This content has been downloaded from IOPscience. Please scroll down to see the full text. Download details: IP Address: 134.76.162.165 This content was downloaded on 19/02/2016 at 12:00 Please note that terms and conditions apply. Russian boreal peatlands dominate the natural European methane budget View the table of contents for this issue, or go to the journal homepage for more 2016 Environ. Res. Lett. 11 014004 (http://iopscience.iop.org/1748-9326/11/1/014004) Home Search Collections Journals About Contact us My IOPscience Environ. Res. Lett. 11 (2016) 014004 doi:10.1088/1748-9326/11/1/014004 LETTER Russian boreal peatlands dominate the natural Europeanmethane budget Julia Schneider1, HermannF Jungkunst1, UlrikeWolf2, Peter Schreiber3,Michal Gazǒvic ̌4, MikhailMiglovets5, OlegMikhaylov5, DennisGrunwald6, Stefan Erasmi6,MartinWilmking7 and LarsKutzbach3 1 Institute for Environmental Sciences, University of Koblenz-Landau, Fortstr. 7, D-76829 Landau,Germany 2 Thünen Institute of Climate-Smart Agriculture, Bundesallee 50, D-38116Braunschweig, Germany 3 Institute of Soil Science, KlimaCampus, University ofHamburg, Allende-Platz 2,D-20146Hamburg, Germany 4 Department of Forest Ecology andManagement, SwedishUniversity of Agricultural Sciences, Skogmarksgränd, SE-90183Umeå, Sweden 5 Institute of Biology, Komi SCUrDRAS, 28Kommunisticheskaya st., 167982 Syktyvkar, KomiRepublic, Russia 6 Institute ofGeography, Georg-August University ofGöttingen, Goldschmidtstr. 5, D-37077Göttingen, Germany 7 Institute of Botany and Landscape Ecology, ErnstMoritz ArndtUniversity Greifswald, Grimmer Straße 88, D-17487Greifswald, Germany E-mail: Schneider_julia@uni-landau.de Keywords:European budget,methane, boreal peatlands, upscaling Abstract About 60%of the Europeanwetlands are located in the European part of Russia. Nevertheless, data on methane emissions fromwetlands of that area are absent.Here we present results ofmethane emission measurements for two climatically different years from a boreal peatland complex in EuropeanRussia. Winterfluxeswere well within the range of what has been reported for the peatlands of other boreal regions before, but summerfluxes greatly exceeded the average range of 5–80mgCH4m −2 d−1 for the circumpolar boreal zone.Half of themeasured fluxes ranged between 150 and 450mgCH4m −2 d−1. Extrapolation of our data to thewhole boreal zone of EuropeanRussia shows that theses emissions could amount to up to 2.7±1.1 TgCH4 a −1, corresponding to 69%of the annual emissions from Europeanwetlands or 33%of the total annual natural Europeanmethane emission. In 2008, climatic conditions corresponded to the long termmean, whereas the summer of 2011waswarmer and noticeably drier. Counterintuitively, these conditions led to even higher CH4 emissions, with peaks up to two times higher than the valuesmeasured in 2008. As Russian peatlands dominate the areal extend of wetlands in Europe and are characterized by very highmethanefluxes to the atmosphere, it is evident, that sound Europeanmethane budgetingwill only be achievedwithmore insight into Russian peatlands. 1. Introduction Methane (CH4) is a greenhouse gas that has significant impacts on the global climate and northern peatlands are one of the largest natural sources of CH4 emissions to the atmosphere. Ground-based reliable budgets of these areas are particularly needed to verify atmo- spheric-based methane budgets. CH4 emissions from tundra and boreal peatlands have previously been reported fromNorth America (e.g. Turetsky et al 2002, Bubier et al 2005, Moore et al 2011), Scandinavia (e.g. Riutta et al 2007, Forbrich et al 2011), Russian tundra (e.g. Heikkinen et al 2004, Sachs et al 2010) and Siberia (e.g. Friborg et al 2003, Glagolev et al 2008), but hardly any from boreal European Russia (e.g. Panikov 1994, Gažovič et al 2010). The European part of Russia includes approximately 129 000 km2 of peatlands, which is about 3% of the European land surface (Joosten et al 2012), and about 80% of these peatlands are located within the boreal zone of European Russia. Nevertheless, wetland CH4 emissions of boreal Russia appear to be underrepresented in the European green- house gas budget of Schulze et al (2009). Despite the sheer size of these wetland areas, virtually nothing is known about their methane fluxes. CH4 flux from a boreal peatland site in Siberia were considerably OPEN ACCESS RECEIVED 15 July 2015 REVISED 30November 2015 ACCEPTED FOR PUBLICATION 16December 2015 PUBLISHED 12 January 2016 Original content from this workmay be used under the terms of the Creative CommonsAttribution 3.0 licence. Any further distribution of this workmustmaintain attribution to the author(s) and the title of thework, journal citation andDOI. © 2016 IOPPublishing Ltd higher than those measured in Scandinavia and Northern America (Friborg et al 2003). Too few actual measurements are available from peatland ecosystems of boreal European Russia, which leaves amajor gap to adequately address the Europeanmethane budget. In order to start filling this knowledge gap, we measured methane fluxes at a boreal peatland in Eur- opean Russia. The results were then extrapolated to larger spatial scales to assess the relative importance of these peatlands to the overall European methane bud- get. Without such conformational data, estimates for European methane budgets run the risk of remaining largely inaccurate. 2. Research site andmethods 2.1. Site description andfluxmeasurements CH4 emissions were studied from March 2008 to February 2009 and during the summer 2011 from a boreal peatland complex (Ust-Pojeg; 61°56′N, 50°13′ E) in the Komi Republic, European Russia (detailed description of study site in Gažovič et al 2010, Schnei- der et al 2012, Runkle et al 2014). The long-term (1984–2013)mean annual temperature in the region is 1.3 °C and mean annual precipitation is 620 mm (RIHMI-WDC 2014). Our intensive study site consists of a Sphagnum angustifolium pine bog in the northern part and a Sphagnum jensenii fen in the Southern part of the peatland. On the basis of vegetation and microrelief, we selected seven microform types: hum- mocks, lawns and hollows in fen and bog, respectively, and Carex lawns in the transition zone between bog and fen. This peatland is representative of themajority of the European Russian peatlands. The largest part of the peatlands in European Russia is situated in the boreal zone and, depending on the data source the peatlands of the Komi Republic make up ¼ to ½ of all peatlands of the European Russia. The peatlands of Komi Republic consist of 48% bogs, 34% fen, and 18%mixed type peatlands (Alekseeva 1999). CH4 fluxes were measured once a week from 23 April to 12 October 2008 using a closed chamber approach (chamber dimensions: base 60 cm×60 cm, height 25 cm). The chamber was equipped with a fan to ensure an even mixing of the air inside the chamber and with a venting tube to avoid under-pressure dur- ing gas sampling. This also allows the ambient pres- sure fluctuations to be transmitted into the chamber headspace. Additionally, measurements were con- ducted once a week from 20 May to 19 September 2011, nearly covering the entire growing season. A total of 18 measurement plots were established within the intensive study site in different microform types: two replicates each in ombrogenous hollows (OHO), lawns (OL) and hummocks (OH), and 3 replicates each in minerogenous hollows (MHO), lawns (ML) and hummocks (MH), and Carex rostrata lawns (CL). Six air samples were taken from the chamber headspace during the 15–20 min chamber closure per- iod using 60 ml plastic syringes. The air sample analy- sis was usually done within a day following field- sampling. Samples were analyzed with a gas chromatograph (GC, Hewlett Packard) equipped with a GFT PORAPAK a 80/100 (MESH-COND1900GC- 015-9239, Hewlett Packard, USA) column and a flame-ionization detector. Flux rates were calculated from the change in the CH4 concentration in the chamber headspace over time by fitting a linear func- tion using least-squares regression. Measurements with unsteady concentration changes during chamber deployment were filtered out (9% of all measurements). During the snow period, CH4 fluxes were mea- sured using a snow-gradient method. Here, 4–6 gas samples were taken per plot from different snow depths. In addition to the methane concentration measurements, profiles of snow density and temper- ature were measured. The diffusive fluxes were calcu- lated from theCH4 concentration gradient in the snow following Mc Dowell et al (2000). Fluxes were deter- mined in March and April 2008 and in February 2009 (in total up to 10 times per plot). For the air sample analysis, the same gas chromatography system was used as for the samples from chambermeasurements. At each plot, soil temperature was measured at depths of 5, 10, 20 and 40 cm with a sampling fre- quency of 30 min (HOBOU12, HOBO, USA) in 2008. Ground water depth near the collars was measured manually each sampling date. Additionally, the green leaf area index was determined to describe the vegeta- tion development during the growing season. To get an individual flux estimate for each mea- surement plot for the whole investigation period 2008 to 2009, CH4 fluxes were empirically modeled using the following exponential function: a a TFCH4 1 exp 2 ,= ´ ´( ) where T is soil temperature and a1 and a2 are fitting parameters. We achieved best results using only soil temper- ature. The inclusion of further control parameters did not improve themodeling results.Modeling was solely used for filling measurement gaps, i.e. the daily emis- sions rates of non-measured days were modeled, which improved the annual estimates of the individual sites. 2.2. Upscaling of thefluxes For calculating the intensive study site’s overall CH4 balance, the relative cover of the different microform types was determined along eight transects. A detailed explanation of the method is given in Schneider et al (2012). The annual emission of the study site is an area-weighted average using the relative land cover fractions of the microform types as weights. We used the method of maximum error estimation for the uncertainty analysis of the upscaled CH4 fluxes. The 2 Environ. Res. Lett. 11 (2016) 014004 error propagation routine for random errors is not suitable in our case, as the error of the area estimates for the different microforms cannot be considered as a random error (Schneider et al 2012). The mean flux of our study site was used to update the estimate of Grunwald et al (2012), in order to assess the new data’s impact on the EuropeanCH4 balance. The new continental balance was calculated using the mean annual methane fluxes measured in this study for the Russian peatlands of the cold zone. For all other peatlands and land use types in Europe, includ- ing the rest of European Russia, the values given in Grunwald et al (2012) were applied. The mean methane fluxes of a certain land use type (forest, wet- lands, agriculture and grasslands, water bodies)within a specific ecological zone (cold climates, temperate, Mediterranean or continental)was identified (via a lit- erature review), and then multiplied by its area as derived from land cover products. Additionally, data from rice cultivation areas were incorporated. Differ- ent scenarios dealing with forest wetlands were calcu- lated in Grunwald et al (2012). For this study, the scenario A3S2 was chosen, assuming 5.2% wet forests in the temperate zone and 13% in the cold climates, based on mean values given in Forest Europe (2011): we deemed these assumptions to be the most realistic for our calculation. 3. Results The winter fluxes ranged between 0.1 and 33 mg CH4 m−2 d−1 (table 1). The average daily fluxes during the vegetation period in 2008 differed between the differ- ent microform types, being highest at the minerogen- ous hollows (256 mg CH4m −2 d−1) followed by Carex lawns (202 mg CH4m −2 d−1). The lowestmean values were measured at ombrogenous hummocks (49 mg CH4m −2 d−1) (figure 1, table 1). The CH4 fluxes correlated well with individual soil temperatures, and therefore measurement gaps could be filled using regression models applied to the flux data from individual measurement plots (figure 1). The annual CH4 fluxes for the year 2008 were esti- mated for each measurement plot using regression models. According to their topographic position, the flux rates ranked from highest at the minerogenous hollows (39±2 g CH4 m −2 a−1) to the lowest at the ombrogenous hummocks (5.7±0.5 g CH4 m −2 a−1) (table 1). As the peatland complex was well mapped, the area-weighted average annual emission was calcu- lated as 25.6±10.6 gCH4m −2 a−1. The natural European CH4 budget was estimated using the land cover classification and literature survey ofGrunwald et al 2012 (figure 2). The basemap of Eur- ope for this study includes five land use classes in four major ecozones (cold, temperate, continental and Mediterranean) (see the Methods section). We inclu- ded the new estimate for Russian cold zone wetlands (i.e., boreal wetlands) from this study and calculated an annual natural European methane emission of 9.8±2.2 Tg CH4 and an uptake of 1.8±0.7 Tg CH4 resulting in a net balance of 8±2.3 Tg CH4 per year. The annual methane emission of the Russian boreal zone wetlands amounts up to 2.7±1.1 Tg CH4 a −1, corresponding to 33% of the annual natural European methane emission. 4.Discussion Russian peatlands must play a significant role in the overall methane budget of Europe based simply on their large surface area. The winter fluxes were well within the range of what has been reported before for the peatlands of boreal regions (Alm et al 1999, Rinne et al 2007). Fluxes during the vegetation period were twice as high as comparable sites in Scandinavia and North America (Turetsky et al 2014). Reasons for the high summer fluxes remain unexplained and have to be verified for other peatlands in European Russia. The most apparent difference in driving factors to Table 1.Methane flux statistics for the differentmeasurement periods andmicroform types: ombrogenous hollows (OHO), hummocks (OH) and lawns (OL),Carex rostrata lawns (CL), andminerogenous hollows (MHO), hummocks (MH) and lawns (ML). Daily CH4flux (mgCH4m −2 d−1) Microform type Winter 2008 (May– September) 2011 (May–September) Annual (2008)CH4flux (gCH4m −2 a−1) Mean Range N Mean Range N Mean Range N OHO 4 0.5–8 10 159 9–643 67 139 46–362 11 32.6±2.1 OH 3 0.1–7 10 49 3–352 49 73 8–308 10 5.7±0.5 OL 5 0.5–14 14 104 3–449 57 227 30–501 22 30.5±2.5 CL 16 5–30 13 202 54–624 80 448 72–1582 20 29.5±1.1 MHO 11 2–33 16 256 1–1020 98 193 75–260 11 39.0±2 MH 7 3–18 8 101 0–600 78 72 16–150 12 15.5±1.2 ML 8 2–20 14 166 2–722 96 ND ND ND 32.5±1.1 Study site 25.6±10.6 NDnot determined. 3 Environ. Res. Lett. 11 (2016) 014004 Figure 1.CH4 emissions over the investigation period 2008 to 2009 at differentmicroform types inUst-Pojeg peatland: ombrogenous hollows (OHO), lawns (OL) and hummocks (OH), minerogenous hollows (MHO), lawns (ML) and hummocks (MH), andCarex rostrata lawns (CL).Dots indicate themeasuredCH4flux; lines indicate the individuallymodeledCH4fluxes. Figure 2.Map ofmean annual naturalmethanefluxes in Europe; dots indicate thefluxmeasurement sites used for the upscaling of CH4fluxes in this study, circled dot indicates theUst-Pojeg investigation site. 4 Environ. Res. Lett. 11 (2016) 014004 Scandinavia would be the continental climate and its possible effects on the driving factors and underlying processes. Temperature has an effect on methane emissions (e.g. Torn and Chapin 1993, Vicca et al 2009). It also most likely has an effect on substrate quality and quantity, which themselves influence the CH4 flux (e.g. Joabsson et al 1999, Ström et al 2003). One main substrate for methane production is dis- solved organic matter (DOM). During winter these substrates may be preserved due to very low tempera- tures reducing microbial processes. During higher temperatures in summer, a possible decrease in the size of DOM and a higher biodegradability of DOM may lead to higher CH4 production (Bridgham et al 2013).Wet–dry cycles during the summer can also contribute to elevated DOM concentrations (Marsch- ner and Kalbitz 2003). This climate type is character- ized by pronounced freeze-thaw cycles in the winter– spring period, which increase the physical disruption of the organic soil, leading to higher fine root mortality. Both processes can result in higher dissolved organic carbon release, which might serve as easily available substrate for the anaerobic microbial food chain fostering CH4 fluxes. Other known influencing factors are vegetation structure (e.g. Bubier 1995, Ström et al 2003, Lai et al 2014), ecosystem productiv- ity (Ström et al 2015) and recently fixed carbon (Chanton et al 1995). A close connection exists between plant biomass and CH4 transport capacity via aerenchyma tissues (Schimel 1995, King et al 1998). Generally, vascular plant production is considered an important control of CH4 flux as a significant fraction of emitted CH4 is derived from recently fixed carbon (Chanton et al 1995) and provides labile carbon compounds for hydrogenotrophic and acetoclastic methanogenesis (Updegraff et al 1995, Ström et al 2012). Laine et al (2015) showed that photosynth- esis in European Russian bogs wasmore intensive than from bogs in Ireland and Finland. European Russian bogs had the highest photosynthesis parameter (max- imal rate of photosynthesis per land surface area, maximal rate of photosynthesis per green leaf area, maximal rate of photosynthesis per total area of vascular plants andmoss), whichmost likely translates to providing more recently fixed carbon to the rhizo- sphere. Thus, European Russia may supports higher CH4fluxes than in Scandinavia. Another possible explanation for high flux rates at our study site is ebullition. We distinguish between two types of ebullition: episodic, which is mainly trig- gered by pressure alteration and occurs episodically and steady ebullition, which is described as a regular pattern with constant accumulation and release of bubbles (Baird et al 2004, Strack et al 2005). The pro- cess of steady ebullition is likely to take place at the Ust-Pojeg peatland due to water table draw-down caused by high temperatures during the summer. This could explain the higher fluxes found during the extreme summer in 2011. If so, a steady rather than an irregular ebullition occurred at the Ust-Pojeg study site as evident by the CH4 concentration increases within the chamber were mostly steady (91% of all measurements). During the warmer and drier summer in 2011 (compared to 2008 and the long term average), mean fluxes were about 30% higher than the fluxes mea- sured in 2008 (table 1), and two and a half times higher than peatland fluxes in Scandinavia and North Amer- ica (Turetsky et al 2014). It is unclear if the warmer projected climatic conditions for this part of Europe in the 21st century will be counterbalanced by an appro- priate amount of increase in precipitation (Kirtman et al 2013). Thus, our extraordinarily high flux rates measured under generally warmer climatic conditions might give a first insight into the future development of methane emissions for this large region. However, since only the ombrogenous part of the peatland responded with higher CH4 fluxes under higher air temperatures, while the minerogenous part showed lower CH4 fluxes (table 1, see also Turetsky et al 2014), the total methane fluxes will depend on the relative spatial proportion of each peatland type. This suggests that better spatial approximations of methane emit- ting ecosystems is still needed. In the present study, we used a land covermap that comprises only a single wetland class for our upscal- ing. This aggregation might lead to uncertainties because differences in peatland and microform types are ignored. Other sources of uncertainty might occur from the accuracy of the land covermap itself, the date of production and the resolution of the underlying satellite data. Different authors already suggested spa- tially explicit global wetland databases that separate different wetland types (e.g. Matthews and Fung 1987, Aselman and Crutzen 1989, Lehner and Döll 2004). However, the data were produced at coarse spatial resolutions (5°–0.5°) and were mostly outdated and only partly validated. In our study, we relied on an up- to-date map (2009) at medium resolution (300 m) and wemade use of comprehensive validation for the calc- ulation of the uncertainty in the distribution of the respective land cover type. Our uncertainty assess- ment were built on the work of Olofsson et al (2013), who propose a method to obtain confidence intervals of land cover areas based on the error matrix. In total, the uncertainties resulting from the upscaling from one peatland complex to the total cold peatlands in European Russia remain uncalculatable. Despite all uncertainties, our study shows that a sound and com- plete greenhouse balance of Europe can only be achieved by including European Russia’s peatlands. To do this, more data are needed from these peatlands. In this case, we also need to assess how representative our CH4 flux measurements are, which may be achieved through detailed field and laboratory experiments. 5 Environ. Res. Lett. 11 (2016) 014004 Acknowledgments This research was financially supported by the EU 6th Framework Programme Global Change and Ecosys- tems (Carbo-North, contract number 036993) and a German Research Foundation (DFG) grant to MW (Wi 2680/2-1). PS and LK were supported by the Cluster of Excellence ‘CliSAP’ (EXC177), University of Hamburg, funded through the DFG. JS was supported by theGerman Science Foundation (Schn 118/2-1). References Alekseeva R 1999 Peatlands forestry and forest resources of Komi RepublicDesign Information Cartography ed GMKozubov andAI Taskaev (Moscow:Design Information Cartography) (in Russian) Alm J, Schulman L,Walden J, NykanenH,Martikainen P J and Silvola J 1999Carbon balance of a boreal bog during a year with an exceptionally dry summer Ecology 80 161–74 Aselmann I andCrutzen PJ 1989Global distribution of natural freshwater wetlands and rice paddies, their net primary productivity, seasonality and possiblemethane emissions J. Atmos. Chem. 8 307–58 BairdA J, BeckwithCW,Waldron S andWaddington JM2004 Ebullition ofmethane-containing gas bubbles fromnear- surface Sphagnum peatGeophys. Res. Lett. 31 L21505 BridghamSD,Cadillo-QuirozH,Keller J K andZhuangQ 2013 Methane emissions fromwetlands: biogeochemical, microbial, andmodeling perspectives from local to global scalesGlob. Change Biol. 19 1325–46 Bubier J,Moore T, Savage K andCrill P 2005A comparison of methaneflux in a boreal landscape between a dry and awet yearGlob. Biogeochem. Cy. 19GB1023 Bubier J L 1995The relationship of vegetation tomethane emission and hydrochemical gradients in northern peatlands J. Ecol. 83 403–20 Chanton J P, Bauer J E, Glaser PA, Siegel D I, Kelley CA, Tyler SC, Romanowicz EH and Lazrus A 1995Radiocarbon evidence for the substrates supportingmethane formationwithin NorthernMinnesota peatlandsGeochim. Cosmochim. Acta 59 3663–8 Forbrich I, Kutzbach L,Wille C, Becker T,Wu J andWilmkingM 2011Cross-evaluation ofmeasurements of peatlandmethane emissions onmicroform and ecosystem scales using high- resolution landcover classification and sourceweight modellingAgric. ForestMeteorol. 151 864–74 Forest Europe 2011 State of Europe’s forests 2011 Status and trends in sustainable forestmanagement in Europe (Aas:Ministerial Conference on the Protection of Forests in Europe) Friborg T, SoegaardH,Christensen TR, LloydCR and PanikovN S 2003 Siberianwetlands: where a sink is a sourceGeophys. Res. Lett. 30 2129 GažovičM,Kutzbach L, Schreiber P,Wille C andWilmkingM2010 Diurnal dynamics of CH4 from a boreal peatland during snowmeltTellus 62 133–9 GlagolevMV,Golovatskaya EA and ShnyrevNA2008Greenhouse gas emission inWest SiberiaContemp. Probl. Ecol. 1 136–46 GrunwaldD, Fender A, Erasmi S and JungkunstH F 2012Towards improved bottom-up inventories ofmethane from the European land surfaceAtmos. Environ. 51 203–11 Heikkinen J E P, Virtanen T,Huttunen J T, ElsakovV and Martikainen P J 2004Carbon balance in east European tundraGlob. Biogeochem. Cy. 18GB1023 JoabssonA,Christensen TR andWallén B 1999Vascular plan controls onmethane emissions fromnorthern peat forming wetlandsTrends Ecol. Evol. 14 385–8 JoostenH, Tapio-BiströmM-L andTol S 2012Peatlands-Guidance for Climate ChangeMitigation ThroughConservation, Rehabilitation and Sustainable Use. (Rome: FAO and Wetlands International) King J Y, ReeburghWS andRegli S R 1998Methane emission and transport by arctic sedges inAlaska: results of a vegetation removal experiment J. Geophys. Res. 103 29083–92 KirtmanB et al 2013Near-term climate change: projections and predictabilityClimate Change 2013: The Physical Science Basis. Contribution ofWorkingGroup I to the VAssessment Report of the Intergovernmental Panel on Climate Change edTF Stocker et al (Cambridge: CambridgeUniversity Press) LaiDYF, RouletNT, TimR andMoore TR 2014The spatial and temporal relationships betweenCO2 andCH4 exchange in a temperate ombrotrophic bogAtmos. Environ. 89 249–59 Laine AM,WilsonD, Alm J, Schneider J andTuittila E-S 2015 Spatial variation in potential photosynthesis inNorthern European bogs J. Veg. Sci. (doi:10.1111/jvs.12355) Lehner B andDöll P 2004Development and validation of a global database of lakes, reservoirs andwetlands J. Hydrol. 296 1–22 Marschner B andKalbitz K 2003Controls of bioavailability and biodegradability of dissolved organicmatter in soils Geoderma 113 211–35 Matthews E and Fung I 1987Methane emission fromnatural wetlands. Global distribution, area, and environmental characteristics of sourcesGlob. Biogeochem. Cy. 1 61–86 McDowell NG,Marshall J D,Hooker TD andMusselmanR 2000 EstimatingCO2flux from snowpacks at three sites in the RockyMountainsTree Physiol. 20 745–53 Moore TR,DeYoungA, Bubier J L, Humphreys ER, Lafleur PMandRoulet NT 2011Amulti-year record of methaneflux at theMer Bleu Bog, SouthernCanada Ecosystems 14 646–57 Olofsson P, FoodyGM, Stehman SV andWoodcockCE 2013 Making better use of accuracy data in land change studies. Estimating accuracy and area and quantifying uncertainty using stratified estimationRemote Sens. Environ. 129 122–31 PanikovN S 1994CH4 andCO2 emissions fromnorthernwetlands of Russia: source strength and controllingmechanisms Proc. Int. Symp. onGlobal Cycles of Atmospheric GreenhouseGases (Sendai) pp 100–12 RIHMI-WDC2014Hydrometeorological data, Baseline Climatological Data Sets, Syktyvkar Site#23804 (http:// meteo.ru/english/data/) Rinne J, Riutta T, PihlatieM, AurelaM, Tuovinen J-P, Tuittila E-S andVesala T 2007Annual cycle ofmethane emission from a boreal fenmeasured by the eddy covariance techniqueTellusB 59B 449–57 Riutta T, Laine J, AurelaM, Rinne J, Vesala T, Laurila T, Haapanala S, PihlatieM andTuittila E-S 2007 Spatial variation in plant community functions regulates carbon gas dynamics in a boreal fen ecosystemTellusB 59 838–52 Runkle BRK,Wille C,GažovičM,WilmkingMandKutzbach L 2014The surface energy balance and its drivers in a boreal peatland fen of northwesternRussia J. Hydrol. 511 359–73 Sachs T,GiebelsM, Boike J andKutzbach L 2010 Environmental controls of CH4 emission frompolygonal tundra on the micro-site scale, Lena RiverDelta, SiberiaGlob. Change Biol. 16 3096–110 Schimel J P 1995 Plant transport andmethane production as controls onmethaneflux from arctic wetmeadow tundra Biogeochemistry 28 183–200 Schneider J, Kutzbach L andWilmkingM2012Carbon dioxide dynamics of a boreal peatland over a complete growing season, Komi Republic, NWRussiaBiogeochemistry 111 485–513 Schulze E-D et al 2009 Importance ofmethane andnitrous oxide for Europe´s terrestrial greenhouse-gas balanceNat. Geosci. 2 842–50 StrackM,Kellner E andWaddington JM2005Dynamics of biogenic gas bubbles in peat and their effects on peatland biogeochemistryGlob. Biogeochem. Cy. 19GB1003 StrömL, Ekberg A,MastepanovMandChristensenTR 2003The effect of vascular plants on carbon turnover andmethane 6 Environ. Res. Lett. 11 (2016) 014004 emissions from a tundrawetlandGlob. Change Biol. 9 1185–92 StrömL, Falk JM, SkovK, Jackowicz-KorczynskiM, MastepanovM,Christensen TR, LundMand SchmidtNM 2015Controls of spatial and temporal variability inCH4flux in a high arctic fen over 3 yearsBiogeochemistry 125 21–35 StrömL, TagessonT,MastepanovMandChristensen TR 2012 Presence of Eriophorum scheuchzeri enhances substrate availability andmethane emission in anArctic wetland Soil Biol. Biochem. 45 61–70 TornMS andChapin F S 1993 Environmental and biotic controls overmethane flux from arctic tundraChemosphere 26 357–68 TuretskyMR,Wieder RK andVitt DH2002 Boreal peatlandC fluxes under varying permafrost regimes Soil Biol. Biochem. 34 907–12 TuretskyMR et al 2014A synthesis ofmethane emissions from71 Northern, temperate, and subtropical wetlandsGlob. Change Biol. 20 2183–97 UpdegraffK, Pastor J, BridghamSDand JohnstonCA1995 Environmental and substrate controls over carbon andnitrogen mineralization innorthernwetlandsEcol. Appl.5 151–63 Vicca S, Janssens I A, FlessaH, Fiedler S and JungkunstHF 2009 Temperature dependence of greenhouse gas emissions from three hydromorphic soils at different groundwater levels Geobiology 7 465–76 7 Environ. Res. Lett. 11 (2016) 014004