Preliminary characteristics of the water quality of small rivers in the forest zone of the Omsk Irtysh region

We studied hydrochemistry and phytoplankton of small rivers in the forest zone of the Omsk Irtysh region (2020).Based on these studies, the trophic status and water quality were established. The waters of the studied rivers are fresh and belong to the hydrocarbonate class, except for the Ibeika River, its water is brackish, and it belongs to the chloride-hydrocarbonate class. The active reaction of waters is in the alkaline range. The content of total phosphorus does not exceed values corresponding to unpolluted natural waters. The content of various forms of nitrogen does not exceed the maximum permissible concentration. The water quality according to BOD5 ranges from 2 to 3 classes in the right-bank tributaries of the Irtysh River. In the left-bank ones there was an excess of the BOD5 standard and the 4th class of water quality. According to the COD index, the Stepanovka river belongs to the 4th class of water quality “polluted”, the waters of other rivers belong to the 3rd class of water quality “satisfactory purity”. In the composition of phytoplankton, 74 species and intraspecific taxa of algae were found from six divisions: Cyanoprokaryota - 9, Dinophyta - 1, Euglenophyta - 12, Bacillariophyta - 22, Chlorophyta - 23, Chrysophyta - 1. By species composition, diatoms, euglenic and green algae predominate in the phytoplankton of the left-bank tributaries of the Irtysh River, while green algae and diatoms predominate in the right-bank ones. The abundance and biomass of phytoplankton in the studied rivers vary widely: abundance varies from 0.47 to 3.14 million cells/dm3, biomass varies from 0.15 to 10.92 g/m3. The dominant species include filamentous cyanoprokaryotes and small-celled green algae. The trophic status of the surveyed rivers ranges from oligotrophic to polytrophic categories; the water quality by phytoplankton biomass varies from class 2 “clean” to class 4 “polluted”.