Molecular Weight Distribution of Humic Acids Isolated from Buried Soils and Yedoma Sediments

: The soils of cold regions store up to 60% of all organic carbon on the planet. As a result of climate change, this organic matter can be biodegraded by microorganisms and thereby make an additional contribution to carbon balance. Nowadays, there are fragmentary data on organic C stocks in high-latitude soils and single works on the analysis of the quality of buried organic matter. This paper presents the ﬁrst data on the molecular weight distributions of humic acids (HAs) extracted from soils and sediments in Yedoma. Molecular weight distributions of HAs preparations were obtained on an AKTAbasic 10 UPS chromatographic system (Amersham Biosciences, Sweden) using a SuperdexTM 200 10/300 GL column (with cross-linked dextran gel, fractionation range for globular proteins 10–600 kDa). As a result of the study, it was found that the buried soil horizons are characterized by the highest content of low molecular weight fraction (with molecular mass ( Mr ) 1.4–1.9 kDa and molar fraction in the range of 54.3–67.1%). The high molecular weight fraction is concentrated mainly in the superﬁcial horizons and decreases with depth (with Mr 299–346 kDa and molar fraction in the range of 3.4–9.8%). In the Yedoma sediments, the maximum content of the medium-molecular fraction is observed (with Mr 24.6 kDa and 39.6% of the molar fraction), which may indicate a low rate of organic matter transformation in the permafrost. The data obtained serve as a database of analysis in terms of modeling the global carbon cycle in the cold regions of the planet.


Introduction
Soil organic matter (SOM) is the basis of life on the earth and accumulation of SOM occurs as a result of processes of stabilization and destabilization of organic residues of plant and animal origin [1].Up to 17% of the Earth's open surface is affected by permafrost and organic matter accumulates in permafrost under these conditions [2].Arctic soils store up to 1500 PgC (Peta gram Carbon; 10 15 g) of organic carbon and about 500 PgC as part of the sediments of the Yedoma and delta complexes [3,4].This corresponds to about 60% of all soil carbon on the planet [4,5].The main component of the ecosystem that stores carbon is peatlands and mineral soils [6].With climate change and a projected warming of 2 • C, more than half of the land affected by permafrost will thaw [2].In addition to climate change, increased microbial activity of soils will thaw organic matter, the transformation of which may have the opposite effect, releasing carbon dioxide and methane into the atmosphere [7].Data on SOM reserves in the Arctic are extremely scarce and fragmentary, the most studied regions being Canada, Spitsbergen, the Scandinavian Peninsula, and some regions of Russia [6,8], while there are almost no works on the quality of organic material of these regions [9].This situation negatively impacts the ability to Agronomy 2023, 13, 1483 2 of 12 predict Arctic carbon balance data and thereby account for the feedback from permafrost melting [10].Understanding ecological and qualitative controls on SOM will be critical to controlling greenhouse gas emissions and rates of organic matter transformation in a changing climate [1].Accurate descriptions of SOM parameters will be essential for predicting organic matter transformation in the pedosphere [10].
A characteristic feature of frozen soils is the process of cryoturbation, in which soil mass mixing and redistribution of organic matter down the profile into the frozen rocks takes place [11].Under conditions of soil cryogenesis, frost cracking, and the formation of ice crystals occur, which lead to frost heaving and cryoturbation [11].The activity of cryogenic processes is related to the position of soil in the topography, hydrological situation, and climatic parameters of the territory [12].The soil profile of cryogenic soils consists of four layers, the active layer (most susceptible to freezing and thawing processes), the transition layer (the upper part of permafrost), the intermediate layer (formed as a result of permafrost degradation), and the "true" permafrost (the layer that is not subject to freezing and thawing processes) [11,13,14].Under the conditions of cryogenesis, organic matter may accumulate in the transient and intermediate layers, thus making it difficult to analyze and account for it in the predictions [15].However, this layer seems to have the greatest effect on the atmosphere under climate change conditions, so the analysis of the qualitative composition of SOM in both the upper and lower layers is an important task of permafrost soil science [9].Thus, in addition to the gaps in the spatial distribution of organic matter in the Arctic, the issue of its movement within the soil profile and its burial in the permafrost composition arises [3].It is generally considered that the largest reserves of organic matter are stored in peat soils, but under conditions of cryoturbation, we face the problem of estimating its reserves in mineral soils, which occupy a substantially larger area in contrast to peat soils [3].Thus, there is a problem with the modeling of organic matter reserves and quality under conditions of cryogenic processes [7].Nowadays, there is no unequivocal opinion on the reverse response of carbon to global warming, there are many papers that refer to both greenhouse gas emissions to the atmosphere and carbon sequestration [7].However, we can definitely state that carbon in the composition of frozen rocks is vulnerable to external influences and will be subject to transformation under conditions of climate change [16].
SOM is a complex heterogeneous system consisting of products of decomposition of plant and animal residues [17].Molecular methods of analysis have traditionally been used to analyze the rates of transformation of organic carbon [18].Organic matter can be conventionally divided into labile and stable forms of carbon [19].However, these concepts are not entirely correct in terms of the stability of organic material because depending on environmental conditions, labile carbon can change into stable [11].This transition is the most important mechanism under permafrost conditions, as the carbon response to environmental changes will determine the composition of our atmosphere and possibly the additional contribution of greenhouse gases [20].Most of the carbon in frozen soil is represented by labile forms (dissolved organic matter, the biomass of soil organisms, and easily oxidizable organic matter), so the study of SOM quality is a relevant modern soil science [19].The most common ways to assess SOM status are chemical fractionation methods as well as various types of spectrochemical analysis (nuclear magnetic resonance, gas and gel chromatography, electron paramagnetic resonance, and infrared spectroscopy) [21].Considering the role of SOM in climate change, quite a few studies have focused on the qualitative composition of organic matter in cryogenic soils.To study the molecular composition of SOM, the analysis of humic acids (HAs) is used [22].HAs play a key role in the stabilization of organic matter.By stabilization, we mean the process in which a biodegradation-resistant SOM is formed.The HAs consist of the least labile compounds of carbon and are less involved in the transformation and emission of greenhouse gases into the atmosphere, but as a result of active degradation of permafrost and changes in the composition of the soil microbiome, they can make a significant contribution to climate change on the planet [23,24].Thus, the aim of this study was to investigate HAs of soils isolated from cryogenic soils and Yedoma sediments of the Lena River delta.In this regard, the following goals were set: 1-to explore factors affecting the formation of HAs in permafrost-affected soils and Yedoma deposits; 2-to identify features of the formation of high-, medium-and low-MW fractions of HAs; 3-to analyze the distribution of MW fractions in permafrost affected soils and Yedoma deposits.

Study Area
The objects of the study were the soils and sediments of the Yedoma complex of the Lena River delta.The Lena River delta is the largest northern river delta in the world, which is located in the Arctic region with an area of about 30,000 km 2 .The Lena River delta is located in a zone with an arctic continental climate.Climatic characteristics are given according to observations from polar weather stations Tiksi, Stolb, and Ust-Olenek [25,26].The average annual air temperature is −13 • C, the average temperature in January decreases to −32 • C, and the average temperature in July is 6.5 • C. The annual amount of precipitation is 190 mm.Most of the land is characterized by the presence of permafrost at a depth of about 1 m.
The Lena River delta is covered with tundra vegetation of various types.The main components are lichens, mosses, grasses (cereals and sedges), and some species of shrubs [25,26].Here, cereal-sedge-moss communities prevail; in the depressions of the relief, hypno-sedge polygonal bogs prevail.The vegetation cover is not closed and has a mosaic character ("spotted tundra").The Lena River delta is dominated by moss-lichen vegetation.Moss groups dominate on loamy and lichen groups dominate on coarse-skeleton, stony soils.It is also not uncommon for moss-lichen vegetation to be replaced by sedge-lichen groupings near lakes of ice origin.The study area is shown in Figure 1.
Agronomy 2023, 13, x FOR PEER REVIEW 3 of 12 climate change on the planet [23,24].Thus, the aim of this study was to investigate HAs of soils isolated from cryogenic soils and Yedoma sediments of the Lena River delta.In this regard, the following goals were set: 1-to explore factors affecting the formation of HAs in permafrost-affected soils and Yedoma deposits; 2-to identify features of the formation of high-, medium-and low-MW fractions of HAs; 3-to analyze the distribution of MW fractions in permafrost affected soils and Yedoma deposits.

Study Area
The objects of the study were the soils and sediments of the Yedoma complex of the Lena River delta.The Lena River delta is the largest northern river delta in the world, which is located in the Arctic region with an area of about 30,000 km 2 .The Lena River delta is located in a zone with an arctic continental climate.Climatic characteristics are given according to observations from polar weather stations Tiksi, Stolb, and Ust-Olenek [25,26].The average annual air temperature is −13 °С, the average temperature in January decreases to −32 °С, and the average temperature in July is 6.5 °С.The annual amount of precipitation is 190 mm.Most of the land is characterized by the presence of permafrost at a depth of about 1 m.
The Lena River delta is covered with tundra vegetation of various types.The main components are lichens, mosses, grasses (cereals and sedges), and some species of shrubs [25,26].Here, cereal-sedge-moss communities prevail; in the depressions of the relief, hypno-sedge polygonal bogs prevail.The vegetation cover is not closed and has a mosaic character ("spotted tundra").The Lena River delta is dominated by moss-lichen vegetation.Moss groups dominate on loamy and lichen groups dominate on coarse-skeleton, stony soils.It is also not uncommon for moss-lichen vegetation to be replaced by sedgelichen groupings near lakes of ice origin.The study area is shown in Figure 1.The problem of the origin of the Lena River delta ice complex is still unresolved.According to geomorphological studies, there was a lake at the place of the ice complex, where mineral and organic residues were washed away, another point of view focuses on the eolian origin of the Yedoma [27].Nevertheless, a significant amount of organomineral sediments was accumulated here, which, as a result of the degradation of the Yedoma, enter the environment and the Laptev Sea.
The studied soils are shown in Figure 2. The problem of the origin of the Lena River delta ice complex is still unresolved.According to geomorphological studies, there was a lake at the place of the ice complex, where mineral and organic residues were washed away, another point of view focuses on the eolian origin of the Yedoma [27].Nevertheless, a significant amount of organomineral sediments was accumulated here, which, as a result of the degradation of the Yedoma, enter the environment and the Laptev Sea.
The studied soils are shown in Figure 2.

Sampling Strategy
The studied soils are formed in relatively young areas of the Lena River delta (Chay-Ary isl., Buor-Chaya isl., and Shrub isl.); the represented islands have relatively recently escaped the flooding process and are formed under conditions of zonal processes (cryogenesis, peat formation, and peat accumulation).Samples from the islands Chay-Ary, Byor-Chaya, and Shrub were taken from all soil horizons.Botulo-Sise Island is a remnant of the Yedoma, samples for analysis were taken from melted areas of the Yedoma (B1), and a B2 sample was also taken as a background sample for the region.Soil samples were

Sampling Strategy
The studied soils are formed in relatively young areas of the Lena River delta (Chay-Ary isl., Buor-Chaya isl., and Shrub isl.); the represented islands have relatively recently escaped the flooding process and are formed under conditions of zonal processes (cryogenesis, peat formation, and peat accumulation).Samples from the islands Chay-Ary, Byor-Chaya, and Shrub were taken from all soil horizons.Botulo-Sise Island is a remnant of the Yedoma, samples for analysis were taken from melted areas of the Yedoma (B1), and a B2 sample was also taken as a background sample for the region.Soil samples were collected in plastic bags and frozen.The description of the studied soils is presented in Table 1.Note: the soil horizons were described by Guidelines for soil description [28]; soil name was described by world reference base [29].

Methods
The HAs were isolated from organic and mineral horizons of soils according to the method recommended by the International Society for the Study of Humic Substances (IHSS).The basic information on HA extraction is presented in Table 2. Decalcification was carried out with H 2 SO 4 in a ratio of 1:10.The HAs were isolated from 50 g air-dry soil samples by 2-fold extraction with 0.1 M NaOH in a ratio of 1:10 for complete extraction of HAs, after which a saturated solution of Na 2 SO 4 was added to the alkaline extract to coagulate colloidal particles.Then, HAs were precipitated with 1 M H 2 SO 4 , adjusting the pH to 1.0.The HAs were purified from fulvic acids and other low molecular weight compounds by dialysis and dried by heating at 35 • C in a forced convection laboratory oven.
Analysis of the molecular weight distribution of HAs was carried out in the Laboratory of Soil Chemistry of the Institute of Biology (Syktyvkar).Molecular weight (MW) distributions of HAs preparations were obtained on an AKTAbasic 10 UPS chromatographic system (Amersham Biosciences, Sweden) using a SuperdexTM 200 10/300 GL column aliquot volume HA solutions 0.1 cm 3 , elution rate 0.5 cm 3 /min., UV filter wavelength 254 nm.The determination of the working capacity of the gel was carried out using solutions of blue dextran and potassium dichromate at a concentration of 1 mg/cm 3 , the column was calibrated by globular proteins.Previously, solutions of HAs at a concentration of 0.1 mg/cm 3 in 0.1 mol/dm 3 NaOH were purified from low MW compounds by passing through a column filled with Sephadex G-10 gel (crosslinked dextran, fractionation range for globular proteins up to 700 Da).Tris-HCl buffer with pH 8.2 containing sodium dodecyl sulfate (0.1%) was used as an eluate to prevent specific adsorption of HAs on the gel, NaN 3 (0.02%) as an antibacterial agent, and NaCl (0.05 mol/dm 3 ) for constant ionic strength and to prevent overexclusion.The original Unicorn 5.10 program was used to process chromatographic data and calculate the MW distribution of fractions of HAs preparations.The molecular weight fraction is presented in Mr (molecular mass).The total organic carbon (TOC) content in the fine earth was analyzed by Tyurin's methods.The method is based on the wet combustion of the sample by K 2 Cr 2 O 7 solution in sulfuric acid followed by the determination of oxidizer value by titration method using Mohr's salt.Therefore, they are described by MW distribution, from which the average MW is calculated.Depending on the method of calculating the average, three types of average molecular weights are used: number average (Mn) (1), weight average (Mw) (2), and average (Mz) (3).
Number average MW-averaging over the number of molecules in a biopolymer: where, n i is the number of molecules with molecular mass M i .Weight average M W -averaging over the mass of molecules in a biopolymer: where, n i is the number of molecules with molecular mass M i .The average MW is calculated by the equation: where, n i is the number of molecules with molecular mass M i .The polydispersity index (M w /M n ) was calculated from the ratio of M w to M n .Polydispersity-a quantitative characteristic of the degree of deviation of MW distribution from monodisperse, consisting of molecules of the same size-is a consequence of the random nature of the reactions of formation of organic substances, and in some cases, a consequence of the destruction or combination of macromolecules.
Analysis of the MW distribution of HAs was carried out in triplicate.Statistical treatment of the data was carried out with STATISTICA 10.0 software.One-way ANOVA was applied in order to test the statistical significance of differences among the selected groups of the obtained data.Differences were considered to be significant at the 95% confidence level.The calculated mean molecular weight of HA fractions and their molar fractions were provided with standard deviations (X ± SD).

Results and Discussion
MW distribution parameters of HAs extracted from soils and sediments of Yedoma were obtained by size-exclusion chromatography.Three clusters of molecular fraction distribution were distinguished on the obtained spectra: high MW region, medium MW, and low MW (Figure 3).The areas belonging to the different fractions have different areas, which confirms the HA distribution in the three regions.
where, ni is the number of molecules with molecular mass Mi.
The polydispersity index (Mw/Mn) was calculated from the ratio of Mw to Mn. Polydispersity-a quantitative characteristic of the degree of deviation of MW distribution from monodisperse, consisting of molecules of the same size-is a consequence of the random nature of the reactions of formation of organic substances, and in some cases, a consequence of the destruction or combination of macromolecules.
Analysis of the MW distribution of HAs was carried out in triplicate.Statistical treatment of the data was carried out with STATISTICA 10.0 software.One-way ANOVA was applied in order to test the statistical significance of differences among the selected groups of the obtained data.Differences were considered to be significant at the 95% confidence level.The calculated mean molecular weight of HA fractions and their molar fractions were provided with standard deviations ( ± ).

Results and Discussion
MW distribution parameters of HAs extracted from soils and sediments of Yedoma were obtained by size-exclusion chromatography.Three clusters of molecular fraction distribution were distinguished on the obtained spectra: high MW region, medium MW, and low MW (Figure 3).The areas belonging to the different fractions have different areas, which confirms the HA distribution in the three regions.The MW distributions obtained are shown in Table 3.The molecular weight distribution curves have two pronounced peaks, in high and low molecular weight regions.The share of the high molecular weight fraction is from 3.4 to 9.8% with Mr 299-327 kDa.The The MW distributions obtained are shown in Table 3.The molecular weight distribution curves have two pronounced peaks, in high and low molecular weight regions.The share of the high molecular weight fraction is from 3.4 to 9.8% with Mr 299-327 kDa.The highest content of the high-molecular weight fraction is observed in the upper CHA1 horizon (0-10 cm), and the lowest value is observed in the same profile at the boundary with permafrost rocks.A similar distribution is observed in the other studied profiles (BH 2, CHA 2, CHA 3, Si 1), which may indicate the fact that high MW fragments may transform into low MW ones as a result of organic matter transformation and cryoturbation processes.In the background sample B 2 the content of a high MW fraction is 5.5% (Mr 325 kDa).This generally corresponds to the values of MW distribution from the islands, which are less affected by zonal soil formation processes.The sample from Yedoma (B 1) has Mr 300 kDa (6.1%) and is quite close in molecular weight to sample CHA 1 (37-43 cm), which is also represented by buried organic matter at the boundary with permafrost rocks.The average MW fraction ranged from 30.2 to 39.6% with Mr 20.6-28.8kDa; the highest content of the average MW fraction was observed in the sample from Yedoma (B 1).A decrease in the content of the medium MW fraction was observed in the CHA 1, BH 2, and CHA 3 profiles, whereas in CHA 2, Si 1, an increase in the content of the medium MW fraction with depth was observed.The low MW fraction predominates in the studied samples and amounts from 54.3% (B1) to 67.1% (CHA 3 (31-42 cm)) and Mr is from 1.4 to 1.9 kDa.Considering the intraprofile distribution we can note that in profiles BH 2, CHA 1, CHA 3 the content of low MW fraction increases, in profiles CHA 2, Si 1 the content of low MW fraction decreases.In the background plot B 2, the content reaches 60.5%, while in the sample from Yedoma, the content is the lowest, which may indicate a relatively low degree of transformation of organic matter in frozen conditions.However, in modern soils with active processes of soil formation and transformation of organic matter, an increase in the low MW fraction is noted.
A characteristic feature of the studied soils is a decrease in the content of high MW fraction, which may be associated with active processes of transformation of organic matter subjected to cryogenic processes.The buried organic matter in the studied soils is characterized by an increased share of low MW compounds, compared to the middle and humus-accumulative horizons.Taking into account the fact that the underlying horizons are more actively affected by cryogenic processes (prolonged stay in the frozen state, cryoturbation), the active transformation of humus substances occurs.The underlying layers have a more aromatic nature due to the evolutionary selection of the most stable structures [30].The low MW of the low-molecular fraction indicates their better solubility and migration capacity, which is generally confirmed by the processes occurring in cryogenic soils.At the same time, hydromorphic soils (BH 1, Si 1, and Yedoma B 1 deposits) which are close to the water table are characterized by a relatively low content of the low MW fraction and an increased content of the medium MW fraction, which may be due to a low degree of microbiological activity, as well as to reduction conditions.A decrease in the MW leads to changes in the physical properties of polymers (density, viscosity, and strength); thus, HAs formed at the boundary with frozen rocks have a greater migration capacity and may migrate to deeper layers of frozen rocks due to freezing/thawing processes.
HAs are polydisperse systems, which means that the number and size of monomers combined into a chain in the polymer are different everywhere.We used the number average MW (M n ), weight average MW (M w ), and average MW (M z ) to evaluate polymers.According to data obtained from the M n index, we can conclude that the average number of molecules contained in the polymer is observed in CHA 2 (21-25 cm) with the highest Mr 42.9 kDa, the lowest average number of molecules is observed in CHA 1 (37-43 cm) with 17.7 kDa.In general, we can note the decrease in the M n index among all the studied HAs, except for the profile of CHA 2. From the index Mw, we can note that the highest average polymer weight corresponds to CHA 2 (21-25 cm), as well as the M n , this may indicate active processes of input and transformation of organic residues and formation of high MW compounds.The lowest average mass was noted in samples CHA 3 (31-42 cm) and B 1, 190 kDa and 197 kDa, respectively.We have already noted that low MW compounds actively accumulate at the permafrost boundary, which may indicate their high migration ability.The polydispersity index (M w /M n ) is an important indicator used in the estimation of HAs by the molecular method.The high polydispersity index corresponds to natural polymers since in artificial polymers this index is significantly lower.Thus, the greatest value of the index of polydispersity has HA extracted from the horizon CHA 1 (37-43 cm), the lowest index value noted in the upper horizon CHA 1 (0-10 cm).Overmoistened horizons, (BH 1, BH 2 (18-43 cm), B 1, Si 1 (20-45 cm)) are characterized by relatively low values of the polydispersity index, which may indicate a weak rate of organic matter transformation and polymerization.The study of the structure of HAs has a long history and to date, there is no clear answer to the questions of HA formation and how the qualitative composition of HA affects its ability to biodegradation [27].The data we obtained are in accordance with those obtained from peat soil in the European part of Russia [31].The content of the high-molecular fraction in peat soils varies from 0.83 to 3.65% with Mr 367.9 to 418 kDa.At the same time, the dominance of low MW fraction is noted, its content reaches 79.88% with Mr 1.05 kDa.However, the polydispersity index is much wider in contrast to the studied soils and reaches 24.4,high polydispersity of polymers may indicate that the HAs is less resistant in the environment, the lower polydispersity index, and the higher strength of polymers to physical stresses [32].The issue of the quality and stability of organic matter under cryogenesis is one of the most important, as climate change on the planet can lead to a significant transformation of the planetary surface [11].A comparison of results of gel chromatography and nuclear magnetic resonance, presented in work by Vasilevich [31], revealed a significant statistical relationship between the proportion of the low molecular weight fraction of HA and the content of aromatic structures, which indicates that low molecular weight HAs can be stable in the environment.Buried organic residues, in terms of microbial properties confirm our results; the buried layer has lower nitrogen mineralization, microbial biomass, and lower values of microbial respiration compared to the upper organomineral horizons [33].Our earlier data on 13 C NMR spectroscopy of buried horizons in soils of the Lena River delta indicate that, under humid conditions, the content of aromatic substances is higher in buried horizons than in the upper organomineral horizons, but their content decreases in drained positions [34].The increase in the proportion of low MW compounds may be related to the formation of humin (an organic substance firmly bound to clay particles and insoluble in acids and alkalis).The humic content in SOM can be up to 50%, and its age can exceed 1000 years according to 14 C dating [35].Organic matter in clay organomineral aggregates is part of the passive pool of organic matter in the soil and has a higher turnover time in the environment as a result of a low degree of biodegradation [36].The development of a database on the qualitative composition of SOM in cryogenic soils is an important task for researchers, as it will allow a more accurate assessment of transformation processes in modern soils and Pleistocene sediments of the Yedoma [37].

Conclusions
The results of the molecular distribution of HAs of cryogenic soils and Yedoma sediments were obtained for the first time.The study revealed that the low MW fraction of HAs prevails in the composition of HAs up to 66.4% in the buried soils.It is noted that the content of low MW fraction increases with depth and maximum in the buried soil horizons.The Yedoma deposits are characterized by a relatively low number of average MW up to 29.1 kDa, compared with modern soils up to 43.1 kDa, but they also show the predominance of the low MW fraction in the composition of HAs.In the Yedoma sediments, the highest content of the medium MW fraction, up to 39.6%, was observed, which may indicate a low rate of transformation of organic matter in long-term permafrost conditions.Based on the polydispersity index data, we noted that soils formed in the hydromorphic positions of the landscape and Yedoma deposits are characterized by a narrow M w /M n ratio, which indicates their relative resistance to dynamic processes of freezing/thawing.
Author Contributions: E.A., E.L. and R.V. conceptualization, E.A. funding, V.P. expedition with fieldwork and soil sampling; V.P. and E.A. wrote the paper, E.L. and R.V. analysis of HAs.All authors have read and agreed to the published version of the manuscript.
Funding: This work was also supported by the Ministry of Science and Higher Education of the Russian Federation in accordance with agreement No. 075-15-2022-322 date 22 April 2022 on providing a grant in the form of subsidies from the Federal budget of Russian Federation.The grant was provided for state support for the creation and development of a World-class Scientific Center "Agrotechnologies for the Future".

Figure 2 .
Figure 2. The studied soils and Yedoma deposits from the Lena River delta.

Figure 2 .
Figure 2. The studied soils and Yedoma deposits from the Lena River delta.

Figure 3 .
Figure 3. MW distribution of HAs isolated from soils of the Lena River delta.

Figure 3 .
Figure 3. MW distribution of HAs isolated from soils of the Lena River delta.

Table 1 .
The study soil description.

Table 2 .
The basic information about HAs extraction.

Table 3 .
The distribution of MW in soils of the Lena River delta.
SD-standard deviation, M n -number average MW, M w -weight average MW, M z -average MW, M w /M n -polydispresity index.