Subfosílne spoločenstvá pakomárov (Diptera: Chironomidae) v sedimentoch horských jazier ako doklad histórie znečisťovania ovzdušia

Abstract

In 1993 Slovakia started to participate on the international program AL:PE (Acidification of Mountain Lake: Paleolimnology and Ecology) with the primary purpose of evaluation of glacial lake research possibilities on analyses of atmospheric pollution. Following AL:PE, project MOLAR (Mountain Lakes Research) had the main objective to utilize the gain data and knowledge on analyses of climate change and oscillation. Minges (Chironomidae) represent one of the domi-nant systematic groups of the lake bottom fauna. They have been used as paleoecological indicators of eutrophication, acidification, climate change, and paleoproductivity. Two model sites, Starolesnianske pleso (glacial lake) and Nižné Terianske pleso, were selected to study midge assemblages in the lake sediments. Samples of profundal zone sediments were taken in October 1993 by Glew’s method. Sediments width varied between 13.5–18.5 cm. They were dated by radionuk-lide method and chemically analyzed to stratify subfossil assemblages. In total, 16 samples were analyzed. Determination of the body fragments was mostly possible only into the level of genus. 3–5 taxons were determined in individual samples. The oldest layers had highest species richness and evenness, yet lower total abundance of head fragments. In the latest sample (layer), only single midge species, Tanytarsus gregarius, was detected. In contrast, three other species except T. gregarius were determined in the recent samples. Decline of species richness from oldest toward youngest samples was described in both studied lakes. Species of genus Tanytarsus dominated in the samples. Heterotrissocladius marcidus group found in all layers except the latest. A statistical ration between Tanytarsus gregarius and T. lugens was applied as an indicator of water quality and ecosystem change. The recent samples and upper layers were dominated by Tanytarsus gregarius. Its abundance starts to decline in the layer 3.25–3.5 cm, whereas they absented in the layer 5.0–5.5 cm and deeper. In deeper sediments Tanytarsus lugens dominated over T. gregarius. The critical time point of the species exchange is the period 1900-50. Concentrations of coal participles started to increase during this period as the result of atmospheric pollution. The trends of lake contamination were similar to the other observed lakes in Europe. In fact, the contamination was 15–20 × higher in comparison to Norway lakes, 2–3 × higher then lakes in Tyrolean Alps, French Pyrenees, and Scotland. High increase of the participle concentration peaked around 1990 that corresponds to the peak of industrial development in the central and eastern European countries. In addition, drastic changes in the assemblage structure were observed in the layer 7.0–7.5 cm corresponding to the period around 1850. It is much more difficult to explain the absence of genera Corynoneura, Eukiefferiella, and Psectrocladius. It could have been the caused by other factors e.g. stream flow through the lake that might have had significant effect in the case of shallow Starolesnianske pleso.