Algological survey of small floodplain backwaters

Fourty-eight small floodplain eutrophic backwaters (pools and oxbows) were sampled once to test the hypothesis, that habitats of this type have specific phytoplakton structure, different from other types of water bodies. Prevailing dominance of flagellates (both as frequency of species occurrence and biomass contribution), namely Cryptophyceae, Euglenophyceae, Dinophyceae, and Chrysophyceae, and low proportion of green chlorococcal algae and Diatoms, and almost absence of Cyanophyceae confirmed such a hypothesis. Unlike the phytoplankton composition, their eutrophic status is fully comparable with many other lakes, reservoirs or fishponds, where the coccal forms as blue-greens or Chlorococcales develop remarkably. Obviously, the poorly mixed water column of studied backwaters (resulting from small surface, large relative depth and wind-protecting barrier of banks and vegetation) and intensive shading of water surface by this vegetation play the key role in the flagellate dominance. The motile forms are able to keep or migrate to the position, where the photosynthesis is still possible; while the coccal forms sediment out from this position not being driven back upwards by any turbulent mixing.