Non-fresh review: the role of hypersaline lakes in global climate change is shown

Salinization of lakes will increase the release of carbon dioxide into the atmosphere and reduce the release of methane. These conclusions were reached by Russian scientists who studied the surface of Lake Baskunchak, one of the largest hypersaline reservoirs in the world. The research will help develop recommendations for the ecological rehabilitation of such natural sites and minimize the negative effects of human activity on the environment, environmentalists believe. For more information about the role of bottom sediments and surface gases of hypersaline lakes, see the Izvestia article.

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Scientists from the Southern Federal University, the Hydrochemical Institute of Roshydromet and the Don State Technical University have shown for the first time that about 55 kg of methane and about 14.7 tons of carbon dioxide are released per day from the surface of Lake Baskunchak, one of the largest hypersaline lakes in the world. The low intensity of methane fluxes was associated with its low concentration in water, while a significant amount of carbon dioxide was associated with the vital activity of microorganisms, salt deposition, and photosynthetic activity reduced due to high salinity. Thus, salinization of water bodies and soils in arid regions of the planet can become an additional source of greenhouse gases in the atmosphere, which contribute to climate change on the planet.

Scientists have determined how greenhouse gas fluxes are formed in the hypersaline Lake Baskunchak. This reservoir belongs to the drainless — that is, the organic substances coming from the waters and forming directly inside it are not washed out, but gradually accumulate. The salinity of Baskunchak is about 300 g/l, which is almost 20 times higher than the salinity of the Black Sea.

The researchers studied the chemical and gaseous composition of water and sediments, as well as their granulometric and mineralogical composition. Using floating storage chambers, the authors measured the fluxes of methane and carbon dioxide into the atmosphere.

— Using the example of Lake Baskunchak, we have shown that salinization of reservoirs and salinization of soils in dry landscapes can become an additional source of carbon dioxide in the atmosphere. At the same time, methane emissions are likely to decrease due to the activation of its sulfate-dependent anaerobic oxidation processes in the sediments," Yuri Fedorov, project manager, Doctor of Geography, Head of the Department of Physical Geography, Ecology and Nature Conservation at the Institute of Geosciences of the Southern Federal University, told Izvestia.

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As a result of the study, it turned out that Lake Baskunchak contains relatively little methane — about 1.5 µl/l of water, so on the surface of the Black Sea this indicator is about 4.8 µl/l. As a result, methane fluxes into the atmosphere were also reduced. Researchers believe: This is due to the fact that the salt crust covering the bottom sediments prevents methane from escaping from the underlying layers into the water. In addition, anaerobic oxidation of methane occurs in the upper layers of bottom sediments, as a result of which its concentrations decrease.

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On the contrary, carbon dioxide fluxes were on average 287 times higher than methane fluxes and 3.3–5 times more intense than its fluxes from the surface of freshwater lakes. According to the authors, increased carbon dioxide emissions may be due to several reasons. Firstly, with the decomposition of organic substances to carbon dioxide and water by microorganisms. Secondly, with the chemical deposition of salts to the bottom, accompanied by the release of carbon dioxide. Thirdly, it is associated with the suppression of photosynthesis due to the extreme salinity in Lake Baskunchak.

— In the future, we plan to study the causal relationships of hydrological and biological characteristics, chemical and gas compositions of water and sediments, as well as their physico-chemical properties. This will make it possible to establish long-term trends in the evolution of lakes in the southern European part of Russia. Our research will also help develop recommendations for the ecological rehabilitation of lakes, minimizing and preventing the negative effects of human activity on their ecosystems in the face of climate change," said Yuri Fedorov.

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Studying water bodies, including the release of methane and carbon dioxide from the surface of reservoirs, is not new, but it is necessary in the light of the global climate change agenda, said Irina Golovacheva, Deputy Director of the Patrice Lumumba Institute of Ecology at the RUDN University, member of the Public Council of the Basic Organization of the CIS Member States for Environmental Education.

— Research allows us to consider the possibility of adjusting the condition of the reservoir (changing properties) to reduce emissions. It should be noted that these issues are not the only ones. Aspects of the state of biocenoses of reservoirs are also important," the specialist said.

Using the data obtained allows us to take into account the impact and contribution of water bodies to the global greenhouse gas balance, Vladimir Pinaev, member of the Public Council at the Ministry of Natural Resources of the Russian Federation, editor-in-chief of the online magazine Waste and Resources, told Izvestia.

— Emissions from reservoirs may not be comparable, for example, with industrial and pollution from active large volcanoes. It is important to note not only the allocation of reservoirs, but also the issues of gas absorption by them," he said.

The results of the study, supported by a grant from the Russian Science Foundation (RSF), are published in the journal Water.