Composition of iron compound groups in the Russian taiga and tundra permafrost soils

The iron compound composition of permafrost-affected soils in tundra and taiga landscapes of the Russian permafrost was examined to determine soil and geochemical properties. Total iron concentrations were evaluated using the X-ray fluorescence method. The physical and chemical properties of soils and concentrations of silicate, non-silicate, crystallized, and organic matter-associated iron compounds were studied using standard methods. These soils were classified as cryometamorphic (Haplic Cryosols), cryozems (Turbic Cryosols), peat-cryozems (Histic Turbic Cryosols), gleezems (Reductic Gleysols), peat-gleezems (Histic Reductaquic Cryosols), podzolic soils (Albic Retisols), podburs and podzols (Entic and Albic Podzols). The permafrost active layer’s thickness in the soils ranged from 0.3 to 1.7 m, and deeper. On average, the total iron content ranged between 1.2 and 4.5, with the maximum reaching 10.2%. Silicate compounds presented up to 85% of the total iron due to the poor pedogenic transformation of the soil’s mass. The non-silicate iron compound content did not exceed 1.2%. Their increased contents occurred morphologically in the upper mineral soil horizons as well as in the soils of the slope landscapes with ginger-red spots and interlayers. Increased lateral difference ratios from 1.1 to 2.3 demonstrated that supra-permafrost horizons at depths lower than 1 m have shown non-silicate iron compound accumulation, the concentrations of crystallized and organic matter-associated compounds were 0.6–0.8 and 0.2–0.4%, respectively. It was probably connected to the accumulation of organic matter, sorption by the clay particles, and reductive conditions above the permafrost horizon.