Effects of river connectivity on marsh vegetation community structure and species richness in montane floodplain wetlands in Jasper National Park, Alberta, Canada

Vegetation communities in floodplain wetlands in montane valleys are adapted to seasonal flooding, and natural and anthropogenic barriers to seasonal flooding can lead to changes in plant community structure. We assessed the plant community structure, species richness, and environmental variables in each of 3 river I ne, beaver-impounded, and railway-impounded floodplain marshes of the Athabasca River in Jasper National Park, Alberta, Canada. We hypothesized that these variables differ significantly among the marsh types in response to varying degrees of disturbance from river flooding. Using a TWINSPAN analysis, we defined 8 plant communities in the 3 marsh areas. Regular flooding in the riverine marshes (no barriers to flood waters) led to very distinct plant community types characterized by Eleocharis palustris, Utricularia minor, and Carex saxatilis. Beaver-impounded marshes (low barriers to flood waters) were defined by 2 distinct community types, both dominated by Carex aquatilis, Carex utriculata, and Equisetum fluviatile, Dominant plant species in the railway-impounded marshes (most extreme barriers to flood waters) were C. aquatilis, E. fluviatile, and Drepanocladus aduncus. Two of the 3 railway-impounded sites had higher moss cover (43-48% versus 29%) and lower emergent cover (51-56% versus 77%), pointing to a Succession to a fen. Overall, we identified 95 vascular and bryophyte species in the 3 wetland areas; species richness was highest in the beaver-impounded marshes (66 species), the railroad-impounded marshes (48 species), and lowest in the riverine marshes (37 species). Plant communities of these marshes were significantly correlated with water conductivity, water depth, organic content of the sediment, and absence/presence off hummocks. In addition, NO3- concentrations in the water had a significant inverse relationship oil marsh species richness. Most of these marshes were N-limited, with N:P quotients below 7. Overall, we showed that natural and anthropogenic barriers to water flow significantly affected plant community composition and species richness, water chemistry, and water levels in these riverine ecosystems.