Selenium Redox Reactions and Transport between Ponded Waters and Sediments
Understanding the cycling of trace elements such as selenium in the environment requires information on mass transfer and reactions occurring across boundaries. Selenium partitioning and redox transformations in ponded laboratory sediments was compared with a model based on the transport of Se(VI) and Se(IV) between surface waters and sediment pore waters. Waters containing Se(VI) were ponded over initially nonseleniferous sediment columns. X-ray absorption spectroscopy demonstrated Se reduction to Se(0) in these sediments. Synchrotron X-ray microprobe analyses revealed very high Se concentrations within mil limeters of the sediment surface. Concentrations of Se(VI) and Se(IV) in sediment pore waters were used as time-dependent boundary conditions to model concentrations of these species in overlying pool waters. Two parameters, the mass transfer coefficient and pool Se(VI) apparent reduction rate constant, were optimized. The successful application of mass transfer coefficients in this study resulted fro...