish caught were identified, examined for disease, damage or abnormalities and measured to the nearest millimetre. For fish with forked tails, length was measured from the snout to the fork (caudal fork length). For species with rounded tails, length was measured from the snout to the end of the tail (total length). Fish observed but not caught, and which could be readily identified, were also recorded. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

86

Table 8.2. Wetland study sites for fish assessment in the Gwydir Valley. Sites are arranged in sequence from east to west Site number

Site name

Site number Site name

F160

Norwood

F169

Gingham Crossing

F166

Boree

F163

Gin Holes

F161

Brageen Crossing

F162

Wondoona Lagoon

F167

Baroona

F164

Big Leather Watercourse

F168

Gingham Waterhole

F165

Second Lagoon

Nested analysis of variance (ANOVA) was used to test differences among long-term water regimes in the number of plant species per quadrat and macroinvertebrate taxa per sample. Site was nested within water regime and each sampling period was analysed separately. Differences in fish species richness according to water regime could not be tested because all sites were classified as wet. For plants, Spearman rank correlation was calculated between number of species per quadrat and water depth at the time of assessment. The ordination method of non-metric multidimensional scaling (NMS), in the PC-ORD software package (McCune and Mefford 1999), was used to examine spatial patterns in vegetation and macroinvertebrate assemblages. Before analysis, vegetation cover of each species in each quadrat (expressed as the mid-point of the percent cover category) was converted to the arcsine square root, a commonly recommended transformation for percentage data. Since the macroinvertebrate sampling method was not quantitative, the occurrence of each taxon was expressed as the proportion of samples from each wetland on each sampling occasion in which it was recorded. Dissimilarity was expressed as the Bray-Curtis coefficient. Differences in vegetation, macroinvertebrate and fish assemblages among wetlands were tested for statistical significance by the multi-response permutation procedure (MRPP) in PC-ORD. Indicator species analysis (Dufrêne and Legendre 1997) was used to determine which plant species were most characteristic of dry quadrats (water depth = 0), shallow quadrats (0 < water depth < 0.25 m) or deep quadrats (water depth > 0.25 m). The Mantel test in PC-ORD was used to test for a significant overall relationship between plant assemblages and quadrat water depth. Dissimilarity was expressed as the Bray-Curtis measure for plants and Euclidean distance for depth. 8.2.2.

Results

Water quality Water quality data spanned a wide range for most variables (Table 8.3). Electrical conductivity results indicated that the sampled wetlands are not highly saline. Table 8.3. Ranges of water quality variables in the Gwydir Valley wetlands during three sampling periods Period

No. of samples

Temperature (°C)

Turbidity (NTU)

Conductivity (µS/cm)

pH

Dissolved oxygen (mg/L)

Nov. - Dec. 1999

4

24–28

2–110

380–490

7.1–7.8

3.4–6.5

Feb. 2000

11

22–33

4–170

220–500

5.5–7.5

0.6–8.9

May - Jun. 2000

8

10–15

3–130

190–670

7.4–8.3

1.9–9.5

Vegetation Forty-seven plant species were recorded. In nested ANOVA, the number of species per quadrat varied significantly according to long-term water regime (P < 0.001). Mean species richness was lower for the dry regime (2.7) than for the intermediate and wet regimes (3.8 and 3.5 respectively). However, the number of species per quadrat was not related to water depth at the time of sampling (Spearman rank correlation: P > 0.05). Two-dimensional NMS showed a tendency for quadrats to group by site, but with no clear separation by water regime (Figure 8.1, left), probably because of variation in water Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

87

depth among quadrats within each site (Figure 8.1, right). The Mantel test confirmed that plant assemblages were significantly related to water depth at the quadrat scale (P < 0.001). The number of sites was insufficient for MRPP testing of site-scale differences according to long-term water regime. 1.5

1.

1.0

1.

0.5

0.

0.0

0.

-0.5

-

-1.0

-

-1.5 -1.5

-1.0

-0.5

0.0

0.5

1.0

Rookery (wet)

Troy (wet)

Crinolyn (int.)

Dromana (int.)

1.5

2.0

-

-

-

0.

0.

1.

1.

2.

The Waterhole (dry)

Figure 8.1. NMS ordination of vegetation cover data in individual quadrats in Gwydir Valley wetlands, June 2000. Left, data points coded by site and site-scale long-term water regime; right, data points shaded and sized in direct proportion to water depth in individual quadrats (maximum 0.7 m), or unshaded to indicate dry quadrats. Stress = 0.25

Indicator species analysis found several species that characterised quadrats with different amounts of water (Table 8.4). The invasive alien weed water hyacinth (Eichhornia crassipes) was the dominant plant in the Gingham Channel at the Rookery. The partial drying of the Gingham watercourse in 1999-2000 facilitated hyacinth control in more elevated areas, but it was able to persist in places that remained wet (Figure 8.2). By contrast another alien weed, lippia (Phyla canescens), was recorded mostly from dry quadrats (Figure 8.2). It is able to compete for moisture effectively because of its deep taproot and extensive surface root system. Plants remain dormant when soil moisture is low, and grow rapidly and out-compete other species after rain. McCosker (1994) found that lippia was unable to grow where inundation was prolonged and deeper than 0.2 m. The transects at the Gingham Channel at The Waterhole, which had the most lippia, lie in an area that dries fast after flooding. Table 8.4. Plant species showing a statistically significant (P < 0.05) association with different levels of quadrat wetness in indicator species analysis for the Gwydir Valley wetlands, June 2000 Species

Indicator value

Wetness category

Eichhornia crassipes

60

Deep

Phyla canescens

52

Dry

Eleocharis plana

31

Dry

Eleocharis sphacelata

27

Shallow

Ludwigia peploides

26

Shallow

Myriophyllum variifolium

26

Deep

Typha domingensis

18

Deep

Persicaria prostrata

15

Deep

Azolla filiculoides

14

Deep

Persicaria lapathifolia

9

Deep


88

The native ribbed spike-rush (Eleocharis plana) was also associated with drier quadrats (Table 8.4). It occurs widely in the Gwydir Valley wetlands in association with water couch (Paspalum distichum). The percentage cover of each species varies among locations, with timing of flooding believed to be a major influence. P. distichum prefers summer flooding (Roberts and Marston 2000) whereas E. plana is favoured by winter flooding (McCosker 2001). Several quadrats in the Big Leather at Old Dromana and the Gingham Channel at Crinolyn were dominated by this association. Tall spike-rush (Eleocharis sphacelata) occurred in wetter situations than E. plana (Figure 8.2). It favours long periods of inundation and deeper water, and dominated the margins of Big Leather at Troy, which has historically been one of the last waterholes in the Gwydir Valley wetlands to dry during drought. Eleocharis plana 100

80

80

Cover score

Cover score

Eichhornia crassipes 100

60

40

20

60

40

20

0 0

0.2

0.4

0.6

0

0.8

0

0.2

Water depth (m)

Eleocharis sphacelata

0.6

0.8

Phyla canescens

100

100

80

80

Cover score

Cover score

0.4

Water depth (m)

60

40

60

40

20 20 0 0

0 0

0.2

0.4

0.6

0.2

0.8

0.4

0.6

0.8

Water depth (m)

Water depth (m)

Figure 8.2. Relationships between water depth and cover of selected plant species in individual quadrats in Gwydir Valley wetlands, June 2000. Cover is scored as the mid-point of each percent cover category

Macroinvertebrates At least 159 aquatic macroinvertebrate species were recorded. The figure is a minimum because not all specimens could be identified to species level. The most diverse families were Chironomidae (midges; at least 21 species), Hydrophilidae (beetles; 16) and Dytiscidae (beetles; 14). Nested ANOVA did not find significant differences in taxonomic richness according to long-term water regime in either sampling period. Two-dimensional NMS showed little evidence of grouping of sites by long-term water regime (Figure 8.3), but the number of sites was insufficient for MRPP testing. The temporal shift was in the same direction in ordination space at most sites, suggesting similar successional patterns. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

89

1.0

0.5

0.0

-0.5

-1.0 -1.5

-1

-0.5

Baroona (wet) Dromana (int.)

0

0.5

Rookery (wet) Tillaloo 1 (int.)

1

1.5

2

Troy (wet) The Waterhole (dry)

1 0ordination of macroinvertebrate frequency data from Gwydir Valley wetlands, Figure 8.3. NMS November-December 1999 and February 2000. Data points are coded by site and long-term water regime. Arrows indicate temporal sequences. Stress = 0.07

Fish Ten fish species were recorded, seven of which are native (Table 8.5). Except for bony herring, alien species were numerically dominant. Small individuals of three large species – bony herring, common carp and goldfish – were abundant in January or February, whereas those caught in June tended to be larger (Figure 8.4). This suggests that these species spawned in the wetlands in the spring or early summer. Size distributions of the smaller common species – crimson-spotted rainbowfish and gambusia – did not show such a pronounced seasonal pattern (Figure 8.4). Table 8.5. Numbers of individuals of each fish species captured or observed in Gwydir Valley wetlands in January, February and June 2000. Species are arranged in order of decreasing abundance Species

Common name

Status

Number of specimens

Gambusia holbrooki

Gambusia

Alien

3819

Nematalosa erebi

Bony herring

Native

1400

Cyprinus carpio

Common carp

Alien

700

Carassius auratus

Goldfish

Alien

369

Melanotaenia fluviatilis

Crimson-spotted rainbowfish

Native

114

Hypseleotris spp.

Western carp gudgeon species complex Native

92

Leiopotherapon unicolor Spangled perch

Native

18

Retropinna semoni

Australian smelt

Native

15

Macquaria ambigua

Golden perch

Native

11

Maccullochella peelii

Murray cod

Native

1


90

140 120

Bony herring

No. of fish

100 80 60 40 20

30 035 0

20 025 0

15 020 0

10 015 0

50 -1 00

050

25 030 0

0

Standard length (mm) 100

Common carp

No. of fish

80 60 40 20

60 070 0

60 -7 0

70 -8 0

70 080 0

50 060 0

40 050 0

30 040 0

20 030 0

10 020 0

010 0

0


Crimson-spotted rainbow fish

No. of fish

20 15 10 5

80 -9 0

50 -6 0

40 -5 0

30 -4 0

20 -3 0

020

0

Standard length (mm) 180 160 140

Gambusia

No. of fish

120 100 80 60 40 20

35 -4 0

40 -4 5

45 -5 0

18 021 0

21 024 0

24 027 0

30 -3 5

25 -3 0

20 -2 5

15 -2 0

10 -1 5

010

0


Goldfish

No. of fish

80 60 40 20

15 018 0

12 015 0

90 -1 20

60 -9 0

30 -6 0

030

0

Standard length (mm)

Jan

Feb

Jun

Figure 8.4. Body length distributions of five fish species at sites in the Gwydir Valley wetlands sampled in January, February and June 2000 Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

91

8.3.

LACHLAN VALLEY

8.3.1.

Sites and methods

In 1998-99, studies were confined to monitoring of bird breeding in the Booligal wetlands complex after a flood event. These wetlands were targeted as they are listed in the Directory of Important Wetlands (EA 2001). Visual estimates of bird numbers were made over one 3 hour period at each of six sites. In 1999-2000, 13 riverine wetlands between Forbes and the Murrumbidgee River junction were selected for sampling (Map 5; Table 8.6). Wetlands were classified into three groups: lower Lachlan billabongs (downstream of Condobolin), lower Lachlan swamps and mid Lachlan billabongs (between Forbes and Condobolin) (Table 8.6). Swamps are shallow water bodies, often with extensive aquatic vegetation, whereas billabongs are deeper and generally retain water for longer periods after flooding. Study sites were mostly selected on random map coordinates; the nearest billabong to each random point was chosen from areas that Landsat satellite imagery showed to be wetted in March 1988. Wetland selection was however constrained to ensure vehicle and boat access, reasonable habitat quality (assessed by a modified version of the ‘wetland condition index’ of Spencer et al. 1998), low risk of vandalism and landowner support. Some of the swamps were chosen non-randomly to represent the Booligal and Cumbung swamp areas listed by EA (2001). The long-term water regimes of the wetlands were characterised by the number of times each wetland was subject to a dry period of two years or more since 1972. Such extended dry periods are likely to have an impact on ecologically dominant taxa such as river red gums (e.g. Roberts and Marston 2000). Table 8.6. Wetland study sites in the Lachlan Valley. Month of flooding in 1999 is indicated for eight wetlands; the remainder did not flood. Letters V, M and B indicate sampling events for vegetation, macroinvertebrates and birds respectively, before flooding and 2, 8 and 12 weeks afterwards. Wetland types are coded as LLB (lower Lachlan billabong), LLS (lower Lachlan swamp) and MLB (mid Lachlan billabong). The historical frequency of extended dry periods is also shown. Sites are arranged in sequence from east to west Site number

Site name

Wetland type

Dry frequency

Month of flood

Before 2 weeks 8 weeks 12 weeks (1999)

Before (2000)

41210168 Bocabidgle

MLB

3

Nov.

M

V, M

V, M, B

V, M, B

V, M, B

41210169 Wilga

MLB

4

Nov.

M

V, M

V, M, B

V, M, B

V, M, B

41210170 Robsar

MLB

3

Nov.

M

V, M

V, M, B

V, M, B

V, M, B

41210171 Morgans

MLB

2

Aug.

M

M

V, M

V, M

V, B

41210172 Hazelwood

LLB

3

41210173 Whealbah

LLB

3

41210174 Thomsons

LLB

3

V, M, B

41210175 Erins

LLB

4

V, B

412129

Booligal

LLS

3

V, M, B

412151

Reed beds

LLS

1

Nov.

412179

Marrool

LLS

0

Nov.

41210177 Azolla

LLS

0

Nov.

V, M, B

41210176 Lignum

LLS

1

Nov.

V, M, B

V, B M

V, B

V, B M

V, M, B

V, M, B

V, B

Water quality, vegetation, macroinvertebrates and birds were assessed in August and September 1999, before wetlands were flooded by high river flows, at approximately 2, 8 and 12 weeks after the first flood in each wetland, and in March-May 2000, before expected flooding in the winter-spring of 2000. Not all wetlands and variables were assessed on all occasions, either because the wetlands did not flood or because of resource constraints. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

92

For water quality assessment, wetlands were divided into four quadrats and water temperature, electrical conductivity and turbidity were measured at one randomly selected location within each with a WTW model LF320 conductivity meter and a Hach 2100P turbidimeter. Vegetation surveys involved 1 hour assessments of plant species presence and Braun-Blanquet (1932) cover categories within a designated area in each wetland extending laterally across the entire wetland and longitudinally for 100 m. The banks were assessed separately from the water body. Macroinvertebrate assessment involved taking six samples among different habitat types as described for the Gwydir Valley. Bird surveys comprised 30 minutes observation on arrival at each wetland plus casual observations made in the course of other activities during the rest of the day. For each survey occasion, Spearman rank correlations were calculated between the historical dryperiod frequency and the number of plant species on the banks and in the water and the number of bird species and individuals per wetland. Separate analyses were run for all bird species and for waterbird species only. In the case of macroinvertebrates, for which there were several samples per wetland on each sampling occasion, nested analysis of variance (ANOVA) was used to test for statistical differences among long-term water regimes in the number of taxa per sample. Site was nested within historical dry-period frequency and the various survey periods were analysed separately. NMS was applied to assemblage data for vegetation on the banks and, in the water, macroinvertebrates and birds. Data transformations for vegetation and macroinvertebrates were the same as for the Gwydir Valley wetlands. For birds (all species and waterbird species only), abundances were transformed to the fourth root. Dissimilarity was expressed as the Bray-Curtis coefficient in all cases. The Mantel test was used to assess relationships between biological assemblages and the historical dry-period frequency. Dissimilarity was expressed as the Bray-Curtis measure for biota and Euclidean distance for dry-period frequency. 8.3.2.

Results

Water quality Water quality data spanned a wide range for most variables (Table 8.7). Electrical conductivity was particularly high at the sites Azolla and Lignum in January 2000. Table 8.7. Ranges of water quality variables in Lachlan Valley wetlands during three sampling periods No. of samples

Temperature (°C)

Turbidity (NTU)


Aug. – Sep. 1999

6

13–26

2–64

420–820

Oct. – Nov. 1999

5

19–27

4–49

330–780

Jan. – Feb. 2000

9

24–37

3–190

400–6500

Period


93

Vegetation The surveys yielded a total of 111 plant species. Spearman rank correlations between number of species and the historical dry-period frequency were significantly positive before inundation for the banks and significantly negative at 8 weeks after inundation for the water (P < 0.05 in both cases; see Figure 8.5). All other correlations were non-significant (P > 0.05). Two-dimensional NMS showed little separation of sites by historical dry-period frequency for either habitat (Figure 8.6). Some sites had wide temporal shifts in ordination space, but without a consistent pattern (Figure 8.6). In Mantel tests, only the water-body assemblages at 8 weeks after inundation showed a significant association with dry-period frequency (P < 0.05). Before

8 weeks

50

30

No. of water species

No. of bank species

40

30

20

20

10

10

0

0 0

1

2

3

4

0

1

Dry frequency

2

3

4

Dry frequency

Figure 8.5. Relationship between the historical frequency of extended dry periods and the numbers of plant species recorded from the banks of Lachlan Valley wetlands before flooding in 2000 (left) and from the water 8 weeks after flooding in 1999 (right)


94

Banks 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.5 -1.5

-1

Azolla (0) Hazelwood (3) Erins (4)

-0.5

0

0.5

Morgans (2) Robsar(3) Wilga (4)

1

1.5

2

Bocabidgle (3) Thomsons (3)

Booligal (3) Whealbah (3)

0

1

Water 1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5 -2

-1.5

Azolla (0) Morgans (2) Thomsons (3)

-1

-0.5

Marrool (0) Booligal (3) Whealbah (3)

0.5

Lignum (1) Hazelwood (3) Erins (4)

1.5

Reed beds (1) Robsar(3) Wilga (4)

Figure 8.6. NMS ordinations of vegetation cover data for banks and water of Lachlan Valley wetlands for all survey periods. Data points are coded by site and historical dry-period frequency (in parentheses). Arrows indicate selected temporal sequences. Some samples could not be included as no plants were recorded. Stress = 0.19 (banks) and 0.24 (water)


95

Macroinvertebrates At least 195 aquatic macroinvertebrate species were recorded from the seven wetlands and four sampling occasions. The figure is a minimum because not all specimens could be identified to species level. The most diverse families were Chironomidae (midges; at least 29 species), Hydrophilidae (beetles; 20) and Dytiscidae (beetles; 13). Nested ANOVA found a significant association between number of species and the historical dry-period frequency during the pre-inundation period in 1999 and at 2, 8 and 12 weeks after inundation (P < 0.001 in all cases). However, the relationship was not significant in the pre-inundation period in early 2000 (P > 0.05). Sites with an intermediate drying frequency generally had the fewest taxa (Figure 8.7). Two-dimensional NMS showed little separation of sites by historical dry-period frequency (Figure 8.8). Two sites had large temporal shifts in ordination space, roughly in the same direction (Figure 8.8). Mantel tests produced non-significant results (P > 0.05) in all cases. 2 weeks 40

30

30

No. of taxa

No. of taxa

Before 40

20

10

20

10

0 0

1

2

3

0

4

0

1

2

Dry frequency

8 weeks

4

3

4

12 weeks

40

40

30

30

No. of taxa

No. of taxa

3

Dry frequency

20

10

20

10

0

0 0

1

2

3

4

0

1

Dry frequency

2

Dry frequency

Figure 8.7. Relationships between historical frequency of extended dry periods and numbers of macroinvertebrate taxa recorded in individual samples from Lachlan Valley wetlands before flooding in 1999 and at 2, 8 and 12 weeks afterwards


96

4.0

3.0

2.0

1.0

0.0

-1.0 -1

-0.5

0

0.5

1

Azolla (0)

Marrool (0)

Lignum (1)

Morgans (2)

Bocabidgle (3)

Booligal (3)

Robsar (3)

Thomsons (3)

Whealbah (3)

Wilga (4)

Figure 8.8. NMS ordination of macroinvertebrate frequency data from Lachlan Valley wetlands for all survey periods. Data points are coded by site and historical dry-period frequency (in parentheses). Arrows indicate selected temporal sequences. Stress = 0.15

Birds Waterbird breeding was triggered at several sites in the Booligal wetlands after uncontrolled flooding began in July 1998. In December, flows receded and DLWC initiated water control in order to avoid nest abandonment. This action followed the recommendations of Magrath et al. (1991) and the 1998-99 flow plan (LRMC 1999). About 2600 ML were provided as part of the environmental contingency allocation, via the regulator at Torriganny Weir. ECA flows in Merrimajeel Creek were sustained until the end of February 1999, when most birds had finished breeding. Longer releases would have artificially increased vegetation growth in Merrimajeel and Muggebah creeks. The Booligal wetlands supported numerous bird species in 1998-99 (Tables 8.8 and 8.9). Table 8.8. Population estimates for breeding birds in the Booligal ‘block bank’ swamp on five dates in 1998-99. Counts are nests for ibis species and birds for other species. n.a., not assessed Species

Common name

26 Oct.

1 Dec.

6 Jan.

13 Jan.

20 Jan.

Aythya australis

Hardhead

200

200

n.a.

n.a.

n.a.

Fulica atra

Eurasian coot

500

500

n.a.

n.a.

n.a.

Platalea regia

Royal spoonbill

500

500

n.a.

n.a.

n.a.

Plegadis falcinellus

Glossy ibis

0

2000

2000

1000

500

Stictonetta neavosa

Freckled duck

10

30

n.a.

n.a.

n.a.

Threskiornis aethiopica

Sacred ibis

4000

4000

200

100

100

Threskiornis spinicollis

Straw-necked ibis

40 000

40 000

2000

1000

100


97

Table 8.9. Population estimates for common waterbirds for wetlands in the Booligal area on 20-22 Jan. 1999 Species

Common name

Anas gibberifrons

Grey teal

Anas rhynchotis

Cuba Booligal Dam Swamp

Moon Lower Moon Gum Swamp Swamp

Murrumbidgil Swamp

Upper Gum Swamp

100

1000

350

300

200

50

Blue-winged shoveller

0

50

0

0

0

0

Anas superciliosa

Pacific black duck

0

60

30

100

30

20

Aythya australis

Hardhead

0

50

0

0

0

0

Biziura lobata

Musk duck

0

50

0

20

0

0

Cygnus atratus

Black swan

30

50

0

20

0

0

Egretta alba and/or Egretta intermedia

Great egret and plumed egret

10

20

100

100

10

800

Fulica atra

Eurasian coot

0

50

0

50

0

0

Gallinula tenebrosa

Moorhen

0

30

0

20

0

0

Himantopus leucocephalus

Black-winged stilt

0

20

0

0

0

0

Malacorhynchus membranaceus

Pink-eared duck

0

100

0

0

0

0

Nycticorax caledonicus

Nankeen night heron

0

100

2000

50

2

100

Platalea flavipes

Yellow-billed spoonbill

0

0

50

0

0

300

Platalea regia

Royal spoonbill

0

50

0

50

0

0

Plegadis falcinellus

Glossy ibis

10

500

10

0

0

0

Podiceps cristatus

Great crested grebe

0

100

0

0

0

0

Poliocephalus poliocephalus Hoary-headed grebe and little grebe and/or Tachybaptus novaehollandiae

0

100

0

70

0

0

Porphyrio porphyrio

Purple swamphen

0

20

2

20

20

0

Threskiornis aethiopica

Sacred ibis

10

100

10

0

0

0

Threskiornis spinicollis

Straw-necked ibis

100

100

20

50

0

0

In 1999-2000, 82 species of aquatic and non-aquatic birds were observed or heard calling. Spearman rank correlation between the historical dry-period frequency and the number of bird species or individuals per wetland was statistically significant in only one instance. The total number of species was positively correlated with dry-period frequency in the pre-flood survey period in 2000 (Figure 8.9). Two-dimensional NMS showed some separation of sites according to dry-period frequency (Figure 8.10). Major temporal shifts in ordination space were not in a consistent direction among sites. Mantel tests showed significant relationships between dry-period frequency and total bird assemblages at 8 weeks after flooding in 1999 and for the pre-flood period in 2000 (P < 0.05). Relationships with waterbird assemblages were significant for the same survey periods (P < 0.01 and P < 0.05 respectively).


98

25

No. of species

20

15

10

5

0 0

1

2

3

4

Dry frequency

Figure 8.9. Relationships between historical frequency of extended dry periods and numbers of bird species observed in Lachlan Valley wetlands before flooding in 2000


99

All birds 1.0

0.5

0.0

-0.5

-1.0 -1.5

-1

Azolla (0) Morgans (2) Robsar (3) Wilga (4)

-0.5

0

0.5

Marrool (0) Bocabidgle (3) Thomsons (3)

1

1.5

Lignum (1) Booligal (3) Whealbah (3)

2

Reed beds (1) Hazelwood (3) Erins (4)

Waterbirds 2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -1.5

-1

Azolla (0) Bocabidgle (3) Whealbah (3)

-0.5

0

Marrool (0) Booligal (3) Erins (4)

0.5

Lignum (1) Robsar (3) Wilga (4)

1

1.5

Reed beds (1) Thomsons (3)

Figure 8.10. NMS ordination of abundance data for all birds and for waterbirds in Lachlan Valley wetlands. Data points are coded by site and historical dry-period frequency (in parentheses). Some samples could not be included as no waterbirds were recorded. Arrows indicate selected temporal sequences. Stress = 0.19 (all birds) and 0.20 (water birds)


100

8.4.

MACQUARIE VALLEY

8.4.1.

Sites and methods

Twelve study sites (Map 6; Table 8.10) were selected to achieve a broad geographic spread across the Macquarie Marshes, and to incorporate examples of various wetland types and water regimes. Some long-term monitoring sites were included to enable comparison with historical data. Some sites were located in the northern and southern portions of the Macquarie Marshes Nature Reserve, in order to provide the National Parks and Wildlife Service with information relevant to reserve management. For this report, each site was assigned to one of the four flooding zones mapped by Kidson (2000) on the basis of association between river flows at Marebone Weir and the extent of periodic flooding as revealed by Landsat TM satellite imagery. These zones are the: •

green zone, flooded by flow events with a total volume of 50-150 GL

•

yellow zone, flooded by 150-250 GL

•

red zone, flooded by 250-400 GL

•

blue zone, flooded by > 400 GL. Table 8.10. Wetland study sites and timing of vegetation and macroinvertebrate assessment in the Macquarie Valley. Sites are arranged in sequence from south to north Site number Site name

Wetland type

Flood zone Vegetation

Macroinvertebrates

42110164

Oxley Station Lagoon

Lagoon

Green

Jan. 00

Jan. 00

42110158

Buckiinguy Lagoon

Lagoon

Green

Jan. 00; Apr. 00 Jan. 00; Apr. 00

42110163

Buckiinguy Swamp

Floodplain

Red

Jan. 00; Apr. 00

42110165

Southern Nature Reserve

Floodplain

Blue

Jan. 00; Apr. 00

42110161

Monkeygar Creek Wetland

Channel

Green

Jan. 00; Apr. 00 Jan. 00; Apr. 00

42110162

Terrigal Creek Wetland

Channel

Green

Jan. 00; Apr. 00 Jan. 00

42110157

Mole Marsh

Floodplain

Green

Jan. 00; Apr. 00

42110055

Lamphs Channel

River red gum Green

Jan. 00; Apr. 00 Apr. 00

42110053

Third Crossing Lagoon

Lagoon

Green

Jan. 00; Apr. 00 Jan. 00; Apr. 00

42110160

Hunts Woodland

River red gum Yellow

Jan. 00; Apr. 00 Jan. 00; Apr. 00

42110051

Ginghet Swamp

River red gum Red

Jan. 00; Apr. 00 Jan. 00; Apr. 00

42110159

Bluelight Wetland

River red gum Yellow

Jan. 00; Apr. 00 Jan. 00; Apr. 00

Sampling occurred twice during the reporting period, in January and April 2000. On each occasion, a Hydrolab probe was used to measure water temperature, electrical conductivity, turbidity, dissolved oxygen and pH at 20 m intervals along a 100 m transect at each site. Three measurements of each variable were taken at each point, unless there was no water. Vegetation at each site was assessed in 5 m square quadrats at 10 m intervals along a 100 m transect aligned along a moisture gradient. Within each quadrat, each plant species was identified (or a sample pressed for subsequent identification), its percent areal coverage estimated and its reproductive status (e.g. flowering, fruiting or vegetative) noted. The moisture level in each quadrat was rated as wet (surface water present), intermediate (damp soil) or dry. At each site where water was present, macroinvertebrate samples were taken from within 20 m either side of the 100 m vegetation transect in a 4000 m2 sampling area. Six samples were taken at each site, distributed among the habitat types present and roughly in proportion to their abundance if there were fewer than six. Habitats included open water with aquatic macrophytes, eucalypt forest with aquatic macrophytes, Typha beds, Phragmites beds, vegetated channel edgewater, vegetated lagoon edgewater and woody debris with aquatic macrophytes. Macroinvertebrate samples were collected Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

101

and processed as described for the Gwydir Valley, except that they were preserved in toto in the field and sorted in the laboratory. Frogs were surveyed at selected sites by night-time searches with a spotlight and recording of calls, and daytime observation of spawn. Statistical analysis of vegetation and macroinvertebrate data was performed in a similar manner to that for the Gwydir Valley. For rank correlation and the Mantel test, quadrat moisture was coded as 1 (wet), 2 (intermediate) or 3 (dry). 8.4.2.

Results

Water quality Water quality data spanned a wide range for most variables (Table 8.11). Dissolved oxygen levels were consistently low in both sampling periods. Table 8.11. Ranges of water quality variables in Macquarie Valley wetlands during two sampling periods Period

No. of sites

Temperature (°C)

Turbidity (NTU)


pH

Dissolved oxygen (mg/L)

Jan. 2000

8

24 – 32

4 – 16

330 – 1100

7.0 – 7.8

0.3 – 1.5

Apr. 2000

7

18 – 21

1 – 80

310 – 650

6.8 – 8.8

0.9 – 3.5

Vegetation Ninety-one plant species were recorded. Nested ANOVA found no significant difference in the number of species per quadrat among flood zones in either January or April (P > 0.05). The number of species per quadrat was significantly associated with quadrat moisture in April (Spearman rank correlation, P < 0.05) but not in January (P > 0.05). In April, dry quadrats averaged 7.5 species, compared with 6.5 for wet quadrats and 6.4 for intermediate ones. Two-dimensional NMS based on species cover data revealed a tendency for quadrats to group by site but not by flood zone (Figures 8.11 and 8.12, top). Likewise, MRPP analysis of data averaged by wetland found no significant differences in vegetation assemblages among flood zones (P > 0.05). Quadrats grouped only weakly by moisture level in the NMS (Figures 8.11 and 8.12, bottom), but the Mantel test found significant relationships between plant associations and quadrat moisture on both sampling occasions (P < 0.001). Indicator species analysis identified several species that characterised quadrats with different moisture levels in January (Table 8.12). However, in April these relationships were much weaker. Table 8.12. Plant species showing a statistically significant association with different levels of quadrat moisture in indicator species analysis for Macquarie Valley wetlands, January 2000 Species

Indicator value

Wetness category

Azolla pinnata

44

Wet

Ludwigia peploides

38

Wet

Marsilea sp.

36

Intermediate

Cyperus difformis

32

Intermediate

Eucalyptus camaldulensis

22

Intermediate

Xanthium spinosum

21

Dry

Pratia concolor

20

Intermediate

Wahlenbergia spp.

17

Dry

Alternanthera denticulata

16

Dry

Cuscuta sp.

16

Intermediate


102

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5 -2

-1.5

-1

-0.5

Buckiinguy Lagoon (Green) Monkeygar (Green) Third Crossing (Green) Buckiinguy Swamp (Red)

0

0.5

Lamphs (Green) Oxley (Green) Bluelight (Yellow) Ginghet (Red)

1

1.5

Mole (Green) Terrigal (Green) Hunts (Yellow) Southern (Blue)

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5 -2

-1.5

-1

-0.5 Wet

0 Damp

0.5

1

1.5

Dry

Figure 8.11. NMS ordinations of vegetation cover data for individual quadrats in Macquarie Valley wetlands, January 2000. Top, data points coded by site and flood zone colours; bottom, data points coded by quadrat moisture level. Stress = 0.24


103

1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

Buckiinguy Lagoon (Green)

Lamphs (Green)

Mole (Green)

Monkeygar (Green)

Terrigal (Green)

Third Crossing (Green)

Bluelight (Yellow)

Hunts (Yellow)

Buckiinguy Swamp (Red)

Ginghet (Red)

Southern (Blue)

1.5

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5

-2.0 -2

-1.5

-1

-0.5 Wet

0 Damp

0.5

1

1.5

Dry

Figure 8.12. NMS ordinations of vegetation cover data for individual quadrats in Macquarie Valley wetlands, April 2000. Top, data points coded by site and flood zone colours; bottom, data points coded by quadrat moisture level. Stress = 0.22


104

Macroinvertebrates At least 168 aquatic macroinvertebrate species were recorded; the figure is a minimum because not all specimens could be identified to species level. The most diverse families were Chironomidae (midges; at least 20 species), Hydrophilidae (beetles; 15) and Naididae (worms; 12). Nested ANOVA found a significant difference among flood zones in January (P < 0.01) but not in April (P > 0.05). In January the number of taxa averaged 19 in the most frequently flooded green zone, 17 in the yellow zone and 25 in the red zone. No macroinvertebrates were sampled in the blue zone because of a lack of water. In two-dimensional NMS, temporal changes at those sites that were sampled in both months were generally in the same direction, mostly along the y-axis (Figure 8.13), suggesting common successional trajectories. MRPP analysis did not reveal significant differences in assemblage composition according to flood zone in either sampling period (P > 0.05). 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -1.5

-1.0

-0.5

Buckiinguy Lagoon (Green) Oxley (Green) Bluelight (Yellow)

0.0

0.5

1.0

Lamphs (Green) Terrigal (Green) Hunts (Yellow)

1.5

2.0

Monkeygar (Green) Third Crossing (Green) Ginghet (Red)

Figure 8.13. NMS ordination of macroinvertebrate frequency data from Macquarie Valley wetlands, January and April 2000. Data points are coded by site and flood zone colours. Arrows indicate temporal sequences. Stress = 0.15

Frogs Four species were recorded: the brown froglet (Crinia parinsignifera), the barking marsh frog (Limnodynastes fletcheri), the spotted marsh frog (Limnodynastes tasmaniensis) and the crucifix frog (Notaden bennettii). Records were sporadic, with no clear spatial or temporal pattern.


105

8.5.

MURRUMBIDGEE VALLEY

8.5.1.

Sites and methods

Fifteen wetlands distributed from upstream of Wagga Wagga to downstream of Hay were chosen for study by a stratified random process (Map 7; Table 8.13). Any wetlands within this area that are altered by earthworks, supply water to irrigation areas or receive irrigation drainage were eliminated from consideration. Wetlands that are replenished by local rainfall or runoff rather than river flow, or inaccessible for sampling during periods of high river flow, were also excluded. The remaining candidates were grouped according to commence-to-flood height, geomorphic type and distance from the mouth of the Murrumbidgee River, and a random selection was made from each category. Table 8.13. Wetland study sites in the Murrumbidgee Valley. Sites are arranged in sequence from east to west Site number

Site name

Frequency Percent filled Wetland type Frequency Percent (1999-2000) of river filled of river inflow (1998-99) inflow (1999-2000) (1998-99)

41010290 Wantabadgery/Coldene Lagoon

Unvegetated

1

10

0

0

41010292 Iris Park Swamp

Aquatic plant

3

100

0

0

41010293 Berryjerry Lagoon

Mixed

3

100

9

100

41010294 Ganmain Station Lagoon 1

Red gum

2

100

0

0

41010295 Ganmain Station Lagoon 2

Aquatic plant

0

0.05). However, the number of species per quadrat was negatively correlated with water depth at the time of sampling (Spearman rank correlation: P < 0.001; see Figure 8.18). Although twodimensional NMS showed a tendency for quadrats to group more strongly by site than by water regime (Figure 8.19, left), the effect of water regime, tested with data pooled by wetland, was statistically significant (MRPP: P < 0.001). Since most quadrats were dry, a relationship between water depth and assemblage composition at the quadrat scale could not be established (Figure 8.19, right). Indicator species analysis identified six taxa that characterised quadrats with different moisture levels (Table 8.17). 12

No. of species

10

8

6

4

2

0 0

0.2

0.4

0.6

0.8

1

Water depth (m)

Figure 8.18. Relationship between water depth and number of plant species in individual quadrats in the Namoi Valley wetlands, June 2000. Many data points are superimposed 1.5

1.5

1

1

0.5

0.5

0

0

-0.5

-0.5

-1

-1

-1.5

-1.5

-2

-2 -2

-1.5

-1

-0.5

0

0.5

1

1.5

B a rbe rs ( we t )

G o a ngra ( we t )

B ulle ra wa ( int .)

B ugilbo ne do wn ( int .)

-2

2

-1

0

1

2

B ugilbo ne up ( int )

Figure 8.19. NMS ordination of vegetation cover data for individual quadrats in Namoi Valley wetlands. Left, data points coded by site; right, data points shaded and sized in proportion to water depth in individual quadrats (maximum 0.83 m), or unshaded to indicate dry quadrats. Stress = 0.29 Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

111

Table 8.17. Plant species showing a statistically significant (P < 0.05) association with different levels of quadrat wetness in indicator species analysis for Namoi Valley wetlands, June 2000 Species

Indicator value

Wetness category

Medicago polymorpha

44

Dry

Paspalidium jubiflorum

38

Dry

Alternanthera denticulata

35

Dry

Paspalum distichum

15

Wet

Azolla filiculoides

14

Wet

Persicaria decipiens

14

Wet

Macroinvertebrates At least 127 aquatic macroinvertebrate species were recorded, a minimum number because not all specimens could be identified to species level. The most diverse families were Chironomidae (midges; at least 19 species), Dytiscidae (beetles; 12) and Hydrophilidae (beetles; 10). Nested ANOVA did not reveal any significant differences in number of taxa per sample according to longterm water regime for either sampling period (P > 0.05). Two-dimensional NMS showed some tendency for sites to group by water regime (Figure 8.20). Data for the second sampling occasion showed a significant difference between the two water regimes (MRPP: P < 0.001); on the first occasion the number of sites sampled was insufficient for testing. The temporal changes in those sites that were sampled twice were in a similar direction in the ordination (Figure 8.20).

1.5

1.0

0.5

0.0

-0.5

-1.0

-1.5 -2

-1.5

-1

-0.5

Barbers (wet)

Goangra (wet)

Bugilbone down (int.)

Bugilbone up (int.)

0

0.5

1

Bullerawa (int.)

Figure 8.20. NMS ordination of macroinvertebrate frequency data from Namoi Valley wetlands, December 1999 and March-April 2000. Data points are coded by site and long-term water regime. Arrows indicate temporal sequences for sites sampled twice. Stress = 0.07


112

8.7.

DISCUSSION

Table 8.18 summarises the outcomes of statistical significance testing of relationships between the abundance, taxonomic richness and assemblage composition of various groups of biota and two aspects of water availability in the IMEF study wetlands. The first of these is the broad, long-term water regime at the spatial scale of study sites, for example the frequency and duration of flooding and drying. The second is small-scale wetting observed at the time of sampling, for example water depth or soil moisture levels in survey quadrats. The second spatial scale of analysis was applied only to sessile biota (i.e., plants). It was not applied to animals because of their ability to move rapidly among habitat patches within a wetland. In some cases the sampling design for plants did not address small-scale variation. At this early stage of the program the amount of data collected varied substantially among valleys and groups of biota. In some instances data were not yet sufficient for statistical testing or at a level that would permit tests with high statistical power. Nevertheless, relationships with long-term water regime were statistically demonstrated, or at least suggested, for vegetation, macroinvertebrates and birds in at least one valley. Linkages between vegetation communities and small-scale wetting were also evident or suggested in most valleys (Table 8.18). It is important to recognise that the classification and quantification of the water regimes of the study sites are still at a preliminary stage of development. The process is most advanced in those valleys where the sampled wetlands are mainly discrete water bodies (e.g. billabongs), and the local river discharges required to flood them have mostly been determined (Lachlan and Murrumbidgee valleys). In these situations, the timing and frequency of wetland flooding can be inferred from flow records for nearby river gauging stations. However, full characterisation of water regimes also requires information on the timing and frequency of drying.


113

Table 8.18. Summary of statistical tests of relationships between biological properties of IMEF study wetlands and both site-scale, long-term water regimes (e.g. flooding or drying frequency) and small-scale moisture levels (e.g. water depth in quadrats) at the time of sampling Biota group

Variable

Valley

Relationship to water regime

Relationship to point moisture

Vegetation

Species per quadrat

Gwydir

Statistically significant

Not statistically significant

Vegetation

Species per site (on banks or in water)

Lachlan

Sometimes statistically significant

Not applicable

Vegetation

Species per quadrat

Macquarie



Vegetation

Species per site

Murrumbidgee


Not applicable

Vegetation

Species per quadrat

Namoi



Vegetation

Assemblage composition

Gwydir

Insufficient sites to test


Vegetation


Lachlan

Rarely statistically significant Not applicable

Vegetation


Macquarie



Vegetation


Murrumbidgee


Not applicable

Vegetation


Namoi


Insufficient moisture to test

Macroinvertebrates

Species per sample

Gwydir


Not applicable

Macroinvertebrates

Species per sample

Lachlan

Mostly statistically significant Not applicable

Macroinvertebrates

Species per sample

Macquarie


Not applicable

Macroinvertebrates

Species per sample

Murrumbidgee


Not applicable

Macroinvertebrates

Species per sample

Namoi


Not applicable

Macroinvertebrates


Gwydir

Insufficient sites to test

Not applicable

Macroinvertebrates


Lachlan


Not applicable

Macroinvertebrates


Macquarie


Not applicable

Macroinvertebrates


Murrumbidgee


Not applicable

Macroinvertebrates


Namoi


Not applicable

Frogs

Species per site

Murrumbidgee


Not applicable

Frogs


Murrumbidgee


Not applicable

Birds

Species per site

Lachlan

Rarely statistically significant Not applicable

Birds

Individuals per site

Lachlan


Not applicable

Birds


Lachlan


Not applicable

The information base on water regimes at IMEF wetland sites will improve over time. Continuous water level recorders have now been installed at a number of wetland sites and opportunities exist to make use of remote sensing data to quantify broad-area flooding and drying. Future reports should therefore be able to use a much more developed characterisation of water regimes, and to explore the relevance of alternative descriptors such as flooding frequency, drying frequency, percent of time wetted and seasonal timing of wetting and drying. There are also questions related to the length of the antecedent period before biological sampling over which the occurrence of flooding and drying are relevant. This is likely to vary for different groups of biota, depending on their mobility and the length of their life cycles. Stronger relationships between wetland biota and water regime are likely to be established once the most relevant hydrological descriptors have been determined. The biological communities of IMEF wetlands are likely to be influenced by many non-hydrological factors, which may mask or confound responses to water regimes. In most valleys, wetlands were characterised as belonging to several types, defined by morphology and vegetation (Tables 8.6, 8.10 and 8.13). This diversity complicates the assessment of hydrological influences. For example, in the Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

114

Lachlan Valley the morphological type known as swamps tends to have a lower frequency of extended dry periods than the type known as billabongs (Table 8.6). It is likely to be difficult to disentangle the comparative influences of morphology and hydrology until a much larger number of wetlands has been sampled, or until individual wetlands have been assessed over a long period, encompassing a broad range of hydrological conditions. Variations in stocking density and water quality are also likely to be influential. For example, livestock can reduce vegetation biomass in Australian wetlands (Robertson 1997) and increased salinity can reduce the diversity and abundance of organisms emerging from wetted wetland sediment in the Murray Valley (Skinner et al. 2001). Data have been obtained on both water quality and stock densities for IMEF wetlands (the latter not reported here), and can be considered in future, more detailed, statistical analysis and modelling. Vegetation assemblages showed frequent significant associations with both aspects of water availability (Table 8.18). To some extent, the second aspect (moisture within quadrats) may have masked the first (long-term water regime at the site scale), since ground elevation, and hence point wetting, often varied considerably within a site. The varied responses of wetland plant species to water regimes in south-eastern Australia have been used as a basis for classifying species into ecological groups, based on both growth form and tolerance of flooding and drying (Brock and Casanova 1997). The indicator species analysis reported here also provided a basis for classifying species according to hydrological requirements or preferences. This approach may provide a useful means for summarising assemblage data in the future. It is possible that environmental flows may help to suppress alien wetland plants (Roberts 2002). Of particular concern are highly invasive ‘transformer’ species such as lippia (Phyla spp.). Results for the Gwydir Valley wetlands confirmed the preference of lippia for drier sites, suggesting that a wetter water regime reduces its competitiveness with native wetland plants, such as the water couch-ribbed spike-rush (Paspalum distichum-Eleocharis plana) association. However, wetter conditions may also favour water hyacinth (Eichhornia crassipes), another invasive weed. An additional complication is that alien plants can sometimes be used by native fauna. For example, the use of flooded Xanthium spp. (Bathurst and Noogoora burr) by emerging dragonflies was noted in a Lachlan Valley wetland. Relationships between macroinvertebrate assemblages and water regimes were established in relatively few cases (Table 8.18). Previous studies of wetland macroinvertebrates in relation to water regimes in eastern Australia have focused mainly on the contrast between temporary wetlands and permanent water bodies (including rivers), rather than the more subtle differences in flooding and drying frequency pertinent to IMEF. Even between these extremes, differences can be subtle. Quinn et al. (2000) found differences in post-flood macroinvertebrate assemblages between permanent and temporary wetlands on the Barmah-Millewa floodplain of the regulated Murray River, but not on the floodplain of the unregulated Ovens River in Victoria. In the Cooper Creek system of central Australia, Sheldon et al. (2002) found associations between water regime variables and macroinvertebrate assemblage characteristics to be generally weak and seldom statistically significant. The apparent lack of strong associations between macroinvertebrate assemblages and long-term antecedent water regimes may partly relate to the ability of wetland macroinvertebrates to colonise soon after flooding. Some macroinvertebrate species may survive dry periods in damp sediments or refuge pools, whereas others may disperse rapidly by flight or in moving floodwaters, or breed rapidly under favourable conditions (Boulton 1999). Thus time since wetting may be more important than the historical water regime in determining which species are present. Strong and fairly consistent successional trajectories after flooding were observed in the IMEF study valleys (Figures 8.3, 8.8, 8.13 and 8.20), as has been reported elsewhere in south-eastern Australia (Hillman and Quinn 2002). Despite the importance of temporal factors, there may be particular species that are highly dependent on long-term water regime, and whose responses are masked when analyses are done at the level of entire assemblages. The identification of such species may be a useful direction for future analysis.


115

Limits on the information currently available on local water regimes in the Gwydir Valley wetlands prevented relationships between water regimes and fish communities from being tested at this stage of the project. Fish sampling of these wetlands revealed a fauna dominated by alien fish, with a low diversity of native species. Fish assemblages with similar characteristics have been reported from wetlands elsewhere in the Murray-Darling Basin (Hillman 1987; Gehrke et al. 1999). There is some debate about the extent to which floodplain wetlands in the Murray-Darling Basin act as spawning and nursery areas for native fish species (Humphries et al. 1999). The data for the Gwydir wetlands sampled in 1999-2000 indicated that the dominant native species, bony herring, probably bred in large numbers, and the crimson-spotted rainbowfish may also have done so. However, there was no evidence of substantive recruitment of flagship native species such as golden perch and Murray cod. On the other hand, these wetlands were apparently effective breeding sites for carp, goldfish and gambusia. Frogs and birds were not assessed as intensively or extensively as vegetation and macroinvertebrates. Nevertheless, some significant relationships with water regime were found for birds in the Lachlan Valley. Several other studies have established that particular bird species favour different wetland water regimes, especially for breeding (e.g. Briggs et al. 1997, 1998). The successful mass breeding of several bird species in the Lachlan Valley’s Booligal wetlands in 1998-99 can be attributed in part to the use of environmental flow allocations to prevent nest abandonment. Although not studied as part of IMEF, large bird breeding events occurred in the wetlands of other valleys at the same time. The NSW National Parks and Wildlife Service undertakes extensive waterbird monitoring across the west of the State. Because the composition, richness and abundance of indigenous wetland animal and plant assemblages vary according to water regime, protection and restoration of the array of natural flooding and drying patterns is likely to be vital to sustaining overall native biodiversity. Preliminary analysis of wetland flooding frequencies, based on commence-to-flood levels and simulation of river flows in the absence of major impoundment and extraction (Chapter 4), indicated that flow management in 1998-2000 produced a relatively natural spectrum of wetland flood frequencies in the lower Lachlan Valley, but not in the Murrumbidgee Valley. In the latter valley, the option of pumping river water into wetlands in order to increase flooding frequency is being evaluated in a separate study. Flood-frequency analyses are not yet available for wetlands in the other IMEF study valleys, but are an important priority for the future.


116

9.

River fish

9.1.

INTRODUCTION

Commercial catch statistics and anecdotal information indicate that populations of at least the larger native freshwater fish species declined dramatically across much of NSW during the last century (Rowland 1989; Brown 1994; Faragher and Harris 1994). Strong circumstantial evidence suggests that the causes of these declines include interference with migration through the construction of dams, weirs and levees, and the disruption of environmental cues for spawning (through temperature depression from hypolimnetic dam releases and reduced flooding frequencies) (Cadwallader 1977, 1978; Cadwallader and Lawrence 1990). For example, the establishment of Dartmouth Dam on the Mitta Mitta River in Victoria resulted in major downstream declines of native warm-water fishes (Koehn et al. 1995 cited in Thoms et al. 2000). In coastal rivers, about half of the total stream length potentially available to migratory species such as Australian bass (Macquaria novemaculeata) has been alienated by the construction of artificial barriers (Harris 1984). Recruitment in this species in the Hawkesbury-Nepean River system also appears to be positively correlated with the magnitude of river discharge (Harris 1988). Gehrke et al. (1995, 1999) compared the native fish fauna at sites on the Darling, Murray, Murrumbidgee and Paroo rivers, and observed a strong correlation between the diversity of native fish (measured by the Shannon-Wiener index) and the deviation of monthly flows from the natural regime. Recent studies (Gehrke et al. 1995; Harris and Gehrke 1997; Gehrke and Harris 2000) have also found that alien species such as carp and gambusia dominate fish catches in many rivers. Native species richness tends to be lower, and the proportion of alien species higher, in highly regulated rivers than in unregulated or semi-regulated systems (Gehrke and Harris 2001). The IMEF study of riverine fish assemblages relates to hypotheses 4 and 8 (see section 2.3). These hypotheses propose that restoring a more natural flow regime will promote more successful breeding and recruitment of native fish. Consequently, the abundance and dominance of native fish should increase in the long term. The study design is based on annual fish sampling at numerous sites, with analysis of the size distribution of individual fish species. This provides information on the occurrence of juvenile fish originating from spawning in the preceding season (young of the year). Numbers of young of individual native (and alien) species can be related statistically to antecedent flow regimes in order to establish the flow patterns most associated with recruitment. Annual sampling can also enable the progress of recruited cohorts to be tracked through to the adult population. 9.2.

SITES AND METHODS

Sixty-four river sites (Maps 2-8; Table 9.1), spread across seven valleys, were sampled once between late November 1999 and April 2000. Sampling was centred on summer because surveys generally catch more fish in summer than in winter (Harris and Gehrke 1997). The sites were chosen by a modified stratified random process. Each river was first divided into a sequence of relatively homogeneous reaches according to water-use infrastructure (weirs, irrigation off-takes and returns) and geomorphology (gradient, channel and floodplain form and the presence of anabranches and distributaries). The number of sites within each reach was determined by dividing that reach’s length by the mean length of all reaches in the same river and rounding up to the nearest integer. For example, if the length of a reach was less than the mean, that reach was allocated one site. If the length of a reach was 2.5 times the mean, it was allocated three sites. Sites were selected within each reach as follows. Sites that had been chosen at random for past fish projects (termed ‘prior sites’) were retained for IMEF. If more prior sites lay within a reach than were needed, some were omitted at random. If insufficient prior sites fell in a reach, a number of map grid squares within the reach, corresponding to the required number of new sites, was selected at random on a 1:100 000 topographic map. The nearest accessible sampling site to the centre of each map square was selected. To ensure dispersion of sites, the minimum distance between sites was set as the Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

117

length of the reach divided by the number of sites within it. Each selected site was inspected to ensure that it had adequate access, was amenable to standard boat electrofishing during normal low-flow periods, was representative of the reach and was not affected by exceptional influences such as urban areas. Sites that did not meet these criteria were replaced. Table 9.1. Fish sampling sites on each river, arranged in sequence from upstream to downstream. Sites sampled in previous studies such as the NSW Rivers Survey (Harris and Gehrke 1997) are indicated by asterisks River system

Site No. Site name

River system

Site No.

Site name

Lachlan

F133 Lachlan River at Darby Falls Bridge

Barwon-Darling

F100* Macintyre River at Yetman

Barwon-Darling

F101 Barwon River at Little Weir

Lachlan

F134 Lachlan River at Merriganowry

Barwon-Darling

F102 Barwon River at Old Pokataroo

Lachlan

F135 Lachlan River at The Angle

Barwon-Darling

F103 Barwon River at Bundabarina

Lachlan

F136 Lachlan River at Timaroo

Barwon-Darling

F104 Barwon River at Gowrie

Lachlan

F137* Lachlan River at Kirkup Park

Barwon-Darling

F105 Barwon River at Old Booroma

Lachlan

F138 Lachlan River at Euabalong Bridge

Barwon-Darling

F106 Barwon River at Wolkara Station

Lachlan

F139 Lachlan River at Gunniguldrie

Barwon-Darling

F107 Darling River at Stony Point pump Lachlan hole

F140* Lachlan River at Wheelba Bridge

Barwon-Darling

F108 Darling River at Jandra

Lachlan

F141 Lachlan River at Erin Station

Barwon-Darling

F109* Darling River at East Toorale

Lachlan

F142 Lachlan River at Geramy

Barwon-Darling

F110 Darling River at Curranyalpa

Macquarie

F125* Macquarie River at Bonada

Barwon-Darling

F111* Darling River at Billilla

Macquarie

F126 Macquarie River at Wellington

Gwydir

F112 Gwydir River at Keera

Macquarie

F127 Macquarie River at Dickygundi

Gwydir

F113* Gwydir River at Benbraggie

Macquarie

F128 Macquarie River at Wambool

Gwydir

F114 Gwydir River at Coulton

Macquarie

F129 Macquarie River at Marebone

Gwydir

F115 Gwydir River at Gum Flat

Macquarie

F130 Macquarie River at Old Oxley

Gwydir

F116* Mehi River at Moree

Macquarie

F131* Macquarie River at Brewon

Gwydir

F117 Mehi River at Barwon confluence Macquarie

F132 Macquarie River at Binghi Bridge

Hunter

F152 Hunter River at Tyrells Vineyards Murrumbidgee

F143 Murrumbidgee River at Glendale

Hunter

F153 Hunter River at Segenhoe Stud

Murrumbidgee

F144 Murrumbidgee River at Wantabadgery

Hunter

F154 Hunter River at Aberdeen

Murrumbidgee

F145 Murrumbidgee River at Kolhagens Beach

Hunter

F155* Hunter River at Muswellbrook

Murrumbidgee

F146 Murrumbidgee River at Buckingbong Station

Hunter

F156 Hunter River at Bureen

Murrumbidgee

F147 Murrumbidgee River at Lamonts Beach

Hunter

F157 Hunter River at Barellan

Murrumbidgee

F148 Murrumbidgee River at Whitton Punt

Hunter

F158 Hunter River at Recluse/Singleton Murrumbidgee F149* Murrumbidgee River at Cookoothama

Hunter

F159* Hunter River at Elderslie

Murrumbidgee

Hunter

F170 Goorangoola Creek downstream

Murrumbidgee F151* Murrumbidgee River at Willow Isles

Hunter

F171 Goorangoola Creek upstream

Namoi

F118 Namoi River at Kibah

Hunter

F172 Glennies Creek downstream

Namoi

F119 Namoi River at 5 Mile

Hunter

F173 Glennies Creek upstream

F150 Murrumbidgee River at Moatfield Reserve

Namoi

F120* Namoi River at Boggabri

Namoi

F121 Namoi River at Broadwater

Namoi

F122 Namoi River at Yarral

Namoi

F123 Namoi River at Wilgamere

Namoi

F124 Namoi River at Yarradool


118

Fish were captured by boat electrofishing as described for the Gwydir Valley wetlands (section 8.2.1), with a maximum of 15 ‘shots’ per site, each lasting 2 minutes. Access at some sites did not allow 15 shots, and in these cases at least eight shots were completed. Fish observed but not caught, and which could be readily identified, were also recorded. All fish caught were identified, examined for disease, damage or abnormalities and measured to the nearest millimetre. For fish with forked tails, length was measured from the snout to the fork (caudal fork length). For species with rounded tails, length was measured from the snout to the end of the tail (total length). Individuals considered to be young of the year for each species were distinguished by their length. The sizes of year-old fish were derived from known growth rates for each species or, if this information was not available, for similar species. Since electrofishing effort was not the same at all sites, fish abundance data were relativised as catch per hour of electrofishing. Relativised data were transformed to the fourth root to reduce skewness and stabilise variances. Analysis of variance (ANOVA) was used to test for significant differences among IMEF valleys in number of species and transformed catch per unit effort. Tukey’s test was used for post hoc comparisons of individual valleys. Transformed catch-per-unit-effort data for individual species and sites were ordinated by non-metric multidimensional scaling (NMS) in the PCORD software package (McCune and Mefford 1999). Dissimilarity was expressed as the Bray-Curtis coefficient. 9.3.

RESULTS

Twenty native and six alien species were caught or observed at the 64 sites (Table 9.2). The average number of native fish species recorded per site was significantly different among valleys (ANOVA: P < 0.001), and Tukey’s test revealed three overlapping groups (Figure 9.1). The Hunter Valley averaged the most native fish species per site, and of the inland valleys, those in the north were richer than those in the south (Figure 9.1). The number of native fish individuals caught per unit effort differed significantly among valleys (ANOVA: P < 0.001), and Tukey’s test produced two overlapping groups (Figure 9.2). Catches in the Hunter Valley were significantly higher than those in all of the inland valleys except the Gwydir, and the inland valleys did not differ significantly from one another. The catch rate of young native fish also differed significantly among valleys (ANOVA: P < 0.001), with two overlapping groups (Figure 9.3). The Hunter Valley yielded significantly more young of the year than most inland valleys. Again, the inland valleys did not differ significantly from one another. Overall, few young native fish were caught (Table 9.2). The number of alien species per site was marginally different among valleys (P = 0.05) but Tukey’s test failed to reveal the location of any significant differences. Alien fish averaged 1.3 species per site overall. The catch of alien fish individuals per unit effort ranged from an average of 35 per hour of electrofishing in the Namoi Valley to 70 in the Hunter Valley, but did not differ significantly among valleys (ANOVA: P > 0.05). Five species constituted 80% of the total catch in terms of numbers: Australian smelt (Retropinna semoni), bony herring (Nematalosa erebi), common carp (Cyprinus carpio), freshwater herring (Potamalosa richmondi) and striped mullet (Mugil cephalus). The first three of these dominated the catch in all inland valleys (Figure 9.4). The last two were found only in the Hunter River system. Two-dimensional NMS produced an ordination that separated sites in the Hunter Valley from all inland sites (Figure 9.5). The inland valleys were not well segregated, but sites in the northern valleys (the Barwon-Darling, Gwydir and Namoi) tended to separate from those in the southern valleys (Macquarie, Lachlan and Murrumbidgee).


119

Table 9.2. Numbers of individuals (total and young of the year) of each fish species recorded from all IMEF river sites in the summer of 1999-2000. Species are arranged in order of decreasing total abundance Species

Common name

Status

Total individuals

Young individuals

Nematalosa erebi

Bony herring

Native

1446

46

Retropinna semoni

Australian smelt

Native

1060

44

Cyprinus carpio

Common carp

Alien

981

9

Mugil cephalus

Striped mullet

Native

977

79

Potamalosa richmondia

Freshwater herring

Native

712

56

Gambusia holbrooki

Gambusia

Alien

167

Gobiomorphus coxii

Cox’s gudgeon

Native

137

19

Melanotaenia fluviatilis

Crimson-spotted rainbowfish

Native

126

6

Philipnodon grandiceps

Flathead gudgeon

Native

120

7

Anguilla reinhardtii

Long-finned eel

Native

116

4

Macquaria ambigua

Golden perch

Native

105

3

Carassius auratus

Goldfish

Alien

66

2

Macquaria novemaculeata

Australian bass

Native

61

Hypseleotris spp.

Western carp gudgeon species complex Native

46

Maccullochella peelii

Murray cod

Native

42

Craterocephalus stercusmuscarum Fly-specked hardyhead

Native

34

Tandanus tandanus

Freshwater catfish

Native

33

Perca fluviatilis

Redfin perch

Alien

25

Salmo trutta

Brown trout

Alien

5

Hypseleotris compressa

Empire gudgeon

Native

5

Bidyanus bidyanus

Silver perch

Native

4

Gobiomorphus australis

Striped gudgeon

Native

4

Oncorhynchus mykiss

Rainbow trout

Alien

3

Leiopotherapon unicolor

Spangled perch

Native

2

Maccullochella macquariensis

Trout cod

Native

2

Gadopsis marmoratus

River blackfish

Native

1


120

11

1

2

7

No. of native species

6 5 4 3 2 1 AB

C

C

A

AB

AB

BC

Barwon-Darling

Gwydir

Hunter

Lachlan

Macquarie

Murrumbidgee

Namoi

0

Figure 9.1. Number of native fish species per site in each valley (mean + standard error). Valleys with the same letter (A, B or C) are not significantly different from one another (Tukey’s test)

No. of native fish per hour

600

500

400

300

200

100 A

AB

B

A

A

A

A

Barwon-Darling

Gwydir

Hunter

Lachlan

Macquarie

Murrumbidgee

Namoi

0

Figure 9.2. Catch per unit effort of native fish for sites in each valley (mean + standard error). Valleys with the same letter (A or B) are not significantly different from one another (Tukey’s test)

No. of native juveniles per hour

60

50

40

30

20

10 A

A

B

A

AB

AB

A

Barwon-Darling

Gwydir

Hunter

Lachlan

Macquarie

Murrumbidgee

Namoi

0

Figure 9.3. Catch per unit effort of native young of the year for sites in each valley (mean + standard error). Valleys with the same letter (A or B) are not significantly different from one another (Tukey’s test) Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

121

Australian smelt

Bony herring

Common carp

Crimsonspotted rainbowfish

Freshwater herring

Goldfish

Striped mullet

1%

0%

1%

0%

Other

70%

Barwon-Darling 21% 1%

7%

Gwydir 30%

26%

25% 11%

8%

0%

0%

0%

Hunter 33% 25% 10% 0%

Lachlan

6%

25%

0%

0%

40% 33% 16% 9% 0%

1%

0%

0%

Macquarie 22%

23%

27% 12%

9% 0%

7% 0%

73%

Murrumbidgee

11%

11% 2%

0%

1%

0%

0%

0%

0%

Freshwater herring

Goldfish

Striped mullet

3%

49%

Namoi

34%

8% 1%

Australian smelt

Bony herring

Common carp

Crimsonspotted rainbowfish

8%

Figure 9.4. Proportions of common fish species in the catch from each valley


122

Other

1.5

Barwon-Darling 1.0

Gwydir 0.5

Hunter

0.0

Lachlan

-0.5

Macquarie

-1.0

Murrumbidgee Namoi

-1.5 -1

-0.5

0

0.5

1

1.5

2

2.5

Figure 9.5. NMS of fish species abundance data at individual sites in the summer of 1999-2000. Stress = 0.16

9.4.

DISCUSSION

Results of the first year of IMEF fish sampling confirmed many of the findings of the Rivers Survey (Harris and Gehrke 1997; Gehrke and Harris 2000), which sampled streams throughout NSW, but with fewer sites in the IMEF study rivers. As in the Rivers Survey, the IMEF data show a clear distinction between the fish faunas of the west-flowing and east-flowing rivers. The east-flowing Hunter River system contains several species that are known or believed to migrate between rivers and estuaries or the ocean to complete their life cycles (Allen 1989; Merrick and Schmida 1984). These species – Australian bass, Cox’s and striped gudgeons, freshwater herring, long-finned eels and striped mullet – are naturally absent from the rivers of the Murray-Darling basin. In the western rivers, both IMEF and Rivers Survey data indicate a north-south difference in fish assemblage composition. IMEF sites on the southern rivers (the Macquarie, Lachlan and Murrumbidgee) had a greater proportion of Australian smelt, a small native species (Figure 9.4), and yielded few specimens of common northern species such as the fly-specked hardyhead and spangled perch. Smelt was the only native species that was abundant in the Murrumbidgee River, although reasonable numbers of bony herring (up to 72 per hour) were caught at some sites. Smelt are a schooling species, favouring open water. They spawn at low temperatures (15–18 °C) and may not require a rise in water level to breed or undergo a spawning migration (Schiller and Harris 2001). It is possible that unlike most native species, they are favoured by the high summer flows of relatively cool water in the Murrumbidgee River. Conversely, species such as spangled perch require warm conditions in summer (Gehrke 1988). Although most specimens recorded in each IMEF river belong to native species, the great majority of native riverine fish were from just four species: bony herring in the inland valleys, striped mullet and freshwater herring in the Hunter Valley and Australian smelt in both eastern and western valleys. None of the popular native angling species of inland rivers – such as golden perch and Murray cod – was recorded in large numbers (Table 9.2). Although freshwater catfish were reasonably common in the Hunter River system, only seven specimens of this formerly abundant species were recorded from all of the IMEF sites on western rivers. A lack of diversity and abundance of native fish was particularly evident in the Lachlan and Macquarie rivers (Figures 9.1 and 9.2).


123

Very few specimens were recorded for fish species or populations listed in the threatened species schedules of the NSW Fisheries Management Act. Only four silver perch (listed as vulnerable) and two trout cod (endangered) were recorded from all IMEF sites sampled in 1999-2000. No Macquarie perch (Macquaria australasica; vulnerable), Murray hardyhead (Craterocephalus fluviatilis; endangered), olive perchlet (Ambassis agassizii; western population endangered), purple-spotted gudgeon (Mogurnda adspersa; western population endangered) or southern pygmy perch (Nannoperca australis; vulnerable) were found, despite being recorded previously from the IMEF study rivers (e.g. Llewellyn 1983). Young of the year made up only a very small proportion of the catch in those study valleys within the Murray-Darling Basin (compare Figures 9.2 and 9.3, noting the difference in y-axis scales). In contrast, numbers of young fish (mostly freshwater herring and striped mullet) were comparatively high in the Hunter River system (Figure 9.3). The apparently poor recruitment of native fish in the western valleys in 1999-2000 could be because environmental allocations did not create conditions greatly conducive to either spawning or post-spawning recruitment, or because recruitment was constrained by other aspects of the flow regime, or by other factors such as migration barriers, cold water or a scarcity of adult fish. Recent research (Humphries et al. 1999, 2002; Humphries and Lake 2000) suggests that most native fish species spawn each year, and that post-spawning conditions, such as the presence of sufficient zooplankton to serve as food for larval fish, may be critical. Repeated surveys at the IMEF fish study sites, under a range of annual flow patterns, should establish the hydrological conditions that lead to successful recruitment.


124

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Appendix: Flow rules for 1999-2000 Barwon-Darling Valley The Barwon-Darling environmental flow rules were not implemented until August 2000 because of delays in establishing five new stream-flow gauging stations. These stations are critical to the operation of the rules. The Unregulated Flow Management Plan for the North-West continued to operate. This plan covers the major regulated rivers in the north-west of NSW as well as the Barwon-Darling River. It seeks to ensure minimum flows for the protection of basic river health as well as protecting high flows for algal suppression and fish migration. New ‘commence-to-pump’ thresholds developed for the Barwon-Darling River for 2000-01 are detailed in Table A1. Gwydir Valley Rule 1:

When tributary inflow downstream of Copeton Dam is less than 500 ML/day, pass flows through to the wetlands.

Rule 2:

Off-allocation extractions are limited to 50% of each flow event and off-allocation will not be declared unless flows exceed immediate water use requirements by at least 1000 ML/day. The volume available to irrigation is calculated from the flow volume above this threshold.

Rule 3:

Each year a volume equal to 25 000 ML multiplied by the percentage allocation available to general security users is to be set aside for use in supporting bird breeding events.

Hunter Valley Rule 1:

Allowance of 20 000 ML on the Hunter, shared between Glennies and Glenbawn dams and 2000 ML on the Paterson in Lostock Dam.

Rule 2:

Access to high flows will be as follows: -

First 12 hours of the flow event be allowed to pass. Water previously ordered can still be diverted.

-

Maintain a minimum river flow in the Hunter River at Singleton of 120 ML/day from 1 May to 30 September and 300 ML/day from 1 October to 30 April. Maintain a minimum river flow at Jerry’s Plains of 100 ML/day from 1 May to 30 September and 150 ML/day from 1 October to 30 April.

Maximum 50% extraction of high flow. End-of-system flow at twice target flow. Rule 3:

Continue the integration of regulated and unregulated river system flow issues and their associated alluvial groundwater areas by developing rules to achieve access security and equity for water users and the environment.

Rule 4:

Conjunctive use of surface water and ground water should continue in 1999-2000, with in-principle support for separation in subsequent years.


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Allocations and access rules will be established for subsequent years, following better definition of the boundary between surface water and ground water, and assessment of economic impacts and the extent of anomalies. Bores within 200 m of the river (i.e., surface water bores) to continue to be assessed as use of surface water and not ground water. Rule 5a:

Rules which introduce variability in delivery of end-of-system flows will be developed following further information on ecological and biological processes and the effectiveness of variability.

Rule 5b:

Licence water use in the tidal zone.

Rule 6:

Water use below Oakhampton Bridge and Gostwyck will be managed in future years, once legislative change is made and a plan is developed which ensures consistent management of the regulated section of the Hunter River. Develop access strategies for users in tidal sections to improve estuarine habitat.

Rule 7:

Continue development of current Salinity Trading Scheme.

Rule 8:

The embargo on the issue of new water licences on the regulated section of the Hunter River continue.

Lachlan Valley Rule 1:

Translucent releases are to be made from Wyangala Dam during the period 1 June to 31 October to attain, in combination with tributary inflows, flows at Lake Brewster of 3500 ML/day to a variable upper window. This is to apply to an upper limit of 350 000 ML per annum, measured at Lake Brewster, including the translucent releases and tributary inflows.

Rule 2:

A 20 000 ML high security Environmental Contingency Allowance (ECA) is established for management of critical (contingent) environmental events, e.g. algal blooms, salinity, bird breeding and fish breeding. The ECA will be eliminated during years when the 1st July allocation announcement is below 50% and is not re-instated until allocation announcements exceed 75%.

Rule 3:

A limit of 30 000 ML per annum on off-allocation diversions.

Rule 4:

Minimum flow of 100 ML/day at Booligal to maintain a visible flow at ‘Geramy’.

Macquarie Valley A Wild Life Allocation (WLA) of up to 125 000 ML is made available each season. It has two components. The first is a 50 000 ML ‘high security’ allocation which is provided every season. The second is a 75 000 ML general security allocation. The general security volume actually provided each year is equal to 75 000 ML multiplied by the percentage allocation announced for general security irrigation licences. Carry over of up to 100% of the WLA and general security irrigator allocations is also permitted with no twelve month limitation. Whenever Burrendong Dam fills and spills, both the WLA carryover account and any irrigator carryover accounts are reduced in proportion to the volume of spill. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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All allocations to be reset at 100% when all carry over water has been spilt. Off-allocation may be declared when flow in the river, in excess of water user orders, is greater than 5000 ML/day at Warren. Off-allocation declarations must not prevent minimum annual stock and domestic flows being met during the year. An annual limit of 50 000 ML also applies to total offallocation diversions. All tributary flows and unused storage releases will be directed to the Marshes for a period of up to 45 days when water is necessary for the satisfactory completion of a waterbird breeding event. Each year, the following creeks will be provided with maximum flow of: -

Marra Creek

15 000 ML

-

Lower Bogan River

15 000 ML

-

Crooked Creek below ‘Mumblebone’

4000 ML

-

Gum Cowal/Terrigal Creek

1000 ML

-

Bogan River between Nyngan and Gunningbar Creek confluence

10 000 ML

-

Beleringar Creek downstream of Albert Priest Canal

1000 ML

-

Reddenville Break

1500 ML

-

Beleringar Creek

5000 ML

Murrumbidgee Valley Rule 1:

Release a minimum of 615 ML/day from Burrinjuck and 560 ML/day from Blowering unless inflows are lower, in which case releases are to be at least equivalent to inflows.

Rule 2:

Flow in the Murrumbidgee at Balranald to be at least 300 ML/day when irrigation water allocations exceed 80% or 200 ML/day when allocations are below 80%.

Rule 3:

Between April and October release a portion of Burrinjuck inflows, which varies with climate and the rate of natural inflow to the storages. •

Wet curve releases – a ceiling level of 50% translucent releases until Burrinjuck reaches an equivalent of 30% storage capacity minus borrow.

•

Normal curve releases – a ceiling level of 50% translucent release until Burrinjuck reaches an equivalent of 50% storage capacity plus carryover minus borrow.

When allocation reaches 80% the clipped translucency volume below the two thresholds identified above is set aside. The allocation cannot increase until the clipped volume is fully paid back and additional storage available to provide an increase. If the clipped translucency volume is set aside before 31 October, 100% of that volume is available for use as additional Environmental Contingency Allowance up to 31 October. Integrated monitoring of environmental flows: State summary report 1998–2000 Department of Infrastructure, Planning and Natural Resources

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If not used by 31 October 50% of that clipped translucency payback is available for use as additional Environmental Contingency Allowance until 31 December (the other half reverts to provisional storage). If the clipped translucency volume is set aside after 31 October but before 31 December, only 50% of that volume is available as additional ECA up until 31 December. If the amount of clipped translucency volume (converted to additional ECA) is not used by 31 December or set aside after this date, it remains in the dam as provisional storage in that year and is available for allocation to irrigators in the following water year. If the allocation in the second year reaches 80%, the clipped volume carrying over from year 1 as provisional storage is again set aside in the provisional storage for allocation to irrigators in the third year. Rule 4:

Reservation of 25 000 ML annually to provide water to meet water quality needs and algal bloom suppression, fish breeding and forest and wetland watering. Water will also be reserved to buffer the impact of environmental releases on irrigators during sequences of dry years and to ensure environmental allocations will be available. This additional volume will be 25 000 ML when allocations are below 80% and will increase from 25 000 to 200 000 ML for allocations between 80% and 100%. The 25 000 ML ECA plus the 25 000 provisional storage (totalling 50 000 ML) is loaned to irrigation for increase in early season announcements. For this year only the 50 000 ML is boosted by 25 000 ML ECA carry over from last year (1998-99) as well as 13 500 ML clipped Gundagai translucency. This amount provides a total potential early season loan to irrigation, for this year only, of 88 500 ML. The ECA/provisional storage borrowed in the early part of the season is to be repaid to the ECA account and provisional storage account when the allocation reaches 60%.

Namoi Valley Rule 1:

A maximum annual off-allocation diversion of water in the Namoi regulated system of 110 GL.

Rule 2:

Retention of the Interim North West Unregulated Flow Plan. This ensures minimum flow for protection of basic river health and protection of high flow for algal suppression and fish migration.

Rule 3:

50:50 sharing of unregulated flows, with off-allocation being declared according to the following thresholds. a) If the available water for irrigation exceeds the valley equivalent of 35% announced allocation, then off-allocation access to be as follows: 1 Aug. to 31 Dec. - starts at 5000 ML/day and stops at 3000 ML/day at Narrabri


138

1 Jan. to 31 Jan. - starts at 4000 ML/day and stops at 2000 ML/day at Narrabri 1 Feb. to 31 Jul. - starts at 2000 ML/day and stops at 1000 ML/day at Narrabri. b) If the available water for irrigation is less than or equal to the valley equivalent of 35% announced allocation, then off-allocation access to be when Narrabri flow exceeds 500 ML/day. c) In the Peel Valley if the flow at Carroll Gap is in excess of, or likely to be in excess of 50 ML/day, the Peel operator may announce access to unregulated flow as offallocation. Access to such flows will be related to the current water ordering sections: 1. Chaffey Dam to Paradise 2. Paradise to Attunga Ck 3. Attunga Ck to Namoi junction. As unregulated flow recedes from an upstream section the off-allocation access will be rescinded. If there is no unregulated flow in a section, then off-allocation will not be declared in that section. Off-allocation access is not available to high security licences.


139


140

Wilcannia to u/s Lake Wetherill

Tilpa to Wilcannia

Louth to Tilpa

Bourke to Louth

Culgoa R. confluence to Bourke

Macquarie R. confluence to Brewarrina Brewarrina to Culgoa R. confluence

Walgett to Macquarie R. confluence

Walgett weir pool

Collarenebri to u/s Walgett weir pool

Mogil Mogil to Collarenebri

Boomi R. confluence to u/s Mogil Mogil weir pool Mogil Mogil weir pool

Mungindi to Boomi R. confluence

Reach

Licence class A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C A B C 190 570

570

Mungindi Presbury Mogil Mogil 230 220 270 1500 220 190 270 230

165 500 1100 165 500 100 430

600 900

900 530 870

Collarenebri Woorawadian Walgett Upstream of Macquarie

530 870

Downstream of Macquarie

460 840

460 840 400 760

Brewarrina Upstream of Culgoa

Table A1. Barwon-Darling en vironmen tal flow rule s for 2000-01 - com me nce-to-p ump thres holds (ML/day)

400 1330

350 1250

350 1250

260 1130

260 1130

123 850

215 123 1010 850

215 1010

Downstream of Bourke Louth Tilpa Wilcannia Culgoa

Appendix: Flow rules for 1999-2000

Appendix: Flow rules for 1999-2000

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