Mobility and storage of metals, metalloids and trace elements in disturbed acid sulfate soils from a tidal estuary in South Australia

Abstract

In Australia, acid sulfate soils (ASS) are widespread in both coastal and inland settings where they pose environmental hazards from acidification and metal mobilisation. In this study, three saturated soil-sediment profiles from distinct positions in a disturbed tidal ASS landscape were hydrogeochemically characterised. The soil profile geochemical data and surface water chemistry were compared in order to find evidence of metal, metalloid and trace element mobilisation. The results showed that concentrations of Cu, Ni, Pb, Zn, S, Al, Mg and Fe were elevated in the near-surface, oxidised layers of sulfuric materials of the ASS profile and were marginally elevated within nearby hyposulfidic material in circum-neutral stream sediments. Metals and metalloids, including Ni, Zn, Al and Fe, were leached to pore waters in sulfuric materials from which a range of salt efflorescences had precipitated. Acidic drain waters also contained elevated Al, Fe and other major cations and anions, but did not contain detectible concentrations of trace elements. Nearby circumneutral stream waters only contained elevated concentrations of Fe. Leaching of trace metals was greatest at the surface of exposed sulfuric materials where salt efflorescences had formed. Covering sulfuric materials with mulch, soil or water could reduce metal mobilization by limiting salt precipitation at the surface.