Lee K. Rhea

How Much Is Enough? Minimal Responses of Water Quality and Stream Biota to Partial Retrofit Stormwater Management in a Suburban Neighborhood

Decentralized stormwater management approaches (e.g., biofiltration swales, pervious pavement, green roofs, rain gardens) that capture, detain, infiltrate, and filter runoff are now commonly used to minimize the impacts of stormwater runoff from impervious surfaces on aquatic ecosystems. However, there is little research on the effectiveness of retrofit, parcel-scale stormwater management practices for improving downstream aquatic ecosystem health. A reverse auction was used to encourage homeowners to mitigate stormwater on their property within the suburban, 1.8 km2 Shepherd Creek catchment in Cincinnati, Ohio (USA). In 2007–2008, 165 rain barrels and 81 rain gardens were installed on 30% of the properties in four experimental (treatment) subcatchments, and two additional subcatchments were maintained as controls. At the base of the subcatchments, we sampled monthly baseflow water quality, and seasonal (5×/year) physical habitat, periphyton assemblages, and macroinvertebrate assemblages in the streams for the three years before and after treatment implementation. Given the minor reductions in directly connected impervious area from the rain barrel installations (11.6% to 10.4% in the most impaired subcatchment) and high total impervious levels (13.1% to 19.9% in experimental subcatchments), we expected minor or no responses of water quality and biota to stormwater management. There were trends of increased conductivity, iron, and sulfate for control sites, but no such contemporaneous trends for experimental sites. The minor effects of treatment on streamflow volume and water quality did not translate into changes in biotic health, and the few periphyton and macroinvertebrate responses could be explained by factors not associated with the treatment (e.g., vegetation clearing, drought conditions). Improvement of overall stream health is unlikely without additional treatment of major impervious surfaces (including roads, apartment buildings, and parking lots). Further research is needed to define the minimum effect threshold and restoration trajectories for retrofitting catchments to improve the health of stream ecosystems.

ENVIRONMENTAL REVIEWS AND CASE STUDIES: Building Green Infrastructure via Citizen Participation: A Six-Year Study in the Shepherd Creek (Ohio)

Green infrastructure at the parcel scale provides critical ecosystem goods and services when these services (such as flood mitigation) must be provided locally. Here we report on an approach that encourages suburban landowners to mitigate impervious surfaces on their properties through a voluntary auction mechanism. We used an economic incentive to place rain gardens and rain barrels onto parcels in a 1.8-km2 watershed near Cincinnati, Ohio. A comprehensive hydrologic, water-quality, and ecological monitoring campaign documented environmental conditions before and after treatment. In 2007 and 2008, we engaged private landowners through a reverse auction to encourage placement of one rain garden and up to four rain barrels on their property. The program led to the installation of 83 rain gardens and 176 rain barrels onto more than 20% of the properties, and preliminary analyses indicate that the overall discharge regime was altered by the treatments. The length of the study (six years) may have precluded observation of treatment effects on water quality and aquatic biological communities, as we would expect these conditions to respond more slowly to management changes. These distributed storm-water installations contributed to ecosystem services such as flood protection, water supply, and water infiltration; provided benefits to the local residents; and reduced the need for larger, expensive, centralized retrofits (such as deep tunnel storage).