Assessment of Water Quality of Reservoirs by a Comprehensive Study of Hydrobiological and Hydrochemical Indicators Using the Example of the Hrazdan Reservoir (Armenia)

Anotace: The water quality of the Razdan reservoir was assessed using hydrobiological, hydrochemical and microbiological methods in different seasons of the year. As a result of studies at three observation stations, it was found that at the outlet of the reservoir, in almost all the seasons under study, the quality of water does not meet the accepted standards used for agricultural irrigation. This is a consequence of the increase in organic pollution of the reservoir due to seasonal fluctuations in its water level in different seasons, leading to significant changes in temperature and concentration of biogenic substances. PCA analysis of bacterial counts, algal cell counts, and water chemistry showed that a total of 65.4% of the data variance was explained by the two principal components. In total, only two different groups showed factor loadings >0.1. The highest abundance of S_20 and Bacillariophyta species may be related to the typical August environmental conditions. In contrast, the high abundance of S_37 and E. coli may depend on the nitrogen availability in autumn (October and November). Such comprehensive studies of reservoirs allow for a more accurate assessment of the quality of their water. At the same time, not all water quality indicators may exceed the accepted standards. However, the appearance of even some indicators exceeding these standards may become a significant argument for developing recommendations for reviewing the possibilities of using reservoirs for agricultural needs.