Gregory E Schwarz
Gregory Schwarz is an Economist with the USGS Water Resources Mission Area.
Science and Products
Filter Total Items: 66
Estimates of long-term mean daily streamflow and annual nutrient and suspended-sediment loads considered for use in regional SPARROW models of the Conterminous United States, 2012 base year
Streamflow, nutrient, and sediment concentration data needed to estimate long-term mean daily streamflow and annual constituent loads were compiled from Federal, State, Tribal, and regional agencies, universities, and nongovernmental organizations. The streamflow and loads are used to develop Spatially Referenced Regressions on Watershed Attributes (SPARROW) models. SPARROW models help describe th
Authors
David A. Saad, Gregory E. Schwarz, Denise M. Argue, David W. Anning, Scott A. Ator, Anne B. Hoos, Stephen D. Preston, Dale M. Robertson, Daniel Wise
Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012
Understanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially-referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary inputs and
Authors
Scott Ator, Ana M. Garcia, Gregory E. Schwarz, Joel Blomquist, Andrew Sekellick
Adapting a regional water-quality model for local application: A case study for Tennessee, USA
We evaluated whether SPAtially Referenced Regression On Watershed attributes (SPARROW) models calibrated for two adjacent USA regions could be applied at the local scale to support management decisions for streams in Tennessee. Nutrient-source apportionment of load is important for this local-scale application and demands careful consideration of uncertainty in the calibrated coefficients. We used
Authors
Anne B. Hoos, Sherry H. Wang, Gregory E. Schwarz
Catchment-level estimates of nitrogen and phosphorus agricultural use from commercial fertilizer sales for the conterminous United States, 2012
Nutrient inputs from commercial agricultural fertilizer, particularly nitrogen and phosphorus, are important factors contributing to the degradation of surface-water quality and the alteration of aquatic ecosystems. Despite this importance, information about the application of fertilizer to agricultural land is not available in a consistent manner across the United States at a scale useful for reg
Authors
Jana S. Stewart, Gregory E. Schwarz, John W. Brakebill, Stephen D. Preston
The role of baseflow in dissolved solids delivery to streams in the Upper Colorado River Basin
Salinity has a major effect on water users in the Colorado River Basin, estimated to cause almost $300 million per year in economic damages. The Colorado River Basin Salinity Control Program implements and manages projects to reduce salinity loads, investing millions of dollars per year in irrigation upgrades, canal projects, and other mitigation strategies. To inform and improve mitigation effort
Authors
Christine Rumsey, Matthew P. Miller, Gregory E. Schwarz, Robert M. Hirsch, David D. Susong
How hydrologic connectivity regulates water quality in river corridors
Downstream flow in rivers is repeatedly delayed by hydrologic exchange with off‐channel storage zones where biogeochemical processing occurs. We present a dimensionless metric that quantifies river connectivity as the balance between downstream flow and the exchange of water with the bed, banks, and floodplains. The degree of connectivity directly influences downstream water quality — too little c
Authors
Judson Harvey, Jesus Gomez-Velez, Noah Schmadel, Durelle Scott, Elizabeth W. Boyer, Richard Alexander, Ken Eng, Heather E. Golden, Albert Kettner, Christopher Konrad, Richard Moore, Jim Pizzuto, Gregory E. Schwarz, Chris Soulsby, Jay Choi
Thresholds of lake and reservoir connectivity in river networks control nitrogen removal
Lakes, reservoirs, and other ponded waters are ubiquitous features of the aquatic landscape, yet their cumulative role in nitrogen removal in large river basins is often unclear. Here we use predictive modeling, together with comprehensive river water quality, land use, and hydrography datasets, to examine and explain the influences of more than 18,000 ponded waters on nitrogen removal through riv
Authors
Noah M. Schmadel, Judson Harvey, Richard Alexander, Gregory E. Schwarz, Richard Moore, Ken Eng, Jesus D. Gomez-Velez, Elizabeth W. Boyer, Durelle Scott
A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA
Intense demand for water in the Central Valley of California and related increases in groundwater nitrate concentration threaten the sustainability of the groundwater resource. To assess contamination risk in the region, we developed a hybrid, non-linear, machine learning model within a statistical learning framework to predict nitrate contamination of groundwater to depths of approximately 500 m
Authors
Katherine M. Ransom, Bernard T. Nolan, Jonathan A. Traum, Claudia C. Faunt, Andrew M. Bell, Jo Ann M. Gronberg, David C. Wheeler, Celia Zamora, Bryant C. Jurgens, Gregory E. Schwarz, Kenneth Belitz, Sandra M. Eberts, George Kourakos, Thomas Harter
Regional effects of agricultural conservation practices on nutrient transport in the Upper Mississippi River Basin
Despite progress in the implementation of conservation practices, related improvements in water quality have been challenging to measure in larger river systems. In this paper we quantify these downstream effects by applying the empirical U.S. Geological Survey water-quality model SPARROW to investigate whether spatial differences in conservation intensity were statistically correlated with variat
Authors
Ana María García, Richard B. Alexander, Jeffrey G. Arnold, Lee Norfleet, Michael J. White, Dale M. Robertson, Gregory E. Schwarz
NHDPlus as a geospatial framework for SPARROW modeling
Successful water-resource management requires thorough knowledge and understanding of the relations among water-quality contaminate sources and the factors that affect the transport throughout a hydrologic system. Surface-water modeling is a valuable tool that can be applied to help advance and achieve the understanding of these dynamic relations. Spatially Referenced Regressions on Watershed Attr
Authors
John W. Brakebill, Gregory E. Schwarz
An evaluation of methods for estimating decadal stream loads
Effective management of water resources requires accurate information on the mass, or load of water-quality constituents transported from upstream watersheds to downstream receiving waters. Despite this need, no single method has been shown to consistently provide accurate load estimates among different water-quality constituents, sampling sites, and sampling regimes. We evaluate the accuracy of s
Authors
Casey J. Lee, Robert M. Hirsch, Gregory E. Schwarz, David J. Holtschlag, Stephen D. Preston, Charles G. Crawford, Aldo V. Vecchia
Sources of fine-grained sediment in the Linganore Creek watershed, Frederick and Carroll Counties, Maryland, 2008-10
Sediment fingerprinting quantifies the delivery of fine-grained sediment from a watershed and sediment-budget measurements quantify the erosion and deposition of fine-grained sediment. Both approaches were used in the agricultural and forested 147-square-kilometer (km2) Linganore Creek watershed in Maryland from August 1, 2008 through December 31, 2010, to determine the sources of fine-grained (le
Authors
Allen C. Gellis, Gregory B. Noe, John W. Clune, Michael K. Myers, Cliff R. Hupp, Edward R. Schenk, Gregory E. Schwarz
Science and Products
Filter Total Items: 66
Estimates of long-term mean daily streamflow and annual nutrient and suspended-sediment loads considered for use in regional SPARROW models of the Conterminous United States, 2012 base year
Streamflow, nutrient, and sediment concentration data needed to estimate long-term mean daily streamflow and annual constituent loads were compiled from Federal, State, Tribal, and regional agencies, universities, and nongovernmental organizations. The streamflow and loads are used to develop Spatially Referenced Regressions on Watershed Attributes (SPARROW) models. SPARROW models help describe th
Authors
David A. Saad, Gregory E. Schwarz, Denise M. Argue, David W. Anning, Scott A. Ator, Anne B. Hoos, Stephen D. Preston, Dale M. Robertson, Daniel Wise
Toward explaining nitrogen and phosphorus trends in Chesapeake Bay tributaries, 1992-2012
Understanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially-referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary inputs and
Authors
Scott Ator, Ana M. Garcia, Gregory E. Schwarz, Joel Blomquist, Andrew Sekellick
Adapting a regional water-quality model for local application: A case study for Tennessee, USA
We evaluated whether SPAtially Referenced Regression On Watershed attributes (SPARROW) models calibrated for two adjacent USA regions could be applied at the local scale to support management decisions for streams in Tennessee. Nutrient-source apportionment of load is important for this local-scale application and demands careful consideration of uncertainty in the calibrated coefficients. We used
Authors
Anne B. Hoos, Sherry H. Wang, Gregory E. Schwarz
Catchment-level estimates of nitrogen and phosphorus agricultural use from commercial fertilizer sales for the conterminous United States, 2012
Nutrient inputs from commercial agricultural fertilizer, particularly nitrogen and phosphorus, are important factors contributing to the degradation of surface-water quality and the alteration of aquatic ecosystems. Despite this importance, information about the application of fertilizer to agricultural land is not available in a consistent manner across the United States at a scale useful for reg
Authors
Jana S. Stewart, Gregory E. Schwarz, John W. Brakebill, Stephen D. Preston
The role of baseflow in dissolved solids delivery to streams in the Upper Colorado River Basin
Salinity has a major effect on water users in the Colorado River Basin, estimated to cause almost $300 million per year in economic damages. The Colorado River Basin Salinity Control Program implements and manages projects to reduce salinity loads, investing millions of dollars per year in irrigation upgrades, canal projects, and other mitigation strategies. To inform and improve mitigation effort
Authors
Christine Rumsey, Matthew P. Miller, Gregory E. Schwarz, Robert M. Hirsch, David D. Susong
How hydrologic connectivity regulates water quality in river corridors
Downstream flow in rivers is repeatedly delayed by hydrologic exchange with off‐channel storage zones where biogeochemical processing occurs. We present a dimensionless metric that quantifies river connectivity as the balance between downstream flow and the exchange of water with the bed, banks, and floodplains. The degree of connectivity directly influences downstream water quality — too little c
Authors
Judson Harvey, Jesus Gomez-Velez, Noah Schmadel, Durelle Scott, Elizabeth W. Boyer, Richard Alexander, Ken Eng, Heather E. Golden, Albert Kettner, Christopher Konrad, Richard Moore, Jim Pizzuto, Gregory E. Schwarz, Chris Soulsby, Jay Choi
Thresholds of lake and reservoir connectivity in river networks control nitrogen removal
Lakes, reservoirs, and other ponded waters are ubiquitous features of the aquatic landscape, yet their cumulative role in nitrogen removal in large river basins is often unclear. Here we use predictive modeling, together with comprehensive river water quality, land use, and hydrography datasets, to examine and explain the influences of more than 18,000 ponded waters on nitrogen removal through riv
Authors
Noah M. Schmadel, Judson Harvey, Richard Alexander, Gregory E. Schwarz, Richard Moore, Ken Eng, Jesus D. Gomez-Velez, Elizabeth W. Boyer, Durelle Scott
A hybrid machine learning model to predict and visualize nitrate concentration throughout the Central Valley aquifer, California, USA
Intense demand for water in the Central Valley of California and related increases in groundwater nitrate concentration threaten the sustainability of the groundwater resource. To assess contamination risk in the region, we developed a hybrid, non-linear, machine learning model within a statistical learning framework to predict nitrate contamination of groundwater to depths of approximately 500 m
Authors
Katherine M. Ransom, Bernard T. Nolan, Jonathan A. Traum, Claudia C. Faunt, Andrew M. Bell, Jo Ann M. Gronberg, David C. Wheeler, Celia Zamora, Bryant C. Jurgens, Gregory E. Schwarz, Kenneth Belitz, Sandra M. Eberts, George Kourakos, Thomas Harter
Regional effects of agricultural conservation practices on nutrient transport in the Upper Mississippi River Basin
Despite progress in the implementation of conservation practices, related improvements in water quality have been challenging to measure in larger river systems. In this paper we quantify these downstream effects by applying the empirical U.S. Geological Survey water-quality model SPARROW to investigate whether spatial differences in conservation intensity were statistically correlated with variat
Authors
Ana María García, Richard B. Alexander, Jeffrey G. Arnold, Lee Norfleet, Michael J. White, Dale M. Robertson, Gregory E. Schwarz
NHDPlus as a geospatial framework for SPARROW modeling
Successful water-resource management requires thorough knowledge and understanding of the relations among water-quality contaminate sources and the factors that affect the transport throughout a hydrologic system. Surface-water modeling is a valuable tool that can be applied to help advance and achieve the understanding of these dynamic relations. Spatially Referenced Regressions on Watershed Attr
Authors
John W. Brakebill, Gregory E. Schwarz
An evaluation of methods for estimating decadal stream loads
Effective management of water resources requires accurate information on the mass, or load of water-quality constituents transported from upstream watersheds to downstream receiving waters. Despite this need, no single method has been shown to consistently provide accurate load estimates among different water-quality constituents, sampling sites, and sampling regimes. We evaluate the accuracy of s
Authors
Casey J. Lee, Robert M. Hirsch, Gregory E. Schwarz, David J. Holtschlag, Stephen D. Preston, Charles G. Crawford, Aldo V. Vecchia
Sources of fine-grained sediment in the Linganore Creek watershed, Frederick and Carroll Counties, Maryland, 2008-10
Sediment fingerprinting quantifies the delivery of fine-grained sediment from a watershed and sediment-budget measurements quantify the erosion and deposition of fine-grained sediment. Both approaches were used in the agricultural and forested 147-square-kilometer (km2) Linganore Creek watershed in Maryland from August 1, 2008 through December 31, 2010, to determine the sources of fine-grained (le
Authors
Allen C. Gellis, Gregory B. Noe, John W. Clune, Michael K. Myers, Cliff R. Hupp, Edward R. Schenk, Gregory E. Schwarz