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What is the future for the Lower Lakes

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The second instalment of the Environment Institute’s Science Seminar series for Semester 2 held at 1pm Friday 14 August in the Benham Lecture Theatre. Dr Kane Aldridge will present the topic ‘What is …

The second instalment of the Environment Institute’s Science Seminar series for Semester 2 held at 1pm Friday 14 August in the Benham Lecture Theatre. Dr Kane Aldridge will present the topic ‘What is the future for the Lower Lakes?’



Lake Alexandrina and Lake Albert (the Lower Lakes) provide important habitat for biota within the Murray-Darling Basin. The current drought has highlighted the over-allocation of water resources in the Murray-Darling Basin, with water levels falling dramatically in the Lower Lakes to unprecedented levels. This has resulted in a dramatic increase in salinity, the exposure of acid sulfate soils and the loss of habitat for many freshwater plants and animals. In this presentation, Kane will examine what is known about the natural water regime and ecology of the Lower Lakes and the current management of the region. This information will be used with predictions of water availability in the Murray-Darling Basin to explore how the lakes may be managed in the future to provide a resilient ecosystem that is able to cope with variability in flow and climatic condition

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  • 1. The Environment Institute Where ideas grow Dr Kane Aldridge What is the future for the Lower Lakes?
  • 2. The Environment Institute Acknowledgements • Justin Brookes • George Ganf • David Paton • Matt Hipsey • Dominic Skinner • Alex Payne Life Impact The University of Adelaide
  • 3. The Environment Institute The Lower Lakes & Coorong • Spiritual home of Ngarrindjeri • Home to diverse flora and fauna • Disproportionately high number of species in MDB • Provides unique habitats • Function of habitat diversity and salinity gradient • Wetland of national and international significance • Ramsar wetland • Icon site in MDB • Irrigation, fisheries, recreation, tourism • Water level drawdown, salinisation, acid sulfate soils, loss of freshwater biota Life Impact The University of Adelaide
  • 4. The Environment Institute What is the future of the Lower Lakes? Talk outline: • The distant past • The not-so-distant past • The present situation • The future • Disclosure: despite the importance of the Lower Lakes, we know very little about their ecological functioning - much of the information provided is based on what we have learnt from elsewhere Life Impact The University of Adelaide
  • 5. The Environment Institute The distant past: a ‘fresh’ system (from Sims & Muller, 2004) Ngarrindjeri connection to the lakes • Permanent settlements, drinking water, reports of freshwater species – Pantaruki (Triglochin procerum), Tjiri (Silverperch) and Tukkeri (Bony Bream) • Dreamtime story = Pondi (Murray Cod) creating bends in river & ending journey in the lakes – cut into pieces becoming freshwater fish - catfish, Callop and Silver Perch European settlement • Settlers - stock had access to the freshwater and feed • Many accounts of fresh, sweet drinking water • George Hamilton 1839: “…it was fresh, and it was not salt; it had a vapid sweet taste, but it quenched our thirst. Millions of wildfowl must have been on the surface of this lake. As we reached its borders they rose in dense clouds, darkening the air.” Life Impact The University of Adelaide
  • 6. The Environment Institute The distant past: a ‘fresh’ system (Adapted by John Tibby from Fluin et al., 2007) Life Impact The University of Adelaide
  • 7. The Environment Institute Barrage flow (GL/day) 200 150 100 The natural flow regime 50 • Spring floods and summer low flows 0 1975 1980 1985 1990 1995 2000 2005 • Highly variable from year-to- -50 year 1 • Water level primarily Water level (mAHD) 0.8 determined by Murray inflows 0.6 • Water levels fluctuating 0.4 between 0.8 and 0.1 mAHD 0.2 0 1975 1980 1985 1990 1995 2000 2005 Data from Bigmod, MDBA Life Impact The University of Adelaide
  • 8. The Environment Institute 200 Barrage flow (GL/day) 150 The natural salinity balance • Salt intrusions did occur, but never 100 marine 50 • Small ‘backflow’ events had a rapid , short-lived impact on salinity 0 1975 1980 1985 1990 1995 2000 2005 • How was a healthy ecosystem maintained -50 in a dynamic environment? 60 – Variability – Intermediate disturbance promotes biodiversity – Connectivity EC (mS/cm) 40 – Allow movement of species with their preferred salinity 20 0 Data from Bigmod, MDBA 1975 1980 1985 1990 1995 2000 2005 Life Impact The University of Adelaide
  • 9. The Environment Institute Connectivity: “Boom” Life Impact The University of Adelaide
  • 10. The Environment Institute Connectivity: “Bust” Life Impact The University of Adelaide
  • 11. The Environment Institute Anecdotal evidence of abundant flora (Sims and Muller, 2004) • “…reeds, bulrushes and waterweed grew around the lake” • “…encircle Lake Albert in one continued belt” • “…the shores were also covered with reedy flats, which were in some places half a mile in breadth’ Water level variability as a primary driver • Extended habitat for macrophytes, Image: www.wisconsinlakes.org increased abundance • Diversity of habitats for aquatic plants, increased diversity Life Impact The University of Adelaide
  • 12. The Environment Institute Life Impact The University of Adelaide
  • 13. The Environment Institute The importance of macrophytes • ‘Umbrella’ species • Food for invertebrates, fish, birds • Habitat for invertebrates, periphytic algae, fish • Reduce sediment resuspension • Compete for nutrients with phytoplankton • Macrophyte dominated = healthy Scheffer 1999 Life Impact The University of Adelaide
  • 14. The Environment Institute The not-so-distant past Life Impact The University of Adelaide
  • 15. The Environment Institute The not-so-distant past 1.2 Natural • Managed for humans Managed – Elevated water levels and little fluctuation Water level (mAHD) 0.8 – Cattle grazing 0.4 • Loss of habitat • Increased water depth • Increased erosion of the lake shore (Coulter 1992) 0 1950 1963 1977 1991 2004 • Increased turbidity • Retreat of lake perimeter - 1 m/yr (Coulter 1992) -0.4 Data from Bigmod, MDBA Life Impact The University of Adelaide
  • 16. The Environment Institute Life Impact The University of Adelaide
  • 17. The Environment Institute A turbid, phytoplankton dominated system • Dominated by an ‘open’ water ecosystem • Carbon flow through foodweb restricted by turbidity (Geddes, 1984) • At times no carbon flow (algal blooms common) • ‘Littoral’ system isolated to shallow areas Life Impact The University of Adelaide
  • 18. The Environment Institute Important refugia for plants, fish and birds • >130 species of plants (Holt et al. 2005; Nicol et al. 2006) • 100 000 birds, >30 species, Lake Albert important breeding habitat in MDB (Kingsford and Porter 2008) • 22 species of fish, >half of MDB (Wedderburn & Hammer, 2003) • Dominated by open water species • Yarra and southern pygmy perch and Murray Hardyhead of conservation significance – only found with dense vegetation for cover Life Impact The University of Adelaide
  • 19. The Environment Institute Important habitat, but not resilient • “One of the most striking features of the Lower Lakes fish community is its vulnerability to future change” (Wedderburn & Hammer, 2003) • Isolated refugia in a large system • Dispersal of vulnerable fish is slow • Dependant on macrophytes for cover Life Impact The University of Adelaide
  • 20. The Environment Institute The current situation • ↓ annual flow at Murray Mouth by 61% • ↓ % of time that flows to sea – Past – 1% – Current – 40% (CSIRO, 2008) Life Impact The University of Adelaide
  • 21. The Environment Institute The drought Life Impact The University of Adelaide
  • 22. The Environment Institute Over allocation + drought + barrages Life Impact The University of Adelaide
  • 23. The Environment Institute Lake Alexandrina Ewe Island Barrage Coorong Life Impact The University of Adelaide Photo: Russell Seaman
  • 24. The Environment Institute Life Impact The University of Adelaide
  • 25. The Environment Institute Loss of biota • Ecological condition reports currently under review • Observations of loss of large stands of a number of species of submerged and semi-emergent macrophytes in Goolwa channel and tributaries • Fish and birds dependant upon macrophyte for habitat/food Life Impact The University of Adelaide
  • 26. The Environment Institute Salinity – likely cause of macrophyte loss • Main bodies of lakes still ‘tolerable’ for many species • If only we had some plants there with connection to Goolwa channel Life Impact The University of Adelaide
  • 27. The Environment Institute Acid sulfate soils Source: Fitzpatrick et al. 2008 Life Impact The University of Adelaide
  • 28. The short-term future: disconnection The Environment Institute Life Impact The University of Adelaide
  • 29. The Environment Institute So why don’t we open the barrages? • Matching evaporation - resultant salinity nearly 2/3 seawater just during refill phase • Salt accumulates • Insufficient flows to remove the salt • Increased siltation • No refuge for many freshwater organisms Life Impact The University of Adelaide
  • 30. The Environment Institute The long-term vision (DEH, 2009) Manage the current threats and plan for the future to secure existing ecological character Manage through the current period of uncertainty and help the system to adapt by building resilience within the system to survive, evolve and adapt to greater climatic variability Implement responsive management arrangements depending upon future climatic scenario Undertake the necessary preparatory works for a transition to a more estuarine character, given current sea level rise predictions Life Impact The University of Adelaide
  • 31. The Environment Institute If biodiversity and resilience are dependant upon connectivity, will the long-term vision be compromised by short-term crisis management? Life Impact The University of Adelaide
  • 32. The Environment Institute What is the future of the Lower Lakes? • Sustainable yields – CSIRO, 2008 • 2030 median climate end-of-system flows = 3575 GL/yr • ≈ 4230 GL/yr into the lakes • Volume of lakes = 1660 GL at 0.3 mAHD with gross evaporation of 650GL → Enough water to maintain as a fresh-estuarine system BUT, • 13% of years - severe drought (<1500 GL/yr) under median climate, 33% under extreme dry climate (CSRIO, 2008) NEED, • A system that can tolerate variability • A resilient ecosystem • Healthy, connected habitat Life Impact The University of Adelaide
  • 33. The Environment Institute So how do you get resilience? • Get the plants right and the rest will follow (George Ganf, pers comm) • Habitat (macrophyte) connectivity through the system • Goolwa channel ↔ Lake Alexandrina ↔ Narrows ↔ Lake Albert • Lower water levels • Reduced erosion – extend habitable area • Shallower water – extend habitable area • Water level variability • Promote diversity and extend habitable area • Remove cattle • Reduced consumption and erosion Life Impact The University of Adelaide
  • 34. The Environment Institute Recovery of macrophytes • The focus of many ecosystem restoration strategies (Jeppesen et al. 2005; Sondergaard et al. 2005) • Restoration doesn’t always follow the same trajectory as degradation (Scheffer, 1990) • Improving one variable not always enough • Reducing water levels – increased turbidity • Established at higher water levels and reduce to expand habitat • Reduce nutrient inputs to improve clarity? • Reduce turbid inputs from Darling river? • Replant and create protected sanctuaries? Life Impact The University of Adelaide
  • 35. The Environment Institute Future mitigation of ASS? Life Impact The University of Adelaide
  • 36. The Environment Institute The future • People want to go back to what we had • Learn from our mistakes • The disconnected system we had was not resilient (drawdown is a natural) • Create a system that can cope with variability • Build resilience • Connectivity • Variability • Manage at lower water levels • ↑ habitable area (and↓ evaporation) • Need upstream storage to provide flows to the Coorong • The big challenge: • Restoration strategy? • Create a system that can deliver water to a number of different users in an unpredictable climate • Getting adequate water will always be the key Life Impact The University of Adelaide
  • 37. The Environment Institute Where ideas grow Next Seminar: 21 August Professor Randy Stringer Agrarian Landscapes, the Environment and World Heritage Sites: Why our region should apply

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