USING WATER QUALITY AND SEDIMENT CHARACTERISTICS TO IMPROVE MANAGEMENT OF ACID SULFATE SOILS AND DRAINAGE

Increased acidic and heavy metal discharges from Acid Sulfate Soils (ASS) on estuary floodplains can occur with inappropriate land use practices. While drainage may not cause the large stores of actual acidity that exist in ASS on the floodplain, injudicious land and drainage management enables the discharge of this acidity and associated metals to the estuary. There is a concern that drain cleaning and maintenance operations contribute to the acidification and deoxygenation of coastal river systems. With ASS characterising 50% of the sugarcane-growing area of NSW, it is imperative that their management is evaluated for their effectiveness in reducing acidic discharge in drain waters from ASS. This involves establishing hydrological responses to rainfall and evaporation, determining sources of acidic discharge and measuring the degree of acidity export from various land uses. Our ongoing research aims to investigate and verify sugar industry best practice techniques for managing ASS and to develop optimal land and drainage management techniques to greatly reduce acidic discharge from ASS under sugarcane. The outcome is an overall improvement in estuarine water quality, both on- and off-farm, with the implementation of a minimum disturbance regime for drain cleaning and maintenance. This paper will compare wet and dry season drain water quality and sediment characteristics in different catchments across the sugarcane growing areas in the Tweed River valley.