Effects of urbanization on the water quality of lakes in Eagan, Minnesota
Water-quality characteristics of 17 lakes and ponds in the city of Eagan were described from data collected from 1972 through 1978. The data showed that differences in water quality between lakes were related to differences in the percentage of urbanization. However, water-quality variations within each lake were affected more by climatic variations than by land-use changes during that period. Dissolved solids, alkalinity, and chloride concentrations varied most in lakes with urbanized watersheds, in lakes with outlets, and in lakes less than 6 feet deep. Certain lakes without outlets showed an increase in chloride during the study, caused in part by urbanization but intensified by drought conditions of 1976-77. Fifteen of the lakes studied are less than 10 feet deep and frequently mix during open water. These lakes are highly eutrophic, primarily because of high nutrient loading and recycling of nutrients. Holland and Fish Lakes, with depths of 52 and 30 feet, respectively, were the least eutrophic. These lakes limit continuous recycling of nutrients from bottom materials to water surface by thermal stratification and entrapment of nutrients in the hypolimnion. Three phosphorus-prediction models developed during the study are applicable to shallow (less than about 12 feet), nonstratifying lakes and ponds. The data base was not sufficient to select an appropriate model to predict the effects of future loading from continuing urbanization on the deeper lakes.