title: Predicting Redox Conditions in Groundwater at a Regional Scale.
abstract: Defining the oxic-suboxic interface is often critical for determining pathways for nitrate transport in groundwater and to streams at the local scale. Defining this interface on a regional scale is complicated by the spatial variability of reaction rates. The probability of oxic groundwater in the Chesapeake Bay watershed was predicted by relating dissolved O2 concentrations in groundwater samples to indicators of residence time and/or electron donor availability using logistic regression. Variables that describe surficial geology, position in the flow system, and soil drainage were important predictors of oxic water. The probability of encountering oxic groundwater at a 30 m depth and the depth to the bottom of the oxic layer were predicted for the Chesapeake Bay watershed. The influence of depth to the bottom of the oxic layer on stream nitrate concentrations and time lags (i.e., time period between land application of nitrogen and its effect on streams) are illustrated using model simulations for hypothetical basins. Regional maps of the probability of oxic groundwater should prove useful as indicators of groundwater susceptibility and stream susceptibility to contaminant sources derived from groundwater.
authors.affiliation: †USGS, 2130 SW Fifth Avenue, Portland, Oregon 97201, United States.
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Tesoriero
authors.affiliation: ‡USGS, 3916 Sunset Ridge Road, Raleigh, North Carolina 27607, United States.
authors.forename: Silvia
authors.initials: S
authors.lastname: Terziotti
authors.affiliation: §Illinois State Water Survey, 2204 Griffith Drive, M/C 674, Champaign, Illinois 61820, United States.
authors.forename: Daniel B
authors.initials: DB
authors.lastname: Abrams
mesh_terms: D004784:Environmental Monitoring / Q000379:methods*; D005844:Geology; D060587:Groundwater / Q000032:analysis / Q000737:chemistry*; D008396:Maryland; D008962:Models, Theoretical; D009566:Nitrates / Q000032:analysis; D009584:Nitrogen / Q000032:analysis; D010084:Oxidation-Reduction; D045483:Rivers; D012987:Soil; D014768:Virginia
chemical_list: D009566:Nitrates; D012987:Soil; D009584:Nitrogen