| Abstract: | Normally, carp rearing at medium densities is connected with the promotion of daphnia and filtration effects up to “clear-water states”. Therefore and because of the reduction of submerged plants and of the periphyton this form of carp rearing should be possible in eutrophic shallow lakes also at a slight nutrient introduction without any considerable eutrophication. Due to a deterioration of the light climate by re-suspension of the sediment even reductions of the primary production are possible. In the case of the Galenbeck lake a drastic reduction of submerged macrophytes occurred in connection with an increased development of plankton, only general estimations being available of the shares of macrophytes and phytoplankton in the overall production. The phytoplankton increase is are perhaps caused by the absence of filtrating zooplankton due to an insufficient reduction of the indigenous fish stocks. In the Galenbeck lake the structural changes of the ecosystem were due both to the high degree of re-suspension of the very mobile lime sediment and the absence of hard bottom areas, which made the total reduction of the macroflora possible. |
