Several modern studies have focused on climate change-related issues and anthropogenic impacts on the environment [1
]. Increasing average atmospheric temperatures are strongly related to the concentration of greenhouse gases (GHGs), such as methane and carbon dioxide. Pristine peatland ecosystems play an important role in the global carbon balance by carbon sequestration and controlling GHG emissions [5
], thus regulating the atmospheric composition and climate. Peatlands occupy only ~3% of the land surface globally but have accumulated an equivalent of half of the atmosphere’s carbon as peat [7
]. Even small changes in their functioning may, therefore, cause a disbalance in the biosphere. One of the most waterlogged areas in the world is the West Siberian Lowland (WSL), where peatlands cover 592,440 km2
and store ~3.2% (70.21 Pg C) of all terrestrial carbon [9
The gaseous exchange between the atmosphere and peatlands is governed by the photosynthetic uptake of CO2
from the atmosphere and by soil and vegetation respiration losses of CO2
. The difference between them is known as the net ecosystem exchange (NEE) of CO2
]. The other major gaseous emission of carbon (C) into the atmosphere is accounted for by methane (CH4
), which is produced via the anoxic decay of organic matter [14
]. According to IPCC estimates [15
], the contribution of natural mires into total natural methane emissions ranges between 61 and 82%. The intensity of GHG fluxes from peat deposits is controlled by different factors, including hydrological and thermal regimes [16
Climatic changes occur on a timescale of a decade and longer, thus requiring long-term monitoring to detect their effect on ecosystems. Continuous monitoring helps to detect ongoing changes in the peatland (biodiversity, net primary production, GHG emission, and carbon and nitrogen sequestration rates) and to define the role of external factors (climate, hydrology) affecting the peatland ecosystems [22
Despite the global importance of peatlands, there are limited long-term monitoring data to quantify the functioning of the extensive peatlands of WSL, which are not covered by continuous comprehensive monitoring programs such as Fluxnet [23
Assessments of the representativeness of the pan-Arctic eddy-covariance site network [24
] showed that large parts of Siberia and patches of Canada are under-represented in carbon balance studies [25
]. Only a few long-term sites with monitoring of GHG are available in Western Siberia, including the ZOTTO tall tower with a supporting eddy-covariance network along the Yenisei river [26
] and the Japan-Russia Siberian Tall Tower Inland Observation Network located in the taiga, steppe, and wetland biomes of Siberia [27
].There automated chamber observations of methane and carbon dioxide fluxes [28
] and manual routine studies of peatland carbon balance [29
] and mire water chemistry have been carried out [30
The most intense field studies of the West Siberian peatlands are related to the investigation of methane fluxes from inland waters [31
], shallow lakes [32
], floodplains [33
] and peatlands [34
], and trace element distribution in snow deposits [35
Because West Siberian peatlands constitute most of all peatlands on the Eurasian continent [8
], the establishment of long-term records of GHG and water vapor exchange between peatlands and the atmosphere in this area under specific hydroclimatological and geological settings are essential. Intact peatlands act as significant sinks and stores of carbon and water, play a vital role as climate-regulators on a global and regional scale, and are safe-havens for unique biodiversity [22
The Mukhrino field station (Mukhrino FS, MFS) was established in 2009 with the aim of filling this shortcoming in peatland data records from the West Siberian middle taiga zone. The research is focused on climate change, carbon cycling, and biodiversity.
A multiscale approach was applied for the investigation of peatland carbon cycling. Vegetation net productivity determined from Sphagnum
growth rates was used to estimate the input carbon of the ecosystem during the snow-free period. The decomposition rate of plant remains characterizes the relative activity of the microbial transformation of peat at various ecological conditions. The resulting carbon dioxide fluxes at the local scale were studied using the chamber method. Eddy-covariance techniques summarized CO2
fluxes at the ecosystem scale. The estimation of long-term peat accumulation rates provides data on mediated peatland carbon balance. All carbon transformation processes essentially depend on meteorological conditions, energy, and water cycles characterized by high temporal variability. The local observations of meteorological and hydrological parameters were organized using automated weather stations and autonomous water level data loggers. A distributed observation network was constructed to collect data from various peatland landscapes. Annual Sphagnum
growth can be used as a complex indicator of the impact of environmental conditions on ecosystem functioning. All information on the Mukhrino FS activities is presented on the official website: www.mukhrinostation.com
(accessed on 1 August 2021). The aim of this paper is to summarize the results of peatland carbon balance studies collected over ten years at the Mukhrino FS, to reveal the gaps in the existing monitoring system, and emphasize milestones for the future development of the MFS.
Annual, seasonal and diurnal variations of the hydrometeorological parameters were observed at the MFS (Figure 4
). The monthly air temperature varied from 13.8 to 17.4 °C in July and from −27.8 to −17.3 °C in January, whereas the absolute temperature minimum was −45.0 °C at 22:00 on 21 December 2016, and the absolute temperature maximum was 32.9 °C at 16:00 on 5 August 2016. For the period from 2010 to 2019, the average mean annual air temperature at the site was −1.0 °C, with the mean monthly temperature of the warmest month (July) recorded as 17.4 °C and for the coldest month (January) as −21.5 °C.
The air humidity in winter was much lower than in summer. The monthly water vapor pressure varied from 0.05 to 0.16 kPa in January and from 1.22 to 1.69 in July. The differences between measurements of air parameters obtained at the ridge and the hollow sites were insignificant. The two sites are closely situated, and intense air mixing equalizes the air conditions.
The incoming photosynthetically active radiation (PAR) registered at both sites has a maximum at noon, and the value of the maximum rises from December to July. The amount of reflected PAR is closely related to the state of the surface. The albedo for the PAR range (the ratio of reflected and incoming PAR) in summer was about 0.03 and 0.06 at the hollow and ridge sites, respectively. The albedo in winter at snow-covered surfaces was about 0.95 at the hollow site and 0.8 at the ridge site, where small dark branches of trees were present.
The net radiation balance had close maximal values at both sites, but the diurnal course of net radiation at the ridge was shifted one hour later compared with the hollow site. The January net radiation was negative and varied within a range from −8 to −18 W m-2 during a day. The daily averaged soil heat flux was negative from October to March. The maximal heat flux into the soil was observed in June at approximately 18:00 local time. The amplitude of diurnal variations of soil heat flux at the hollow was two to three times higher than at the ridge. The soil heat flux sensors at the ridge were located under a porous mat of weakly decomposed dead mosses isolating the peat layers from heating.
Maximum snow storage was recorded on 18 March 2013 when the snow depth reached 95 cm on the ridge site. The winter of 2010–2011 was the season with the weakest snowpack. The snow cover at the end of winter on 16 February 2011 was only 64 cm. Complete melting of the snow took place between 16 April and 19 May depending on the year. The average duration of the snow cover period was 191 days. South-south-east winds prevail at the observation site, but winds with speeds above 5 m s−1 were mostly of a north-east origin. The median wind speed value at 10 m was 1.8 m s−1, while at 2 m above the surface it was only 1.0 m s−1. The wind rose structure was similar for all observation years, except 2017 and 2019.
The meteorological data presented and described is available for download from [42
]. Gap-filled, quality controlled, and raw observation data are provided separately.
Water saturation of the peat is one of the leading factors of GHG balance in peatland ecosystems. Favorable conditions for overwatering of soils were formed in the taiga of Western Siberia. Positive water balance is formed due to predominance of precipitation over evaporation by more than 1.5 times. Such wetting conditions have existed in the taiga of Western Siberia for about 10,000 years. However, the annual water balance in the peatland can vary, and in some years it has even been negative (for example, 2010 and 2020).
The Mukhrino bog is fed only by rain and snowmelt water. The average annual amount of precipitation is 470 ± 68 mm, where ¼ is snow (~126 mm). Most of the snow is accumulated by ryams and ridges, with snow depths of ~61 cm and ~67 cm (~139 mm and ~131 mm of precipitation), respectively. Hollows accumulate a thinner snowpack with depths of ~38 cm (90 mm of precipitation).
The highest water level coincides with the melting of snow at the end of April to the beginning of May. Upper peat layers (up to 50 cm depth) are usually frozen during the snowmelt period so that the produced snowmelt water cannot infiltrate into the peat and is also blocked by the frozen ridges; therefore, ponds are formed in the hollows. As soon as the ridges are defrosted the water flows superficially over and through the acrotelm (overland flow) to the streams [38
]. When the upper peat layer melts down, a part of the ponded water rapidly percolates downward into the peat layers causing a dramatic increase of the water level. During the summer period the WTE is lowered gradually by the evapotranspiration surplus over precipitation [49
]. The lowest water level is recorded at the end of summertime (usually in August); however, the WTE rose temporarily after intense rain events in summer or autumn. In autumn, such a temporal rise was more prominent while the evapotranspiration decreased with the lowering of air temperatures (see plot “Average” in Figure 5
). Discharge from the streams stopped in mid-October when the water froze.
The occurrence of superficial water flows was proved with the hydrological model [38
], not only during the period of existence of frozen peat layers but also during the summer, and in particular after rain events. The low hydraulic conductivity of the peat layers limits infiltration and favors overland flow. It appeared from the modelling that more than 90% of the water was discharged superficially across the acrotelm mostly through hollows.
WTE change is dependent on the microtope (Figure 5
). It is small in the center of the bog and high at its edges. The smallest fluctuations were found at the hollows, where water rose to 15 cm above the surface in April and dropped to 10 cm below the surface in September (average WTD is ~2 cm). The ridges had wider WTD movement, rising to 4 cm above the surface in April and falling to 14 cm below the surface in September (average value was 5 cm).. A piezometer on the ridge was installed in a local depression ~25 cm deep, i.e., the actual WTD was ~30 cm below the peatland surface. The water table can rise into the acrotelm at ridges, which in the lower part have a lower effective porosity. After rain the WTD may rise a little above the water level in the adjacent hollow but falls down a few cm below the hollow through evapotranspiration.
The highest WTD amplitude was found for the well-drained ryam, where in early spring when the water rose close to the peatland surface (4 cm below) and dropped to ~120 cm below surface (some years even 190 cm below the surface) at the beginning of autumn (the average value was 41 cm).
Near the margin of the bog, close to the terrace scarp, the upper peat layers are drained. As a result, the peat settles, and cracks are formed. During rain events the cracks were filled up with water, which resulted in a relatively high rise of the WTE as measured in the peat. After rain, the WTE was lowered deeply by vertical percolation and evapotranspiration.
Because the peat soil is fully water-saturated, precipitation events result in a WTE rise comparable to the precipitation intensity. An amount of 10 mm precipitation results in a maximum rise of about 1 cm, but less in summer when part is evaporated, and another part is lost by lateral run off.
The evapotranspiration values for different microtopes are presented in Table 1
The WTD cannot be easily measured everywhere and at all times. Water levels have been recorded in filter tubes at some depths below the surface. In particular, the water levels in hollows cannot be directly converted to water levels below the moss surface. If precipitation or snow melt water is supplied, the floating root mat (quak mire) will partially move upwards, and a measured groundwater level rise is not seen as a change in WTD. In the case of very intensive water supply, the root mat cannot follow completely and ponding results. Conversely, during a dry period, due to evapotranspiration, the root mat lowers and the environmental conditions for the vegetation (and therefore the carbon gases exchange with the atmosphere) remain almost the same. This process of root mat rise and fall may be subject to hysteresis.
3.3. Carbon Dioxide Fluxes at a Local Scale
Time series of gap-filled modeled ER, GPP, and NEE fluxes were integrated for each month of the study period. The annual variability of monthly carbon fluxes for ridge and hollow sites is shown in Figure 6
. The largest ER efflux was obtained in July 2019 at the ridge site (98.1 gC m−2
). Respiration rate at the hollow site reached maximum values in July 2018, and were somewhat lower than at the ridge site (55.8 gC m−2
). In May, the total respiration did not exceed 21.4 gC m−2
at the hollows and 41.5 gC m−2
at the ridge sites. The most intense emission was obtained for the ridge site where various vascular species strongly contribute to the autotrophic part of respiration and a thicker acrotelm layer promotes the aerobic decomposition of plant residuals. The ER rate in September and October was still high at the ridge site, but because of low GPP the ridge acted as a source of CO2
for the atmosphere.
The photosynthetic activity of bog vegetation began in early spring, and the GPP rate reached rather high values in May at 37 and −55.5 gC m−2 for hollow and ridge sites, respectively. GPP reached its maximum rates in July with −117 gC m−2 at the ridge site and −73.7 gC m−2 at the hollow site. June and August were characterized by lower values of GPP because of lower PAR values.
The largest variations of carbon flux were observed at the ridge site, where seasonal maximums in absolute values of ER and GPP significantly exceeded the corresponding values at the hollow site. The hollow site had smoother flux dynamics and lower absolute values of ER and GPP. Despite the differences in GPP and ER between both sites, monthly NEE was higher at the hollow site. The summer month rates of NEE are presented in Table 2
. The maximal carbon uptake occurred in July at both sites. Positive NEE values (up to 22.9 gC m−2
) were obtained for September–October at the ridge site.
The growing season (May–October) cumulative NEE, calculated by integrating the monthly averaged diurnal NEE rates at the hollow site was−110, −107.8, and −57.8 gC m−2 in 2017, 2018, and 2019, respectively. Our results show that the amount of CO2 captured from the atmosphere at the ridge site was lower, resulting in −22 and −32.1 gC m−2 in 2018 and 2019. A net CO2 emission of 13.4 gC m−2 was observed at the ridge site in 2017.
The results of field measurements of CO2 fluxes at the ridge-hollow complex in combination with the suggested mathematical model allowed us to adequately estimate the NEE, ER, and GPP rates for ridge and hollow sites at an oligotrophic bog in the middle taiga zone of West Siberia. The cumulative CO2 uptake rates exceeded cumulative respiration rates at both experimental sites. The three-year average growing season NEE at the hollow site was significantly higher (−91.9 gC m−2) than at the ridge site (−13.6 gC m−2). GPP and ER rates at the ridge site were higher than at the hollow site.
3.4. Carbon Dioxide Fluxes at Ecosystem Scale
The cumulative May-August NEE was −202 gC m−2
in 2015, with the monthly cumulative values being −35, −72, −79, and −16 gC m−2
for May-August, respectively. The May-August cumulative NEE of −202 gC m−2
splits into Re = 157 g C m−2
and GPP = 359 g C m−2
). High net C uptake was likely driven by an early, warm, and wet spring, which allowed for the early development of aboveground biomass. Although several cold fronts later in the summer almost completely stopped GPP for short periods, they did little to affect the steady seasonal course of C uptake. This ecophysiological stability is corroborated by the Bowen ratio, which very gradually reduced from 0.32 in May to 0.26 in August (for further details on the study, see [48
EC measurements using the same setup were continued in 2016. Drier, hotter conditions in that year resulted in a much lower cumulative May-August NEE than in 2015 (paper in preparation). In 2019, the EC setup was expanded with a CH4 analyzer (Li-Cor LI-7700); CH4 fluxes similar to those of other boreal mire ecosystems were observed (paper in preparation).
3.5. Sphagnum Annual Growth and Production
A total of 832 measurements of annual Sphagnum growth increments were performed during two years of monitoring. About a half of the measurements (338) of Sphagnum balticum annual growth were installed in plots under experimental warming (OTC) and used to study the effect of climate warming on primary production.
The mean annual growth increment differed between the studied species from 1.5 to 3.6 cm per vegetation season (Figure 8
). Five up-growing species had the lowest annual growth rate and did not differ significantly between each other (Sphagnum divinum
, S. capillifolium
, S. balticum
, S. papillosum
, S. fuscum
). Three side-growing species (Sphagnum jensenii
, S. angustifolium
, S. majus
) showed a higher annual growth rate and varied significantly between each other.
Two subsequent years of measurements showed differences in annual growth rate (Figure 8
). The values were significantly higher in 2020 compared to 2019 for almost all species. The climate conditions influencing the annual dynamics will be studied in more detail after the accumulation of data for several years.
The study of Open Top Chambers showed no significant effect of temperature rise on Sphagnum balticum growth rate in both vegetation types (Eriophorum-Sphagnum bog and graminoid-Sphagnum bog). This might be explained by the insignificance of a slightly increased temperature impact on the primary production of Sphagnum as opposed to other factors (species-specific physiology, precipitation, or ground-water level).
3.6. Decomposition Rate of Native and Standardized Substrates
Around 1500 litter bags had been extracted by the spring 2021 (see Table A4
in Appendix A
). The native litter types have one series of a four-year decomposition period (eight bags per type), two series of three years (16 bags), three series of two years (24 bags), and four series of annual decomposition period (32 bags). The standard tea had one full series of long-term decomposition (1, 2, 3 and 4 years) and four series for decomposition for three months.
The most resistant substrates (minimal weight loss after one year of decomposition) were Eriophorum vaginatum
, Scheuchzeria palustris
, Sphagnum balticum
, Andromeda polifolia
, and Sphagnum fuscum
. The fastest decomposition was observed in Rubus chamaemorus
and forest leaves (Figure 9
). Only five litter types continued to lose mass after four years of decomposition, nine litter types continued mass loss after three years, and all types continued decomposition during the second year. On average, 83% of the total mass loss between all litter types occurred during the first two years of decomposition. About 93% of the weight loss of green tea occurred during the first year of decomposition, and 7% during the second. The weight of rooibos showed a less abrupt loss, corresponding to 49, 36, and 15% loss during the first three years of decomposition.
There was no significant difference (Wilcoxon rank sum test) between the mass lost in different forest types (old-growth coniferous forest and its deciduous stages after clear-cutting). A significant difference was, however, shown between the forests (all types), treed bogs, and lawns (see Table A4
in Appendix A
for more details).
Interannual variations (influence of year-specific weather conditions on decomposition) were studied on one-year decomposition series for native litters and three-month series for tea (four series of bags from 2016 to 2019). The differences were significant (Wilcoxon rank sum test) in interannual variation for several substrates: Rubus chamaemorus, Populus tremula, Carex limosa, Sphagnum balticum, and rooibos tea. This might be caused rather by local installation differences rather than being related to year-specific weather conditions. There were no significant differences (Wilcoxon rank sum test) between the plots with OTC and control plots both for green and rooibos teas.
3.7. Peat Stratigraphy and Rates of Peat and Carbon Accumulation
The Mukhrino bog was initiated as a minerotrophic fen in the Preboreal stage (9360 cal.yr.BP) but older layers of gyttja (10,052.5 cal.yr.BP) and reed peat (10,989 cal.yr.BP) were found in depressions of lakes and ancient riverbeds. Dominant remains of trees (birch, pine, fir), herbs (Menyanthes
, Thelypteris palustris
, Equisetum fluviatile
) and tussock-forming sedges (Carex juncella
, C. cespitosa
) were found at the bottom layer (average thickness 0.65 m) for the whole area of the peatland. The transitional/mesotrophic peat (~0.5 m) overlays the minerotrophic peat layer and consists of the Scheuchzeria palustris, sedges, dwarf shrubs, and Sphagnum
moss remains. The upper part of the peatland (about ⅔) is formed by oligotrophic peat and consists of Sphagnum
with interlayers of thin cotton-grass- or sedge-Scheuchzeria
]. The average peatland depth is 310 cm with local depressions down to 530 cm depths and shallow peat deposits at the peatland edge.
The most frequent peat types are Sphagnum
fuscum-peat (share in the peat deposit 22.5%), Sphagnum
hollow peat (S. balticum
, S. papillosum
(12.0%), and Sphagnum
oligotrophic peat (S. fuscum
, S. angustifolium
, S. divinum
, S. papillosum
, S. balticum
The calculated average peat accumulation rate was 0.075 cm yr−1 (ranging between the different cores in 0.013–0.332 cm yr−1). The maximal rates were found for the upper oligotrophic (0.33 cm yr−1, 50–0 cm, 800 cal. year BP-till now) and bottom minerotrophic (0.28 cm yr−1, 520–360 cm, 10,900–10,000 cal. year BP) layers with the rate dropping to 0.013 cm yr−1 in between.
The carbon accumulation rate was 38.8 gC m−2 yr−1 (ranging in 28.5 and 57.2 gC m−2 yr−1 between the cores). It was evenly distributed over the depth with local peaks (up to 176.2 gC m−2 yr−1) at the different depths.
An investigation of carbon exchange processes is required to better understand the links between terrestrial ecosystems and both the regional and global climate systems. The peatland carbon cycle represents a component of the global carbon budget with a continuous sink of carbon from the atmosphere [63
]. An imbalance between plant uptake of atmospheric CO2
by photosynthesis and the release of CO2
to the atmosphere through ecosystem respiration (the emission of CO2
from vegetation—autotrophic and soil—heterotrophic respiration) results in peat (plant remains) accumulation [64
]. A knowledge of the response of GHG fluxes between ecosystems and the atmosphere to climatic variability is crucial for the prediction of future atmospheric levels of GHG [65
]. Eddy-covariance and chamber methods are the most widespread in the study of GHG fluxes.
The EC approach is an established and robust technique to quantify turbulent exchanges of scalars such as trace gases, momentum, and energy, between the Earth’s surface and the atmosphere [66
]. Chamber measurements have been the prevailing technique to monitor the CO2
exchange between the atmosphere and soil, plant organs, or complete ecosystems [67
The tower-based EC technique provides continuous observations of carbon, water, and heat fluxes integrated at the ecosystem scale. These multiple years observation results in a variety of sites and biomes in different climatic zones are a critical tool for the quantification of global and regional GHG dynamics [65
]. Chamber observation results represent an estimation of GHG fluxes at the local scale. Each chamber plot characterizes a certain form of local peatland microrelief (ridge, hummock, lawn, hollow, pond) with a specific vegetation type. An automated chamber system allows the dynamics of carbon exchange to be studied at a high temporal resolution for extended periods at the local scale [68
]. In combination with the appropriate sample allocations, chamber methods are adaptable for the study of the carbon exchange processes at the ecosystem scale [67
Both EC system and transparent chamber register NEE—a dynamic balance between photosynthetic fixation of CO2 from the atmosphere (GPP) and losses of CO2 by soil and vegetation respiration combining into ER. According to chamber observations, ecosystem respiration rates reached their maximum values in July (55.8 gC m−2 at ridge sites and 98.1 gC m−2 at hollow sites) and minimum values in May (21.4 gC m−2 at hollows and 41.5 gC m−2 at ridge sites). GPP reached the maximum rates in July (−117 gC m−2 at the ridge and −73.7 gC m−2 at the hollow sites). The maximal carbon uptake occurred in July at both sites (−27.2 and −28.4 gC m−2 for the hollows and ridges, respectively). Positive NEE values (up to 22.9 gC m−2) were obtained for September-October at the ridge site. The growing season (May-October) cumulative NEE, calculated by integrating the monthly averaged diurnal NEE rates at the hollow site, was−110, −107.8 and −57.8 gC m−2 in 2017, 2018 and 2019, respectively. Our results show that the amount of CO2 captured from the atmosphere at the ridge site was lower. resulting in −22 and −32.1 gC m−2 in 2018 and 2019. A net CO2 emission of 13.4 gC m−2 was observed at the ridge site in 2017.
A comparison of NEE estimates obtained through EC measurements in 2015 with NEE data from chamber observations shows that EC data are 1.8–3.5 times higher than NEE obtained at the hollow site due to the impact of pine tree photosynthesis, which is not registered by the chamber method. The cumulative May-August NEE from EC measurements was −202 gC m−2 in 2015, with the monthly cumulative values being −35, −72, −79 and −16 gC m−2 month−1 for May-August, respectively. The May-August cumulative NEE splits into ER = 157 g C m−2 and GPP = 359 g C m−2.
Combining EC and chamber observations can provide additional details about the input of peatland tree layers into carbon cycling. The proper estimates of CO2 assimilation by trees require detailed maps of micro landscapes within the EC footprint area and simultaneous observations by EC and chamber methods.
Carbon fluxes essentially depend on meteorological conditions, energy, and water cycles characterized by a high temporal variability. Spatially distributed observations of meteorological and hydrological parameters are required for assessments of factors controlling peatland carbon balance.
The climate conditions of the Mukhrino bog location are continental, with an average annual temperature of −1.0 °C, mean monthly temperatures in July of 17.4 °C, and in January of −21.5 °C. The total amount of precipitation is 470 ± 68 mm, where 25% is snow (~126 mm). Snow melting starts at the end of April and significantly increases the peatland water level. During the summer season, peatland water level slowly drops down with a short-term rise as a response to rainfall. Due to the intensification of the autumn precipitation and decrease in the air temperature and evapotranspiration, a peatland’s water level increases in September. Discharge completely stops at the end of September, beginning in October when the permanent snow cover appears.
The photosynthesis of peatland vegetation is greatly influenced by high-frequency variation in solar radiation [69
] and by changes in the groundwater table [70
mosses completely cover the surface of the Mukhrino peatland and provide an important input into the carbon cycle. The share of moss cover in total above-ground net primary production is about 53–63% [29
]. The linear annual Sphagnum
growth varied from 1.5 to 3.6 cm depending on the species in 2019–2020, and from 0.7 to 3.5 cm in 2013–2015 [54
]. Considering the density of the top moss layer and carbon content allows the annual net primary production of Sphagnum
mosses to be determined. The net annual accumulation of carbon in the live part of mosses was estimated at 24–190 gC m−2
depending on the species of Sphagnum
moss. This estimate can vary significantly depending on the annual precipitation and water table level [54
The expenditure part of the carbon cycle, due to peat decomposition, is highly dependent on rapid changes in peat surface temperature and on the slower changes in temperature and moisture content of the deeper peat [72
]. Mass loss of plant remains through decomposition gives a valuable measurement of net carbon loss, which can be useful for comparing ecosystem or litter substrates. Carbon withdrawal occurs through gaseous emissions of carbon dioxide or methane into the atmosphere or bog water, and through dissolved or particular organic carbon removal with running water [72
]. According to our assessments up to 86% (Rubus chamaemorus
) of plant remains were removed from the peat after the first four years of decomposition. Sphagnum
mosses are more resistant to decomposition, and therefore from 24% (S. balticum
) to 48% (S. fuscum
) of initial weight was lost over 4 years. Assuming that the total carbon fixed by mosses during the photosynthesis directly enters peat formation allows the maximum carbon accumulation in peat due to Sphagnum
mosses to be estimated. The maximal annual carbon accumulation in peat varied from 27 to 100 gC m−2
for S. fuscum
and from 18 to 80 gC m−2
for S. balticum
. These values are difficult to interpret because they do not include the input of carbon from other plant species and partial decomposition of dead standing plants before coming to the peatland surface. On another hand, these data do not interfere with the observed long-term carbon accumulation rates obtained by radiocarbon analysis, ranging from 28.5 to 57.2 gC m−2
with local extremes of up to 176.2 gC m−2
5. Current Challenges and Future Development
Global climate warming requires close scientific attention, an adaptation of society, social services and institutions, and urges the development of a mitigation program to reduce the anthropogenic impact on the natural ecosystems [15
]. The Russian Federation initiated a pilot project directed at controlling GHG emissions, including as a part of all activities creating the “carbon polygons” network [74
]. It aims to assess the carbon fluxes from both natural and anthropogenically influenced ecosystems, and to develop a comprehensive methodology of carbon balance measurements. The Mukhrino FS has one of the longest available continuously acquired datasets on the fluxes of carbon dioxide in West Siberia. Together with the existing scientific infrastructure, long-term data on biodiversity and environmental conditions, and international experience, it may provide unique information to the government initiative.
Native peatlands are vulnerable to carbon loss under increasing temperatures and frequency of drought events; large uncertainties prevail in the future carbon budget of peatlands and its feedback to climate change [75
]. GHG flux data from the Mukhrino FS provide representative results for the taiga zone covering about one third of the West Siberian area. So far, the available data on GHG fluxes covers several seasons and reveals an emission dynamics for the pristine peatland with relation to various microtopes (hollow, ridge, lawn). Future work involves expanding the existing observation network to cover the typical ryam and mixed forest ecosystems by eddy-covariance towers.
An analysis of the obtained results on meteorological and hydrological parameter variability, the spatial structure of the studied peatland, and various components of the peatland carbon cycle, revealed knowledge gaps in the organized monitoring system at the Mukhrino FS. Routine surveys of vegetation productivity are needed to describe the temporal and spatial variability of the incoming part of the carbon cycle. Hydrological studies should be extended by monitoring carbon-containing gases and dissolved and particulate carbon transport with moving water in peatlands, outgoing rivers, and creeks. Full peatland carbon balance accounting requires the monitoring of methane emissions from the peatland surface and lakes. The studied peatland has a complex structure with a high diversity of landscape units. Therefore, the expansion of the carbon flux monitoring network will provide new data for correct carbon balance assessment for ecosystems not yet covered by the EC tower footprint.
Biodiversity, global climate change, and environmental dynamics require a multi-proxy research approach to discover the complex linkages between the ecosystem elements [36
]. Thus, the actual scientific challenge is to organize a platform to facilitate access for diverse researchers in studying the objective. The Mukhrino FS provides all-year-around access to the scientific infrastructure and allows long-term experiments to be carried out and data collecting to be integrated into BigData. This advances research from the descriptive level to the level of understanding ecosystem functioning.
Another challenge is that peatlands are increasingly under pressure from human activities related to the exploitation of gas and oil. Such infrastructure can have a profound impact on the environment in and surrounding peatlands [76
]. Environmental changes may, via hydrology and changes in soil characteristics, have a large impact on the functioning of natural peatlands and cause significant degradation. To what extent such activities affect peatland functioning, and whether peatlands can adapt to such changes, remains an open question.