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

new pollution effect. It is not as serious as at Pilisszentlászló, the removal of rubbish and the sewage-system in Visegrád are obviously more developed. The degree of pollution in the creek on the basis of the values of dissolved oxygen content correlate with water chemical results of Simonyi (1981). Altogether 1376 individuals of aquatic insects and amphipods were collected in 174 samples during the sampling program. The collected aquatic insects larvae are as follows: Ephemeroptera: Baeüs rhodani (277) Rhithrogena semicolorata group (132) Electrogena lateralis group (96) Epeorus silvicola (80) Ecdyonurus sp. I. (25) Ecdyonurus sp. II. (6) Habroleptoides modesta (16) Trichoptera: Hydropsyche pellucidula (51) Rhyacophila fasciata (5) Rhyacophila obliterata (3) Lymnephilidae (35) Coleoptera: Elmidae (18) Plecoptera: Megaloptera: Nemoura sp (71) Sialis fuliginosa (3) Leuctra sp. (23) Leuctra hippopus (1) Diptera: Capnia bifrons (4) Empidiae (4) Isoperla grammatica (9) Simuliidae (18) Tabanidae (3) Among the aquatic insects Ephemeroptera, Plecoptera and Trichoptera can be found in largest number of species and individuals. Coleoptera, Megaloptera and Diptera can be found in small number. This is why the distribution of mayflies, stoneflies and caddis-flies will be discussed below. Juvenile larvae of some species could be identified only to generic level. Fig. 3 and Table 3 also demonstrate the pollution well. The smallest number of individuals was detected at Pilisszentlászló and number of individuals slightly descreased in the area of Visegrád. Mayflies and stoneflies indicated continuous pollution. The abundance of mayflies and stoneflies was increasing after Pilisszentlászló. Then at Visegrád, at the new source of pollution, the curves fell almost to the level of Pilisszentlászló. Distribution of Ephemeroptera and Plecoptera were different from the ones of Trichoptera and Amphipoda (Fig. 3). The two latter curves are running parallel to each other. The reason is probably that habitat and food of the two animal groups are the same. Fig. 4 illustrates the distribution of 8 species (5 Ephemeroptera, 1 Plecoptera, 2 Trichoptera). Frequency of individuals strongly decreased in the cross-section of Visegrád (except Baetis rhodani), but not so specifically as at Pilisszentlászló, so the degree of pollution is smaller at Visegrád. Baetis rhodani was the most euryecious species. It was distributed uniformly, its number decreased only at Pilisszentlászló. Electrogena lateralis was found in large number in the clean upper half of the creek. Rhitrogenia semicolorata group, Epeorus silvicola, Ecdyonurus spp. had small number of individuals in the middle and lower transects but a uniform distribution was found in the clean water section. Number of individuals of Plecoptera and Trichoptera