title: Biogeochemical mechanisms of selenium exchange between water and sediments in two contrasting lentic environments.
abstract: The biogeochemical mechanisms of Se exchange between water and sediments in two contrasting lentic environments were assessed through examination of Se speciation in the water column, porewater, and sediment. High-resolution (7 mm) vertical profiles of <0.45 μm Se species across the sediment-water interface demonstrate that the behavior of dissolved Se(VI), Se(IV), and organo-Se are closely linked to redox conditions as revealed by porewater profiles of redox-sensitive species (dissolved O2, NO3-, Fe, Mn, SO4(2-), and ΣH2S). At both sites Se(VI) is removed from solution in suboxic near-surface porewaters demonstrating that the sediments are serving as diffusive sinks for Se. X-ray absorption near edge spectroscopy (XANES) of sediments suggests that elemental Se and organo-Se represent the dominant sedimentary sinks for dissolved Se. Dissolved Se(IV) and organo-Se are released to porewaters in the near-surface sediments resulting in the diffusive transport of these species into the water column, where between-site differences in the depths of release can be linked to differences in redox zonation. The presence or absence of emergent vegetation is proposed to present a dominant control on sedimentary redox conditions as well as on the recycling and persistence of reduced Se species in bottom waters.
authors: Lorax Environmental Services Ltd., Vancouver, British Columbia V6J 3H9, Canada. ajm@lorax.ca
authors: Alan J
authors: AJ
authors: Martin
authors: Stephanie
authors: S
authors: Simpson
authors: Skya
authors: S
authors: Fawcett
authors: Cheryl I E
authors: CI
authors: Wiramanaden
authors: Ingrid J
authors: IJ
authors: Pickering
authors: Nelson
authors: N
authors: Belzile
authors: Y-W
authors: YW
authors: Chen
authors: Jacqueline
authors: J
authors: London
authors: Dirk
authors: D
authors: Wallschläger
mesh_terms: D002244:Carbon / Q000032:analysis; D055669:Ecological and Environmental Phenomena; D004777:Environment; D005618:Fresh Water / Q000737:chemistry*; D019015:Geologic Sediments / Q000737:chemistry*; D006863:Hydrogen-Ion Concentration; D009584:Nitrogen / Q000032:analysis; D010084:Oxidation-Reduction; D012643:Selenium / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism; D014874:Water Pollutants, Chemical / Q000032:analysis / Q000737:chemistry* / Q000378:metabolism
chemical_list: D014874:Water Pollutants, Chemical; D002244:Carbon; D012643:Selenium; D009584:Nitrogen