Identifying the Largest Nutrient Input Sources for HUC8 Sub-basins across the United States
On this page:
Nutrient pollution is among the most significant and costly environmental challenges for protecting and improving surface water and ground water quality. Limited resources need to be leveraged efficiently and effectively to prioritize watersheds for restoration and management of nitrogen (N) and phosphorus (P) pollution. Accurate, complete and timely information about pollution sources is foundational for decision making. EPA-ORD has assembled information about the sources of nitrogen (N and phosphorus (P) into a nutrient inventory for 8-digit Hydrologic Unit Code (HUC8) watershed units across the contiguous US. The largest anthropogenic source of both N and P to the contiguous US landscape is the agricultural sector, consisting of livestock waste, synthetic fertilizers, and cultivated crop biological N fixation (Sabo et al., 2019, 2021). Agricultural inputs account for 60-64% of nitrogen (N) and 90% of phosphorus (P) inputs. Even with ongoing declines in NOx emissions due to the Clean Air Act policies, atmospheric N deposition is still the largest N input in many sub-basins. Urban associated inputs, consisting of urban fertilizer and wastewater loads to surface water, are the largest inputs in some of most urbanized and highly populated sub-basins across the United States. This analysis and the corresponding database provide decision makers a succinct platform for identifying key sources and prioritizing nutrient management and watershed restoration efforts across the US.