Global climate change is one of the most serious environmental problems. It leads to rising air temperatures, melting permafrost, rising sea levels, desertification of landscapes, and an increase in the frequency and severity of natural disasters such as tsunamis, floods, and extreme droughts. One of the causes of climate change is considered to be the accumulation of greenhouse gases — carbon dioxide and methane — in the atmosphere. At the same time, their source may be not only emissions from factories and other facilities related to human activity, but also natural components, such as lakes. However, the amount of greenhouse gases emitted from their surface remains almost unexplored.

Scientists from the Southern Federal University, the Hydrochemical Institute of the Russian Hydrometeorological Service and the Don State Technical University have determined how greenhouse gas fluxes form in the hypersaline Lake Baskunchak. This reservoir belongs to drainless lakes — that is, the organic substances coming from the waters and forming directly in the lake are not washed out, but gradually accumulate. The salinity of Baskunchak is about 300 grams per liter, 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.

It turned out that Lake Baskunchak contains relatively little methane — about 1.5 microliters per liter of water — so, on the surface of the Black Sea, this figure is about 4.8 microliters per liter. 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.

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 on the bottom of the lake, accompanied by the release of carbon dioxide. Thirdly, it is associated with the suppression of photosynthesis due to the extreme salinity in Lake Baskunchak.

"Using Lake Baskunchak as an example, 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 release is likely to decrease due to the activation of its sulfate-dependent anaerobic oxidation processes in the sediments. 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 allow us 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," says Yuri Fedorov, PhD, Head of the Department of Physical Geography, Ecology and Nature Conservation at the Institute of Earth Sciences of the Southern Federal University, head of the project supported by an RNF grant.