Nitrogen is an essential nutrient, but too much pollutes waters and degrades ecosystems. Excess nitrogen can alter food quality and community composition, lead to eutrophication, and may cause harmful algal blooms.
How is it scored?
We scored samples as pass/fail using U.S. EPA ecoregion-specific thresholds for TN (regions 55 and 57 = 2.18 mg/L, region 56 = 1.15 mg/L) and NN (regions 55 and 57 = 1.5 mg/L, region 56 = 1.15 mg/L). The Huron River watershed was scored using NN, while all other watersheds were scored using TN. Samples above the threshold failed (0%) while samples below thresholds passed (100%). Stations sampled multiple times were averaged. Station scores within a watershed were averaged to score watersheds, which were area-weighted to calculate an overall region score.
Data sources: Total nitrogen (TN) data from the National Water Quality Monitoring Council Water Quality Portal (waterqualitydata.us) and Nitrate-Nitrite (NN) data from the Huron River Watershed Council.