Validation of an agricultural non-point source model in a watershed in southern Ontario

As part of an integrated watershed management study for watersheds of southern Ontario, the agricultural non-point source (AGNPS) model was interfaced with a decision support system that reduces the time-consuming data input steps and scenario testing. The objectives of this study were to define appropriate model input parameters for the region and to define a protocol for model validation at the sub-watershed and watershed scale. The model provided realistic estimates of nutrient loads in run-off water for a wide range of storm events. For tested grid sizes, both the peak flows and historic run-off values were well reproduced by the AGNPS model. High coefficient of efficiency (CE) values of 0.821–0.919 for peak flows and of 0.713 for run-off volumes were obtained. The CE values for nutrient loads are extremely high: 0.990 for nitrogen and 0.965 for phosphorus. These results show that the model is well suited to applications in southern Ontario, and with the described interface, should be a useful tool for watershed management by conservation authorities in the region.