DIATOM ANALYSIS OF A PAIRED RESERVOIR SYSTEM WITH DIVERGENT NUTRIENT LOADING HISTORIES IN RURAL INDIANA

Shakamak State Park, established in 1929, is located in the center of Clay, Green, and Sullivan counties in Indiana. Lake Shakamak and neighboring Lake Lenape are adjacent sub-impoundments in the park, which were both constructed around 1930, when drainage through the railroad grade was blocked. These two reservoirs trap significant amounts sediment and nutrients before out-letting to a third impoundment, Lake Kickapoo. Nutrient utilization is evident in the comparison of dissolved oxygen levels between the two reservoirs. Modern Lake Shakamak displays a more eutrophic status, with dissolved oxygen values of 5ppm around 2 meters below the air-water interface . Preliminary, low resolution diatom anlaysis suggests that Lake Shakamak has overall greater diatom productivity and from the sediment record, has a history of fossil diatom assemblages that favor phosphate. Despite being adjacent systems, the sediment history of Lake Lenapeis composed of fossil diatom assemblages that indicate higher nitrogen and moderate to low phosphate levels.

The goal of this study is to perform diatom analysis on a set of cores from the paired reservoir systems of Lakes Shakamak and Lenape to better understand the anthropogenic impact on the ecosystem throughout the history of these closely-related lakes. Here we present findings of a paleolimnological eutrophication study using fossil from sediment cores collected from Shakamak and Lenape Lakes. We attribute higher phosphate levels in Lake Shakamak may result from the fact that this reservoir is more developed for public use, including the presence of a sewage systems associated with campgrounds and cabins in the park. Higher nitrate and low to moderate phosphate levels in Lake Lenape are probably the result of a higher contribution of fertilizer runoff from local farms. Modern Lake Lenape has much more turbid water, probably because of a higher influx of sediment from in-flowing streams. Our research will provide a more detailed analysis of the trophic evolution of this paired reservoir system, which has resulted in divergent modern ecosystems.