Can rain garden implementation support multiple ecosystem services in Cleveland, OH?

Stormwater runoff is a serious water quality issue within urban areas. Rainfall of greater than an inch can cause the combined sewer system in Cleveland, OH to overflow into Lake Erie. To combat this effluent, the Northeastern Ohio Regional Sewer District is examining infrastructure strategies to reduce runoff. To evaluate the impact of green infrastructure investment, rain gardens were installed on formerly vacant land in the Slavic Village neighborhood of Cleveland, OH. In addition to reducing stormwater runoff, our goal was to measure ecosystem services influenced by this land use change. Specifically, we measured whether rain gardens influenced local bee biodiversity within urban greenspaces. Pollinators were sampled during June, July, and August in 2014 within 6 rain gardens and 8 control lots using pan traps and soapy water. A total of 1,016 bees were collected including 21 different genera in all of the sites. A majority of bees were in the family Halictidae (n=752) with small sweat bees being most common (Lasioglossum spp., n=477). Bee richness and community were similar between sites. However, bee abundance based on average number of bees collected per trap was lower at rain garden sites. These results imply that the initial installation of rain gardens may not offer significant support to the local pollinator community. The differences in bee abundance could be due to the lack of floral abundance at the rain gardens compared to controls. Thus, to maximize ecosystem services, rain gardens should be designed to include a greater abundance of flowering vegetation.