Stormwater runoff to an impaired lake: impacts and solutions

Stormwater runoff can represent a significant source of pollutants to downstream water bodies. An integrated assessment was conducted for the Spring Lake watershed in western Michigan because of concerns that increased impervious land cover in the watershed, especially in sub-basins adjacent to Spring Lake, would result in greater stormwater runoff and pollutant loads. Spring Lake has a history of high total phosphorus (TP) concentrations and cyanobacterial blooms. An alum treatment, paid for by an assessment, was applied to Spring Lake in 2005 to control internal phosphorus loading; hence, there was an economic incentive for stakeholders to limit new phosphorus from entering the lake, which otherwise would reduce the long-term efficacy of the alum treatment. This study provides a novel six-step process that identifies priority areas and optimally reduces nonpoint sources of pollution. We identified a suite of best management practices to be placed in the watershed, assessed their optimal locations based on pollutant sources, and modeled the degree to which their implementation would reduce TP and total suspended solids. Application of the modeled best management practices (BMPs) resulted in a 15 % reduction in TP load and a 17 % reduction in total suspended solid load. Reductions were not uniform throughout the watershed, with the greatest reductions closest to Spring Lake. We also developed a flow chart for BMP selection, which may be transferable to other watersheds with similar issues.