scholarly journals From sink to source: long-term (2002-2019) trends and anomalies in net ecosystem exchange of CO2 from a Scottish temperate peatland.

2020 ◽  
Author(s):  
Karen Hei-Laan Yeung ◽  
Carole Helfter ◽  
Neil Mullinger ◽  
Mhairi Coyle ◽  
Eiko Nemitz
Keyword(s):  
Water Table ◽  
Ecosystem Respiration ◽  
Net Ecosystem Exchange ◽  
Growing Season ◽  
Water Table Depth ◽  
Sink Strength ◽  
Summer Drought ◽  
C Cycle ◽  
Dry Spell

<p>Peatlands North of 45˚ represent one of the largest terrestrial carbon (C) stores. They play an important role in the global C-cycle, and their ability to sequester carbon is controlled by multiple, often competing, factors including precipitation, temperature and phenology. Land-atmosphere exchange of carbon dioxide (CO<sub>2</sub>) is dynamic, and exhibits marked seasonal and inter-annual variations which can effect the overall carbon sink strength in both the short- and long-term.</p><p>Due to increased incidences of climate anomalies in recent years, long-term datasets are essential to disambiguate natural variability in Net Ecosystem Exchange (NEE) from shorter-term fluctuations. This is particularly important at high latitudes (>45˚N) where the majority of global peatlands are found. With increasing pressure from stressors such as climate and land-use change, it has been predicted that with a ca. 3<sup>o</sup>C global temperature rise by 2100, UK peatlands could become a net source of C.</p><p>NEE of CO<sub>2</sub> has been measured using the eddy-covariance (EC) method at Auchencorth Moss (55°47’32 N, 3°14’35 W, 267 m a.s.l.), a temperate, lowland, ombrotrophic peatland in central Scotland, continuously since 2002. Alongside EC data, we present a range of meteorological parameters measured at site including soil temperature, total solar and photosynthetically active radiation (PAR), rainfall, and, since April 2007, half-hourly water table depth readings. The length of record and range of measurements make this dataset an important resource as one of the longest term records of CO<sub>2</sub> fluxes from a temperate peatland.</p><p>Although seasonal cycles of gross primary productivity (GPP) were highly variable between years, the site was a consistent CO<sub>2</sub> sink for the period 2002-2012. However, net annual losses of CO<sub>2</sub> have been recorded on several occasions since 2013. Whilst NEE tends to be positively correlated with the length of growing season, anomalies in winter weather also explain some of the variability in CO<sub>2</sub> sink strength the following summer.</p><p>Additionally, water table depth (WTD) plays a crucial role, affecting both GPP and ecosystem respiration (R<sub>eco</sub>). Relatively dry summers in recent years have contributed to shifting the balance between R<sub>eco</sub> and GPP: prolonged periods of low WTD were typically accompanied by an increase in R<sub>eco</sub>, and a decrease in GPP, hence weakening the overall CO<sub>2</sub> sink strength. Extreme events such as drought periods and cold winter temperatures can have significant and complex effects on NEE, particularly when such meteorological anomalies co-occur. For example, a positive annual NEE occurred in 2003 when Europe experienced heatwave and summer drought. More recently, an unusually long spell of snow lasting until the end of March delayed the onset of the 2018 growing season by up to 1.5 months compared to previous years. This was followed by a prolonged dry spell in summer 2018, which weakened GPP, increased R<sub>eco</sub> and led to a net annual loss of 47.4 ton CO<sub>2</sub>-C km<sup>-2</sup>. It is clear that the role of Northern peatlands within the carbon cycle is being modified, driven by changes in climate at both local and global scales.</p>

scholarly journals Drivers of long-term variability in CO<sub>2</sub> net ecosystem exchange in a temperate peatland

2014 ◽  
Vol 11 (10) ◽  
pp. 14981-15018 ◽  
Author(s):  
C. Helfter ◽  
C. Campbell ◽  
K. J. Dinsmore ◽  
J. Drewer ◽  
M. Coyle ◽  
...  
Keyword(s):  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Net Ecosystem Exchange ◽  
Growing Season ◽  
Sink Strength ◽  
Co2 Uptake ◽  
Annual Variability ◽  
Dormant Season ◽  
Carbon Dioxide Co2

Abstract. Land–atmosphere exchange of carbon dioxide (CO2) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO2. NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland, since 2002. Hence this is one of the longest peatland NEE studies to date. For 11 yr, the site was a consistent, yet variable, atmospheric CO2 sink ranging from −5.2 to −135.9 g CO2-C m−2 yr−1 (mean of −64.1 ± 33.6 g CO2-C m−2 yr−1). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating a phenological memory-effect. Plant productivity exhibited a marked hysteresis with respect to photosynthetically active radiation (PAR) over the growing season, indicative of two separate growth regimes. Ecosystem respiration (Reco) and gross primary productivity (GPP) were closely correlated (ratio 0.74), suggesting that autotrophic processes were dominant. Whilst the site was wet most of the year (water table depth <5 cm) there were indications that heterotrophic respiration was enhanced by drought, which also depressed GPP. NEE was compared to 5 other peatland sites which have published long-term NEE records. The CO2 uptake rate during the growing season was comparable to 3 other European sites, however the emission rate during the dormant season was significantly higher.

Net ecosystem exchange of CO2 and ecosystem respiration in two bogs in Estonia along disturbance gradient

2021 ◽  
Author(s):  
Martin Maddison ◽  
Gert Veber ◽  
Ain Kull
Keyword(s):  
Climate Change ◽  
Water Level ◽  
Water Table ◽  
Air Temperature ◽  
Ecosystem Respiration ◽  
Net Ecosystem Exchange ◽  
Growing Period ◽  
Disturbance Gradient ◽  
Study Sites

&lt;p&gt;Northern peatlands are important terrestrial carbon (C) stores, but their ability to sequestrate C is at delicate balance affected by management and also by climate change. The climate change causes less snow pack and warmer winters with faster water table drop in spring and drier summers in most boreal areas. Due to those changes natural peatlands may become C source instead of sink.&lt;/p&gt;&lt;p&gt;This study presents ecosystem respiration (ER) over five-year period and the annual estimates of net ecosystem exchange (NEE) of CO&lt;sub&gt;2&lt;/sub&gt; in Umbusi and Laukasoo in Estonia along disturbance gradient from drained to natural ombrotrophic bog. Both study sites locate next to the active cutaway peatlands. There were four CO&lt;sub&gt;2&lt;/sub&gt; flux measurements plots with three measurements points at different distance from the drainage ditch (10, 50, 100 and 200 m in Umbusi; 3, 40, 50, 125 m in Laukasoo) to form a water table depth and soil moisture gradient on both study sites. ER was measured using opaque static chamber throughout of the year in period 2012-2016. A vented and thermostated transparent plastic chamber with removable opaque cover was used for CO&lt;sub&gt;2&lt;/sub&gt; exchange measurements. NEE measurements occurred biweekly from April to December in 2015, totally were done 648 measurements. NEE was derived from modelling of ER and gross primary production with temperature, photosynthetically active radiation, water level and days of year (as phenological phase) as driving variables.&lt;/p&gt;&lt;p&gt;Annual mean NEE at four different distance from the ditch toward undisturbed area in Umbusi and Laukasoo were 0.37, 0.28, 0.15, 0.08 and 0.44, 0.34, 0.04, 0.21 kg C m&lt;sup&gt;-2&lt;/sup&gt; y&lt;sup&gt;-1&lt;/sup&gt;, respectively. Although mean NEE was positive for all plots on both sites, there were also negative annual NEE values in some points in undisturbed plots (100 and 200 m from the ditch in Umbusi and 50 and 125 m in Laukasoo).&lt;/p&gt;&lt;p&gt;Average water level at four different distance from the ditch toward undisturbed area in Umbusi and Laukasoo during growing period (from the beginning of May to the end of October) in 2015 were -94, -45, -22, -22 and -124, -33, -21, -22 cm, respectively. Monthly mean air temperature and sum of precipitation were not different from the long-term measurements in studied growing period in 2015 while winter was significantly warmer.&lt;/p&gt;&lt;p&gt;Modelled ER remained high for cold period because of higher air temperature in 2015. Due to higher respiration rate from non-frozen peat layer in cold season, more CO&lt;sub&gt;2&lt;/sub&gt; was released back to atmosphere and annually less C was accumulated. Monthly mean air temperature for cold period was 3.5 &amp;#186;C warmer than the long-term average.&lt;/p&gt;

Long-term feedbacks result in the recovery of the CO2 sink in a remnant peatland following water table lowering

2020 ◽  
Author(s):  
Joshua Ratcliffe ◽  
David Campbell ◽  
Louis Schipper ◽  
Aaron Wall ◽  
Beverley Clarkson
Keyword(s):  
Water Table ◽  
Carbon Sink ◽  
Ecosystem Respiration ◽  
Chemical Properties ◽  
Sink Strength ◽  
Raised Bogs ◽  
Time Periods ◽  
The Stability ◽  
Pristine Site

&lt;p&gt;Peatland biological, physical and chemical properties change over time in response to the long-term water table position. Such changes complicate predicting the response of peatland carbon stocks to sustained drying. Here we use Eddy Covariance measurements of CO&lt;sub&gt;2&lt;/sub&gt; exchange to study the effect of sustained water table lowering on peatland carbon dynamics. We compare measurements from a near-pristine peatland with those of a drying remnant, both raised bogs dominated by &lt;em&gt;Empodisma robustum&lt;/em&gt; (Restionaceae), across two different time periods separated by a 16-year interval. We found that the remnant bog was initially a source of CO&lt;sub&gt;2 &lt;/sub&gt;following water table lowering. However, the CO&lt;sub&gt;2&lt;/sub&gt; sink recovered and strengthened after the 16-year interval between measurements. The increase in CO&lt;sub&gt;2 &lt;/sub&gt;sink strength in the remnant bog was primarily due to increased photosynthetic uptake of CO&lt;sub&gt;2&lt;/sub&gt;, which exceeded that of the near-pristine site in both time periods. Additionally we found the loss of CO&lt;sub&gt;2 &lt;/sub&gt;via ecosystem respiration to have declined with time, however, ecosystem respiration remained elevated compared to the near-pristine site. These trends of increasing photosynthesis and declining ecosystem respiration resulted in the CO&lt;sub&gt;2 &lt;/sub&gt;sink in the dry bog reaching half the sink strength of the near-pristine bog. We consider two factors to have been key for the recovery of the CO&lt;sub&gt;2&lt;/sub&gt; sink in the remnant bog. These were 1) resilience of the peat-forming plant community to water-table change and 2) the expansion of ericoid shrubs. Our results demonstrate that the peatland carbon sink can recover from drying over a multi-decadal timescale, but questions remain as to the long-term trajectory of dry bogs and the stability of carbon fixed after water table lowering.&lt;/p&gt;

scholarly journals Drivers of long-term variability in CO<sub>2</sub> net ecosystem exchange in a temperate peatland

2015 ◽  
Vol 12 (6) ◽  
pp. 1799-1811 ◽  
Author(s):  
C. Helfter ◽  
C. Campbell ◽  
K. J. Dinsmore ◽  
J. Drewer ◽  
M. Coyle ◽  
...  
Keyword(s):  
Air Temperature ◽  
Net Ecosystem Exchange ◽  
Growing Season ◽  
Sink Strength ◽  
Co2 Uptake ◽  
Annual Variability ◽  
Dry Spells ◽  
Co2 Sink ◽  
Winter Air Temperature

Abstract. Land–atmosphere exchange of carbon dioxide (CO2) in peatlands exhibits marked seasonal and inter-annual variability, which subsequently affects the carbon (C) sink strength of catchments across multiple temporal scales. Long-term studies are needed to fully capture the natural variability and therefore identify the key hydrometeorological drivers in the net ecosystem exchange (NEE) of CO2. Since 2002, NEE has been measured continuously by eddy-covariance at Auchencorth Moss, a temperate lowland peatland in central Scotland. Hence this is one of the longest peatland NEE studies to date. For 11 years, the site was a consistent, yet variable, atmospheric CO2 sink ranging from −5.2 to −135.9 g CO2-C m−2 yr−1 (mean of −64.1 ± 33.6 g CO2-C m−2 yr−1). Inter-annual variability in NEE was positively correlated to the length of the growing season. Mean winter air temperature explained 87% of the inter-annual variability in the sink strength of the following summer, indicating an effect of winter climate on local phenology. Ecosystem respiration (Reco) was enhanced by drought, which also depressed gross primary productivity (GPP). The CO2 uptake rate during the growing season was comparable to three other sites with long-term NEE records; however, the emission rate during the dormant season was significantly higher. To summarise, the NEE of the peatland studied is modulated by two dominant factors: - phenology of the plant community, which is driven by winter air temperature and impacts photosynthetic potential and net CO2 uptake during the growing season (colder winters are linked to lower summer NEE), - water table level, which enhanced soil respiration and decreased GPP during dry spells. Although summer dry spells were sporadic during the study period, the positive effects of the current climatic trend towards milder winters on the site's CO2 sink strength could be offset by changes in precipitation patterns especially during the growing season.

Remotely sensed temperature is a proxy of greenhouse gas emissions in intact and managed peatlands

2021 ◽  
Author(s):  
Ain Kull ◽  
Iuliia Burdun ◽  
Gert Veber ◽  
Oleksandr Karasov ◽  
Martin Maddison ◽  
...  
Keyword(s):  
Soil Temperature ◽  
Greenhouse Gas Emissions ◽  
Greenhouse Gas ◽  
Water Table ◽  
Ecosystem Respiration ◽  
Ghg Emissions ◽  
Remotely Sensed ◽  
Water Table Depth ◽  
Gas Emissions

&lt;p&gt;Besides water table depth, soil temperature is one of the main drivers of greenhouse gas (GHG) emissions in intact and managed peatlands. In this work, we evaluate the performance of remotely sensed land surface temperature (LST) as a proxy of greenhouse gas emissions in intact, drained and extracted peatlands. For this, we used chamber-measured carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) and methane (CH&lt;sub&gt;4&lt;/sub&gt;) data from seven peatlands in Estonia collected during vegetation season in 2017&amp;#8211;2020. Additionally, we used temperature and water table depth data measured in situ. We studied relationships between CO&lt;sub&gt;2&lt;/sub&gt;, CH&lt;sub&gt;4&lt;/sub&gt;, in-situ parameters and remotely sensed LST from Landsat 7 and 8, and MODIS Terra. Results of our study suggest that LST has stronger relationships with surface and soil temperature as well as with ecosystem respiration (R&lt;sub&gt;eco&lt;/sub&gt;) over drained and extracted sites than over intact ones. Over the extracted cites the correlation between R&lt;sub&gt;eco&lt;/sub&gt; CO&lt;sub&gt;2&lt;/sub&gt; and LST is 0.7, and over the drained sites correlation is 0.5. In natural sites, we revealed a moderate positive relationship between LST and CO&lt;sub&gt;2&lt;/sub&gt; emitted in hollows (correlation is 0.6) while it is weak in hummocks (correlation is 0.3). Our study contributes to the better understanding of relationships between greenhouse gas emissions and their remotely sensed proxies over peatlands with different management status and enables better spatial assessment of GHG emissions in drainage affected northern temperate peatlands.&lt;/p&gt;

Assessing the impact of exceptional inter-annual climatic variability on rates of net ecosystem carbon dioxide exchange at Clara bog.

2021 ◽  
Author(s):  
Matthew Saunders ◽  
Ruchita Ingle ◽  
Shane Regan
Keyword(s):  
Water Table ◽  
Elevated Temperatures ◽  
Ecosystem Respiration ◽  
Anthropogenic Activities ◽  
Climatic Variability ◽  
Growing Season ◽  
Carbon Dioxide Exchange ◽  
Mean Annual Temperature ◽  
Monitoring Networks ◽  
The Impact

&lt;p&gt;Peatland ecosystems are integral to the mitigation of climate change as they represent significant terrestrial carbon sinks. In Ireland, peatlands cover ~20% of the land area but hold up to 75% of the soil organic carbon stock however many of these ecosystems (~85% of the total area) have been degraded due to anthropogenic activities such as agriculture, forestry and extraction for horticulture or energy. Furthermore, the carbon stocks that remain in these systems are vulnerable to inter-annual variation in climate, such as changes in precipitation and temperature, which can alter the hydrological status of these systems leading to changes in key biogeochemical processes and carbon and greenhouse gas exchange.&amp;#160; During 2018 exceptional drought and heatwave conditions were reported across Northwestern Europe, where reductions in precipitation coupled with elevated temperatures were observed. Exceptional inter-annual climatic variability was also observed at Clara bog, a near natural raised bog in the Irish midlands when data from 2018 and 2019 were compared. Precipitation in 2018 was ~300 mm lower than 2019 while the average mean annual temperature was 0.5&amp;#176;C higher. The reduction in precipitation, particularly during the growing season in 2018, consistently lowered the water table where ~150 consecutive days where the water table was &gt;5cm below the surface of the bog were observed at the central ecotope location. The differing hydrological conditions between years resulted in the study area, as determined by the flux footprint of the eddy covariance tower, acting as a net source of carbon of 53.5 g C m&lt;sup&gt;-2&lt;/sup&gt; in 2018 and a net sink of 125.2 g C m&lt;sup&gt;-2&lt;/sup&gt; in 2019. The differences in the carbon dynamics between years were primarily driven by enhanced ecosystem respiration (R&lt;sub&gt;eco&lt;/sub&gt;) and lower rates of Gross Primary Productivity (GPP) in the drier year, where the maximum monthly ratio of GPP:R&lt;sub&gt;eco&lt;/sub&gt; during the growing season was 0.96 g C m&lt;sup&gt;-2&lt;/sup&gt; month in 2018 and 1.14 g C m&lt;sup&gt;-2&lt;/sup&gt; month in 2019. This study highlights both the vulnerability and resilience of these ecosystems to exceptional inter-annual climatic variability and emphasises the need for long-term monitoring networks to enhance our understanding of the impacts of these events when they occur.&lt;/p&gt;

scholarly journals Effects of experimental nitrogen deposition on peatland carbon pools and fluxes: a modelling analysis

2015 ◽  
Vol 12 (1) ◽  
pp. 79-101 ◽  
Author(s):  
Y. Wu ◽  
C. Blodau ◽  
T. R. Moore ◽  
J. Bubier ◽  
S. Juutinen ◽  
...  
Keyword(s):  
Ecosystem Respiration ◽  
Model Performance ◽  
Net Ecosystem Exchange ◽  
N Fertilization ◽  
N Deposition ◽  
Competitive Advantages ◽  
Long Term Effects ◽  
N Content ◽  
Modelling Analysis

Abstract. Nitrogen (N) pollution of peatlands alters their carbon (C) balances, yet long-term effects and controls are poorly understood. We applied the model PEATBOG to explore impacts of long-term nitrogen (N) fertilization on C cycling in an ombrotrophic bog. Simulations of summer gross ecosystem production (GEP), ecosystem respiration (ER) and net ecosystem exchange (NEE) were evaluated against 8 years of observations and extrapolated for 80 years to identify potential effects of N fertilization and factors influencing model behaviour. The model successfully simulated moss decline and raised GEP, ER and NEE on fertilized plots. GEP was systematically overestimated in the model compared to the field data due to factors that can be related to differences in vegetation distribution (e.g. shrubs vs. graminoid vegetation) and to high tolerance of vascular plants to N deposition in the model. Model performance regarding the 8-year response of GEP and NEE to N input was improved by introducing an N content threshold shifting the response of photosynthetic capacity (GEPmax) to N content in shrubs and graminoids from positive to negative at high N contents. Such changes also eliminated the competitive advantages of vascular species and led to resilience of mosses in the long-term. Regardless of the large changes of C fluxes over the short-term, the simulated GEP, ER and NEE after 80 years depended on whether a graminoid- or shrub-dominated system evolved. When the peatland remained shrub–Sphagnum-dominated, it shifted to a C source after only 10 years of fertilization at 6.4 g N m−2 yr−1, whereas this was not the case when it became graminoid-dominated. The modelling results thus highlight the importance of ecosystem adaptation and reaction of plant functional types to N deposition, when predicting the future C balance of N-polluted cool temperate bogs.

scholarly journals Partitioning CO<sub>2</sub> net ecosystem exchange fluxes on the microsite scale in the Lena River Delta, Siberia

2018 ◽  
Author(s):  
Tim Eckhardt ◽  
Christian Knoblauch ◽  
Lars Kutzbach ◽  
Gillian Simpson ◽  
Evgeny Abakumov ◽  
...  
Keyword(s):  
Water Table ◽  
Net Ecosystem Exchange ◽  
Growing Season ◽  
Arctic Tundra ◽  
High Water ◽  
Water Levels ◽  
River Delta ◽  
Lena River ◽  
Hydrological Conditions ◽  
Lena River Delta

Abstract. Arctic tundra ecosystems are currently facing rates of amplified climate change. This is critical as these ecosystems store significant amounts of carbon in their soils, which can be mineralized to CO2 and CH4 and released to the atmosphere. To understand how the CO2 net ecosystem exchange (NEE) fluxes will react to changing climatic conditions, it is necessary to understand the individual responses of the physiological processes contributing to CO2 NEE. Therefore, this study aimed: (i) to partition NEE fluxes at the soil-plant-atmosphere interface in an arctic tundra ecosystem; and (ii) to identify the main environmental drivers of these fluxes. Hereby, the NEE fluxes were partitioned into gross primary productivity (GPP) and ecosystem respiration (Reco) and further into autotrophic (RA) and heterotrophic respiration (RH). The study examined flux data collected during the growing season in 2015 using closed chamber measurements in a polygonal tundra landscape in the Lena River Delta, northeastern Siberia. The measured fluxes on the microscale (1 m–10 m) were used to model the NEE, GPP, Reco, RH, RA and net ecosystem production (NPP) over the growing season. Here, for the first time, the differing response of in situ measured RA and RH fluxes from permafrost-affected soils to hydrological conditions have been examined. It was shown that low RA fluxes are associated to a high water table, most likely due to the submersion of mosses, while an effect of water table fluctuations on RH fluxes was not observed. Furthermore, this work found the polygonal tundra in the Lena River Delta to be a sink for atmospheric CO2 during the growing season. Spatial heterogeneity was apparent with the net CO2 uptake at a wet, depressed polygon center being more than twice as high as that measured at a drier polygon rim. In addition to higher GPP fluxes, the differences in NEE between the two microsites were caused by lower Reco fluxes at the center compared to the rim. Here, the contrasting hydrological conditions caused the CO2 flux differences between the microsites, where high water levels lad to lower decomposition rates due to anoxic conditions.

scholarly journals Moist moss tundra on Kapp Linne, Svalbard is a net source of CO<sub>2</sub> and CH<sub>4</sub> to the atmosphere

2021 ◽  
Author(s):  
Anders Lindroth ◽  
Norbert Pirk ◽  
Ingibjörg S. Jónsdóttir ◽  
Christian Stiegler ◽  
Leif Klemedtsson ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Air Temperature ◽  
Ecosystem Respiration ◽  
Net Ecosystem Exchange ◽  
Growing Season ◽  
Mean Value ◽  
The Arctic ◽  
Spatial And Temporal Variability ◽  
Annual Nee ◽  
Greenness Index

Abstract. We measured CO2 and CH4 fluxes using chambers and eddy covariance (only CO2) from a moist moss tundra in Svalbard. The average net ecosystem exchange (NEE) during the summer (June–August) was −0.40 g C m−2 day−1 or −37 g C m−2 for the whole summer. Including spring and autumn periods the NEE was reduced to −6.8 g C m−2 and the annual NEE became positive, 24.7 gC m−2 due to the losses during the winter. The CH4 flux during the summer period showed a large spatial and temporal variability. The mean value of all 214 samples was 0.000511 ± 0.000315 µmol m−2s−1 which corresponds to a growing season estimate of 0.04 to 0.16 g CH4 m−2. We find that this moss tundra emits about 94–100 g CO2-equivalents m−2 yr−1 of which CH4 is responsible for 3.5–9.3 % using GWP100 of 27.9 respectively GWP20. Air temperature, soil moisture and greenness index contributed significantly to explain the variation in ecosystem respiration (Reco) while active layer depth, soil moisture and greenness index were the variables that best explained CH4 emissions. Estimate of temperature sensitivity of Reco and gross primary productivity showed that a modest increase in air temperature of 1 degree did not significantly change the NEE during the growing season but that the annual NEE would be even more positive adding another 8.5 g C m−2 to the atmosphere. We tentatively suggest that the warming of the Arctic that has already taken place is partly responsible for the fact that the moist moss tundra now is a source of CO2 to the atmosphere.

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