Roy, A.H., L.K. Rhea, A.L. Mayer, W.D. Shuster, J.J. Beaulieu, M.E. Hopton, M.A. Morrison, and A. St. Amand. 2014. How much is enough? Minimal responses of water quality and stream biota to partial retrofit stormwater management in a suburban neighborhood. PLoS ONE 9: e85011
Decentralized stormwater management approaches (e.g., biofiltration swales, pervious pavement, green roofs, rain gardens) that capture and detain, infiltrate, and filter runoff are now more commonly used throughout catchments 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 for improving downstream 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 (5x/year) physical habitat, macroinvertebrate and periphyton assemblages in the streams for the three years before and after treatment implementation. There were very few significant differences in water quality and biotic variables from rain garden and rain barrel installations. Observed responses show trends (p < 0.10) toward increased iron, conductivity, filamentous algae, and macroinvertebrate diversity in control sites, with a corresponding lack of change (or decrease) in experimental sites, indicating a significant treatment effect. We attributed the minimal shifts in stream water quality and biota to the relatively small reductions in stormflow volume associated with the treatment. Improvement in overall stream health is unlikely without treatment of all major impervious surfaces (including roads, apartment buildings, and parking lots), stream bank and riparian improvements, and mitigation of septic tanks and other water quality stressors. Despite the challenges of catchment-scale restoration, additional research is needed to determine the extent of management necessary to improve the health of stream ecosystems.