Annual Nutrient Loads at Illinois EPA Ambient Water Quality Monitoring Network Sites, Water Years 1976–2021

This data release contains estimates of annual nitrogen and phosphorus loads, as well as loads of other constituents, from sites in the Illinois Environmental Protection Agency (Illinois EPA) Ambient Water Quality Monitoring Network. The loads were estimated using Weighted Regressions on Time, Discharge, and Season with Kalman filtering (WRTDS-K) and existing discrete water-quality data and discharge data collected by Illinois EPA, the U.S. Geological Survey, and Illinois State Water Survey from water year 1976 to 2021 (Hirsch and others, 2015; Lee and others, 2019). All water-quality and discharge data used in this work are available from the Water Quality Portal and the National Water Information System database (U.S. Geological Survey, 2022). The data release comprises a single comma-separated values (CSV) file containing annual loads, load uncertainty, and sample counts for each ambient monitoring site. These data supersede Hodson (2021), which was based on data through water year 2020.