L. Forró szerk.: Miscellanea Zoologica Hungarica 9. 1994 (Budapest, 1994)

Andrikovics, S.; Hadnagy, T.: Ecological evaluation of aquatic invertebrates distribution of Apátkút Creek (Visegrádi Mountain, Hungary) in winter

Results and conclusions First those two ecological factors have to be discussed that have the greatest influence on the distribution of aquatic insect larvae: water velocity and the dissolved oxygen content. The most difficult, and, at the same time, the most interesting parts of conclusions are those relationships between environmental factors and the distribution of aquatic insect larvae. The water velocity changed between 0.1 m/sec and 3.8 m/sec (Table 1). The water velocity values change in a wide range, the average velocity is rather high (about 1 m/sec). Oláh (1967) and Kiss (1977, 1979) measured much smaller values in the creeks of Mátra and Bükk Mts. Table 1. Mean velocity of water along the Apátkút Creek No. V No. V No. V No. V No. V 1 0.O95 6 2.120 11 2.378 16 2.179 21 3.874 2 0.345 7 1.526 12 1.191 17 0.215 22 1.896 3 2.403 8 3.693 13 0.095 18 1.784 23 1.483 4 0.334 9 2.378 14 2.210 19 1.088 24 2.068 5 1.423 10 0.500 15 1.268 20 2.326 25 1.165 No. - number of sampling sites V - water current (m/sec) Those sites, where water velocity minimums were observed (Nos 1, 13) - widenings of the creek on flat field - can essentially be considered to be still waters. Sites showing velocity maximums (Nos 8, 21) are micro-waterfalls. The water velocity largely depends on the slope, so the wide interval of its values shows the micro-range of slope of the watercourse. Two interesting facts can be studied on Fig. 2. The first one is that water velocity changes periodically and it can be explained by the variety of slope, the other one is that beside periodicity, considering the length of the creek, the value of average velocity does not change, and remains about 1 m/sec. Water velocity is determined by water discharge beside the slope. The larger the slope and water discharge are, the bigger is water velocity. Moving downstream along the creek from the source, the water output is increasing because water coming from lateral arms increases the water output. The slope shows decreasing tendency. These two effects compensate each other. This can be the reason that the average velocity is permanent at the whole length of the creek. The periodicity and wide range of the water current result in wide variety of different aquatic insect community assemblages. Dissolved oxygen content varied from 4.85 mg/dm to 19.48 mg/dm (Table 2, Fig. 2). The sampling sites were the same as the points of velocity measurements. Table 2. Results of dissolved O2 measurements No. O2 °C No. O2 °C No. O2 °C 1 4.85 1 9 14.53 2 17 8.15 0 2 7.91 1 10 9.68 2.5 18 12.66 0 3 8.60 1 11 14.84 2.5 19 13.10 0 4 5.05 1 12 11.35 2.5 20 17.60 0 5 8.13 1 13 9.52 0 21 19.48 0 6 11.03 1 14 14.23 0 22 9.69 0 7 11.29 1 15 13.83 0 23 14.31 0 8 15.82 1 16 15.95 0 24 25 15.19 9.90 0 0 No.- number of water samples O2- dissolved oxygen content (mg/1) °C- water temperature (°C)