Acid sulfate soils and acid drainage, Lower Shoalhaven floodplain, New South Wales

An eight-month long investigation is reported of watertable fluctuations and water quality in an area of acid sulphate soils at Jaspers Brush, lower Shoalhaven floodplain, south coast of NSW. Watertable fluctuations were analysed in a backswamp transect across a large main flood mitigation drain to understand groundwater movement and its influence on the severity of acid drainage. As the watertable dropped, groundwater acidity increased rapidly and sulphate, iron and aluminium concentrations in groundwater rose to elevated concentrations. Water quality was also analysed along the length of the main drain studied. The influx of saline creek waters into the drain during high tides was shown to have an acid neutralising effect. Water quality in Broughton Creek was analysed for a month after a minor flood event, with results (mainly lowered pH and elevated aluminium concentrations) highlighting the movement of acid drainage from the floodplain into the creek.