M. V. Sakirko

Seasonal behavior of the CO2 gas exchange process in the “atmosphere-water” system of the littoral zone of southern Baikal. 1. Hydrological spring

Analysis of the mechanisms determining the direction and intensity of CO2 fluxes in the “atmosphere-water” system seems to be important in the context of studying the problem of present-day increase in the content of one of the greenhouse gases (carbon dioxide) in the atmosphere. This paper starts a series of publications devoted to the analysis of seasonal features of the CO2 gas exchange process in the littoral zone of southern Baikal and presents the results obtained in the spring period.It is shown that the greatest transformation of all components of the carbon dioxide gas exchange process between the water surface and the atmosphere is observed during “hydrological spring” period in the littoral zone of Lake Baikal. The amplitude of the diurnal behaviors of the CO2, O2, and N3− concentrations in water increases from May to June. The diurnally average CO2 flux, which is directed to the atmosphere in mid-May, changes its direction as soon as June, and a distinct CO2 sink to the water surface becomes evident. The tendency toward increase in the amplitude of the diurnal CO2 behavior in water and enhancement of the carbon dioxide sink from the atmosphere to the water surface continues; that the sink, on average, may reach 70 mg CO2 m−2 day−1 by mid-July.

Diurnal rhythms of carbon dioxide concentration in the sea-level air layer and in the surface water of Lake Baikal in different hydrological seasons

Results of studying processes of gaseous exchange of carbon dioxide (CO2) in the water surface-atmosphere system of Lake Baikal are considered. Measurements were carried out in the littoral of the lake near the settlement of Bol’shie Koty. The measurement point was selected for the following reasons. First, it is the place where water chemistry and biota have been studied for several tens of years. Second, by its meteorological conditions the place can be considered as background. It is shown that during all hydrological seasons the gas exchange of CO2 in the Baikal water surface-atmosphere system has a well-pronounced trend, whose amplitude depends on the season. The data obtained are indicative of the main role that Lake Baikal biota plays in regulating the intensity of gas exchange.

Daily variation of CO2 exchange and photosynthesis intensity in surface water of Lake Baikal

ISSN 1028-334X, Doklady Earth Sciences, 2007, Vol. 413A, No. 3, pp. 402–405.

Estimation of CO2 fluxes in the “atmosphere–water” system in the south Lake Baikal littoral with the floating chamber method

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.

Spatial distribution of carbon dioxide fluxes, biogenic elements, and phytoplankton biomass in the pelagic zone of Lake Baikal in spring period of 2010–2012

The paper presents the measurements of concentrations of oxygen, biogenic elements, phytoplankton biomass, and partial pressures of carbon dioxide in water and the near-water atmosphere in the pelagic zone of Lake Baikal in June, 2010–2012. Very contrasting weather conditions were observed in the region in winter-spring months of 2010–2012, which largely determined the character of hydrologic and biologic processes in the pelagic water zone of Baikal. The cardinal difference in weather conditions before expeditions of 2010–2012 made it possible to estimate a wide range of interannual variations in these characteristics and to analyze their role in the formation of fluxes at different stages of springtime warming on the basis of three datasets. The quantitative characteristics of phytoplankton biomass are compared with the difference in partial pressure of carbon dioxide in the air-water system.

Phytoplankton of the Irkutsk Reservoir as an indicator of water quality

The species composition of phytoplankton and quantitative parameters of its abundance are indicators of ecological conditions in a water body. This paper deals with the analysis of phytoplankton in the Irkutsk Reservoir, which was formed more than 50 years ago on the Angara River flowing out of Lake Baikal. The level of phytoplankton development in the reservoir is directly dependent on the abundance of diatoms in Lake Baikal. The dominant assemblage of algal species is stable and consists mainly of diatoms, chlorophytes, and chrysophytes. Cyanobacteria are represented by a small number of species with low abundance. According to the composition of indicator species, the water in the lower reaches of the Irkutsk Reservoir can be classified as clean. The saprobity index in the open-water period is 1.2, increasing to between 1.3 and 1.5 in small bays. The values of phytoplankton biomass and chemical parameters of water recorded in 2008 indicate that the Irkutsk Reservoir is an oligotrophic water body. Its trophic status has not changed significantly since the time of impoundment (1956–1958).

Estimation of the spacial variability of carbonic acid stream direction in different hydrological seasons at Lake Baikal

The spatial and seasonal variability of the direction of carbonic acid streams in the water-atmosphere system is analyzed based on the results of ship measurements in the pelagial of Lake Baikal in May–June and September of 2008. The main stream of CO2 in May–June is directed to the atmosphere, and its runoff to the water surface is observed in September. A correlation between the biomass of phito- and pico-plankton and the content of CO2 and biogenic elements in the lake water is revealed. It is shown that biota specific change is a key factor determining the seasonal variability of carbonic acid stream direction.

Seasonal behavior of the CO2 gas exchange process in the “atmosphere-water” system of littoral zone of Southern Baikal. 3. Autumn

This paper is the next in a series of publications dealing with the analysis of seasonal features of the carbon dioxide exchange process in the littoral of the Southern Baikal during the open-water period, and devoted to results obtained during the fall period. It is shown that variations in the concentrations of dissolved gases and biogenic elements in the surface waters of the Lake Baikal littoral during fall are opposite in character to the process observed during the spring-summer period. The concentrations of carbon dioxide, oxygen, nitrates, and phosphates increase from the second half of September toward December. The sink of CO2 from the atmosphere into the water surface is still observed during early October in the Baikal littoral, with its diurnal budget being comparable in value to the daily average sink during the period of hydrological summer. The daily average CO2 flux reverses sign in November, and the lake surface becomes a source supplying carbon dioxide to the near-water atmosphere; the CO2 supply rate keeps increasing and reaches a maximum level during December, i.e., until the beginning of freezing-over period. At the beginning of this period, an additional small CO2 amount can be expected to be supplied to the atmosphere of the littoral zone due to the process of premorning freezing and a subsequent ice melt.

Carbon dioxide, oxygen, and biogenic elements in subglacial water in the littoral zone of Southern Baikal (2004–2016)

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.

Co-occurrence Networks Among Bacteria and Microbial Eukaryotes of Lake Baikal During a Spring Phytoplankton Bloom

The pelagic zone of Lake Baikal is an ecological niche where phytoplankton bloom causes increasing microbial abundance in spring which plays a key role in carbon turnover in the freshwater lake. Co-occurrence patterns revealed among different microbes can be applied to predict interactions between the microbes and environmental conditions in the ecosystem. We used 454 pyrosequencing of 16S rRNA and 18S rRNA genes to study bacterial and microbial eukaryotic communities and their co-occurrence patterns at the pelagic zone of Lake Baikal during a spring phytoplankton bloom. We found that microbes within one domain mostly correlated positively with each other and are highly interconnected. The highly connected taxa in co-occurrence networks were operational taxonomic units (OTUs) of Actinobacteria, Bacteroidetes, Alphaproteobacteria, and autotrophic and unclassified Eukaryota which might be analogous to microbial keystone taxa. Constrained correspondence analysis revealed the relationships of bacterial and microbial eukaryotic communities with geographical location.