Bioretention Soil Media: Understanding the effects of compost and finding predictors for phosphorus leaching

Abstract

This study is intended to 1) investigate the effect of compost rate and compost type on bioretention soil media (BSM) performance, and 2) explore possible predictors of phosphorus leaching from bioretention systems. Columns with 14 different bioretention soil media (BSMs) were analyzed in a greenhouse over the course of 60 weeks, during which 14 storm events were staged. Removal rates of metals (Cu, Pb, and Zn) and nutrients (N and P) were analyzed, as well as infiltration rate, plant yield, and chemical soil properties. All BSMs acted as sinks for copper and zinc when real stormwater was used as influent, with BSMs containing pure biosolids showing most effective removal. BSMs with 80% compost by volume were less effective than 40% or 20% compost mixtures at metals removal when varying influent levels were used. Nitrogen leaching results were counter to expectations - it is posited that hydraulic features of the BSMs may have played a larger role than BSM ingredients in determining nitrogen leaching. Mehlich-III phosphorus saturation ratio (PSR) was found to be an adequate predictor of phosphorus leaching from all BSMs, while the ammonium oxalate phosphorus saturation index (PSI) was a poor predictor, possibly due to the wide variety of BSMs in this study.