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Stream Responses to a Watershed-Scale Stormwater Retrofit
Roy, A., L. Rhea, H. Thurston, W. Shuster, AND A. St. Amand. Stream Responses to a Watershed-Scale Stormwater Retrofit. Presented at New England Association of Environmental Biologists (NEAEB), Falmouth, MA, March 23 - 26, 2012.
Aggregate impacts of GI on stormwater volume, ecology, and contaminants in headwater streams.
Green infrastructure can reduce stormwater runoff and mitigate many of the problems associated with impervious surfaces; however, the effectiveness of retrofit stormwater management for improving aquatic health is largely untested. In the suburban, 1.8 km2 Shepherd Creek catchment in Cincinnati, Ohio (USA), we used a reverse auction approach to provide economic incentive for homeowners to allow rain gardens and rain barrels on their property. We sampled continuous stream discharge, monthly baseflow water quality, and seasonal macroinvertebrate and periphyton assemblages (5 times/year) in two control and four experimental subcatchments three years before and after stormwater treatment implementation. Following successive auctions in spring 2007 and 2008, we installed 170 rain barrels and 83 rain gardens on approximately one-third of the 350 properties within the experimental portion of the watershed. Stormwater management led to a small, but highly significant reduction in runoff volume in experimental subcatchments. Density of filamentous algae increased in control sites following treatment; however, this was explained by the reduced canopy cover associated with riparian clearing in these sites that was unrelated to the project. We attributed the minimal shifts in macroinvertebrate metrics to the relatively small changes in stream hydrology and water quality. This suggests that extent of stormwater management, recovery time, or other factors were insufficient to drive improvements in stream biota. While green infrastructure can mitigate excess stormwater from impervious surfaces and provide social and economic benefits, improvement in stream health is unlikely without treatment of all major runoff sources (including roads and parking lots) within catchments.