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Wetland Symposium

Limnological Characteristics of Wetlands in the Prairie Pothole Region of Western Wisconsin


RICHARD A. LILLIE

Wisconsin Department of Natural Resources, 1350 Femrite Drive, Monona, WI 53716

Limnological characteristics of selected Waterfowl Production Area wetlands in the Prairie Pothole Region of northwestern Wisconsin were monitored during 1983-92 concurrent with evaluations of various upland management techniques intended to maximize waterfowl production on existing wetlands. Numerous abiotic and biotic parameters including water level; surface area; water clarity; nutrient concentrations; and fish, plant, and macroinvertebrate communities were monitored. Data reported in this presentation correspond to samples collected during the peak of the waterfowl brood use period, early to late June.

Wisconsin's prairie pothole wetlands have relatively fresh water (conductivities 9-383 umhos cm-1, alkalinities 1-201 mg l-1, chlorides 1-10 mg l-1, sulfates 1-5 mg l-1) compared with western counterparts, which have generally saline and hard water. Despite this basic difference and corresponding differences in vegetative composition, Wisconsin's prairie wetlands provide a rich habitat for waterfowl. Many wetlands have total phosphorus and total nitrogen concentrations in excess of 100 g l-1 and 1 mg l-1, respectively, resulting in highly eutrophic conditions with chlorophyll-a concentrations greater than 100 g l-1. Wetlands with dense submersed macrophyte communities generally have much lower in-lake nutrient concentrations and greater water clarity. Macroinvertebrate densities commonly range from 2,000 to 30,000 individuals/m2.

A severe drought during 1987-89 resulted in the loss of most small Class I-IV wetlands and the concentration of waterfowl on the remaining larger Class V wetlands. The lowered water levels promoted severe anoxia during ice cover and the subsequent loss of resident fish communities. Limnological responses to the drought during the drawdown phase varied among wetlands. The initial structure of the wetland's submersed macrophyte community (i.e., the presence or absence of a deep-water community) appeared to influence the response among the macroinvertebrate community and waterfowl.


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