OBSERVED CHANGES IN AQUATIC ECOSYSTEMS OVER THE PAST 20 YEARS IN THE UPPER MIDWEST

Environmental and ostracode assemblage data were collected from over 100 lakes across the Upper Midwest between 1987 and 1994. During July of 2013, 33 of the lakes in Wisconsin, Minnesota and Iowa were revisited for the purpose of documenting changes in water quality and freshwater ostracode distributions, and for developing a contemporary dataset to quantify past climatic conditions in the region. Multivariate analyses of the environmental data indicate that lakes located on the prairies and in the prairie-forest transition zone have undergone changes in water chemistry, whereas lakes in the coniferous forest have exhibited few changes. Ostracode assemblage data for the two sampling periods will be presented, and causes of the observed differences in the aquatic ecosystems between the two periods will be discussed.