Institute of Water Problems of the North Karelian Research Centre

In vertebrates, the intestinal microbiota significantly influences metabolic processes, immune development, and resistance to pathogens. Unlike terrestrial animals, fish are in constant contact with an aquatic environment, making their microbiota particularly sensitive to environmental changes. The aim of this study was to determine the structure and taxonomic composition of the intestinal microbiota of Coregonus nasus based on metagenomic sequencing of two 16S rRNA regions. Eighty-eight operational taxonomic units (OTUs) were identified for the V3–V4 region and 25 OTUs for the V4–V5 region. Analysis of the microbial community structure revealed the dominance of Proteobacteria, Firmicutes, and Bacteroidota. Comparison of OTU representation between the two groups (Affected and Control) revealed taxa associated with different host or environmental conditions. The data obtained expand our understanding of the intestinal microbiota of freshwater fish and also open up prospects for the use of microbiome markers to monitor the health of fish in aquaculture and natural populations.

The possible nutrient load on Lake Onego and its catchment area by the middle of the 21st century is substantiated, taking into account the RCP climate change scenarios and socioeconomic conditions. The assessments of socioeconomic development were derived from the analysis of official statistical data and model estimates for the seven largest regions included in the lake catchment area. Possible climate changes and their impact on the water balance of the lake are considered. It is shown that the implementation of the RCP 2.6 scenario may reduce the nutrient load on the lake from the main tributaries due to a decrease in river runoff, and if the RCP 8.5 scenario is implemented, an increase in runoff and a corresponding increase in the export of phosphorus and nitrogen by 14.0–22.5% should be expected. Calculations based on the ILLM model (Institute of Limnology of theRussian Academy of Sciences) for assessing the diffuse nutrient load showed that the introduction of the best available technologies in agricultural production will not have a noticeable effect on the ecological conditions of Lake Onego. Estimates of a possible increase in the input of nitrogen and phosphorus from the catchment area and its sub-basins into the lake by 2050 at the current growth rate of fish farming in water bodies of the catchment area, show that a slight increase in the nutrient load on the lake in terms of phosphorus by <4% compared to 2021 can be expected. However, if the rate of production growth increases, the nutrient load may increase up to 30% compared to the current level. The permissible nutrient load and the assimilation potential of the lake for nutrients to maintain the trophic status of the lake are estimated. The obtained calculations formed the basis for assigning the nutrient load on the lake until 2050 to assess the possible changes in the lake ecosystem on a 3-D SPLEM model of high spatial resolution (1 km), which showed that, if the considered scenarios are implemented, the main increase in primary production of phytoplankton until 2050 will be observed in the bays and gulfs of Lake Onego, while in the open areas of the lake, a slight increase in primary production may be observed.

The paper deals with reproduction potential features (including seasonal occurrence and frequency of female maturation during the year) of rainbow trout under fish farming. Several hypotheses explaining biannual spawning phenomenon are discussed; farming conditions (i.e. photoperiod duration and temperature) and long-term selection for early maturation are among of them. On the basis of fish sexual cycle evolution analysis, the authors suggest that the significant potential of genetic variability of rainbow trout reproductive features and genetic determination of some individuals to its appearance can be viewed as the reason of biannual spawning. Uncovering of theoretical backgrounds of multiple maturation of rainbow trout during the year can serve as a basis for practical use of biannual spawning phenomenon in fish farming.

A new parameterization is presented to describe the space and time variations of Secchi depth depending on the integral phytoplankton biomass and surface water temperature. The parameterization was verified against field data in lakes with different types of physiographic and chemical–biological characteristics—from deep oligotrophic northern regions of Lake Ladoga to shallow hypereutrophic Pskovskoe Lake. The results of verification show that the new parameterization can be used for solving a wide range of either hydrothermodynamic or hydrobiological problems. In particular, in the simulation of the thermal regime of water bodies, the proposed parameterization can be used to evaluate the coefficient of extinction of solar radiation. In the development of models to describe aquatic ecosystem functioning, the new parameterization can be used to evaluate the thickness of the trophogenic layer and phytoplankton primary production.

The intensity of vertical heat and mass transfer remains among the challenging topics in the study of ice-covered lakes. Presumably, internal waves (IWs) make a significant contribution to the heat transfer in the water column. However, the mechanisms of mixing enhancement by generation, interaction, and breaking of IWs of different scales, especially short-wavelength ones, have not been sufficiently studied. Furthermore, the experimental data required for estimating the key parameters of IWs (wavelengths, propagation velocities) are rather fragmentary, which makes it difficult to quantify the turbulent transfer caused by IWs. This paper presents the estimates of these IW parameters based on data obtained in the winter months of 2014 and 2016 in a small boreal ice-covered lake. Having analyzed horizontally spaced thermistor chain data, we managed to detect the presence of short standing and propagating IWs, and to estimate their length (from several meters to several tens of meters) and phase and group velocities (from several mm/s to several tens of mm/s). Also, their vertical mode structure was detected. It was shown that IW generation events were characterized by a high degree of spatial localization, and the IW energy was unevenly distributed through the water column.

The invasive species Gmelinoides fasciatus (Stebbing 1899) (Crustacea: Amphipoda) is able to successfully form stable populations in the recipient reservoir Lake Onego. In conditions of latitudes 62° N (Petrozavodsk Bay)—63° N (Kumsa area of the Povenets Bay) of Lake Onego, the temperature factor does not limit the development of the amphipod population. Successful naturalization of G. fasciatus under new conditions on the northern border of the range of the European part of Russia (Petrozavodsk Bay and Povenets Bay of Lake Onego) is explained by a sufficient number of degree-days (2269–2626 for the period end of May–beginning of October), which determine the one-year life cycle with generations previous year and current year.

See the retraction notice E3S Web of Conferences 420, 00001 (2023), https://doi.org/10.1051/e3sconf/202342000001

The objectives of this study were to analyze satellite data on the ice conditions in the White Sea available for the period 1979-2021 so that to identify statistically significant trends in closeness of ice during that period, and to establish spatial and temporal characteristics of the sea ice regime in this area. It was found that according to the satellite data a statistically significant negative trend (-0.34±0.11% year-1 at a significance level of 0.05) of the ice closeness changes was observed over the above period for all areas of the sea, which corresponds to the general tendency of reducing the area of the Arctic ice cover due to the global warming. However, contrary to the statements of J.C. Comiso, D.K. Perovich, M.C. Serreze, J. Streve, D. Notz that since the beginning of the XX century the reduction of the ice area in the Arctic Ocean accelerates, no tendency in decrease of mean annual values of the ice closeness for the White Sea was revealed. In addition, the results of the regression analysis showed a slight decrease in the absolute value of the trend from - 0.74±0.38% year-1 in 1979-1996 to -0.47±0.25% year-1 in 1997-2020. It is also shown that the results of a comparative analysis of two trends in the year-to-year variability of ice closeness in the White Sea: the first one obtained from the microwave radiometer data provided by the National Snow and Ice Data Center, and the second one revealed from data of advanced microwave scanning radiometers (the University of Bremen), are in good agreement with each other. The difference in the slope coefficients of the linear approximation is only 0.038% year-1 for the period 2002-2020. This is the important argument in support of using microwave radiometer data to determine trends in variability of ice closeness in the White Sea.

This paper presents for the first time data on the lateral distribution of total mercury in the water-suspended matter-bottom sediments system for the entire water area of Lake Onego, the second largest lake in Europe. The patterns of the total mercury vertical distribution in two types of bottom sediments stratification, have been established. The total mercury content in the Lake Onego water averages 0.32 ± 0.07 μg/L. The most common form of mercury in water is dissolved+colloid, with the exception of water samples from the Kondopoga and Povenetsky Bays. In the material of the sedimentation traps, the mercury content is 0.5 ± 0.3 μg/g, and in the upper and lower parts of the bottom sediments section is 0.067 ± 0.003 and 0.041 ± 0.001 μg/g, respectively. The paper considers the factors responsible for the mercury content increasing from the bottom sediments up through the sections. These factors include anthropogenic pollution, migration of Hg and its redeposition at the geochemical barrier together with Fe and Mn.