This USGS data release contains long-term mean annual total nitrogen and total phosphorus load estimates, and the model coefficients used to obtain the load estimates, for streams in the Midwest Region of the United States. The loads were estimated using the Fluxmaster program (Schwarz and others, 2006, https://pubs.usgs.gov/tm/2006/tm6b3) with a 5-parameter model and detrending to 2012 following the methods described in Saad and others, 2011 (https://doi.org/10.1111/j.1752-1688.2011.00575.x). A subset of these load estimates are described in Robertson and Saad, 2021 (https://doi.org/10.1111/1752-1688.12905) and were used to evaluate differences in load estimates in the Mississippi/Atchafalaya River Basin based on this method and the methods described in Saad and others, 2019 (https://dx.doi.org/10.3133/sir20195069). The flow and water-quality input files necessary to reproduce the load estimates included in this data release can be found in Saad and others, 2019 (https://doi.org/10.5066/F7DN436B).

Estimated seasonal total nitrogen and total phosphorus loads during 1999 through 2020 in selected streams of the conterminous United States and water-quality and stream flow data used to generate those estimates are presented in this dataset. Loads were generated as part of the Integrated Water-Availability Assessment (IWAA) Program of the U.S. Geological Survey (www.usgs.gov/mission-areas/water-resources/science/integrated-water-availability-assessments#overview) using Fluxmaster (Schwarz and others, 2006, https://doi.org/10.3133/tm6B3) and Weighted Regression on Time, Discharge, and Season (WRTDS) (Hirsch and De Cicco, 2015, https://doi.org/10.1016/j.envsoft.2015.07.017). Loads were estimated initially for the Illinois River Basin (IRB) and later for the wider conterminous United States (including the IRB). Along with the water-quality data, streamflow data, and estimated nitrogen and phosphorus loads, this release also includes computer code that can be run to recreate the load estimates or modified for similar applications.

Estimated seasonal total nitrogen and total phosphorus loads during 1999 through 2020 in selected streams of the conterminous United States and water-quality and stream flow data used to generate those estimates are presented in this dataset. Loads were generated as part of the Integrated Water-Availability Assessment (IWAA) Program of the U.S. Geological Survey (www.usgs.gov/mission-areas/water-resources/science/integrated-water-availability-assessments#overview) using Fluxmaster (Schwarz and others, 2006, https://doi.org/10.3133/tm6B3) and Weighted Regression on Time, Discharge, and Season (WRTDS) (Hirsch and De Cicco, 2015, https://doi.org/10.1016/j.envsoft.2015.07.017). Loads were estimated initially for the Illinois River Basin (IRB) and later for the wider conterminous United States (including the IRB). Along with the water-quality data, streamflow data, and estimated nitrogen and phosphorus loads, this release also includes computer code that can be run to recreate the load estimates or modified for similar applications.

In this data release, we provide the data used to compute total annual phosphorus loads from tributaries and direct drainages to the Great Lakes during 2012-18 using the model load ratio approach and the unit area load approach and the resulting annual loads for 2012–18. This data release consists of: (1) measured loads at 24 sites, computed using the surrogate regression approach (Robertson et al., 2018; Koltun, 2020) that were monitored as part of the Great Lakes Restoration Initiative project, (2) estimated annual loads at point source facilities throughout the Great Lakes Basin obtained from the U.S. Environmental Protection Agency and state agencies, (3) loads subdivided into nonpoint and point source contributions, (4) extrapolation factors for each basin (nonpoint model load ratios, nonpoint yields, point source delivery factors), and (5) estimated annual loads for each tributary and direct drainage area to the Great Lakes during 2012–18. This data release consists of three tab delimited files: (1) ReferenceSite.txt, which contains all of the information (site data and phosphorus loads from SPARROW (Robertson and Saad, 2019) and measured during 2012–18 for the 24 reference (extrapolation sites) used in this study, (2) PointSource.txt, which contains all of the measured or extrapolated point source information for wastewater treatment plants in the Great Lake Basin for 2012–18; and (3) ExtrapolatedLoads.txt, which contains all of the nonpoint model load ratios, point source delivery ratios, measured wastewater treatment plant loads, and resulting annual loads for each tributary and direct drainage area in the Great Lakes Basin for the long-term average and 2012–18.

In this data release, we provide the data used to compute total annual phosphorus loads from tributaries and direct drainages to the Great Lakes during 2012-18 using the model load ratio approach and the unit area load approach and the resulting annual loads for 2012–18. This data release consists of: (1) measured loads at 24 sites, computed using the surrogate regression approach (Robertson et al., 2018; Koltun, 2020) that were monitored as part of the Great Lakes Restoration Initiative project, (2) estimated annual loads at point source facilities throughout the Great Lakes Basin obtained from the U.S. Environmental Protection Agency and state agencies, (3) loads subdivided into nonpoint and point source contributions, (4) extrapolation factors for each basin (nonpoint model load ratios, nonpoint yields, point source delivery factors), and (5) estimated annual loads for each tributary and direct drainage area to the Great Lakes during 2012–18. This data release consists of three tab delimited files: (1) ReferenceSite.txt, which contains all of the information (site data and phosphorus loads from SPARROW (Robertson and Saad, 2019) and measured during 2012–18 for the 24 reference (extrapolation sites) used in this study, (2) PointSource.txt, which contains all of the measured or extrapolated point source information for wastewater treatment plants in the Great Lake Basin for 2012–18; and (3) ExtrapolatedLoads.txt, which contains all of the nonpoint model load ratios, point source delivery ratios, measured wastewater treatment plant loads, and resulting annual loads for each tributary and direct drainage area in the Great Lakes Basin for the long-term average and 2012–18.

This dataset consists of input and output datasets for estimating trends in river loads using the Weighted Regressions on Time Season and Discharge (WRTDS) model. The input datasets includes a discharge datafile and concentration datafiles for 6 water quality constituents: Total Phosphorus, Total Nitrogen, Nitrate plus Nitrite, Ammonium, Orthophosphate and Suspended Sediment. The period of record for the water quality data is from 1975 to 2017. The concentration and discharge data are for one site, the Mississippi River Outflow site, which is based on concentration data from USGS site 07373420, Mississippi River near St. Francisville, LA, and the discharge data are the sum of US Army Corps of Engineers Sites 01100 (Tarbert Landing) and 02600 (Old River Outflow) . Output dataset has the annual WRTDS estimates for time period 1975 to 2017 for all six constituents.

This dataset consists of input and output datasets for estimating trends in river loads using the Weighted Regressions on Time Season and Discharge (WRTDS) model. The input datasets includes a discharge datafile and concentration datafiles for 6 water quality constituents: Total Phosphorus, Total Nitrogen, Nitrate plus Nitrite, Ammonium, Orthophosphate and Suspended Sediment. The period of record for the water quality data is from 1975 to 2017. The concentration and discharge data are for one site, the Mississippi River Outflow site, which is based on concentration data from USGS site 07373420, Mississippi River near St. Francisville, LA, and the discharge data are the sum of US Army Corps of Engineers Sites 01100 (Tarbert Landing) and 02600 (Old River Outflow) . Output dataset has the annual WRTDS estimates for time period 1975 to 2017 for all six constituents.

This dataset consists of input and output datasets for estimating trends in river loads using the Weighted Regressions on Time Season and Discharge (WRTDS) model. The input datasets includes a discharge datafile and concentration datafiles for 6 water quality constituents: Total Phosphorus, Total Nitrogen, Nitrate plus Nitrite, Ammonium, Orthophosphate and Suspended Sediment. The period of record for the water quality data is from 1975 to 2017. The concentration and discharge data are for one site, the Mississippi River Outflow site, which is based on concentration data from USGS site 07373420, Mississippi River near St. Francisville, LA, and the discharge data are the sum of US Army Corps of Engineers Sites 01100 (Tarbert Landing) and 02600 (Old River Outflow) . Output dataset has the annual WRTDS estimates for time period 1975 to 2017 for all six constituents.

This dataset consists of input and output datasets for estimating trends in river loads using the Weighted Regressions on Time Season and Discharge (WRTDS) model. The input datasets includes a discharge datafile and concentration datafiles for 6 water quality constituents: Total Phosphorus, Total Nitrogen, Nitrate plus Nitrite, Ammonium, Orthophosphate and Suspended Sediment. The period of record for the water quality data is from 1975 to 2017. The concentration and discharge data are for one site, the Mississippi River Outflow site, which is based on concentration data from USGS site 07373420, Mississippi River near St. Francisville, LA, and the discharge data are the sum of US Army Corps of Engineers Sites 01100 (Tarbert Landing) and 02600 (Old River Outflow) . Output dataset has the annual WRTDS estimates for time period 1975 to 2017 for all six constituents.

This dataset consists of input and output datasets for estimating trends in river loads using the Weighted Regressions on Time Season and Discharge (WRTDS) model. The input datasets includes a discharge datafile and concentration datafiles for 6 water quality constituents: Total Phosphorus, Total Nitrogen, Nitrate plus Nitrite, Ammonium, Orthophosphate and Suspended Sediment. The period of record for the water quality data is from 1975 to 2017. The concentration and discharge data are for one site, the Mississippi River Outflow site, which is based on concentration data from USGS site 07373420, Mississippi River near St. Francisville, LA, and the discharge data are the sum of US Army Corps of Engineers Sites 01100 (Tarbert Landing) and 02600 (Old River Outflow) . Output dataset has the annual WRTDS estimates for time period 1975 to 2017 for all six constituents.