Collaborative Research: Field Investigation of Se Oxvanion Reduction and Se Sources in Wetlands: Application of Se Isotopes

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0003381JohnsonThis project will apply selenium (Se) stable isotope ratios as a new toolfor understanding the transport and chemical transformations of Se inwetlands. Se contamination poses a threat to wildlife in many wetlandareas of the western United States, in fly-ash disposal areas, and in othersettings worldwide. The complex chemistry of Se determines the element'smobility and bioavailability, and efforts to understand its long-termcycling and transport in wetlands depend on accurate understanding ofchemical transformations there.Previous work by this group suggests that Se isotope ratio measurements canbe used as indicators of reduction reactions, which transform Se oxyanionsinto forms that are less mobile and less bioavailable. The present studywill address critical questions arising from that work by performing thefirst detailed Se isotope field study, at a Se-contaminated wetland atBenton Lake National Wildlife Refuge, Montana. The primary objectives areto determine Se reduction rates using this new technique and constrain therelative importance of reduction by bacteria versus assimilation by plantsand algae. The work will involve detailed measurements of Seconcentrations, Se isotope ratios, and related geochemical variables insurface water, sediment pore waters, sediment components, and microcosmexperiments. Sampling will be timed according to seasonal variations inwater management and biogeochemistry. If possible, Se from the varioussources will be traced through the system via their isotopic "signatures".The study is designed as a Ph.D. project for a graduate student, who willbe trained in environmental geochemistry, hydrogeology, isotopegeochemistry and geomicrobiology.