This project will apply selenium (Se) stable isotope ratios as a new tool for understanding the transport and chemical transformations of Se in wetlands. Se contamination poses a threat to wildlife in many wetland areas of the western United States, in fly-ash disposal areas, and in other settings worldwide. The complex chemistry of Se determines the element's mobility and bioavailability, and efforts to understand its long-term cycling and transport in wetlands depend on accurate understanding of chemical transformations there. Previous work by this group suggests that Se isotope ratio measurements can be used as indicators of reduction reactions, which transform Se oxyanions into forms that are less mobile and less bioavailable. The present study will address critical questions arising from that work by performing the first detailed Se isotope field study, at a Se-contaminated wetland at Benton Lake National Wildlife Refuge, Montana. The primary objectives are to determine Se reduction rates using this new technique and constrain the relative importance of reduction by bacteria versus assimilation by plants and algae. The work will involve detailed measurements of Se concentrations, Se isotope ratios, and related geochemical variables in surface water, sediment pore waters, sediment components, and microcosm experiments. Sampling will be timed according to seasonal variations in water management and biogeochemistry. If possible, Se from the various sources will be traced through the system via their isotopic "signatures". The study is designed as a Ph.D. project for a graduate student, who will be trained in environmental geochemistry, hydrogeology, isotope geochemistry and geomicrobiology

National Science Foundation (NSF)
Division of Earth Sciences (EAR)
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Thomas Torgersen
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Geological Survey-Menlo Park
Menlo Park
United States
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