Loading estimate methods to support integrated watershed-lake modelling: Duffins Creek, Lake Ontario

Integrated watershed-lake modelling requires high quality data for calibration and validation. The two-phase loading estimate approach presented here provides a more confident estimate of nutrient loads for these models. Phase 1 establishes the initial range of the loading estimates using averaging algorithms, ratio estimators, event mean concentration (EMC) and regression-based methods. For Duffins Creek outlet, the 2007, 2008 and 2009 ranges are 6.2-30, 22.3-78 and 19.5-242 tonnes of total phosphorus (TP), respectively. After combining the Beale ratio estimator and the regression-based methods in Phase 2, the 2007, 2008 and 2009 ranges are reduced to 13-17, 57-73 and 69-92 tonnes TP, respectively. The reduction represents the 0 and 28.07% upper bound bias of the regression-based method. Applying this information to the regression-based methods, daily and monthly ranges with a lower bound with no adjustment and with upper bound as 1.2807 times the regression-based TP load estimates are established. These loads are then used in integrated watershed-lake model calibration and validation to improve the model predictions.