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<br />A <br /> <br />e <br /> <br />TABLE 3-9 <br /> <br />COMPARISON BY TROPHIC STATUS OF <br />RCWD LAKES WITH ALL MINNESOTA LAKES <br /> <br />Trophic State <br /> <br />Minnesota Lakes <br />Number Percent <br /> <br />RCWD Lakes <br />Number Percent <br /> <br />Oligotrophic <br />Mesotrophic <br />Eutrophic <br />Hypereutrophic <br /> <br />1,203 <br />3,009 <br /> <br />6,017 <br />1,805 <br /> <br />10% <br />25% <br />50% <br />15% <br /> <br />o <br />2 <br /> <br />16 <br />14 <br /> <br />0% <br /> <br />6% <br />50% <br />44% <br /> <br />The table shows that RCWD has a greater percentage of hypereutrophic lakes and lower <br />percentage of oligotrophic and mesotrophic lakes than all Minnesota lakes. Most of this can <br />be explained in that local geology and topography makes lakes in the North Central <br />Hardwoods Region naturally more eutrophic than northern Minnesota lakes. In this region, <br />in-lake phosphorus, the parameter on which the value is based, is negatively correlatad with <br />mean lake depth (MPCA<1990). Since lakes in the RCWD are generally shallow, they are <br />more susceptible to eutrophication. For example, the Rice Creek chain oflakes in Lino Lakes <br />are not truly lakes, but are more appropriately classified as Type 5 wetlands. Due to their <br />shallow depths, organic bottom material, and emergent vegetation, it is generally not <br />"normal" for these lakes to have low TSI. <br /> <br />e <br /> <br />TSI can also be used to determine suitability for recreational uses. MPCA (1988) classifies <br />lakes as fully supporting swimming, partially supporting, and non-supporting. Fully <br />supporting swimming corresponds to a TSI S 59. A TSI between 60 and 65 indicates the lake <br />is partially supporting swimming. Non-supporting of swimming corresponds to a TSI < 65. <br />Based on this classification, only two lakes, Turtle and White Bear, out of the 33 lakes <br />monitored in the past fully support swimming. An additional 10 lakes partially support <br /> <br />swimming. <br /> <br />Macrophytes. In a cooperative effort between RCWD, MDNR, Ramsey County, and local <br />lake associationsl the exotic nuisance weed Eurasian water milfoil has been positively <br />identified in four lakes within the Rice Creek Watershed. These lakes are White Bear, Bald <br /> <br />e <br /> <br />3-24 <br /> <br />8/94 <br />