V. A. Beznosikov

Molecular composition of humic substances in tundra soils (13C-NMR spectroscopic study)

Functional groups and molecular fragments of humic substances (HSs) from cryohydromorphic peat gley tundra and surface-gley tundra soils have been identified by 13C-NMR spectroscopy. The analysis of HS preparations has shown that the molecules of humic acids (HAs) are enriched with aromatic fragments compared to fulvic acids (FAs). Aliphatic chains, carbohydrate- and amino acid-type structures prevail in the carbon skeleton of the FAs. An integrated parameter of the HS hydrophobicity has been proposed. The parameter represents the total portion of unoxidized carbon atoms and allows indirectly assessing the amphiphilic properties of HSs.

Polycyclic aromatic hydrocarbons in tundra soils of the Komi Republic

The qualitative and quantitative composition of polycyclic aromatic hydrocarbons (PAHs) in tundra soils has been studied by gradient high-performance liquid chromatography. The differentiation of the PAHs in the soil profile is of clear accumulative character. The pool of polyarenes in the soils is determined by the cryogenesis processes and mainly consists of low-molecular-weight bi- to tetranuclear PAHs, the high-molecular-weight PAHs in the organic horizons make up no more than 20% of the total polyarenes in the soil, and penta- and hexanuclear structures are almost absent in the mineral layer.

Complexation of mercury(II) ions with humic acids in tundra soils

The interaction mechanisms of mercury(II) ions with preparations of humic acids (HAs) isolated from organic horizons of surface-gleyed soils (Haplic Stagnosol (Gelic, Siltic)) of shrub tundra and hydromorphic peat gley soils (Histic Cryosol (Reductaquic, Siltic)) of moss-lichen tundra have been studied. The particular features of the interactions between the mercury(II) ions and the HAs are related to the molecular structure of the HAs, the mercury concentration range, and the environmental parameters. The fixation of mercury(II) ions into stable coordination compounds is most efficient in the pH range of 2.5–3.5. At the element concentrations below 0.50 μmol/dm3, the main complexing sites of HAs are their peripheral aminoacid functional groups. Pyrocatechol, salicylate, and phenolic groups from the nuclear moiety of molecules interact in the concentration range of 0.0005–0.50 mmol/dm3; the physical sorption of mercury hydroxo complexes by the surface of HAs is the main process occurring in the system.

Accumulation of polycyclic aromatic hydrocarbons in soils and plants of the tundra zone under the impact of coal-mining industry

Thirteen polycyclic aromatic hydrocarbon (PAH) compounds were identified in organic horizons of tundra surface-gleyed soils ( Histic Stagnosols (Gelistagnic) and plants. The total content of PAHs in contaminated soils exceeded the background values by three times. Concentrations of low-molecular weight hydrocarbons in soils at different distances from the coalmines were relatively stable. Concentrations of highmolecular weight hydrocarbons had a distinct maximum at a distance of about 0.5 km from the source of emission. The increased values of correlation coefficients were found between PAH concentrations in organic soil horizons, plants, and coal of the Vorkutinskaya mine. Mostly low-molecular weight structures predominated in the organic soil horizons and in the studied plant species. The maximum capacity for the biological accumulation of PAHs was displayed by Pleurozium schreberi and the minimum capacity was displayed by Vaccinium myrtillus. Mosses and lichens actively absorbed polyarenes from the surface; most of the PAHs were transported into the plants. This phenomenon was not observed for Vaccinium myrtillus Concentrations of PAHs on the surface and in plant tissues decreased with an increase in the distance from the mine. Distribution of polyarenes in plant organs was nonuniform. Insignificant excess of concentration of polyarenes was found in dead part of Pleurozium schreberi in comparison with its living part. The accumulation of polyarenes in the leaves of Vaccinium myrtillus was higher than that in its stems and roots.

Polycyclic aromatic hydrocarbons in soils and lower-layer plants of the southern shrub tundra under technogenic conditions

In soils and plants of the southern shrub tundra, 15 polycyclic aromatic hydrocarbons (PAHs) have been detected by high-performance liquid chromatography. Polyarenes in emissions, soil organic horizons, and plants mainly include low-molecular-weight PAHs: naphthalene, fluorine, and pyrene. The contents of the total PAHs in soils and plants exceed the background levels by 3–5 times. The distribution of polyarenes among the organs of the studied plants is nonuniform and depends on the plant species and technogenic load on the area. The studied plants include both hyperaccumulators of polyarenes (Pleurozium schreberi) and indicators of PAHs in the soil (Polytrichum commune). Pleurozium schreberi is the most abundant species in the areas under study, and it accumulates the largest mass fraction of PAHs. The differences in the accumulation of PAHs by the plants of the tundra and taiga zones have been revealed.

Molecular composition of raw peat and humic substances from permafrost peat soils of European Northeast Russia as climate change markers

Humic substances (HSs) from the mire 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 13C nuclear magnetic resonance (13C 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.

Amino acid composition of humic substances in tundra soils

Peripheral amino acid fragments of humic and fulvic acid molecules from tundra soils have been identified and quantified. A significant weight fraction of amino acids has been found in humic acid preparations, which exceeds their content in fulvic acids. Features of the amino acid composition of humic substances along the soil profile and depending on the degree of hydromorphism and the proportions of different (neutral, basic, acidic, cyclic) groups in amino acids have been revealed. The molar ratio between the hydroxy and heterocyclic amino acids reflects the degree of humification of the soil.

Effect of climate changes in the holocene on the distribution of humic substances in the profile of forest-tundra peat mounds

The molecular composition of humic substances in permafrost peatlands of the forest-tundra zone in northeastern European Russia has been characterized for the first time on the basis of systematic studies. Changes in the molar x(H): x(C) ratio along the peat profiles have been revealed, which is due to the activation of cryogenic processes in the upper part of the seasonally thawing layer, the natural selection of condensed humic molecules, and the botanical composition and degree of degradation of peat, which reflect the climatic features of the area in the Holocene. Dry-peat soils of mounds are worse heated during the summer period because of the buffering effect of moss litter, which results in a lower degree of condensation of humic and fulvic acid molecules in the peat horizons down to the permafrost table. Transformation of quantitative and qualitative parameters of specific organic compounds occurs at the permafrost boundary of peatlands, which can serve as an indicator of recent climate changes in high latitudes.

Study of polydispersity of humic substances by the gel chromatography method

Molecular weight distribution of humic and fulvic acid preparations extracted from podzolic, peaty podzolic weakly gleyed, and arable soils is investigated. The effect of the agricultural use of soils on the fractional composition of humic compounds is assessed.

Paramagnetic Properties of Humic Substances in Taiga and Tundra Soils of the European Northeast of Russia

The study of paramagnetic activity of humic substances in taiga and tundra soils of the Komi Republic and the assessment of the influence of soil hydromorphism on concentrations of free radicals in the structure of humic acids (HAs) and fulvic acids (FAs) have been performed. The concentration of free radicals in HA specimens was up to 11 times higher than that in FA specimens due to a higher content of aromatic and other condensed structures in HA molecules. This fact attests to the high capacity of HAs to polymerization and complexation reactions with participation of radicals. The average value of g-factor is higher for FA specimens than for HA specimens, which attests to a greater electron density shift of unpaired electron to oxygen atom in the structure of FAs because of its spin-orbital interaction with oxygen-containing functional groups, the concentrations of which are significantly higher in FAs than in HAs. An increase in the concentration of free radicals in the molecular structure of HAs is observed in taiga soils with an increase in the degree of their hydromorphism (from automorphic to semihydromorphic soils), which is related to the biohydrothermal conditions of humus formation in bog-podzolic soils with retarded biochemical processes and low degree of plant litter humification. As a result, HAs with the high content of free radicals in their structure are formed. An opposite situation is observed for HAs in tundra soils with a decrease in the content of unpaired electrons under conditions of the increased hydromorphism. The difference in the character of changes in the paramagnetic activity of HAs in taiga and tundra soils with different degrees of hydromorphism may be related to different natures of plant residues participating in humification processes. A tendency for a decrease in the paramagnetic activity in both HAs and FAs from the south to the north is observed, which may be related to a general decrease in the content of poly-conjugated systems in the structure of humic substances in tundra soils.