Acid sulfate soils
Acid sulfate soils naturally occur in coastal and fresh water areas, including the Coorong and Lower Lakes region, where there are large amounts of sulfate and organic material in the water.
As long as the soils are covered by water they are harmless to the environment. But if water levels drop and the soils are exposed to air, they react with oxygen to form sulfuric acid (the same acid as in a car battery) and can release heavy metals, such as manganese, aluminium, and arsenic from the soil.
Natural cycles of flooding and drying once flushed the small amounts of acid formed by the soils from the system. Controlling the River Murray's flow has resulted in a build up of acid sulfate soils.
When water levels in the region were at their lowest in March 2009, up to 20,000 hectares of acid sulfate soils were exposed in the Lower Lakes region.
The main way to prevent acidification is to ensure acid sulfate soils are kept wet and not exposed to air. Managing water levels in the Lower Lakes is one way that acid sulfate soils are being addressed.
Bacteria in the soil can reverse the process of acid sulfate soils forming sulfuric acid and help return the contaminated environments to a healthy state. This is called bioremediation. The bacteria use iron and organic matter, as well as sulfate in the acid to do this.
Plants can provide organic matter and iron to the soil, which are needed by the bacteria, so planting vegetation can help bioremediation take place. If the water is too acidic then the bacteria will struggle. Adding finely ground limestone can neutralise acid released from exposed soils, also helping bioremediation to take place.
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Further resources:
- Acid sulfate soil assessment in Finniss River, Currency Creek, Black Swamp and Goolwa Channel
- Management of acid sulfate soils in the Lower Murray Lakes (572kb pdf)
- Preliminary assessment of acid sulfate soil materials in Currency Creek, Finniss River, Tookayerta Creek and Black Swamp region
- Management options for acid sulfate soils in the Lower Murray Lakes - preliminary assessment of treatment options (703kb pdf)
- Management options for acid sulfate soils in the Lower Murray Lakes - preliminary assessment of prevention, control and treatment options (2.62mb pdf)
- Acid sulfate soils in subaqueous, waterlogged and drained soil environments of nine wetlands below Blanchetown (Lock 1): properties, distribution, genesis, risks and management
- Acid, metal and nutrient mobilisation following rewetting of acid sulfate soils in Lower Murray
- Community monitoring of Acid Sulfate Soils in the Lower Lakes, South Australia: Four surveys between August 2009 and June 2010
- Monitoring and Assessment of Reflooded Acid Sulfate Soil Materials in Currency Creek and Finniss River Region, South Australia
- Management of Acid Sulfate Soils along the River Murray in SA
- Acid sulfate soils in the Murray-Darling Basin May 2011
- ASSAY - Acid Sulfate Soils newsletter.
