L. Hably szerk.: Studia Botanica Hungarica 23. 1992 (Budapest, 1992)

Buczkó, Krisztina; Ács, Éva: Preliminary studies on the periphytic algae in the branch-system of the Danube at Cikolasziget (Hungary)

According to many papers the quality of the host in flowing waters (esp. quick rivers) is not as important as in standing waters (lakes, ponds), where the substrate seems to be the determinant factor. This hypothesis needs to be tested. More or less regularly the branches in the Szigetköz section of the Danube are flooded from time to time by the rising Danube. During the flood the water flows for days or weeks in the branches. In this sense, the Szigetköz is a flowing water. On the other hand the dams close the branches when the level of water is low. In this case the water cannot flow through the small branches often for months. It is a very long period compared to the generation time of the algae, so in this sense we can regard the Szigetköz as many neighbouring ponds, separated by dams. So the Szigetköz section of the Danube is especially suitable for a study of the connection of the substrate and its coating (to test host specificity), and to compare the periphyton community of running and standing water periods. According to WETZEL (1983), there are more significant differences between the biotic (macrophyte, leaves, twigs) and abiotic (stones, sand, mud) hosts then among the biotic ones. At first we tried to find differences among coats of macrophyte hosts. MATERIALS AND METHODS The samples were collected on 13 and 15 July, 1991, in the second branch system of Szigetköz (Fig. 1). Sampling points 1, 3 and 4 were in flowing water, No. 2 was in standing water. On 13 July, 14 samples were collected from these points on substrates as follows, 1. sampling point: old reed (o) in 5 repetitions green reed (g) Rorippa amphibia L. (Bess.) stem (R) Polygonum amphibium L. stem (P) 2. sampling point: Carex acutiformis Ehrh. leaf (Ca) green reed (g) twig (Bl) Myriophyllum verticillatum L. stem (M) 3. sampling point: green reed (g) 4. sampling point: green reed (g) July the 15th was the first day of a remarkable flood of the Danube, so our sampling points were flooded by water. This way we could collect only 1 sample from the 2nd sampling point, namely a twig (B2). Collection methods: the reeds were cut off at water level, and 8-10 cm below this level, then the stems were carefully taken off and put into the collecting jar. The other submersed plants were also carefully taken off, the leaves were cut off, and only the stems were placed into the jars. Water temperature, conductivity and the total hardness were measured at every sampling point. 51