ОЦЕНКА КАЧЕСТВА ВОДЫ УСТЬЯ РЕКИ ВЕЛИКОЙ ПО ПОКАЗАТЕЛЯМ ФИТОПЛАНКТОНА

Abstract

The article gives the description of the Velikaya River as the largest river in the Pskov region, which collects water from half of region area and in many respects determines not only the water balance of Lake Pskov-Peipsi, but also is a source of anthropogenic pollution 
 of a unique water reservoir. In water resources management the priority is given to studying phytoplankton as the primary link in a trophic chain. Microalgae participate in carbon and energy cycles, self-purification of water bodies, serve as a food resource; they first respond to initial changes in the aquatic ecosystem, thereby being an excellent object for bioindication. The aim 
 of the work was to study the taxonomic composition, quantitative characteristics, and ecological features of phytoplankton in the mouth of the Velikaya River in order to assess quality of the aquatic environment. For the period 2015 - 2016 138 microalgae species were identified, the largest number of which was identified in the late spring (84 species), the smallest - in the autumn (47 species). Planktonic algoflora of the lower reaches of the Velikaya River can be characterized as diatom-chlorophylic with a minor contribution of cyanobacteria and golden algae. The comparison of phytoplankton composition with the use of the Sierensen-Chekanovsky index showed that species composition is closest between winter and autumn algocenoses 
 (Ks-ch = 0.6). The abundance of phytoplankton in the mouth of the Velikaya River changed in a wide range depending on the season: from 232.0 thousand cells/liter in winter to 2.07 million cells/liter in summer, biomass - from 60.3 mg/m3 in winter to 773.6 mg/m3 in summer. According to the ecological and geographical characterization of the studied water area, widespread freshwater planktonic forms of phytoplankton prevailed, which prefer a weak alkaline water environment. The average saprobity index for Pantle and Bucc was 2.05, which shows a moderate pollution of the lower reaches of the Velikaya River.