HISTORICAL CHANGES IN WATER QUALITY OF LOTUS LAKE AND HORSE LAKE, POLK COUNTY, WISCONSIN

Joy M. Ramstack, St. Croix Watershed Research Station, Science Museum of Minnesota
Mark B. Edlund, St. Croix Watershed Research Station, Science Museum of Minnesota
Jeremy Williamson, Polk County Land and Water Resources, Balsam Lake WI

Within the glaciated regions of the Upper Midwest, lakes feature prominently in the landscape and are a valued resource for tourism, municipalities, home and cabin owners, recreational enthusiasts, and wildlife. Current and historical land and resource uses around the lakes in Polk County, WI, including shoreline development, sport fisheries, waste and stormwater discharge, water level management, logging, grazing, and agriculture, have raised concerns about the state of the lakes and how to best manage them in a future certain to bring change. To effectively develop management plans, knowledge of the natural state of a lake and an understanding of the timing and magnitude of historical ecological changes become critical components.

Sediment cores were obtained from Lotus Lake and Horse Lake in Polk County, WI and paleolimnological techniques were used to reconstruct the trophic and sedimentation history of the lakes. Analytical tools used include radioisotopic dating of the cores, geochemical analyses to determine local sediment accumulation rates, and analysis of subfossil algal (diatom) communities. Multivariate analyses, diatom-based transfer functions, and comparison of algal assemblages with an 89 Minnesota lake data set were used to relate changes in trophic conditions and algal communities to human impacts in the local watershed.