This dataset utilized available water-quality data from the Mississippi Department of Environmental Quality and streamflow from the U.S. Geological Survey to estimate total nitrogen and total phosphorus loads and changes in loads from water years 2008 through 2018. Nutrient loads and changes in loads were estimated at 22 state ambient water-quality network sites, and were estimated using LOADEST regression models, Beale-Ratio Estimator, or WRTDS (Weighted Regression on Time, Discharge, and Season). The method selected is based on the evaluation of the flux-bias statistic and use of multiple graphical tools through EGRET to identify and characterize issues with particular models for each given dataset and is included in this data release.

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.

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 nitrogen (N) and phosphorus (P) balances for the Mississippi River Basin from 1950 to 2017. The N balance was calculated as the difference between inputs (fertilizer, manure, wastewater treatment facility effluent, N fixation, and atmospheric deposition) and outputs (crop uptake and removal in harvest and gaseous emissions to the atmosphere). The P balance was calculated as the difference between inputs (fertilizer, manure, wastewater treatment facility effluent, and weathering) minus outputs (specifically, P harvested and removed in crops, hay, and pasture).

This dataset consists of input and output datasets for estimating nitrogen (N) and phosphorus (P) balances for the Mississippi River Basin from 1950 to 2017. The N balance was calculated as the difference between inputs (fertilizer, manure, wastewater treatment facility effluent, N fixation, and atmospheric deposition) and outputs (crop uptake and removal in harvest and gaseous emissions to the atmosphere). The P balance was calculated as the difference between inputs (fertilizer, manure, wastewater treatment facility effluent, and weathering) minus outputs (specifically, P harvested and removed in crops, hay, and pasture).

The United States Geological Survey’s (USGS) SPAtially Referenced Regressions On Watershed attributes (SPARROW) model was developed to aid in the interpretation of monitoring data and simulate water-quality conditions in streams across large spatial scales. SPARROW is a hybrid empirical/process-based mass balance model that can be used to estimate the major sources and environmental factors that affect the long-term supply, transport, and fate of contaminants in streams. The spatially explicit model structure is defined by a river reach network coupled with contributing catchments. The model is calibrated by statistically relating watershed sources and transport-related properties to monitoring-based streamflow and water-quality load estimates. Streamflow and load estimates considered for use in regional SPARROW model applications (2012 base year) are described in Saad and others, 2019 (https://dx.doi.org/10.3133/sir20195069). Load estimation methods described in this report include the Beale Ratio Estimator and Fluxmaster models. This USGS data release contains all of the input and output files necessary to reproduce the load estimates considered for inclusion in the 2012 regional SPARROW models. Data preparation for input to the load estimation models is also fully described in the above-mentioned report.