Limnology of Four Lakes in Pictured Rocks National Lakeshore
Kamke, Kendall K.
University of Wisconsin-Stevens Point, College of Natural Resources
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Physical, chemical, and biological linmological data were collected from Miners (4.6 ha), Chapel (30.5 ha), Big Beaver (308.4 ha), and Grand Sable Lakes (306.6 ha), Pictured Rocks National Lakeshore, Michigan in the period July 1983 - May 1985. The four lakes were well oxygenated, light to medium brown in color, with predominantly sand substrate. Miners Lake was a eutrophic impoundment of Miners River and strongly influenced by its discharge. Chapel Lake was meromictic due to morphogenic and biogenic factors. Various ions were present in excessive concentrations in its monimolimnion. The mixolimnion was dimictic and mesotrophic. Big Beaver Lake was mesotrophic, and due to its size, mean depth (6.8 m), and orientation to prevailing wind was polymictic. Grand Sable Lake was oligotrophic and stratified yearly. Chemically the lakes were circumneutral with low to moderate buffering. Dissolved iron was present in all the lakes. Heavy metals (Al, Pb, Hg, Zn) were not detected, or were present in naturally low concentrations. Nutrient levels varied, but were below levels associated with algal blooms. Water color was the most important indicator of trophic status because levels of nutrients and chlorophyll-a were low. The degree of substrate heterogeneity influenced the bentic diversity among the lakes. Zooplankton fauna was dominated by four species in the lakes although overall densities were low. I found no evidence that anthropogenic use had affected the lakes. The lakes are potentially susceptible to changes in water chemistry from acidic precipitation.