MURRAY-DARLING BASIN COMMISSION
Narran Ecosystem Project The response of a terminal wetland system to variable wetting and drying. Final report to the Murray-Darling Basin Commission Project Leader Professor Martin Thoms Science Team Dr Samantha Capon, Dr Cassandra James, Dr Mark Padgham, Dr Scott Rayburg
September 2007
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Published by the Murray-Darling Basin Commission Postal address: GPO Box 409, Canberra ACT 2601 Office location: 51 Allara Street, Canberra City Australian Capital Territory Telephone: (02) 6279 0100, international + 61 2 6279 0100 Facsimile: (02) 6248 8053, international + 61 2 6248 8053 Email:
[email protected] Internet: http://www.mdbc.gov.au For further information contact the Murray-Darling Basin Commission office on (02) 6279 0100 This report may be cited as: The Narran Ecosystem Project: the response of a terminal wetland system to variable wetting and drying. Final report to the Murray-Darling Basin Commission. MDBC Publication No. 40/08 ISBN 978 1 921257 80 3 © Murray-Darling Basin Commission /e Water CRC 2008 This work is copyright. Graphical and textual information in the work (with the exception of photographs, artwork and the MDBC logo) may be stored, retrieved and reproduced in whole or in part provided the information is not sold or used for commercial benefit and its source (The Narran Ecosystem Project: the response of a terminal wetland system to variable wetting and drying. Final report to the Murray-Darling Basin Commission) is acknowledged. Such reproduction includes fair dealing for the purpose of private study, research, criticism or review as permitted under the Copyright Act 1968. Reproduction for other purposes is prohibited without the permission of the Murray-Darling Basin Commission or the individual photographers and artists with whom copyright applies. To extent permitted by law, the copyright holders (including its employees and consultants) exclude all liability to any person for any consequences, including but not limited to all losses, damages, costs, expenses and any other compensation, arising directly or indirectly from using this report (in part or whole) and any information or material contained in it.
Contents 1. Executive Summary....................................................................................1 2. Preamble....................................................................................................................5 3. Overview of Study Area. .........................................................................7 4. Overview of Project......................................................................................9
6.3 Ecological Responses............................................................. 44
6.3.1 Aquatic ecology............................................................... 44
6.3.2 Vegetation. ............................................................................ 48
6.3.3 Waterbirds............................................................................ 57
6.3.3.1 W aterbird breeding in the Narran Ecosystem................................ 57
5.2 Physical template........................................................................ 12
6.3.3.2 L andscape scale influences on waterbirds in the Narran Ecosystem...................................................... 58
5.2.1 Regional context............................................................ 12
6.4 Conceptual Model........................................................................ 61
5.2.2 Topography.......................................................................... 13
6.4.1 Physiacl factors.............................................................. 63
5.2.3 Soils.............................................................................................. 13
6.4.2 Hydrological factors.................................................. 64
5.2.4 Channel network.......................................................... 13
6.4.3 Ecological factors......................................................... 65
5.2.5 Environmental history............................................ 15
6.4.4 Interactions among physical, hydrological and ecological factors........ 67
5. Key Activities....................................................................................................12 5.1 Overview.................................................................................................. 12
5.3 Hydrological drivers.................................................................. 16
5.3.1 Climate..................................................................................... 16
5.3.2 Hydrology............................................................................... 16
6.5 Knowledge Exchange.............................................................. 68 6.5.1 Community and Industry fact sheets............................................................................ 68
5.4 Ecological responses............................................................... 18
6.5.2 Oral History......................................................................... 68
5.4.1 Aquatic ecology............................................................... 18
6.5.3 Newsletters......................................................................... 69
5.4.2 Vegetation. ............................................................................ 20
6.5.4 Scientific papers............................................................ 69
5.4.3 Waterbirds............................................................................ 23
6.5.5 Community presentations................................. 70
5.5 Knowledge Exchange.............................................................. 23
6.5.6 Industry presentations........................................... 71
6. Key Findings......................................................................................................24
6.5.7 Scientific presentations and conferences......................................................................... 71
6.5.8 Media.......................................................................................... 73
6.1 Physical template........................................................................ 24
6.1.1 Regional context............................................................ 24
6.1.2 Topography.......................................................................... 25
Appendix 1: Groundcover species list.....................................75
6.1.3 Soils.............................................................................................. 26
Appendix 2: Tree species list. .............................................................77
6.1.4 Channel network.......................................................... 27
6.1.5 Environmental history............................................ 27
6.2 Hydrological drivers.................................................................. 30
Appendix 3: Narran Science Application Project.......78 References................................................................................................................ 106
6.2.1 Climate..................................................................................... 30 6.2.2 Hydrology............................................................................... 30 6.2.3 Hydraulic and hydrologic models............. 38
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1. Executive Summary
1. Executive summary Background Large floodplain ecosystems are a feature of Australia’s dryland rivers. They are associated with numerous wetlands, lakes and small creeks that dissect the extensive floodplain surfaces. The Narran Ecosystem, located in northwest New South Wales, is a key refugia for many aquatic and waterdependent terrestrial plants and animals in an otherwise dry landscape. In June 1999, the Narran Lakes Nature Reserve, which occupies the northern section of the Narran Ecosystem was inscribed on the List of Wetlands of International Importance under the Convention on Wetlands of International Importance (Ramsar). It is also an integral part of three international migratory bird agreements: the Chinese Australian Migratory Bird Agreement (CAMBA), the Japanese Australian Migratory Bird Agreement (JAMBA) and the Republic of KoreaAustralia Migatory Bird Agreement (ROKAMBA). The ecological integrity of floodplain ecosystems, like Narran, is maintained by hydrological connections between the floodplain and its associated wetlands, lakes and the adjacent river channel. The Narran Ecosystem is part of the Lower Balonne floodplain region within the Condamine Balonne catchment. It is a region of diverse physical habitats and wetland types, and of high biodiversity. Downstream of St George, the Condamine-Balonne River divides into five main channels; the Culgoa and Narran Rivers are the main channels, conveying 35% and 28% respectively, of the long-term mean annual flow at St George. Unlike the other river systems of this region the Narran River does not flow into the Barwon Darling system but flows into a terminal floodplain–wetland complex – the Narran Ecosystem. Water, sediments and associated nutrients supplied to the Narran Ecosystem originate from the catchments of the Condamine and Maranoa Rivers, which drain the Eastern Australian Highlands. Although these inputs are highly variable over time, they produce a complex mosaic of patches of varying physical and ecological character within the Narran Ecosystem. No detailed environmental studies of the Narran Ecosystem have previously been undertaken. Indeed, studies of the structure and function of large floodplain wetland ecosystems are limited, especially those subjected to naturally high variability in terms of water supply. Answers of how
to manage these types of systems have not been based on sound scientific data and information to date. Questions remain concerning how much water these ecosystem require in order to maintain and conserve their ecological integrity. The Lower Balonne region has been subjected to large water resource developments. Most water resource development in the Condamine-Balonne Catchment has occurred since the advent of irrigated agriculture in the 1960s. There are three main irrigation developments within the Condamine-Balonne catchment; the St George Irrigation Area located on the Lower Balonne Floodplain is the largest. There are also four significant public water storages in the catchment, which service irrigation, agricultural and domestic supply. These being Leslie Dam (106 250 Ml); Chinchilla Weir (9800 Ml); Beardmore Dam (81 800 Ml) and Jack Taylor Weir (10 100 Ml). There are also numerous private off-stream water storages on the Lower Balonne Floodplain that have an estimated combined storage volume in excess of 500 000 Ml (Thoms, 2003). This report provides the results of a four-year interdisciplinary scientific study of the Narran Ecosystem. The overall aim of the study was to investigate the ecosystem response of this floodplain wetland complex to flow variations. This scientific study was funded by the Murray Darling Basin Commission. While focused on the Narran Ecosystem, it was established to also increase our understanding of terminal floodplain-wetlands in the dryland region of Australia and more importantly to allow the prediction of the response of these types of systems to disturbances – both natural and those induced by continued water resource and floodplain development. While this integrated project recognised the importance of the Narran Ecosystem itself, it was also important that this ecosystem be viewed as part of a network of floodplains and wetlands within the Murray-Darling Basin. Therefore, three scales of investigation were employed with ecological questions framed at the local, catchment and broader landscape scale. The fundamental aims of this project concerned linking ecological (both physical and biological) responses of selected components of the Narran Ecosystem to variability in flow regime. Specifically, it aimed to: • Determine the physical and biological responses of the Narran Ecosystem to variations in the flow regime.
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• Predict the responses of selected components of the Narran Ecosystem to alterations in flow regime under different water resource development and long-term climate change scenarios. These predictive models would emphasise the links between flow regime and biota through habitat availability and changes in ecological processes such as primary productivity. • Evaluate the ecological significance of the Narran Ecosystem in the regional context of wetlands within the northern Murray Darling Basin. • Develop a conceptual model that links physical and biological responses of the Narran Ecosystem to past and future changes in water resource development, land-usage and climate. In order to address these specific aims, the project was organised to investigate and report information in four key areas: • Characterising the physical template of the Narran Ecosystem and surrounding regions, • Analysing the principal drivers of change in the Narran Ecosystem and surrounding regions, • Interpreting the change in the template as a result of these drivers in the Narran Ecosystem and the surrounding regions, and, • Investigating the ecosystem responses to any changes in the original template of the Narran Ecosystem and surrounding regions.
Key findings The Narran Ecosystem is comprised of several physical units: • the main Narran River channel • an extensive secondary river channel network • four lakes, the Narran Lake in the south, Clear Lake, Back Lake and Long Arm in the north and • a series of floodplains. The four lakes have a combined surface area of 131.1 km2, with the Narran Lake being the largest (122.9 km2), followed by Clear Lake (5.4 km2), Long Arm (1.5 km2) and Back Lake (1.3 km2). The river channel network contains over 8000 individual channel sections of 44 distinct channel types with a combined length of 804.5 km. As a collective they offer a high degree of physical diversity to the floodplain–wetland complex. As a collective the floodplains of the study area have a surface area of 135.7 km2. These four physical units are intimately linked especially during periods of inundation thus forming the physical template of this ecosystem.
The Narran Ecosystem has been functioning as a wetland ecosystem for at least 46 000 to 70 000 years. It is an old aquatic feature of the Australian landscape. Indeed, water and sediments have been flowing into the Narran floodplain region for even longer. Dating of sediments from cores extracted from various locations in the northern lakes provide an age of 440 000 years. Flows into the Narran Ecosystem were available for the Wilby Wilby gauging station (the nearest upstream station to the Narran Ecosystem) from the 1960s. This allowed an assessment of the actual hydrology of inflows to the Narran Ecosystem. Flows into the Narran Ecosystem occurred in nearly 90% of all years on record. Medium to large floods have also been relatively common historically with more than 66% of all years recording 50 000 Ml or more of discharge at the Wilby Wilby gauge. However, flows at Wilby Wilby show a systematic decline in the occurrence of medium-sized floods since 1992 and an overall decrease in discharge volumes when compared to the earlier part of the record. This has resulted in an increase in the recurrence intervals for all flood magnitudes (floods are more rare irrespective of size) since 1992. The high variability of inflows to the Narran Ecosystem results in a high degree of spatial and temporal variability in terms of the inundation of the floodplains, lakes and channel network in the Narran Ecosystem. However, the lakes have been partially inundated in 27 out of the last 32 years. A coupled hydraulic–hydrologic model was developed for the Narran Ecosystem. This model predicts the spatial patterns of wetting and drying across the Narran Ecosystem and can be used to assess the impact of different hydrological scenarios such as climate, water resource development and land-use change on the timing, magnitude and duration of inundation. This model has an accuracy of nearly 90% when correlated between actual and predicted flow levels. The model predicts that significant inundations of each lake (taken to be 50% full or more) are common with Narran Lake being at least 50% full more than 40% of the time and the Northern Lake being at least 50% full more than 30% of the time under a natural-flow scenario –— one that has no water resource development and influenced by the same climatic regime. A comparison of other scenarios suggests the impact of land use and water resource development far outweighs any potential climate change impacts on the frequency, timing and duration of inundation in the Narran Ecosystem.
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1. Executive Summary
Under current water development levels the longest dry periods (times without significant inundation) increase from about 1–2 years to nearly 20 years. Vegetation in the Narran Ecosystem is spatially and temporally heterogeneous and distinctive in terms of its floristic composition in comparison to that supported by surrounding upland ecosystems. There are large, diverse soil seed banks present throughout the Narran Ecosystem and these comprise more than 70 groundcover species including at least 23 monocot and 54 dicot species. The abundance and diversity of propagules which may germinate are greatest in soil seed banks of intermediately flooded habitats such as the large areas of lignum floodplain. Groundcover vegetation development from soil seed banks depends primarily on recent flooding characteristics. High floristic diversity and productivity occurs in response to intermediate durations of submergence followed by long periods of floodwater drawdown. Exotic groundcover species are present in the vegetation of the Narran Ecosystem and in soil seed banks, especially those of more frequently flooded habitats. Establishment of exotic species from soil seed banks, however, may be limited by long durations of submergence and slow drawdown of floodwaters. The character of lignum (Muehlenbeckia florulenta) shrubland varies throughout the Narran Ecosystem in relation to long-term flood history. Frequently flooded areas are dominated by few but large individual clumps while infrequently flooded areas support many small lignum clumps. Lignum is absent from the most frequently flooded habitats, e.g. the centre of Clear and Narran Lakes. Recent flood history exerts a strong influence on the condition of lignum shrubland. The establishment of lignum seedlings is favoured by waterlogged and damp conditions and is likely to be inhibited by long periods of submergence. Mature-tree communities vary considerably in their composition and structure throughout the Narran Ecosystem and are dominated by four species; Eucalyptus camaldulensis, E. coolabah, Acacia stenophylla and Eremophila bignoniiflora. Little recent recruitment was observed for these species within the surveyed tree communities.
High mortality (38–54% dead) is evident amongst all commonly occurring tree species with seedlings and saplings of Eucalyptus camaldulensis, E. coolabah and mature Acacia stenophylla exhibiting particularly high levels of mortality and stress. During a flow event in 2004 a relatively small area of the Narran Ecosystem was inundated. During this event 31 955 fish were collected from eight families including 11 species. This included eight native species and three exotic species. This suggests there is rapid colonisation of the Narran Ecosystem upon receiving a filling event. Analysis of the fish population during this inundation event also notes that spawning did occur in the lakes. Thus the duration of the event is important. A diverse and abundant zooplankton fauna was observed in the 2004 flood event. Micro-invertebrate assemblages varied over time as the system dried out as well as between habitat types. A high number of taxa (24) were recorded solely in floodplain habitats. The Narran Ecosystem is a significant refugia for birds. At least 65 species of waterbirds have been recorded in the complex of which five are listed as threatened within NSW, with an additional nine being noted of conservation concern in western New South Wales, these being the Australian Pelican, Little Egret, Glossy Ibis, Pacific Heron, Intermediate Egret, Straw-necked Ibis, Pied Cormorant, Great Cormorant and Royal Spoonbill. In addition, over 1.1 million waterbirds were recorded at Narran in 1984. By comparison, data from the Eastern Australian Water Bird Survey (1983 to the present) recorded in excess of seven million waterbirds associated with the various wetlands in the survey area. Thus, the Narran Ecosystem is important at the landscape scale for water birds. There is a high degree of association between water in Narran and waterbird breeding at this site. 17 waterbird breeding events have occurred in 34 years in the Narran Ecosystem. For successful waterbird breeding both the lakes and the floodplain must be inundated. Floodplain inundation is essential as this functions as a feeding area whilst water in the lakes is required to initiate breeding. Both functions (feeding and breeding) must be satisfied for successful breeding in the Narran Ecosystem. At the landscape scale waterbirds have declined in abundance along eastern Australia by around 85% since 1983, but numbers vary enormously from year to year. Climatic variation is the major determinant of inter-annual variations in waterbird abundance
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across eastern Australia. The climatic systems of greatest influence are coherent rainfall systems that traverse distances of 700–1000 km over periods of 13–21 days. Bird numbers, and the structure of these coherent rainfall systems, are very significantly related to the Madden–Julian Oscillation (a global, equatorial climatic cycle). Climatic influences explain 70% of the inter-annual variation in avian abundance, but only 12% of the overall decline. The remaining portion of this decline in waterbird numbers is very strongly related to declines in flow volumes within the MDB. Declines have been far more pronounced within the Murray-Darling Basin than surrounding regions. Flow volumes within the MDB are also related to the same climatic systems, but their declines are similarly independent of climate. Declines in flow volumes that have occurred independent of climatic influences have the largest influence on avian declines.
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2. Preamble Floodplain ecosystems Large floodplain ecosystems are a characteristic feature of Australian inland river systems (Pickup, 1986; Thoms, 1995). Many are associated with extensive wetlands and terminal lakes. The ecological integrity of these floodplains, wetlands and terminal lake ecosystems is maintained by hydrological connections between them and the adjacent river channels. The abundance of floodplain wetlands in Australia is not well known, but Blackley et al. (1996) lists 900 in a directory of important Australian wetlands. Of these, 263 are associated with the rivers of Australia’s inland river systems. In another inventory, Kingsford et al. (1999) identified over 28 000 floodplain wetlands across the Murray-Darling Basin, covering about six million hectares. However, a glance at any water resource or topographical map of Australia would suggest these numbers to be an underestimate. Floodplains are a vital part of any riverine ecosystem because their biota rely on floodplains for refuge, breeding and replenishment of food resources. Floodplain wetlands are areas of high biodiversity (Williams, 1988; Kingsford and Porter, 1999) and have been referred to as ‘oases’ in an otherwise dry landscape (Morton et al., 1995). At many different scales, floodplain wetlands are key refugia for both terrestrial and aquatic biota in Australia’s dry interior. They have a crucial role as feeding, breeding and resting sites for migratory birds as well as for fish and other animals. The role as biodiversity hotspots is maintained despite their highly variable and unpredictable hydrology and thus wetting and drying regimes. They have been referred to as ‘boom–bust’ systems, with high productivity occurring in periods inundation (booms) and very little in periods of dry. Indeed, floodplain ecosystems are dynamic mosaics where water plays an important role in connecting the various patches that occur within them (Thoms, 2003). Flooding facilitates exchanges of water, sediments, nutrients and biota between river channels and floodplain patches and these transfers are considered to be essential for the functioning and integrity of these systems (Amoros and Bornette, 2002).
The Narran Ecosystem The Lower Balonne floodplain wetland complex which straddles the Queensland–New South Wales border between St George (Qld) and Walgett (NSW) is a region that supports the largest number of
wetlands greater than 5 ha in size within the Murray Darling Basin (Blackley et al., 1996). In excess of 3400 wetlands have been identified, the majority of which are freshwater wetlands associated with floodplain areas (53%). This floodplain ecosystem is sustained by water, sediments and nutrients from the upstream Condamine-Balonne catchment – which comprises 14% of the Murray Darling Basin. Hydrological variability is a feature of this system and is influenced by climatic conditions such as El Nino– Southern Oscillation (ENSO) events, because flows in the Condamine-Balonne correlate significantly with the Southern Oscillation Index (SOI). The long-term hydrograph of the Condamine-Balonne is highly variable, with a large proportion of average flows occurring in very wet years. Indeed, the coefficient of variation (CV) for flows in the Condamine-Balonne ranges from 1.35 to 2.78, which is comparable to other dryland systems worldwide. The Narran Ecosystem is a significant floodplain wetland in the Lower Balonne region. It has been identified as one of nine significant refugia for biological diversity in semi-arid and arid New South Wales (Kingsford, 1999). Its significance was recognised in 1999 when a section of the northern lakes was listed as a Ramsar Wetland of International Importance in June 1999, 11 years after being gazetted as a Nature Reserve by the NSW National Parks and Wildlife Service. The Narran Lakes Nature Reserve is also listed on the Register of National Estate as a natural heritage site. This listing of the Narran Lakes Nature Reserve as a Ramsar site was in recognition of it being an excellent example of a relatively undisturbed terminal lake system for NSW. It is a significant site for waterbirds, both nationally and internationally; and because it provides habitat for some species that are recognised as being of conservation concern, either regionally, at the State level or nationally. Together these attributes reflect the underlying ‘ecological character’ (incorporating the physical, chemical and biological attributes of an ecosystem and including the ideals of health and integrity) of the site, which the Ramsar Convention obliges Australia to protect. Similarly, national legislation (Environment Protection and Biodiversity Conservation Act, 1999) is committed to protection of such sites from threats. In addition, the site offers important habitat for several species listed under Australia’s bilateral agreements with the Governments of China (CAMBA), Japan (JAMBA) and Republic of Korea (ROKAMBA) for the conservation of migratory birds.
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Threats to the Narran Ecosystem Whilst recognised as being environmentally and economically valuable, wetlands are also a threatened resource due to past and current land and water management practices. The character of many Australian inland river systems has been altered since European settlement (Thoms et al., 1999, 2000; Ogden, 2000) because of large-scale floodplain development and the loss of connectivity due to flow regulation and the construction of levees. The grazing industry has had a long association with floodplain wetland systems (Heathcote, 1988). However, since the 1980s these systems have become the focus for major water resource developments. These activities have the potential to severely degrade these ecosystems. The ‘flow regime’ of the Narran Ecosystem is important and central to maintaining its ‘ecological character’ (Thoms et al., 2001) i.e. the combination of physical, chemical and biological components of the system. Floods in the Narran River in particular are important for the filling of the Narran Ecosystem and the success of waterbird breeding colonies is highly dependent on water levels. Water resource development on the nearby Macquarie River system has decreased the frequency and abundance of breeding of colonial waterbirds in the Macquarie Marshes (Kingsford and Johnson, 1998). Further, waterbird breeding in terms of reproductive success and clutch size appears to be directly related to flooding. The wetlands of the Narran Ecosystem need to reach at least 86% capacity in order to trigger breeding (Qld DNRM, 2000). Since the late 1980s, flows in the Condamine Balonne River upstream of the Narran Ecosystem have been modified by large-scale water resource development. Median annual flows at St George have been reduced by 30% and there have been major reductions in the magnitude and frequency of important flood events. Furthermore, recent studies on the Lower Balonne floodplain demonstrate that rates of sediment delivery to this area have increased by an order of magnitude as a result of upstream land use changes since European settlement (Thoms et al., 2007). Combined, these developments have the potential to significantly influence the ecological character of the Narran Ecosystem.
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3. Overview of study area The Narran Ecosystem is a terminal floodplain complex of the Narran River; a major distributary channel located in the lowland section of the Condamine Balonne Catchment (Fig. 3.1). Like many Australian inland rivers the Condamine-Balonne is an allogenic river originating in a well-watered area but flowing for most of its length across a dry landscape (Thoms and Sheldon, 2000). According to the Köppen Climate Classification scheme the lower sections of the catchment and the Narran region in particular, are classified as hot with minimal rainfall. Maximum summer temperatures often exceed 50°C while winter minimums are around 20°C. The longterm median annual rainfall (n = 73 years) decreases from east (1105 mm at Toowoomba) to west (517 mm at St George) across the Condamine Balonne catchment. Most rainfall occurs in the summer months (November–April) and is associated with tropical monsoonal activity. Overall, rainfall is highly variable both within and between years but there is a pronounced wet/dry periodicity, a common feature of dryland regions in Australia (Gentilli, 1986). Mean annual evaporation ranges from 230 mm in the headwaters to over 2000 mm in the lower catchment. Thus large portions of the lower floodplain region of the Condamine Balonne catchment have a large negative water balance. Flows in the CondmaineBalonne are also highly variable, with annual flows
at St George, in the lower catchment, ranging between 23 960 Ml and 7 385 000 Ml (1975–2000) with an annual median of 728 175 Ml. Flood events generally occur between November and April; hence the annual flow pattern is summer-dominated. Downstream of St George, the Condamine-Balonne River divides into five separate channels (Fig. 3.1). The Culgoa and Narran Rivers are the main channels, conveying 35% and 28% respectively, of the long-term mean annual flow at StGeorge. The Ballandool River, Bokhara River and Briarie Creek only flow during higher discharge periods. All five rivers have low channel gradients (0.0002 to 0.0003), are tortuous in planform (sinuosities exceed 2.2, cf. Schumm, 1977) and transport predominantly fine sediments. Bankfull cross-sectional areas of most of the channels (the Briarie is the exception) decrease with distance downstream, so there are regular overbank flows. The hydrology of the five main channels in the Lower Balonne differs substantially. A large proportion of average flows occur in very wet years. Variability in flow is also high: coefficients of variation (CVs) for annual flows range from 1.03 to 2.00, and median annual flows are less than 30% of mean annual flow. Flows (both annual volumes and flood peaks) generally decrease downstream towards the end
Figure 3.1: Location of Narran Lakes within the Murray-Darling Basin.
Narran River
Long Arm Back Lake
Condamine-Balonne Catchment
Clear Lake Narran Lakes
Narran Lake
Floodplain
Murray-Darling Basin
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of the system because of transmission losses and a lack of tributary contributions, which are a characteristic feature of Australian inland river systems (Thoms and Sheldon, 2000). There have been changes in the hydrological regime of the Lower Balonne over the last 100 years, with the period prior to the 1900s and since the mid-1940s being wetter, on average. This has been associated with greater runoff and flood activity than for the period 1900 to 1945 (Riley, 1988). These changes reflect the shift in the geographical pattern of correlation between precipitation and the SOI for the years before the 1950s compared with the years since the 1950s (Simpson et al., 1993). The local catchment area of the Narran Ecosystem is relatively small (~ 46 km2). Consequently, the lakes do not fill as a result of local precipitation. Rather, floods in the Narran River, which are generated in the upper catchment areas of the Condamine and Maranoa (Fig. 3.1), are responsible for lake-filling events. No flows occur approximately 60% of the time in the Narran River immediately upstream of the Narran Ecosystem. Mean annual flow in the Narran River is about 141 000 Ml with a standard deviation of greater than 150 000 Ml and a maximum recorded annual flow of 567 100 Ml. The high inter-annual variability of flows in the Narran River insures that the Narran Ecosystem has a complex flood history with periodic wet/dry cycles (Thoms, 2003). The Narran Ecosystem is comprised of four distinct morphological features; a complex network of river channels, floodplain lakes, ephemeral wetlands and an extensive floodplain surface. There are four main lakes or water bodies; Clear Lake, Back Lake and Long Arm (the northern Lakes) and Narran Lake, and a large floodplain area (Fig. 3.1). These have been the focus of previous work in the region and for current management. Filling of the various waterbodies occurs sequentially with Clear Lake filling first, then Back Lake, Long Arm, and if the event is sufficiently large, Narran Lake. Over the last 33 years Clear Lake and Narran Lake have filled with water from the Narran River 23 and 16 times respectively, while the intervening floodplains have only been inundated on six occasions. A significant portion (5531 ha) of the northern section of the Narran Ecosystem was designated as a Ramsar site in June 1999. This lake–wetland system is characterised by large areas of the floodtolerant shrub Muehlenbeckia florulenta (tangled lignum) that provides an important breeding habitat for waterbirds, most notably Threskiornis spinicollis (Straw-necked ibis).
Land use in the surrounding region is predominantly sheep grazing and mineral exploration. Further upstream, in the Lower Balonne, land use is increasingly dominated by intensive irrigation which has been associated with substantial water resource developments in recent years, influencing the catchment’s hydrology on a number of scales (Thoms, 2003). Consequently, altered hydrology is currently perceived as a major threat to the ecological integrity of the Narran Lakes Ramsar site (Thoms and Parsons, 2003).
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4. Overview of project The Narran Lakes Ecosystem Project Floodplain ecosystems, like the Narran Ecosystem, are important ecotones that regulate interactions across a broader riverine landscape. They respond to disturbance (both natural and human induced) over a range of scales – from organism-level responses, through population and community changes and finally ecosystem-level changes. The nature of these changes depends on the organism or group of organisms or ecosystem component in question. Additionally, there will be a lag time before an ecosystem response can be detected in floodplain water bodies and the extent of this lag time will again depend on the component in question. For many of the more familiar organisms (large fish, riparian trees), there would be a considerable lag time, with the effects of changing water regimes possibly taking decades to be detected. Studies of similar systems (e.g. Kingsford, 2000) have tended to ignore their multi-scaled functioning and the requirement for an interdisciplinary and integrated approach to study these ecosystems. The Narran Ecosystem Project was established to investigate the responses of this key ecosystem to variations in the flow regime. Based upon a series of initial conceptual models of the key ecological functioning of the Narran Ecosystem, it takes an interdisciplinary approach to the study of this floodplain ecosystem (for further methodologies see appendix 2). This integrated project recognises the importance of the Narran floodplain, lakes and the river network, which make up the Narran Lakes ecosystem. It also notes the importance of viewing the Narran Lakes ecosystem as part of a mosaic of floodplain ecosystems within the Murray-Darling Basin and beyond. Therefore, three scales of investigation are used.
Local scale. The ecological character of the Narran Ecosystem itself and its role as providing significant refugia for a range of organisms is largely determined by the flow regime in the Narran River. This river is being subjected to changing hydrological regimes because of upstream developments. However, the ecological effects of changed flow regimes can only be investigated, at least in the short term, by understanding the links between hydrology and habitat availability for key biota. These flow-habitat connections are being recognised as an increasingly important component in the sustainability of the ecological character of our
inland river systems (Thoms and Sheldon, 2000). However, there are limited data on the role of flow in maintaining habitat connections for many of Australia’s inland river systems, like the Narran. At the local scale the project was to determine • the habitat requirements of key biotic components of the ecosystem (plants, fish, waterbirds), • the distribution of habitats for the key biota under different flow states, and • the importance of bottom-up control of ecosystem processes, especially productivity.
Catchment scale. The Narran Ecosystem is an ephemeral, terminal system in the lower reaches of the Condamine Balonne River, in the northwest section of the Barwon Darling system. The ecology of this ecosystem is influenced by the supply of water, sediments, nutrients and carbon from upstream and through the exchanges between the river and adjacent riverine landscape as well as colonisation of organisms. These ecological components will also depend upon the stage of wetting and drying in the system. However, changes in flows in the Narran River and across the floodplain will have consequences for the ecology of the lakes. Impacts that may arise as a result of catchment modifications may include the reduction in the abundance of zooplankton colonising the lakes after drying events because of decreases in floodplain interactions. Fish communities in the river and hence fish communities colonising the lakes after drying events may also change as a result of increases in base flows. There are no data to investigate, or begin to model, the response of the Narran Ecosystem to changing water resource development or land use modifications. This project aimed, through the development of a hydrological model, to predict habitat availability under different flow scenarios for the Narran Ecosystem. It also aims to determine the significance of patterns of wetting and drying of the lakes and how these patterns are modified by changing flow regimes in the Narran River. Therefore data from this project has enabled the development of a model that can be used to predict the influence of water resource development and changing catchment conditions on the ecology of the Narran Ecosystem.
Landscape scale. Wetland systems, of varying degrees of water permanency, are a feature of inland Australia (Williams, 1998). Hence, the Narran
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Ecosystem must be put into this larger landscape context. It has been suggested (e.g. Kingsford et al., 1999; Thoms et al., 2001) that the Narran Ecosystem has a unique collection of habitats that are important for migratory birds in that they provide a key refugium when other wetlands are not providing appropriate habitat. However, this has not been quantitatively assessed. Data collected from the Eastern Australian Water Bird Survey has enabled the construction of a landscape model of the use of wetlands in the region and therefore assess the importance of the Narran Ecosystem for both local and migratory birds.
Research aims This project is built on a conceptual framework that was formulated from a detailed review of the relevant scientific literature on the structure and functioning of floodplain ecosystems in dryland regions. This review was supplemented with a review of information, mostly management orientated, on the Narran Ecosystem. The initial conceptual framework was that flood pulses and dry phases are particularly important for the ecology of the Narran River system and its associated floodplains, wetlands and lakes. Therefore, the fundamental aims of this project focus on the linkage of ecosystem (both physical and biological) responses of selected components of the Narran Ecosystem to variations in flow. Specifically, the project aimed to: • Determine the physical and biological responses of the Narran Ecosystem to variations in the flow regime. • Predict the responses of selected components of the Narran Ecosystem to alterations in flow regime under different water resource development and long-term climate change scenarios. These predictive models would emphasise the links between flow regime and biota through habitat availability and changes in ecological processes such as primary productivity. • Evaluate the ecological significance of the Narran Ecosystem in the regional context of wetlands within the northern Murray Darling Basin. • Develop a conceptual model that links physical and biological responses of the Narran Ecosystem to past and future changes in water resource development, land-usage and climate.
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The approach taken The focus of Narran Ecosystem Project was interdisciplinary in nature, in that it required the collaboration of different scientific disciplines. For this study, the disciplines of ecology, geomorphology and hydrology were brought together to address the research aims of the project. Previous works in the lower Balonne floodplain and that on the Narran Lakes all acknowledge the complexity of the physical environmental and its ecology. The ecosystem structure and behaviour of the Narran Ecosystem reflect many internal and external influences – geomorphological, hydrological and ecological – that interact closely. While the importance of this interaction has been recognised, issues of how to study complex and variable ecosystems, like Narran, are not prescribed in any text book or manual. In addition, there are few large interdisciplinary studies of such ecosystems. Successful interdisciplinary studies require that the separate disciplines gain a common understanding of the nature of the problem at hand, and identify the scales of relevant subsystem components, the underlying processes or phenomena, and the important variables involved. Conceptual frameworks are useful tools for ordering phenomena and material, thereby revealing patterns and processes. Recent interdisciplinary ecosystems studies (Dollar et al., 2007; Hughes et al., 2007; Parsons and Thoms, 2007) all recommend the establishment of a conceptual framework upon which to base research activities. A conceptual framework can help different disciplines work together in an integrated way by ordering phenomena and materials, thereby revealing patterns (Rapport, 1985). The basis for the Narran science framework recognises the key aspects of the driver, template, altered state and the ecosystem response (Fig. 4.1). Drivers create, maintain or transform structural and functional features of an ecosystem. Drivers include biotic activities and abiotic disturbances such as floods. The template is the entity the driver(s) act(s) upon. Templates are bounded spatially by the research question and they can be both abiotic and biotic. The physical surface of a floodplain or lake bed is an abiotic template while vegetation is an example of a biotic template. The interaction between a driver and the template produces an altered state or template. The inundation of a floodplain surface (template) by floodwaters (a driver) produces a wetted floodplain landscape which represents an altered template or state.
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The ecosystem responds to the formation of this altered state. Frameworks, like the Narran Ecosystem Project framework, have been used to demonstrate, among other things, modes of change in heterogeneity (Pickett et al., 2003), but such models are not generally spatially explicit. For our framework we use a multi-level framework to allow integration between processes operating at different scales (Fig. 4.1). This structure accommodates feedback responses, allowing biotic consequences to contribute to the altered state. It also allows for consideration of downward constraint by higher levels and upward integration of processes from lower levels – an important factor in hierarchically
organised systems like floodplain ecosystems. The relative importance of downward constraint and upward integration is different at each level of organisation. The higher levels are controlled predominantly by downward influence, while features at lower levels are more manifestations of upward influence. At all levels, the altered state depends on the context provided from above and the integration of processes from below – the same basic drivers could produce different forms within different constraining contexts. Interpreting the relationship between downward constraint and upward integration of explanation is critical in interpreting complex ecosystems like floodplain wetlands.
Figure 4.1: The conceptual framework for the study of the Narran Ecosystem.
Scale one
Ecosystem response
Driver
Abiotic Altered template
Template Biotic
Ecosystem response
Driver Scale two Abiotic Template Biotic
Altered template
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5. Key activities 5.1 Overview
5.2 Physical template
The Narran Ecosystem Project comprised four major arenas of research activity:
5.2.1 Regional context
1. Physical template 2. Hydrological drivers
PT1 Activity description:
3. Ecological responses
• Mapping of key wetlands along the Narran River using satellite imagery and radiometric data.
4. Knowledge exchange.
Aims:
This chapter outlines the key activities conducted in each of these components including research aims, and methods produced as a result. A summary of the key activities is provided in Table 5.1 and Fig. 5.1.
• To determine the local extent of the Narran Ecosystem using radiometric characteristics. • To compare the Narran Ecosystem with known wetlands in the region in terms of wetland area, volume and radiometric characteristics.
Table 5.1: Summary of key activities Activity code
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Activity description
Activity code
Activity description
1. Physical template
3. Ecological responses (continued)
PT1
Mapping of key wetlands along the Narran River using satellite imagery and radiometric data
ER3
Zooplankton egg bank mesocosm experiment
PT2
Collection and analysis of LiDAR data
ER4
Aquatic macroinvertebrate field sampling
PT3
Soil mapping of the Narran lakes Ecosystem
ER5
Fish sampling
PT4
Digitisation and change analysis of the Narran Lakes Ecosystem channel network
ER6
Vegetation survey
PT5
Sediment coring of the Narran Lakes Ecosystem
ER7
Lignum survey
2. Hydrological drivers
ER8
Lignum establishment experiment
HD1
Collection and analysis of climate data For the Narran Lakes Ecosystem and region
ER9
Tree patch survey
HD2
Collection and analysis of surface water flow data for the Narran River
ER10
Soil seed bank mesocosm 1 experiment
HD3
Mapping of wetted extents for historical floods in the Narran Lakes Ecosystem from Landsat imagery
ER11
Soil seed bank mesocosm 2 experiment
HD4
Patch analysis of wet and dry patches In the Narran Lakes Ecosystem
ER12
Waterbird breeding in the Narran Lakes Ecosystem.
HD5
Hydraulic and hydrologic modelling of the Narran Lajes Ecosystem
ER13
Landscape scale influences on waterbirds in the Narran Lakes
3. Ecological responses
4. Knowledge exchange
ER1
Water quality sampling
KE1
Publications
ER2
Zooplankton field sampling
KE2
Presentations
KE3
Field days
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5. Key Activities
Figure 5.1: Location of research activities within the Narran Ecosystem.
Mesocosm 1 Infiltration Soil cores Surface soils Aquatic sampling Productivity Shrub facilitation Tagged lignum Tree survey Vegetation survey Elevation (m) High: 124 Low: 118
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Methods: • Large format Landsat images for 1990 and 2000 were acquired and used to delimit all of the 12 known wetlands along the Narran River. • Surface areas and estimated volumes were computed for each of these 12 wetlands.
• To map soil characteristics across the Narran Ecosystem.
Methods: • 163 surface soil samples were collected throughout Narran Ecosystem including: – 130 samples from a regular 1800 m square grid.
• An independent verification of wetland extent was determined using three radioactive elements: thorium, uranium and potassium.
– an additional 33 soil samples from vegetation survey sites.
• Potassium concentrations highlight lake and floodplain regions and high potassium concentrations show areas that are filled by Narran River flows.
– Each soil sample comprised five sub-samples collected from the corners and centre of a 10 m quadrat. – 22 soil properties were measured (see below).
5.2.2 Topography PT2 Activity description: • Collection and analysis of LiDAR data.
Aims: • To obtain an accurate digital elevation model of the Narran Ecosystem. • To describe the topography of the Narran Ecosystem. • To determine heights of dominant structural vegetation across the Narran Ecosystem.
Methods: • LiDAR was flown in October 2004.
grain size distribution soil colour organic matter content aluminium barium calcium cobalt copper iron lead magnesium
pH liquid limit plastic limit manganese nitrogen phosphorous sodium potassium strontium titanium zinc
– Interpolation of soil properties was conducted using geostatistical approaches in order to map the soil characteristics for the entire Narran Ecosystem.
• LiDAR data was calibrated using more than 20 000 ground control points with positional and vertical accuracies of less than 1 cm.
5.2.4 Channel network
• Areas of the Narran Ecosystem that were wet during the LiDAR survey (i.e. several deep waterholes) were surveyed using differential GPS with positional and vertical accuracies of less than 1 cm.
Activity description:
• Hypsometric curves were produced from the LiDAR data to determine the surface area and volume of each of the principal lakes within the Narran Ecosystem. Surface areas and volumes were computed at 10 cm elevation intervals.
• To describe the distribution and character of the Narran Ecosystem channel network.
5.2.3 Soils PT3 Activity description: • Soil mapping of the Narran Ecosystem.
Aims: • To determine the physical and chemical properties of soils within the Narran Ecosystem.
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PT4 • Digitisation and change analysis of the Narran Ecosystem channel network.
Aims:
• To determine the stability of the channel network through time.
Methods: • The channel network for the Narran Ecosystem was digitised from three sets of 1 : 50 000 scale aerial photographs: 2003, 1992 and 1969. • The area covered by river channels during each time was determined: 1969, 1992 and 2003. • Changes in the channel network through time were assessed by comparing the extent of the channel network at each time.
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• The character of the river channel network at each time was determined by classifying the links and nodes comprising the network. This was accomplished through the development of a new technique specifically designed to characterise anastomosing river channel networks (Fig. 5.2).
5.2.5 Environmental history PT5 Activity description: • Sediment coring of the Narran Ecosystem.
Aims: • To investigate the long-term environmental history of the Narran Ecosystem. • To determine how long the Narran Ecosystem has existed in the landscape.
Methods: This section of the project is based upon the premise that sediments in a depositional sequence are indicative of the environment in which they were laid down. Floodplain–wetland complexes, like Narran, that are located at the termini of river systems are three-dimensional sinks into which eroded and sorted sediments accumulate. Unlike other river floodplains, they are not temporary storage areas of alluvium because they do not experience significant episodic working and/or removal of sediment during extreme events, or when certain threshold Figure 5.2: A method for the classification of channels in distributary networks. Each two letter code represents a link identifier with the from node first and the to node second. For example, FJ = From fork to Join.
conditions are exceeded. The character of these alluvial stores is dependent upon the nature of the depositing environment, the type of sediments and processes that govern their delivery to a site. • 31 sediment cores up to a depth of 25 m were extracted using a piston-driven coring rig from the Narran Ecosystem. • The stratigraphy of each core was described using modified lithofacies classifications of Lewin (1996) and Miall (1985). Sediments were classified as mud, muddy sand (> 50% mud), sandy mud ( 30 cm). • Three replicate samples from each habitat were taken at each site on each sampling occasion. Back Lake and Long Arm sites could not be sampled in July 2004 as they dried out earlier. A total of 171 samples were collected. • Macroinvertebrates were collected by sweeping a standard triangular 250 µm mesh dip net along a 1 m transect for 30 seconds. • Samples were sieved, transferred to storage jars, preserved in 70% ethanol and transported to the laboratory where macroinvertebrates were sorted, enumerated and identified to family level.
ER5 Activity description: • Fish sampling.
Aims: • To describe the species composition, abundance and size structure of fish assemblages in the Narran Ecosystem. • To examine spatial and temporal patterns in assemblage composition and structure during a wetting and drying event in the Narran Ecosystem.
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entrance of off-take channel, Clear Lake at the midden, Back Lake and Long Arm). • Sampling occurred up to four times February 2004, April 2004, July 2004, and November 2004 depending on the presence of water at sites. • Fish were sampled using large fyke nets and large and small seine nets. Three fyke nets were set at each site. Three replicate hauls of the small and large seine net were also made at each site.
5.4.2 Vegetation ER6 Activity description: • Vegetation survey.
Aims: • To describe spatial and temporal patterns in vegetation composition and structure in the Narran Ecosystem. • To determine environmental factors influencing spatial and temporal patterns in vegetation composition and structure in the Narran Ecosystem.
Methods: • A total of 33 sites were surveyed comprising: – 15 sites in each of two regions (northern basin, southern basin) – in each region, three replicate sites in each of five flood frequency classes (frequent, moderate, infrequent, rare and terrestrial) – additional three sites located in bird colony, Back Lake. • Sites selected based on flood frequency classes determined using prior inundation mapping as this represented the best available information prior to the more detailed analyses conducted as part of the current project. • Sites were surveyed in November 2004 following the recession of floodwaters and again in May 2005 following 6 months of drying. • During surveys, the following variables were recorded within each site (50 m × 50 m quadrat): – tree counts
Methods:
– % cover of lignum
• Sampling was conducted at six sites selected to cover the main aquatic patches at the ecosystem scale. These included two river sites (Narran River at the weir and Narran River at the offtake channel) and four lake sites (Clear Lake at
– % cover of groundcover species (within 10 random 1 m2 quadrats) – soil samples collected for analysis.
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ER7 Activity description: • Lignum survey.
Aims: • To describe spatial patterns in the character and condition of lignum shrubland within the Narran Ecosystem. • To determine environmental factors influencing the character and condition of lignum shrubland.
• 25 buckets (five per watering treatment) were randomised in a glasshouse. Eight pots (four clay and four sand/clay mix) each containing a single lignum seedling were placed in each bucket. • On each of four harvest times (1, 2, 4 and 6 months), one seedling growing in each sediment type in each bucket was destructively harvested (total = 50 harvested per time interval) and the following variables recorded: – total biomass and biomass of roots, shoots and leaves separately
Methods:
– length of shoot and root
• A total of 75 5 m × 5 m quadrats were surveyed with five quadrats in each of 15 sites haphazardly distributed throughout study area in places where lignum cover was greater than 10% .
– leaf area
• The survey was conducted in May 2006. Within each 5 m × 5 m quadrat, the following variables were measured: – % cover of lignum
– leaf and shoot number. • Analysis conducted as a split plot design using a partially nested ANOVA model with treatment, sediment type and time as fixed variables and bucket as random. Where sediment effects were weak, sediment types were pooled.
– number of lignum clumps (density)
ER9
– morphology (clump height, clump perimeter)
Activity description:
– reproductive status (flowering, sex)
• Tree patch survey.
– condition (presence of leaves, % greenness, evidence of grazing)
Aims:
– soil moisture and soil samples collected for analysis.
ER8 Activity description: • Lignum establishment experiment.
Aims: • To investigate growth responses of lignum seedlings to flooding, waterlogging and water stress. • To determine effects of sediment type (i.e. clay and sand) on growth of lignum seedlings.
Methods: • A glasshouse experiment was conducted in the first 6 months of 2005 in which lignum seedlings were grown under one of five water treatments: – Deeply submerged (DF) – Shallowly submerged (SF) – Waterlogged soil (WL) – Damp soil (DP) – Dry soil (DRY) • Two sediment types (100% clay and a 50 : 50 mix of clay and river sand) were crossed with water treatment in a factorial design. Clay sediment was collected from the Narran Ecosystem.
• To describe spatial patterns in the distribution, character and condition of mature tree communities in the Narran Ecosystem. • To determine environmental factors influencing the character and condition of mature tree communities in the Narran Ecosystem.
Methods: • A total of 15 mature-tree patches were identified within the study area based on vegetation height, density and area criteria (determined using LiDAR and Landsat imagery). Tree patches were identified by selecting those which had a > 50% tree coverage and which were greater than 50 000 m2. • Within each patch, four randomly located replicate 25 m × 25 m sites were surveyed between November 2005 and May 2006. • The following variables were measured with respect to every tree within each 25 m x 25 m quadrat: – species – position – morphology (height, dbh) – developmental stage – reproductive status (i.e. presence of fruit) – condition (index from 0–5 where 0 represents dead trees and 5 represents healthy trees)
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• Environmental variables recorded for each site: – elevation (from LiDAR)
Activity description:
– soil characteristics (soil sample collected)
• Soil seed bank Mesocosm 2 experiment.
– soil moisture
Aims:
– canopy cover – litter cover.
ER10 Activity description: • Soil seed bank Mesocosm 1 experiment.
Aims: • To determine the composition and structure of soil seed banks in the Narran Ecosystem. • To describe spatial patterns in the distribution of the soil seed bank in relation to broad hydrogeomorphic habitats.
Methods: • Soil sampling was conducted within seven predefined hydrogeomorphic habitats: Clear Lake centre (CLC), Clear Lake shore (CLS), Back Lake (BL), Lignum floodplain (LFP), Chenopod floodplain (CFP), the Narran River channel (NRI) and the Narran River bank (NRB). • Three sites were selected randomly within each habitat and within each site three replicate soil samples were taken producing a total of 63 samples. • A seedling emergence experiment was conducted at Goondiwindi in which sediment samples were subjected to two treatments: waterlogging and submergence. The experiment was run for 5 months from March to September 2004 to encompass a broad range of temperatures. • Species were counted and identified as they germinated and removed prior to further contributions to the soil seed bank. Species identifications were verified with the NSW Herbarium • At the final harvest, species that were not sufficiently developed for identification were transplanted and grown in pots until positive identifications could be made. • Controls containing vermiculite only were also monitored to check for wind dispersed seed contamination. None was observed. • Analysis conducted as a partially nested ANOVA design with habitat and treatment treated as fixed variables and site within habitat as random.
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ER11
• To determine the effects of flood pulse characteristics (e.g. duration, timing, frequency and rate of drawdown) on the productivity and diversity of plant communities establishing from the soil seed bank. • To determine effects of long-term flood history on plant community responses from the soil seed bank to annual flood pulse scenarios.
Methods: • A large mesocosm experiment was run from January to December 2005 using soil samples collected from vegetation survey sites during November 2004 (excluding bird colony and terrestrial sites). • Soil samples from each site were distributed amongst 13 pots and subjected to annual flood pulse scenarios as follows: – 6SF: 6 month summer flood with fast drawdown – 6SS: 6 months summer flood with slow drawdown – 3SF: 3 month summer flood with fast drawdown – 3SS: 3 month summer flood with slow drawdown – 6W: 6 month winter flood (drawdown not relevant as still submerged at 12 month harvest time) – 3WF: 3 month winter flood with fast drawdown – 3 WS: 3 month winter flood with slow drawdown – 12: 12 month flood – 3S3W: 3 month summer flood with fast drawdown and 3 month winter flood with fast drawdown (N.B. Of the 13 pots from each vegetation survey site, nine pots with all of the above treatments were harvested after 12 months. An additional four pots were harvested after 6 months with treatments comprising (1) 6 months submerged, (2) 3 month summer flood with fast drawdown, (3) 3 month winter flood with slow drawdown and (4) rainfall only.) • Weekly rainfall was delivered by hose across all pots as per Walgett rainfall station data obtained from the Bureau of Meteorology.
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• At 6 and 12 months, all plants in relevant pots were harvested, counted, identified and their reproductive status noted. • Total biomass, above-ground biomass and below-ground biomass (i.e. dry weights) were then obtained for each species for each pot.
analyses to separate the effects of inter-annual climatic variation from those of the extraction and regulation of water for human purposes.
5.5 Knowledge exchange KE1
5.4.3 Waterbirds
Activity description:
ER12
•
Activity description: • Waterbird breeding in the Narran Ecosystem.
Aims: • To determine the history of waterbird breeding in the Narran Ecosystem. • To associate waterbird breeding with the hydrology of the Narran Ecosystem.
Publication of findings from the Narran Ecosystem Project.
Aims: • To publish the findings of the Narran Ecosystem Project in a range of community, management and scientific fora.
Methods: • Publication of manuscripts in refereed scientific journals
Methods:
• Publication of an oral history of the Narran region
• Records of colonial waterbird breeding events at Narran were collated from journal articles, government reports, and anecdotal evidence.
• Publication of fact sheets detailing main findings of the Narran Ecosystem Project.
• These data were compared to hydrological conditions at the time of breeding events.
KE2
ER13
• Presentation of the approach and main findings of the Narran Ecosystem Project.
Activity description: • Landscape scale influences on waterbirds in the Narran Ecosystem.
Aims: • To understand the important landscape-scale influences and constraints upon the ability of waterbirds to successfully utilise the larger landscape region of the Narran Ecosystem to complete a cycle of breeding, dispersal, and return to the larger landscape.
Methods: • Semi-continental scale analyses were conducted on climatic and hydrological influences on patterns of migration and abundance within the area covered by the Eastern Australian Aerial Waterbird Survey. • Techniques were developed to establish and confirm connections from global-scale climatic patterns, to semi-continental scale climatic manifestations, to more localised hydrological response, and avian abundance. By doing so, to develop a comprehensively detailed understanding of the major causes of interannual variations in the abundance of migratory waterbirds within the larger landscape. This may then be combined with detailed hydrological
Activity description:
Aims: • To present the approach taken and main findings of the Narran Ecosystem Project in a variety of community, management and scientific fora.
Methods: • Presentation of the Narran Ecosystem Project at a range of community meetings • Presentation of the Narran Ecosystem Project to the various management jurisdictions • Presentation of the Narran Ecosystem Project at national and international scientific conferences.
KE3 Activity description: • Community field days at the Narran Ecosystem.
Aims: • To promote interaction between the Narran science team and the local and regional community.
Methods: • Field day for community participation in the Narran Ecosystem Project.
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6. Key findings
Figure 6.1. Satellite image showing the locations of the 12 principal wetlands (outlined in yellow) and the four stream gauging sites (orange dots) along the Narran River.
6.1 Physical template 6.1.1 Regional context • Twelve lakes and wetlands were identified along the Narran River; the largest of which is the Narran Ecosystem at the terminus of the Narran River (Fig. 6.1). The physical character of each of these floodplain features is provided in Table 6.1. These floodplain lakes and wetlands were identified using geophysical data.
Dirranbandi
Bokhara
New Angledool Angledool
• The normalised Potassium (K) ratio: K/(K + Th + U); where Th is Thorium and U is Uranium, also depicts those floodplain lakes and wetlands that were predominantly filled by stream flow (shown as red in Fig. 6.2) and those that are filled by rainfall (shown as light blue in Fig. 6.2). East Mullane and Wilkie are two large floodplain wetlands in the Narran region that are shown to fill primarily from rainfall rather than flows from the Narran River.
Bohdi
Coocoran
Wilby Wilby Morendah
Marella Lianillo
Narran Park Northern
• The use of the normalised K ratio also appears to clearly depict the floodplain area of the Narran Ecosystem; a task that is often difficult in very flat terrain.
Narran
Rotten Wilkie East Mullane
Table 6.1: The sizes of the principle lakes and wetlands along the Narran River. Wetland Narran Lake
Storage volume (ML)
122.9
122 876
19.5
9 372
Clear Lake
5.4
4 476
Back Lake
1.3
861
Long Arm
1.5
0.6
11.3
4 035
Narran floodplains
135.7
13 730
All Narran
Northern Lake
Intervening storages
278.1
145 210
Bokhara
11.6
1 152
Angledool
15.9
15 885
110.4
110.54
Bohda Coocoran
39.1
39.07
Morendah
193.0
193.00
Morella
16.6
16 580
Lianillo
15.4
15 366
Rotten
34.5
34 516
East Muflane
41.6
41 569
Willkie
11.6
11 644
Note: assumes 1 m depth for all non-Narran wetlands
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Surface area (km2)
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6. Key Findings
6.1.2 Topography • A detailed digital elevation of the Narran Ecosystem highlights its complex topography (Fig. 6.3). The study area is characterised by several lakes, wetlands, floodplains and a diverse channel network. • In general the topography of the Narran Ecosystem is very flat but the two lake systems (Narran and the northern lakes of Clear, Back Lake and Long Arm) are clearly defined within the landscape (Fig. 6.4).
• There are two principal lakes within the Narran Ecosystem: Narran Lake and the Northern Lakes have their own unique isometric relationship – (water depth vs surface areas). This is because of a number of different sub-storages within the different lake systems being activated at different inundation levels (Fig. 6.5). Figure 6.4: A close-up of the LiDAR topography data. Note that the lakes show up clearly as broad flat areas within the landscape. 122 121
Figure 6.2: Geophysical map of the 12 principal wetlands along the Narran River overlaid on the regional topography.
120 119 118
5000
10000
15000
From To
Angledool
135 From
130
Northern
Marella
125 120
Rotten
Narran East Mullane
To
Barwon floodplain
2500
5000
7500
10000
12500
Figure 6.5: Hypsometric curves for the Northern (a) and Narran (b) Lakes. (a)
25000 2500
3000 2500 surface area
2000
15000
1500 10000
volume
1000
5000
0
121.6
121.4
121.2
121.0
120.8
120.6
120.4
120.2
120.0
500 119.8
119.6
0
Elevation (m) (b) 14000
180000 160000 140000
12000
surface area
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120000
8000
100000 80000
6000
60000 40000
volume
4000
120.0
119.8
119.6
119.4
119.2
119.0
118.8
118.6
118.4
118.2
2000 118.0
20000 0
117.8
Volume (ML)
Figure 6.3: The LiDAR derived data for the Narran Ecosystem: (a) the topography of the Narran Ecosystem; and (b) vegetation heights.
Volume (ML)
20000 2000
Surface area (ha)
Morendah
Surface area (ha)
Coocoran
0
Elevation (m)
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6.1.3 Soils • The soils of the Narran Ecosystem are very fine in texture, with over 65% of the material being comprised of silts and clays, on average. Soils of the Narran Ecosystem can therefore be classified as being clayley mud soils according to the standard soil nomenclature. • There are several distinct patterns in both the physical and chemical character of the soils within the Narran Ecosystem. The lakes and floodplains show relatively high concentrations of some chemical elements (Fig. 6.6) and these soils are predominantly fluvial in origin. In contrast, other soil properties have higher levels in areas around the boundary of the Narran Ecosystem (Fig. 6.7). For these soil properties, local geology or rainfall may be the dominant control on their character. • Sodium displays a west to east pattern in concentration which is consistent with the dominant wind direction (Fig. 6.8). Therefore wind action has an important influence on the character of some of the soils in the Narran Ecosystem. • Several other soil properties show no obvious pattern. For these, it is difficult to determine the factors controlling their distribution (Fig. 6.9). • In combination with the topographic information presented earlier, the Narran Ecosystem can be broken up into a series of geomorphic subregions (Fig. 6.10) including Lakes, Floodplains Figure 6.6: Kriged soil surfaces showing soil properties which have higher concentrations or levels in lakes and wetlands.
Clay (%)
26
Aluminium (%)
Calcium (%)
and the boundary Red Soils to provide a more robust way to analyse the soil data. • Multivariate statistical approaches show that the Red Soils are significantly different to the Lake and Floodplain soils within the Narran Ecosystem (Fig. 6.11) and several of the Lake and Floodplain regions are different in soil character to one another (Table 6.2). Figure 6.7: Kriged soil surfaces showing soil properties which have higher concentrations or levels in the red soil regions surrounding the lakes and wetlands.
Titanium (%)
Sand (%) 03.60–14.35
0.40–0.48
14.35–20.75
0.48–0.50
20.75–26.30
0.50–0.51
26.30–32.75
0.51–0.52
32.75–40.00
0.52–0.54
40.00–48.35
0.54–0.56
48.35–56.35
0.56–0.57
56.35–63.35
0.57–0.59
63.35–69.50
0.59–0.61
69.50–82.00
0.61–0.67
Figure 6.8: Kriged soil surfaces showing soil properties which show higher concentration in a west to east pattern reflective of the dominant wind direction.
Sodium (%)
01.50–12.25
2.50–4.65
0.09–0.31
0.08–0.16
12.25–18.90
4.65–5.10
0.31–0.51
0.16–0.20
18.90–26.60
5.10–5.50
0.51–0.66
0.20–0.23
26.60–34.60
5.50–5.95
0.66–0.80
0.23–0.26
34.60–42.00
5.95–6.35
0.80–0.96
0.26–0.31
42.00–48.65
6.35–6.75
0.96–1.11
0.31–0.38
48.65–55.65
6.75–7.25
1.11–1.27
55.65–63.70
7.25–7.75
1.27–1.45
0.38–0.48
63.70–74.40
7.75–8.40
1.45–1.70
74.40–87.10
8.40–9.70
1.70–2.48
0.48–0.62 0.62–0.83 0.83–1.32
400
500
600
700
6. Key Findings
Figure 6.9: Kriged soil surfaces showing soil properties which show no distinguishable pattern in concentration or level.
Figure 6.11: Multi-dimensional scaling plot showing the soil character for each of the eight geomorphic regions in multidimensional space. Ne floodplain
1.5
Northern Lake
Narran Lake
1.0 0.5
–1.5 Silt (%)
Lead (ppm)
Manganese (ppm)
07.25–16.50
05.6–9.3
0203.6–373.8
16.50–20.75
09.3–10.2
0373.8–433.0
20.75–23.85
10.2–10.9
0433.0–507.0
23.85–27.25
10.9–11.5
0507.0–588.4
27.25–31.15
11.5–12.1
0588.4–677.1
31.15–34.50
12.1–12.7
0677.1–788.1
34.50–37.90
12.7–13.4
0788.1–943.5
37.90–41.50
13.4–14.3
0943.5–1158.0
41.50–48.00
14.3–15.9
1158.0–1461.4
48.00–79.30
15.9–20.0
1461.4–2097.6
Figure 6.10: The eight geomorphic units used to analyse the soils in the Narran Ecosystem showing the locations of 163 soil sample points. North-eastern floodplain
Northern Lakes
North-western floodplain
0
–0.5
Ce floodplain 0.5
1.0
1.5
–0.5
S floodplain Nw floodplain Red soil
–1.0 –1.5
6.1.4. Channel network • The river channel network of the Narran Ecosystem is very complex and comprises more than 8000 channels spanning 44 link types, as shown in the 2003 aerial photographs (Fig.6.12), (Rayburg and Thoms, in press). • Overall, the channel network maintained its extent between 1969 and 1992 but contracted over the period between 1992 and 2003 (Fig. 6.13). • In addition to this contraction, the channel network has also shown a loss of complexity with four fewer link types in 2003 than were present in 1969 (Fig. 6.14). • A more detailed comparison between 1969 and 2003 shows that the channel network is very dynamic with less than 20% of the network unchanged over this period (Fig. 6.15).
Central-western floodplain
Central-eastern floodplain Narran Lake
Red soil
Southern floodplain
–1.0
Cw floodplain
6.1.5 Environmental history • Contemporary flows in the Narran River are very low energy, transporting mostly fine silts and clays. Consequently, the surface material in the study area is of similar origin and character. The dominance of clay-size sediment differentiates the surface sediment layers from those found at depth in each of the four cores investigated (Fig. 6.16). Given the close proximity of the cores and their similarity in geological setting (i.e. down thrust basin), it should come as no surprise that the cores exhibit a great deal of overlap in sediment characteristics. In fact, there are no statistically significant differences in the sediment properties of the cores when taken as a whole. However, the stratigraphy of the individual cores suggests there to be a great deal of spatial and temporal variability in the sedimentation
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of the Narran Ecosystem. This is reflected in the clear differences between sediments within individual cores and stratigraphic sequences between cores. • The Narran Ecosystem has been in the landscape functioning as a terminal floodplain ecosystem for at least 46,000 and 70,000 years. • The infilling of sediment to Clear Lake has occurred in three distinct phases (figure 6.16): surface sediments are unique in character and are dominated by fine clay-size sediments; the middle phase exhibits irregular sediment
deposition patterns; and the lower phase is characterised by regular episodic fining upwards sequences. The lowest portion of the Clear Lake core exhibits four cyclic periods of deposition, suggesting a periodic change in the hydraulic environment from high energy (sand deposition) to low energy (deposition of fines). The chaotic nature of the sediments mid-core illustrates a much more irregular and unsettled period of sediment supply to Clear Lake. Finally, in the uppermost section of the core, a shift to a dominance of fine sediments likely reflects a shift towards conditions similar to those seen today
Table 6.2: Similarity between geomorphic regions (ANOSIM results) Groups Northern Lake
Narren Lake
Red soil
S Fp
NE Fp
NW Fp
CE Fp
CW Fp
Northern Lake Narran Lake
0.337
Red soil
0.877
0.834
S Fp
0.446
0.009
0.76
NE Fp
0.147
0.613
0.839
0.608
NW Fp
0.213
0.5
0.696
0.427
0.18
CE Fp
0.183
0.068
0.672
0222
0.264
0.085
CW Fp
0.182
0.114
0.68
0.162
0.326
0.097
0.062
Global R = 0.688 Significance level of sample statistic: 100% Number of permuted statistics greater than or equal to global R: 999 >0.75 well separated S Fp = southern floodplain, NE Fp = north east floodplain 0.50 some overlap but clearly different NW Fp = north west floodplain, CE Fp = central east 1 000 000
Years 76 8 17 17 15 15 2 1 1
% Chance 10.5 22.4 22.4 19.7 19.7 2.6 1.3 1.3
400
500
600
700
6. Key Findings
• A more detailed comparison of pre- and post 1992 flows shows that the recurrence intervals for floods of all magnitudes has increased (meaning floods have become more rare) since 1992 (Table 6.6).
Lake hydrology • There is a high degree of spatial variability in the frequency and duration of inundation in the Narran Ecosystem (Fig. 6.24). • The Northern and Narran Lakes are inundated in most years (27 out of 32 years) while floodplains areas are inundated with much less regularity (Fig. 6.25 (a)).
• Water is much more persistent in the larger Narran Lake, however, resulting in a much lower score (than the Northern Lake) for the number of times uniquely inundated (Fig. 6.25 (b)). In floodplain areas, the number of times uniquely inundated equates to the total number of years inundated which highlights the rapid drying times in floodplain areas. • In Narran Lakes, the average time to dry, in the absence of top up events, is about 15 months although this depends on the season in which inundation occurs (Fig. 6.26)
Figure 6.21: Comparisons between annual flow levels at the three principal gauges on the Narran River. 140 000 120 000
Wilby Wilby New Angledool Dirrinbandi
Total flow (ML)
100 000 80 000 60 000 40 000 20 000
1965 1966 1967 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006
0
Year
Figure 6.22: Daily flows at the New Angledool gauge. 20 000 18 000
14 000 12 000
10 000 8 000 6 000
4000 2000 0
1/10/1929 1/10/1931 1/10/1933 1/10/1935 1/10/1937 1/10/1939 1/10/1941 1/10/1943 1/10/1945 1/10/1947 1/10/1949 1/10/1951 1/10/1953 1/10/1955 1/10/1957 1/10/1959 1/10/1961 1/10/1963 1/10/1965 1/10/1967 1/10/1969 1/10/1971 1/10/1973 1/10/1975 1/10/1977 1/10/1979 1/10/1981 1/10/1983 1/10/1985 1/10/1987 1/10/1989 1/10/1991 1/10/1993 1/10/1995 1/10/1997 1/10/1999 1/10/2001 1/10/2003
Discharge (ML)
16 000
Date
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Table 6.6: Changes in the number of floods and flood recurrence intervals pre- and post- large-scale development upstream of the Narran system. Number of floods
Recurrence interval
1969–1991
1992–2003
1969–1991
1992–2003
Larger than 50 000 ML
17
7
1.30y
1.85y
Larger than 100 000 ML
14
5
1.50y
2.63y
Larger than 200 000 ML
8
2
2.78y
6.67y
Larger than 300 000 ML
7
1
3.13y
12.50y
Larger than 400 000 ML
4
0
5.56y
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