A decision support system approach for identifying polIutant source for optimization of beneficial management practices scenario modelling in Lake Winnipeg watersheds

Session H3: Agro-Ecosystem Modeling for Spatial Solutions to Watershed Conundrums

The Soil and Water Assessment Tool (SWAT) results can be used to source trace loading "hotspots• for optimally locating beneficial management practices (BMP). It is possible to trace upstream and compute the relative contribution of each sub-basin to a point of interest, accounting for in-stream processes, reservoirs and point sources. A decision support system (DSS) framework was developed to run SWAT, perform the otherwise tedious process of source tracing "hotspots" and to optimize BMP locations. The "Crop to Hay- land use change BMP scenario was applied in an attempt to reduce annual loadings of total phosphorus (TP) for three Lake Winnipeg Basin watersheds: Boyne, La Salle and Little Saskatchewan. This BMP scenario was applied to all the sub-basins, starting from the highest TP contributing sub-basin to the lowest ("best case") and then applied starting from the smallest contributing sub-basin to the highest ("worst case"). When comparing the best case to the worst case to meet the 10% reduction target, the Boyne, La Salle, and Little Saskatchewan watersheds required 49, 57, and 63% less area of BMP to be applied, respectively. These results showed the importance of BMP placement in the watershed and the impact on pollutant reduction efficiency and, therefore, demonstrated the importance of the use of source tracing technique in developing efficient BMP scenarios.