468 - Evaluating the Effect of Residential Catchment Maturity on Phosphorus Export Coefficients in Ontario

The phosphorus export coefficients from different land uses, have been utilized for offsetting and credit purposes in Ontario. The current coefficients used for this purpose were selected conservatively based on both modeling and field monitoring performed during early 2000s. While these coefficients have proven useful, they lack consideration for the effect of catchment maturity. The presence and maturation of vegetation and topsoil may play a significant role in phosphorus exported from high intensity residential catchments as well as the effect of aging infrastructure. Previous studies in the broader region and local modeling have shown a wide coefficient range (0.19-6.23 kg/ha/yr). This study aims to provide a more localized estimation of annual and seasonal phosphorus loads exported from several high intensity residential catchments in Ontario. It also evaluates how catchment maturity influences the physical and chemical properties of stormwater runoff. Over two years, runoff from three residential catchments was monitored using automated samplers and area velocity sensors. The catchments were categorized as less than 5 years old, 10-15 years old, and more than 20 years old. Comparing export coefficients from the two years of the study, one a dry year and another a wet year (current), might shed light on the impact of climate change on pollutant export.