Lake Winnipeg eutrophication results from excess nutrient loading due to agricultural activities across the watershed. Estimating nonpoint-source pollution and the mitigation effects of beneficial management practices (BMPs) is an important step in protecting the water quality of streams and receiving waters. The use of computer models to systematically compare different landscapes and agricultural systems across the Red-Assiniboine basin has not been attempted at watersheds of this size in Manitoba. In this study, the Soil and Water Assessment Tool was applied and calibrated for three pilot watersheds of the Lake Winnipeg basin. Monthly flow calibration yielded overall satisfactory Nash-Sutcliffe efficiency (NSE), with values above 0.7 for all simulations. Total phosphorus (TP) calibration NSE ranged from 0.64 to 0.76, total N (TN) ranged from 0.22 to 0.75, and total suspended solids (TSS) ranged from 0.29 to 0.68. Based on the assessment of the TP exceedance levels from 1993 to 2007, annual loads were above proposed objectives for the three watersheds more than half of the time. Four BMP scenarios based on land use changes were studied in the watersheds: annual cropland to hay land (ACHL), wetland restoration (WR), marginal annual cropland conversion to hay land (MACHL), and wetland restoration on marginal cropland (WRMAC). Of these land use change scenarios, ACHL had the greatest impact: TSS loads were reduced by 33 to 65%, TN by 58 to 82%, and TP by 38 to 72% over the simulation period. By analyzing unit area and percentage of load reduction, the results indicate that the WR and WRMAC scenarios had a significant impact on water quality in high loading zones in the three watersheds. Such reductions of sediment, N, and P are possible through land use change scenarios, suggesting that land conservation should be a key component of any Lake Winnipeg restoration strategy.

Removal of trees for pasture or crop production is common along the stream reaches in the Canadian Prairies, resulting in a patchwork of forested and nonforest riparian vegetation along most streams. The effect of vegetation type on channel geomorphology and potential to influence sediment dynamics was studied using eight paired reaches (forested and nonforest) within agricultural watersheds in southern Manitoba, Canada. High potential for bank erosion was observed at all sites (bank erosion hazard index scores), but Pfankuch channel stability scores were significantly higher for forested reaches compared with nonforested reaches. Furthermore, forested reaches had higher width to depth ratios, but flood-prone widths did not differ significantly, resulting in lower entrenchment ratios. Reduced channel width and cross-sectional area in nonforested reaches created an overall reduction of in-stream habitat, increased velocity, and increased potential for exceedance of channel capacity and floodplain access during high-flow events. Channel widening in response to riparian afforestation efforts has been observed in a variety of other locations globally and the results of this study suggest that widening with afforestation can still be anticipated in this region where stream gradients are low, hydrology is dominated by snowmelt, and forest cover is minimal.