Abstract: Nutrient phosphorus (P) export from urban areas via stormwater runoff contributes to eutrophication of downstream aquatic ecosystems. Bioretention cells are a Low Impact Development (LID) technology promoted as a green solution to attenuate urban peak flow discharge, as well as the export of excess nutrients and other contaminants. Despite their rapidly growing implementation worldwide, a predictive understanding of the efficiency of bioretention cells in reducing P runoff remains limited. Here, we present a reaction-transport model data and codes that was used to simulate the fate and transport of P in a bioretention cell facility in the greater Toronto metropolitan area. The model incorporates a representation of the biogeochemical reaction network that controls P cycling within the cell. We used the model as a diagnostic tool to determine the relative importance of processes immobilizing P in the bioretention cell. The model predictions were compared to multi-year observational data on 1) the outflow loads of total P (TP) and soluble reactive P (SRP) during the 2012-2017 period, 2) TP depth profiles collected at 4 time points during the 2012-2019 period, and 3) sequential chemical P extractions performed on core samples from the filter media layer obtained in 2019. According to the modeling results, groundwater recharge was principally responsible for decreasing the surface water discharge from the bioretention cell (63% runoff reduction). From 2012 to 2017, the cumulative outflow export loads of TP and SRP only accounted for 1% and 2% of the corresponding inflow loads, respectively. Accumulation in the filter media layer was the predominant mechanism responsible for the reduction in P outflow loading (57% retention of TP inflow load) followed by plant uptake (21% TP retention). Of the P retained within the filter media layer, 48% occurred in stable, 41% in potentially mobilizable, and 11% in easily mobilizable forms. There were no signs that the P retention capacity of the bioretention cell would approach saturation in the near future. The design of this bioretention facility seems therefore especially efficient at controlling urban P runoff.
This Dataset includes the model scripts and modelled results dataset for Elm Drive bio retention cell.