Science

More fresh water, no weir: Coorong science review

Ibis chick. (Photo: Kate Brandis)
Monday, 23 November, 2009
Bob Beale

About one-third of the Murray River's natural flow at its lower end is needed to sustain the collapsing ecosystems in the wetlands of the Lower Lakes and Coorong, a new scientific review has found.

The review's key recommendation is for a median target of 3,800 gigalitres (GL) a year - about 600 GL more than at present - to be measured at the tidal barrages built 60 years ago near the river mouth.

This is the first time a volume of water has been identified to provide for the long-term health of the wetlands, which were declared a Ramsar Wetland of International Importance in 1985.

As well, the scientists recommend shelving proposed engineering solutions to the crisis: building a weir to separate the Murray from the Lower Lakes, allowing the lakes to fill with seawater and building a channel between the Coorong and Lake Albert.

Professor Richard Kingsford from the University of NSW, who led the team, says: "History is unfortunately finally catching up and we are seeing one of Australia's iconic wetlands moving rapidly towards a state of ecological collapse as a result of building dams and over-allocating this river."

Another author, Associate Professor Keith Walker of The University of Adelaide, says: "We support some of the South Australian government's initiatives. We believe that new weirs are not a solution, and will hinder rather than help the prospects for recovery. The last thing we need is to repeat past mistakes, dis­­connecting parts of the system with weirs, levees and other structures. It is one of the reasons why the ecological health of the Murray has declined."

The report, Engineering a crisis in a Ramsar wetland: the Coorong, Lower Lakes and Murray Mouth Australia, is critical of the long-term management of the wetlands. It was prepared as an independent assessment of the best available scientific evidence. The team of six scientists from the UNSW Australian Wetlands and Rivers Centre, the University of Adelaide and Flinders University includes leading researchers on the river and its ecology and the report was reviewed in draft stage by other experts in the field.

The report recognises important contributions made by current initiatives, particularly the Australian Government, including the buyback of irrigation water and the new Murray-Darling Basin Authority, and recognises also that current governments have largely inherited the problem. It finds that declining river flows from upstream diversions, caused by drought and over-allocation, and seawater incursions have combined to bring the ecosystem to a state of crisis.

For the first time in 7,000 years, Lake Alexandrina and Lake Albert are below sea level and drying fast, and the habitats of many plants and animals are affected. Waterbirds are in sharp decline, including migratory shorebirds for which Australia has international responsibilities.

"All our modelling of the system shows that increased flows are really the only hope. None of the engineering solutions proposed to date have anywhere near the same ecological benefits" says Dr Rebecca Lester of Flinders University, another of the report's authors.

The survival of at least three freshwater fish species is threatened, and one is possibly locally extinct. Marine and estuarine organisms are invading the lakes as they become more saline. Tubeworms have colonised hard surfaces in Lake Alexandrina, producing heavy, coral-like growths that weigh down and kill freshwater turtles and other animals.

The salinity of the Coorong has increased to such high levels that it can no longer support the plants and fish that were part of the food chain for the spectacular bird populations that have been the hallmark of the region. One proposal that might improve this is to pump hypersaline water to the ocean.

As well, the team questions what it calls a "reactive focus" on acid sulphate soils and its risk management to the exclusion of other ecological issues. The report notes that weirs have been  constructed, or are proposed, across some freshwater creeks to avoid potential problems of acidification. It recognizes that the threat of acidification is real, but may be overstated compared to the impacts of weirs and seawater on the natural freshwater system.

"We believe from our analysis of the data available that a transparent scientific review process needs to assess the confidence with which governments are making decisions based primarily on the potential problem of acid sulfate soils" says Professor Kingsford.

Associate Professor Walker says: "Warnings by scientists over the past 25 years that this crisis was inevitable have gone largely unheeded and we are now all being held to account. It is not a matter for blame, but a call to action. If we are to keep what was once one of the world's most magnificent wetlands, we need to move very quickly. Quite simply, wetlands need water."

For full report: Wet Rivers web site

Media contacts:
Professor Richard Kingsford - mobile 0419 634 215
UNSW Faculty of Science: Bob Beale 0411 705 435