What is the future for the Lower Lakes

The Environment Institute
Where ideas grow

Dr Kane Aldridge
What is the future for the Lower Lakes?


Acknowledgements

• Justin Brookes
• George Ganf
• David Paton
• Matt Hipsey
• Dominic Skinner
• Alex Payne

Life Impact The University of Adelaide


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



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



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.”



The distant past: a ‘fresh’ system
(Adapted by John Tibby from Fluin et al., 2007)


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



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
1975 1980 1985 1990 1995 2000 2005



Connectivity:
“Boom”



Connectivity:
“Bust”



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



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



The not-so-distant past



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




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



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



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



The current situation
• ↓ annual flow at
Murray Mouth by
61%

• ↓ % of time that
flows to sea
– Past – 1%
– Current – 40%

(CSIRO, 2008)



The drought



Over allocation + drought + barrages


Lake Alexandrina

Ewe Island Barrage

Coorong

Photo: Russell Seaman


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



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



Acid sulfate soils

Source: Fitzpatrick et al. 2008


The short-term future: disconnection



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



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



If biodiversity and resilience are
dependant upon connectivity, will
the long-term vision be
compromised by short-term crisis
management?



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



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



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?



Future mitigation of ASS?



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


Where ideas grow

Next Seminar: 21 August
Professor Randy Stringer
Agrarian Landscapes, the Environment and World
Heritage Sites: Why our region should apply

What is the future for the Lower Lakes

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