Assessment of the Performance of Field-Scale Bioretention Systems to Reduce Phosphorus Loads from Urban Stormwater

High nutrient loading can degrade surface water quality worldwide. Bioretention systems are low impact development stormwater management features designed to remove pollutants, including phosphorus (P), from urban stormwater runoff. In this study, two field-scale bioretention systems installed in London, Ontario, Canada were monitored to develop detailed understanding of P behaviour and the hydro-biogeochemical mechanisms that govern overall P retention. Net retention of total P and dissolved organic P, and net release of soluble reactive P (SRP) and total dissolved P were observed. Prolonged input of road de-icing salts (NaCl) in winter and early spring may result in high P release from the bioretention systems in spring. Porewater samples revealed the distribution of SRP within the bioretention systems to be highly heterogeneous and without a monotonic decrease with depth as commonly assumed in literature, highlighting complex temporal and spatial behaviour of P and controlling biogeochemical processes within field-scale bioretention systems