Benthic Macroinvertebrate Community Composition after 2026 Potomac River Sewage Spill

Abstract

Benthic macroinvertebrate communities are widely used bioindicators for water quality and ecological health in estuarine systems since their limited mobility and varying tolerances to pollution make them sensitive to local disturbances. On January 19, 2026, a collapse in the Potomac Interceptor sewer pipe released 240-300 million gallons of untreated wastewater into the Potomac River. Currently, the ecological consequences of the burst on the river’s benthic communities remain undocumented. As part of an ongoing monitoring effort, benthic samples were collected via triplicate Ponar grabs at 11 sites along the Potomac from February to June 2026. Across the samples, 41 distinct taxa were identified from 154 individual grabs. Community composition was analyzed using a permutational multivariate analysis of variance (PERMANOVA), determining that site explained approximately 39-41% of variation in community composition (p < 0.001), consistent with the Potomac’s natural salinity gradient, while sampling month explained an additional 9-12% of variation (p < 0.001) after accounting for site. Similarity percentage (SIMPER) analyses were used to identify taxa driving compositional differences, finding that five organisms contributed consistently to differences between sites (worms: Oligochaeta, Syllidae, and Spionidae, amphipod: Leptocheirus plumulosus, and bivalve: Macoma balthica), alongside an overall dominance of pollution-tolerant taxa like Oligochaeta and Chironomidae. These results demonstrate a shift in benthic community composition, contributing to baseline data towards evaluating the effects of a major wastewater release.