L. Forró szerk.: Miscellanea Zoologica Hungarica 7. 1992 (Budapest, 1992)

Andrikovics, S., Bankovics, A. , Csörgő, T. , Gere, G. , Sass, M.; Török, J.: Hydrozoological characters of a reconstructed wetland

Hydrozoological characters of a reconstructed wetland by S. Andrikovics, A. Bankovics, T. Csörgő, G. Gere, M. Sass and J. Török (Received May 28,1992) Abstract: On the western shore of Lake Balaton there was a large territory of wetland, inhabited by diverse aquatic life and many species of birds. During the last century this marshy habitat was dried up by draining and broken into smaller areas. As a consequence the self-purification of the Zala River flowing into Lake Balaton greatly decreased. This situation is linked with the increasing anthropogenic effects and has endangered the water quality of Lake Balaton. Recently, large reservoir systems nearly re-establishing the original conditions have been built. This system gives an opportunity for studying the recolonization and succession types of different living systems. Key words: Kis-Balaton Landscape Protection Area, reservoir system, water insect, waterfrogs, avifauna. Introduction Kis-Balaton wetland area situated at the western end of Lake Balaton, was a huge marshy area the until middle of the last century. The great drainings during the last century caused the ancient swampy area to shrink to a small plot of land of 1.5 km. Although the reclaimed lands were suitable for cultivation only to a small degree, the harmful consequences of the different interferences became more and more evident. Of these we should like to discuss the following two. The first is that the formerly very rich bird-fauna of this area (Keve 1976, 1977) became alarmingly endangered, in spite of declaring the nature protection area. The second is that we must be fully aware that this area is crossed by the Zala River which is the biggest inflow of Lake Balaton. Formerly, the water of this river crossed an extensive marshy area and became biologically purified. As the result of draining this process of purification did not take place. The lack of purification caused the Zala River, which transports water from Western Hungary, to bring harmful subtances in great quantities and increasing anthropogene loads. This endangers the water quality of Lake Balaton (Joó & Lötz 1980). After the conditions had been evaluated, large scale reconstruction works begun in the Kis-Balaton area. Under this program a water-reservoir was constructed by the middle of the last decade, and there is an another one under construction. The water of the Zala River flows through this reservoir system in a wave line for the sake of biological cleaning and depositing. The changes taking place in this area make it possible for us to make clear in a theoretical sense whether any ecologically degraded complex of associations could really be reconstructed. In this case we talk about the reversion of succession in the sense that we want to change a strongly polluted swamp, a bog, a