Influence of Critical Bioretention Design Factors and Projected Increases in Precipitation due to Climate Change on Roadside Bioretention Performance

This research assessed how design factors (i.e., soil media and vegetative composition) influenced flow rates and pollutant mass removal in eight roadside bioretention systems under simulated increases in precipitation due to climate change. Labile and nonlabile nitrogen and phosphorus (N and P) mass and total suspended solids (TSS) removal was evaluated on an equal volume basis. Results confirm that bioretention systems are a useful tool for increasing local climate change resiliency; peak flow rates and volumes were significantly reduced in all treatments. Water quality performance was highly dependent on the design factors. Sorbtive Media was found to significantly enhance soluble reactive phosphorus removal, which was exported in the conventional media treatments. Labile and nonlabile pollutant retention in the two-species plant palette was higher than in the seven-species palette. This was attributed to the deep, fibrous rooted systems of the Panicum virgatum. Nonlabile pollutant constituents (i.e., TSS and nonlabile N and P) were well retained in all treatments, yet the labile N and P in the compost amended soil media (60% sand and 40% compost) were found to exceed the mass loads in incoming stormwater.