Prediction and management of acidity production and export from acid sulphate soils used for sugar production final report SRDC Project DNR004

Abstract

The experimental design of this project successfully enabled runoff and groundwater drainage flow components to be distinguished in a cane-farming context at Pimpama, southeast Queensland. The majority of acidity exported from the soils of the study area occurred via groundwater flow to drains. Measurements of water composition showed that iron, aluminium and hydrogen ions are major components of total acidity. Iron will also contribute chemical oxygen demand to the receiving waters. Other heavy metals in drainage water were often in excess of ANZECC (2000) water quality guidelines. Mineralogy of the soils at each site was measured and minor differences were detected. Evapotranspiration was found to be the major factor controlling the watertable in these soils. For the Pimpama drainage network groundwater flow to the drains is small compared to surface runoff and evapotranspiration. An analytical model of the hydrological system was developed, based on drainage and evaporation components. A model that included water balance components and an empirical model for acid generation was developed using the Modelmaker software. This was used to show how changing drainage design would affect acid export and periods of waterlogging on soils. A copy of this model is included in this report.