Backwaters and their significance for aquatic vegetation [Altgewässer und ihre Bedeutung für die Wasservegetation]

Abstract

Different development stages of backwaters representing important habitats and offering shelter for hydrophytes will be described. In the Elbe river valley between Dessau and Magdeburg, 38 hydrophyte species could be identified in 7 backwaters of different seral stages. Among these, 6 species are among the 13 aquatic and amphibious plant species stated in the German Red Data Book as mostly characterising backwater areas. These findings show the importance and worthiness of nature protection of the backwaters in the Middle Elbe region. The relatively high number of even rare species is due to the fact that here, as also occurs in parts of the Upper Rhine Region, hydrophytes of different range types share the same habitat. Comparative studies of backwater relevés from specific Rhine, Danube and Amper sections reveal that, although the studied Elbe, Rhine and Upper Danube sections show equal total species numbers, there are important differences concerning the number of specific rare species found in each single section. 73 species were found in total. Only 11 of them occur in all studied river sections, whereas 20 species were only found in a single section of the rivers, respectively. Among the 12 endangered species which mostly occur in backwaters, only 4 species were found in at least half of the sections, even 7 endangered species are not present in more than one or two river sections.