Acid Sulfate Wetlands in the Nsw Coast, Australia: Chemical Characteristics and Their Implications for Environmental Remediation

Abstract. Acid sulfate wetlands are widespread in the New South Wales (NSW) coast, Australia. Acid sulfate soils have caused severe environmental problems in the area with land scalding, accompanied by the discharge of highly acidic drain water into estuarine waterways being the worst-case scenario in these landscapes. The investigated acid sulfate scalds are characterized by an extremely acidified topsoil layer (0–0.6 m). In general, the scalded acid sulfate soils have less organic matter and soluble phosphorus, and a greater salinity, soluble acidity, soluble Al, Mn and Zn concentrations, compared to the adjacent non-scalded acid sulfate soils. These are the most likely soil constraints for re-vegetation of the scalded lands and treatment will require acid neutralization (e.g. application of lime) and addition of P fertilizers to reduce the soluble acidity, immobilize soluble Al, Mn and Zn, and increase P availability. The evidence also shows that the higher soluble Al concentration in the scalded soils, relative to the non-scalded soils, is associated with their lower organic matter content. Hence, rehabilitation of these scalded lands should involve the addition of organic matter to reduce soluble Al concentrations; this may also help reduce Mn and Zn toxicity, and salinity. Water quality monitoring in the estuarine waterways draining the acid sulfate wetlands shows that acidic flows (pH < 4.5) of several months occurred intermittently. This may be attributed to the hydrolysis of Fe after the oxidation of Fe that is exported into the creek from acid sulfate soils through artificial drainage network. It is hypothesized that Fe is being generated by biological iron reduction, which consumes H and thereby drives the conversion of retained acids to soluble acids. This allows the release of retained acids and subsequently the translocation of acids from soils to the adjacent waterway. Because many acid sulfate soils in the NSW coast contain large amounts of existing acidity, flooding or liming to eliminate acidity is either ineffective or cost-prohibitive. Treatment of the acidic water appears to be a more cost-effective strategy for managing acid sulfate wetlands in the NSW coast.