Julia Alexandrovna Kryukova

The mineralogical composition of the silt fraction of marshes soils on the tombolo, a bridge between the mainland and a small island on the Pomorsky coast of the White Sea, has been studied. The soils on different parts of the marshes are characterized by different sequences of sediments and soil horizons embedded in them. Mica minerals (“illites”), kaolinite, chlorite and mixed-layer illite-vermiculite and chlorite-smectite were present in the silt fraction of all soils. Variation of mineralogical composition of clays was noted both between soil horizons and between the studied profiles. In our opinion, the variation is determined both by sediment composition and soil weathering of minerals, which confirms the idea of T.A. Sokolova about the complex character of formation of mineralogical composition of clays in soils on sediments re-deposited by water. The main weathering process in marsh soils was the degradation transformation of chlorite and, possibly, mica with the formation of smectite packages. These processes are spatially associated with the aeration zones of the marsh soils, at least periodically under oxidative regime.

The most important factor affecting the soil organic carbon (SOC) stocks is the degree and nature of soil moisture content. This factor is especially important when assessing SOC in forest soils. In this paper, the results of a comparative statistical analysis of the variability of SOC in automorphic, semihydromorphic and hydromorphic forest soils in Karelia are discussed. To estimate SOC stocks and calculate quantitative indicators of their variability, soil survey data were used over an area of 1 km2. The information was collected into a single array, which includes the characteristics of 95 soil profiles of forest ecosystems. Of these, 61 profiles characterize automorphic soils, 12 profiles characterize semihydromorphic soils and 22 profiles characterize hydromorphic soils. The results of the studies showed that the mineral horizons of forest soils are largely heterogeneous in terms of SOC content, while organogenic horizons are more heterogeneous in terms of thickness and density. The results of statistical analysis showed that the average SOC stocs in the 0–30 and 0–50 cm soil layers increase depending on the degree of hydromorphism. The results of statistical analysis showed that SOC stocks in semihydromorphic soils are characterized by higher variability, as evidenced by a larger range of changes, higher standard deviations and coefficient of variation. In automorphic soils, the 0–5 cm layer, corresponding to the litter, accounts for up to 30% of the total organic carbon reserves in the 0–50 cm layer. With increasing hydromorphism, this share decreases to 17% in semihydromorphic soils and to 6% in hydromorphic soils. The share of SOC reserves in the 30–50 cm layer in total reserves increases from 23% in automorphic soils to 43% in hydromorphic soils.