GENERAL WETLAND SCIENCE Hydrogeology and Landform Morphology Affect Plant Communities in a Great Lakes Ridge-and-Swale Wetland Complex Martha L. Carlson Mazur 1 & Douglas A. Wilcox 2 & Michael J. Wiley 3 Received: 11 December 2019 /Accepted: 7 May 2020 # Society of Wetland Scientists 2020 Abstract Trajectories of vegetative change in wetlands can be influenced strongly by shifts in water-table elevation driven by evapotrans- piration 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 hydro- geology 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. Keywords Ecohydrology . Coastal wetland . Great Lakes . Hydrogeology . Plant community . Water balance Introduction The sensitivity of wetland vegetation to changes in climate (e.g., Doss 1993; Winter 1999) often has been observed in paleoecological records, particularly at sites without sub- stantial groundwater influx (Singer et al. 1996; Booth and Jackson 2003; Burkett et al. 2005; Ireland et al. 2012). Groundwater dynamics are generally slow relative to surface-water dynamics, however, suggesting that local groundwater loading may buffer impacts of climate change on the structure of some wetland plant communities. Despite rapid changes in ambient temperature and precipitation, wa- ter availability in a groundwater-fed wetland often remains effectively constant, leading to characteristic and relatively stable phreatophytic plant communities in which plants have roots that extend below the water table (e.g., fens and cedar swamps). Thus, an examination of groundwater dynamics across landscapes can help in resolving wetland vulnerabil- ity to changes and variations in climate (Jackson et al. 2009). Groundwater dynamics, however, are linked to plant tran- spiration rates when phreatophytic vegetation is present. A more thorough understanding of the linkages between groundwater flow, transpiration, and plant community com- position will help us better understand and predict wetland response to climate change. Furthermore, quantifying cur- rent groundwater supply and plant community water utiliza- tion can provide a baseline for comparison to future climate scenarios (Restrepo et al. 1998; Sun et al. 1998). Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13157-020-01312-6) contains supplementary material, which is available to authorized users. * Martha L. Carlson Mazur mmazur@bellarmine.edu 1 Environmental Studies Department, Bellarmine University, 2001 Newburg Road, Louisville, KY 40205, USA 2 Department of Environmental Science and Biology, SUNY-College at Brockport, 350 New Campus Drive, Brockport, NY 14420, USA 3 School for Environment and Sustainability, University of Michigan, 440 Church Street, Ann Arbor, MI 48109, USA https://doi.org/10.1007/s13157-020-01312-6 / Published online: 17 June 2020 Wetlands (2020) 40:2209–2224