Article

Heterotrophic microorganisms and viruses in the water of the Gorky reservoir during a period of anomalously high water temperature

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Abstract

During the anomalously hot summer of 2010, the water temperature in the Gorky reservoir reached 27–33°C. Pronounced cyanobacterial blooms occurred in the limnetic part of the reservoir. The average values for bacterioplankton abundance (11.58 ± 1.25 × 106 cell/mL), biomass (886 ± 96 mg/m3), and production [169 ± 32 mg C/(m3 day)] were twice as high as in the year with temperatures comparable to long-term average values. These parameters were higher in the limnetic part than in the river one. The abundance (4.86 ± 0.75 × 103 cell/mL) and biomass (138 ± 9 mg/m3) of heterotrophic nanoflagellates were 2.3 and 1.7 times higher, respectively, than in years with regular temperature regimes. The average number of plank-tonic viral particles (N v) in 2010 was 48.89 ± 9.54 × 106 particles/mL, while virus-induced bacterial mortality (VMB) accounted for 26.9 ± 4.6% of the bacterial production. The N v and VMB values in the limnetic part of the reservoir were, respectively, 1.5 and 1.8 times higher than in the river one.

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... Apparently, these processes have a significant effect on the development of heterotrophic bacteria in mesotrophic and eutrophic reservoirs of the Volga cascade. In summer 2010, a twofold increase in the abundance, biomass, and production of bacterioplankton was recorded in the Gorky Reservoir when compared to years with a normal thermal regime (Kopylov et al., 2013). ...
... In the sum- mer of 2010, phytoplankton bloom was observed in the Gorky Reservoir when the water temperature exceeded the normal temperature on average by 4.6-6.9 о С (Lazareva et al., 2012;Kopylov et al., 2013). The chlorophyll concentration in the surface (0-2 m) water layer in the lake part of the reservoir reached 119 mg/L during that period, which corresponded to hypertrophic waters. ...
... During the surveyed period, the frequency of infected bacterial cells (13.1 ± 1.2% N B ) and virusinduced mortality of bacterioplankton (17.2 ± 2.0% Р B ) were lower in the mesoeutrophic Rybinsk Reservoir than in eutrophic reservoirs of the Volga River: in the Gorky (17.8 ± 2.2% and 26.9 ± 4.6%) and Cheboksary (16.1 ± 1.2% and 22.4 ± 2.7%, respectively) reservoirs (Kopylov et al., 2013a(Kopylov et al., , 2013b. ...
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Bakterioplankton vodokhranilishch Verkhnei i Srednei Volgi (Bacterioplankton of Reservoirs of the Upper and Middle Volga)
  • A I Kopylov
  • D B Kosolapov
  • AI Kopylov
Formation, Movement, and Transformation of Water Masses in the Gorky Reservoir
  • Edel
  • K K Shtein
Zakonomernosti pervichnoi produktsii v limnicheskikh eosistemakh (Patterns of Primary Producc tion in Limnetic Ecosystems
  • V V Bul 'on
Bul'on, V.V., Zakonomernosti pervichnoi produktsii v limnicheskikh eosistemakh (Patterns of Primary Producc tion in Limnetic Ecosystems), St. Petersburg: Nauka, 1994.
Hydrological Characteristics of Reservoirs, in Sovremennaya ekologicheskaya situatsiya v Rybinskom i Gor’kovskom vodokhranilishchakh (Current Ecological Situation in the Rybinsk and Gorky Reservoirs)
  • A S Litvinov
  • A V Zakonnova
  • AS Litvinov
Pigments of Phytoplankton of the Rybinsk Reservoir, in Ekologicheskie problemy Verkhnei Volgi (Environmental Problems of the Upper Volga), Yaroslavl: Izd
  • I L Pyrina
Characteristics of Thermal Conditions
  • A S Litvinov
  • V F Roshchupko
  • AS Litvinov
Complex ecological classification of the quality of surface inland waters
  • O P Oksiyuk
  • V N Zhukinskii
  • L P Braginskii
  • OP Oksiyuk
Mikrobiologicheskie protsessy produktsii i destruktsii organicheskogo veshchestva vo vnutrennikh vodoemakh
  • V I Romanenko
Ekologiya mikroorganizmov presnykh vodoemov. Laboratornoe rukovodstvo (Ecology of Microorganisms of Freshwater Bodies: A Laboratory Manual)
  • V I Romanenko
  • S I Kuznetsov
  • VI Romanenko
The Relationship between Biomass and Volume of Bacteria, Handbook of Methods in Aquatic Microbial Ecology
  • S Norland
Pigments of Phytoplankton of the Rybinsk Reservoir
  • I L Pyrina
  • IL Pyrina
Mikrobiologicheskie protsessy produktsii i destruktsii organicheskogo veshchestva vo vnutrennikh vodoemakh (Microbiological Processes of Production and Destruction of Organic Matter in Inland Water Bodies)
  • V I Romanenko
  • VI Romanenko