Stormwater storage among remnant, degraded and restored urban prairies and wetlands of varying ecological quality

Colleen Mary O'Brien , Jennifer Jenkins, Vivien Rivera, Liliana Hernandez Gonzalez , Jordan Gurneau , Upasana Larson, Karl Gnaedinger, Emilie Pfeiffer, Shane Tripp, Colin Phillips, Martha Lopez-Salazar, William M. Miller , Aaron Packman

In response to increasing intensification of land use and more frequent and severe flooding, urban green spaces and natural areas are being relied upon to provide additional stormwater storage. Natural grasslands and wetlands provide extensive ecosystem services, including stormwater storage. These types of ecosystems were once widespread across the globe, but much of this habitat has been lost due to conversion for agriculture and urban development, and many remaining prairie-wetland ecosystems have experienced degradation. However, there has been limited research into how this degradation and subsequent restoration impact the stormwater storage these areas provide. To improve our understanding of the impacts of ecosystem degradation and restoration on stormwater storage and hydrologic response, we installed a network of groundwater level and electrical conductivity sensors at Indian Boundary Prairies, a prairie and wetland complex in southern Cook County, IL, USA. We used the resulting 15-month time series to estimate stormwater storage across locations that have experienced varying levels of historical degradation and more recent restoration by The Nature Conservancy. Our analysis indicates that the prairies store nearly half of the stormwater runoff originating from the surrounding urban neighborhoods. Variations in stormwater storage reflected underlying soil and habitat structure; poorly drained loams in wetland and swale areas retained water for longer than the loamy fine sands of the sand ridge. However, storage did not vary with habitat quality. Low-quality areas at Indian Boundary Prairies likely retain intact soil structure and hydrologic function, therefore, stormwater behavior appears governed more by these subsurface properties than by above-ground vegetation. This suggests that the primary ecohydrological function of these greenspaces is stormwater infiltration followed by evapotranspiration that reduces soil moisture and groundwater levels between storms. These findings highlight the ecosystem services provided by restored urban prairies and their ability to contribute to local flood reduction.