Indicator: Nitrogen, Phosphorous, and Sediment Loads to the Chesapeake Bay (1985-2023)

<p><strong>Access the Indicator Materials:</strong><br />- <a target='_blank' href='https://d18lev1ok5leia.cloudfront.net/chesapeakeprogress/chart-assets/AM-2023-NPS-Loads-and-River-Flow-2025-05-01.pdf' rel='nofollow ugc noopener noreferrer'>Analysis &amp; Methods</a><br />- <a target='_blank' href='https://d18lev1ok5leia.cloudfront.net/chesapeakeprogress/chart-assets/Data-2023-NPS-Loads-and-River-Flow-2025-05-01.xlsx' rel='nofollow ugc noopener noreferrer'>Data File</a></p><p>This Indicator quantifies annual loads of nitrogen, phosphorus, and suspended sediment delivered to the Chesapeake Bay, along with long-term trends, to support assessment of water quality conditions and management effectiveness. River discharge, total nitrogen, total phosphorus, and suspended sediment concentrations are measured directly at River Input Monitoring (RIM) sites. Wastewater discharges and nutrients are reported to EPA by the seven Bay watershed jurisdictions. RIM load estimates are generated by USGS using the WRTDS-K model, wastewater loads are estimated from EPA discharge monitoring adjusted by delivery factors from the Phase 6 Watershed Model, below-RIM loads are calculated using the Phase 6 Watershed Model, and nitrogen atmospheric deposition to tidal waters is estimated using CMAQ-based dry and wet deposition model. The Indicator also uses WRTDS flow-normalized trends to show how loads are changing over time while reducing the influence of year-to-year river-flow variability.</p><p><strong>Note: This Indicator supported progress tracking toward the Water Quality Standards Attainment and Monitoring Outcome in the original Chesapeake Bay Watershed Agreement, adopted in 2014. The Watershed Agreement and Clean Water Goal outcomes were revised in 2025.</strong></p>