Minneapolis Chain of Lakes Phosphorus Reduction Strategy

摘要

The Minneapolis Chain of Lakes is a group of five heavily used urban lakes located approximately 1.5 miles southwest of downtown Minneapolis, MN. The 8,000-acre watershed was developed over the last 100 years and is now completely urbanized. Watershed development and human activities have lead to water quality degradation over the last 40 years. In 1991, a diagnostic study of urban runoff and lake water quality lead to the development of an 8-year, multi-million dollar watershed management effort. A key component of the management strategy was quantification of phosphorus load reduction goals. The watershed management plan is based on reductions of inflow phosphorus loads to the lakes to attain long-term water quality goals. The phosphorus load reduction strategies were developed for each of the lakes based on lake water quality modeling and watershed load analysis. The load reduction goals established for each of the lakes are (percent of total watershed load): Brownie -10%; Cedar - 40%; Lake of the Isles - 20%; Calhoun - 30%; and Harriet - 20%. The two main structural best management practices (BMPs) being implemented are wetland/pond systems and grit chambers. The structural BMPs, in conjunction with increased street sweeping and public education, are being implemented to reduce phosphorus loading from this fully developed watershed. The Minneapolis Chain of Lakes are located 3 miles southwest of downtown Minneapolis, MN. The Chain's five lakes are the central natural resource feature of the Minneapolis Chain of Lakes Regional Park. The regional park receives over 2.25 million visitors per year, making it the second most heavily used regional park in the Twin Cities Metropolitan Area. The chain receives urban runoff from a fully developed 8,000-acre watershed that includes portions of Minneapolis and the adjoining suburban communities of St. Louis Park and Edina. Major land use categories presently include residential development (51%), industrial/commercial (19%), and open space (14%). The lakes in the Chain (Brownie, Cedar, Isles, Calhoun and Harriet) are interconnected with navigable channels, culverts or pumping systems. The lakes and the watershed drain from north to south, flowing from the upper chain (Brownie to Calhoun), where water is pumped to Harriet, which discharges to Minnehaha Creek, a tributary to the Mississippi River. Demand for this study and watershed management effort arose from public concerns over increased recreational use of the lakes and attendant deterioration in water quality.