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
sphere shell, and of the chironomids reflect the high productivity of this impoundment. This leads to the conclusion that the interaction of such factors as low velocity of flow and simultaneaous supply of great amounts of organic and inorganic substances was responsible for the population outbreak. In addition the extension of the areas with water depths between 2 and 5 m had a promoting effect on the food supplies of plankton feeders and detritus feeders. Although the chironomid outbreak had reached its climax already in the summer of 1988, direct control actions were demanded by the people living in the area, including an association for midge pest control, which was formed and registered meanwhile. For some time it was discussed whether the Bacillus thuringiensis israelensis (abbreviated B.t.i.) which is regularly used on the Upper Rhine to control Culicidae, should be employed. However, because of considerably higher amounts and concentrations that would have been necessary here, the consequnces for the entire benthic fauna would have been incalculable, so that the idea of B.t.i. application was finally abandoned. As an ecologically reasonable action for controlling the outbreak it was suggested to reduce the nutrient load and additionally to promote predators (Tittizer et al. 1989). As a short-term measure, the Federal Institute of Hydrology (BfG) recommended the stocking of the impoundment with Prussian carp (Carassius carassius) and wild carp (Cyprinus carpio). However, the fishery associations objected against these two non-predatory fish species. Finally, in late August 1989, 150,000 little female eels were released. Consequently, in September 1990 the average population densities of chironomid larvae had dropped to merely one tenth of the values of September 1989. Fig. 12. Percentage of the three dominant taxa of the whole settlement on the river bottom (rkm 2355-2370)
