Accumulation of schwertmannite impact on water quality in acid sulfate soil landscapes

Schwertmannite [Fe8O8(OH)6SO4] has recently been found to be the dominant mineral of iron precipitate accumulations from surface environments surrounding waterways (e.g. the sides of drains and in litter layers) in acid sulfate soil landscapes in eastern Australia. In this study the yellowish-brown, orange-brown, and reddishbrown coatings on macropores (such as channels and planar pores) in 21 soil layers from 10 sites all located within severely-acidified acid sulfate soil landscapes in eastern Australia, were isolated and examined by both differential XRD and SEM-EDS to determine if schwertmannite was present. Schwertmannite was detected in these coatings in 14 of these 21 soil layers. The finding that schwertmannite is common in the acid sulfate soil materials within severely-acidified acid sulfate soil landscapes has implications for the behaviour of these soil materials and in particular how these soil materials affect water quality in these landscapes. The results presented here indicates that the accumulation of schwertmannite as, for example macropore coatings, may exert a strong influence on the geochemistry of waters within severely-acidified acid sulfate soil landscapes. The results of this study indicate that a better understanding of the role of iron precipitate minerals (such as schwertmannite) in regulating the quality of surficial waters leaving acid soil landscapes will provide a much better understanding of processes governing fluxes of acidity etc. in these landscapes, and provide better tools for both risk assessment and management.