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.
To study the spatial distribution of the direction of carbon dioxide and methane fluxes at the Irkutsk water reservoir and their variability in the warm season, three measurement cycles covering the period from June to September 2018 were conducted. The content of carbon dioxide and methane was recorded continuously in the surface water and near-surface atmosphere along the ship route from Lake Baikal to the dam in the upstream pool and the dam area in the downstream pool. It is shown that in the summer-fall period the intense photosynthetic activity of biota leads to a significant decrease in the carbon dioxide concentration in water, and the Irkutsk water reservoir is an absorber of carbon dioxide. In the same period, the results of СН4 study indicate that in the summer-fall period the water reservoir is a source of methane inflow into the atmosphere.
From the results of three measurement cycles, it is shown that significant dynamics is observed in the spatial distribution of the amplitude and direction of carbon dioxide flux at the water reservoir of the Krasnoyarsk hydro power plant (HPP) in the summer-fall season. In June and August, the sink of carbon dioxide from the atmosphere to the water surface was observed all over the area of the water reservoir and at the territory downstream of the dam. In September, the entire water reservoir was mostly a source of carbon dioxide. It was found that in the three measurement periods the value of ΔРСН4 is positive, that is, in the summer-fall period the Krasnoyarsk water reservoir is a source of methane inflow into the atmosphere. The widest differences are observed just near the dam of the Krasnoyarsk HPP (from minimal in June to maximal in September).
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.
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