Planktonic algoflora of small rivers in urban conditions (on the example of the Mirozhka and Pskova rivers, Pskov, the Pskov Region)

The paper studies the planktonic algoflora of the Mirozhka and the Pskova Rivers. The research was carried out in the early autumn period of 2019. The taxonomic composition of the Mirozhka River included 107 species and intraspecific taxa of microalgae, the Pskova river – 76 species taxa of algae from 7 phylums: Bacillariophyta, Cyanobacteria, Chlorophyta, Ochrophyta, Cryptophyta, Euglenozoa, Miozoa. The basis of the floral complex in both rivers were diatoms and green algae. The representatives of the Ochrophyta department also made a visible contribution to the species richness of the algoflora of the Mirozhka River. The degree of floral similarity of phytoplankton communities of the Mirozhka and Pskova rivers, calculated using the Sorensen-Chekanovsky index, was 55,7% (51 species of microalgae were common to the rivers). The average phytoplankton abundance in the Mirozhka River was 891,9 thousand cells/l, and in the Pskova river – 199,6 thousand cells/l, biomass – 366,9 micrograms/l and 79,6 micrograms/l, respectively. According to ecological and geographical analysis, freshwater widespread planktonic forms of microalgae predominated in both rivers, preferring slightly alkaline waters. Beta-mesosaprobionts prevailed in relation to organic matter pollution in rivers (38,5% – the Mirozhka River; 41,8% – the Pskova River), which indicates moderate pollution of the studied watercourses. The average saprobity index of the Mirozhka River and the Pskova River was 2,1 and 1,9, respectively, which makes it possible to attribute the waters of the studied watercourses to the 3^rd class of quality – moderately polluted.