L. Forró szerk.: Miscellanea Zoologica Hungarica 10. 1995 (Budapest, 1995)

Tittizer, T., Leuchs, H.; Banning, M.: The consequences of river impoundments for the macrozoobenthos - demonstrated at the example of the River Danube in Germany

MISCELLANEA ZOOLOGICA HUNGARICA Tomus 10. 1995 p. 73-84 The consequences of river impoundments for the macrozoobenthos - demonstrated at the example of the River Danube in Germany by T. Tittizer, H. Leuchs & M. Banning (Received April 30, 1995) Abstract: At the time before damming the river Danube in the area between Regensburg and Geisling, because of the pollution the prevailing macrozoobenthic community could not be characterized as a natural or near-natural potamal community. At that time generalists dominated and only a few stenoecious species of running water had a small share in the species spectrum. In the first year after the filling of the impoundment Geisling (1986) a massive appearance of chironomid populations occured. The analysis of the catches proved an outbreak of two chironomid species: the Chironomus-plumosus-group and Glyptotendipes paripes. In unusually high densities the sphere shell Sphaerium corneum and the crustacean Corophium curvispinum were found, too. Until today the productivity of the impoundment Geisling has still remained high. But it seems now that the community begins to stabilize. Key words: Chironominac, Sphaerium corneum, Corophium curvispinum, River Danube (Germany), faunistic studies Introduction River Danube is navigable as a Federal waterway on the reach from the entry of the Main-Danube Canal to the German-Austrian border downstream of Passau. The earliest anthropogenic interferences with River Danube date back to the 15th century ("B'

Schlacht near Straubing"). The year 1850 marked the beginning of the mean-water regulations involving the break of riparian forests, numerous river corrections and cut offs. It was followed in 1922 by the low-water training of the river, many groynes were built, and wide sections of the banks were secured by rip-rap rocks. At some accretion banks, however, larger accumulations of gravel remained preserved. The Danube river system experienced further interventions when several impoundment weirs were erected: As early as 1918, were the first plans devised to build a weir for hydropower generation at the end of the 21-km reach shared by Germany and Austria, near Jochenstein. However, this project was postponed then in favour of the plan to build an impoundment near the "Danube-Kachlef

', a rocky reach upstream of Passau, which was much more beneficial for navigation. This project was implemented in 1922. Then, through the energy shortage after World War II the harnessing of hydropower at Jochenstein again gained special importance, so that the impoundment there became operational already in 1956. The period between 1952 and 1984 a whole chain of 15 weirs for energy generation had been constructed upstream of the Federal waterway. Further river regulation in the Federal waterway served mainly the purposes of navigation and was closely related to the construction of the Main-Danube Canal as part of the Rhine-Main-Danube waterway (cf. Fig. 1).