The impact of stream‐groundwater exchange on seasonal nitrate loads in an urban stream

Urbanization negatively impacts water quality in streams by reducing stream-groundwater interactions, which can reduce a stream's capacity to naturally attenuate nitrate. Meadowbrook Creek, first order urban stream Syracuse, New York, has an inverse urbanization gradient, with heavily urbanized headwaters that are disconnected from the floodplain and downstream reaches have intact riparian floodplains connection aquifers. This system allows assessment of how interactions impact net sources sinks nitrate at reach scale. We used continuous (15-min) streamflow measurements weekly grab samples three gauging stations positioned longitudinally along creek develop load estimates inlet outlet two contrasting reaches. Nitrate were determined using USGS linear regression model, RLOADEST, differences between loads quantify sink source behaviour year-round. observed 1.4 × 104 kg NO3− per year, on average, while downstream, connected was 1.0 average. found more urbanized, hydrologically-disconnected regardless season. In contrast, exchange caused hydrologically be both for nitrate, depending time year. Both alter various spatiotemporal scales. Groundwater reduces annual provides opportunities year-round than reach. Mechanisms include groundwater discharge into variable concentrations, surface-water foster denitrification, loss surrounding near-stream study emphasizes important understanding scale export streams.