Effect of soil freezing on physical and microbiological properties of permafrost-affected soils

Soil systems consist of solid materials, liquids, and gases. In permafrost-affected soils ice causes significant changes in physico-chemical and microbial properties of the soil. The soil contains variable amounts of water, gas or ice, depending on ground temperature. Gas flux measurements were carried out in combination with other monitoring studies on Samoylov Island, Lena Delta, Siberia. Bi-directional freezing tests were conducted to observe freezing induced changes of soil properties and gas conductivity. The thermal regime, changes of unfrozen water content, and the radial stress state of the soil are logged automatically. The stresses recorded mainly depend on soil water/ice content and soil composition. A fine-grained soil reacts on cooling with cryosuction and contraction which leads to aggregation and the building of microfissures. Coarse-grained soils behave differently, because high pressures develop as a function of soil water content and freezing rate but without larger changes in soil structure.