Search

The Danube is the second-longest river in Europe that is subjected to various man-made alterations, including those related to hydro-power plants. We surveyed and analyzed the presence and abundance of macrophytes in the main channel from 2582 river kilometers (rkm) to 171 rkm. We also assessed selected habitat parameters in the sampled river stretches. Sixty-eight different plant species were recorded along the entire course. Among neophytes, we found Elodea nuttallii, E. canadensis, Vallisneriaspiralis and Azolla filiculoides. Based on similarity analysis, we distinguished 15 plant communities, most of which were defined as associations, which were classified into 5 alliances and represented three vegetation classes, namely vegetation of rooted hydrophytes Potamogetonetea, the vegetation of pleustophytes Lemnetea and vegetation of marshes Phragmitetea. The number and abundance of plant species, as well as plant communities recorded in single stretches, varied along the course. Canonical correspondence analysis (CCA) revealed that environmental parameters explained 21% of plant species composition. CCA runs with neophytes explained 41% of the variance, and current velocity, water transparency, species number and bank structure were significant variables. The present study revealed that the free-running sections of the river are poor in number and abundance of plant species, whereas impounded reaches mainly show an opposite result.

The Lobau wetland and oxbow ensemble is part of the large Danube River floodplain area between Vienna (Austria) and Bratislava (Slovakia). The Danube River regulation scheme implemented in the late 19th century considerably affected the Lobau area, which is part of the Danube National Park today. Terrestrialization processes in the floodplain started with the river regulation and pose an increasing threat to the aquatic and wetland vegetation of this ecosystem. Former vegetation studies were either directed toward phytosociological description of associations or to a general vegetation inventory and mapping, where transitions between vegetation types are not accounted for. Our purpose is to provide a detailed insight into the vegetation zonation pattern along the aquatic-terrestrial inundation gradient in the Lobau floodplain area. We sampled a total of 49 belt transects. Samples in each transect were classified into groups using two-way indicator species analysis (TWINSPAN). Resulting groups of all transects were subjected to fuzzy c-mean clustering (FCM), defining ‘community types’ by means of indicator species analysis (ISA). We found 36 significant indicator species typifying 14 community types. Nine types belong to the shoreline vegetation and five types characterize the aquatic habitats. In addition to these community types, two transitional zones were found, one defined as open water/wetland transition and one as wetland/upland transition. Along the aquatic-terrestrial environmental gradient, different floristic and quantitative relations of community types and transition zones were identified. Finally, the importance of such a fine-scale description of zonation patterns along the inundation gradient is discussed in relation to long-term monitoring programmes as the basis for rehabilitation or wetland conservation measures.