The results of studies (1989–1999) on the flora and dominant assemblages of planktonic greens (Chlorophyta and Streptophyta) in seven shallow weakly mineralized forest lakes are presented. The lakes are located on the area of the Darwin State National Reserve (Vologda Oblast, Russia). It is shown that the process of increasing lake acidity is accompanied by decline in the general richness of greens, especially of order Sphaeropleales and Chlorellales. At the same time, the proportion of species preferring high acidity and low content of organic matter and salts increases, as well as of number of dominant species, relative biomass of Chlorophyta and Streptophyta owing to algae of orders Zygnematales and Desmidiales. The possible morphological and physiological adaptations of individual representatives of greens promoting their development in acidic lakes are discussed.
Keywords: phytoplankton, Chlorophyta, Streptophyta, lakes, acidification
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