Effective Nutrient\nManagement of Surface Waters in\nthe United States Requires Expanded Water Quality Monitoring in Agriculturally\nIntensive Areas

The U.S. Clean Water Act is believed to have driven widespread\ndecreases in pollutants from point sources and developed areas, but\nhas not substantially affected nutrient pollution from agriculture.\nToday, the highest nutrient concentrations in surface waters are often\nassociated with agricultural production. In this Perspective, we explore\nwhether challenges stemming from the Clean Water Act’s inability\nto mitigate agricultural nutrient pollution are also exacerbated by\ncoarse nutrient monitoring. We evaluate the current state of nutrient\nmonitoring in surface waters of the contiguous U.S. relative to agricultural\nnutrient inputs to assess how monitoring effort varies across agriculturally\nintensive areas. The locations of nutrient monitoring stations with\napproximately seasonal sampling frequency (4 samples per year, on\naverage) from 2012 to 2021 were compiled from the U.S. Water Quality\nPortal. Monitoring station locations were then compared to watershed-scale\n(HUC-8) nutrient inventory estimates for agricultural fertilizer and\nlivestock manure inputs. From this assessment, we found that many,\nbut not all, of the nation’s most agriculturally intensive\nareas are under-monitored, and often unmonitored. While it is well-known\nthat the Midwest is the epicenter of agricultural production in the\nU.S., our results reveal it is poorly monitored relative to its agricultural\nnutrient inputs. Other regions, like the California Central Valley\nand parts of the southeastern Coastal Plain were also coarsely monitored\nrelative to nutrient inputs. Conversely, some agriculturally intensive\nwatersheds were moderately-to-well monitored (e.g., western Lake Erie\nbasin, eastern North Carolina, and the Delmarva Peninsula), with these\nbasins largely having established Total Maximum Daily Loads and discharging\nto prominent waterways. In closing, we argue that sparse monitoring\nacross many of the nation’s most agriculturally intensive areas\nmotivate a need to re-envision nutrient monitoring networks, and that\nincreased resources and advanced technologies are likely required\nto enable effective nutrient source identification throughout the\nnation.