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Abstract

Reactions to current velocity by the dominant diatom taxa of a small, soft-water stream were investigated in an experimental channel placed in the stream. Ten out of 13 taxa reacted to the different current velocities (0.5-50 cm/sec). Navicula pelliculosa was a very abundant taxon which did not react to different current velocities. Taxa growing on stalks (Gomphonema spp.), as well as smaller taxa that grow directly on the substratum (Nitzschia archibaldii, N. cf. paleacea) tended to be most adapted to resisting the mechanical force of current velocity. Small cells were dominant at all current velocities, no large taxa were dominant at any current velocity. There was a slight tendency for increasing diversity values when current velocity values increased. This means that there was a comparatively high number of species that tolerate the possible mechanical stress of current velocities of 50 cm/sec. The species composition differed from the one found at low current velocities. Hence, different diatom communities developed under different current velocities. This information is important to floristic studies as well as in the assessment of water quality. A variety of sites of differing current velocities should be analyzed to gain an accurate overview of the microalgal community in a stream (or any flowing water) or a reliable assessment of water-quality data.