The composition of humus in permafrost-affected soils of the Bol’shezemel’skaya and Kolyma tundra areas

Tundra soils (except for the soils of barren circles) in the moderately and extremely continental tundra areas are characterized by the pronounced surface accumulation of humic substances. The humate-fulvate nature of humus is typical of the upper horizons of surface eluvial-gley soils, gley soils, and raw-humus mountainous brown soils; the C ha/C fa ratio in them varies from 0.5 to 0.91. The fulvate-humate nature of humus (C ha/C fa = 1.27-1.50) is typical of cryozems and sandy podburs. The first and the third fractions of humic substances (hs 1 and hs 3) predominate in the composition of humus. The coefficients of correlation (R) between the major parameters of soil humus and the physicochemical characteristics of tundra soils have been calculated. These coefficients between the contents of C org, C ha, C fa, C ha1, and C ha3 and the total acidity are equal to 0.73, 0.76, 0.72, 0.85, and 0.67, respectively; for the exchangeable Mg2+, their values are equal to 0.66, 0.88, 0.85, 0.74, and 0.90, respectively; and for the exchangeable Ca2+, 0.55, 0.47, 0.39, 0.41, and 0.61, respectively (p < 0.05). The composition of exchangeable cations and the total acidity specify the conditions of fractionation of humic substances in the studied soils. The differentiation of the qualitative composition of humus in the profiles of tundra soils is well pronounced and is mainly controlled by the distribution of clay and fine silt particles.