Current state of phytoplankton in Batak reservoir (Southwestern Bulgaria)

Ivan Iliev, Velika Kuneva, Angelina Ivanova, Kostadin Dochin

Abstract: The aim of the present study was to update the current status of the phytoplankton composition in Bulgarian reservoir with high social, environmental and economic importance such as the Batak reservoir and to analyze its relationship with the total bacterial count (TVC) and the environmental factors. A total of 106 phytoplankton taxa were identified for the study period. Class Bacillariophyceae was presented by the highest number of species (34) followed by divisions Chlorophyta (26) and Cyanoprokaryota (17). The maximum of species diversity was established in the samples from September at the station situated
near the dam wall (S1) with the lowest number being detected in July at the same station. The phytoplankton abundance (PhN) and biomass (PhB) has reached their maximum in September with highest values in the epilimnion samples with a steep
decrease in depth of the reservoir. Seasonally and spatially waters were dominated by the diatoms Tabellaria fenestrata var. asterionelloides Grunow, Fragilaria crotonensis Kitton, green algae Pandorina morum (O.F.Müller) Bory, and Desmodesmus communis (E. Hegewald) E. Hegewald. Aphanizomenon flosaquae Ralfs ex Bornet & Flahault is presented with relatively high numbers. A Woronichinia naegeliana (Unger) Elenkin bloom was established in November at the tail of the reservoir. Significant positive correlations were established between phytoplankton abundance and the nitrogen forms, total phosphorus, with
negative correlations between PhN and TVC. According to cluster analysis, the surveyed stations are grouped into two separate clusters each with similar spatial and seasonal characteristics. The stations at the dam wall and at the tail of the reservoir are characterized by the highest hierarchical distance.

Keywords: abundance; algal bloom; Batak reservoir; biomass; phytoplankton; TVC

Date published: 2018-08-30