Current state and prediction of changes in soils of the middle Lena Valley (Central Yakutia)

The data describing the state of soil and soil cover prior the anthropogenic impact were obtained during geotechnical and ecological investigations which were carried out for the assessment ofpotential impact on the environment caused by gas pipeline and bridge construction across the Lena River. The studied area is located in the central part of the Lena River valley and is adjacent to the city of Yakutsk (61°5' N). It covers all geomorphological levels of the floodplain complex and includes lower fluvial terraces (I and II) on the both banks of the river. The soils of the floodplain complex are represented by typical gley, gleyic, chernozemic and muck subtypes of alluvial sod soils. On the basis of morphological, physical and chemical properties, typical alluvial sod soils with thick humus horizon (up to 20-30 cm), which are optimally moistened and packed, are the most resistant to mechanical treatment and chemical pollution of all floodplain soils. On the lower fluvial terraces, meadow-chernozemic and chernozemic-meadow soils with different salinity are widely represented. The type of salinity is predominantly sulphatic and chloridic that is accountedfor the main role of sulphates and chlorides in saline composition of the ascending solutions. Sod-meadow soils with clearly marked sod horizon and neutral pH are less saline and more fertile. Almost all soil types in the upper part consist of packed sod-humus horizon of sandy-loam and light-loam granulometric composition. Mechanical disruption of humus horizon may cause deterioration ofphysical properties of soil and an increase or initiate gleization and thixotropic processes; it may also lead to thawing of permafrost and activation of water erosion. Within the right of the way of earthmoving machines, the disruption of the entire soil profile was observed, particularly mixing and transforming horizons, thermal erosion and unwanted cryogenic processes (thermokarst, mudflow and subsidence) increased as well. In over-moistened areas of alluvial sod-gley and sod-muck soils the disruption of soil and vegetation cover may be accompanied by temporal or permanent swamping of the territory. It was also determined, that the average concentration of heavy metals and oil products in all the studied soils is significantly lower than their permissible concentrations recommended in a series of Russian regulatory documents for sandy loam soils. However, the poor ability of soils of central Yakutia to self-purification predetermines a high risk of stable accumulation ofpollutants in the studied soils.

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