SEASONAL CHANGES OF PHYTOPLANKTON IN A SMALL SHALLOW DAM LAKE PART OF THE PROTECTED AREA NATURE 2000

K. Dochin, A. Ivanova

Abstract: During the research in the Kavaka dam lake 98 taxa of phytoplankton from 6 divisions have been identified: Cyanoprokaryota (24, 24.48%); Chlorophyta (44, 44.89%); Streptophyta (5, 5.1%); Euglenophyta (8, 8.16%); Pyrrhophyta (3, 3.06%) and division Ochrophyta (class Bacillariophyceae) (14, 14.28%). The most numerous are the species of the green algae (44) from the division Chlorophyta. Despite the secondary importance of blue-green algae in terms of species abundance, ubiquitous blooms of cyanobacteria have been identified in Kavaka dam lake. They are potential producers of toxins such as: Anabaena spiroides, Microcystis aeruginosa, Aphanizomenon flos-aquae and Microcystis wesenbergii, and these types are always present in dominant phytoplankton complexes. According to the data from our research, the reasons for the dominance of cyanobacteria are: the shallow depth, the low water level of the Kavaka dam lake during almost the whole period, with the exception of autumn, when the level of the reservoir is significantly higher and the effect of dilution of its waters causes a significant decrease in phytoplankton numbers. The reported average value of the biomass (2.169 mg.l-1) as well as the rest of the data from the phytoplankton research confirm that the Kavaka dam lake is at a state of a highly advanced degree of eutrophication.

Keywords: biomass; blooms; cyanobacteria; eutrophication; phytoplankton

Date published: 2017-12-20