The phytoplankton of Koprinka Reservoir (Central Bulgaria): species composition and dynamics

The aim of the study was to determine the species composition and dynamics of the phytoplankton community of Koprinka reservoir. We have identified a total of 109 taxa assigned to 6 divisions including Chlorophyta (37), Ochrophyta (26), Cyanoprokaryota (22), Euglenophyta (11), Streptophyta (11) and Pyrrhophyta (2). The highest phytoplankton biomass (PhB) and numbers (PhN) and the lowest species richness were detected in September. In October with the decrease of the PhB the species diversity has increased.The highest species richness was observed at station 3, situated in the riverine area, with the phytoplankton abundance being significantly higher compared to the other two stations. The species Hariotina polychorda(Korshikov) E.Hegewald dominated in thewater samples in the summer at all stations. In the early autumn, a bloom of the potentially toxic species Microcystis wesenbergii(Komárek) Komárek ex Komárek was detected, which is an indicator for eutrophication process in the reservoir. Cluster analysis (CA) based on the phytoplankton composition isolated the samples from each sampling periods in a separate water cluster, characterized by significant spatial heterogeneity. The phytoplankton species composition, and the values for biomass, and chlorophyll aare evident for the eutrophic state of the reservoir.