Effects of Stream Restoration on Nitrogen Removal and Transformation in Urban Watersheds: Lessons from Minebank Run, Baltimore, Maryland
Paul M. Mayer,a Shannon P. Schechter,b* Sujay S. Kaushal,c and Peter M. Groffmand
aResearch Ecologist, US Environmental Protection Agency, National Risk Management Research Laboratory, Ground Water and Ecosystems Restoration Division, Ada, OK
c Assistant Professor, Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD
d Senior Scientist, Cary Institute of Ecosystem Studies, Millbrook, NY
* Corresponding author
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.
Building Blue in Franklin, Massachusetts
Julie Wood,a* Nigel Pickering,b and Kate Bowditchc
b Senior Engineer/Scientist, Horsley Witten Group, Sandwich, MA
c Director of Projects, Charles River Watershed Association, Weston, MA
* Corresponding author.
This study compared two methods of developing subwatershed-scale stormwater management plans to bring a small subwatershed into compliance with a nutrient total maximum daily load (TMDL) study using low-impact development (LID) stormwater treatment systems. We developed one plan using a step-wise professional judgment method and the second using an optimization algorithm set to maximize phosphorus reduction while minimizing cost. The resulting management plans offer insight into the benefits of subwatershed-scale stormwater planning efforts, and specifically the benefits of mathematical optimization in stormwater management planning. Finally, the study presents multiple accessible options for compliance with a nutrient TMDL using LID systems sited and designed to provide a host of additional public benefits, such as reduced flooding, increased groundwater recharge, decreased stress on drinking and surface water resources, and the addition of public green space.