Phosphorus in urban stormwater runoff: a review of sources, transport pathways, and control solutions

Urbanization significantly impacts phosphorus (P) cycling and transport from terrestrial to aquatic ecosystems, hence, contributing to the eutrophication of receiving water bodies. Global urban growth projections underscore the need for a better understanding of the P sources, pathways, and eutrophication potential of urban stormwater runoff, as well as the effectiveness of current stormwater best management practices (BMPs) in mitigating urban P export. Traditional and low-impact development BMPs, including stormwater ponds (SWPs) and bioretention cells (BRCs), while primarily intended to decrease peak flows, have the potential to attenuate P loads across urban areas. Here, we consolidate current knowledge on urban stormwater P, in the literature and through analysis of the International Stormwater BMP Database (ISBD), focusing on P concentrations, yields, loads, and chemical speciation. Moreover, we assess the P reduction or enrichment effects of urban stormwater BMPs and identify key knowledge gaps and research priorities. In particular, we propose that future research should comprise more detailed studies on the diversion of P to the subsurface by BMPs, the P biogeochemical transformation processes within BMPs, the interactions of P with other urban pollutants, the current and future impacts of climate change on urban P speciation and export loads, and expanding data collection across geographies.