The migration of 137Cs and 90Sr in soil-vegetation cover at accidental underground nuclear explosion site «Kraton 3»

Here, we report studies on content and distribution of 137Cs and 90Sr artificial radionuclides in soil-vegetation cover at «Kraton 3» accidental underground nuclear explosion site. This site is located in the territory of northwestern Yakutia, within the northern taiga subzone of the permafrost-taiga region of eastern Siberia boreal belt. In geomorphological aspect, this object belongs to steep slope of the divide connecting the flood-lands of the Markha River and peneplain of the divide. Sod-carbonate (redzina) soils prevail in soil cover of «Kraton 3» underground nuclear explosion site. This type of soil is typically characterized by a thin soil profile, weak alkaline reaction, heavy granulometric composition, saturated soil-absorbing complex, and drastically decreasing profile distribution of humus. Despite the considerable time after the accident, the radiation situation at the site is still very disturbing. Gamma ray background radiation levels at the site varied from 10 to 200 μR/h, which were 2–25 folds higher than average natural background radiation. The isotope contamination densities in soils of sites interconnected along the drainage were 34–1025 kBq/m2 for 137Cs and 57–781 kBq/m2 for 90Sr, which exceeded 30–1000 times the global fallout levels of these radionuclides. The rates of vertical migration of studied radionuclides were also determined as 0.11–0.84 % (137Cs) and 0.79–1.44 % (90Sr) per year of total radiation contamination density. The minimum vertical migration rates of 137Cs (0.11 %) were observed in leached sod-carbonate soil, while maximum rates (0.84 %) were determined in immature sod-carbonate soil, the profile of which lacks organogenic and humus-accumulative horizons. The migratory capabilities of 137Cs and 90Sr in this soil were very close and made 0.84 and 0.79 % respectively. Migration factors of 137Cs and 90Sr in permafrost soils of the studied area were determined with the use of principal component analysis. This study also revealed that radioactive contamination levels of local vegetation remain considerably high. The concentration of radioactive cesium in plants growing on the site of accidental underground nuclear explosion is 40–5000 times higher than its natural background levels

Magnetic susceptibility of permafrost soils of the forest catena in Central Yakutia

The magnetic susceptibility (MS) of three types of permafrost forest soils (pale-yellow, pale-brown, and podzolic) formed on permafrost soil-forming rocks in the cryoarid climate of Central Yakutia for the first time was studied. It is noted that the studied permafrost soils develop within various high-altitude geomorphological levels of the ancient alluvial Central Yakut plain and form a regular zonal series from bottom to top, that is, with an increase in the absolute height of the terrain: pale-yellow gray ‒ pale-yellow typical and solodic ‒ pale-yellow leached ‒ pale-brown typical ‒ pale-brown podzolized and podzolic soils. At the same time, in this series of zonal soils, the values of their volume (VMS) and specific (SMS) magnetic susceptibilities also naturally decrease, due to the increased intensity of eluvial soil processes, such as solodization and podzolization in the genesis of these soils. The weighted average values of the specific magnetic susceptibility calculated for 9 sections of the studied permafrost forest soils, taking into account individual values of SMS and the thickness of their genetic horizons, changed for pale-yellow soils in the range of 21.6–42.1, pale-brown – 3.9–12.4, podzolic – 1.8–5.7 × 10–8 m3/kg. It is also established that based on certain values of the VMS of these soils, all the studied types of permafrost forest soils in Central Yakutia belong to the group of low-magnetic ones and differ in the values of volumetric magnetic susceptibility that do not exceed 100 × 10–5 Si units. Among the studied pedons of zonal forest soils of Central Yakutia, various types of their magnetic profiles are noted, which are determined by the geographical and genetic features of these soils