title: Water Table Dynamics and Biogeochemical Cycling in a Shallow, Variably-Saturated Floodplain.
abstract: Three-dimensional variably saturated flow and multicomponent biogeochemical reactive transport modeling, based on published and newly generated data, is used to better understand the interplay of hydrology, geochemistry, and biology controlling the cycling of carbon, nitrogen, oxygen, iron, sulfur, and uranium in a shallow floodplain. In this system, aerobic respiration generally maintains anoxic groundwater below an oxic vadose zone until seasonal snowmelt-driven water table peaking transports dissolved oxygen (DO) and nitrate from the vadose zone into the alluvial aquifer. The response to this perturbation is localized due to distinct physico-biogeochemical environments and relatively long time scales for transport through the floodplain aquifer and vadose zone. Naturally reduced zones (NRZs) containing sediments higher in organic matter, iron sulfides, and non-crystalline U(IV) rapidly consume DO and nitrate to maintain anoxic conditions, yielding Fe(II) from FeS oxidative dissolution, nitrite from denitrification, and U(VI) from nitrite-promoted U(IV) oxidation. Redox cycling is a key factor for sustaining the observed aquifer behaviors despite continuous oxygen influx and the annual hydrologically induced oxidation event. Depth-dependent activity of fermenters, aerobes, nitrate reducers, sulfate reducers, and chemolithoautotrophs (e.g., oxidizing Fe(II), S compounds, and ammonium) is linked to the presence of DO, which has higher concentrations near the water table.
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Steven B
authors.identifier: 0000-0003-1040-0182
authors.initials: SB
authors.lastname: Yabusaki
authors.affiliation: The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Wilkins
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Yilin
authors.initials: Y
authors.lastname: Fang
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Williams
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Bhavna
authors.initials: B
authors.lastname: Arora
authors.affiliation: Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory , Menlo Park, California 94025, United States.
authors.forename: John
authors.initials: J
authors.lastname: Bargar
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Harry R
authors.initials: HR
authors.lastname: Beller
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Nicholas J
authors.initials: NJ
authors.lastname: Bouskill
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Eoin L
authors.initials: EL
authors.lastname: Brodie
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: John N
authors.initials: JN
authors.lastname: Christensen
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Mark E
authors.initials: ME
authors.lastname: Conrad
authors.affiliation: The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Robert E
authors.initials: RE
authors.lastname: Danczak
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Eric
authors.initials: E
authors.lastname: King
authors.affiliation: The Ohio State University , Columbus, Ohio 43210, United States.
authors.forename: Mohamad R
authors.initials: MR
authors.lastname: Soltanian
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Nicolas F
authors.initials: NF
authors.lastname: Spycher
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Carl I
authors.initials: CI
authors.lastname: Steefel
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Tetsu K
authors.identifier: 0000-0003-0861-6128
authors.initials: TK
authors.lastname: Tokunaga
authors.affiliation: Subsurface Insights , Hanover, New Hampshire 03755, United States.
authors.forename: Roelof
authors.initials: R
authors.lastname: Versteeg
authors.affiliation: Pacific Northwest National Laboratory , Richland, Washington 99354, United States.
authors.forename: Scott R
authors.initials: SR
authors.lastname: Waichler
authors.affiliation: Lawrence Berkeley National Laboratory , Berkeley, California 94720, United States.
authors.forename: Haruko M
authors.initials: HM
authors.lastname: Wainwright
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry; D060587:Groundwater / Q000737:chemistry*; D009566:Nitrates; D010084:Oxidation-Reduction; D013431:Sulfates / Q000737:chemistry; D014501:Uranium / Q000737:chemistry*; D014874:Water Pollutants, Chemical; D014875:Water Pollutants, Radioactive
chemical_list: D009566:Nitrates; D013431:Sulfates; D014874:Water Pollutants, Chemical; D014875:Water Pollutants, Radioactive; D014501:Uranium