Annotation of the results obtained in 2020
Field research was carried out in the Yamalo-Nenets Autonomous Okrug in the northern taiga in the vicinity of the village. Khanymei within the interfluve of the Pyakupur, Chuchuyakha and Apakapur rivers. In the course of the expeditionary work within the large basins, as well as in the floodplain of a small river, the following types of work were carried out: survey of the territory, selection of sites for the establishment of points for a comprehensive biogeochemical survey of ecosystems; complex biogeochemical studies, according to the project program; sampling of water from residual reservoirs within the khasyreys basins; study of the structure of floodplain sediments and placement of CAM sensors (Inflay, Tomsk) for conducting thermometric studies, including those with a GSM module. In total, about 230 soil samples were collected to determine general properties, 143 samples to measure the concentrations of mineral nitrogen. 74 samples were taken to determine the carbon of dissolved inorganic and organic compounds, chlorides, sulfates, nitrates, ammonium ions, as well as the content of truly dissolved and colloidal forms of finding a whole spectrum of chemical elements (Li, B, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Cd, Sb, Te, Cs, Ba, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb, Th, U). To determine the concentrations of CO2 and CH4 in the water, 40 samples of upstream and residual ponds were taken. 63 samples were taken to determine the content of stable isotopes of carbon and oxygen. For 50 water samples, a centrifugal ultrafiltration procedure was applied to obtain a low molecular weight bioavailable fraction. For 33 points, the productivity of plants was determined and an herbarium was collected. Gas flows were measured at more than 40 points. For 31 peat samples, the age of drainage of the basins of thermokarst lakes, as well as the rates of peat accumulation and the formation of rafts, were determined by the radiocarbon method. For 31 peat samples, the age of drainage of the basins of thermokarst lakes, as well as the rates of peat accumulation and the formation of floating mats, were determined by the radiocarbon method. The work covered 9 khasyreys of different ages and degrees of drainage. Ash content and elemental composition were determined for 155 samples of plants, determined to a species or genus, using the ICP-MS method (on an Agilent-7700x mass spectrometer). Silicon was determined spectrophotometrically using ash. The rate of coastal abrasion of swamps was estimated from space images of different times. The contribution of this pool of elements to a possible increase in the bioproductivity of ecosystems in a cascade landscape-geochemical system was estimated, taking into account the possible rates of entry of elements during ice thawing during climate warming. An article in the journal Chemosphere provides an analysis of the literature on the influence of climate warming on elements in frozen peat of bogs. This article presents data on the results of estimating the volume of the reactive pool of elements in frozen bogs stored in dispersed ice. The areas of khasyreys and lakes in the three key areas studied were calculated using Sentinel-2 and Landsat-8 satellite images. Archival satellite images of Corona, as well as topographic maps, were used to determine the time of the appearance of the khasyreis. The analytical processing of the materials that were received in 2018 and 2019 site ("Tazovsky" and "Syoyakha") has been fully completed. AMS-dating of several samples of bottom peat from the "Syoyakha" key site at the Poznan Radiocarbon Laboratory. Laboratory and analytical studies of soil samples from the sites "Tazovsky" and "Syoyakha" were completed, as well as the data obtained for the floodplain of the small river site "Khanymey" in the expedition of 2019. The ICP-MS method analyzed data on soil water samples and samples from surface ponds (background lakes and residual ponds, streams) of the Syoyakha key site. The results of studying the succession processes and the diversity of phytocenoses in the basins of drained thermokarst lakes and floodplains are generalized. At an early stage of overgrowth of khasyreys, cotton grass-sedge plant communities (Carex aquatilis, C. rostrata, Eriophorum polystachyon), sometimes horsetail (Equisetum fluviatile), or arctophiles (Arctophila fulva) are formed on flat, seasonally flooded surfaces. Arctophila fulva is confined to bottom sediments composed of redeposited peat. The herbaceous layer is well developed, the projective cover varies from 30–35% to 80–95%, its height is 70–110 cm. The moss cover is not developed. Reed grass (Calamagrostis langsdorffii) predominates on elevations in the herbage, hypnum mosses have a sparse projective cover (30–40%). Sedge bogs (projective cover 10–30%, height 50 cm) with a developed moss cover of hypnum and sphagnum (2–30%) are formed in closed depressions. Low sandy embankments are occupied by a birch forest up to 6–8 m in height, 10–15 cm in diameter, from pine and cedar, as well as willow. Mountain ash is found in the shrub layer. The herb-dwarf shrub layer in them is sparse (2–5%) of marsh dwarf shrubs, reed grass and sedges, in the moss cover (5–10%) – hypnum and sphagnum mosses, the latter grow in synusia, without forming a continuous cover. The projective cover of the grass stand varies greatly from year to year, which is associated with the general moisture content of the growing season. At the middle stage of overgrowth in plant communities, due to the accumulation of litter, the density of the grass cover becomes less (projective cover 10–20%, height 40–60 cm), the moss cover is better developed (cover from 5–20% to 80–90%) with domaining of hypnum mosses. The participation of sphagnum mosses in some places reaches 10–25%, and even 100% in depressions with stagnant moisture. In moss-reed birch forests on sandy shafts, the cover of dwarf shrubs is higher (up to 15%), the moss cover is better developed (up to 50%) – from hypnum and sphagnum mosses. At the late stage of khasyrey overgrowing, plant communities with a poorly developed grass cover (projective cover 10–15%, height 35–50 cm) of sedges (Carex aquatilis, Carex rostrata, Carex chordorrhiza, Carex limosa, etc.) are formed on flat surfaces, sometimes with horsetail (Equisetum fluviatile). The moss cover in them is well developed (95–100%) – with a predominance of sphagnum mosses. In the form of floating mats, these communities grow inside the residual micro-lakes. On the other hand, as the peat horizons form in the mouth zones of the khasyreys, the entire basin is dammed up. This leads to a partial restoration of the water supply in the basin, which is especially pronounced in wet years. The rise of water leads to the transformation of the succession along the hydromorphone path, the role of sphagnum mosses increases. They grow to the level of parcels, and become edificatory species. Therefore, even early-stage meadows gradually acquire a floating mats appearance. Forests with rare birch, pine and cedar up to 6–7 m in height, up to 10–12 cm in diameter, with a dense layer (25–65%) of marsh dwarf shrubs (Ledum palustre, Betula nana) and a continuous sphagnum cover are formed on the sandy coastal ramparts. The productivity of the aboveground part of herbaceous vegetation decreases from the early (557±349 g/m2) to the middle stage (179±165 g/m2). This is due to the appearance of a moss-dwarf shrub layer in all microlandscapes of the basin and trees on the coastal ramparts and rises of the former lake bottom. In the latter, ANPP (365±241 g/m2) is significantly higher than in the grass layer. Thus, the overall productivity of the early and middle stages does not differ significantly. The productivity of the grass stand depends on humidity, so in the drier June 2017, the flooding height was 20±4 cm lower than in the wetter 2020. In 2017, the ANPP was 860±317 g/m2, and in 2020 it was 557±349 g/m2, reaching 73.2% from the more favorable 2017. The vegetation of the late khasyreys in structure and productivity is close to the communities of a flat-hilly bog. The ash content of the vegetation in the basins of the Khanymei key site increases from early to late stages. This is due to the high content of silicon in the plant ash of late stages, which can be explained by the large participation of mosses, shrubs, and sedges in phytocenoses. Of the biogenic elements at the late stage, there is more potassium and phosphorus. Sodium and lithium accumulate in young khasyreys. This is due to the participation of talik zones of the marginal part of the considered interfluve in their groundwater feeding. The maximum ash content is typical for Equisetum fluviatile, the maximum is 20.8%. In the ash of early khasyreys plants, the content of manganese is higher. This is due to the mineral layers in the lower part of the root zone. In the peat horizons of late khasyreys, there is less manganese in soil solutions. The effect of maximum ash content in late khasyreys contradicts the fact of minimum ash content in sphagnum mosses. A common feature for the two zones is a decrease in the concentration of all elements in the dissolved fraction of natural waters from the khasyreys to the lakes, in the accumulation of which the biogenic factor and the corresponding distribution of organic matter are largely involved. Among these elements are: Ca, Mg, Si, K, Li, P, Fe, Mn, Co. Such a distribution pattern is associated with the intensive involvement of bottom sediments in the biochemical circulation in the drained areas of the khasyreys and the active leaching of these elements with the subsequent transition to a dissolved form. The fertility of lacustrine sediments in the basins of drained thermokarst lakes is largely due to the presence of sources of easily mobilized forms of nutrients. One of these resources is dispersed ice in the upper part of permafrost sediments. This source of nutrients has not been studied enough, therefore, within the framework of the project, we also focused on studying it. Dispersed ice is a significant source of nutrients in conditions of climate warming and destruction of lake shores. In the report, we will consider the hydrochemical parameters of ice using the example of the Tazovsky site. We studied two columns in a polygonal bog (polygon and swamp) and late khasyrey, about 1000–1200 years old. The thickness of the peat deposit in the khasyreys is 40 cm; frozen lacustrine loams lie below. Concentrations of polygonal bog elements in peat ice increase down the profile, with a maximum in the middle of the column, below the lower boundary of the active layer. The maximum concentration of elements at the polygon is 70–80 cm, at fens 110–120 cm. The distribution of the concentrations of elements in the ice of the khasyrey column is mostly monotonic (for example, DOC, Na, K, P), for some elements (Na, Mg, Si, Mn, Fe, Co, Ni, Ge and W) concentrations increase down the column. The Si content is higher than in the landfill and basin. Analysis of the data by the method of principal components showed that the pore waters of the active layer of the khasyreys and bog swamps are close. One can only speak of a tendency for a higher content of a number of biogenic elements in the khasyreys pore waters. At the same time, the water in the active layer of the landfill is richer in dissolved and colloidal organic matter associated with aluminum, but the content of nutrient elements is lower. The average concentrations of pore water elements in the thawed layer of the 3 studied cores are identical, with the exception of rare earth elements, the concentrations of which are 2–5 times lower. During the period of implementation of the 3rd stage of the project, 10 publications were published, 8 of them in the journals indexed by the Web of Science Core Collection and Scopus databases, included in the 1st quartile (Q1). Information about this project was posted 19 times in the media. Following the results of the 2020 expedition to the northern taiga (Khanymei settlement), a video was edited and posted on the "photosoil" channel in Youtube. Bilingual materials have been added to the photosoil website using the "khas" tags. All field, laboratory and office work planned for 2020 has been completed in full. The results were reported at several conferences, namely at the International Scientific Conference dedicated to the 90th anniversary of the Department of Soil Science and Soil Ecology at TSU; online at the General Assembly of the European Earth Sciences Union "General Assembly 2021 (vEGU21: Gather Online)"; IV All-Russian conference with international participation "Diversity of soils and biota of North and Central Asia"; IV International scientific-practical conference "Geographic aspects of sustainable development of regions" (May 27–29, 2021, Gomel, Republic of Belarus).

 

Publications

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Annotation of the results obtained in 2018
As part of the field work in the summer season of 2018, studies were conducted within key sites in the southern tundra (KS «Tazovsky») and the northern taiga (KS «Khanymey»). The main key site «Tazovsky» is located in the northern part of the Pur-Tazovsky interfluve (West Siberian Plain), near the village of Tazovsky. The side coordinates are 67.3532–67.4258° N and 78.6011–78.7311° E. The second, additional, key site (63.7951–63.705° N and 75.6833–76.2678 ° E) was laid for reconnaissance studies in the northern taiga of Western Siberia. Within KS «Tazovsky», studies were conducted within 8 basins of drained thermokarst lakes (khasyrey). We also conducted hydrochemical studies in background intrazonal landscapes (polygonal bogs and floodplains of rivers) in order to obtain comparative material. In the course of the work, the khasyreys of various ages and degrees of drainage were covered. The studies within the basin were performed on 157 points (including residual reservoirs) that were selected on the basis of a preliminary study of satellite images in order to identify the main microlandscapes. At selected points, studies of various degrees of detail were made (from basic water sampling, measuring the active layer thickness, to a full set of studies). Complex sites are confined to typical ecosystems of drained lakes basins. A total of 150 soil and surface water samples were taken. Collected waters were immediately filtered in pre-washed 30 mL PP Nalgene® flacons through single-use Minisart filter units (0.45 μm pore size, Sartorius, acetate cellulose filter). In filtered waters dissolved CH4 and CO2, specific conductivity (Cond), dissolved oxygen, pH, spectral characteristics, DIC, DOC, 13C, δ18O, Cl, SO4, major and trace elements (Li, B, Na, Mg, Al, Si, P, K, Ca, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Rb, Sr, Y, Zr, Nb, Mo, Cd, Sb, Te, Cs, Ba, Ba, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Hf, Ta, W, Tl, Pb, Th, U) were measured. Major cations and trace elements were determined with an Agilent ce 7500 ICPMS with In and Re as internal standards and 3 various external standards in the GET laboratory of the Midi-Pyrenees Observatory (Toulouse, France). Water temperature, pH, dissolved oxygen and conductivity were measured under field conditions using portable instruments WTW. To determine the concentrations of CO2 and CH4 in water, samples were taken in 25 ml glass tubes and fixed with HgCl2. Measurements were made on a Bruker SCION 456-GC analyzer at Tomsk State University with an uncertainty of 3 and 5%, respectively. Major anion (Cl, SO4) concentrations were measured by ion chromatography (HPLC, Dionex ICS 2000) with an uncertainty of 2%. International certified samples ION, PERADE, and RAIN were used for validation of analysis. DOC and DIC were analyzed using a Carbon Total Analyzer (Shimadzu TOC VSCN) with an uncertainty better than 3%. Measurements of CO2 and CH4 fluxes were carried out using plastic cameras with a diameter of 30 cm, equipped with loggers with a non-destructive infrared sensor (ELG, SenseAir). In total, measurements were carried out at 22 points in 3 replicates. About 70 samples were taken using soil ceramic lysimeters from SDEC (France). This allowed for sampling at depths. This is important for understanding the differences in the hydrochemical parameters of the rooting horizon with a deeper-lying horizon, as well as for determining the difference between oligotrophic peats and lake sediments in the old khasyreys. In 66 water samples on-site, a low molecular weight fraction of the dissolved components was studied by centrifugal ultrafiltration using disposable cartridges Amicon Ultra 15 (15 ml; 3.5 kDa). In these samples, all listed chemical elements, as well as DOC and spectral characteristics were measured. The magnitude of the content of elements in these fractions indirectly indicates their bioavailability. The 24 samples of water were collected in the floodplain of the Taz River and the floodplains of its tributaries, as well as the 33 samples of water in the polygonal bogs. In the selected samples, the water parameters listed above were also determined. The 8 soil profiles were laid in the floodplain of the Taz River and the 36 soil samples were collected. Three columns were drilled in permafrost in 10 cm steps to a depth of 1.2–1.4 m. In the obtained 40 water samples, the parameters were analyzed, similarly to the above-mentioned samples. For one of the columns (12 samples), ultrafiltration of the samples was carried out as described above. Also for these columns are obtained data on humidity and density. A total of 124 geobotanical descriptions completed. The aboveground biomass reserves were determined for 60 ecosystems without shrubs and low shrubs. Mowing was done in areas of 20x20 cm in 3 replicates. At the same areas samples were taken to determine the underground biomass. Underground biomass was measured in the main types of khasyrey ecosystems (12 points). The chemical composition of plants is determined using the ICP-MS method (on an Agilent-7700x mass spectrometer). Within the research sites, soils were studied in 43 ecotopes. A total of 177 samples were selected. The following parameters were determined in soil samples: ash content, exchange bases, hydrolytic acidity, pH, P aqueous, color in CIE l*a*b and Mansell systems, total carbon and nitrogen, nitrate nitrogen, mobile potassium and mobile phosphorus, exchange ammonium. At the moment, the listed types of analyzes are performed for 98 samples. All analyzes are performed by standard methods. The analysis of nitrogen and carbon in the soil was performed on a Thermo Flash 2000 NS Soils. The color of soil samples was measured on an X-Rite VS450. For 25 samples, the total elemental composition was determined by the ICP–MS method. The content of 13C and 15N isotopes was determined in 24 samples. Determination of the drainage time of the studied lakes basins was determined for old khasyrey by radiocarbon dating of the grass-fens layer of peat, located under moss-sedge peat. On adjacent polygonal bogs, the time of formation of the 7 subsidences are dated to identify the activation time of thermokarst processes, for the purpose of subsequent correlation with the drainage time of thermokarst lakes (24 dates were obtained in the radiocarbon laboratory of IMCES SB RAS, Tomsk). On the border of lake sediments and fens peat, old charcoals were found in old khasyrey. Found charcoals, as well as samples from the peat horizons, were transferred to the radiocarbon laboratory in Poznan (Poland). To determine the khasyrey stages within the study area, NDVI data was processed from Sentinel-2B satellite images obtained through the EO Browser. To identify the drainage time of the youngest thermokarst lakes, Landsat images were used. For all the studied the khasyreys, mapping schemes of the main ecosystems were compiled. To do this, we use the public resources of Google Maps and Yandex Maps. The data was updated using the DJI Phantom, as well as Sentinel-2B satellite images. The need to update the data is associated with a high dynamic relief of the khasyreys of the young and middle stages. Also, an analysis of a variety of remote information on the north of Western Siberia was conducted in order to select fieldwork objects in the summer of 2019. For the investigated territory of the Pur-Taz interfluve, the trend of stepwise reduction in the area of individual lakes (their complete or partial disappearance) has been established. As water descends on a bare bottom, grass vegetation appears, the productivity and species composition of which radically differs from both background zonal and intrazonal bog ecosystems. With the development of a new superaqual mode, the depletion of soil by mineral nutrition elements occurs, the productivity of communities decreases, endoecogenetic succession begins to take place, on which the formation of microrelief is superimposed. As a result, relatively homogeneous superaqual vegetation groups are divided into neo-automorphic groups with frozen soils on mounds and superaqual at the foot of the mounds. In the future, mounds can again subside, and the territory is colonized by oligotrophic vegetation. As a result, the homogenization of geochemical microcontrasts, the alignment of the microrelief and the convergence of the nature of land cover with the zonal matrix of tundra autonomous and heteronomic microlandscapes occurs. Climate warming activates thermokarst processes in the Arctic, such as increased coastal abrasion in lakes of the tundra, an increase in the frequency of drainage of lakes. The bottom sediments of the drained lake are quickly colonized by plants that form highly productive meadows with productivity and species composition other than in the zonal tundra. In this work, the species composition and productivity of the vegetation of the drained lakes (khasyrey) basins of the southern tundra of the Pur-Tazovsky interfluve of the West Siberian Plain are considered. According to the vegetation and limitation of drainage, all the studied khasyreys are divided into young, medium and old. Pioneer species colonizing the lake bottom on nutrient-rich substrates are Arctophila fulva, Carex rostrate, Tephroseris palustris. Carex aquatilis, Carex acuta, Eriophorum polystachyon, Eriophorum scheuchzeri and Equisetum fluviatile settle on a poorer substrate. On the coastal slopes willows grow. The highest above-ground net primary productivity of 2538 g/m2 was recorded for the meadow of Arctophila fulva in the central region of the young khasyrey. As the permafrost aggravates, a micro-relief is formed in the lake basin, and the young khasyrei becomes medium (productivity is 927±417 g/m2.). Calamagrostis langsdorffii dominates on medium khasyrey on the permafrost mounds. In the hollows, Carex, acatelils meadows are distributed with an average productivity of 780±657 g / m2. Over time, sphagnum mosses (Sphagnum obtusum, Sphagnum squarrosum) are introduced into the medium khasyrey. The formation of the peat horizon occurs, and plant productivity drops sharply. In the old khasyreys, the grassy species account for an order of magnitude less production than in the young. The average productivity of sedges and cotton grass in fens is 79±22 g/m2. Most of the old khasyreys are frozen bogs. In total, the 46 species of vascular plants and the 32 species of mosses were found in the studied khasyreys. The 36% of vascular plants of the young khasyreys are not found in the basins of the later stages. There are no specific mosses in young khasyreys. All mosses found in young khasyreys were also found in other basins belonging to the later stages. The number of unique species of mosses in the medium khasyreys is 31%, and in old ones it is 47%. Flat-bottomed drained lakes basins provide ideal conditions for the formation of wetlands due to permafrost which prevents the water outflow from the basin. As a result, hydrophilous vegetation is formed in most of the area of drained basins. The studied basins of thermokarst lakes in the first hundreds of years are the «hot spots» of the tundra landscape. They have high productivity and residual reservoirs attract migratory birds. Khasyreys are used for grazing deer and active waterfowl hunting for.

 

Publications

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Annotation of the results obtained in 2019
All field work planned for the summer season of 2019 was completed in full. Field studies were conducted in the Yamal-Nenets Autonomous Okrug. The work was carried out by two expeditionary units. The teams included members of the research team, as well as students and graduate students of Tomsk State University. The first group of 4 people completed three weekly studies on the eastern coast of the Yamal Peninsula. Six members of the second expeditionary unit completed two-week field work in the northern taiga on the key site of Hanymey. On Yamal, we explored ecosystems around the village of Sho-Yah. We searched for ecosystems with enhanced biological productivity. Previously, these ecosystems were searched in satellite images, after which they were examined in the field. We have studied the basins of drained thermokarst lakes, baijerahi, lakes, river floodplains, frozen floodplain and beam swamps, meadows on the coast of the Gulf of Ob, as well as other objects of the hydrological continuum (stream, hollows, rivers). In total, during the expedition we studied 120 sites. We collected 130 soil samples, 118 water samples. We collected 46 cuttings of vegetation. At 46 points we collected a herbarium. We measured greenhouse gas flows at 40 sites. We took samples from 10 dialysis membranes. We took 14 samples for radiocarbon analysis. Khasyrei of various ages and degrees of drainage were covered by the work. They conducted studies of various degrees of detail: from basic sampling of surface and soil waters, with measuring the thickness of the seasonal thawing layer (STS), to a complete set of studies (hydrochemical, soil, geobotanical). We drilled floodplain polygonal bogs for sampling frozen peat and lake sediments. We extracted melt water from the cores of frozen peat. We are researchers in the water track (hollows) of a typical tundra surface and soil water. The second expedition was in the northern taiga. We performed comprehensive biogeochemical studies in the grassy ecosystems of floodplains. The studies were carried out using the transect method, which crossed floodplains and flat-bumpy swamps. At each site, we selected soil water using ceramic lysimeters from two depths of the soil profile. The selected samples were passed directly in the field through a Minisart syringe nozzle (Sartorius, cellulose acetate filter) having a diameter of 25 mm and a pore size of 0.45 μm to separate suspended and colloidal particles and preserve the sample for subsequent laboratory and analytical studies. Development of vegetation is primarily controlled by the spatial heterogeneity of the lake sediments and the relief of the bottom. The most important factors are (1) the heterogeneity of the physical properties of the substrate, (2) concentrations of mineral nutrients elements and particle-size distribution of the sediment, (3) soil moisture, and (4) duration of flooding. In addition, the permafrost aggradation leads to a differentiation of the microtopography, which, in turn, determines the distribution of the vegetation in the khasyreys. After the drainage, the ALT increases. Afterwards, the first signs of permafrost aggradation appear, which are expressed in the formation of ice lenses in wet sites with peaty sediment. This leads to the formation of mounds of different sizes on the flat surface of the lake basin. This process has been studied in the drained lakes in the north of European Russia. Aggradation begins there in the first ten years after the lake drainage. The permafrost aggradation proceeds at a similar speed and produces a similar spatial pattern in the WSL and the north of European Russia. At the early and mid stages of succession, the parameters of soil fertility are significantly higher than at the later stages (U-test) with the exception of mineral nitrogen stocks. High fertility of soils favors the formation of plant communities dominated by Arctophila fulva, Carex aquatilis and Carex rostrata. The colonization of Arctophila fulva in the lake basin, just after drainage, is due to the ability of this species to spread rapidly, with perennial creeping roots, thus producing large phytomass. This species withstands summer water flooding of 20–40 cm during the growing season. However, when the depth of flooding decreases, Carex sp. efficiently compete with A. fulva. Over the vegetation succession in wet ecotopes, the abundance of Carex aquatilis increases in the transition from the early to the mid stage, and the abundance of Carex rostrata decreases. The ratio of land cover by these two species (C. rostrata/C. aquatilis) during the early successional stage is 4:1, and in areas with communities of the mid stage, it is 2:3. A slow increase in the abundance of Carex aquatilis in plant communities of overgrowing lake basins is also noted for the Northern Arctic plain of Alaska. The lower ash content of Carex aquatilis, compared with that of Arctophila fulva and Carex rostrata, allows this species to form a greater phytomass due to its lower soil nutrient requirement. In addition, Carex aquatilis is a more frost-resistant species than Arctophila fulva. For these reasons, Carex aquatilis increases its occurrence as the khasyrey is being overgrown, while the occurrence of Arctophila fulva and Carex rostrata decreases. The microtopography associated with permafrost aggradation in khasyreys is closely linked to soil conditions. Already at the early stage, small (several dozens of centimeters) frost mounds are formed. They are most likely raised in winter due to the formation of local ice lenses within the peat layers of lake sediments. On these small and relatively dry mounds, willows grow. In winter, growing willow bushes accumulate snow, which leads to the permafrost thawing and subsidence. This further leads to secondary pond formation, in which willows die due to over-wetting. Over the course of 10 years, willow bushes transition from the primary overgrowth of the khasyrey bottom to dying out due to flooding. The presence of residual or secondary ponds near the convex frost mound further increases the height of this mound to between 1 - 1.5 m due to the capillary rise of water. The dynamic processes of the formation/degradation of the frost mounds, occurring within first two decades, are characteristic of the mid stage khasyreys. Another important factor contributing to the aggradation of permafrost and the change in soils and vegetation over time is the accumulation of newly produced plant litter and its gradual transformation into a peat horizon. For example, early successional meadows dominated by Arctophila fulva are flooded with melted snow waters in spring. The waves arising in the temporary ponds due to strong winds lead to the separation of the arctophila straw from the bottom and the transferal of it to the shores, where it accumulates in the form of mats, with a thickness of several dozen of centimeters. The accumulated straw does not have time to decompose completely during the season and turns into grassy litter, thereby worsening the conditions of growth for Arctophila fulva. Under the thick litter, permafrost is usually preserved for a longer time, which can later lead to the formation of an elongated frost mound along the shore ledge. The amount of accumulated straw varies from year to year. For three years of observations from 2016 to 2018, the largest amount of straw was accumulated in 2017, and the smallest was found in 2018. After reducing the frequency and duration of spring flooding, the grassy litter of Arctophila fulva remains in the place of its accumulation and turns into a peat litter. As the litter is formed, the abundance of Arctophila fulva decreases (via decreasing cover and height of shoots), whereas the coverage of mosses (Bryales) increases. The introduction of sphagnum mosses at a late successional stage enhances the accumulation of peat and increases the thickness of organogenic horizons. A decrease in the active layer thickness suppresses the growth of willow bushes and graminoids, which are replaced by dwarf shrubs and mosses. These further decrease the snow accumulation in winter and consequently lead to less thawing. Over time, the formation and degradation of frost mounds become less pronounced, their rate of growth slows down, and their height decreases. Ultimately, perhaps after a couple of thousand years, a polygonal bog will form in the khasyreys. The soil waters of the late khasyreys have pH and Sp. conditions similar to those previously obtained in the fen of the frozen polygonal bogs of the Taz tundra. The results of PCA demonstrate that the plant productivity is mostly controlled by the peat thickness. We consider the peat accumulation as a process that controls the changes in all other parameters used in the PCA model (except for Nmineral pool). In this case, a decrease in the Sp. cond and the pool of labile P and K in the course of succession can be explained by the disconnection of rooting zone from nutrient-rich lake sediments occurring during the peat thickening. Therefore, the P content may be a limiting factor of vegetation succession, because it reflects the decrease of trophicity in the course of plant development. Consistent with this, the pool of P, unlike that of N, is significantly (p < 0.003, U-test) lower in soils of the late successional stage, compared to those of the early and mid stages. The ANPP correlates with both factor 1 and 2 (–0.44 and 0.45, respectively). Factor 1 is strongly linked to the physical and physico-chemical properties of soils, such as their density, pH, and peat thickness, whereas factor 2 reflects the pools of nutrients. As a result, the ANPP is highly correlated with labile P and K. However, via factor 2, the ANPP is correlated to pools of the mineral N and, to a lesser extent, to labile P and K. This rather unexpected result can be explained by the removal of nutrients from soils by actively growing biomass. The ratio of the N content in the aboveground phytomass (Nplant) to the N mineral content in the 0–30 cm soil layer (Nsoil) is equal to an average of 5.7 for the site of the early successional stage, 1.1 for the site of the mid stage, and 0.5 for the site of the late stage. In other words, at the early and mid successional stage, the plants completely use the existing pool of N (Nplant : Nsoil > 1), whereas at the late stage, the soil N pool is not completely exhausted (Nplant : Nsoil < 1). The N:P ratio in the phytomass of WSL khasyrey ecosystems ranges from 3.7 to 12.2. The threshold of N vs. P limitation (N:P < 13.5) suggests that the plant communities are N-limited rather than P-limited. The exception is communities that are dominated by A. fulva and C. aquatilis, where the N can be supplied by suprapermafrost flow, where the P is immobilized by Fe hydroxides. The availability of nutrients in the ecosystem is most fully reflected by their total pool in soil and vegetation. In this work, the chemical composition of the roots was not measured; therefore, the total pool was estimated only for the aboveground phytomass. The ratio of the P pool in the aboveground biomass of khasyreys of 7.3 (1st stage): 2.8 (2nd stage): 1 (3rd stage) reflects a much stronger decrease of P, compared to the ratio of N (3.0 (1st stage): 1.8 (2nd stage): 1 (3rd stage)) and K (2.8 (1st stage): 4.8 (2nd stage): 1 (3rd stage). However, although the evolution of nutrient pools differs between elements, their total content in the ecosystem systematically decreases from the first to the late stage of khasyrey development, which reflects an increase in the oligotrophicity of the ecosystem. The first estimates of zonal differences in biogeochemical processes in intrazonal highly productive ecosystems (floodplains and Khasyrei) are obtained. Data on the drainage mechanisms of thermokarst lakes in various geomorphological conditions are obtained. The oligotrophization rates of highly productive ecosystems are estimated depending on latitude, landscape conditions, and sediment characteristics at zero moment. The driver of the primary succession of the Khasyrei ecosystems is the accumulation of peat in hollows. An increase in the thickness of peat leads to a separation of the root systems of the herb from the fertile sediment. According to the accumulated grass peat, sphagnum is introduced into the ecosystem, and, therefore, oligotrophization and waterlogging begin with it. This process proceeds most rapidly in a typical tundra, starting already in the first decade in the driest and most flat areas. In the northern taiga and southern tundra, the process is more extended, it also begins with flat areas without spring flooding. However, both in the northern taiga and in the southern tundra, ecosystems of middle and late succession stages of more than a century can be combined within the same basin. In a typical tundra, the case of complete oligotrophization of the basin over 15–20 years is recorded. For each key site, a local specificity of primary succession was also discovered. (1) In a typical tundra, part of the Khasyreys are influenced by tidal phenomena, which is why succession in the place of their influence is inhibited at the grassy stage. A contrasting vegetation cover was recorded in the southern tundra, which is associated with a complex microrelief caused by favorable conditions for the formation of heaving tubercles. In the northern taiga, an active increase in flooding was discovered, which is atypical for undrained lakes, and partial drainage serves as the trigger for this.

 

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