Floodplain hydrology, acid discharge and change in water quality associated with a drained acid sulfate soil

A two-year study of the relationships between water chemistry, hydrology an d climatology in areas of acid sulfate soils has demonstrated that discharg e of sulfuric acid to estuaries is not dependent solely on the magnitude of a rainfall event. Large rain events did not always produce significant cha nges to water chemistry, and small rain events could produce large changes if the prevailing conditions were suitable. The magnitude of changes to est uarine waters was found to be dependent on the position of the watertable, and therefore the available soil pore space, and the store of acidic water in floodgated drains at the time of rainfall. These results have significan ce for predicting the discharge of acid drainage to estuarine environments and the possible impacts on aquatic organisms. A water balance equation, wh ich estimated acid discharge to surface waters as high as 317 t of H2SO4 in one month, can be used to predict monthly discharges for rain events of va rying magnitude if prevailing weather conditions are known.