Extent of sedge-grass meadow in a Lake Michigan drowned river mouth wetland dictated by topography and lake level

Water-level fluctuations are critical in maintaining diversity of plant communities in Great Lakes wetlands. Sedge-grass meadows are especially sensitive to such fluctuations. We conducted vegetation sampling in a sedge-grass dominated Lake Michigan drowned river mouth wetland in 1995, 2002, and 2010 following high lake levels in 1986 and 1997. We also conducted photointerpretation studies in 16 years dating back to 1965 to include responses to high lake levels in 1952 and 1974. Topographic data were collected to assess their influence on areal extent of sedge-grass meadow. Dominant species in short emergent and submersed/floating plant communities changed with water availability from 1995 to extreme low lake levels in 2002 and 2010. Sedge-grass meadow was dominated by Calamagrostis canadensis and Carex stricta in all years sampled, but Importance Values differed among years partly due to sampling in newly exposed areas. Photointerpretation studies showed a significant relation between percent of wetland in sedge-grass meadow and summer lake level, as well as the number of years since an extreme high lake level. From the topographic map created, we calculated the cumulative area above each 0.2-m contour to determine the percent of wetland dewatered in select years following extreme high lake levels. When compared with percent sedge-grass meadow in those years, relative changes in both predicted land surface and sedge-grass meadow demonstrated that accuracy of lake level as a predictor of area of sedge-grass meadow is dependent on topography. Our results regarding relations of plant-community response to hydrology are applicable to other Great Lakes wetlands.