STUDIES ON ALGAL DRIFT IN A SMALL SOFT-WATER STREAM IN THE SPESSART MOUNTAINS, GERMANY

Bimonthly drift samples were taken over the course of a year at three stations in a small soft-water stream, the Bieber (Spessart mountains, Germany), which has been under observation for many years. The statio ns were located upstream and downstream of the first village, and upst ream of the mouth. 29 algal taxa (excluding diatoms and some unicellul ar green algae) were identified, (3 Rhodophyta, 16 Chlorophyta, 2 Chry sophyceae, 2 Tribophyceae, 5 Cyanophyceae, 1 Cryptophycae). There were no differences in the total number of taxa in the drift samples from the three stations, but the taxal composition varied. Taxa detected in the drift samples were compared to those growing at the stations. At station 2 and 3 the number of taxa in the drift was twice as high as t he number growing at the stations. Some taxa were found more frequentl y at one rather than at another station. With respect to seasonal occu rrence, some taxa were found all year round whereas others occurred on ly once. The number of taxa found only once increased from station 1 t o station 3. Coincidence in taxa composition was low between the three stations but higher between their drift samples. This points to the p ossibility that taxa which were present in the drift may not be able t o establish themselves in all parts of the stream. Station 2 and 3 res embled each other in taxa composition and seasonal occurrence in the d rift samples, whereas station 1 was different. One reason for the simi larity of stations 2 and 3 might be water quality. This part of the Bi eber is impaired by waste water, whereas the water is pure at station 1.