The Effects of Water Level Fluctuations on Three Lake Ontario Shoreline Marshes

Abstract

The purpose of this study was to evaluate the nature and magnitude of changes in three Lake Ontario shoreline marshes in relation to lake level fluctuations. The mapping at various lake levels showed that the marshes do not exhibit significant areal change in response to lake level conditions. Lake levels, however, did have a strong influence on the plant community structure of the marshes. Succession appeared to follow a cyclical pattern in concert with long-term lake level fluctuations. At least four major stages have prevailed since 1927.During extended periods of low lake levels, sedges and grasses dominated the marshes. Extended periods of high water resulted in greater interspersion due to the increased amount of open water and the colonization of emergent plants. The long term average lake level trend was characterized by the rapid colonization of emergent plants in the central basins of the marshes. The long term high lake levels which followed this long term average lake level stage caused massive vegetation dieoff resulting in near lake-like conditions. In total there was a 46.7 percent decline in the extent of the littoral vegetation of the marsh between extended low and extended high lake levels.A model is presented to predict the plant community structure of the marshes at various lake levels. The need for a universal wetland boundary definition is emphasized.