Biogeochemical mechanisms of arsenic mobilization in Haiwee Reservoir sediments

摘要: Naturally-occurring arsenic (As) in the Los Angeles Aqueduct, a major drinking water source for City of Angeles, is removed by precipitating an amorphous iron (Fe) oxyhydroxide floc aqueduct waters. The via sedimentation at Haiwee Reservoir, where Fe- and As-rich sediments provide unique field site studying mechanisms As mobilization to sediment porewater. A gel probe equilibrium sampler was developed measure porewater concentrations sorption behavior Reservoir sediments. gels consisted polyacrylamide polymer matrix were 92% water. Undoped (clear gels) used determine composition, hydrous ferric oxide (HFO)-doped situ adsorption chemistry. Gels placed plastic holder, covered with membrane filter, allowed equilibrate porewaters. This study combined data from samplers, gravity cores, laboratory studies, elucidate biogeochemical processes governing partitioning between solid aqueous phases. device observation effect chemistry on adsorption. Arsenic reduced As(V) As(III) upper layers sediment, but change redox state did not cause be mobilized into occurred during reductive dissolution Fe(III) oxides. Arsenate reduction probably microbially mediated. onto HFO-doped inhibited intermediate depths, due dissolved carbonate produced organic carbon mineralization. this region may primarily controlled chemistry, rather than availability. Deeper column, phase partially transformed green rust, possibly sequestering carbonate. In region, phosphate. accumulation lack available surface sites sediment. phases depends driven diagenetic processes, as well composition.