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

in. ÍV. v. VI. VII. Fig. 2. Water current, dissolved oxygen content and number individuals of invertebrates It can be seen on the Fig. 2 that the dissolved oxygen curve follows the average velocity curve. High water velocity goes together with large amount of O2 and (vica versa) low water velocity goes together with low 02-level. In many places the water current is fast, but the amount of O2 does not reach the saturation. Watersamples 13-25 were taken from water of 0 °C, where the surface of water was frozen. The ice prevents the physical solution of oxygen. The other reason is the pollution. The low oxygen level refers to pollution. At Pilisszentlászló the dissolved oxygen content is really small, although the water velocity is high in some places. Fig. 2 shows well that the water current at Pilisszentlászló goes together with much lower oxygen-level, than with the similar water velocity of further places of the creek. For example at sampling site No. 3 (Pilisszentlászló) water velocity is 2.4 m/sec with 8.6 mg/dm O2 content, while at the site No. 11 at similar water velocity (2.4 m/sec) the dissolved oxygen content is much higher, almost two times more than the previous one (14.84 mg/dm

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). The most polluted part of the creek can be found immediately at Piliszentlászló. The origin of the pollution is the sewage water coming from the settlement standing on the sites of the creek and the great amount of litter deposited into the creek. Fig. 2 shows that the oxygen concentration is increasing after the small values of the beginning, then at the end of the creek it is slightly decreasing again. At Pilisszentlászló the water is strongly polluted, and then from the next place it is clearing up and at Visegrád has