The results of describing the spatial distribution of methane concentration in the surface water of Lake Baikal in the spring are presented. The basis was the measurements of CH4 content which were first carried out in the round-the-clock continuous mode along the entire route of the passage of research vessel in the complex expeditions of Limnological Institute, Siberian Branch, Russian Academy of Sciences, in the spring seasons of 2013, 2016, 2017, 2018, 2021, and 2022. Based on the results of six expeditions, a merged data array was compiled; it included 12 100 segments (with a step of 0.005° in latitude and 0.01° in longitude) which covered the total area 4466.7 km2, or 14

The gross and net primary production is estimated for the most characteristic seasonal life cycles of Baikal plankton based on long-term measurement series of carbon dioxide concentrations in the near-water atmosphere and surface and bottom water and “water–air” carbon dioxide fluxes. The calculations are carried out according to the scheme similar to the diel technique. With regard to the conditions of the coastal zone, the methodological issues are analyzed, neglect of which can lead to a significant uncertainty in these characteristics. We show that it is impossible to correctly estimate the net primary production only from CO2 concentration measurements in this technique. For periods of open water, the net primary production is calculated from the daily average CO2 flux. The estimates of the productivity for individual series of measurements in different periods quite adequately show the main features and are consistent with long-term observations.

Проанализированы многолетние ряды наблюдений потоков углекислого газа и метана в системе «вода-атмосфера» в прибрежной зоне озера Байкал. По результатам многолетних измерений показано, что суммарный сток углекислого газа из атмосферы на водную поверхность составляет 5,9 гСО2 м-2 год-1, а выход метана из воды оценивается в 100мгСН4 м-2 год-1. Для сравнительной оценки радиационного эффекта предположим, что молекула метана поглощает ИК излучение в 20 раз эффективней по сравнению с молекулой СО2. Показано, что суммарный сток углекислого газа из атмосферы в течение года достоверно снижает радиационный эффект, обусловленный выходом метана.

Long-term observation series of carbon dioxide and methane fluxes in the water-atmosphere system in the coastal zone of Lake Baikal are analyzed. It is shown that the total sink of carbon dioxide from the atmosphere to the water surface is 5.9 gСО2 m-2 year-1, while the methane emission from water is estimated as 80 mgСН4 m-2 year-1. For comparative estimation of the radiative forcing, it is taken that the contribution of the atmospheric methane molecule to global warming is 27 times greater than that of the СО2 molecule. Then, the coastal area of Lake Baikal contributes to global warming due to the methane emission 8-20% more than to the cooling due to absorption of carbon dioxide by the water.

Long-term observation series of the methane content in the near-water atmosphere and in water in the coastal zone of Lake Baikal are analyzed. The measurements were carried out in the Baikal Atmospheric-Limnological Observatory (BALO SB RAS, which is a part of the Resource Sharing Center “Atmosfera”). A steady increase of the methane content in the atmosphere by about 12 ppb per year is observed. The average diurnal methane content in March 2021 (the last measurement cycle) was 2.012 ppm. For the period of ling-term observations, the measured partial methane pressure in the surface water always exceeded that in the atmosphere. This fact indicates that this part of Lake Baikal is a source of methane into the atmosphere. For the coastal zone, the average value of methane flux from water was 380μgСН4 m-2 day1 . The observed increased methane concentration in the near-bottom layer indicates the predominance of bottom methanogenesis. Our data show that the increment rate of dissolved methane in surface water of Lake Baikal is 0.015 μgCH4/l per year.

Currently, with an increase in technological progress, anthropogenic impact on the environment is increasingly apparent. Since surface waters are the most vulnerable part of the natural environment, a detailed study of water pollution is one of the urgent tasks. This article presents the results of the instrumental measurements and the assessment of the pollution of the surface waters in the littoral zone of the Barguzin and Chivyrkuy bays of Lake Baikal. To determine the degree of water pollution, we compared hydrochemical indicators with the standards of the maximum permissible concentrations. We revealed that in different parts of the Chivyrkuy Bay, water quality varies in a wide range from slightly polluted to very polluted and, in some cases, highly polluted. The waters in the Barguzin Bay can mainly be classified as slightly polluted, and only in some areas – as moderately polluted or highly polluted. According to the comprehensive water pollution index, the waters in the Chivyrkuy and Barguzin bays is assessed as conditionally polluted and conditionally pure, respectively.

Within the framework of many-year studies of the carbon cycle in the water-atmosphere system and in order to determine high-priority measures for conservation of the unique ecosystem of Lake Baikal, the specialized combined expedition was carried out in August 2019 in Barguzin and Chivyrkuy Bays of Lake Baikal. With the unique onboard instrumentation system, we have measured the gas content in the surface water and the near-water atmosphere, as well as concentrations of biogenic elements and organic matter at the sampling stations. The spatial distribution of the increased methane concentrations in the surface water of Barguzin Bay has been analyzed to determine the main direction of the Barguzin River’s water inflow into the bay. The observational data were compared with the results of scenario calculations by a large-scale model of currents in the lake. This model gives us some understanding of a general nature of water mass circulation in the bay. For modelling small-scale manifestations in the near shore zones, it is necessary to use higher resolution models for nested regions.

Starting from 2006, we conduct combined spring expeditions over the water area of Lake Baikal. These expeditions include measurements of fluorescent characteristics at different water levels from the surface down to the bottom. Direct methods for determination of biomass and chlorophyll concentration in algae are quite laborious and do not allow in situ analysis of the results. Fluorescent methods, which are fast enough, are generally indirect and should be specially justified to provide the quantitative information about biomass or chlorophyll concentration. In this study, the results of synchronous measurements are used to examine the feasibility of empirical calibration and quantitative reconstruction of the chlorophyll content from measured fluorescent characteristics.

Shipborne and ground-based enroute measurements along the southern and eastern coasts of Lake Baikal from Kultuk village to Turka village were conducted in August 15-21, 2018. This period was chosen, because in this period the recreation load on the Baikal coast is the highest and the summer peak in development of the water biota is observed. The route included ten stations with a priori different anthropogenic load. At each station, the content of carbon dioxide and methane in the atmosphere and dissolved in water, as well as their fluxes in the water-atmosphere system, were measured. Here, samples of surface and bottom water were taken, in which the pH value, the concentration of dissolved oxygen, bicarbonate, nitrate, phosphate and fluorescence characteristics were determined. It is shown that the minimum concentrations of nutrients were recorded at the Boyarskii village. The strongest water pollution was found near the coast of Novyi Enkhaluk village. Particularly this part of the coast is subjected to the highest anthropogenic impact from tourist complexes located along this coast line.

We report long-term comprehensive measurements of CO2 in the atmosphere, surface water and the major nutrients obtained for the period 2004-2018. The research was conducted at the Baikal Atmospheric and Limnological Observatory (BALO), which is located in the coastal zone of South Baikal (coordinates 51 degrees 54' N, 105 degrees 05' E). The seasonal variation of these characteristics was analyzed. For our site, during the open water period (May-December) we assessed average flux of CO2, which amounted to -155 mmol m(-2) y(-1) (sink from the atmosphere to the water surface). Carbon dioxide content in the near-water air of Lake Baikal rises with a rate of 2.46 ppm per year, which is in good agreement with the global trend. The common effect of many factors (often multi-directional), such as variability of weather conditions, hydrological processes and productivity cycles of aquatic plankton in the Baikal waters, cause strong variations in the water characteristics, which we observed in different seasons and years. Under these conditions of strong inter-annual and seasonal variability of all characteristics, trend calculations using our long-term observations did not allow us to reveal reliable tendencies of changes in surface water CO2 concentrations. (C) 2019 International Association for Great Lakes Research. Published by Elsevier B.V. All rights reserved.

The spatial distribution of the partial pressures of carbon dioxide and methane in the surface water and near-water atmosphere over the Lake Baikal area (shipborne expeditions in late May-early June of 2013 and 2016–2018) is analyzed. It is found that in the zones, where the process of formation of spring homothermy begins to develop, the CO2 concentration increases and the CH4 content decreases in the surface water. The analysis of water samples at hydrological stations has shown that the vertical distribution of biogenic elements and fluorescent characteristics at these parts of the pelagic zone in the upper 200-m water layer alternates considerably.

This study continues the thorough investigation of the impact of physical, hydrological, chemical, and biological processes on the СО2 gas exchange in the water-atmosphere system at Lake Baikal. The results of measurements of the СО2 flux direction, biogenic elements, and fluorescent characteristics over the entire Baikal territory in the spring periods of 2016 (from 25.05 to 06.06.) and 2017 (25.05 to 05.06) are compared. Fluorescent characteristics were measured with a flow-through fluorimeter, whose operation is based on the principle of pulse-amplitude modulation. It is shown that most significant year-to-year differences in the analyzed characteristics are observed in the Middle Baikal region. In 2016, the surface temperature in this zone approaches 40°C, and probably the vertical exchange process manifests itself here.

The seasonal dynamics of the CO2 gas exchange process in the atmosphere-water system is formed as a result of combined action of hydrometeorological conditions and biological rhythms on photosynthesis (production) and destruction of organic matter. The diurnal dynamics of the coefficient of photosynthetic activity, phytoplankton population, and the carbon dioxide concentration in water is analyzed. The Gross Primary Production is estimated with the DIEL method (calculation from the diurnal dynamics of CO2 concentration) in the surface and bottom water of the Baikal coastal zone in the open-water period for three measurement cycles. It is shown that the productivity decreases in the coastal zone from June to December. In terms of the carbon. concentration, it varies from 0.9 to 0.17 mg.dm(-3).day(-1)

Results of the annual series of complex measurements of carbon dioxide, oxygen, and biogenic elements in the subglacial water in the littoral zone of the southern area of Lake Baikal, carried out from 2004 to 2016, are analyzed. It was found that the plankton photosynthetic activity significantly decreases the partial pressure of carbon dioxide in water (to 240–350 μatm) as compared to the partial pressure of CO2 in the atmosphere (about 385 μatm) by the end of ice cover season. Hence, the CO2 flux can be directed only from the atmosphere to the water surface during the ice breakup in the littoral zone of Southern Baikal.

Results of three long cycles of 24-hour measurements of the carbon dioxide content in the surface and bottom water in the ice period of 2014-2016 in the Baikal coastal zone are analyzed. The diurnal dynamics of the СО2 concentration in the subglacial water, in which photosynthesis plays the leading role, is described. It is found that, in comparison with the surface subglacial water (that is, directly adjacent to the ice bottom), the more pronounced diurnal rhythm of СО2 is observed in the bottom layer in all realizations. This rhythm is well correlated with pyranometer readings. The data on the diurnal dynamics of СО2 are used to estimate the gross primary production in the bottom water with the DIEL method based on the analysis of temporal variability of the carbon dioxide concentration in water in situ.

The photosynthesis plays an important role in the spatiotemporal variability of the content of dissolved gases and biogenic elements in Baikal water. At the same time, the sampling of representative water samples for analysis with the use of direct methods for measurement of the biomass of plankton algae and the intensity of photosynthesis in the entire lake depth (maximum depth exceeds 600 m) is connected with many technical and material difficulties. To a certain extent, they can complement the express methods of fluorescent analysis. This work continues the study of the influence of physical, hydrological, chemical, and biological processes on the CO2 exchange in the "water-atmosphere" system of Lake Baikal. The aim of this work was to examine the spatial (vertical and horizontal) distribution of fluorescent characteristics obtained in spring voyages of combined research expeditions all over the Baikal water area in 2010-2016.

A long-term series of regular measurements of the carbon dioxide concentration in the surface water and СО2 fluxes in the Baikal littoral zone demonstrated a diurnal rhythm related to processes of photosynthesis activity of plankton during the entire period of open water (from May to December). To isolate the role of only the photoperiodicity process on the background of many various factors having an effect on the change in the concentration of carbon dioxide in the surface water and СО2 fluxes in the atmosphere–water system, the scheme of the diurnal behavior of СО2 during the open water period in 2007–2015 in the littoral zone of South Baikal is considered in coordinates of sunshine duration which was calculated proceeding from the theoretically possible sunshine duration (from sunrise to sunset in the case of clear sky and open horizon). The proposed scheme of parameterization and reconstruction of these characteristics for any time instant can find application in estimating calculations in carbon cycle models and be useful in planning the optimum regime for studying biological and chemical processes in Lake Baikal.

Measured СО2 flux between the atmosphere and water and the dynamics of biogenic elements in cardinally different water basins: Lake Baikal and coastal maritime conditions, are compared. We conduct regular cycles of combined observations at the Southern Baikal shore for different seasons at the Baikal Atmospheric-Limnological Observatory (BALO). The measurements under maritime conditions were conducted at the stationary station of the Far East Branch of the Russian Academy of Sciences at Schultz Cape in the period of October 6-10 of 2012 and October 7-13 of 2013, as well as in 2014 a cycle of investigations on the assessment of spatial variability was carried out. The most remarkable distinctive feature of the content of dissolved gases and their flux under maritime conditions (Far East) is the permanent sink of carbon dioxide from the atmosphere onto the water surface. At Lake Baikal in this period, we observed the pronounced diurnal dynamics characterized by the daytime sink and nighttime emission of СО2 into the atmosphere.

In this work, we discuss the applicability of the chamber method for measurements of carbon dioxide fluxes between the atmosphere and water in the littoral of Lake Baikal. Advantages and disadvantages of the method are considered. Previously submitted data are compared with observations in 2011–2014, when dramatically different weather situations occurred. It is shown that interannual variations in the total CO2 fluxes are much weaker than their seasonal variations. The annual flux of carbon dioxide from atmosphere to the water surface in the littoral of Lake Baikal is assessed to be at least 6.5–7 g/m2 per year in an “open water” period.

The paper presents the present-day structure of stationary and mobile hardware-software gas-analytical complexes of Baikal atmospheric-limnological observatory (BALO) Siberian Branch Russian Academy of Sciences (SB RAS), designed to study the processes of gas exchange of carbon-containing gases in the "atmosphere-water" system, which are constantly updated to include new measuring and auxiliary instrumentation.