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Estuaries in NSW

Estuarine Water Quality

Acid sulphate soils

Many of the soils of low-lying areas around estuaries, especially in the north of the State, were formed by deposition in shallow estuarine waters. The lower layers, which are normally below the water table, contain high levels of pyrite (iron sulphide) derived from sea water. As long as the soil remains saturated, high pyrite levels are of no consequence. However, any excavation or drainage works which expose the soil to the air allows the pyrite to react with oxygen, producing sulphuric acid. Very low pH results, which also mobilises aluminium from the soil.

The steady leakage of acid and aluminium into an estuary has an adverse affect on the ecosystem, but the effects of sudden flushes caused by floods can be catastrophic. Massive fish kills in the Tweed River in 1987 have been attributed to the effects of acid and aluminium toxicity (Creagh, 1991). It is also suspected that a common fish disease - Epizootic Ulcerative Syndrome (EUS), or Red Spot Disease, is caused by fungal invasion of the fish following exposure to acid water.

Although recognised as a major concern to adjacent fisheries, acid sulphate soils are also detrimental to pasture growth and production from grazing.

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