Advances in the Integration of Watershed and Lake Modeling in the Lake Winnipeg Basin

Estimating non-point source pollution from watersheds and the effects of mitigation measures (e.g. beneficial management practices or BMPs) is an important step in managing and protecting water quality, not only at the basin level where it originates, but also at the receiving waters such as reservoirs, lakes or oceans. Lake Winnipeg is a prime example of such land-lake interactions, where eutrophication and increased algal blooms in the lake are fueled, as evidence suggests, from agricultural sources of nutrients in the region. Over the years, simulation models at the watershed level have been applied to aid in the understanding and management of surface runoff, nutrients and sediment transport processes. Similarly, models with different degrees of complexity are used to simulate the aquatic ecology and water quality in lakes. The Soil and Water Assessment Tool (SWAT) is a widely known watershed model, which provides estimations of runoff, sediment yield, and nutrient loads at a sub-basin level. Here we examine the application of SWAT to one of three pilot watersheds on the Lake Winnipeg basin in order to investigate the impacts and uncertainties of different BMPs on nutrient loading in the targeted catchment areas. We also explore avenues for scaling and propagating such loads and uncertainties into the receiving lake models.