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
Material and methods Water temperature and dissolved oxygen concentrations were measured oh-site and the latter was precipitated immediately for the Winkler method. Further chemical analyses were made according to the appropriate Hungarian Standards collected from the surface. Table 1 summarizes the available flow/discharge data (m 3 /sec), for 1997 where the monthly ranges and averages are also given (minimum, maximum and averages). In general it is concluded that the discharge values of most of the streams were below 100 1/sec. Some exception prevails, the Örvényesi creek that has maximum flow in this range and the Tapolca creek with 0.5 m 3 /sec flow rate and the Zala river with highly variable discharge, occasionally reaching the m 3 /sec value. Table 1. Discharge data of the streams in 1997 No. Name of stream 06. 1997. 07. 1997 09. 1997. Flow rate (mVsec) Min. Average Max. Min. Average Max. Min. Average Max. 1 Vörösberényi creek 0,012 0,021 0,024 0.017 0,018 2 Lovasi creek 0,054 0,011 0,015 3 Csopaki creek 0,013 0,011 0,008 4 Örvényesi creek 0,089 0,104 0,089 0,101 0,039 0,052 5 Burnót creek 0,051 0,091 0,034 0,030 6 Egervíz 0,050 0,102 0,061 0,068 0,035 0,458 7 Tapolca creek 0,402 0,440 0,340 0,478 0,264 0,402 11 Zala 3,30 4,94 6,20 4,10 7,46 10,90 1,80 2,37 2,90 12 Nyugati channel 1,312 1,437 0,930 14 Keleti-Bozót channel 0,902 0,750 0,300 16 Jamai creek 0,030 0,003 0,001 17 ABC channel 0,731 18 Tetves creek 0,055 0,128 0,050 0,397 0,044 0,048 19 Nagymetszés trench 0,072 0,022 0,016 20 Köröshegyi creek 0,107 0,087 0,043 21 Endrédi creek 0,033 0,027 0,030 The creeks and sampling sites are shown in Fig. 1. Zooplankton samples were surface samples, filtered water volume was 50 liters at each of the sampling sites. Filter mesh size was 70 urn. Filtrate was conserved in Lugol-iodine solution. Determination of the species was conducted by using light microscope in the laboratory. Quantitative studies were made by using Utermöhl-type inverted plankton microscope with 5 ml chamber. For the crustacean investigation the whole sample was used, while in case of the Rotatorians provided that they occurred in large numbers the 1 /20 th of the sample was analyzed. Results 1. Vörösberényi creek The specific electric conductivity varied between 870-1020 pS/cm. Higher than average values of salt contents are indicated by the above average Ca 2+ , and Mg 2+ , total hardness and HC0 3 " values. On the basis of the inorganic ionic composition the water falls to the beta-limnotype, Ca - Mg - HC0 3 , and in one occasion to Mg - Ca - HC0 3 water type. Indicators of organic pollution COD ps and COD k indicated good water quality. 90% percentile value of the dissolved oxygen was 121.5%, in spite of the fact, that the maximum value of the chlorophyll-a
