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Future options for the Lower Lakes.
 

Future options for the Lower Lakes.

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Kane Aldridge presents a seminar from the second Water Wednesday entitled "Future options for the Lower Lakes." Kane Aldridge is a postdoctoral fellow with Water Research Centre with The Environment ...

Kane Aldridge presents a seminar from the second Water Wednesday entitled "Future options for the Lower Lakes." Kane Aldridge is a postdoctoral fellow with Water Research Centre with The Environment Institute at The University of Adelaide.

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    Future options for the Lower Lakes. Future options for the Lower Lakes. Presentation Transcript

    • The Environment Institute Water Research Centre Water Wednesday Managing the Murray Icon Sites: can engineering save the environment
    • The Environment Institute Where ideas grow Future options for the Lower Lakes Kane Aldridge, Justin Brookes and George Ganf
    • The Lower Lakes & Coorong
    • The Lower Lakes: a predominately fresh system Adapted by John Tibby from Fluin et al., 2007
    • Variable salinity regime 200 Barrage flow (GL/day) 150 100 The natural flow regime and salinity balance 50 • Spring floods and summer low 0 flows 1975 1980 1985 1990 1995 2000 2005 -50 • Salt intrusions did occur, but never 60 marine • Small ‘backflow’ events had a EC (mS/cm) 40 rapid, short-lived impact on salinity 20 • ‘Fresh’ 95% of the time 0 1975 1980 1985 1990 1995 2000 2005 Data from Bigmod, MDBA
    • Water level variability 200 Barrage flow (GL/day) 150 The natural flow regime 100 • Water levels fluctuating between 0.8 and 0.1 mAHD 50 0 • Highly variable from year-to- 1975 1980 1985 1990 1995 2000 2005 year -50 1 • Salinity and water level Water level (mAHD) 0.8 primarily determined by Murray 0.6 inflows 0.4 0.2 0 1975 1980 1985 1990 1995 2000 2005 Data from Bigmod, MDBA
    • The Lower Lakes: a macrophyte dominated system 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’ Increased habitat and food complexity for fish and birds Image: www.wisconsinlakes.org
    • Connectivity: the key to resistance and resilience • A large, dynamic estuary • Fresh-hypersaline • Spatial and temporal variability • Abundant and diverse biota • Intermediate disturbance • Tolerance – short-term incursions • Migration - connectivity • Recruitment - connectivity • Barrage construction and operation • Regular disconnection of the estuary
    • Lower Lakes in early 2000s: an important freshwater ecosystem of MDB • Disproportionately high number of species of MDB – >130 species of plants (Holt et al. 2005; Nicol et al. 2006) – 100 000 birds, >30 species, Lake Albert important breeding habitat (Kingsford and Porter 2008) – 22 species of fish, >half of MDB, stronghold for 3 endangered small bodied fish (Wedderburn & Hammer, 2003; Barnes and Wedderburn, 2009)
    • Over-allocation, drought and water level drawdown
    • Water level drawdown and loss of connectivity Jan 2007 Jan 2008
    • Water level drawdown and salinisation
    • Loss of plants, fish and birds • Plants – Complete loss of extensive beds of submerged macrophytes (Marsland and Nicol, 2009) – Disconnection of fringing vegetation (Marsland and Nicol, 2009) • Fish – Likely extinction of Yarra Pygmy Perch and large declines in Murray Hardyhead and Southern Pygmy Perch (Barnes and Wedderburn, 2009) • Waterbirds – 100,000 in 2007 to 20,000 in 2008 (Kingsford and Porter, 2008; Kingsford and Porter, 2009)
    • If salinity and water level variability are a natural feature of the Lower Lakes, why have they had such an impact during the current drought?
    • Early 2000s: an important ecosystem, but vulnerable • Important, but “vulnerable to future change” (Wedderburn & Hammer, 2003) – Refugia for many species dependant upon submerged macrophytes for habitat complexity – Submerged macrophytes isolated and restricted to sheltered areas, particularly Goolwa channel
    • Salt intrusions and macrophyte loss • Freshwater macrophytes sensitive to salinity (Nielsen et al. 2003) – 1 g/L – adverse impacts – 4 g/L - loss • Submerged macrophyte loss due to salinity (initially improved habitat availability during drawdown) →Decreased habitat complexity for small bodied fish → Loss of food sources for waterbirds Salinity (g/L)
    • Why was macrophyte distribution limited? 1.2 Natural • Construction and operation of Managed Water level (mAHD) barrages 0.8 • Loss of suitable habitat for submerged 0.4 macrophytes from main bodies of Lake Alexandrina and Lake Albert • Increased water depth - reduced access to 0 1950 1963 1977 1991 2004 light Source: MDBA (Bigmod) • Increased erosion - reduced access to light -0.4 • Lower water level variability – reduced habitable area • Loss of complex littoral zone and habitat complexity • Phytoplankton dominance
    • Barrage operation: constriction of littoral zone to fringing vegetation
    • Habitat disconnection = reduced resistance and resilience
    • Don’t open the barrages without sufficient freshwater flows • Matching evaporation - resultant salinity nearly 2/3 seawater during refill • Salt accumulates with insufficient flow • No refuge for many freshwater organisms • Increased siltation and dependence upon dredging
    • Disconnection in a time of crisis Ensure that temporary means temporary Photo: Paul Harvey Photo: Dominic Skinner Photo: Paul Harvey
    • Disconnection of a system that needs connectivity to deal with future variability
    • So what do we do? • Enough water to maintain as a fresh system (CSIRO, 2008) BUT, – 13% of years - severe drought (<1500 GL/yr) under median climate NEED, – Build a system that thrives on variability • Use the barrages as an ecological lever rather than a storage device • Manage at lower water levels • Reinstate salinity and water level variability • Create a salinity gradient (estuary) rather than a boundary • Optimal barrage operation needs robust plans • Match habitat preferences (salinity and water level) of biota against inflows and barrage operation • Engineering can be a lever, but securing adequate water will always be the key