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
stands resulted in hypertrophic water quality classification. Nevertheless, rare species are present and species richness indicate moderate pollution level. 15. E-W channel (Ordacsehi trench) Specific electric conductivity values were higher than in the previous creek (610-1020 pS/cm), indicating alpha-oligohalobic-oligo-mesohalobic stages. On the basis of the inorganic ionic composition the water is within the beta-limno-type that is characterized by the dominance of Mg - Ca - HC0 3 , and on one occasion Mg - Ca - HC0 3 - S0 4 ions. Dissolved oxygen content varied widely as evidenced by the fluctuating saturation values (18.9-166.2%). COD values indicate heavy pollution. Due to the high phytomass the plant nutrient content was low. Of the nitrogen forms only the ammonium and from the phosphorus forms only the total phosphorus value were higher, while the rest was low. The chlorophyll-a content (14.1-38.0 pg/1) was found to be medium. Similarly to the previous creek the Zooplankton showed rich species composition, 28 Rotatoria, 13 Cladocera and 7 Copepoda taxa were detected. The abundance was extremely high with only one exception (530-12892 ind./100 1), the highest amongst the evaluated streams. Dominant species were similar to those that were identified in the Zichy channel, the Brachionus species were represented only by B. angularis with large stands. Apart from this the following could be mentioned: Keratella cochlearis cochlearis, K. quadrata, Polyarthra vulgaris, Pompholyx sulcata, Bosmina longirostris, Chydorus sphaericus, Pleuroxus aduncus, Acanthocyclops robustus f. limnetica, Eucyclops serrulatus. Some rare taxa occurred here, which were not found in previous streams: Lophocharis oxystemon, Platyas patulus, Alona guttata, Bosmina coregoni, Ceriodaphnia pulchella, Daphnia galeata, Ectocyclops phaleratus, Eucyclops speratus. The species richness of Cladocera is worth mentioning, most of them is tichoplanktonic species. Due to the very large stands of the zooplankton the water of the creek is hypertrophic, but it does not prevent the occurrence of rare species, and species richness indicates moderate degree of pollution. 16. Jamai creek Specific electric conductivity value is quite similar to the Ordacsehi trench (630-860 pS/cm), indicating alpha-oligohalobic conditions. On the basis of the inorganic ionic composition the water is within the beta-limno-type with characteristic Mg - Ca - HC0 3 -and Mg - Ca HC0 3 - S0 4 ionic composition. Dissolved oxygen contents and their changes as well as fluctuations in saturation values are similar to the patterns registered at the Ordacsehi trench. Difference emerges in the minimum of the oxygen content, which was slightly higher here. The slightly better water quality is also evidenced by the values of the COD content on the basis of which the water is not heavily polluted, but the water quality of the creek is tolerable. Nutrient concentrations (nitrogen and phosphorus forms), as well as the amount of chlorophyll-a is slightly higher than in the previous creek. These values are obviously highly effected by the dense vegetation. Richest species composition of Rotatoria and Crustacea plankton was found in this stream amongst the investigated ones, 37 Rotatoria, 6 Cladocera and 6 Copepoda taxa were recorded here. The abundances were lower than in the previous creeks, varying between 417-2749 ind./100 liter. Most frequently occurring species are also those mentioned earlier, predominantly species of Brachionus, Keratella, Lecane, Bosmina, Chydorus, Acanthocyclops, and Eucyclops formed large populations. No other rare species that was described before occurred at this particular sampling site.
