TOMSK, April 22. /TASS/. Experts in soil sciences at the Tomsk State University studied swampy plains in the Russian Federation's Arctic Zone to find that residual small lakes in bowls of descended bigger thermokarst lakes are a source of greenhouse gases, Russia's Ministry of Science and Higher Education told TASS.

Thermokarst lakes are reservoirs that began developing after soil subsidence due to melting of underground ice (permafrost), scientists said. Normally, they are small shallow lakes 1-2 meters deep, irregular in shape, and they are typical for northern regions. In recent decades, many lakes of the kind have been shallowing actively due to destructing thawing shores. Earlier, Chinese researchers, led by Aobo Liu from the Shandong University, reported that 2,712 lakes in Yamal alone became shallow in 2000-2020.

Research methods

"The Tomsk University's soil scientists were measuring concentrations of dissolved carbon dioxide (CO2) and methane (CH4) in reservoirs with different drainage periods after shallowing - from recently drained basins to those drained more than a hundred years ago, with well-developed marsh vegetation. Besides, they estimated carbon dioxide fluxes off the water surface, the content of dissolved organic and inorganic carbon, and about 40 basic and trace elements. They compared residual reservoirs with "untouched" mature thermokarst lakes," the ministry said.

To assess the contribution of those reservoirs to greenhouse gas emissions, the scientists selected three contrasting sites: Se-Yakha (the Yamal Peninsula, a continuous permafrost zone of the Arctic tundra), Tazovsky and Khanymey in the Yamalo-Nenets Autonomous Region. According to Artyom Lim, head of the Soil Science Laboratory, the flow of carbon dioxide off the surface of shallow reservoirs was quite big and did not depend directly on the amount of time after shallowing, or on the degree of permafrost coverage of the catchment area. However, the concentrations of dissolved carbon dioxide and methane were increasing sequentially from the early stages of succession (replacement of some plant communities by others - TASS) to later and background lakes.

Waters' chemical composition

This discrepancy may be explained by the fact that the conditions for the release of gases from water in shallow reservoirs are more dynamic, which leads to bigger flows. At the same time, the waters' chemical composition also changes greatly after shallowing. For example, as the basins got overgrown, the amount of dicarboxylic acids, basic ions, and nutrients decreased there.

"This reflects an intensive biogeochemical cycle: after drainage, grasses quickly populate fertile bottom; they capture from the bottom sediments the nutrients, which enter the water of shallow reservoirs, where algae become active. Later on, mosses displace grasses, isolate bottom sediments, and the waters' chemical composition changes towards the composition of the original poor northern lakes. In the continuing warming and disruption of the Arctic hydrological regime, the contribution of these residual basins to CO2 and CH4 emissions and landscape transformation will only increase," the ministry added.

After the study, scientists have suggested including residual reservoirs in monitoring systems and carbon cycle models to assess adequately the feedback between permafrost melting and climate. The research was supported by the Russian Science Foundation grant and was assigned by Russia's Ministry of Science and Higher Education. The research results are published in the journal Science of The Total Environment (Q1).