Geochemical Features of Organo-Accumulative Soils of Subtaiga and Subtaiga–Forest-Steppe Light Coniferous Forests of Northern Mongolia

We have studied geochemical features of organo-accumulative soils (Eutric Regosols (Loamic, Ochric)), Cambic Someric Phaeozems (Loamic)) widely spread in the soil cover of subtaiga and subtaiga-forest-steppe light coniferous forests and forming the lower boundary of the forest zone in the mountains of Northern Mongolia. Data on the microelement composition of soil-forming rocks are given; the paragenetic association of trace elements in them is composed of Pb, Cu, Zn, Co, V, Cr, Ni, Mn, Mo, Ba, Sr, Zr, and B. The residual and redeposited weathering crusts of igneous rocks are enriched with Zn, Cr, Mo, and B as compared to the mean content of these elements in the lithosphere, but they contain less Pb, Co, Mn, Ba, Sr, and Zr. The residual and re-deposited weathering crusts of calcareous rocks are enriched in Pb, Cu, Zn, V, Cr, Sr, and B, and are impoverished in Co, Ni, Mn, Mo, Ba, and Zr. The morphological, physicochemical and chemical properties of soils, as well as the content and radial distribution of trace elements in soils are discussed. The data obtained testify to the accumulation of most trace elements in the surface organic and humus-accumulative soil horizons. This is associated with the heterogeneity of soil-forming rocks and with the effect of soil processes, which cause the accumulative redistribution of elements and their deposition at organic-sorption and carbonate geochemical barriers. It is shown that the studied soils differ not only in the absolute contents of trace elements, participating in the biological cycle, but also in the intensity of their involvement in biogenic migration.