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Effects of stream restoration on nitrogen removal and transformation in urban watersheds: lessons from Minebank Run, Baltimore, Maryland.
Mayer, PM; Schechter, SP; Kaushal, SS; Groffman, PM
Stream restoration is an important green infrastructure tool that may improve water quality and protect watershed function and services. Runoff from impervious surfaces and leakage from sewage infrastructure, septic systems, agricultural ditches, and tile drains creates excess nitrogen (N) in groundwater, surface water, and coastal waters, which is detrimental to human and ecosystem health. Degraded urban streams suffer from altered hydrology and biogeochemistry that can impair a stream’s capacity to process and remove excess N in stream water. This case study of Minebank Run in Baltimore, Maryland, found factors that limit the removal of excess N in degraded streams and identified restoration and management approaches that enhance N removal. We found three stream restoration strategies that can greatly improve N removal capacity: (1) increasing hydrologic residence time, (2) increasing hydrologic connectivity between the stream channel and floodplains, and (3) increasing organic carbon availability to foster denitrification “hot spots.” The findings suggest that combining approaches—such as prioritizing nonpoint N source reductions in watersheds and integrating green infrastructure with stream and floodplain wetland restoration approaches, which reduce peak flow, increase hydrologic residence time, and supply organic matter (e.g., maintaining riparian zones)—will be the most efficient way to enhance N removal and protect ecosystem services in urban streams.
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