Urban Runoff Phosphorus Removal Pathways in Bioretention Systems

Abstract

The role of vegetation and saturated zones in stormwater-dissolved phosphorus (PO43--P) removal was investigated using bioretention microcosms. Nine bioretention columns were dosed with synthetic stormwater under various hydrological conditions and phosphorus loading rates and monitored over a 12-month period. Remarkable phosphorus removal (>90%) was achieved using the mixed filter media of sand and local soil, with or without vegetation. Bioretention columns in which P. alopecuroides was planted could significantly enhance PO43--P removal. The saturated zones could also reduce the effluent PO43--P concentrations, but had no significant effect on total phosphorus removal. Approximately 50% of the input phosphorus retained in the filter media was extracted in the top 0-22.5 cm, where it could be available for uptake by plants. Further, 57.1% to 76.1% of the total phosphorus input recovered in the total plant biomass was stored in the above-ground shoots. Thus, periodic harvesting of shoots can be a sustainable method of phosphorus removal from stormwater bioretention systems.