ANALYSIS OF REGIONAL PATTERNS IN LAKE WATER QUALITY: USING ECOREGIONS FOR LAKE MANAGEMENT IN MINNESOTA

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Abstract
Developing lake management strategies that have utility across diverse geographic areas is difficult. For example, with over 12,000 lakes in Minnesota, determining carrying capacities, restoration goals, and lake protective standards cannot be practically made on a lake-by-lake basis. In light of this, the aquatic ecoregion approach was employed to assess regional patterns in watershed characteristics and inlake parameters such as phosphorus concentration, Secchi transparency, and lake mixing pattern. This approach defined seven distinct ecoregions, of which, the following four contain the majority of lakes in Minnesota: Northern Lakes and Forest (NLF), North Central Hardwood Forests (CHF), Western Corn Belt Plains (WCP) and the Northern Glaciated Plains (NGP). Analysis of total phosphorus data from approximately 1,100 lakes by ecoregion resulted in the following median epilimnetic concentrations: NLF – 23 μg P/L, CHF – 50 μg P/L, WCP – 121 μg P/L, and NGP – 176 μg P/L. Lake mixing patterns may be a further basis for organizing the data. These analyses indicate that the aquatic ecoregion approach is a valid method for grouping lake data and identifying spatial patterns of lake characteristics. Further, for Minnesota, this analysis indicates that no single total phosphorus concentration can be used as a basis for setting standards across Minnesota because of its tremendous diversity of lakes and attainable trophic states. Lake management schemes based on the ecoregion analysis presented.

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