Formation and fate of disordered Mackinawite (FeS) in acid sulfate soil landscapes
Coastal lowland acid sulfate soils (CLASS) impact over 8 million ha of valuable land in Australia, and over 24 million ha throughout the world. Poor water quality in CLASS landscapes is a major threat to ecosystem health, agricultural sustainability and fisheries productivity. Research into this problem over the past three decades has focussed largely on pyrite oxidation and the release of acid-sulfate leachate into nearby waterways. However, extreme concentrations of a newly identified sulfide mineral, disordered mackinawite (FeS), exist in many CLASS landscapes. Our research indicates that the formation and fate of sedimentary FeS in floodplain drains and wetlands has a strong influence on water quality in these landscapes. Concentrations of FeS represent a balance between the rates of formation (SO4 reduction and reaction with Fe) and loss (oxidation to Fe(III)/S(0), and conversion to pyrite). The formation of FeS can be viewed in terms of availability of organic matter, SO4 and Fe. Furthermore, the relative ratios of available SO4 and Fe largely regulate the rate of FeS conversion to pyrite. Accumulation of FeS enhances water quality as FeS formation consumes Fe, S and acidity, and can result in the sorption of significant quantities of trace metals. However, these benefits may be short-lived as FeS oxidation (half-time < 1 hr) can cause rapid deoxygenation, followed by delayed acidification and severe trace element release. An improved understanding of the formation and fate of FeS is therefore important to developing appropriate water quality management strategies for CLASS landscapes.
Burton, ED, Bush, RT & Sullivan, LA 2006, 'Formation and fate of disordered Mackinawite (FeS) in acid sulfate soil landscapes', Abstracts and programme: Soil science solving problems : ASSSI-ASPAC-ACMS National Soils Conference, Adelaide, SA, 3-7 December, Australian Society of Soil Science Inc., the Australasian Soil and Plant Analysis Council, in association with the Australian Clay Minerals Society.
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