Mobilisation of metals and acidity during reflooding of a wetland containing acid sulfate soils

Abstract

Many wetlands along the River Murray in Australia have been impacted by drought in recent years. The hazards associated with acid sulfate soils (ASS), largely related to acidification and metal release from sulfide oxidation, have only recently been realised. Preliminary data are presented for a study of wetland ASS and waters following reflooding of a wetland where drought-induced soil acidification occurred. A number of trace metals were released during the early stages of refilling and subsequently decreased with dilution. Over time (weeks-months), the soil pH initially increased as alkalinity production occurred (mainly by sulfate reduction), but subsequently decreased. Surface water alkalinity was consumed and the surface waters acidified to pH < 4, and several trace metal concentrations remained high. The study highlights the timescales over which recovery may be necessary and provides critical information for management options in the wetlands.