HEADLINE TO BE PLACED IN THIS SPACE CL L AMMe c o lo gy Re se arc h Cluste r partne rs: The changing state of the Lower Murray Lakes S uppo rte d by: With the c o llabo ratio n o f:
Acknowledgements • Authors • Justin Brookes • Brian Deegan • Sebastien Lamontagne • Perran Cook • Ian Webster • Matt Hipsey • Andrew Bissett • DWLBC, MDBC,EPA, AWQC • ICE WaRM • International Liaison Programme • Travelled to Max Planck Institute, Bremen, Germany • Water Cluster of the University of Adelaide AMM e c o lo gy CL L
The Lower Murray Lakes SA’s largest permanent lakes (306 and 106 km 2 ) • • Shallow - average depth approx 3.5 m, maximum depth 4.1 m (Geddes 1984) • Terminus of the River Murray, their principal source of water (Sims and Muller, 2004) • Local stream contribution significant during periods of low River Murray inputs (MDBC, 2007) • Estuarine prior to European settlement (Geddes 1984, Von Der Borch and Altman 1979), • Fresh more than 95% of the time (Sims and Muller, 2004) • Post European settlement • Water extractions • More frequent intrusions of salt water into the lakes (Sims and Muller, 2004) • Construction of five barrages between 1935 and 1940 • Lake Alexandrina discharges into the Murray Mouth and Coorong • Controlled by barrage operations AMM e c o lo gy CL L
AMM e c o lo gy CL L
Important for agriculture, fisheries, water supply, … AMM e c o lo gy CL L S.Wedderburn
AMM e c o lo gy … recreation, residence, … L CL
... biota … • Along with Coorong and Murray Mouth are listed as a wetland of international significance (Ramsar agreement, 1984) S.Wedderburn AMM e c o lo gy CL L S.Wedderburn
... and a supply of resources to downstream ecosystems • Water, nutrients, organic material supplied to Coorong, Murray Mouth and near-shore environment C. Matthews AMM e c o lo gy CL L C. Matthews
The Lower Murray Lakes • Eutrophic-hypereutrophic (Geddes 1984, 1988) • Marginal for phytoplankton growth? • A majority of the nutrients are in particulate forms • Dissolved nutrients not available for algal growth • Highly turbid environment - resuspension • Algal blooms common, particularly during periods of low flow (low turbidity) • First recorded toxic bloom of blue-green algae ( Nodularia spumigena ) in Australia (Francis 1878) • Pico-cyanobacterial blooms now occur annually • Blooms of Nodularia spumigena , Anabaena circinalis Aphanizomenon/Anabaena are common • First bloom of Cylindrospermopsis raciborskii occurred in the lakes in 2006 • Impact fisheries, water supply and biotia • We know very little about the functioning of the Lower Murray Lakes AMM e c o lo gy CL L
AMM e c o lo gy A turbid, eutrophic environment L CL
Barrage operations • Barrages separate from the Coorong and the Murray Mouth to prevent saline intrusions • Operations • Maintain an average water level of 0.75 m Australian Height Datum (AHD) (MDBC, 2007) • As river flow increases, barrage gates are opened to maintain this level. • Surcharged to 0.85 m AHD at the beginning of Summer to ensure >0.60 m AHD in Autumn • Altered flow • Reduced size (magnitude and duration) of peak flow • Extends period of no outflow • Increase lake levels • Reduces water level fluctuations • Increase water residence times • ‘Environmental’ flow releases AMM e c o lo gy CL L M. Geddes
Original project objectives • Examine the processing of resources (nutrients, organic matter) within the Lower Murray Lakes • Develop historical nutrient and ion budgets for the Lower Murray Lakes • Examine how resource delivery from the Lower Lakes could impact primary and secondary production in the Coorong and Murray Mouth region • Develop a model capable of predicting organic matter and nutrient delivery from the Lower Lakes to the Coorong and Murray Mouth under various flow regimes AMM e c o lo gy CL L
The current situation – Murray inflows AMM e c o lo gy CL L
The current situation – falling water levels AMM e c o lo gy CL L
The current situation – falling water levels AMM e c o lo gy CL L
The current situation – falling water levels AMM e c o lo gy CL L
The current situation – some benefits? AMM e c o lo gy CL L
AMM e c o lo gy The current and future situation L CL • Text (DWLBC, 2007)
AMM e c o lo gy The current and future situation L CL • Text (DWLBC, 2007)
The current and future situation Island??? Pomanda •Weir at
Additional objectives • Monitoring salt intrusions • Impacts of drying-reflooding on nutrient release and bacterial activity • Impacts of salinity on phytoplankton communities AMM e c o lo gy CL L
Steps involved • How have the Lower Murray Lakes functioned in the past? • Analysis of historical data • How are the Lower Murray Lakes currently functioning? • Monitoring and field/laboratory experiments • How will the Lower Murray Lakes function in the future? • 3D hydrodynamic-ecological model AMM e c o lo gy CL L
How have the Lower Murray Lakes functioned in the past? • Nutrient and ion budget • Water quality data from AWQC, EPA and MDBC • HCO 3 , K, Mg, Na, SO 4 , Ca, Cl, NO 3 , pH, Si, TKN, FRP and TP • Only consistent parameters • Only 1979–1996 were considered, most comprehensive • Collection of flow data from BIGMOD (J. Davis, MDBC) • Inflow = Tailem Bend • Closest to the inflow • Outflow = Milang • Closest to barrages • Nutrient concentrations at Goolwa barrage not significantly different ( t -test, P>0.05) • Monthly loads were obtained at the inflow and outflow points • Average monthly concentrations x monthly flow AMM e c o lo gy CL L
Annual inflow v nutrient & ion inputs AMM e c o lo gy CL L
Retention in the Lower Murray Lakes AMM e c o lo gy CL L
Retention in the Lower Murray Lakes AMM e c o lo gy CL L
The nutrient budget 1979-1996 • Assimilation of inorganic nutrients • Conversion to organic forms (TKN (little NH 4 )) • Consistent with autotrophic system • Contrasts with Australian reservoirs • Increasing N:P • Exports will be N ‘rich’ • Flow provisions across the barrages are likely to provide environmental benefits • Estuarine and marine systems generally N limited • Initial response likely to be observed in zooplankton and bacterial communities Units = Kmol • Benefits cascade through the foodwebs AMM e c o lo gy CL L
How are the Lower Murray Lakes currently functioning? • Field and laboratory experiments • Thermistor chains • Temp - 5 depths, 4 sites, every 15 min since December 2006 • Sediment character survey. At 40 sites: • Water column - chlorophyll, POM, PSD, light intensity profiles. • Sediment – nutrients, chlorophyll, POM, PSD • Wind-driven sediment resuspension – P release • Influence of drying-reflooding on sediment nutrient release • Routine monitoring. At 20 sites: • Nutrients, chlorophyll, POM, TSS, PSD • DO, temp, conductivity, turbidity, pH and light profiles • Algal counts at 12 sites in January 2007 • Phytoplankton activity with PhytoPAM AMM e c o lo gy CL L
Drying-reflooding – nutrient release • Impacts of sediment exposure (drying) and reflooding on nutrient fluxes • Dessication – cell lysis and nutrient leaching • Incubation experiment • Permanently wet sediments vs. wet-dry-wet • Changes in water column nutrient concentrations through time • Microsensor profiles for DO, NO x , NH 4 • Flux rates given by rate of change through profiles • Injection of ‘labelled’ N for calculation of denitrification rates • Added to water column (NO x ) – sample from air (N 2 ) AMM e c o lo gy CL L
AMM e c o lo gy Drying-reflooding – nutrient release L CL
AMM e c o lo gy Drying-reflooding – nutrient release L CL
AMM e c o lo gy L CL Routine monitoring
Salinity Electrical conductivity (mS/cm) 40 River Murray Lake Alexandrina body Narrows 30 Lake Albert Lake Alexandrina arm Barrages 20 10 ANZECC, 2000 0 Jan Mar May Jul Oct Nov AMM e c o lo gy CL L
Electrical conductivity (mS/cm) Salinity 0 10 20 30 40 50 0 Jan Water depth (m) 1 Mar 2 May Jul 3 Oct 4 Goolwa Nov 5 Electrical conductivity (uS/cm) 0 1 2 3 4 5 0 Point Sturt- Jan Water depth (m) 1 Mar Point McLeay 2 May Jul 3 Oct 4 Nov AMM e c o lo gy CL L 5
2.5 River Murray Lake Alexandrina body Nutrients Narrows 2 Lake Albert Total P (mg/L) Lake Alexandrina arm 1.5 Barrages 1 0.5 ANZECC, 2000 0 Jan Mar May Jul Oct Nov 25 River Murray Lake Alexandrina body Narrows 20 Lake Albert Lake Alexandrina arm DOC (mg/L) Barrages 15 10 5 0 AMM e c o lo gy CL L Jan Mar May Jul Oct Nov
Nutrients 0.3 River Murray Lake Alexandrina body Narrows Lake Albert NH 4 -N (mg/L) 0.2 Lake Alexandrina arm Barrages 0.1 ANZECC, 2000 0 Jan Mar May Jul Oct Nov AMM e c o lo gy CL L
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