Tracking downstream water quality benefits of urban stream restoration using high spatial- resolution longitudinal monitoring
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Urbanization and impervious surface cover contribute to increased nonpoint sources of pollution in stormwater runoff. Additionally, urban streams suffer from streambank erosion and hydrologic disconnection, further degrading water quality. Stream restoration is considered a best management practice (BMPs) frequently implemented to mitigate the impacts of urbanization, reduce pollutant concentrations, and improve stream health. Under many federal programs and restoration plans, it is presumed that the benefits of localized stream restoration propagate downstream, however there is little research to validate this assumption. To better understand if and how stream restoration improves water quality both locally and downstream of restoration activities, we sampled Paint Branch Creek, an urban stream in Maryland, USA, monthly using high spatial resolution longitudinal synoptic monitoring to identify how water quality changes along the entire flowpath. We focused monitoring efforts around two restored stream reaches, sampling just above the restored reach and 0, 100, and 200 meters below the restored reach, to characterize how far downstream the water quality benefits of various restoration activities propagate. Results suggest that stream restoration can cause observable decreases in the concentrations of several contaminants of concern, with water quality improvements persisting up to 200 meters downstream of restoration activities. Additionally, longitudinal synoptic monitoring revealed the ability of urban land use features to either act as sources or sinks for contaminant loading. Improving our understanding of the efficacy and benefits of stream restoration activities will allow stakeholders to better design, select, and implement restoration activities to maximize pollutant load reductions on watershed scales.