Spatial patterns of phyto- and zooplankton diversity in floodplains from the Danube River (Austria): comparisons between free-flowing and impounded stretches

THOMAS HEIN; O'FARRELL, INÉS; CHAPARRO, GRISELDA N.

Natal

Workshop; 18th IAP Workshop; 2017

International Association of Phytoplankton

Natural riverine floodplains are among the most important diversity hosts of the world, which is mainly attributed to an elevated temporal and spatial heterogeneity associated to the discharge regime of the river. Due to the dramatic rates of river regulation worldwide, dams and artificial levees blocked the dynamic effect of the discharge regime in a vast majority of floodplain areas. We compared patterns of phyto- and zooplankton alpha and beta diversitiesand environmental heterogeneity in floodplains along a free-flowing stretch (dynamic floodplains) vs a floodplain located in an impounded section (stable floodplain) of the Danube River (Austria).We included two nested spatial scales: 1- habitats (e.g. open waters, submerged, floating-leaved and emergent macrophytes) and 2- water sections within the floodplain wetlands; we also considered two contrasting hydrological conditions (post-flood vs no-flood). In both hydrological conditions, environmental heterogeneity was higher in dynamicwetlands than in the stable wetland; it was higher among water sections than among habitats in dynamic floodplains but similar across scales in the stable one. Local diversity showed different patterns among the studied groups and hydrological conditions. In general, overall phytoplankton and rotifer β-diversities were lower in the stable than in dynamic floodplains inpost-flood conditions and similar among all wetlands in no-flood conditions. Formicrocrustaceans, overall β-diversity was similar among all wetlands in both hydrological conditions. β-diversities were higher at the among sections than at the among habitats scale in dynamic floodplains; these differences were more pronounced for phytoplankton and rotifers and in no-flood conditions. Our results show marked differences on diversity and environmental heterogeneity between dynamic and stable floodplains, potentially affecting ecosystem functioning. We are currently comparing the diversity patterns using a functional approach based on ecological traits of the species registered for a further understanding of the ecological strategies promoting species replacement.