Comprehensive monitoring of the water quality of the Velikaya river estuary by a set of hydrochemical and hydrobiological indicators (Pskov Region)

The purpose of our study was to study the dynamics of the water quality of the Velikaya River estuary in the growing season of 2023 according to a number of hydrochemical and hydrobiological indicators. The data of one-year hydrochemical and sanitary-microbiological monitoring of a natural reservoir, the mouth of the Velikaya River, are presented. The water area was studied based on data from the analysis of 5 stations. 21 hydrochemical indicators were determined. The water quality class has been determined according to the water pollution index. The sanitary and microbiological monitoring included the determination of OHMS of allochthonous and autochthonous microflora. It followed from the results that the reservoir is experiencing bacterial pressure largely than chemical pressure. The geological features of the region explain the exceeded hardness value, and natural processes and pollution of the reservoir may cause the increased values of BOD-5 in some seasons. The values of the integrated pollution assessment were in the range of 1,88–2,29. Water quality is characterized in the transitional value of water quality class III–IV. According to the water assessment, according to the average indicators of bacterial contamination, the waters were classified as moderately polluted, but in the summer at one point, the water samples were classified as polluted. The waters are characterized as "moderately polluted", which corresponds to an average concentration of hydromicrobiota in the order of 10³ (CFU)/ml.