Modeling Ecological Aspects of Bioretention Cell Function

A bioretention cell is a vegetated stormwater best management practice (BMP) that reduces stormwater runoff load and energy, by encouraging parts of the water cycle that are inhibited in urban areas—infiltration, evaporation, and subsurface recharge. Current guidance for the design of bioretention cells is very general and relies on engineering the cell media to achieve the desired hydraulic properties. Thus, current guidance neglects the important role that plants and associated belowground processes play in cell function and longevity and how this might differ by region. This study focused on Midwestern climate and biota by assessing the impacts of a native tallgrass prairie mixture and earthworms on the pollutant removal and hydraulic function in a bioretention cell over one growing season, from April to October 2008. In one season, the interaction of plant roots and soil macrofauna improved hydraulic conductivity, storage capacity, and nutrient reduction. Results were supported in the Comprehensive Bioretention Cell Model, which was used to show physical changes in the soil media resulting from plant growth and earthworm activity over three seasons of growth. The results of this study contribute to a growing pool of information to guide effective BMP design with initial and long-term sustainability.