Cryogenic Effect on the Formation of Permafrost-Affected Loamy Tundra Soils at Different Stages of Their Development

The morphology of soil profiles during their summer and winter period was studied as well as the microstructure and major physic chemical properties of permafrost-affected loamy tundra soils. Studied objects were the initial (zero-moment) soils and the same profiles after 7 and 23 years up to the fully developed soil profiles of Middle and Early Holocene age. The leading role of the cryogenic processes in formation of morphology and properties and structure organization at different stages of development was determined. This effect realizes through the thermal yield ability and ice segregation. The difference of summer and winter structural organization was obtained. The instability of morphological features formed by cryogenic processes was also determined. These features may change and disappear due to the changes in hydrothermal regime, freezing-thawing processes, ice segregation forms. The stability of soil structure is determined by the formation of soil-aggregate chemical complexes. It was also shown that the structural morphological features in soil diagnostic horizons form before the significant differences of chemical properties appear. The cryogenic effect on soil formation is mainly realized through the microturbations of the uppermost horizons at the initial stages of soil formation. Later on, the horizontal and vertical migration of organogenic material may affect the structure and properties of the middle and lowermost soil horizons. One of the leading processes in permafrost-affected soils’ formation is the physical (cryogenic) disintegration of plant litter and forming of detritus in the upper parts of the profiles and coarse humus enrichment of the middle and lowermost soil horizons due to the cryoturbation.