Hydrologic Change in Seasonal Flood Pulse Dynamics Influences Fish Community Composition in a Freshwater Wetland

Abstract

Abstract Seasonal flooding is a defining feature of freshwater wetlands, shaping ecological dynamics and influencing community structure. In large lake systems, fringing wetlands provide critical habitat for many fish species, yet these communities remain largely understudied, particularly in relation to variability in spring flood regimes. This study examined how spring flood progression (April–June) affects fish community composition in a large wetland complex within the Lake Champlain basin (Vermont, New York, and Quebec). I analyzed community shifts across three months representing different flood phases, evaluated how interannual variation in flood characteristics (e.g., duration, timing, ice-free days) influenced species abundance, and assessed long-term changes in flood dynamics using a century-long water-level record. Multivariate ordinations revealed strong seasonal structuring, with distinct species assemblages in each phase: early spring was dominated by White Sucker and Yellow Perch, while late spring featured generalist foragers such as Lepomis spp. Longer, later floods increased the abundances of key taxa, emphasizing the importance of extended access to flooded habitat for recruitment and resource use. Analyses of long-term hydrologic data showed that spring floods have become longer and end later over time, indicating that the flood characteristics associated with fish abundance are already changing within the system. Together, these findings suggest that continued shifts in flood dynamics may alter the nursery function, productivity, and species composition of wetland fish communities. As climate change and wetland loss continue, understanding these hydrologically driven patterns is critical for conserving ecosystem function and forecasting ecological change in large lake systems.