The Kislaya Bay currently refers to the water reservoirs formed as a result of the construction of the dam of the tidal power station (TPP) in the Russian Federation (1968). As a result of the reduction in the influence of tidal currents mixing the water column of the bay, the hydrological regime of the reservoir has changed. The reduction in water exchange led to the appearance of bottom stagnant waters deprived of oxygen, as well as hydrogen sulfide contamination. In the 90-s of the twentieth century, the operation of the Kislogubskaya TPP ceased and the flow regime was partially restored. In the winter season of 2024, we conducted microbiological and biogeochemical studies of the Kislaya Bay. It was shown that there was no hydrogen sulfide in the bottom water of the bay, and the processes of sulfate reduction, methane formation and methane oxidation were extremely low. At the same time, in the subsurface layer of sediment, bacteria and archaea were found that dominate the microbial communities of anoxic waters of meromictic reservoirs. We believe that with a stable exchange of water through the TPP dam, the composition of the microbial community of water and sediment will be restored. In case of negative developments, it is possible to predict the transformation of the bay into a reservoir with a community of microorganisms similar to meromictic reservoirs.

The aim of this study was to obtain quantitative hydrological characteristics, intensity of microbial processes and sedimentation conditions in the water column and upper layer of bottom sediments in the Kanda Bay and the basin of the Kislogubskaya tidal power plant. The results of studies in the meromictic reservoirs of the Kanda Bay, artificially separated from the Kandalaksha Gulf by a railway filtering dam at different stages of isolation, and the experience of the operation of the Kislogubskaya TPP and its impact on the basin regime, are an important factor in predicting the origin of hydrogen sulfide contamination during the separation of marine water bodies from the adjacent sea areas, the design of the Northern TPP in the Long Barents Sea Bay and the environmental consequences of the construction of protective dams and dikes, overpasses and embankments when laying roads.

— Formation of the Kanda Bay resulted from construction of a railway dam (1916) and subsequent isolation of the sea lagoon from the main basin of the Kandalaksha Gulf, White Sea. Decreased action of tidal flows, which mix the water column of the lagoon, altered the hydrological regime of the basin. Decreased water exchange resulted in formation of oxygen-depleted near-bottom water and to sulfide contamination. A freshwater lake was, however, preserved in the southern part of the Kanda Bay. The composition of microbial communities was studied for the near-bottom water horizons at different sides of the Kanda Bay. The oxygen regime in this layer was found to change, with increasing concentrations of sulfide and methane and active processes of sulfate reduction and methane oxidation. The composition of the microbial community changed noticeably, with lower abundance of true marine and freshwater microorganisms and development of bacteria and archaea predominant in microbial communities of anoxic water in meromictic basins. Among the microbial diversity, indicator species with increased abundance were revealed. These are archaea of the genera Methanoregula and Methanosaeta (phylum Halobacterota ). The sulfur cycle microorganisms, which were the indicators of stagnant marine water, included anoxygenic phototrophic bacteria of the class Chlorobia , ( Chlorobium phaeovibrioides, Pelodictyon phaeoclathratiforme ), Chloroflexi of the genus Chloronema , nonsulfur purple bacteria related to the genus Rhodoferax , colorless sulfur bacteria of the family Beggiatoaceae , and sulfur oxidizers of the genus Thiobacillus . Archaea of the genus Nitrosopumilus (phylum Crenarchaeota ) and bacteria of the genus Woeseia may be considered opposites to the indicator microorganisms, since they were found only in the open sea water. In our opinion, stable water exchange through the dam will result in the stable composition of the Kanda Bay microbial community, with only seasonal variations and year-to-year fluctuations. The negative scenario supports prediction of conversion of the Kanda Bay into a stratified basin with anoxic near-bottom water and the microbial community similar to that found in meromictic lakes.

The composition of microbial communities and the rates of microbial processes in the water column of a meromictic trough in the Biofilter Bay, Kandalaksha Bay, White Sea were investigated in September 2020 and March 2021. The chemocline zone was located at the depths from 8 to 9 m. Sulfide was present in the monimolimnion, its concentration at the bottom reaching 25‒38 mg L–1 (0.7‒1.1 mmol). Conditions of the redox zone favored development of both anaerobic anoxygenic phototrophs and aerobic sulfur-oxidizing chemoautotrophs. A pinkish-brown bacterial plate was formed in this zone. Sequencing of the 16S rRNA gene fragments revealed predominance of green sulfur bacteria (GSB) Chlorobium phaeovibrioides. Aerobic sulfur-oxidizing bacteria Sulfurimonas sp. were the second most abundant group. Plating of chemocline samples on selective media resulted in massive formation of brown-colored Chlorobi colonies, while green GSB colonies were few. Both morphotypes were identified as Chlorobium phaeovibrioides. At the time of our study, purple sulfur bacteria (PSB) did not form a bacterial plate in the redox zone, although few PSB colonies were revealed. The PSB isolate was identified as Thiocapsa rosea. Members of this species are able to switch from photosynthesis to aerobic chemosynthesis and may compete for sulfide with sulfur-oxidizing chemo-autotrophs. We suggest that due to its openness the Biofilter Bay meromictic trough may act as a source for the propagation of anoxygenic phototrophic bacteria in the Kandalaksha Bay.

Spatial and temporal variability of the transformation of dissolved matter runoff in the Mezen’ River estuary is studied by results of the complex hydrological-hydrochemical researches lead in 2009 and 2015. The conservative behavior of major ions and dissolved forms of Li, Rb, Cs, Sr, B, F, As, Sb, and Mo is demonstrated. The additional input into solution reaching 93 and 32–38% of content in the river water mass is determined for phosphates and silicon. This is caused, apparently, by mobilization of these nutrients from pore waters of regularly tide-stirred bottom sediments and vertical mixing of the water column. The desorption flux of barium and uranium due to long-term interaction of terrigenic material with saline waters exceeded their input with a continental runoff reaching 180–380 and 90–150% of content of these elements in the river waters. Up to 50, 43, 29, 32, 44, 50, and 45% of Fe, Pb, Y, La, Ce, Pr, and Nd supplying with river runoff which are present in the form of strong organic complexes are removed from solution at the beginning of the mixing zone due to coagulation of colloids. It is drawn a conclusion on spatial homogeneity and long-term stability of transformation features of dissolved matter runoff in the Mezen’ River estuary. Peculiar characteristic of migration of dissolved phosphates, silicon, barium, and uranium are caused by hydrological features of the estuary.

Изучена пространственно-временная изменчивость трансформации стока растворенных веществ в эстуарии Мезени по данным комплексных гидролого-гидрохимических исследований 2009 и 2015 гг. Установлено консервативное поведение ионов основного солевого состава и растворенных форм Li, Rb, Cs, Sr, B, F, As, Sb и Mo. Для фосфатов и кремния характерно дополнительное поступление в раствор, достигающее 93 и 32–38% их содержания в речной водной массе, которое связано, по-видимому, с выносом биогенных элементов из поровых вод донных отложений, регулярно взмучивающихся под действием приливов, и вертикальным перемешиванием водной толщи. Десорбционный поток бария и урана из продолжительно контактирующего с осолоненными водами терригенного материала превышает их поступление в составе материкового стока, достигая 180–380 и 90–150% содержания этих элементов в речных водах. До 50, 43, 29, 32, 44, 50 и 45% поступающих с речным стоком Fe, Pb, Y, La, Ce, Pr и Nd, находящихся в форме прочных органических комплексов, при проникновении в морскую среду извлекается из раствора в результате коагуляции коллоидов. Сделан вывод о пространственном единстве и многолетней устойчивости закономерностей трансформации стока растворенных веществ в эстуарии Мезени при сохранении специфических черт миграции растворенных фосфатов, кремния, бария и урана, обусловленных гидрологическими особенностями эстуария.

— The community of anoxygenic phototrophic bacteria (APB) from the water column of the meromictic Lake Trekhtsvetnoe (Kandalaksha Bay, White Sea, Russia) was studied in March 2012 and 2013 and in September 2013 and 2014. The community structure below the chemocline was shown to restore during three years after partial mixing resulting from seawater admixture into the lake in autumn 2011; a dense layer (at least 10 8 cells mL –1 ) of green-colored (g/c) sulfur bacteria (GSB) was formed. During winter, development of low numbers of brown colored (b/c) GSB was observed in the upper layer of green water. During summer seasons, b/c GSB were found to be located in the oxic zone above the green water layer, which was unusual for these organisms. The APB community was found to contain purple bacteria. Four APB strains were isolated from the upper part of the sulfide zone. The b/c and g/c GSB strains were phylogenetically close to each other and to the type species Chlorobium phaeovibrioides DSM 265 (99% similarity gene sequences). One strain of purple bacteria was phylogenetically related to the brackish sulfur bacteria Thiocapsa marina , while the other was related to freshwater bacteria Rhodopseudomonas palustris . The strains of sulfur bacteria were phylogenetically close to the chemocline bacteria from the stratified Lake Kislo-Sladkoe, also located in the coastal zone of the Kandalaksha Bay, White Sea.

The paper presents information on joint research of the short-term (tidal and synoptic) variability of the hydrological and hydrochemical parameters during the summer 2016 low-water period in mesotidal estuary of the Kyanda River, which flows into Onega Bay, the White Sea. It is demonstrated that semidiurnal, diurnal, and synoptic variations of almost all observed parameters are significant and differ notably along the estuary.

In the Mezen River estuary, morpholithodynamic processes are regulated by tidal currents, river runoff, wind waves, and alongshore sediment flows. Due to the movement of a huge mass of sediments in the Mezen River estuary, intense deformations of silty sand banks occur, reforming the bottoms of channel grooves and displacing navigable waterways. On the whole, the Mezen River estuary is gradually being filled with river and marine sediments. Various sandy ridges form in the channel grooves of the estuary.

The paper presents new data on the morpholithodynamic regime of the foredelta and deltaic branches of the Northern Dvina River. Based on data from field sonar investigations, the bottom structure and lithology of bottom sediments are described. Using hydrographic and topographic charts and satellite images, we traced the dynamics of deltaic branches and bottoms in the outfall offshore zone of the Northern Dvina River for the period of 1832–2013.

Sings of meromixis are found by means of microbiological and biogeochemical investigations in the southernn part of the Kanda Bay, an artificial water body separated front the White Sea with a railway dam. The concentration of oxygen in the bottom layer attained 1.9 mmol/L, intensity of the process of microbial sulfate reduction, 3.0 μmol of sulfur/(L day). The concentration of dissolved methane, 3.7 μmol/L. Isotopic composition of carbon in methane (δ13C (CH4) =–79.2‰) indicates to its microbial genesis. At present, Kanda Bay is a sole in Russia man-made marine water body for which there are data on the rate of microbial processes responsible for formation of bottom water layer containing hydrogen sulfide and methane.

Natural observations were analyzed to study the distribution of dissolved species of major and trace elements in the Onega and Mezen’ mouth areas and the tendencies in the chemical transformations of the is continental runoff in the river mouths of the White Sea drainage system. It is shown that the migration of major ions and dissolved species of Li, Rb, Cs, Sr, B, F and Mo is consistent with a conservative behavior and is controlled by hydrodynamic processes. The amounts of uranium and barium additionally supplying in the Mezen’ mouth exceed those removed with a continental runoff, whereas the Onega, Severnaya Dvina, and other rivers of the White Sea drainage system are characterized by the conservative behavior of uranium, while barium desorption from particulate matter reaches no more than 33% of its content in the riverine waters. The growth of concentrations of these elements in the Mezen’ mouth is caused by the long-term interaction of solid matters of the continental runoff with saline waters in the tide-affected estuary. 28–59, 12–63, 25–67 and 20–63% of concentrations of iron, aluminum, lanthanum, and cerium are removed from the riverine waters in the mouth areas of all studied rivers of the White Sea drainage system mainly owing to the coagulation and flocculation of organic and organomineral colloids. The distribution of dissolved species of mineral phosphorus and silicon in the Mezen’ mouth is presumably controlled by the remineralization of the organic matter in the bottom sediments, which due to the hydrological features of estuary are regularly stirred up and interact with vertically mixing water sequence. Up to 20–46% of dissolved phosphates and 3–22% of silicon are removed from the continental runoff during vegetation period in the mouths of the Onega, Severnaya Dvina, and other rivers of the White Sea drainage system mainly owing to their biological consumption.