Christopher T Green, Ph.D.
Christopher Green is a Research Hydrologist with the USGS Water Resources Mission Area.
Research Interests
- Flow and reactive transport in complex geological media
- Nitrogen cycling and fluxes in groundwater in agricultural areas
- Flow and solute transport in the unsaturated zone
- Gas transport in the unsaturated zone
- Effects of biofuels crops on groundwater quality
Science and Products
Filter Total Items: 45
Field-scale sulfur hexafluoride tracer experiment to understand long distance gas transport in the deep unsaturated zone
A gas-tracer test in a deep arid unsaturated zone demonstrates that standard estimates of effective diffusivity from sediment properties allow a reasonable first-cut assessment of gas contaminant transport. Apparent anomalies in historic transport behavior at this and other waste disposal sites may result from factors other than nonreactive gas transport properties.
A natural gradient SF6 tracer e
Authors
Michelle Ann Walvoord, Brian J. Andraski, Christopher T. Green, David A. Stonestrom, Robert G. Striegl
Linking aquifer spatial properties and non-Fickian transport in mobile-immobile like alluvial settings
Time-nonlocal transport models can describe non-Fickian diffusion observed in geological media, but the physical meaning of parameters can be ambiguous, and most applications are limited to curve-fitting. This study explores methods for predicting the parameters of a temporally tempered Lévy motion (TTLM) model for transient sub-diffusion in mobile–immobile like alluvial settings represented by hi
Authors
Yong Zhang, Christopher T. Green, Boris Baeumer
Decadal surface water quality trends under variable climate, land use, and hydrogeochemical setting in Iowa, USA
Understanding how nitrogen fluxes respond to changes in agriculture and climate is important for improving water quality. In the midwestern United States, expansion of corn cropping for ethanol production led to increasing N application rates in the 2000s during a period of extreme variability of annual precipitation. To examine the effects of these changes, surface water quality was analyzed in 1
Authors
Christopher T. Green, Barbara A. Bekins, Stephen J. Kalkhoff, Robert M. Hirsch, Lixia Liao, Kimberlee K. Barnes
Effect of correlated observation error on parameters, predictions, and uncertainty
Correlations among observation errors are typically omitted when calculating observation weights for model calibration by inverse methods. We explore the effects of omitting these correlations on estimates of parameters, predictions, and uncertainties. First, we develop a new analytical expression for the difference in parameter variance estimated with and without error correlations for a simple o
Authors
Claire R. Tiedeman, Christopher T. Green
The impact of medium architecture of alluvial settings on non-Fickian transport
The influence of heterogeneous architecture of alluvial aquifers on non-Fickian transport is explored using the Monte Carlo approach. More than two thousand high-resolution hydrofacies models representing seven groups of alluvial settings are built to test the effects of varying facies proportions, mean length and its anisotropy ratio, juxtapositional tendencies, and sub-facies heterogeneity. Resu
Authors
Yong Zhang, Christopher T. Green, Graham E. Fogg
Factors controlling nitrate fluxes in groundwater in agricultural areas
The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO3-, N2 from denitrification, O2, Cl-, and environmental tracers of groundwate
Authors
Lixia Liao, Christopher T. Green, Barbara A. Bekins, J.K. Böhlke
Relations of hydrogeologic factors, groundwater reduction-oxidation conditions, and temporal and spatial distributions of nitrate, Central-Eastside San Joaquin Valley, California, USA
In a 2,700-km 2 area in the eastern San Joaquin Valley, California (USA), data from multiple sources were used to determine interrelations among hydrogeologic factors, reduction-oxidation (redox) conditions, and temporal and spatial distributions of nitrate (NO 3), a widely detected groundwater contaminant. Groundwater is predominantly modern, or mixtures of modern water, with detectable NO 3 and
Authors
Matthew K. Landon, Christopher T. Green, Kenneth Belitz, Michael J. Singleton, Bradley K. Esser
Inverse modeling with RZWQM2 to predict water quality
This chapter presents guidelines for autocalibration of the Root Zone Water Quality Model (RZWQM2) by inverse modeling using PEST parameter estimation software (Doherty, 2010). Two sites with diverse climate and management were considered for simulation of N losses by leaching and in drain flow: an almond [Prunus dulcis (Mill.) D.A. Webb] orchard in the San Joaquin Valley, California and the Walnu
Authors
Bernard T. Nolan, Robert W. Malone, Liwang Ma, Christopher T. Green, Michael N. Fienen, Dan B. Jaynes
The fate and transport of nitrate in shallow groundwater in northwestern Mississippi, USA
Agricultural contamination of groundwater in northwestern Mississippi, USA, has not been studied extensively, and subsurface fluxes of agricultural chemicals have been presumed minimal. To determine the factors controlling transport of nitrate-N into the Mississippi River Valley alluvial aquifer, a study was conducted from 2006 to 2008 to estimate fluxes of water and solutes for a site in the Bogu
Authors
Heather L. Welch, Christopher T. Green, Richard H. Coupe
Unintended consequences of biofuels production?The effects of large-scale crop conversion on water quality and quantity
In the search for renewable fuel alternatives, biofuels have gained strong political momentum. In the last decade, extensive mandates, policies, and subsidies have been adopted to foster the development of a biofuels industry in the United States. The Biofuels Initiative in the Mississippi Delta resulted in a 47-percent decrease in cotton acreage with a concurrent 288-percent increase in corn acre
Authors
Heather L. Welch, Christopher T. Green, Richard A. Rebich, Jeannie R.B. Barlow, Matthew B. Hicks
Sustainability of natural attenuation of nitrate in agricultural aquifers
Increased concentrations of nitrate in groundwater in agricultural areas, coinciding with increased use of chemical and organic fertilizers, have raised concern because of risks to environmental and human health. At some sites, these problems are mitigated by natural attenuation of nitrate as a result of microbially mediated reactions. Results from U.S. Geological Survey (USGS) research under the
Authors
Christopher T. Green, Barbara A. Bekins
Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer
Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field‐scale (apparent) estimated reaction rates and isotopic fractionations and local‐scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and fie
Authors
Christopher T. Green, John K. Böhlke, Barbara A. Bekins, Steven P. Phillips
Science and Products
Filter Total Items: 45
Field-scale sulfur hexafluoride tracer experiment to understand long distance gas transport in the deep unsaturated zone
A gas-tracer test in a deep arid unsaturated zone demonstrates that standard estimates of effective diffusivity from sediment properties allow a reasonable first-cut assessment of gas contaminant transport. Apparent anomalies in historic transport behavior at this and other waste disposal sites may result from factors other than nonreactive gas transport properties.
A natural gradient SF6 tracer e
Authors
Michelle Ann Walvoord, Brian J. Andraski, Christopher T. Green, David A. Stonestrom, Robert G. Striegl
Linking aquifer spatial properties and non-Fickian transport in mobile-immobile like alluvial settings
Time-nonlocal transport models can describe non-Fickian diffusion observed in geological media, but the physical meaning of parameters can be ambiguous, and most applications are limited to curve-fitting. This study explores methods for predicting the parameters of a temporally tempered Lévy motion (TTLM) model for transient sub-diffusion in mobile–immobile like alluvial settings represented by hi
Authors
Yong Zhang, Christopher T. Green, Boris Baeumer
Decadal surface water quality trends under variable climate, land use, and hydrogeochemical setting in Iowa, USA
Understanding how nitrogen fluxes respond to changes in agriculture and climate is important for improving water quality. In the midwestern United States, expansion of corn cropping for ethanol production led to increasing N application rates in the 2000s during a period of extreme variability of annual precipitation. To examine the effects of these changes, surface water quality was analyzed in 1
Authors
Christopher T. Green, Barbara A. Bekins, Stephen J. Kalkhoff, Robert M. Hirsch, Lixia Liao, Kimberlee K. Barnes
Effect of correlated observation error on parameters, predictions, and uncertainty
Correlations among observation errors are typically omitted when calculating observation weights for model calibration by inverse methods. We explore the effects of omitting these correlations on estimates of parameters, predictions, and uncertainties. First, we develop a new analytical expression for the difference in parameter variance estimated with and without error correlations for a simple o
Authors
Claire R. Tiedeman, Christopher T. Green
The impact of medium architecture of alluvial settings on non-Fickian transport
The influence of heterogeneous architecture of alluvial aquifers on non-Fickian transport is explored using the Monte Carlo approach. More than two thousand high-resolution hydrofacies models representing seven groups of alluvial settings are built to test the effects of varying facies proportions, mean length and its anisotropy ratio, juxtapositional tendencies, and sub-facies heterogeneity. Resu
Authors
Yong Zhang, Christopher T. Green, Graham E. Fogg
Factors controlling nitrate fluxes in groundwater in agricultural areas
The impact of agricultural chemicals on groundwater quality depends on the interactions of biogeochemical and hydrologic factors. To identify key processes affecting distribution of agricultural nitrate in groundwater, a parsimonious transport model was applied at 14 sites across the U.S. Simulated vertical profiles of NO3-, N2 from denitrification, O2, Cl-, and environmental tracers of groundwate
Authors
Lixia Liao, Christopher T. Green, Barbara A. Bekins, J.K. Böhlke
Relations of hydrogeologic factors, groundwater reduction-oxidation conditions, and temporal and spatial distributions of nitrate, Central-Eastside San Joaquin Valley, California, USA
In a 2,700-km 2 area in the eastern San Joaquin Valley, California (USA), data from multiple sources were used to determine interrelations among hydrogeologic factors, reduction-oxidation (redox) conditions, and temporal and spatial distributions of nitrate (NO 3), a widely detected groundwater contaminant. Groundwater is predominantly modern, or mixtures of modern water, with detectable NO 3 and
Authors
Matthew K. Landon, Christopher T. Green, Kenneth Belitz, Michael J. Singleton, Bradley K. Esser
Inverse modeling with RZWQM2 to predict water quality
This chapter presents guidelines for autocalibration of the Root Zone Water Quality Model (RZWQM2) by inverse modeling using PEST parameter estimation software (Doherty, 2010). Two sites with diverse climate and management were considered for simulation of N losses by leaching and in drain flow: an almond [Prunus dulcis (Mill.) D.A. Webb] orchard in the San Joaquin Valley, California and the Walnu
Authors
Bernard T. Nolan, Robert W. Malone, Liwang Ma, Christopher T. Green, Michael N. Fienen, Dan B. Jaynes
The fate and transport of nitrate in shallow groundwater in northwestern Mississippi, USA
Agricultural contamination of groundwater in northwestern Mississippi, USA, has not been studied extensively, and subsurface fluxes of agricultural chemicals have been presumed minimal. To determine the factors controlling transport of nitrate-N into the Mississippi River Valley alluvial aquifer, a study was conducted from 2006 to 2008 to estimate fluxes of water and solutes for a site in the Bogu
Authors
Heather L. Welch, Christopher T. Green, Richard H. Coupe
Unintended consequences of biofuels production?The effects of large-scale crop conversion on water quality and quantity
In the search for renewable fuel alternatives, biofuels have gained strong political momentum. In the last decade, extensive mandates, policies, and subsidies have been adopted to foster the development of a biofuels industry in the United States. The Biofuels Initiative in the Mississippi Delta resulted in a 47-percent decrease in cotton acreage with a concurrent 288-percent increase in corn acre
Authors
Heather L. Welch, Christopher T. Green, Richard A. Rebich, Jeannie R.B. Barlow, Matthew B. Hicks
Sustainability of natural attenuation of nitrate in agricultural aquifers
Increased concentrations of nitrate in groundwater in agricultural areas, coinciding with increased use of chemical and organic fertilizers, have raised concern because of risks to environmental and human health. At some sites, these problems are mitigated by natural attenuation of nitrate as a result of microbially mediated reactions. Results from U.S. Geological Survey (USGS) research under the
Authors
Christopher T. Green, Barbara A. Bekins
Mixing effects on apparent reaction rates and isotope fractionation during denitrification in a heterogeneous aquifer
Gradients in contaminant concentrations and isotopic compositions commonly are used to derive reaction parameters for natural attenuation in aquifers. Differences between field‐scale (apparent) estimated reaction rates and isotopic fractionations and local‐scale (intrinsic) effects are poorly understood for complex natural systems. For a heterogeneous alluvial fan aquifer, numerical models and fie
Authors
Christopher T. Green, John K. Böhlke, Barbara A. Bekins, Steven P. Phillips