Eco-Geochemical Assessment of the Content of Pollutants in Hummocky Bogs of the Kola Peninsul

    The results of eco-geochemical survey of hummocky bogs of the Kola Peninsula at the southern border of their area showed that the climate changes in the recent 60–80 years and the impact of aerotechnogenic pollution did not affect the area of hummocky bog complexes and the depth of the thawing peat layer of conventionally reference and impact high-moor bogs. In the zone affected by the emissions from the Severonikel smelter (Monchegorsk), the content of Ni and Cu in the peat high-moor soils (Cryic Ombric Fibric Histosols) is 60–90 times higher than the level of accumulation of the same metals in the peat of conventionally reference bogs. The S, Cd, Cr, and Pb contents in the compared bog massifs did not differ significantly. In the frozen horizon of the impact bogs, the Ni and Cu content was significantly greater (~ 2 times) than their content in the same layer of the conventionally background bogs, which indicates a vertical migration of pollutants down the peat profile and a deeper technogenic transformation of cryogenic massifs due to the effects of atmospheric emissions from the plant. The profile distribution of pollutants (Ni, Cu, Pb, S, Cr, and Cd) in the peat layer of the impact and conventionally background bogs has its own specific features. Keywords: palsa, peat high-moor bog soils, Cryic Ombric Fibric Histosols, aerotechnogenic pollution, ash composition of peat, heavy metals
DOI: 10.1134/S106422931812002

    On the Kola Peninsula, although it is almost entirely located to the north of the Arctic Circle, there is no real permafrost, and permanent glaciers are practically absent due to the influence of the northern Gulf Stream branch. Nevertheless, on the peninsula, as in other regions of Northern Fennoscandia with the average annual air temperature of –1…–2°C [41], bog systems composed of hummocky–fen massifs with permafrost in the hummocks are distributed. According to the international classification, such bogs are called “palsa” (the term of Lappish origin). The specific features and genesis of hummocky–fen bogs were studied in detail for different regions of the world: Alaska, northern Canada, northeastern and western Siberia, and Fennoscandia, including the Kola Peninsula [8, 11, 12, 14–18, 21, 22, 28–32, 34, 36, 40, 43, 47–54, 56].
    The permafrost in peat hummocks on the Kola Peninsula is not a relic of the last glaciation (10– 12thousand years ago). Based on the palynological analysis of peat from hummocky bogs at Lake Nyud’yavr near Monchegorsk, Blagoveshchenskiy [12] dates their formation approximately 3000 years ago, by the end of the post-Littorina time, i.e. about 3000 years ago. The analysis of the spore–pollen diagrams of the peat supplied by a series of radiocarbon dates for bogs of the Lovozero Plain on the Kola Peninsula indicated that the formation of hummocky–fen complexes passed six stages. During the third stage (about 4000 years ago), a dissection of the microrelief and formation of permafrost began, and this process ended about 2000 years ago [14, 15].
    In literature, the causes and ways of the formation and transformation of hummocky–fen complexes are considered [17, 18, 22, 24, 30, 31, 34]. The discussion of these issues is not the task of this work. We note only that, in the opinion of Koptseva et al. [22], the current climatic conditions on the Kola Peninsula do not promote the maintenance of existing and newly forming cryogenic forms of the bog relief. Apparently, the most probable result of the hummocky frozen bogs degradation in this region will be the formation of hummocky–ridge bogs in their place with the dominance of dwarf shrub-moss associations [22]. The southern boundary of palsa bogs on the Kola Peninsula passes approximately at the latitude of Monchegorsk (67°50? N), along the northern coast of Vite Bay of Imandra Lake) [12, 23, 35, 36], where terrestrial ecosystems, including bog ecosystems, are subjected to aerotechnogenic pollution.
    This article focuses on the analysis of the content of chemical elements in the peat layer and frozen horizon of hummocky-fenny bog complexes at their southern boundary on the Kola Peninsula, which are influenced by atmospheric emissions of the Severonikel smelter (Monchegorsk). The aims of this work were to find out, what kinds of transformations occur in cryogenic bog massifs under aerotechnogenic pollution; to determine the depth of technogenic fluxes and their distribution by horizons of the peat layer; to quantify the local level of technogenic pollution of hummocky peatlands; to perform an ecological–geochemical analysis of the chemical elements contents in the peat of bogs and their frozen horizons.

The investigated region is located in the center of the Kola Peninsula in the northern taiga and the forest zone adjacent to the tundra. A larger part of this territory belongs to the Lapland State Natural Biosphere Reserve; in the eastern part, industrial enterprises are located, such as the Severonikel smelter (Monchegorsk), the railway connecting the city of Murmansk with other regions of Russia, the federal highway E18 (Murmansk–St. Petersburg), open quarries, and oredressing plants of the cities of Olenegorsk and Apatity. The main contribution to the pollution of natural ecosystems on the Kola Peninsula is made by acidforming sulfur compounds and heavy metals (HM) entering the atmosphere as part of the emissions of the largest in Europe copper–nickel integrated plant Severonikel, which is included into the Mining and Metallurgical Company Norilsk Nikel [44]. This plant using local low-sulfur ores came into operation in 1939 [33, 45]. After the depletion of local ore reserves in the late 1960s, the plant began to use high-sulfur ore (up to 30%) of the Norilsk deposit, which led to a sharp increase in the volume of atmospheric sulfur dioxide emissions and associated solid substances to 220– 250thousand tons per year. Since 1998, the smelting shop of ore raw materials stopped working, which led to a sharp reduction in the amount of SO2 emissions to 35–40 thousand tons per year and of metal emissions by more than twice. According to the latest data, the annual volume of emissions of SO2 and solids from the Severonikel smelter is 37.3 and 2.7 thousand tons per year, respectively [13]. In the fine-dispersed polymetallic dust, sulfides and metal oxides predominated, as well as metallic Ni and Cu [2, 42] particles. In addition, it contained iron oxides and calcium, magnesium, aluminum silicates. In the flat territory of the Kola Peninsula, low-productive lichen and dwarf shrub–green moss spruce and pine forests predominate on the Al-Fe–humus soils (Folic/Histic Albic Podzols, according to the WRB classification). Pine and spruce forests occupy about 40 and 30%, respectively; 30% of the area are bogs and wetlands with bog soils. According to the origin, moistening and ash content, peatbog soils and peat gleyzems are divided in three groups: high-moor (oligotrophic), transitional, and low-moor (eutrophic) [20]. The following horizons are distinguished in the profiles of the peatbog soils (Histosols in the WRB classification): TO–TT in the low-moor soils and TE–TT in the transitional soils.
    The surface organic horizon consists of live mosses, plant roots and falloff, which corresponds to the composition of the ground cover. The yellowish brown, brown, or dark brown peat TO horizon of the high-moor soils is composed of peat of low and medium degree of decomposition. The TE peat horizon of the low-moor and transitional bog soils is brown, dark brown, sometimes black; it consists of peat decomposed to the low (transitional bogs), medium or high degrees. In the peat soils, the thickness of the TO(TE) horizon is 50 cm. With depth, it passes to the organic TT layer. The diversity of lowmoor biogeocenoses determines the high variability of their moisture conditions, botanical composition of peat, chemical properties, and density. In the peat gley soils (peat gleyzems–Histic Gleysols, according to the WRB classification) of highmoor, transitional and low-moor bogs, the organic TO (TE) horizon is underlain by a dove–gray, bluish dove or olive–gray mineral gley massive G horizon. Peat and peat gley high-moor bog soils are confined to watersheds and terraces with gentle slopes and weakly dissected surface. They develop under stagnant moisture regime influenced by fresh or weakly mineralized precipitation water without the effect of groundwater.
    The soils of the high-moor bogs are strongly acid (pHKCl 2.5–3.8) and base-unsaturated (up to 90%). Peat is characterized by low ash content (2.0–6.5% per dry matter), low density (0.03–0.10 g/cm3) and very high moisture capacity (up to 1000%). Low-moor and transitional bogs are formed, as a rule, in subordinate elements of the landscape: depressions, lowlands, drain troughs, and river valleys. They are formed under the influence of mineralized groundwater. The peat and peat gley soils of low-moor and transitional bogs have a weakly acid or neutral reaction (pH 4.0–6.5), base saturation of up to 80%, and the ash content of 5–15% per dry matter. The moisture capacity of the peat low-moor soils rarely exceeds 100%. However, in peat of the transitional bogs it can reach 500% [20]. On the Kola Peninsula, vast complex bogs of the aapa type refer to the bogs of the transitional type. They are extensive, have great, strongly watered twisty hollows, with sharply pronounced ridges of 1.0–1.5 m high, on which vegetation inherent to the high-moor sphagnum bogs develops. These bogs are often called complex hummocky–ridge.

High-moor bogs on the Kola Peninsula, including ice lenses in palsa, are the object of this research. The typical vegetation of high-moor bogs with the hummocky surface is represented by sparse pine forests, dwarf birch, ledum, blueberry, fen berry, sedges, sphagnum and green mosses, and lichens. The soils belong to the peat oligotrophic type (Cryic Ombric Fibric Histosols, according to the WRB classification). A schematic map of sampling peat oligotrophic soils is shown in Fig. 1; the coordinates of the peat sampling points and a brief description of the studied hummocky bogs are given in Table 1. Under the impact of atmospheric emissions of the Severonikel smelter, on some bogs (sampling points 1–7), the vegetation was completely eliminated. Only dry fallen tree trunks and dry stumps were found. On the other bogs, the living ground cover with rare short pine trees, dwarf birches and willows was described.
    In September of 2002–2003, in randomly located 10–15 points of the bog, the depth of the upper boundary of the permafrost in hummocks was measured using a steel probe. Samples of peat and ice lenses were taken from the surface deep into the peat layer every 5 or 10 cm. Roots and other inclusions were removed from the samples that were dried at room temperature and analyzed. After fusing the sample with a mixture of lithium carbonate and boric acid at 970°C and leaching with 0.7 M HCl, the content of Ni, Cu, Co, Fe, Pb, Cr, Mn, Sr, Cd, Na, K, Ca, Mg, Al, and As was determined by the atomic-emission method with inductively coupled plasma using a Prodigy7 spectrometer.

The sulfur content was measured after combustion of the sample at 1350°C, absorption of released sulfur dioxide with water, and titration with iodine. The relative error in the determination of each metal did not exceed 10–15%, the error of the definitions corresponded to the norms for determining the chemical composition of mineral raw materials in accordance with the third category of accuracy (OST41-08-212-04). The control of the accuracy of the results was carried out in accordance with OST41-08-214-04 and 41-08-265-04. The statistical processing of the analytical results was carried out using the Statistica 10.0 package. To assess the reliability of the differences, the nonparametric Kruskal–Wallace (H) and Mann–Whitney (z) criteria were used. The tables and figures present the average values with standard errors.

According to publications [1, 12, 40], bog hummocks on the Kola Peninsula thaw by the end of summer to the depth of 30–55 cm. The upper boundary of permafrost in a bog near Lake Nyud’yavr (point 2) in 1936 was at the depth of 35–60 cm; in 2002, 45– 70cm; near the Yagelnyi Bor (point 9) in 1920 and 2002, the depths were 55–93 and 40–75 cm, respectively. Under the impact of aerotechnogenic emissions from the Severonikel smelter, the vegetation on bogs 1–7 was destroyed almost completely; in natural conditions, vegetation affects the absorption and emission of heat by peat hillocks—palsa [11, 27, 37, 47]. The measurement of the peat layer thickness in 2002 and 2003 showed that the depth of thawing was 35–75cm regardless of the presence or absence of vegetation in the bog.
    The height and number of hummocks on bogs 2 and 9 did not change for 66 and 82 years. Unfortunately, we do not have measurements for such long periods in other bogs, but if to judge by the remained stumps and dry trunks, the height of the hummocks did not change in any bog, despite the disappearance of vegetation. In the impact bogs, on all hummocks without vegetation, dry trunks and stumps of pine trees were preserved. By the time of the death of these trees, their age determined by counting the annual rings of dry trunks was 150 years. By our observations, trees perished about 30 years ago, in 1973–1975, due to effects of aerotechnogenic emissions of the Severonikel smelter.
    Consequently, the mean age of trees on hummocks of the bogs studied was about 200 years. It is worth of noting that the root system of all trees on the impact bogs is clearly limited to the depth of 45–50 cm, that is, the level of permafrost in the palsa. Thus, one can suggest that 200years ago the depth of thawing of the peat layer did not differ much from the depth observed at present. Thus, the comparison of the results of surveys performed in 1920–1935 and 2002–2003 showed that over the last 60–80 years, the area of hummocky peatlands with a permafrost core on the Kola Peninsula did not change both on the conventionally reference bogs and the impact ones. According to the Mann-Whitney criterion, the depth of the thawing (active) peat layer by the end of summer did not differ significantly between the impact and conventionally reference bogs (z = –0.50, p = 0.62) and averaged 54.6 ± 2.0 and 55.2± 4.6 cm, respectively. Thus, aerotechnogenic pollution does not have a significant effect on the cryogenic massifs of the investigated bogs on the Kola Peninsula. At the same time, in the Nadym region of Western Siberia, the removal of the plant cover along the gas pipeline route resulted in an increase in the thickness of the seasonally thawed layers in all the studied natural complexes [27].
    In the opinion of some specialists [28, 29, 31], the preserved cryogenic bogs have practically ceased now to develop, the accumulation of peat has slowed down or completely stopped, the processes of erosion and destruction of peat hummocks take place. The current destruction of peat hummocks occurs mostly owing to wind erosion and thermal erosion, but it practically does not lead to the development of thermokarst; in this case, the peat mineralization may increase under aerobic conditions against the background of permafrost degradation [29, 31]. In the Nadym region of Western Siberia, under the influence of air temperature increase (by 0.04°C per year), the seasonally thawed layer became thicker, the temperature of the sediments increased, single birch, pine and cedar trees appeared on the peatlands, and the occurrence, height, and projective coverage of shrubs increased [27]. At the same time, in the Kola Peninsula, the preservation of the area of hummocky–fenny bog complexes and the depth of the thawed peat layer by the end of summer appears to show the absence of the climate warming effect in the last 60–80 years under prominent fluctuations in air temperature from year to year [43]. Some researchers believe that in natural, anthropogenically undisturbed conditions, frozen hummocky peatlands are stable ecological systems, despite the climate warming [29].
    The average HM content in the thawing layer of the hummocky bogs with the living ground cover that we referred to the conventionally background bogs was 19± 8 mg/kg for Ni, 13 ± 5 for Cu, 2.2 ± 1.2 for Cr, and 8.2 ± 2.8 mg/kg for Pb. These values are compared to those of the HM content in the background peatlands of the Noril’sk industrial region [16]. Despite the lower HM concentrations in the frozen horizon (Ni = 9.6 ± 3.8, Cu = 6.9 ± 1.7, Pb = 3.5 ± 1.5 mg/kg) relative to the thawing peat layer, there were no significant differences in their content (Mann-Whitney criterion z = –0.48–1.07, p = 0.28– 0.91). The average sulfur content in the thawing peat layer (1225 mg/kg) is similar to its concentration in the frozen horizon (1040 mg/kg) (z = 2.0, p = 0.046). The very wide range of HM content variation was noted both in the thawing and frozen layers of the conventionally background bogs; the variation coefficients of all the HM concentrations exceeded 100% (Tables 2, 3). The sulfur content in the same samples varied to a lesser degree.
    The level of HM contamination of the peat hummocky bogs in the zone subjected to atmospheric emissions from the Severonikel smelter differed significantly from the level of accumulation of the same metals in the peat layer of the conventionally background bogs. The content of the main pollutants in the thawing peat layer of the impact hummocky–fenny bogs averaged 1120 ± 355 mg/kg for Ni, 1135 ± 250 for Cu, and 1980 ± 355 mg/kg for S, that is, 60, 87 and 1.8times, respectively, more than their concentrations in the peat layer of the conventionally background bogs. The sulfur content in the compared bogs was not different (z = 1.05, p = 0.29), as well as the average content of Cd, Cr, Pb (z = 0.92–2.95, p = 0.18–0.36). In the frozen horizon of the impact bogs, the content of Ni and Cu was (~2 times) greater than that in the same layer of the conventionally background bogs. The variation range of HM concentrations in the thawing peat layer of the impact bogs was very wide; the variation coefficients were in the range of 115–215%.

For the cryogenic horizon of the same bogs, the variation in HM content was lower (coefficients of variation were 50–70%). Some other authors [16] also noted the high variability of the HM and sulfur contents in the thawing layer of the hummocky peatlands in the Noril’sk industrial region, where the variation coefficients were 80–260%. Among the impact bogs, the lowest heavy metal concentrations were characteristic of the hummocky– fenny bog located at Lake Nyud (Fig. 1, point 2; Table2), where the average Ni and Cu contents in the thawing peat layer exceeded the regional background concentrations of heavy metals in the podzols (4.3 and 5.5 times, respectively). In the rest bogs without ground cover, the Ni and Cr contents little differed, but they were higher than the regional background values in the podzols by 24 and 39 times, respectively.

The Cr and Pb concentrations in the thawing peat of the impact bogs strongly varied, but remained much lower than the regional background values. The average sulfur content in the peat of the impact bogs varied from 1370 to 3625 mg/kg and did not significantly differ from its concentration in the frozen horizon (1650mg/kg) (z = 0.64, p = 0.52). Unlike the S content, the Ni, Cu, and Cr concentrations were higher in the thawing peat layer as compared to the frozen horizon (z = 0.98–3.12, p = 0.002–0.047). The distribution of pollutants within the profile of the peat layer has its own features both for various chemical elements and for the impact and conventionally background bogs. The maximum concentration of almost all the heavy metals investigated was found in the uppermost peat layer of the impact and conventionally background hummocky bogs, which confirms their anthropogenic origin. In bogs without plant cover in the impact zone, the average HM content was 17 (Cr)– 2290 (Cu) times higher in the uppermost thawing peat layer than in the lowest one. In the conventionally background bogs with the live ground cover, this characteristic was 11(Cu)–21(Ni) timer greater in relation to the same layer. According to the Kruskal–Wallis criterion, the concentration of Ni, Cu, Cr only differed significantly over the peat layer of the impact bogs (H = 16.9–27.4, p = 0.0006–0.03); for the conventionally background bogs, these differences were found only for Ni and Cu (H = 12.6–13.0, p = 0.01).
    The S, Cd, and Pb concentration did not differ significantly over the whole thawing peat layer, however, their vertical distribution varied. The content of Ni, Cu, and Pb along the profile of the conventionally background peatland and of Ni, Cr, and Pb in the impact bog decreased abruptly from the uppermost to the lower layers; the contents of other pollutants (S, Cd) decreased more evenly. In the impact bogs, the Cu content decreased with depth more gradually as compared with its profile distribution in the peat layer of the conventionally background bogs. For some elements (Cd, Cr for conventionally background bogs and S, Pb for impact bogs), the distribution along the profile had anomalies, their contents in the frozen horizon were greater or equal to their content in the lowest peat layer. The anomalous distribution of Cu and Zn along the profile of the peat layer in the Vydrinskiy bog (southern Baikal region) is noted in [4].
    The authors suggest that in the Holocene, along with atmospheric emissions, there was an additional source of chemical elements—deep thermal waters. In the surface layer (0–5 cm) of the peat in the conventionally background hummocky bogs, the Ni and Cu concentrations were comparable with the regional background values in the soils, while the content of the other heavy metals was much lower. The lower layers of the thawing peat layer contained smaller HM amounts, the concentrations of which did not differ from their content in the frozen horizon (Fig. 2). In the same layer of the impact hummocky–fenny bogs, technogenic HM flows affected the deeper layers (Fig. 3).
    For example, the Ni and Cu content in the thawing layer exceeded their regional background concentrations in the soils up to the depth of 30–40 cm. At the depth of 20–30 cm, the Ni and Cu content was 137 and 26 times higher in the peat layer of the impact bogs compared with that in the conventionally background bogs. The data on the accumulation of main pollutants in the frozen horizon of the hummocky bogs is of special interest. Fig. 4 presents the HM content in this horizon of the impact and conventionally background bogs. The Ni and Cu concentrations were much (1.7– 2 times) higher in the frozen horizon of the bogs without the plant cover relative to their content in the same horizon of the bogs with the living ground cover (z = 2.2–2.6, p = 0.008–0.03).
    There were no differences in the Cd, Cr, and Pb contents in the frozen horizons of the compared bogs. The S content was also much greater in the impact zone as compared to the conventionally background peatlands (z = 2.53, p = 0.011). The significantly higher concentrations of the main pollutants (Ni, Cu, S) in the frozen horizon of the impact bogs with respect to those in the conventionally background bogs indicate a vertical migration of the pollutants down the peat profile and a deeper technogenic transformation of the cryogenic massifs in the zone subjected to the effect of emissions from the Severonikel smelter. It is known from geocryology that between the thawing peat layer and the permafrost layer there is a so-called transition layer, which can thaw once in some (from tens to thousands) years, and this layer is in the frozen state most of the time [39].
    The thickness of this most dynamic layer, its composition, spatial variability and other characteristics were largely due to the cryogenic soil formation and to a large extent determine a response of the soil and its upper permafrost layer to fluctuations in climatic conditions and the effect of anthropogenic loads [25, 46]. It is this temperature regime of peat substrate that can cause penetration of pollutants into the permafrost layers of impact peatlands. The increase in the HM content in the upper layers of the peatbogs caused by various types of anthropogenic activities (land reclamation, pollution from highways, cities, industrial enterprises) is noted in a number of works [5–7, 10, 16, 26]. Similar data were also obtained for the upper organic soil horizons in the zone subjected to atmospheric emissions of non-ferrous metallurgy enterprises even under a sharp reduction in aerotechnogenic loads [3, 9, 19, 26]. The ash composition of peatbog soils is of interest in studying the geochemical background of atmospheric aerosol for a long period, as well as in the investigation of migration flows of chemical elements in the process of peat accumulation.
    The results of our studies showed an ambiguous picture of chemical accumulation along the depth of the peat layer in the conventionally background and impact hummocky bogs (Table 4). The high degree of variation in the content of chemical elements in the thawing peat layer and permafrost horizon of the bog soils, which is not associated with aerotechnogenic pollution was noted by other researchers [5, 6, 24]. This fact allows one to characterize only some trends in migration flows of inorganic peat components. The distribution of almost all investigated elements (Fe, Al, B, Mn, Na, Zn, Mg) along the peat layer of the conventionally background bogs was approximately uniform, and their content did not differ significantly from that in the frozen horizon. Concentrations of K, Ca, P decreased with the depth of peat sampling in these bogs (H = 9.2–9.6, p = 0.022–0.027), but only the P content was significantly lower in the frozen horizon compared to the thawing peat layer (z =3.4, p = 0.0003).

The content of Fe, K, and P (z = 14.1–15.6, p = 0.03– 0.05) decreased reliably along the profile of the peat layer in the impact bogs. The concentrations of other elements were not different, but for Ca content, there was a tendency of increase from the upper to the lower peat layer, which is not statistically confirmed. In addition, there is no difference in the content of all the chemical elements investigated in the thawing peat layer and frozen horizon of the impact bogs. The comparative analysis of chemical elements content in the peat layer of the conventionally background and impact bogs, as well as in the frozen horizons of the same bogs revealed the absence of significant differences in the concentrations of all the elements studied, with the exception of Mn, Na, Zn.
    This fact showed that aerotechnogenic emissions did not affect the ash content of the peat. The quite stable composition of inorganic components in the peat and frozen horizon of the bog soils appeared to be due to the weak leaching of these elements compounds by atmospheric precipitation from the upper layers and their weak migration to the underlying horizons. However, some researchers point to the uneven (often anomalous) accumulation of many elements with depth related both to the migrational and depositional features of elements, the botanical composition of peat, hydrological characteristics of bogs, and the mineralogical composition of the parent rock [4–6, 55].

The results of the ecological–geochemical research of hummocky bogs on the Kola Peninsula allow concluding that the preservation of the area of hummocky-fenny complexes and the depth of the thawing peat layer in conventionally reference and impact high-moor bogs can indicate the absence of the influence of aerotechnogenic emissions and climate warming over the past 60–80 years, despite the large variations in air temperature from year to year. The average content of heavy metals (Ni, Cu, Pb) in the thawing peat layer of the hummocky bogs with the living ground cover belonging to conventionally background ones was much smaller than the regional background values in podzols. It is comparable to their concentrations in the background hummocky bogs of the Noril’sk industrial region; the sulfur content was much lower.

The average content of heavy metals (Ni, Cu, Pb, Cd, and Cr) and of almost all the investigated elements (Fe, Al, B, Mn, Na, Zn, Mg) in the thawing peat layer of the conventionally background bogs did not differ significantly from that in the frozen horizon. The level of Ni and Cu pollution of the thawing peat layer in the hummocky bogs of the zone subject to emissions of the Severonikel smelter exceeded by 60– 90 times the accumulation of the same metals in peat of the conventionally background bogs. The S, Cd, Cr, and Pb content did not differ. The average Ni and Cu content in the thawing peat layer was higher than their regional background concentrations in the podzols by 24 and 39 times, respectively, which indicated a high and very high level of HM contamination of the peatbog soils. In the permafrost horizon of the impact bogs, the content of Ni and Cu was significantly (~2 times) higher than their content in the same layer of the conventionally background bogs. There were no differences in the content of Cd, Cr, Pb in the frozen horizons of the compared bogs. The S concentration was also higher in the impact zone as compared with the conventionally background peatlands.
    The profile distribution of Ni, Cu, Pb, S, Cr, and Cd in the peat layer had specific features both for different chemical elements and for impact and conditionally background bogs. The highest concentrations of almost all heavy metals studied were found in the surface peat layer of the impact and conventionally background hummocky bogs, which confirms their anthropogenic nature. The content of Ni, Cu, and Pb along the profile of the conventionally background peatland and of Ni, Cr, and Pb in the impact bog decreased abruptly from the surface to the lower peat layers; the content of S and Cd decreased more uniformly. For the content of Cd and Cr (conventionally background bogs) and S, Pb (impact bogs), an anomalous distribution along the peat profile was noted: their content in the frozen horizon was higher or equal to their content in the lowest peat layer. In the thawing peat layer of the impact hummocky–fenny bogs, technogenic flows of heavy metals affected deeper layers. The higher concentrations of the main pollutants (Ni, Cu, S) in the frozen horizon of the impact bogs with respect to these values in the conventionally background bogs indicated a vertical migration of pollutants down the peat profile and a deeper technogenic transformation of cryogenic massifs in the impact zone subjected to the emissions of the Severonikel smelter.
    The effect of aerotechnogenic pollution on the ash composition of the thawing peat layer and frozen horizons in the conventionally background and impact bogs was not revealed since there were no significant differences in the concentrations of almost all the elements investigated. It is necessary to emphasize the high degree of variation in the content of pollutants and other chemical Cu, Pb, Cd, and Cr) and of almost all the investigated elements (Fe, Al, B, Mn, Na, Zn, Mg) in the thawing peat layer of the conventionally background bogs did not differ significantly from that in the frozen horizon. The level of Ni and Cu pollution of the thawing peat layer in the hummocky bogs of the zone subject to emissions of the Severonikel smelter exceeded by 60– 90 times the accumulation of the same metals in peat of the conventionally background bogs.
    The S, Cd, Cr, and Pb content did not differ. The average Ni and Cu content in the thawing peat layer was higher than their regional background concentrations in the podzols by 24 and 39 times, respectively, which indicated a high and very high level of HM contamination of the peatbog soils. In the permafrost horizon of the impact bogs, the content of Ni and Cu was significantly (~2 times) higher than their content in the same layer of the conventionally background bogs. There were no differences in the content of Cd, Cr, Pb in the frozen horizons of the compared bogs.
    The S concentration was also higher in the impact zone as compared with the conventionally background peatlands. The profile distribution of Ni, Cu, Pb, S, Cr, and Cd in the peat layer had specific features both for different chemical elements and for impact and conditionally background bogs. The highest concentrations of almost all heavy metals studied were found in the surface peat layer of the impact and conventionally background hummocky bogs, which confirms their anthropogenic nature. The content of Ni, Cu, and Pb along the profile of the conventionally background peatland and of Ni, Cr, and Pb in the impact bog decreased abruptly from the surface to the lower peat layers; the content of S and Cd decreased more uniformly.
    For the content of Cd and Cr (conventionally background bogs) and S, Pb (impact bogs), an anomalous distribution along the peat profile was noted: their content in the frozen horizon was higher or equal to their content in the lowest peat layer. In the thawing peat layer of the impact hummocky–fenny bogs, technogenic flows of heavy metals affected deeper layers. The higher concentrations of the main pollutants (Ni, Cu, S) in the frozen horizon of the impact bogs with respect to these values in the conventionally background bogs indicated a vertical migration of pollutants down the peat profile and a deeper technogenic transformation of cryogenic massifs in the impact zone subjected to the emissions of the Severonikel smelter. The effect of aerotechnogenic pollution on the ash composition of the thawing peat layer and frozen horizons in the conventionally background and impact bogs was not revealed since there were no significant differences in the concentrations of almost all the elements investigated. It is necessary to emphasize the high degree of variation in the content of pollutants and other chemical elements in the peat oligotrophic soils unrelated to the impact of aerotechnogenic pollution, but associated with other causes.

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            Translated by L. Kholopova

EURASIAN SOIL SCIENCE Vol. 51 No. 12 2018