Robust spatial analysis of sequestered metals in a Southern California Bioswale

Bioswales are a type of permeable green infrastructure designed to slow stormwater and clean runoff by sequestering pollutants such as heavy metals. Measurements of dissolved pollutants before and after the bioswale often justify their ability to clean this runoff, but research addressing the physical and chemical sequestration of these pollutants is scarce. Soil samples were taken from an arid bioswale and analyzed for concentrations of aluminum, cobalt, chromium, copper, iron, magnesium, manganese, nickel, lead, vanadium and zinc. Heat maps of the concentration of these metals in soil were generated via Empirical Bayesian Kriging (EBK) and demonstrate that location-specific sequestration differs between metals within the same swale. Sequential extraction with a modified Tessier et al. (1979) protocol coupled with profiles of metal concentration versus distance along the main flow axis in the bioswale illustrate that the carbonate soil fraction contains elevated concentrations of zinc, lead, cobalt, and manganese, metals sequestered by the bioswale with statistical significance.