Archive of the Load Estimation Models Used in the Analyses of Temporal Changes in Nutrient Concentrations in the Lower Grand River and Selected Drainage Basins, Missouri and Iowa (2010–23)

A model archive to document the data preparation and analysis process for the Scientific Investigations Report by Kamrath and others (2025). In Kamrath and others (2025), three data analysis methods were used to estimate total nitrogen and total phosphorus concentrations in streams and rivers with drainage basins spanning across northwest Missouri and southern Iowa. First, survival regressions were used to estimate annual total nitrogen and phosphorus concentrations at three locations in the Lower Grand hydrologic unit (Missouri, USA). Second, the flow-adjusted concentration method was used to estimate flow-adjusted total nitrogen and phosphorus concentrations at the same three locations. Third, the Weighted Regression on Time, Discharge, and Season (WRTDS) model was used to estimate annual flow-normalized total nitrogen and phosphorus concentrations in the Grand River, the Chariton River, the Nodaway River, and two locations on the Missouri River. The Archive.zip data set contains R source code, inputs, and selected outputs associated with analyses used to estimate total nitrogen and phosphorus concentrations for selected sites within the Lower Grand River watershed and on the Missouri River and Missouri River tributaries for water years 1994–2023.