Nitrogen, phosphorus, and suspended-sediment loads and trends measured at the Chesapeake Bay Nontidal Network stations: Water years 1985-2023

Nitrogen, phosphorus, and suspended-sediment loads, and changes in loads, in rivers across the Chesapeake Bay watershed were calculated using monitoring data from the Chesapeake Bay Nontidal Network (NTN) stations for the period 1985 through 2023. Nutrient and suspended-sediment loads and changes in loads were determined by applying a weighted regression approach called WRTDS (Weighted Regression on Time, Discharge, and Season). Load results, representing the total mass of nitrogen, phosphorus, and suspended sediment exported from each of the NTN watersheds, are provided as both flow-normalized loads and actual loads by year and month using the WRTDS method, and WRTDS with Kalman filtering method, respectively. Flow-normalization reduces the influence of year-to-year streamflow variability on measured loads and aids in the detection of trends. The trend in load is derived from the flow-normalized load timeseries and represents the change in load resulting from changes in sources, delays associated with storage or transport of historical inputs, and (or) implemented management actions. Four data tables are provided that describe nitrogen, phosphorus, and suspended-sediment conditions across the NTN: (1) Annual Loads, (2) Monthly Loads, (3) Trends in Annual Loads, and (4) Average Annual Yield (mass per watershed area). Additionally, essential WRTDS Input and Output files, model software (R, EGRET and EGRETci versions used), and a summary PDF file highlighting short-term loads and trends in flow-normalized loads are provided.