Kaykhosravi, S., Shafii, M., Bhusal, Y., Slowinski, S., Chomicki, K. M., Rezanezhad, F., Van Cappellen, P. (2022) ESTIMATING SEASONAL AND ANNUAL EXPORT CONCENTRATIONS FOR URBAN PHOSPHORUS EXPORT LOADS CALCULATION. In Fall Meeting 2022. AGU. https://agu.confex.com/agu/fm22/meetingapp.cgi/Paper/1168210

We estimated annual and seasonal phosphorus (P) export loads from urban landscapes using the Stormwater Management Model (SWMM) platform. We focused on different operational P fractions including total P (TP), dissolved P (DP), particulate P (PP), reactive P (RP) consisting of dissolved RP and particulate RP, and unreactive P (UP) representing TP minus RP and used a regression model to calibrate the P module in SWMM. Model calibration was based on discharge and P data acquired from October 2020 to October 2021 in two urban sewersheds located in the town of Ajax, referred to as AJE (134 ha) and AJW (118 ha). Land use in these catchments is mixed (residential, commercial, industrial, and green space) with AJE being more impervious and urbanized than AJW. For simulating P loads with SWMM, we introduced a novel export concentration (EC) approach for each of the different P fractions and for each of the sewersheds. We determined EC with regression models of discharge and concentration. The model calibration yielded NSE (Nash Sutcliffe Efficiency) values of 0.84 to 0.97 for the hydrology, and 0.50 to 0.81 for the P export loads. Results indicated that AJE generates higher runoff and surface area-normalized P loads compared to AJW. The EC values for each of the P fractions at different seasons are marginally different where the difference is more pronounced for PP compared to DP fractions. Annual and seasonal P loads were estimated and compared; annual TP load for AJE is 0.61±0.05 kg/ha and for AJW 0.39±0.07 kg/ha. Moreover, the results showed that the PP contributes most to the TP load (91±12%), followed by RP forms that represent 23.6±3.9% of TP. This study successfully introduced EC as a calibration parameter and concept that is transferable to similar urban sewersheds. Comparing EC and P loads provides insights into the relative composition of TP loads, including contributions of reactive versus unreactive P, and the significant role of imperviousness and runoff.

https://agu.confex.com/agu/fm22/meetingapp.cgi/Paper/1168210