GEOCHEMICAL CONDITIONS OF SULLAR SPRING: FORMATION OF AUTHIGENIC MINERALS AND METHANE FLUXES

Abstract

Link for citation: Soldatova E.A., Sidkina E.S., Kiriukhin B.A., Maximov P.N., Krivenok L.A., Ivanov V., Tananaev N.I. Geochemical conditions of Sullar spring: formation of authigenic minerals and methane fluxes. Bulletin of the Tomsk Polytechnic University. Geo Аssets Engineering, 2023, vol. 334, no. 10, рр. 16-33. In Rus. Relevance and the research object. Interpermafrost aquifers and areas of their discharge with seasonal ice covers are special permafrost-hydrogeological and hydrochemical systems that are not typical for the thick continuous permafrost zone of Central Yakutia. Differences in chlorofluorocarbon content indicate the anaerobic conditions of some springs suggesting microbial degradation of these compounds by methanogenic bacteria. In the discharge area of such springs, a sharp change in the geochemical conditions takes place leading to a transformation in the water chemical composition and boosting the processes of authigenic mineral formation in this buffer area. In current work we considered the geochemical system of the Sullar spring – the most northern and the least studied among interpermafrost groundwater discharge zones of the Lena River right bank. Intensive accumulation of authigenic minerals was found in the Sullar discharge area during field research. It was Fe compounds with bacterial mats as an opalescent film. Some researchers state the connection between the transformation of Fe compounds during permafrost melting and the migration and transformation of organic matter, including its consumption by microorganisms with further methane emission. We assumed that there is a relationship between the authigenic mineral formation and the content and emission of methane in the discharge area of the spring. This research is the first comprehensive description of the hydrochemistry of the interpermafrost water of the Sullar spring. The aim of the research was to explore influence of geochemical conditions and microbial communities on formation of authigenic minerals and methane fluxes, in particular the effect of the change of geochemical conditions due to groundwater discharge on Fe precipitation and to analyze the relation of that process with methane fluxes. For this purpose, we study water chemical composition of the Sullar spring, measure methane fluxes from water surface and analyze mineral and microbial composition of secondary mineral crusts and bottom eluvium collected near water sampling points. Methods. The main element content was determined by ion chromatography. The concentrations of the bicarbonate ion and dissolved carbon dioxide were calculated by the equilibrium modeling method based on the pH and Eh values of the system. The content of trace elements was measured by mass spectrometry with inductively coupled plasma. To identify seasonal and annual variability, a retrospective analysis of the water chemical composition of the Sullar spring for the period from 1962 to 2020 was carried out. Methane fluxes were measured using the chamber method. The methane concentration was determined by gas chromatography with a flame ionization detector. The features of the secondary mineral crusts and bottom eluvium were determined using a petrographic microscope. The chemical composition of individual mineral phases was evaluated using a scanning electron microscope equipped with a detector for energy dispersive X-ray spectral microanalysis. The DNA concentration was measured on a fluorimeter. Amplicon libraries were generated by polymer chain reaction with universal primers for the V4 region. Equilibrium modeling was carried out using the HCh software.