The changing state of the Lower Murray Lakes S uppo rte d by: - - PowerPoint PPT Presentation

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The changing state of the Lower Murray Lakes

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

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The Lower Murray Lakes

• SA’s largest permanent lakes (306 and 106 km2)
• Shallow - average depth approx 3.5 m, maximum

depth 4.1 m (Geddes 1984)

• Terminus of the River Murray, their principal source
• f 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

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Important for agriculture, fisheries, water supply, …

S.Wedderburn

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… recreation, residence, …

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... biota …

• Along with Coorong and Murray Mouth are listed as a wetland of

international significance (Ramsar agreement, 1984)

S.Wedderburn S.Wedderburn

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• Water, nutrients, organic material supplied to Coorong, Murray

Mouth and near-shore environment

... and a supply of resources to downstream ecosystems

• C. Matthews
• 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

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A turbid, eutrophic environment

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

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• 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

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The current situation – Murray inflows

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The current situation – falling water levels

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The current situation – falling water levels

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The current situation – falling water levels

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The current situation – some benefits?

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The current and future situation

• Text

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(DWLBC, 2007)

The current and future situation

• Text

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(DWLBC, 2007)

The current and future situation

• Weir at

Pomanda Island???

Additional objectives

• Monitoring salt intrusions
• Impacts of drying-reflooding on nutrient

release and bacterial activity

• Impacts of salinity on phytoplankton

communities

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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

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• Nutrient and ion budget
• Water quality data from AWQC, EPA and MDBC
• HCO3, K, Mg, Na, SO4, Ca, Cl, NO3, 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

How have the Lower Murray Lakes functioned in the past?

Annual inflow v nutrient & ion inputs

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Retention in the Lower Murray Lakes

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Retention in the Lower Murray Lakes

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The nutrient budget 1979-1996

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Units = Kmol

• Assimilation of inorganic

nutrients

• Conversion to organic

forms (TKN (little NH4))

• 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
• bserved in zooplankton

and bacterial communities

• Benefits cascade through

the foodwebs

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

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Drying-reflooding – nutrient release

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• 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, NOx, NH4
• Flux rates given by rate of change through profiles
• Injection of ‘labelled’ N for calculation of denitrification rates
• Added to water column (NOx) – sample from air (N2)

Drying-reflooding – nutrient release

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Drying-reflooding – nutrient release

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Routine monitoring

Salinity

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10 20 30 40 Jan Mar May Jul Oct Nov

Electrical conductivity (mS/cm)

River Murray Lake Alexandrina body Narrows Lake Albert Lake Alexandrina arm Barrages

ANZECC, 2000

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1 2 3 4 5 10 20 30 40 50

Electrical conductivity (mS/cm) Water depth (m) Jan Mar May Jul Oct Nov

1 2 3 4 5 1 2 3 4 5

Electrical conductivity (uS/cm) Water depth (m) Jan Mar May Jul Oct Nov

Goolwa Point Sturt- Point McLeay

Salinity

Nutrients

0.5 1 1.5 2 2.5

Jan Mar May Jul Oct Nov

Total P (mg/L)

River Murray Lake Alexandrina body Narrows Lake Albert Lake Alexandrina arm Barrages

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Jan Mar May Jul Oct Nov

DOC (mg/L)

River Murray Lake Alexandrina body Narrows Lake Albert Lake Alexandrina arm Barrages ANZECC, 2000

Nutrients

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0.1 0.2 0.3 Jan Mar May Jul Oct Nov

NH4-N (mg/L)

River Murray Lake Alexandrina body Narrows Lake Albert Lake Alexandrina arm Barrages

ANZECC, 2000

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1 2 3 4 5 2 4 6 8 10 12

DO (mg/L, sal corrected) Water depth (m) Jan Mar May Jul Oct Nov

1 2 3 4 5 2 4 6 8 10 12

DO (mg/L, sal corrected) Water depth (m) Jan Mar May Jul Oct Nov

Dissolved

• xygen

Goolwa Points

Nutrients

0.0 0.2 0.4 0.6 NH4-N Total-P

Concentration (mg/L)

Surface Bottom

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3 6 9 12 15 Surface Bottom

DOC (mg/L)

Phytoplankton

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30 60 90 120 150 Jan Mar May Jul Oct Nov

Chlorophyll a (ug/L)

River Murray Lake Alexandrina body Narrows Lake Albert Lake Alexandrina arm Barrages

100 200 300

River Alex body Narrows Albert Alex arm Barrages River Alex body Narrows Albert Alex arm Barrages River Alex body Narrows Albert Alex arm Barrages River Alex body Narrows Albert Alex arm Barrages River Alex body Narrows Albert Alex arm Barrages Mar May Jul Oct Nov

Total chlorophyll (ug/L)

Brown total chlorophyll Green total chlorophyll Blue-green total chlorophyll

How are the Lower Murray Lakes currently functioning?

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• Reducing water levels and increasing salinity
• Increasing nutrient concentrations (TP, NH4)
• Decomposition???
• External inputs???
• Increasing DOC
• Decomposition???
• Release from phytoplankton???
• Salinity inhibition of microbial community???
• A transition state

How will the Lower Murray Lakes function in the future?

• Develop predictive model of Lower Lakes water quality
• 3D hydrodynamic-ecological model (ELCOM-CAEDYM)
• Quantify biogeochemical dynamics of Lower Lakes

(ie. fluxes, phytoplankton groups)

• Predict physical, chemical and biological parameters

under various flow scenarios

• Predict resource (nutrients, organic matter) delivery

loads to Coorong under different flow conditions

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ELCOM

Estuary, Lake & Coastal Ocean Model

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Hydrodynamics: velocities, temperature and salinity

CAEDYM

Computational Aquatic Ecosystem Dynamics Model

• Suspended sediment (SS)
• Oxygen (DO)
• Organic nutrients (POM, DOM)
• Inorganic nutrients (NH4, NO3, PO4, SiO2, DIC)
• Heterotrophic bacteria (BAC)
• Phytoplankton (Chl-a/C, internal nutrients, metabolites)
• Higher biology (zooplankton, fish, larvae)
• Benthic biology (macroalgae, clams, seagrasses)
• Pathogens & microbial indicators (crypto, coliforms, viruses)
• Geochemistry (pH, major ions, minerals, metals)
• Sediment diagenesis

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Required data

• Bathymetry
• Inflow/outflows:
• River inflows, water quality
• Barrage outflows
• Tide (if sim mouth)
• Extractions
• Meteorological data:
• Solar radiation; Long-wave Radiation
• Wind speed and direction
• Air temperature & humidity
• WQ parameter data: SOD, nutrient

fluxes

• Phyto assemblage
• Organic Matter
• Validation data
• Temp
• DO
• Nutrients
• Chlorophyll a, cell counts

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Lake Alexandrina - calibration

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Chlorophyll a - capabilities

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Next steps

• Analyse results
• Complete routine monitoring
• Further model calibration
• Model validation
• Identify scenarios
• Run scenarios
• Assess the use of satellite imagery to estimate water quality parameters

within the Lower Murray Lakes

• Primary productivity
• Sediment resuspension
• Use for larger scale measurements than grab samples
• May be incorporated into model

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Conclusions & project outcomes

• Lower Murray Lakes are a modulator of resources
• Outputs will impact on Coorong, Murray Mouth and near-shore

productivity

• Lower Murray Lakes are in a transition state
• Currently unsure where its headed
• More complications ahead
• Drawdown, weir, reflooding (nutrient fluxes, acid sulfate soils), saltwater

inputs

• Model will provide a predictive tool for management
• Impacts of various scenarios
• Impacts of inflows on the lake functioning
• Environmental flows and resources to the Coorong

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