L. Forró szerk.: Miscellanea Zoologica Hungarica 13. 2000 (Budapest, 2000)

Gulyás, P.: Rotatoria and Crustacea plankton communities of the feed-water streams of the Lake Balaton

Literature survey The first results of the floristic and faunal investigations of the feed-waters of the Lake Balaton were published at the turn of the century. First publication on the algal flora elements of the Kis-Balaton and lower Zala section appeared also at the end of the past century. Istvánffy (1897) published algological data by analysing samples from several habitats of the Kis-Balaton region including sediment, "foam", and the surface of higher plants as well as fish fries. Francé (1897) published a study on protozoan species that also included the description of microscopic Flagellata alga to our present knowledge from the water of the Kis-Balaton and the southern wetlands of Balaton. During the fifties the Biological Research Institute of the Hungarian Academy of Sciences, Tihany conducted extensive surveys on the Aszófő creek, the Pécsely creek and feed springs, as well as the physiological, hydrological, hydrochemical and hydrobiological state of the small feed-waters of the Balaton (Entz era/. 1954, Entz 1958). Results on the Pécsely creek (= Örvényesi creek) at Örvényes were summarized in a study by Entz et al. (1954). The report contains many sections including the analysis of hydrographie conditions, the assessment of planktonic and bentonic algal communities, the communities of the creek, the Rotatoria and other worm species, beetles, Dipterans, Mollusca, fish, epibiontic communities, and the occurrence and ecology of crustacean species, and the biological processes of lime formation. Hydrographie conditions of the Aszófői creek and the distribution and ecology of the aquatic and surface dwelling Hemiptera, and Malacostraca species were described by Lukacsovics (1957, 1958a, b) in several studies. Varga ( 1957) identified and described a very rich Rotatoria fauna on the slow-flowing sections of the Aszófői creek embedded in Chara population and concluded that the surfaces of living and inorganic objects covered by lime are favoring the formation of habitats for the Rotatoria. Highest species richness and individual abundance of Gastrotricha also occurred here, at the sections of rich Chara vegetation. The first comprehensive survey on the water chemistry of the feed-waters of the Balaton was compiled by Entz (1959). This study classified these streams into three basic categories: spring-fed waterways, Balaton and other surface water inlets. Of the large variety of the chemically different waters on the Balaton region is largely due to the diverse geological conditions, acidic water, karstic water, dolomite and basalt springs, springs from Pannonic layers and its karstic types are all occurring in the region. Downstream towards to the lake these are becoming more and more similar to the lake water from chemical viewpoint. Surface runoff and mostly precipitation feed water are predominant on the southern shore of the lake, these are usually rich in organic materials (wetlands). Researches of the water quality of the feed-waters of the Lake Balaton started when the eutrophication of the lake gained attention. Under the supervision of the Inspectorate for Water Quality of the National Water Authority several laboratories started to investigate the water quality (Székesfehérvár, Szombathely, Pécs). In 1970 the regular survey of the water quality of the feed-waters began including the investigations of water chemistry and hydrobiology. The primary aim of these investigations was to assess the eutrophication process and the nutrient loads to the lake. On the basis of the results of the investigation on 17 streams and 16 point sources it was concluded that the surface streams carry 80-90% of the total nitrogen load and 57-96% of the total phosphorus load. Hydrobiological investigation of the streams at this time only included the evaluation of the saprobiological para-meters and the determination of the chlorophyll-a contents. The regular measurements have been continued since then within the frame of the national monitoring network but investigations were later completed by new parameters. Ponyi ( 1997) summarized the results of the faunistical researches on invertebrates from the turn of the century until now. On the basis of the detailed literature survey he concluded that the organized creek research has started in 1952. It was recognized at this time that the ecological state of the feed-waters intimately relates to the water quality of the lake itself. Further research is needed to investigate to what extent these factors are determined by hydrographical conditions and how the biological water quality of the streams and the lake relates. Further parts of the paper assess in details the results of the most important fauna elements. It emphasizes the relation of the creeks and the Balaton and the priority tasks for their protection.