Temporal variation in methane emission from tundra wetlands in a permafrost area, northeastern Siberia

Atmospheric Environment 34 (2000) 1205}1213

Temporal variation in methane emission from tundra wetlandsin a permafrost area, northeastern Siberia

Tomoko Nakano!,*, Shunich Kuniyoshi", Masami Fukuda#

!Department of Geography, Tokyo Metropolitan University, Hachioji 192-0397, Japan"Graduate School of Agriculture, Hokkaido University, Sapporo 060-0009, Japan

#Institute of Low Temperature Science, Hokkaido University, Sapporo 060-0819, Japan

Received 8 February 1999; accepted 10 August 1999

Abstract

Summer variations in net methane #ux and environmental variables were investigated in a Siberian permafrost areaduring the summers of 1993 and 1995. In each region, the measurements were made at two "xed sites: waterloggedwetlands and relatively dry grasslands. Methane #ux from the waterlogged site at Tiksi (71.53N, 130.03E) averaged46.3 mg CH

4m~2 d~1. Flux from the waterlogged site at Chersky (68.53N, 161.43E) was approximately one order of

magnitude greater than that at Tiksi and averaged 281.1 mg CH4

m~2 d~1. Fluxes from the relatively dry sites were nearzero and frequently negative in both regions. The emissions from the waterlogged sites showed diurnal and intraseasonalvariation, while no signi"cant variation in #ux was observed at the dry sites. Our results suggest that temporal variationin methane #ux from waterlogged sites in permafrost areas was controlled by the thermal regime of a seasonal thaw layer.The diurnal variation in the #ux was correlated with ground temperature at a depth of 10}30 cm. For summer-seasonvariation, the correlation between #ux and centimeter}degrees, which is the product of ground temperature and thawdepth, was quite strong. The parameter, centimeter}degrees, is expected to be a good predictive indicator of methaneemission from wetlands in permafrost areas. ( 2000 Elsevier Science Ltd. All rights reserved.

Keywords: Methane; Natural wetlands; Siberia; Permafrost area; Temporal variation

1. Introduction

Natural wetlands are major source of methane (CH4),

emitting approximately 21% of the total global emissionsto the atmosphere (Intergovernmental Panel on ClimateChange (IPCC, 1995)). Boreal wetlands comprise overhalf the wetland area in the northern hemisphere (Asel-mann and Crutzen, 1989). The wetlands distributed in theArctic permafrost area are of particular interest becausethese regions are predicted to experience signi"cantchanges in surface temperature and precipitation, ac-cording to climate scenarios that model the doubling ofCO

2(Hansen et al., 1988; IPCC, 1996). These regions are

*Corresponding author. Tel.: #81-426-77-2595; fax: #81-426-77-2589.

E-mail address: [email protected] (T. Nakano).

estimated to hold 14% of the global soil carbon (Postet al., 1982). Increased temperatures could result in thenet transfer of some of this soil carbon to the atmosphereas CH

4and CO

2, since many northern bacterial popula-

tions respond quickly to temperature change (Svensson,1984). In permafrost areas, methane production occurs ina seasonal thaw layer during thaw season. Thus changesin the thaw depth or in the length of the thaw seasonwould also a!ect the rate of annual methane emission.

Studies to date on methane emission in high-latitudewetlands indicate that methane #ux is correlated withground temperature (Bartlett et al., 1992; Samarkin et al.,1994; Christensen et al., 1995; Granberg et al., 1997;MacDonald et al., 1998), thaw depth (Whalen andReeburgh, 1992), and soil moisture or position of thewater table (Svensson and Rosswall, 1984; Sebacher et al.,1986; Morrissey and Livingston, 1992; Funk et al., 1994).In order to estimate future changes in methane emission

1352-2310/00/$ - see front matter ( 2000 Elsevier Science Ltd. All rights reserved.PII: S 1 3 5 2 - 2 3 1 0 ( 9 9 ) 0 0 3 7 3 - 8

with climatic change, it is therefore important to investi-gate the quantitative relationships between methane #uxand environmental parameters.

This paper addresses the intraseasonal and diurnalvariation in methane #ux and environmental parametersobserved in tundra wetlands, northeastern Siberia, dur-ing the summers of 1993 and 1995. The purposes of thisstudy were (1) to evaluate the rate of methane emissionfrom tundra wetlands in the Siberian permafrost regionand (2) investigate the physical environmental para-meters a!ecting net methane emission from these wet-lands.

2. Study sites

The observations were carried out at two places inArctic Siberia: at Tiksi (71.53N, 130.03E), near the mouthof Lena River, and at Chersky (68.53N, 161.43E), on thelower Kolyma River about 100 km from the EastSiberian Sea of the Arctic Ocean (Fig. 1). Vegetation atTiksi is classi"ed as `tundraa, which is de"ned as treelessterrain with a continuous cover of vegetation by theNational Research Council of Canada (1988). Chersky isnot located in the true tundra, but exactly in a transitionzone between the tundra and taiga (boreal coniferousforest). These regions are located in a continuous perma-frost area; the depth of the seasonal thaw layer reachesfrom 0.4 to 0.7 m. Mean annual air temperature is!13.43C at Tiksi (Kunitsky, 1989) and !12.43C atChersky (Zimova, personal communication), and annualprecipitation is about 200 mm at both places.

The observations at Tiksi were made in the summerof 1993. The measurement sites were selected on Mus-takh Island, located 30 km o! shore, because the arti"cialimpact on the environment there was less, and theisland was easier to approach than an inland locationwould have been. Mustakh Island has a very #at surface

Fig. 1. Northeastern Siberia, showing the locations of Tiksi andChersky.

covered with ponds, waterlogged and moist wetlands,and sporadic peat mounds about 50 cm high. The plantcommunities on the island are typical tundra com-munities dominated by sedges (Eriophorum spp. andCarex spp.), Sphagnum spp., mosses, and shrubs(Salix spp. and Vaccinium spp.). Two "xed sampling sites,which had di!erent vegetation and soil moisture condi-tions, were chosen on the island. One was located ina waterlogged wetland dominated by Eriophorum (TW).The other was in a relatively dry location on a peatmound covered with moss communities and shrubs (TD).Height of the vegetation in the chambers was approxim-ately 30 cm at TW and 15 cm at TD. The water table wasabout 3 cm above the surface at TW and 20 cm below thesurface at TD at the start of the observation period. TheTD site was about 5 m away from TW.

Observations at Chersky were conducted duringthe summer of 1995. Landscapes at Chersky comprise amosaic of habitats, such as sparse taiga of Larix spp.,shrubs (Alnus spp., Betula spp., and Salix spp.), and herba-ceous communities, which are partly common to those ofthe Arctic tundra. The observation sites were located inthe #ood plain of the Kolyma River. The #ood plaincontains waterlogged wetlands with lakes and ponds,grasslands, and alder forests. Two "xed sampling siteswere selected on the #ood plain: a waterlogged wetland(CW) and a grassland site (CG). These sites were separ-ated from each other by a 100-m wide alder zone. Twolocations not more than 1 m apart were sampled at eachsite. Soils on the #ood plain were composed of poorlydrained, strati"ed silts and clays below a thick organic-rich layer. The organic layer was about 40 cm thick atCW and about 10 cm thick at CG. The pH of surface andpore water ranged from 5.5 to 6.5. The vegetation wasdominated by Carex spp. and Eriophorum spp. at CWand by Festuca spp. and mosses at CG. The plant coverwas about 45% at both sites. The moss cover at CG(24%) was roughly twice that at CW (11%). The vegeta-tion enclosed in the chambers was approximately 40 cmhigh at CW and 30 cm high at CG.

3. Methods

The net methane #ux was determined by a static cham-ber technique. At the measurement sites, open-bottomedacrylic resin chambers were placed on stainless-steel col-lars installed at the measurement sites for the entire studyperiod. The collars enclosed an area of 0.09 m2 and wereinserted into the ground to a depth of about 10 cm at TDand CG. At the waterlogged sites, the collars were placedon the sediments in water. The chambers "t into a water-"lled notch in the collars and were well sealed. Volume ofchamber was 0.032 m3 at TD and CG and variedfrom 0.020 to 0.032 m3 with standing water level at TWand CW. Head-space samples were removed from the

1206 T. Nakano et al. / Atmospheric Environment 34 (2000) 1205}1213

chamber every 10 min over a 30-min period using 60-mlplastic syringes and stored in two 10-ml vacuum vials.These samples were brought back to Japan and analyzedin the laboratory of the National Institute for Environ-mental Studies in 1993 and at Hokkaido University in1995, using a Shimadzu gas chromatograph with a #ameionization detector. Analytical error on duplicatesamples was less than 2%. Gas standards were run beforeand after each set of the four duplicate vials representingone chamber. Methane #ux was calculated from the slopeof the change in concentration over time. The calculationwas checked using the regression coe$cient of the slope.The gas chromatograph had a detection limit of 0.1 ppmvCH

4and the minimum detectable #ux is 0.2 mg

CH4

m~2 d~1. Gas standards stored in the vials showedno signi"cant change in concentration during a month ofstorage in the laboratory or during transport from the"eld site to the laboratory in Japan, suggesting that thequality of sample air in the vials did not change duringthe transportation as well.

Net methane #ux was measured over a one-monthperiod, from 26 July to 29 August 1993, at Tiksi and overtwo months, from 7 July to 30 August 1995, at Chersky.The measurements were made once a day, at about10.00 h. Diurnal variation in #ux was also observed atChersky. The measurements were conducted on threeoccasions, from 11 to 13 July, 3 to 5 August and 21 to 23August 1995 at 4-h interval.

Environmental data were collected concurrently with#ux measurement at both Tiksi and Chersky. Thawdepths were determined by inserting a 1-cm diameterstainless-steel rod into the soil to the frozen horizon.A ground temperature pro"le was established by measure-ments at 10- or 20-cm intervals from the surface to a depthof 1 m, and air temperature was recorded automatically at1 h intervals using platinum-resistance thermosensors atpoints close to each pair of collars at each site. We cal-culated mean daily ground temperatures (MDGT) in thethawed layer by averaging temperature data from the soilsurface to the permafrost table. At Chersky, the position ofthe water table above the ground surface was measured atCW. At CG, the water table was monitored in a well boredadjacent to the collars, and volumetric water content wasmeasured by Time Domain Re#ectometry (TDR). Precipi-tation data were collected at the meteorological station inChersky (Zimova, personal communication).

4. Results

4.1. Intraseasonal variation in yux and environmentalvariables

4.1.1. At TiksiThe temporal variations in methane #ux and environ-

mental variables were measured at a waterlogged (TW)site and at a drier peat mound (TD) on Mustakh Island,

Tiksi. Summary data for the methane #ux and environ-mental variables are listed in Table 1. The magnitudes ofthe #ux were obviously di!erent between TW and TD. AtTW, the #ux varied from 15.9 to 76.3 mg CH

4m~2 d~1

and averaged 46.3 mg CH4

m~2 d~1. On the other hand,the methane emission was nearly zero, and negative#uxes (net methane consumption) were sometimes ob-served at TD. Maximum thaw depths were 33.0 cm atTW and 39.0 cm at TD. Mean daily air temperature(MDAT) #uctuated between !0.3 and 10.93C and aver-aged 3.23C. Mean daily ground temperature (MDGT),calculated from the ground temperature pro"le, averaged2.33C at TW and 2.53C at TD.

Temporal changes in methane #ux, thaw depth, andmean daily air and ground temperatures are illustrated inFig. 2. The #ux at TW had two maxima, on 9 and 18August. These two peaks coincided with similar peaks inair and ground}surface temperatures. The ground tem-peratures showed a damped response to changes in thesurface temperatures. The temporal variation in #uxat TD was quite small, although ground temperaturechanges at TD were similar to those at TW.

4.1.2. At CherskyThe data from the waterlogged site (CW) and the

grassland site (CG) at Chersky are summarized inTable 1. At CW, all #uxes obtained during the entireobservation period were positive, as was the case at TW.The #uxes ranged from 117.3 to 467.5 mg CH

4m~2 d~1

at CW1 and from 194.8 to 520.4 mg CH4

m~2 d~1 atCW2. These values were quite large compared to the #uxmeasured at TW. Fluxes at CG were approximately twoorders of magnitude less than #uxes at CW and rangedfrom !3.2 to 0.8 mg CH

4m~2 d~1 at CG1 and from

!4.2 to 1.5 mg CH4

m~2 d~1 at CG2. Negative #uxeswere frequently observed at CG. Overall, mean #uxes atCW and CG were 281.1 and !0.6 mg CH

4m~2 d~1,

respectively. Collar pairs were statistically identical atboth CW and CG, suggesting that small-scale variabilitywas relatively low.

Permafrost had thawed to depths of approximately30}70 cm at both CW and CG. The average mean dailyair temperature and mean daily ground temperature dur-ing the observation period were 11.6 and 4.23C, respec-tively, at CW and 11.9 and 4.23C, respectively, at CG.These results indicate that the thermal regimes of thethaw layer were similar at both sites. In contrast, soilmoisture conditions were quite di!erent. Mean watertable positions were about 12 cm above the surface atCW, but 15 cm below the surface at CG. Comparisonof the thermal parameters at Chersky and Tiksi showsthat at Chersky both air and ground temperatures werehigher than at Tiksi. Moreover, thaw depth at Cherskywas approximately twice as deep as at Tiksi.

Temporal patterns of methane #ux and environmentalvariables are shown in Fig. 3a and b. At CW (Fig. 3a),

T. Nakano et al. / Atmospheric Environment 34 (2000) 1205}1213 1207

Table 1Summary of net methane #ux and environmental variables at Tiksi and Chersky, northeastern Siberia

Tiksi Chersky

TW TD CW1 CW2 CG1 CG2

CH4#ux n 14 11 19 17 19 17

(mg CH4

m~2 d~1) max. 76.3 2.3 467.5 520.4 0.8 1.5min. 15.9 !1.5 117.3 194.8 !3.2 !4.2mean 46.3 0.3 290.2 271.0 !0.7 !0.5

MDAT! (3C) max. 10.9# 19.2 21.8min. !0.3 5.2 5.4mean 3.2 11.6 11.9

MDGT" (3C) max. 5.3 5.2 6.1 5.8min. 0.5 0.8 2.9 2.3mean 2.3 2.5 4.2 4.2

Thaw depth (cm) max. 33.0 39.0 69.3 67.3 70.6 69.1min. 25.2 30.1 28.5 26.5 35.5 34.0mean 29.8 35.2 51.8 49.8 59.3 57.8

Water table position (cm) max. * * 20.5 21.0 2.7 3.5min. * * 7.3 7.8 !65.8 !65.0mean * * 11.8 12.3 !15.8 !14.8

!Mean daily air temperature at the height of 1.5 m."Mean daily ground temperature averaged in thawed layer.#Air temperature was measured at a point between TW and TD in Tiksi.

methane emissions increased with time during July andthe highest #uxes occurred in early August. Then the#uxes rapidly decreased before leveling o! during Augustat about 370 mg CH

4m~2 d~1 at CW1 and about

260 mg CH4

m~2 d~1 at CW2. The variation in #uxcorresponding to air temperature #uctuation found inTW data was not obtained at CW. On the other hand,temporal variations in #ux were considerably small atCG (Fig. 3b).

Air temperature and ground temperatures #uctuatedover a period of about one week. Although climate in thisregion is generally very dry, much rain fell in the summerof 1995. During the observation period, heavy precipita-tion events were observed twice: 37.0 mm fell from 4 to5 August and 28.3 mm fell from 25 to 27 August. Afterthese two rainfalls, volumetric water content increasedrapidly and the water table rose from the level ofthe permafrost table up to the ground surface at CG(Fig. 3b). However, changes in methane #ux correspond-ing with this increase in water content were not found.

4.2. Diurnal variation in methane yux at Chersky

At Chersky, the diurnal variation in methane #ux atCW1 and CG1 was measured over a 48-hour period on

three occasions in 1995, from 11 to 13 July (DV1), 3 to5 August (DV2), 21 to 23 and August (DV3). Themeasurements were conducted at 4-h intervals from14.00 h on the "rst day to 10.00 on the last day of eachperiod.

We elaborate on the results only from CW1 as follows,because the variations in #ux at CG1 were quite small,within the sampling error. Net methane #ux and con-toured isotherms that pro"le the temperature belowground are shown for CW1 in Fig. 4. A diurnal cyclein #ux was obtained for the DV1 and DV3 series.The pattern of variation was, however, di!erent: a max-imum and a minimum occurred at 02.00 and at 14.00 h,respectively, for the DV1 series, while a maximumwas observed in the afternoon and a minimum inthe morning for the DV3 series. The range of dailyvariation was also di!erent. The variation forDV3 was considerably larger than that for DV1. As forDV2, a diurnal cycle was not obtained. The #ux reacheda maximum value at 02.00 h on 4 August and thendecreased to about 330 mg CH

4m~2 d~1 at 10.00 h

on 5 August. During this time, the air and groundtemperature had continuously decreased with heavyrain falling from the evening of August 4 to midday onAugust 5. This drop in temperature is considered


Fig. 2. Net methane #ux and environmental variables measuredat Tiksi during the summer of 1993. Top: Net methane #uxes forwaterlogged (TW) and drier (TD) sites. Second from the top:Thaw depth at TW and TD. Second from the bottom: Airtemperature at the middle point between TW and TD. Bottom:Ground temperatures at the surface and at depths of 20 and50 cm at TW.

to explain the lack of a diurnal peak in the #ux onAugust 5.

Some previous work reported strong diurnal #uctu-ation in net methane #ux from a natural wetland (Alm etal., 1996) and from a rice paddy (Chanton et al., 1997). Inthese studies, the emission increased after sunrise andpeaked around midday. These authors suggest that thisdiurnal variation could be explained by mass #owthrough the reed stems, initiated by the morning rise intemperature and the opening of stomata in light. Ourresults are not consistent with these earlier results, sug-gesting the existence of di!erent factors controlling meth-ane emission.

The ground temperature showed a damped responseto change in surface temperature because of insulation(Fig. 4). The range of variation in temperature in the zonedeeper than 20 cm was less than 0.53C. The relationshipbetween methane #ux and ground temperature will bediscussed in the next Section.

5. Discussion

5.1. Correlation to physical environmental variables

Methane emission is complexly controlled by physical,chemical, and biological factors. Therefore, single-factorenvironmental relationships are insu$cient to explainfully the variation in methane #ux (Whalen andReeburgh, 1992; Christensen et al., 1995). It is, however,necessary to "nd indicators of methane #ux in order toestimate the methane emission from widely distributedwetlands. Furthermore, the indicators must be easilyavailable over a broad area. In this paper, we discuss thetemporal relationship in a permafrost region betweenmethane emission and physical environmental factorsthat can be readily obtained by observation or computa-tion.

The Spearman's rank correlation coe$cients betweenmethane #ux and environmental factors from TW, TD,CW, and CG are given in Table 2. At TD and CG,statistical correlations were not obtained. Not even thewater table level correlated with the #ux at CG, althoughit varied greatly from the permafrost table to above theground surface (Fig. 3b). The water table position deter-mines the degree of aerobism/anaerobism in wetlandsediments (Moore and Roulet, 1993). Although it hasbeen reported that a decrease in methane #ux occurredwith a drop in water table position (Bartlett et al., 1992;Christensen, 1993), our results suggest that factors otherthan soil anaerobic condition, for example organic mat-ter supply or transport processes from the sediments tothe atmosphere, may be important in methane emissionat CG.

At both TW and CW, the best relationship was foundbetween methane #ux and centimeter}degrees. The para-meter `centimeter}degreesa has been de"ned by Whalenand Reeburgh (1992) as the absolute value of the productof thaw depth and mean ground temperature abovepermafrost table. Similar high correlations have beenobtained in data from Alaskan tundra wetlands (Whalenand Reeburgh, 1992). The thaw depth is related to micro-bial population sizes and the ground temperatureregulates the rate of CH

4production. Therefore, the

centimeter}degrees is a reasonable index of net microbialactivity. In tundra wetlands where vegetation is com-posed of simply (Carex dominant) and thus transportprocesses are assumed to be similar, it is considered to bean appropriate indicator of methane emission to theatmosphere. The methane #ux versus centimeter}degreesrelationship for TW and CW is well approximated bya quadratic curve (Fig. 5). The correlation coe$cient forthis curve is quite high (r"0.94). It is also signi"cant thatthe #uxes from two distant places can be "tted by thesame curve. This result indicates that centimeter}degreesis a valid parameter for the estimation of emission, be-cause the ground temperature pro"le and thaw depth can


Fig. 3. (a) Net methane #ux and environmental variables measured at waterlogged (CW) sites at Chersky during the summer of 1995.Top: Net methane #uxes at CW1 and CW2. Second from the top: Thaw depth at CW1. Middle: Air temperature (line) and precipitation(bar). Second from the bottom: Ground temperatures at the surface and at depths of 20 and 60 cm. Bottom: Water table position atCW1. (b) Net methane #ux and environmental variables measured at grassland (CG) sites at Chersky during the summer of 1995. Top:Net methane #uxes at CG1 and CG2. Second from the top: Thaw depth at CG1. Middle: Air temperature (line) and precipitation (bar).Second from the bottom: Ground temperatures at the surface and at depths of 20 and 50 cm. Bottom: Water table position andvolumetric water content at CG1.

Fig. 4. Diurnal variations in methane #ux (top) and soil isotherms (contour interval: 33C) with depth at CW1 (bottom); (a) 11}13 July(DV1), (b) 3}5 August (DV2), and (c) 21}23 August (DV3).


Table 3Spearman's rank correlation coe$cient (r

4) for correlations between methane #ux and environmental factors at CW1. Only values of r

4signi"cant at p(0.05 are shown

11}13 July (DV1) 3}5 Aug. (DV2) 21}23 Aug. (DV3)

Air temp.Water depthGround temp. 10 cm

0 cm!10 cm 0.68 0.90!20 cm 0.81 0.80 0.67!40 cm 0.59!60 cm!80 cmMGT! 0.65

!Mean ground temperature averaged with thaw layer during each observation period.

Table 2Spearman's rank correlation coe$cient (r

4) for correlations be-

tween methane #ux and environmental factors at TW and TD inTiksi, and at CW and CG in Chersky

TW TD CW CG

n 14 11 36 34

Thaw depth 0.40MDATMDGT 0.68 0.35Water table position ND NDCentimeter}degrees 0.75 0.83

Only values of r4signi"cant at p(0.05 are shown.

ND means no data collected.

Fig. 5. Relationship of methane #ux at CW and TW to cen-timeter-degrees. The solid line approximates all data.

be computed from air temperature data, which is mea-sured all over the world.

Table 3 shows the Spearman's rank correlation coe$-cient between diurnal variations in #ux and environ-mental parameters at CW1. All series show a signi"cant

correlation with ground temperature, especially at depthsfrom 10 to 30 cm. It is interesting that the depth at whichthe ground temperature correlated best with the #uxappears to become deeper from DV1 to DV3. The rela-tionship between the average temperature within thethaw layer was found only for DV3.

5.2. Comparison with other measurements

Net methane #ux from tundra and tundra-like wet-lands in continuous permafrost area has been measuredmainly in North America (Sebacher et al., 1986; Whalenand Reeburgh, 1990; Morrissey and Livingston, 1992;Christensen, 1993). Studies of methane emissions fromthe Siberian Arctic have been recently reported (forexample, Samarkin et al., 1994; Christensen et al, 1995),although those were observations on spatial variation in#ux. It is di$cult to compare those data with our studybecause of di!erent site-selection techniques. Neverthe-less, there is the fairly general coincidence that the #uxfrom wet (waterlogged) sites is higher than that from dry(moist, mesic) sites.

Samarkin et al. (1994) measured methane emissionsfrom the Arctic tundra and from the boundary betweentundra and taiga in the Kolyma Lowland (68340@N and69320@N). The mean #ux ranged from 0 to252.9 mg CH

4m~2 d~1 and was correlated with soil

moisture conditions. The maximum #ux was observedfor subaquatic (waterlogged) sites in the tundra}taigaboundary region. This value is comparable with the #uxmeasured at CW in our study. The "rst transect study of#ux measurements from the Eurasian and Siberian Arctic(673N}773N) was carried out during July and August1994 by Christensen et al. (1995). Mean methane #ux was2.3$0.7 mg CH

4m~2 d~1 for mesic tundra sites and

46.8$5.9 mg CH4

m~2 d~1 for wet habitats. Their datasuggest a trend of decreasing #uxes with increasing latit-ude. Our data from waterlogged sites in both Tiksi and


Chersky, when compared with #uxes measured at similarlatitudes, are somewhat higher than those measured byChristensen et al. (1995), while the #uxes from drier sitesare comparable.

Studies to date have found that single-parameter rela-tionships between environmental factors and methane#ux are insu$cient to predict the variation in the #ux(Whalen and Reeburgh, 1992; Christensen, 1993;Christensen et al., 1995). The relationship between tem-poral variation in #ux and environmental variables inhigh-latitude wetland ('603N) have been reported asfollows. Svensson and Rosswall (1984) found a correla-tion between #ux and temperature only for wetter sites,while drier sites showed no correlation. Bartlett et al.(1992) reported that seasonal changes in #ux were closelycorrelated with ground temperature in a logarithmicrelationship for both wetter and drier sites. NykaK nenet al. (1998) suggested that seasonal variations in meth-ane #ux have been found to correlate with temperature atwet tundra sites, whereas at dry tundra sites the methane#uxes correlated only with the water table. From obser-vations made over a 4-yr period, Whalen and Reeburgh(1992) obtained the best correlations between methane#ux and the parameters thaw depth and centimeter}degrees.

6. Conclusions

Summer methane emissions from wetlands in theSiberian permafrost area were obtained in this study.Fluxes from waterlogged sites averaged 46.3(15.9}76.3) mg CH

4m~2 d~1 and 281.6 (117.3}520.4) mg

CH4

m~2 d~1 at Tiksi and Chersky, respectively. In con-trast, #uxes from relatively dry sites were near zero andfrequently negative. Temporal (intraseasonal and diur-nal) variation in #ux was large at the waterlogged sites,whereas the variation was quite small at the dry sites.

The relationship between net methane #ux and phys-ical environmental variables was discussed based on theobserved data. At the drier sites, no statistical correla-tions were obtained. We suggest that the thermal regimeof the thaw layer was important as a controlling factorfor methane emission at the waterlogged sites. The di-urnal variation in #ux was correlated with ground tem-perature at depths from 10 to 30 cm. With respect tointraseasonal variation, the correlation between #ux andcentimeter}degrees was quite strong. We expect cen-timeter}degrees to be a good predictive indicator ofmethane emission from waterlogged wetlands in perma-frost regions.

Acknowledgements

We would like to express our appreciation to Dr. A.A.Arkhangelov and Mr. A.G. Muradov, Moscow Univer-

sity, Russia, Dr. A. Akiyama, Tokyo Institute of Techno-logy, Japan, and Drs. S. Zimov and G. Zimova of theNortheastern Science Station, Paci"c Institute of Geo-graphy, Russia, for supporting our "eld observation inSiberia, Russia. Also thanks to Dr. Y. Nojiri, NationalInstitute for Environmental Studies, and Dr. N. Tanakaand Mr. Y. Kim, Hokkaido University, Japan for helpingwith the analysis of methane concentration. This workwas supported by a grant-in-aid from the Overseas Re-search Fund of the Ministry of Education, Science, andCulture, Japan.

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Documents

Temporal variation in methane emission from tundra wetlands in a permafrost area, northeastern Siberia