Data to Incorporate Water Quality Analysis into Navigation Assessments as Demonstrated in the Mississippi River Basin

This data release includes estimates of annual and monthly mean concentrations and fluxes for nitrate plus nitrite, orthophosphate and suspended sediment for nine sites in the Mississippi River Basin (MRB) produced using the Weighted Regressions on Time, Discharge, and Season (WRTDS) model (Hirsch and De Cicco, 2015). It also includes a model archive (R scripts and readMe file) used to retrieve and format the model input data and run the model. Input data, including discrete concentrations and daily mean streamflow, were retrieved from the National Water Quality Network (https://doi.org/10.5066/P9AEWTB9). Annual and monthly estimates range from water year 1975 through water year 2019 (i.e. October 1, 1974 through September 30, 2019). Annual trends were estimated for three trend periods per parameter. The length of record at some sites required variations in the trend start year. For nitrate plus nitrite, the following trend periods were used at all sites: 1980-2019, 1980-2010 and 2010-2019. For orthophosphate, the same trend periods were used but with 1982 as the start year instead of 1980. For suspended sediment, 1997 was used as the start year for the upper MRB sites and the St. Francisville (MS-STFR) site, but 1980 was used for the rest of the sites. All parameters and sites used 2010 as the start year for the last 10-year trend period. Reference: Hirsch, R.M., and De Cicco, L.A., 2015, User guide to Exploration and Graphics for RivEr Trends (EGRET) and dataRetrieval: R packages for hydrologic data (version 2.0, February 2015): U.S. Geological Survey Techniques and Methods book 4, chap. A10, 93 p., doi:10.3133/tm4A10