ИСТИНА

Ecological monitoring of sub-Arctic water bodies is essential for studying their evolution under the action of global climate change and other natural processes; it becomes extremely important when solving such practical problems as construction of tidal power plants, seawalls, bridges, and other hydraulic structures leading to the separation of water areas from the sea. As a result of isolation, the ecosystem of a saline water body undergoes irreversible changes: the surface water layer gradually becomes fresh and the near-bottom water stagnates with the formation of oxygen deficiency and hydrogen sulfide contamination. This leads not only to changes in the physicochemical characteristics of the water mass but also implies sharp changes in the microbial community which distribution can be monitored using optical spectroscopy. Along the coastline of the Kandalaksha Bay of the White Sea several lakes are known to be at different stage of separating from the Sea. We summarize the results of complex inspection of 5 meromictic lakes and lagoons performed in different seasons in 2014-2018. We sampled water from various depths and measured water temperature, salinity, pH, Eh, dissolved oxygen content, and illumination in the field. In laboratory conditions spectroscopic investigations of natural water samples and measurements of dissolved oxygen and sulfide anions (S2–) were carried out. The total Chl d and e concentrations were calculated from absorption spectra of pigment extractions in acetone:methanol mixture or directly from absorption spectra of intact bacterial cells in natural water using the recently developed technique. Spectroscopic methods allowed us not only to determine the presence of green sulfur bacteria (Chlorobiaceae), anoxygenic phototrophic bacteria, at different horizons but also to draw conclusions about relative concentrations of two forms of green sulfur bacteria (green-colored and brown colored) in each lake. Comparing the photosynthetic pigment concentrations with physicochemical parameters of water in the lakes made it possible to reveal favorable conditions for green sulfur bacteria: a layer with a sharp gradient of hydrogen sulfide concentration, salinity, and change of the redox potential from positive to negative. This study was supported by the Russian Foundation for Basic Research, project No 16-05-00548, and by the grant from the “Bazis” Foundation for Development of Theoretical Physics and Mathematics.