RAPID: Ecosystem Response to a Major Sewage Spill in the Potomac River Estuary: Disturbance, Contaminant Legacies, and Biological Thresholds

Acute nutrient pollution, such as raw sewages spills into waterways, represent one of the most pervasive and ecologically damaging stressors to freshwater and estuarine systems in the U.S., with recovery timescales often spanning decades. Changes in water quality and biodiversity immediately and soon after a pollution event are rarely studied in real time and are proposed to have outsized effects on the long-term trajectory of water systems. In January 2026, the Potomac Interceptor sewer outside of Washington DC collapsed, causing one of the largest raw sewage spills in history until it was capped in March 2026. This discharge released into the river a mixture of nutrients, pathogens, heavy metals, pharmaceuticals, and per- and polyfluoroalkyl substances, including E. coli concentrations reaching up to 10,000 times above recreational water quality limits. This project documents an intensive investigation of ecosystem response, from tidal freshwater to brackish water regions of the Potomac River Estuary, following the sewage spill. Data will be collected monthly at eleven sites for six months. This data will be examined in the context of 3 months of rapid-response monitoring as well as baseline data since 1984, which allows it to contextualize impacts on biodiversity, community structure, and ecosystem function. These initial and near-term changes may later be used to understand longer term ecological trajectories and consequences. This project will generate policy-relevant, publicly accessible data to directly inform human health advisories, recreational use decisions, and adaptive management strategies for the Potomac River, while developing a framework useful for future sewage spill events nationally. It engages community members and students in data collection and labwork, as well as includes results in on-going education programs. The Potomac Interceptor spill introduced a massive and discrete nutrient and contaminant pulse into an ecologically important estuarine system, creating a natural experiment for testing foundational ecological theory, including the intermediate disturbance hypothesis and alternative stable state dynamics, in a real-world context. Through monthly data collection, in conjunction with historical data and immediate post-pollution data, this project will document early responses that represent a transient disturbance signature that cannot be reconstructed once the system begins to reorganize. The project will quantify biodiversity and functional composition of bacteria, phytoplankton and zooplankton, macroinvertebrates, and fish across eleven sites, using eDNA metabarcoding and whole organism taxonomic identification. By tracking contaminant redistribution across water column, sediment, and biological compartments simultaneously, this study will generate mechanistic understanding of recovery trajectories, ecological thresholds, and the cascading trophic consequences of large-scale disturbance that is broadly applicable to impaired river systems nationwide. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria. NSF Award ID: 2623281 | Program: 01002627DB NSF RESEARCH & RELATED ACTIVIT | Principal Investigator: Jennifer Salerno | Institution: George Mason University, FAIRFAX, VA | Award Amount: $299,886 View on NSF Award Search: https://www.nsf.gov/awardsearch/show-award/?AWD_ID=2623281 View on Research.gov: https://www.research.gov/awardapi-service/v1/awards/2623281.html