Hydrogeology and Landform Morphology Affect Plant Communities in a Great Lakes Ridge-and-Swale Wetland Complex

Trajectories of vegetative change in wetlands can be influenced strongly by shifts in water-table elevation driven by evapotranspiration and spatial-temporal variability in groundwater. The specific dynamics of such interactions are difficult to quantify because of spatial complexities associated with local climate, geomorphology, and underlying geology. Nonetheless, a better understanding of the effects of groundwater and landform pattern on plant communities in wetlands can help with future predictions of change. Over two successive growing seasons, we investigated water-balance dynamics in 15 wetlands in a forested Great Lakes coastal wetland complex consisting of relict beach ridges and intervening swales. Our goal was to explore how variation in hydrogeology and landform morphology affected plant community composition. Water-balance analyses from water-level fluctuation methods, along with interpretation of underlying stratigraphy and slope, were used to explain plant-community ordination results. Our findings showed that phreatophytic plant communities developed in locations where hydrogeology or greater slopes allowed for supplemental groundwater flow to the swales. Conversely, shallow water-table slopes maintained standing water in swales, leading to obligate wetland plant communities. This study provides a clearer representation of hydrogeologic and ecohydrologic interactions to help inform our understanding of the relationship between groundwater hydrology and plant communities in wetlands.