Phytoplankton Annual Dynamics and Ecological Characteristics in the Irpin River (Ukraine) Prior to the Beginning of Military Activities

Abstract

Phytoplankton annual dynamics and ecological structure were studied in the Irpin River (the right bank tributary of the Kyiv Reservoir) near the town of Irpin (50°31'N, 30°15' E). On the whole, 121 algal species of nine divisions were identified. Chlorophyta (57) and Bacillariophyta (27) included the largest number of species. During the year, phytoplankton species composition, and also the complex of dominant species, varied significantly. This is supported by rather low values of the Sorensen coefficient of community similarity (on the average 53% and 41%, respectively). The quantitative indices of its development also varied significantly. The lowest number of species (25), cell numbers, and biomass of plankton algae (on the average 662 thousand cells/L and 0.165 mg/L) were registered in winter and the largest number of species (83) - in summertime. At the same time, the highest cell numbers and biomass (19,480 thousand cells/L and 5.143 mg/L) were observed in autumn (in September). Direct significant correlations were established between phytoplankton quantitative indices and water temperature. However, it has been found that phytoplankton annual dynamics in the Irpin River depended not only on water temperature, but also on the trophic status of the watercourse. As a result of the performed bioindication analysis, it has been found that in terms of such indices as the contribution of species - indicators of the trophic status, nutrition type, and organic contamination, and also in terms of phytoplankton biomass, the waters of the studied section of the Irpin River can be characterized as eutrophic ones, which is supported by the data of direct hydrochemical measurements. The pattern of phytoplankton annual dynamics was characterized by the formation of the peak of its numbers and biomass in early autumn. The maximum quantitative indices of phytoplankton development were conditioned by intensive development of blue-green algae with a predominance of <i>Aphanizomenon flos-aquae </i>(L.) Ralfs belonging to water bloom forming species. Such pattern of phytoplankton annual dynamics is typical to eutrophic water bodies. The obtained information on the development of algae in the Irpin River in the period preceding military activities can be used to assess their consequences.