title: The influence of nitrate on selenium in irrigated agricultural groundwater systems.
abstract: Selenium (Se) contamination of groundwater is an environmental concern especially in areas where aquifer systems are underlain by Se-bearing geologic formations such as marine shale. This study examined the influence of nitrate (NO₃) on Se species in irrigated soil and groundwater systems and presents results from field and laboratory studies that further clarify this influence. Inhibition of selenate (SeO₄) reduction in the presence of NO₃ and the oxidation of reduced Se from shale by autotrophic denitrification were investigated. Groundwater sampling from piezometers near an alluvium-shale interface suggests that SeO₄ present in the groundwater was due in part to autotrophic denitrification. Laboratory shale oxidation batch studies indicate that autotrophic denitrification is a major driver in the release of SeO₄ and sulfate. Similar findings occurred for a shale oxidation flow-through column study, with 70 and 31% more reduced Se and S mass, respectively, removed from the shale material in the presence of NO₃ than in its absence. A final laboratory flow-through column test was performed with shallow soil samples to assess the inhibition of SeO₄ reduction in the presence of NO₃, with results suggesting that a concentration of NO₃ of approximately 5 mg L or greater will diminish the reduction of SeO₄. The inclusion of the fate and transport of NO₃ and dissolved oxygen is imperative when studying or simulating the fate and transport of Se species in soil and groundwater systems.
authors.affiliation: Dep. of Civil and Environmental Engineering, colorado State Univ., Fort Collins 80523-1372, USA. rtbailey@engr.colostate.edu
authors.forename: Ryan T
authors.initials: RT
authors.lastname: Bailey
authors.forename: William J
authors.initials: WJ
authors.lastname: Hunter
authors.forename: Timothy K
authors.initials: TK
authors.lastname: Gates
mesh_terms: D057914:Agricultural Irrigation; D003120:Colorado; D055593:Geological Phenomena; D060587:Groundwater / Q000737:chemistry*; D009566:Nitrates / Q000737:chemistry*; D010084:Oxidation-Reduction; D045483:Rivers; D012643:Selenium / Q000737:chemistry*; D013997:Time Factors; D014874:Water Pollutants, Chemical / Q000737:chemistry*
chemical_list: D009566:Nitrates; D014874:Water Pollutants, Chemical; D012643:Selenium