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.
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.
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.
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.
The seasonal dynamics of the СО2 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 СО2 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 С concentration, it varies from 0.9 to 0.17 mg·dm-3·day-1
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 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 СО2 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.
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 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.
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.
All our many-year studies of the gas-exchange processes were carried out at one observation site (BALO) in the littoral of Southern Baikal. Thus, the question about applicability of conclusions and estimates based on these data to the entire littoral zone inevitably arises. In 2014, we succeeded for the first time in organizing the combined research campaign for detailed mapping of the spatial variability of water characteristics in general for the littoral of southern Baikal. The spatial partial distribution of biogenic elements and the pressure of carbon dioxide and methane in the atmospheric surface layer and the surface water layer were studied in August 5-11 of 2014 from onboard of I.D. Papanin Research Vessel (RV). These studies covered, in section, the entire water area of the southern Baikal. The fluorescent characteristics, concentration of biogenic elements, partial pressure of carbon dioxide and methane in the surface water layer and the atmospheric surface layer were determined there. The continuous measurements of carbon dioxide and methane in the surface water and in the atmosphere in the course of the vessel were conducted by a mobile shipborne system, which was complemented with the flow-through fluorimeter. It has been found that the main features of fluxes and the value of dРg, as well as fluorescent characteristics are in a good agreement with the results of many-year measurements obtained in the BALO Observatory for the summer period.
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