Inundation and isolation: dynamics of phytoplankton communities in seasonal inundated flood plain waters of the Lower Odra Valley National Park — Northeast Germany

The flood plains of the Lower Odra are inundated in winter and spring and are desiccated in summer and autumn. Phytoplankton composition as well as its seasonal succession in permanent oxbows and separate lakes were investigated between 1993 and 1996. Solitary centric diatoms were the characteristic phytoplankton taxa of these flood plain waters. They dominated the main channel non-seasonally, the flood plains during the entire inundation phase and long periods of the isolation phase. Only during long phases of low mixing (maximal 1.5-2 months in summer) separate water bodies were dominated by Cyano- and/or Dinophyceae. This special feature of the Lower Odra Valley is explained by the Inundation-Isolation-Model of phytoplankton development influenced by inundation. Out of a high diverse algal spectrum of 495 taxa, specialities such as 9 endangered taxa and 6 halophilous taxa were discussed. Additionally, taxon specific cell-volumes and maxima of biovolumes were given.