Distribution of phytoplankton in a German lowland river in relation to environmental factors

In comparison to lentic systems, the species composition and community structure of phytoplankton in lotic habitats are still poorly understood. We investigated the spatial and temporal dynamics of the phytoplankton community in a German lowland river, the Kielstau catchment, and the relationships with environmental variables. Among the 125 taxa observed, Desmodesmus communis, Pediastrum duplex and Discostella steligera were dominant species at lentic sites while Tabellaria flocculosa, Euglena sp., Planothidium lanceolatum, Cocconeis placentula and Fragilaria biceps dominated at lotic sites. Remarkable spatial and temporal variations of the phytoplankton community were revealed by non-metric multidimensional scaling. Canonical correspondence analysis indicated that physical factors (e.g. hydrological variables) and major nutrients [e.g. total phosphorus, dissolved inorganic nitrogen (DIN)] were of equal importance controlling the variation in structure of riverine phytoplankton assemblages. Weighted averaging regression and cross-calibration produced strong models for predicting DIN, water temperature (WT) and total suspended solid (TSS), which enabled the selection of algal taxa as potentially sensitive indicators: for DIN, Ulnaria ulna var. acus, U. ulna, D. communis and Euglena sp.; for WT: D. steligera, Scenedesmus dimorphus, D. communis and Euglena sp.; for TSS, Nitzschia sigmoidea, D. communis and Oscillatoria sp. The results from this relatively small survey indicate the need for further monitoring to gain a better understanding of riverine phytoplankton and to capitalize on the environmental indicator capacity of the phytoplankton community.