Watershed derived nutrients for Lake Ontario inflows: Model calibration considering typical land operations in Southern Ontario

Continuous daily simulation of watershed-derived nutrient and sediment loads is required to estimate nearshore water quality in Lake Ontario and the impact of watershed beneficial management practices on lake water quality. In this study, the Soil and Water Assessment Tool (SWAT) is used to build watershed models that incorporate detailed information about representative land operation activities applicable to agricultural watersheds in Southern Ontario. SWAT is calibrated in a multi-objective simulation–optimization framework for the Rouge River watershed with a relatively high spatial resolution monitoring network. These parameters were directly applied to the model for an adjacent watershed, Duffins Creek. The model performed satisfactorily in both watersheds in terms of water balance and temporal, vertical, and spatial redistribution of water. Assessment of the model performance metrics shows a good agreement in the frequency distribution of measured and simulated water quality constituents. Both watersheds are experiencing rapid urbanization, so decision makers in the region may find the developed model useful to analyze the impact of future landuse and operation changes on watershed-derived sediment and nutrients to be delivered into Lake Ontario.