Seasonal and Spatial Patterns of the Diatom Actinocyclus Normanii in the Weser Estuary (NW‐Germany) in Relation to Environmental Factors

During late summer and fall the tidal freshwater reaches of the estuaries of Elbe and Weser are dominated by the autochthonous Actinocyclus normanii, a large centric diatom which forms up to 95 % of phytoplankton biomass (Schuchardt, to be published). In spite of much work that has been done on phytoplankton dynamics in the outer reaches of estuaries, seaward of high suspended matter (SPM) concentrations (Cloern, 1987), only few studies have focussed on phytoplankton dynamics and the controlling processes within the tidal freshwater reaches.