Determining Stream Influence on Nitrate Concentrations within the Potomac River

Nutrient enrichment remains a persistent driver of water quality impairment throughout the Potomac River and Chesapeake Bay watershed, motivating localized stream restoration efforts aimed at reducing downstream nitrogen transport. This study characterized spatial patterns in dissolved inorganic nitrogen along a newly constructed stream corridor in Loudoun County, Virginia, during active restoration construction. Five monitoring sites spanning an upstream control, three construction zone locations, and a downstream reference were sampled twice daily over three weeks and analyzed for nitrate, nitrite, and ammonium using colorimetric methods. Nitrate concentrations did not decline systematically downstream; the two sites nearest active earthwork exhibited the highest mean values, exceeding the upstream control, while no statistically significant differences were detected across sites for any nitrogen species (Kruskal-Wallis, p > 0.05). However, pooled nitrite concentrations within the construction zone were significantly elevated relative to the downstream reference (Mann-Whitney U = 867.5, p = 0.033), consistent with active nitrification of ammonium released from disturbed sediments. These findings suggest the corridor functions during construction as a biogeochemically active zone where nitrogen speciation is transiently altered rather than reduced, contrasting with the denitrification the restoration is designed to promote long-term. This work provides field-based baseline data and a replicable monitoring framework for evaluating post-construction nutrient attenuation.