The nonpoint source challenge: causes, challenges, and opportunities to meeting nutrient reduction goals in the Chesapeake Bay

Authors: EASTON, ZACHARY - Virginia Tech; STEPHENSON, KURT - Virginia Tech; BENHAM, BRIAN - Virginia Tech; BOHLKE, J.K. - Us Geological Survey (USGS); Buda, Anthony; COLLICK, AMY - Morehead State University; FOWLER, LARA - Pennsylvania State University; GILINSKY, ELLEN - Consultant; MILLER, ANDREW - Consultant; NOE, GREGORY - Us Geological Survey (USGS); PALM-FORSTER, LEAH - University Of Delaware; SHABMAN, LEONARD - Resources For The Future; WYNN-THOMPSON, TESS - Virginia Tech

Submitted to: Journal of the American Water Resources Association
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/4/2025
Publication Date: 6/14/2025
Citation: Easton, Z., Stephenson, K., Benham, B., Bohlke, J., Buda, A.R., Collick, A., Fowler, L., Gilinsky, E., Miller, A., Noe, G., Palm-Forster, L.H., Shabman, L., Wynn-Thompson, T. 2025. The nonpoint source challenge: causes, challenges, and opportunities to meeting nutrient reduction goals in the Chesapeake Bay. Journal of the American Water Resources Association. 61(3). Article e70034. https://doi.org/10.1111/1752-1688.70034.
DOI: https://doi.org/10.1111/1752-1688.70034

Interpretive Summary: Actions to restore the Chesapeake Bay, the nation’s largest estuary, are mainly centered around the Chesapeake Bay Total Maximum Daily Load (TMDL). The TMDL, which was established in 2010 by the US EPA, aims for a 25 percent reduction in nitrogen, 24 percent reduction in phosphorus, and 20 percent reduction in sediment relative to the annual loading of these pollutants in 2009. As the 2025 TMDL deadline draws closer, it is apparent that efforts to reduce nutrient and sediment loading to the Bay will fall short of TMDL goals. In this paper, we suggest that nutrients and sediments from agricultural and urban nonpoint sources pose the greatest remaining challenge to meeting the Bay TMDL. Using literature and data synthesis, we find that the existing nonpoint source control programs are not producing the expected levels of pollutant reductions established in the TMDL. To remedy these issues, we identify possible reasons for the gaps, and we summarize possible programmatic changes that could enhance future efforts to reduce nonpoint source pollution in the Chesapeake Bay watershed.

Technical Abstract: This document examines the Chesapeake Bay watershed response to long term nutrient and sediment reduction efforts to achieve estuary water quality standards under the Clean Water Act’s Total Maximum Daily Load (TMDL) regulation. As the 2025 Chesapeake Bay TMDL deadline approaches, water quality goals remain largely unmet. This analysis focuses on the management of agricultural and urban nonpoint source pollution, the largest remaining sources of nutrients and sediment, and the primary obstacle to meeting TMDL goals. We focus on the factors influencing the gap between the expected effect of management programs to reduce nitrogen (N), phosphorus (P), and sediment loads reaching the Chesapeake Bay and empirical evidence suggesting that decades of effort have not produced adequate water quality improvement. This gap may be caused by both insufficient implementation of water quality management practices and by an overestimation of practice effectiveness, as the water quality programs track practice implementation instead of measured water quality outcomes. There are a number of additional possible reasons water quality goals remain unmet, including legacy nutrients and lag times masking the effect of management efforts, areas with large nutrient mass imbalances contributing disproportionate nutrient loads, and the difficulty incentivizing behavior change under conventional voluntary, nonpoint source programs. Some of these challenges are well recognized (e.g., lag times) while others remain largely unaddressed. However, all continue to impact water quality. Closing the gap between current nutrient and sediment loadings and the TMDL goals will require fundamental changes to water quality programming. Above the common refrain of additional funding, water quality improvement efforts must develop policy and programs to more effectively incentivize behavior change, identify and target high loading areas, and address nutrient mass imbalances.