Mahyar Shafii, Sarah Kaykhosravi, Steph Slowinski, Yubraj Bhusal, Calvin Hitch, William Withers, Fereidoun Rezanezhad, Philippe Van Cappellen (2022). Phosphorus dynamics in urban sewersheds: speciation, bioavailability, and export. Proceedings of the GWF Annual Open Science Meeting, May 16-18, 2022.

The sources (e.g., wastewater) and sinks (e.g., stormwater ponds) of nutrient phosphorus (P) in urban watersheds differ significantly from those in rural watersheds. Furthermore, the high imperviousness in urban areas magnifies the loadings of pollutants and nutrients moving through surface runoff to receiving waters. Urban stormwater nutrient management requires a comprehensive understanding of the emissions, speciation and export fluxes of P at the catchment scale. Our research involves the collection of P speciation, flow and meteorological data and the development of statistical models to estimate loadings of different P pools in three urban sewersheds in southern Ontario with a range of drainage areas (10-140 ha) and land-use (i.e., different fractions of residential, commercial, and industrial development). Water and suspended sediments from stormwater runoff are analyzed in the lab using multiple techniques to identify the various P pools according to their reactivity and bioavailability. The statistical analysis of the data shows that the precipitation regime and the type of land cover (particularly the extent of green spaces and imperviousness) play key roles in regulating the export of particulate and dissolved P pools, respectively. These findings are mainly attributed to the generated amount of runoff and commercial fertilizer application in this study’s sewersheds. We present an empirical methodology that is transferrable to estimate urban P emissions in sewersheds with limited or no water quality monitoring data. The approach provides a tool for decision-makers to rank and compare sewersheds based on their annual P export loads (especially, the dissolved and bioavailable P pools), which can then help them in optimizing the implementation of Stormwater Management (SWM) infrastructure, such as stormwater ponds and bioretention cells, that can reduce the export of bioavailable P to downstream water bodies.

AOSM2022 core modelling First Author: Mahyar Shafii (UW) Additional Authors: Sarah Kaykhosravi (UW), Steph Slowinski (UW), Yubraj Bhusal (UW),, Calvin Hitch (Toronto and Region Conservation Authority),, William Withers (City of Richmond Hill, ON),, Fereidoun Rezanezhad (UW),, Philippe Van Cappellen (UW)