THECAMOEBIANS AS AN ENVIRONMENTAL PROXY FOR THE MIDDLE MISSISSIPPI RIVER FLOODPLAIN

Thecamoebian tests from recent lacustrine sediments have been shown to be a useful proxy to study environmental changes such as land-use changes, pollution, and climate shifts. In this study, the usefulness of thecamoebians as an environmental proxy for the Middle Mississippi River (MMR) floodplain is explored. Sediment cores and surface samples were collected from two sites in Alexander County, IL: Southern Illinois University’s Middle Mississippi River Wetland Field Station near East Cape Girardeau, IL and Horseshoe Lake, a dammed oxbow managed by the IL Department of Natural Resources, near Olive Branch, IL. These sites represent different floodplain environments, management histories, and flooding patterns. The thecamoebian populations were expected to reflect these differences while also responding to regional signals associated with development, agriculture, and climate. Cores were subsampled at a 5cm interval and all samples were sieved with 150μm and 45μm screens to retain thecamoebian tests. Sieved sediment was examined under a microscope and at least 100 tests were identified in each sample. Preliminary analyses indicate that there are distinct assemblages associated with each site as well as changes in assemblages throughout the cores, suggesting that the thecamoebian populations are fluctuating. These patterns will be compared to the known history of the sites and the MMR to determine the driving variable. The results of this study will provide a better understanding of the use of thecamoebians as a proxy, for past and ongoing changes, in the MMR region.