ISSN 0097-8078, Water Resources, 2018, Vol. 45, Suppl. 2, pp. S44–S52. © Pleiades Publishing, Ltd., 2018.
Response of Methane Emission to Temperature Anomalies of Mires: Case Study of the Southern Taiga in Western Siberia M. V. Glagoleva, b, c, d, *, D. V. Ilyasova, b, **, A. F. Sabrekova, d, Y. V. Littia, e, and V. M. Goncharovc aWater
Problems Institute, Russian Academy of Sciences, Moscow, 119991 Russia of Forest Science, Russian Academy of Sciences, Uspenskoe, Moscow oblast, 143030 Russia c Faculty of Soil Science, Moscow State University, Moscow, 119991 Russia dUNESCO Department “Environmental Dynamics and Global Climate Changes,” Yugra State University, Khanty-Mansiysk, 628012 Russia eWinogradsky Institute of Microbiology, Research Center of Biotechnology, Russian Academy of Sciences, Moscow, 117312 Russia *e-mail:
[email protected] **e-mail:
[email protected] bInstitute
Received September 4, 2018
Abstract—In the summer and autumn of 2017, anomalously high methane fluxes were measured using the chamber method on oligotrophic, mesotrophic, and eutrophic mires in the southern taiga in Western Siberia (mean ± std): up to 42.4 ± 18.7, 10.9 ± 6.1, and 17.9 ± 8.1 mg C m–2 h–1, respectively. The winter periods of the previous 3 years (2013–2016) showed air temperatures 1.3–2.1°C higher than the average over the past 13 years, which, combined with the maximum snow cover height and relatively windless weather, had led to heating of the peat layer by 3.5–5.5°С in 2017. The incubation experiments, made to calculate the potential methanogenic activity, confirmed the possibility of the formation of the amount of methane in peat that is necessary to explain the results of field studies. Keywords: methanogenesis, wetlands, West Siberia, greenhouse effect, temperature regime of soils DOI: 10.1134/S0097807818060234
INTRODUCTION The temperature regime of the atmosphere can be significantly changed by “minor gas components” of the atmosphere, such as CO2, CH4, N2O and some other greenhouse gases. Three greenhouse agents are considered most important (according to their effect on the radiation balance of the atmosphere)—water vapor, CO2, and methane. According to the submissions, the latter is significantly inferior to carbon dioxide in its contribution to the global greenhouse effect: methane accounts for only 13–15% of the total greenhouse effect in the Earth’s atmosphere. However, the reason is the low concentration of CH4 in the atmosphere. On the other hand, as a greenhouse agent, methane is 21 times more active than CO2 per unit mass. Taking into account the greater (in comparison with СО2) increase in methane atmospheric concentration [1], the equal interest of modern researchers to СО2 and methane as greenhouse gases is quite understandable. Mire ecosystems play an important role in the natural water cycle and simultaneously act as an important component of the carbon cycle. While mire vege-
tation accumulates atmospheric carbon through photosynthesis, organic matter decomposition in a peat deposit promotes its release in the form of methane [9] (as a result of the microbiological anaerobic digestion of organic matter [23]) and CO2 (as a result of respiration [17]). Mires cover 6.2–7.6% of the earth’s surface [24] and serve as the most important natural source of atmospheric methane [18]. In this regard, the gas exchange (CH4, CO2, etc.) of mires with the atmosphere is intensively and globally studied [2, 3, 5, 6]. However, the problem of mires in greenhouse subject is especially relevant for Russia, where they occupy more than 8% of the area and, along with shallow-peat lands (where the peat is less than 30 cm thick), cover more than 1/5 of the country’s territory. As a result, more than one third of the world’s mires are located in Russia [33]. Moreover, in the Russian Federation this field was studied the most intensively in the territory of Western Siberia [14, 16, 27, 29], as the most mire–rich region. However, the major problem in these studies is the measuring of the flux of gases at the soil–atmosphere boundary. Measurements of greenhouse gas fluxes are important for understanding the current state of the
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RESPONSE OF METHANE EMISSION TO TEMPERATURE ANOMALIES
N
O
E
F
O-2
S45
West Siberia
O-2
Middle taiga O, E
,F
South taiga
500 km
Fig. 1. Study sites in middle and south taiga subzones of West Siberia. South taiga: O is an oligotrophic bog, E is a poor fen (mesotrophic), F is fen (eutrophic); middle taiga: O–2 is an oligotrophic bog.
Earth’s climate system. However, if we speak, for example, about methane, this is not enough for a meaningful prediction of its future atmospheric concentration. The fact is that the flux of methane is the difference between its production and oxidation [23], and each of these processes is exposed to environmental impacts, and their effect can be multidirectional. For example, water table level (WTL) rise usually leads to an increase in methane production (since, formerly, aerobic soil layers have been involved in methane production), but reduces its oxidation (because the thickness of the aerobic soil layer–the “methanotrophic filter”–on the contrary, shrinks) [7, 11, 23]. Therefore, to predict methane emissions in the future (i.e., under climate change conditions), it is necessary not only to predict the change in WTL in a given area, but also to know the potentialities of individual processes, for example, how much methane can be produced by a known volume of soil under optimal conditions of watering. In view of this, the purpose of the work was to measure the CH4 fluxes in the mires of the middle and southern taiga with different degrees of trophicity (at the ongoing rapid change in the temperature regime of peatlands) in comparison with their potential methanogenic productivity. STUDY SITES The study was carried out from July to September 2017 in the southern (Bakcharsky raion of the Tomsk oblast) and middle (Khanty–Mansiysk raion of the Khanty–Mansi Autonomous Area) taiga of Western Siberia (WS). The objects of the study were chosen to encompass the spectrum of the types of mire landscapes typical of Western Siberia, taking into account the features of their mineral nutrition. The oligotrophic and mesotrophic sites (their designations are O WATER RESOURCES
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and E, respectively) were located in the southern taiga on the Bakchar bog (another oligotrophic site in the middle taiga was in the Mukhrino bog), and a eutrophic site (site F) was on the Blizhnee fen (southern taiga) (Fig. 1). The Bakchar bog with a total area of 450 km2 [26] is located on the watershed between the rivers of Bakchar and Iksa. Its central part is an oligotrophic bog practically devoid of forest (site O); the periphery of the bog is covered with pine woodlands. The plant community includes Eriophorum sp., Carex sp., and Sphagnum sp.; typical peat depth is 2.6–3 m. The stratigraphy of the peat deposit has been studied in [22]. On the mesotrophic site (site E), under different plant associations, the content of Cl– is 0.2–1.0 mg/L; 2– NH4+ 0.1–0.4 mg/L; PO3– 4 , 1.0–5.0 mg/L; and SO4 , 2.5–4.5 mg/L [21]. The annual precipitation in the Bakcharsky bog area is 420 mm with a maximum (70 mm) in June. The snow cover, which is about 90 mm during the winter season, melts at the end of April [31] or in May, as a result of which the water level in June becomes quite high, but gradually decreases by autumn. Site O is an oligotrophic ridge–hollow–lake complex (measurements were made in the hollows of this complex), the vegetation of which includes mosses and dwarf pines with shrubs along the ridges. Site E is an open mesotrophic, strongly moistened part of the poor fen with small hummocks and mosses [31] located in the eastern part of the Bakchar bog [26] 4 km north of the site O. The Blizhnee (56.85° N, 83.07° E) is a eutrophic fen in the old cut–off meander on the left bank of the Iksa River about 1 km south of Plotnikovo Village (site B). Peat thickness varies from 0.7 to 3 m and more, the main part of the deposit is composed of lowlying peat with a degree of decomposition more than
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Table 1. Brief description of the measurement sites and peat sampling WTL, cm* Site О E F О–2
Latitude 56°48.8′ 56°51.3′ 56°50.9′ 60°53.4′
EC, μS/cm
pH
Longitude 82°51.2′ 82°50.9′ 83°04.2′ 68°40.8′
sum.
aut.
sum.
aut.
sum.
aut.
0 10–15 –40 –1–7
0 10–15 –30 –3–8
4.4–5.6 4.3–5.4 6.5–7.1 4.1
4.1–4.3 4.6–5.1 6.6–7.3 4.0–4.1
30–115 39–143 298–378 30–31
33–79 32–51 287–303 40–46
* WTL was measured down into the soil from its surface (thus, negative values correspond to state of water above the soil surface).
35%. The plant cover includes sedges, marsh shrubs and horsetail, and individual willows in places. The study in the subzone of the middle taiga (site O–2) was conducted on an oligotrophic hollow (the relief depression covered with sphagnum moss, where water stands close to the surface of moss or even higher) on a typical oligotrophic (upper, ombrothrophic) Mukhrino bog, 30 km southwest of Khanty– Mansiysk (60.89° N, 68.68° E). Vegetation types and their projective cover (in percentage of the total area of the considered ecosystem) for vascular plants are 5 for Andromeda polifolia, 5–7 for Carex limosa, 1–3 for Rhynchospora alba, 1 for Scheuchzeria palustris, 1 for Drosera rotundifolia/anglica, and 1 for Oxycoccus palustris; for the moss layer, it was 80 for Sphagnum papillosum and 20 for Sphagnum balticum. A brief description of the sites for measuring CH4 fluxes, as well as the sampling of peat for incubation experiments, is presented in Table 1 (the studies carried out in July are given in the summer column; and those for August, in the autumn column, because of the drop in the average daily air temperature up to 9– 15°C for the sites O, E, and B. METHODS CH4 fluxes were measured in triplicate spatial– temporal repetition in summer and autumn in each of the three site types (eutrophic, oligotrophic, and mesotrophic) using a static chamber method in the modification described in [32]. Air samples were taken with 12 mL syringes from the chamber at time t0, t1, t2, and t3 through a rubber stopper with a hose sealed in the upper part of the chamber. The exposure time (Δt = t3 – t0) was 30 min. Syringes were stored in a concentrated NaCl solution until analysis to prevent gas leakage. The measurement of methane concentration in the samples was carried out using a modernized HPM-4 chromatograph: a flame ionization detector was taken from an LHM–80 chromatograph (Chromatograph, Moscow); the column with a diameter of 2.5 mm and a length of 1 m was filled with Sovpol sorbent (80– 100 mesh); the column temperature was 35°C. Hydrogen was used as the carrier gas (flow rate of 5 mL/min); the loop volume was 0.5 mL, “artificial
air” (AA) was used for calibration with concentrations of CH4 1.99 ± 0.01, 5.08 ± 0.01, and 9.84 ± 0.01 ppm (NIES, Tsukuba, Japan). The flux was calculated using a linear regression method (in time–concentration coordinates) in the case of gas evolution and a nonlinear regression method (exponential) in the case of absorption [28]. Measurements of CH4 fluxes were accompanied by measurements of air and soil temperatures, as well as the level of bog waters, their pH, and electrical conductivity (EC). Thermal sensors THERMOCHRON iButton DS1921G (DALLAS Semiconductor, USA) were installed in the soil to the depths of 0, 10 (15), 30, 50, 75 (85), and 100 (120) cm below the soil surface, and about 2 m above it. Water samples were taken from the same depths in which the acidity and electrical conductivity were measured using Hanna HI–98129 Combo (Hanna Instruments, USA). The geographic coordinates of the sampling points were determined using GARMIN eTrex 10 GPS navigator (Garmin Ltd., USA). Peat samples were collected in summer and autumn in oligotrophic, mesotrophic and eutrophic wetlands in the Tomsk region, and on an oligotrophic bog in the Khanty–Mansi Autonomous District. The peat from the layer 15–20 cm below the WTL was placed in 1–liter plastic containers. Sampling was carried out in digs after WTL stabilization (WTL was 40 cm above the soil surface on the eutrophic bog, and peat was taken from a depth of 15 cm, that is, 55 cm under the surface of the water, in a single replication). In the process of sampling, the containers were immersed in water, filled first with water, and then gradually with peat, displacing the water, and then, also under water, covered with a lid (at the same time, the ratio of the solid-to-liquid phases in the tanks became approximately 2 times greater than that in the natural peat bog) to preserve anaerobic conditions. After that, containers were removed from water and the lid was sealed with Parafilm M film. The samples were transported (first, to the Soil Station of the Institute of Soil Science and Agrochemistry, Siberian Branch, Russian Academy of Sciences, in Plotnikovo, then to Tomsk, and, finally, by plane, to a laboratory at the Institute of Microbiology, Russian Academy of Sciences, in Moscow) in a thermos bag with coolants. WATER RESOURCES
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Table 2. Average methane fluxes, methanogenic activity, and temperature at measurement sites (n.d. means not detected) Mean temperature, °C
CH4 flux (mean ± std) Site
Season
Peat depth, m
soil, at depth, cm
measured calculated*
О
20.4 ± 7.6
13.5
4.6 ± 1.7
101.1
F
6.0 ± 1.4
О–2 О
air 0
5
10–15
45–55 75–85 100–120
1.5
32.3
32.8
24.6
22.1
14.9
11.5
8.5
2
29.8
27.3
22.2
18.5
14.0
n.d.
9.5
68.8
1.5
31.2
17.8
16.5
15.5
14.0
11.5
9.5
6.8 ± 3.5
59.7
4
29.3
26.5
19.1
14.0
8.3
n.d.
n.d.
42.4 ± 18.7
12.8
1.5
20.6
19.1
16.8
15.9
14.9
13.3
10.5
10.9 ± 6.1
108.6
2
21.1
17.1
15.6
15.0
14.1
10.5
10.5
F
17.9 ± 8.1
59.6
1.5
23.5
15.5
13.5
12.8
11.5
10.5
9.0
О–2
1.4 ± 0.6
70.6
4
10.1
8.9
8.1
7.5
7.9
n.d.
n.d.
Е sum.
Е aut.
* Methane flux, calculated using the data of incubation experiment.
At the soil station, the samples were stored in a refrigerating compartment. Peat specimens were stored at 4°C before the incubation experiments to determine the methanogenic activity. Glass medical bottles with a total volume of 265 mL were used to incubate the samples of peat. Fifty-five grams of peat were placed in a vial and 110 mL of distilled water was added (thus returning to approximately the ratio of the solid–liquid phases in the natural peat bog). The bottle was thoroughly purged with nitrogen, and sealed with a rubber stopper with a metal cap, and the bottles were kept at 4°C for 24 h for the complete release of the remaining oxygen from the peat suspension. After this exposure, the vials were opened and thoroughly purged with nitrogen again. The incubation was carried out without stirring at a temperature of 15°C. The concentration of CH4 in the gas phase of the incubated vials was analyzed at intervals of 5 or more days, depending on the observed rate of methanogenesis. Before chromatographic analysis, the withdrawn volume of gas (1 mL) was compensated for by the injection of a similar volume of argon. The methane content of the gas phase was determined on a gas–liquid chromatograph Crystal 5000.2 (CJSC CHROMATEK, Yoshkar-Ola). The sorbent used to determine CH4 and O2 was NaX 60/80 mesh. The length of the steel column was 3 m, the inner diameter was 2 mm, the temperature was 60°C, the temperature of the evaporators was 43°C, the katharometer was 200°C, the methanator was 325°C, the FID was 200°C; and the flow of carrier gases through a column of NaX (helium) was 20 mL/min. The concentrations of CH4 and O2 were determined on a katharometer and then on a FID (through a methanator). WATER RESOURCES
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RESULTS AND DISCUSSION The results of methane flux measurements and the intensity of methanogenic activity as a result of the incubation experiment are given in Table 2. The emission of methane in the site of the middle taiga (site O–2) was significantly lower than that in the southern taiga. The maximum average observed values did not exceed 6.8 ± 3.5 mg C m–2 h–1. In this case, the autumn methane fluxes were significantly (5 times) (Table 2) less than those in summer. This observation corresponds to numerous publications [4, 8, 25, 30]. Emission in the middle taiga has a clearly expressed seasonal changes and decreases 5–10 times as the average daily air temperature approaches zero. There were no specific features of the soil temperature regime and methanogenic activity. However, the CH4 fluxes at the measurement sites in the southern taiga (sites O, E, and F) were unusually high and reached, in the oligotrophic site, the values of 20.4 ± 7.6 in July, and 42.4 ± 18.7 in August– September (hereafter, mean ± std, mg C m–2 h–1), which have never been observed before, especially in autumn (though, comparable fluxes were previously observed at the mesotrophic site of the mire: in August and September 2003–2005, they reached 5–20 mg C m–2 h–1, and in July, 10–30 mg C m–2 h–1 [15], although in July and September 2006, they did not exceed 5 ± 0.3 and 3 ± 1.2 mg C m–2 h–1, respectively, which is close to the results of measurements on the mesotrophic bog in 2017 [13] and to the median flux (5.59) for these ecosystems on the basis of the longterm measurements data [29]). In addition, it may be a surprise, but the autumn fluxes in these sites are also significantly higher (2.1–3 times) than summer ones.
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130
‒11.8 10.0 31.7
‒6.6 28.0 42.6
‒8.0 11.0 41.3
‒8.5 10.0 26.3
‒12.8 11.0 43.0
‒9.0 22.0 40.2
‒8.4 9.0 16.5
‒11.9 10.0 46.4
‒6.9 15.0 34.3
‒7.7 28.0 54.7
‒6.9 11.0 34.7
‒9.9 12.0 66.5
30
20 70 10
40
WS, m/s
AT, °C; HSC, cm
100
10 0 ‒20 ‒10
‒50 '05‒'06 '06‒'07 '07‒'08 '08‒'09 '09‒'10 '10‒'11 '11‒'12 '12‒'13 '13‒'14 '14‒'15 '15‒'16 '16‒'17 HSC
WS
AT
Fig. 2. Air temperature (AT), wind speed (WS) and height of snow cover (HSC) on Bakchar weather station in winters (October– April) 2005–2017. Values on the top of the figure (top–down in column): mean AT, max WS, and mean HSC.
If this is not a measurement artifact, then the explanation of both facts can be the following: an abnormally warm beginning of the autumn with daytime air temperature only 6–11°C below its summer values was observed in the area in recent years, whereas from the middle of August there was a cold snap with a daytime temperature drops of 15–17°C or more during at least the previous two decades. Thus, methanogenic microorganisms could actively develop in the peat bog for several weeks longer. Moreover, according to local residents, the bog has not frozen in these areas in winter in the past two years, whereas this occurred to a depth of tens centimeters earlier. This could lead to an anomalous heating of the peat layer. Measurements on the Bakcharsky bog have been made on a regular basis since 1995. At the same time, if the temperature was almost always fixed at about 5°C at a depth of 120 cm in July at the end of the last and at the beginning of this century, then during the measurements in July 2017 it was 8.5–9.5°C and has not changed much at the beginning of autumn (Table 2). Consider the average monthly snow cover height, air temperature, and wind speed over the past 13 years based on the Bakchar weather station data [34] (Fig. 2). Meteorological data were analyzed from October to April (the period of precipitation in the form of snow based on long-term observations, which could lead to the maintenance of a relatively high soil temperature at the end of the summer–autumn season). From October 2016 to April 2017 (i.e. in the winter preceding the field study), the maximum average snow cover thickness was observed for the last 13 years (66.5 cm), while it usually reaches only 39.8 cm for the
same period. An important factor that has a significant effect on the thickness of the snow cover directly on the bog (in this case, at O and E sites, which represent an open space nearly devoid of woody vegetation) is the wind speed. It should be noted that there was a periodically high wind speed in winter or spring in the Bakchar district of the Tomsk region (every 4 years for the last 13 years), reaching 28 m/s in January 2007, 22 m/s in March 2011 and 28 m/s in February–April 2015. The wind speed did not exceed 12 m/s after snowfall in 2016 and until its thawing in the spring of 2017, which, with a high probability, contributed to the preservation of a relatively stable snow cover and the maintenance of high soil temperature, for which it acted as a heat-insulating layer. Also, it is noteworthy that in the 3-year winter intervals preceding the winter of 2016–2017, anomalously high average air temperatures (°C) were noted: –6.9, –7.7 and –6.9 (2013– 2014, 2014–2015, and 2015–2016, respectively), while the average for 13 years was –9.0. In the winter of 2016–2017, the average air temperature was –9.9°C, which is close to the average long–term value, while in some years (2005–2006, 2009–2010, and 2012– 2013), it dropped to –11.8, –12.8, and –11.9°C, respectively. Taking into account the wave character of the temperature fluctuations in the soil [10] and also the delay [19] in the propagation of thermal waves, the soil temperature at a depth of 100 cm could raise not higher than the temperature of the atmospheric air near its surface with a time lag of about 3 months. As mentioned above, the observed increase in soil temperature at a depth of 100 cm was 3.5–5.5°C compared to earlier periods. At the same time, the dynamics of the average air temperature over the past 13 years is WATER RESOURCES
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Site
qp (CH4, mg C m–3 h–1)
O E F O–2
10.25 37.14 45.79 43.06
Depth, m
characterized by periodic oscillations with a period of 3–4 year and a range of 3.5–6.2°C (an amplitude corresponding to 1.75–3.10°C). Other researchers confirmed the increase in soil temperature, as well as the reduction of its cooling periods to near-zero temperatures at these natural sites in recent years [20]. Thus, the soil temperature could also be anomalously high even at a depth of 100–120 cm or more for 4 years before our field observations of 2017. This may be a consequence of a combination of a favorable coincidence of meteorological conditions (the high air temperature in the recent 4 years, the maximum observed height of the snow cover for the last 13 years in 2017, and the absence of high wind speed) that could affect the methanogenic community of the wetland and cause an intensification of methane emission through a change in the soil temperature regime. In order to assess the magnitude of the potential methane formation for the studied bogs, incubation experiments were carried out with samples of peat collected in July on oligotrophic bogs of the middle and southern taiga, as well as on mesotrophic and eutrophic bogs in the southern taiga. The accumulation of
0
10
0.2 0.4 0.6 0.8 1.0 1.2 0
10
0.2 0.4 0.6 0.8 1.0 1.2
20
30
0
10
0
10
30
The lowest activity of methanogenesis under laboratory conditions was observed in the samples of peat of an oligotrophic bog (site O) in the southern taiga, which, however, showed the largest observed values of methane flux (Table 2). In this case, the activity of methanogenesis in other peat samples (sites E, F and O–2) was much higher and similar. It is interesting to compare our measurements of methane fluxes with those that could be provided by the CH4 productivity inherent in the corresponding peat bogs. We applied a calculation method used earlier and described in [29]. The peat temperature profile T(z) was approximated by an exponential dependence T(z) = bexp(cz), where b and c are parameters of the equation that were fitted for each type of bog and measurement period; z is the depth of the layer in meters (Fig. 3). The intensity of methane formation (qp, mg C m–3 h–1) in the peat volume at temperature Tz was calculated taking into account the temperature coefficient T 10 Q10 = 2.3 and the dependences qp = q0Q10 , where q0 is the rate of methanogenesis at 0°С. The value of q0 can be obtained from the data of incubation experi1.5 , ments: since they were carried out at 15°C, q0 = qi/Q10 here qi is the methane production (mg C m–3 h–1) obtained as a result of incubation experiments. Then,
Temp., °C 30 0 10
Tz = 19exp(‒0.8z)
Tz = 26exp(‒1.1z)
20
20
methane in incubation vessels (with allowance for experimental error) was practically linear; therefore, peat samples can indeed be characterized by a certain constant value, certainly, for each object. The results of the product measurement are given in Table 3.
Tz = 19exp(‒0.5z)
20
30 0
Tz = 15exp(‒0.3z)
20
30
0
Tz = 17exp(‒0.5z)
10
20
30
10
20
30
Tz = 22exp(‒2.5z)
0
Tz = 13exp(‒0.3z)
10
20
30
Tz = 9exp(‒0.3z)
0 0.2 0.4 0.6 0.8 1.0 1.2 0 0.2 0.4 0.6 0.8 1.0 1.2
Depth, m
Table 3. Methanogenic activity of peat samples (at 15°C) in incubation experiments
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Fig. 3. Measured (dots) and predicted (dashed line) temperatures of peat layer 0–120 cm (the top line is for summer, and the bottom line, for autumn; columns from left to right: O, E, F, and O–2 site). Errors are the modulus moduli of differences between measured and predicted values. WATER RESOURCES
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given the thickness of the peat deposit (zm = 1.5 m in the case of oligotrophic bog in the southern taiga and 4 m in the middle taiga, 1.5 m for the eutrophic bog, 3 m for the mesotrophic bog) and WTL (Table 1), qp was integrated over depth in the range from zm to WTL, thereby obtaining the maximum possible flux F (mg C m–2 h–1), from which the emission (Ew) was calculated, taking into account the oxidizing capacity of the methanotrophic layer: Ew = (1 – а/(1 – zw/zm))F, where a is the fraction of the produced methane that is oxidized under the conditions of standing water on the bog surface (for bogs where there are no direct measurements of a, according to [29], а = 0.63, the value а = 0.35 was taken from [12] for the site E). As estimated on the basis of experimental data on the potential methanogenesis rate, the CH4 flux (mg C m–2 h–1) observed in the field should not exceed 13.5, 101.1, 68.8, and 59.7 in summer and 12.8, 108.6, 59.6, and 70.6 in autumn for sites O, E, F, and O–2, respectively. In general, it can be seen that the values of the fluxes obtained by the calculation method are significantly higher than those observed in the field or approximately equal to them (in the case of the site O in summer), which is quite natural, since, usually, the value of the potential meteorological formation obtained in the laboratory is larger than the methane fluxes obtained in the field by the chamber method. It should be noted that the autumn measurements of methane flux have some inconsistency only in the case of the site O–2: the flux along the lower bound of the confidence interval is equal to 23.7 mg C m–2 h–1, whereas a sample of peat from this site could provide only 12.8 mg C m–2 h–1, according to the results of the incubation experiment. A significant contribution to the calculation of the flux is made by the value of methane oxidation understanding-water conditions (parameter a) used to calculate Ew–it has been derived from the analysis of a large number of publications, and generally shows wide variations in direct measurements in specific areas of various bogs (thus, according to [12], the oxidation of methane in a mesotrophic bog can reach 15–45% in Equisetum fluviatile or Carex rostrata communities and up to 55–80% under Menyanthes trifoliata or Eriophorum vaginatum). The less the number of vascular plants on the site, the less the parameter a. As site O showed few vascular plants, the parameter a should be smaller. For example, assuming a = 0.315, the methane production in peat samples will be such that the flux for site O could be 23.7 mg C m–2 h–1. It can be concluded that the proportion of methane produced in peat that reaches its surface and releases into the atmosphere is much larger in the case of an oligotrophic bog in the southern taiga than it is in other bogs. The considerable excess of the estimated fluxes over those for other types of bogs (sites E, F, O–2) can be partially explained by the intensity of methane oxidation in the aerobic peat layer in the presence of
sedges and other higher plants. It should be noted that, in the calculations of methane fluxes based on incubation experiment, no correction was made for the drop in the intensity of methanogenesis when the peat properties and composition changed with depth. In this respect, our results can also be an overestimate. CONCLUSIONS The complex of meteorological parameters estimated within 3–4 summer periods is probably one of the factors that can significantly change the temperature regime of the soil and its methanogenic activity as a consequence. A stable increase in soil temperature by 3–4°C within the observed temperature anomalies can lead to a significant increase in the observed methane fluxes. Certainly, the obtained results require additional verification in the framework of further research. Provided their confirmation, they should attract close attention, especially in the context of current climate change and the accounting of the potential response of wetland ecosystems as sources of methane to the increase in the average annual air temperature. ACKNOWLEDGMENTS The authors are grateful to all participants of the expedition: R.A. Runkov (N.P. Lavyorov lyceum) and A.I. Churkina (Moscow State University), who provided a part of the field study results presented in this article. The research was supported by Russian Science Foundation, “Comparative analysis of methane production and oxidation at the wetlands of West Siberia” (project no. 17–17–01204). REFERENCES 1. Adushkin, V.V. and Kudryavtsev, V.P., Estimating the global flux of methane into the atmosphere and its seasonal variations, Izv., Atmos. Ocean. Phys., 2013, vol. 49, no. 2, pp. 128–136. 2. Alekseychik, P., Mammarella, I., Karpov, D., Dengel, S., Terentieva, I., Sabrekov, A., Glagolev, M., and Lapshina, E., Net ecosystem exchange and energy fluxes measured with the eddy covariance technique in a western Siberian bog, Atmos. Chem. Phys., 2017, vol. 17, no. 15, pp. 9333–9345. 3. Alm, J., Saarnio, S., Nykanen, H., Silvola, J., and Martikainen, P.J., Winter CO2, CH4 and N2O fluxes on some natural and drained boreal peatlands, Biogeochemistry, 1999, vol. 44, no. 2, pp. 163–186. 4. Altor, A.E. and Mitsch, W.J., Pulsing hydrology, methane emissions and carbon dioxide fluxes in created marshes: A 2–year ecosystem study, Wetlands, 2008, vol. 28, no. 2, pp. 423–438. WATER RESOURCES
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