The purpose of this data release is to provide the original data, analysis methods, and nitrogen loading models in support of a study of the upper South Platte River annual total nitrogen loads attributed to atmospheric deposition of reactive nitrogen during 2017-2018. The data release includes water-quality and stream discharge data and associated predictive regression models used in the estimation of South Platte River nitrogen loads upstream from Weldona, Colorado and sub-basin runoff coefficients for the reach between Chatfield Dam and the South Platte River at Denver gage. The water-quality data were obtained from monthly unfiltered grab samples collected by the Denver Department of Public Health and Environment and analyzed by Standard Methods 4500-NO2-B (nitrite); 4500-NO3-F (nitrate); and 4500-NORG-B+NH3 (Total Kjeldahl Nitrogen). Stream discharge data were obtained for gaging stations from the National Water Information System and Colorado Division of Water Resources with two exceptions as follows. The Englewood wastewater reclamation facility discharge data were supplied by the facility. Discharge values for site N25E were calculated by subtracting the discharge from Cherry Creek at Denver (site W17) from the discharge at South Platte River at Denver. In addition to supplying the data used to calculate nitrogen loads and sub-basin runoff coefficients, this data release also provides the equations and diagnostic statistics for the models developed using the LOADEST software configured for R (rloadest package). Data users are referred to R help to define the many diagnostic statistics presented.

Total Nitrogen (TN) rloadest models were developed to compute TN flux at School Branch at three USGS monitoring stations: School Branch at Maloney Road near Brownsburg, Indiana (03353415); School Branch at CR750N at Brownsburg, Indiana (03353420); and School Branch at Noble Drive at Brownsburg, Indiana (03353430). Frequently, TN models developed in rloadest regress discrete TN concentrations against concurrent daily mean streamflow values. However, due to the flashy nature of streamflows on School Branch, the developed TN models regressed discrete TN concentrations against the closest unit-value (15-minute) streamflows. Once TN flux models were calibrated, unit-value streamflows were used to estimate average TN fluxes for selected time periods, which in turn were used to compute loads. This data release contains calibration data sets and R code used to create regression models for estimating daily flux of total nitrogen and summary information for the models for each site.

Total Nitrogen (TN) rloadest models were developed to compute TN flux at School Branch at three USGS monitoring stations: School Branch at Maloney Road near Brownsburg, Indiana (03353415); School Branch at CR750N at Brownsburg, Indiana (03353420); and School Branch at Noble Drive at Brownsburg, Indiana (03353430). Frequently, TN models developed in rloadest regress discrete TN concentrations against concurrent daily mean streamflow values. However, due to the flashy nature of streamflows on School Branch, the developed TN models regressed discrete TN concentrations against the closest unit-value (15-minute) streamflows. Once TN flux models were calibrated, unit-value streamflows were used to estimate average TN fluxes for selected time periods, which in turn were used to compute loads. This data release contains calibration data sets and R code used to create regression models for estimating daily flux of total nitrogen and summary information for the models for each site.

This U.S. Geological Survey data release presents tabular daily data on nitrate plus nitrite nitrogen and total nitrogen loads for the Connecticut River at Middle Haddam, Connecticut, from December 6, 2008, to September 30, 2014. The data release contains total nitrogen concentration estimates at 15-minute intervals from December 2011 to September 2014. The data release also includes tabular information on the total nitrogen loads from the Connecticut River at Thompsonville, Connecticut, from October 1, 2008, to September 30, 2014. Load data for each site and constituent include the daily loads and upper and lower 95-percent prediction intervals (where applicable); the method used in the load calculation for each site is also included in this data release.

This U.S. Geological Survey data release presents tabular daily data on nitrate plus nitrite nitrogen and total nitrogen loads for the Connecticut River at Middle Haddam, Connecticut, from December 6, 2008, to September 30, 2014. The data release contains total nitrogen concentration estimates at 15-minute intervals from December 2011 to September 2014. The data release also includes tabular information on the total nitrogen loads from the Connecticut River at Thompsonville, Connecticut, from October 1, 2008, to September 30, 2014. Load data for each site and constituent include the daily loads and upper and lower 95-percent prediction intervals (where applicable); the method used in the load calculation for each site is also included in this data release.

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 spatial data set was created by the U.S. Geological Survey (USGS) to represent the amount of wet deposition of reduced nitrogen in the Pacific Northwest region of the United States (Hydro Region 17; Major River Basin 7 (MRB7)) during 2002.

This metadata record documents an ascii comma-delimited file representing estimated nitrogen in kilograms by NHDPlus v2.1 catchments for the conterminous United States. Nitrogen estimates were taken from Estimated nitrogen from septic for the conterminous United States, 2010 published by the U.S. Geological Survey. Nitrogen values by individual reach catchments (COMID) were determined by calculating a zonal mean in a GIS.

This metadata record documents an ascii comma-delimited file representing estimated nitrogen in kilograms by NHDPlus v2.1 catchments for the conterminous United States. Nitrogen estimates were taken from Estimated nitrogen from septic for the conterminous United States, 2010 published by the U.S. Geological Survey. Nitrogen values by individual reach catchments (COMID) were determined by calculating a zonal mean in a GIS.

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.