Consequences of climate-induced redox oscillations on iron, sulfur, and contaminant geochemistry in freshwater re-flooded acid sulfate soil wetlands

Consequences of climate-induced redox oscillations on iron, sulfur, and contaminant geochemistry in freshwater re-flooded acid sulfate soil wetlands.

Dr. Niloofar Karimian Faculty of Science and Engineering Southern Cross University, Lismore, Australia

A complex interplay between hydrology, redox conditions and iron (Fe) and sulfur (S) mineralogy leads to diverse reactions that determine the geochemical behaviour of contaminants and water quality in acid sulfate soil (ASS) wetlands. Acid sulfate soils are soils and sediments containing elevated concentrations of Fe sulfides or reaction products resulting from oxidation of these sulfidic materials (e.g. acidity and secondary Fe(III)-containing minerals). Many of the iron minerals that commonly occur in ASS environments are both metastable and capable of being potent scavengers for toxic trace metals and metalloids under oxidising acidic conditions. Some trace metals and metalloids (such as arsenic (As) and antimony (Sb)) may have a large impact on environmental quality. Therefore, a sound understanding of metastable host-mineral phases and the corresponding behaviour of associated trace metal/metalloid contaminants under fluctuating redox conditions is essential for ASS wetlands management.

This talk will present some novel aspects of the geochemical cycling of Fe, S and trace metal/metalloids (with the specific focus on As and Sb) in freshwater re-flooded ASS wetlands using a wide range of advanced analytical techniques including X-ray absorption spectroscopy (XAS). A major focus will be made on improving our understanding of the potential effects of seasonal redox oscillations on Fe and S mineralogy in these wetlands and exploring the consequences for mobility and speciation of As and Sb. There is a need for improved interpretation of the important processes and pathways, which are likely to occur in conditions relevant to ASS environmental settings under fluctuating redox conditions in order to better predict prospective environmental outcomes and choose optimal management strategies.