The molecular structure of humus substances from permafrost-affected peat mounds of the East European forest-tundra has been studied with the use of up to date physicochemical methods (C-13 NMR, EPR spectroscopy). The structural-functional parameters of humus substances from these soils are specified by the integral action of cryogenic processes in the active layer, natural selection of aromatic structures in the course of humification, and by the species composition and degree of peat decomposition; they reflect the climatic conditions of peat formation in the Holocene. Humic acids of peat bogs are represented by low-condensed molecular structures with the low portion of carbon atoms of aromatic components, which increases down the soil profile, and by with the high content of non-oxidized aliphatic fragments. Active changes in the portions of aromatic and non-oxidized aliphatic fragments take place at the lower boundary of the active layer in the soils of bare peat spots. Such changes may serve as the basis for further search of the bioindicators of recent climate changes.

Humic substances (HSs) from themire peat soils of the forest-tundra zone of the European northeast part of Russia have been characterized in terms of molecular composition. This was accomplished using solid-state C-13 nuclear magnetic resonance (C-13 NMR) techniques and electron spin resonance (ESR) spectroscopy. The composition depended on the intensity of cryogenic processes in the active layer, the quality of the humification precursors (the degree of peat material transformation), and the biochemical selection of aromatic fragments during humification. Humic acids (HAs) and fulvic acids (FAs) of the peat soils showed the presence of compounds with a low extent of condensation and a low portion of aromatic fragments, which increased with depth. A higher proportion of aliphatic carbon species was found in the HAs, indicating a low degree of organic matter stabilization. Based on the data from the two types of peat soils, we suggest that particular changes in the proportion of aromatic and unoxidized aliphatic fragments on the border of the bottom of the active layer and permafrost layers can be used as markers of current climatic change. (C) 2017 Elsevier B.V. All rights reserved.

Humification plays an important role in stabilization of organic matter in soils of the cryolithic zone. In this context, the degree of organic matter stabilization has been assessed, using instrumental methods, for permafrost peat soils of the eastern European Arctic, based on selected plots from within the Komi Republic (Russian Federation). Humic substances (HSs) isolated from the mire permafrost peats of the forest-tundra sub-zone of the European Arctic have been characterized in terms of molecular composition. This was accomplished using elemental and amino acid fragments (AAFs) composition. Solid-state C-13 nuclear magnetic resonance (C-13 NMR) spectroscopy was utilized to identify the structure of HSs. Changes in the molar x(H) : x(C) ratio, ratio of aromatic to paraffin fragments and ratio of hydroxy AAFs to heterocyclic AAFs along the peat profiles have been revealed. They are due to the activation of cryogenic processes in the upper part of the seasonally thawing layer, the natural selection of condensed humic molecules, the botanical composition and degree of degradation of peat, which reflect the climatic features of the area in the Holocene. Humic acids and fulvic acids of the peat soils showed the prevalence of compounds with a low degree of condensation and a low portion of aromatic fragments. The aromaticity degree showed the trend to increase within the depth. Changes of quantitative and qualitative parameters of specific organic compounds occur at the permafrost boundary of peatlands, which can serve as an indicator of recent climate changes in environments from the high latitudes. The presented data can be useful in the evaluation of soil organic matter stabilization degree in the active layer and below the permafrost table.