Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 83. (Budapest 1991)

Lakatos, Gy., Ács, É. ; Buchtijarova, L. N.: Study on reed-periphyton in Lake Velence

Small mass periphyton categorised as organic-inorganic, -characteristic of 1978, prevails (in this category which was taken only from Német-tisztás). Besides inorganic deposits, the increase in non-chlorophyll organic contents is significant and thereby the reed-periphyton can be classified as heterotrophic. After evaluating and discussing the data resulting from non-taxonomical investigations, some more important data of the phytotecton algological analysis are presented (the list of taxa in 1988 is presented in Table 5, that of 1978 is seen in LAKATOS & BARTHA 1989). Percentual distribution of phyla in the phytotecton in Lake Velence is presented in the Table 2. The identified number of taxa in both years are almost identical, some percentual increase is characteristic only of the diatom composition of the phytotecton. The algological picture is more interesting, when the results of phytotecton analysis of samples collected in the three characteristic water areas are compared. The percentual distribution of algal phyla in the phytotecton samples taken from green reed in Vendel-tisztás, Nagy-tisztás and Fürdető is presented in Table 3. The number of identified alga taxa in the phytotecton samples taken from the green reed in Vendel-tisztás belonging to the brown water areas, shows a significant decrease, more than 35 %. Cyanophyta and Euglenophyta were not found at all, the composition of diatom species was significantly altered, and the phytotecton also became less diverse in the other spots of the brown water areas. In the case of Nagytisztás belonging to the grey water area, changes in the composition of phytotecton were less significant, although the increase in the number of diatom species and the decrease in Chlorophyta species are worth mentioning. The most important change took place in Fürdető (it is a green water area), where high individual number of composition of phytotecton was recorded with a large number of diatom species which contrasted the previous low number. Before dealing with the alteration of algal species and the redistribution of the phytotecton structure in detail, Table 4 is shown. Our table illustrates that the small-size Achnanthes minutissima became a more dominant species, especially in Vendel-tisztás and Fürdető. The number of Navicula genus significantly decreased in the periphyton of each open space. The individual number of Nitzschia linearis being a good indicator of the organic pollution of the water (EVENSON et al. 1981, RUSHFORTH et al. 1981), decreased to 1 % from its earlier 50 % in Fürdető, but Cymbella lacustris and Fragilaria capucina var. vaucheriae appeared in high individual number, instead. The individual number of Rhoicosphenia abbreviata, a gelatinous shafted alga, decreased in the samples from Nagytisztás. The same tendency was observed for the largesized Fragilaria ulna, with the exception of Fürdető, where no such species was identified earlier and its present proportion of the total individual number of diatoms is only about 1 %. The phytotecton analysis suggests a significant alteration in the structure of species and the dry mass. The phytotecton collected from the brown water areas became more uniform and monotone, and the same from the grey water areas altered only little. The change in the structure of phytotecton is advantageous at Fürdető (green water area), where the water was planktonically eutrophized in 1978. The change of phytotecton composition is in accordance with the results of water chemistry and plankton studies