Overview and final remarks

Abstract

This study has, for the first time made it possible to describe the aquatic vegetation of the Danube River on the basis of a unified methodology for field surveying, data processing and the display of results. Some features of species richness, species composition and dominance are presented. As the surveyed reaches of the river and the flood plain water body systems represent only a miniature section of the river a complete picture is far away, although surveys were made in all important parts of the Danube. Yet, some aspects are very clear and may not change much in any future, more detailed surveys. The total number of aquatic macrophyte species was high and made up of 4 charaphytes, 10 mosses and liverworts and 66 vascular species (only hydrophytes and amphiphytes were counted; filamentous algae and helophytes were excluded). The occurrence of mosses is almost exclusively restricted to the upper reach. With respect to species richness, habitats outside the main river channel such as side channels, oxbows, and artificial canals have an inherently high value. The occurrence of classical rheophilic species is rather limited in the main channel and last but not least, the frequency of Ceratophyllum demersum is surprisingly high for a species supposedly confined to still water habitats. All this information forms a new, and at least in part, unexpected picture of the aquatic flora of the largest river of Central Europe, the Danube.