Scenario-testing of agricultural best management practices in Lake Erie watersheds

Current research has shown that reductions in nonpoint nutrient loading are needed to reduce the incidence of harmful algal blooms and hypoxia in the western and central basins of Lake Erie. We used the Soil and Water Assessment Tool (SWAT) to test various sediment and nutrient load reduction strategies, including agricultural best management practice (BMP) implementation and source reduction in various combinations for six watersheds. These watersheds, in order of decreasing phosphorus loads, include the Maumee, Sandusky, Cuyahoga, Raisin, Grand, and Huron, and together comprise 53% of the binational Lake Erie Basin area. Hypothetical pristine nutrient yields, after eliminating all anthropogenic influences, were estimated to be an order of magnitude lower than current yields, underscoring the need for stronger management actions. However, cover crops, filter strips, and no-till BMPs, when implemented at levels considered feasible, were minimally effective, reducing sediment and nutrient yields by only 0–11% relative to current values. Sediment yield reduction was greater than nutrient yield reduction, and the greatest reduction was found when all three BMPs were implemented simultaneously. When BMPs were targeted at specific locations rather than at random, greater reduction in nutrient yields was achieved with BMPs placed in high source locations, whereas reduction in sediment yields was greatest when BMPs were located near the river outlet. Modest nutrient source reduction also was minimally effective in reducing yields. Our model results indicate that an “all-of-above” strategy is needed to substantially reduce nutrient yields and that BMPs should be much more widely implemented. •Modest BMP use is minimally effective for reducing sediment and nutrient yields.•Modest nutrient source reduction also was minimally effective.•Spatially targeted implementation of BMPs increases the effectiveness.•Aggressive BMP implementation and natural restoration programs will be needed.