Planktonic and Contour Algal Communities in the Ukrainian Section of the Western Bug River and its Tributaries. 2. Spatial Heterogeneity of Quantitative Indicators of Planktonic and Contour Algae Communities

The spatial distribution of cell count, biomass, dominant complexes, and diversity of plankton and contour communities of the Western Bug River and its tributaries were studied. The trophicity and quality of the aquatic environment of the studied rivers were determined. The spatial heterogeneity of phytoplankton, microphytobenthos and phytoperiphyton during the summer-autumn low water period caused high counts and biomass values. An increase in cell count and biomass from sources downstream was revealed, which clearly correlates with an increase in the width of the watercourse. A significant quantitative diversity of algal communities was determined by the development of <i>Bacillariophyta. Cyanobacteria</i> and <i>Chlorophyta</i> were subdominants. The trophic status of the studied ecosystems varied from oligotrophic to eutrophic, and the information diversity according to the Shannon index was in the range from 1.58 to 4.62 bits/individual and from 1.60 to 4.40 bits/mg. Values of trophicity and diversity of contour communities were higher comparing to phytoplankton. This indicates that in the summer-autumn low water season, a transparent water regime is formed in the studied watercourses. These results differ from those obtained earlier for the Kaniv Reservoir, in which phytoplankton played a leading role. The spatial heterogeneity of algal communities was largely determined by the structure of the dominant complexes. Usually this is either monodominance of <i>Bacillariophyta</i>, or oligodominant complexes <i>Bacillariophyta-Cyanobacteria</i> or <i>Bacillariophyta-Chlorophyta</i>. A comprehensive assessment of aquatic environment quality was based on abiotic components and saprobiological characteristics showing that the modal classes of water quality are in the 2nd and 3rd classes (clean waters - waters of satisfactory purity). Therefore, the water quality of the studied Ukrainian section of the Western Bug River and its tributaries does not pose a significant threat of water pollution to neighboring European countries.