The present paper is aimed at studying hydrophilic and hydrophobic interactions via the modeling behavior of carbonate-clayey soil in a laboratory experiment. The typical aspects of human impact on the biogeochemical processes of natural soils such as decompression, disintegration, hydration and introducing easily oxidized organic matter were simulated. The experimental settings were adjusted regarding common field conditions for the clay near-surface layers in the temperate zone. The model system consisted of a carbonate-clayey soil, filtering water, and a psychrophilic microbial community desorbed from cave calcite formations (speleothems). The carbonate-clayey soil was collected from eluvium on red clay bedrock deposits of the Permian system along the right bank of the Volga River in the Republic of Tatarstan. The microbial community was stimulated with a modified R2A growth medium and inoculated into the clay using ceramic carrier discs. In order to explain the results of the experiment auxiliary materials presented simplified systems of the carbonate clay components were used. Soil properties such as the size distribution of mechanically strong particles and microaggregates, mineral composition, organic matter content, water wettability, and the chemical composition of filtered water were determined. The experiment being carried out during six months showed the appearance of new hydrophobic contacts between soil particles, crystalline cement deposition and the high sensitivity of these processes to microbial activity. The results of the study may help in understanding the processes that occur when foundations for constructions or underground facilities contact microbially produced substances, as well as predicting soil weathering.

The typical situation of technogenic influence on biogeochemical processes of previously unaffected soils of the terrigenous carbonate complex was simulated experimentally. The dynamics of some physical, chemical and physico-chemical properties of the model system consisting of: a carbonate clay soil, filtering water, and a psychrophilic heterotrophic microbial community washed away from calcite speleothems, was investigated. The carbonate clay soil was sampled from eluvium on red clay bedrock deposits of the Permian system. The rock to extract the psychrophilic microbial community was selected from the aphotic zone of the Yuryevskaya cave, Republic of Tatarstan. The microbial community was stimulated by the modified R2A nutrient medium. We used standard methods to determine the soil and filtrate physical and chemical properties, as well as the captive bubble method in the author's modification for wetting contact angle of soils. The experiment showed that the model technogenic impact on the carbonate clay soils modified their properties. The microbial activity during 6 months caused a redistribution of microaggregates in size, increased the fraction of crystalline contacts between soil particles, immobilized some inorganic ions, and increased soil heterogeneity and hydrophobicity. The results of the study can be considered when designing the foundations for constructions contacted with organic substances, weathering soil behavior predicting, as well as when planning caves’ restoration and preservation.