Epilithic algal communities on natural and artificial substrata in the River Danube near Vienna (Austria)
Schagerl, M.; Donabaum, K.
Investigations of the microphytobenthic community were carried out at the right bank of river Danube between river km 1943.2 and 1938.9. Pigment markers analyzed by means of HPLC were used to determine predominating algal classes. Whereas phytoplankton consisted mainly of diatoms, blue-greens prevailed in the benthic community. Diatoms and green algae were of minor importance in the phytobenthos. On small pebbles blue-greens decreased for the benefit of diatoms due to a more frequent relocation. Maximum chlorophyll-a quantities were analyzed in summer approximating 40 µg · cm-2, the minimum was found in late fall with 0.1 µg · cm-2. On average periphyton dry mass consisted to 73 % of inorganic components. This reflects the high amount of inorganic suspended solids in the Danube. The average chlorophyll-a content on the basis of ash free dry mass was 0.4 % (r2 = 0.699; n = 93). Additionally, artificial substrates (tiles, sterile coarse gravel) were exposed for four ten- to fourteen day periods. In contrast to natural periphyton communities, diatoms and green algae predominated and no significant quantities of blue greens were observed. Blue-greens could not establish within the short exposure time which was chosen with regard to the strong water-level fluctuations.