Evaluation of Surface and Groundwater Management Strategies for Drained Sulfidic Soil using Numerical Models

The effective management of acid sulfate soils is a major issue for many coastal regions in Australia. Simulations were conducted to evaluate 4 different water management strategies that could be applied to agricultural land on the south coast of New South Wales, Australia, to minimise acid generation from acid sulfate soils. The water management strategies are compared with the existing extensively drained situation which generates and discharges large quantities of acidic pyrite oxidation products. The 4 water management strategies include elevated drain water levels using a weir, 25 mm irrigation on a 7- or 14- day cycle, and elevated drain water levels with irrigation. All of these strategies were designed to minimise the generation of acid by reducing the transport of oxygen to the sulfidic soil. Simulations were conducted for weather and site conditions experienced during a 12-month period starting in July 1997. Model simulations showed that maintenance of elevated drain water levels using a weir in the drain significantly reduced the amount of acid generated by 75% and 57%, at 10 and 90 m distance from the drain, respectively, by comparison with the existing drained state. The addition of 25 mm irrigation on a 14-day cycle to the weir simulation reduced the oxidation of pyrite by a further 1–2%. Application of irrigation only on a 7-day cycle also reduced the acid generated by 89% and 94% at 10 and 90 m distance from the drain, respectively, by comparison with the existing drained state. Irrigation on a 14-day cycle was not as successful in reducing pyrite oxidation as either the 7-day irrigation or weir strategies. Evaluation of the 4 water management options showed that significant improvements can be made with respect to the amount of acid generated by relatively simple and cost-effective land management practices