The Bloom and Toxicity of Cyanobacteria in Lake Sevan

Abstract

Seasonal hydrochemical, hydrophysical, and phytoplankton studies were conducted in a littoral zone of Lake Sevan in 2019. It is known that in recent years widespread algal blooms were usually started from the littoral zone of Big Sevan, and then spread towards the pelagic zone of the lake. The bloom was mainly caused by species belonging to the genus Dolichospermum (previously Anabaena). Our study has revealed that the physical and chemical properties of water were changed as a result of algal bloom. Particularly, the transparency of water and concentration of dissolved oxygen decreased, while the concentrations of ammonium, nitrite and phosphate ions increased. For the first time, the presence of the toxins microcystin and anatoxin-a was recorded in the lake.

A review of anthropogenic stressors on Lake Sevan, Armenia

“…Average values of phytoplankton biomass in Lake Sevan decreased from 2005-2009 and approached values typical for mesotrophic lakes. In some periods, however, cyanobacteria blooms were recorded (e.g., in October 2009, July 2018-2020) indicating that the nutrient supply in the lake can still support eutrophic conditions (Gevorgyan et al, 2020;Hambaryan et al, 2020;Sakharova et al, 2020).…”