1Department of Zoology, Kingsway Campus, University of Johannesburg, Auckland Park, 2006, South Africa ... Sites DPD and GLEN showed the highest.
Using macro-invertebrate community assemblages to determine water quality within drought conditions Nathan Jay Baker*1, Richard Greenfield1 1Department of
Zoology, Kingsway Campus, University of Johannesburg, Auckland Park, 2006, South Africa
ABSTRACT The Nyl & Mogalakwena rivers are under pressure from increased urbanisation, industrial development, mining and agriculture. Results from low flow sampling showed that the Modimolle STW is severely affecting the water quality, nutrient loads and the macroinvertebrate taxa present within these systems. Fifteen families were present at STW, while JASP, 8km downstream, had 28 families present. Water nutrient data at JASP was worse than that of STW, perhaps due to a lower pH. Macroinvertebrate families at each of the site correlate with that of water nutrient data, identifying STW as having significant impacts on water quality and other downstream sites.
NYL RIVER FLOODPLAIN • • • • •
THREATS TO THE SYSTEM
SA’s largest ephemeral floodplain (McCarthy et al. 2011) 16 000 ha (Friends of Nylsvley, 2008) Ramsar site Nylsvley Nature Reserve & privately owned farms (Friends of Nylsvley, 2008) 400+ bird & 100+ mammal species (Greenfield et al., 2007; Friends of Nylsvley, 2008; NCC Environmental Sciences, 2015) • 23 Red Data bird species • Wild rice (Oryza longistaminata) • Endangered Roan Antelope upload.wikimedia.org
idtools.org
3.bp.blogspot.com
www.mining.com
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MATERIALS & METHODS Field Procedures
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Lab Analyses • •
In Situ Water Quality Kick, Stir, Sweep in all available biotopes Macro-invertebrate preservation Water collection
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Statistical Analyses •
Water Nutrient Analyses Cleaning of macroinvertebrate samples Identification of macroinvertebrate taxa to lowest taxonomical level.
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SITE SELECTION
Macro-invertebrate biodiversity indices Student T-tests Redundancy Analyses (RDA) (Clarke & Warwick, 1994)
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This study aimed to: (1) determine the macro-invertebrate community assemblages present within the Nyl & Mogalakwena river systems and, (2) determine the macro-invertebrate community assemblages present within the Nyl & Mogalakwena river systems. It was hypothesized that: (1) Anthropogenic activities within the Nyl & Mogalakwena Rivers are having negative effects on the macro-invertebrate community assemblages, (2) Water quality is being affected by increases in nutrient levels and, (3) Macro-invertebrate community assemblages reveal that the water quality of the Nyl & Mogalakwena rivers is declining.
RESULTS •
SOUTH AFRICA (LIMPOPO)
BOTSWANA
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Modimolle
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AIMS & OBJECTIVES •
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houghtsfromthedarkness.weebly.com
GLEN •
Mookgapong
• Mokopane Alldays
KNO DPD
In total, 139 taxa were identified from the low flow sampling survey, with an average number of 2045 individuals per site. Sites DPD and GLEN showed the highest Shannon-Weiner Diversity Index (SWDI) scores of 3,92 and 3,42 respectively. Sites STW (1,92) and JASP (1,86) showed the lowest SWDI index scores with JASP, surprisingly being lower than that of STW. The RDA represented by figure 2 explains 78,5 of the variation in the ordination. The two major drivers of the ordination of Figure 2 are Chlorides (Cl) and Dissolved Oxygen (DO). DO & Cl contribute 45% and 25% to the ordination respectively.
GLEN
JASP KNO DPD
STW
DISCUSSION •
STW JASP Figure 1: Map of the Nyl & Mogalakwena River (Limpopo Province, South Africa) with low flow sampling sites indicated.
SITE CODE
SITE NAME
REASON FOR SELECTION
KNO
Klein Nyl Oog
Reference site
DPD
Donkerpoort Dam
Downstream of impoundment
STW
Modimolle Sewage treatment works
Runs through the Modimolle sewage treatment works
JASP
Jasper
Wetland after STW
GLEN
Glen Alpine Dam
Downstream irrigation dam
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Syrphidae – Ceriodes sp. (Source : Levon Biss)
Sites STW & JASP are positively correlated to eutrophic . Therefore, the macro-invertebrate families present at these sites are more tolerant to these eutrophic conditions. Eutrophic conditions often cause DO concentrations to decrease, accounting for the negative correlation of these sites and taxa to DO. The taxa present at these sites would be able to tolerate the anoxic conditions. Inversely, sites GLEN, KNO & DPD are negatively correlated to these eutrophic conditions. Taxa represented here are more sensitive to eutrophic conditions and are better suited for waters with lower levels of these nutrients. These sites also show a positive correlations to and are strongly driven by DO within the water column and represent sensitive taxa. Chlorides were the second most influential driver for the ordination in figure 2. Chlorides enter the system through environmental pollution, presumably due to Modimolle sewage treatment work facility that continues to pump raw, untreated sewage into the Nyl River. GLEN is separating away from the other sites. During the drought, JASP & GLEN were separated by 240km of dry river bed, isolating the upper Nyl river from that of the Mogalakwena River. Therefore, the macroinvertebrate community assemblages observed at GLEN were unique to those of the other sites.
Figure 2: RDA showing the most significant driving environmental variables for family and site ordination.
CONCLUSION • • •
Macro-invertebrates are good biological indicators of anthropogenic impacts on the Nyl & Mogalakwena river systems Macro-invertebrate community assemblages are being affected by environmental variables & water quality Anthropogenic activities are putting strain on the important river systems & the biota that are dependent on it, including human beings.
REFERENCE LIST • • •
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Clark, K. & Warwick, R. 1994. Change in marine communities: an approach to statistical analysis and interpretation. Plymouth: Plymouth Marine Laboratory. Friends of Nylsvley. 2008. The Nyl Floodplain. Available from: www.Nylsvley.co.za/?go=flood [Accessed on 3/9/2016]. McCarthy, T.S., Tooth, S., Jacobs, Z., Rowberry, M.D., Brandt, D., Hancox, P.J., Marren, P.H., Woodborne, S. & Ellery, W.N. 2011. The origin and development of the Nyl River floodplain wetland, Limpopo Province, South Africa: trunk – tributary river interactions in a dryland setting. South African Geographical Journal. DOI: 10.1080/03736245.2011.619324. NCC Environmental Services. 2012. Five year strategic plan for the Nylsvley Nature Reserve, Limpopo Province, South Africa. Department of Economic Development, Environmental and Tourism, Limpopo Provincial Government.
ACKNOWLEDGEMENTS Gregg Jansen Van Rensburg, Kelly Dyamond, Simone Dahms, Ryaz Musa
