Mapping pollutant source to enhance water quality conservation in agricultural watersheds: Nonpoint no more?

This article argues that modern geospatial technologies, such as lidar-derived topography, remote sensing–based crop rotation mapping, and advanced soil surveys, can transform agricultural water quality management by mapping nutrient and sediment sources at the field scale. The authors critique decades-old “hotspot” concepts for nonpoint-source pollution (NPSP) control, finding that nutrient pollution, especially nitrogen in tile-drained Midwestern watersheds, is widespread and cannot be addressed solely by visually identified sites. Using the Agricultural Conservation Planning Framework (ACPF), they propose integrating by-field nitrogen application estimates, hydrologic flow path mapping, and conservation practice siting tools to rank and target locations for the greatest nutrient and sediment reduction. They also outline methods for estimating nitrogen loss from cropping histories, applying conservation practices (e.g., bioreactors, saturated buffers), and extending similar targeting approaches to sediment and phosphorus using streambank erosion analysis and erosion risk mapping. Ultimately, they call for watershed-scale experiments and “conservation-citizen science” to refine and apply these tools, aiming to make NPSP sources definable, mappable, and more effectively managed.