Biogeochemical Aspects of Transformation of Humic Substances and Silicate Rocks during Freezing–Thawing.

In the northern regions, seasonal temperature fluctuations cause cyclic thawing and freezing of soils and rocks, which is accompanied by dangerous natural phenomena, including landslides. Special conditions arise on the mountain slopes of many reservoirs due to the fluctuations of water levels and the interaction of humified waters with rocks. The paper presents the results of an experimental study of the biotransformation of sodium humate (SH) and changes in the microstructure of the surface of silicate rock that is a part of the Bureya landslide body under various conditions of cyclic freezing–thawing (CFT). Freezing of samples was carried out at a temperature of –18°C, and thawing at different temperature ranges (+4 and +23°C). The role of biogenic factor was played by four strains of microorganisms isolated from the surface and bottom waters in the Bureya Reservoir above and below the landslide body. The nature of the SH biotransformation during CFT was studied by spectral methods at different wavelengths (254, 275, and 465 nm). Analysis of the composition of water-soluble forms of chemical elements in an aqueous environment during rock destruction was carried out by ICP-MS, and changes in the surface microstructure was studied using scanning electron microscopy. It was found that the aromatic component of SH was subjected to the most intense transformation. After CFT, the strain Actinomyces sp. 45VD isolated from bottom waters showed maximum activity at a thawing temperature of +4°C relative to SH and leaching of elements from rock (Al, Ca, Mg, Mn). Its activity was comparable to the intensity of element leaching by a natural microbial consortium of non-sterile rock. Rocks subjected to CFT in deionized water were used for comparison; in this case, the content of water-soluble forms of many chemical elements (Fe, Ni, Cu, Zn, As, Mo, Ag, Cd, Tl, Bi, As) was below the detection limits (<0.001). The high biogeochemical activity of Actinomyces sp. 45VD is confirmed by the analysis of SEM-images of the microstructure of the silicate rock surface and the formation of a wide variety of isomorphic biominerals. [ABSTRACT FROM AUTHOR]