The occurrence of inland acid sulphate soils in the floodplain wetlands of the Murray-Darling Basin, Australia, identified using a simplified incubation method

From 2006 to 2010, low water levels resulted in the drying of previously submerged inland acid sulphate soils (IASS) in wetlands of the Murray-Darling Basin (MDB). The potential for widespread severe acidification resulting from the oxidation of pyrite in these wetland soils triggered a basin-wide study to assess the occurrence and risks posed by IASS material in the floodplain wetlands of the MDB. The results of pH measurements before and following soil incubation from more than 7200 samples (representing ca. 2500 profiles from 1055 georeferenced wetlands) were used to assess the potential occurrence of sulphuric and sulphidic material in IASS across the MDB. Their occurrence was investigated on a regional basis by dividing the MDB into 13 geographical regions whose boundaries roughly follow hydrological catchment boundaries. A total of 238 floodplain wetlands, representing 23% of the total wetlands assessed, were found to contain soils that became ultra-acidic (pH < 4) when oxidized and therefore present a severe acidification hazard. These soils, the majority of which are likely to be IASS materials, were found in 11 of the 13 geographical regions. Among the 11 geographical regions likely containing IASS materials, the proportion of wetlands that presented an acidification hazard varied between 2 and 52% of those assessed. The geographical regions found to present the greatest acidification hazard were in the southern MDB, downstream of the Murray-Darling confluence, and in catchments on the southern side of the Murray River channel in Victoria. This study provided policy makers with a valuable screening tool, which helped them to identify priority wetlands and regions that required more detailed IASS investigations.