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.

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).

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).

This metadata record describes mean seasonal time-step estimates of daily streamflow and daily baseflow, and total and baseflow estimates of loads of total nitrogen, total phosphorus, and total suspended solids at surface-water stations in the southeastern United States for the period 2001-14. Streamflow and load estimates described in this data release were obtained using the Fluxmaster approach described in Saad and others (2019). Saad, D.A., Schwarz, G.E., Argue, D.M., Anning, D.W., Ator, S.W., Hoos, A.B., Preston, S.D., Robertson, D.M., and Wise, D.R., 2019, 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: U.S. Geological Survey Scientific Investigations Report 2019-5069, 51 p., https://doi.org/10.3133/sir20195069.

This metadata record describes mean seasonal time-step estimates of daily streamflow and daily baseflow, and total and baseflow estimates of loads of total nitrogen, total phosphorus, and total suspended solids at surface-water stations in the southeastern United States for the period 2001-14. Streamflow and load estimates described in this data release were obtained using the Fluxmaster approach described in Saad and others (2019). Saad, D.A., Schwarz, G.E., Argue, D.M., Anning, D.W., Ator, S.W., Hoos, A.B., Preston, S.D., Robertson, D.M., and Wise, D.R., 2019, 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: U.S. Geological Survey Scientific Investigations Report 2019-5069, 51 p., https://doi.org/10.3133/sir20195069.

This data release contains data in support of "Diverging trends in Nitrate and Phosphorus Loads and Yields Across Illinois Watersheds, 1997–2022" (Kamrath and others, 2025). It contains input and output data used to estimate total nitrate + nitrite, dissolved phosphorous and total phosphorous loads for sites in Illinois from water years 1974 to 2022. The input data includes "input-data_WQ.csv," which contains water quality data for nitrate + nitrite, dissolved phosphorous and total phosphorous. The water quality data comes from (1) the Water Quality Portal (WQP), (2) the Illinois Environmental Protection Agency (IEPA), and (3) the Environmental Protection Agency (EPA) STORET warehouse. The WQP includes the most complete record of U.S. Geological Survey and IEPA water quality samples. The most recent IEPA water quality samples, which are not yet in the WQP, were provided directly from IEPA. Legacy IEPA data that is housed via the EPA STORET warehouse was used to fill in any gaps in the data record. See the Entity and Attribute section of the metadata for details. The output data provides results calculated using the water-quality method Weighted Regressions on Time, Discharge, and Season (WRTDS) from the R package 'EGRET' (Exploration and Graphics for RivEr Trends, available from https://doi-usgs.github.io/EGRET/). The file "model-runs.csv" includes a list of all the models run using WRTDS with additional information for each run; for each run, WRTDS stationary and generalized flow normalization (SFN and GFN, respectively) were used along with the WRTDS Kalman (WRTDS-K) post processing. The results of each WRTDS run are saved in 'eList,' the native output format from 'EGRET,' in "eLists.zip." There are two eLists per run, one with SFN results and the other with GFN and WRTDS-K results. For more information on 'EGRET' and the WRTDS method see https://doi-usgs.github.io/EGRET/index.html. Additional output data includes estimated annual and monthly loads and concentrations of nitrate + nitrite, dissolved phosphorous and total phosphorous for all sites. The files are broken up by constituent, nitrate + nitrite (N) or phosphorous (P), and time frame, annual or monthly.

This data release contains data in support of "Diverging trends in Nitrate and Phosphorus Loads and Yields Across Illinois Watersheds, 1997–2022" (Kamrath and others, 2025). It contains input and output data used to estimate total nitrate + nitrite, dissolved phosphorous and total phosphorous loads for sites in Illinois from water years 1974 to 2022. The input data includes "input-data_WQ.csv," which contains water quality data for nitrate + nitrite, dissolved phosphorous and total phosphorous. The water quality data comes from (1) the Water Quality Portal (WQP), (2) the Illinois Environmental Protection Agency (IEPA), and (3) the Environmental Protection Agency (EPA) STORET warehouse. The WQP includes the most complete record of U.S. Geological Survey and IEPA water quality samples. The most recent IEPA water quality samples, which are not yet in the WQP, were provided directly from IEPA. Legacy IEPA data that is housed via the EPA STORET warehouse was used to fill in any gaps in the data record. See the Entity and Attribute section of the metadata for details. The output data provides results calculated using the water-quality method Weighted Regressions on Time, Discharge, and Season (WRTDS) from the R package 'EGRET' (Exploration and Graphics for RivEr Trends, available from https://doi-usgs.github.io/EGRET/). The file "model-runs.csv" includes a list of all the models run using WRTDS with additional information for each run; for each run, WRTDS stationary and generalized flow normalization (SFN and GFN, respectively) were used along with the WRTDS Kalman (WRTDS-K) post processing. The results of each WRTDS run are saved in 'eList,' the native output format from 'EGRET,' in "eLists.zip." There are two eLists per run, one with SFN results and the other with GFN and WRTDS-K results. For more information on 'EGRET' and the WRTDS method see https://doi-usgs.github.io/EGRET/index.html. Additional output data includes estimated annual and monthly loads and concentrations of nitrate + nitrite, dissolved phosphorous and total phosphorous for all sites. The files are broken up by constituent, nitrate + nitrite (N) or phosphorous (P), and time frame, annual or monthly.

This data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading to streams across the Illinois River basin (25,620 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model. Input data including calibration loads, output predictions, model control files, and model source code are provided to fully reproduce results. The modeled period was from December 1999 through November 2020 in seasonal timesteps, or 84 periods, and the following seasonal definitions were applied: winter includes December, January, and February; spring includes March, April, and May; summer includes June, July, and August; and fall includes September, October, and November. See Schmadel and others (2024) for further details.

This data release contains seasonal source-specific estimates of total nitrogen (TN) and total phosphorus (TP) loading to streams across the Illinois River basin (25,620 reaches) for 21 years from 2000 through 2020 using a dynamic SPARROW (Spatially Referenced Regressions on Watershed attributes) model. Input data including calibration loads, output predictions, model control files, and model source code are provided to fully reproduce results. The modeled period was from December 1999 through November 2020 in seasonal timesteps, or 84 periods, and the following seasonal definitions were applied: winter includes December, January, and February; spring includes March, April, and May; summer includes June, July, and August; and fall includes September, October, and November. See Schmadel and others (2024) for further details.

This data set contains county-level estimates of nitrogen and phosphorus from fertilizer, for both farm and nonfarm uses, for the conterminous United States, for 1987 through 2006. State-level farm and nonfarm nitrogen and phosphorus were derived from the Association of American Plant Food Control Officials (AAPFCO) commercial fertilizer sales data. State estimates were then allocated to the county-level using fertilizer expenditure as county weights for farm fertilizer, and population density as county weights for nonfarm fertilizer.