SEASONAL CHANGES IN THE DIATOM FLORA IN A SMALL RESERVOIR WITH SPECIAL REFERENCE TO SKELETONEMA POTAMOS

Abstract

Seasonal changes in the phytoplankton of the small eutrophic River Rott in Bavaria have been studied over a 2 year period. Total phytoplankton peaks in May and then several times later in the summer and autumn, before declining to a minimum in winter. Diatoms are usually the dominant algae, most of them belonging to centric genera. In a reservoir along the Rott, Skeletonema potamos is abundant during August and September, sometimes in concentrations of 10⁶ml⁻¹; S. potamos also occurs in the riverine sections of the Rott, but in smaller numbers. Silicate concentrations do not appear to be significantly affected by these massive growths of S. potamos but are reduced during the growth of more heavily silicified centric diatoms. Brief comparisons are made with other river systems, especially with respect to 5. potamos.