Cyanobacterial blooms in freshwater continental reservoirs: a review

Cyanobacterial blooms of continental freshwater reservoirs are currently one of the global challenges facing humanity. The main factors increasing the scale and frequency of cyanobacterial blooms are increasing human population, intensification of agriculture, growth in industrial production, increased consumption of ores and other minerals, and global climate change. Mass development of cyanobacteria causes the breakage of trophic links between primary producers and consumers, leading to the excessive accumulation of cyanobacterial biomass and soluble products of their metabolism and autolysis, including biologically active secondary metabolites and cyanotoxins, and contributes to the formation of hypoxic conditions in the water column. Cyanobacterial blooms significantly reduce the consumer qualities of aquatic ecosystems, including their recreational attractiveness, water quality and its suitability for drinking and household purposes. The main reason for the excessive development of phytoplankton in continental freshwater reservoirs is the influx of an excessive amount of nutrients, primarily phosphorus, as well as a decrease in water circulation, causing stagnation, and high air temperatures, leading to excessive heating of water for a long period. The requirement of specialized monitoring is emphasized in order to assess and control the factors leading to the mass development of certain species of cyanobacteria. The review discusses the main bloom-forming species of cyanobacteria in freshwater reservoirs, the features of their development and environmental requirements, the consequences of cyanobacterial blooms for aquatic ecosystems and the population. The necessity of reducing the external biogenic load on reservoirs as the most important condition for the long-term prevention of cyanobacterial blooms is emphasized. An overview of various intra-reservoir methods of restoration and rehabilitation of reservoirs is given. Since their effectiveness strongly depends on the limnological and hydrobiological characteristics of the reservoir, the choice of certain methods should be based on a complete and comprehensive description of the ecosystem of the rehabilitated reservoir.