title: Nitrate bioreduction in redox-variable low permeability sediments.
abstract: Lowpermeability zone (LPZ) can play an important role as a sink or secondary source in contaminant transport in groundwater system. This study investigated the rate and end product of nitrate bioreduction in LPZ sediments. The sedimentswere fromthe U.S. Department of Energy's Hanford Site,where nitrate is a groundwater contaminant as a by-product of radionuclide waste discharges. The LPZ at the Hanford site consists of two layerswith an oxidized layer on top and reduced layer below. The oxidized layer is directly in contact with the overlying contaminated aquifer, while the reduced layer is in contact with an uncontaminated aquifer below. The experimental results showed that nitrate bioreduction rate and end-product differed significantly in the sediments. The bioreduction rate in the oxidized sediment was significantly faster than that in the reduced one. A significant amount of N2O was accumulated in the reduced sediment; while in the oxidized sediment, N2O was further reduced to N2. RT-PCR analysis revealed that nosZ, the gene that codes for N2O reductase, was below detection limit in the reduced sediment. Batch experiments and kinetic modeling were performed to provide insights into the role of organic carbon bioavailability, biomass growth, and competition between nitrate and its reducing products for electrons fromelectron donors. The results revealed that it is important to consider sediment redox conditions and functional genes in understanding and modeling nitrate bioreduction in subsurface sediments. The results also implied that LPZ sediments can be important sink of nitrate and a potential secondary source of N2O as a nitrate bioreduction product in groundwater.
authors.affiliation: China University of Geosciences, Wuhan 430074, China; Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Sen
authors.initials: S
authors.lastname: Yan
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Yuanyuan
authors.initials: Y
authors.lastname: Liu
authors.affiliation: China University of Geosciences, Wuhan 430074, China; Pacific Northwest National Laboratory, Richland, WA 99354, USA. Electronic address: chongxuan.liu@pnnl.gov.
authors.forename: Chongxuan
authors.initials: C
authors.lastname: Liu
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Liang
authors.initials: L
authors.lastname: Shi
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Jianying
authors.initials: J
authors.lastname: Shang
authors.affiliation: China University of Geosciences, Wuhan 430074, China; Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Huimei
authors.initials: H
authors.lastname: Shan
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: John
authors.initials: J
authors.lastname: Zachara
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Jim
authors.initials: J
authors.lastname: Fredrickson
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: David
authors.initials: D
authors.lastname: Kennedy
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Charles T
authors.initials: CT
authors.lastname: Resch
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Christopher
authors.initials: C
authors.lastname: Thompson
authors.affiliation: Pacific Northwest National Laboratory, Richland, WA 99354, USA.
authors.forename: Sarah
authors.initials: S
authors.lastname: Fansler
mesh_terms: D001673:Biodegradation, Environmental; D019015:Geologic Sediments / Q000737:chemistry*; D009566:Nitrates / Q000032:analysis*; D009589:Nitrogen Oxides; D010084:Oxidation-Reduction; D010088:Oxidoreductases; D010539:Permeability; D014875:Water Pollutants, Radioactive / Q000032:analysis*
chemical_list: D009566:Nitrates; D009589:Nitrogen Oxides; D014875:Water Pollutants, Radioactive; D010088:Oxidoreductases
keywords: Kinetic model; Low permeability zone; Nitrate bioreduction; Nitrous oxide; Organic carbon speciation; Subsurface redox transitional sediments