Protozoan communities, macrophyte vegetation and trophic status of northern Michigan wetland lakes

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Virginia Polytechnic Institute and State University


Freshwater wetland lakes have long been ignored by biologists and limnologists. This was the first study to simultaneously sample protozoan communities, macrophyte vegetation, water chemistry and nutrient status, and primary productivity of the phytoplankton in each of the four major types of wetlands -- bogs, fens, marshes, and swamps.

The following hypotheses were supported by data from this study: 1) that differences in plant communities, as measured by a coefficient of similarity, would be greater than differences in protozoan communities from the four different types of wetlands; 2) that common measures of trophic status -- primary productivity, chlorophyll a, and phosphorus and nitrogen nutrients -- would show that bog lakes were eutrophic; and 3) that there would be a positive correlation between the rate of colonization of polyurethane foam unit (PFU) artificial substrates by Protozoa and the trophic status of the wetland lakes.

Other evidence of highly eutrophic conditions in the bogs studied were the high ratios of autotrophic to heterotrophic protozoa in the PFU samples, and the general appearance of some bog sites -- like that of·thick green soup. One bog was oligotrophic as indicated by the very slow rate of colonization of the PFUs placed in it. It was concluded that low pH, brown water bog lakes can span the full range from oligotrophy to eutrophy, and that bog lakes should probably not be labeled dystrophic, since that term implies an extreme degree of oligotrophy.