Abstract
A total of 98 taxa of algae were observed in phytoplankton, sampled monthly, from the Khmelnitsky monitoring station in the Southern Bug River, Ukraine, between April 2010 and March 2011. Chlorophyta species are the richest taxonomic group with 46 taxa, followed by Bacillariophyta, Euglenophyta, Cyanoprokaryota, Dinophyta, Chrysophyta, Streptophyta, and Xanthophyta. Seasonal dynamics of species distribution in taxonomic divisions shows that the role of Bacillariophyta in communities was high in January-March, which were replaced by greens in March-September. Euglenoids were developed in February-December and bluegreen algae in summer communities only. Strong positive correlations between temperature and species richness was observed. Abundance and biovolume of phytoplankton were maximal in summer, caused mostly by Dolichospermum flos-aquae (Lyngb.) Wacklin, Hoffmann and Komarek and Ceratium hirundinella (O. Müll.) Bergh. The river ecosystem has two periods of trophic levels - high at summer and low at winter. Bioindication characterizes the river as low alkaline and low mineralized with a moderate organic pollution level, revealed aspects of seasonal changes and revealed the main source of organic pollution as flowing from the catchment area during ice melting and rains. Organic pollution indices fluctuate within narrow limits suggesting relative stability of the river ecosystem that is shown also by Shannon indices. The calculated indices, comparative statistics, CCA, and bio-indication analysis exhibits a low pollution level in the Khmelnitsky monitoring station that can be used as a model of aquatic community dynamics under seasonal fluctuation in the southern boreal province climate, applicable for monitoring of the Southern Bug River.