Toward a statistical description of methane emissions from arctic wetlands

Pirk, Norbert; Mastepanov, Mikhail; López‐Blanco, Efrén; Christensen, L.; Christiansen, Hanne H.; Hansen, Birger Ulf; Lund, Magnus; Parmentier, Frans‐Jan W.; Skov, Kirstine; Christensen, Torben R.

doi:10.1007/s13280-016-0893-3

Cited by 22 publications

(22 citation statements)

References 42 publications

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“…Shallower soil temperatures largely underestimated the persistence of deeper unfrozen soils up to 96 days. Even if the main transport mechanisms is stifled by upper soil layers freezing, CH 4 production may still be occurring below the surface and could be released in bursts (Mastepanov et al, ; Pirk et al, ) or after spring thaw (Pirk et al, ). Our results suggest that CH 4 emissions are decoupled from air temperature especially in the fall shoulder season, consistent with previous work (Byun et al, ) and with the understanding that CH 4 is largely produced in anoxic soil layers below the surface (Lai, ; Treat et al, ; Zehnder, ).…”

Section: Discussionmentioning

confidence: 99%

Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems

et al. 2019

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The atmospheric methane (CH 4 ) concentration, a potent greenhouse gas, is on the rise once again, making it critical to understand the controls on CH 4 emissions. In Arctic tundra ecosystems, a substantial part of the CH 4 budget originates from the cold season, particularly during the "zero curtain" (ZC), when soil remains unfrozen around 0°C. Due to the sparse data available at this time, the controls on cold season CH 4 emissions are poorly understood. This study investigates the relationship between the fall ZC and CH 4 emissions using long-term soil temperature measurements and CH 4 fluxes from four eddy covariance (EC) towers in northern Alaska. To identify the large-scale implication of the EC results, we investigated the temporal change of terrestrial CH 4 enhancements from the National Oceanic and Atmospheric Administration monitoring station in Utqiaġvik, AK, from 2001 to 2017 and their association with the ZC. We found that the ZC is extending later into winter (2.6 ± 0.5 days/year from 2001 to 2017) and that terrestrial fall CH 4 enhancements are correlated with later soil freezing (0.79 ± 0.18-ppb CH 4 day −1 unfrozen soil). ZC conditions were associated with consistently higher CH 4 fluxes than after soil freezing across all EC towers during the measuring period (2013)(2014)(2015)(2016)(2017). Unfrozen soil persisted after air temperature was well below 0°C suggesting that air temperature has poor predictive power on CH 4 fluxes relative to soil temperature. These results imply that later soil freezing can increase CH 4 loss and that soil temperature should be used to model CH 4 emissions during the fall.

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Section: Discussionmentioning

confidence: 99%

Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems

et al. 2019

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“…Seasonal patterns of CH 4 emissions vary among sites in the Arctic. Significant emissions during spring and autumn are a common feature in high‐frequency time series and often coincide with snowmelt or soil freeze events (Sturtevant et al, ; Raz‐Yaseef et al, ; Zona et al, ; Pirk et al, ). Spring thaw emissions may result from the release of previously produced shoulder season CH 4 , trapped in frozen soils.…”

Section: Discussionmentioning

confidence: 99%

Methane Efflux Measured by Eddy Covariance in Alaskan Upland Tundra Undergoing Permafrost Degradation

et al. 2018

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Greenhouse gas emissions from thawing permafrost in arctic ecosystems may amplify globalwarming, yet estimates of the rate of carbon release, and the proportion of carbon released as methane (CH 4 ) or carbon dioxide (CO 2 ), have a high degree of uncertainty. There are many areas where no measurements exist, and few year-round or long-term records. Existing year-round eddy covariance measurements of arctic CH 4 fluxes suggest that nongrowing season emissions make up a significant proportion of tundra systems emissions on an annual basis. Here we present continuous CH 4 flux measurements made at Eight Mile Lake, an upland tundra ecosystem undergoing permafrost degradation in Interior Alaska. We found net CH 4 emissions throughout the year (1.2 ∓ 0.011 g C-CH 4 m 2 /yr) that made up 61% of total radiative forcing from annual C emissions (CO 2 and CH 4 ; 32.3 g C m 2 /yr) when taking into account the greenhouse warming potential of CH 4 relative to CO 2 . Nongrowing season emissions accounted for 50% of the annual CH 4 budget, characterized by large pulse emissions. These were related to abrupt increases in air and shallow soil temperatures rather than consistent emissions during the zero curtain-a period of the fall/early winter season when subsurface soil temperatures remain near the 0°C freezing point. Weekly growing season CH 4 emissions in 2016 and 2017 were significantly related with thaw depth, and the magnitude of CH 4 emissions between these seasons was proportional to the rate of active layer thaw throughout the season.Arctic tundra systems account for an estimated 19 Tg/yr of global CH 4 emissions at present, but there are large uncertainties (8-29 Tg/yr) owing to scarce spatial coverage and the paucity of year-round or TAYLOR ET AL. 2695 Key Points: • Arctic permafrost tundra ecosystem is an annual net source of CH 4 • Nongrowing season emissions make up 45% of annual CH 4 loss • Thaw depth is a significant driver of growing season CH 4 emissions Data gaps were filled using the marginal distribution sampling (MDS) algorithm (Reichstein et al., 2005) in REddyProc (Wutzler et al., 2018) that excluded data >2 standard deviations from the overall mean of the

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“…Second, methane (CH 4 ) is another important contributor to the total C budgets in these ecosystems (Mastepanov et al, , ; Tagesson et al, ; Zona et al, ). However, CH 4 modeling is challenging due to its different transport mechanisms, but possible (Kaiser et al, ; Walter et al, ; Walter & Heimann, ), and some studies can be used to set up future modeling efforts at this site (Pirk et al, ). Third, permafrost dynamics brings an additional layer of complexity to the C exchange (Åkerman & Johansson, ; Koven et al, ; Schuur et al, ) and its application and modeling is required due to the increased permafrost thaw in warmer temperatures (Rasmussen et al, ; Riseborough et al, ).…”

Section: Discussionmentioning

confidence: 99%

Plant Traits are Key Determinants in Buffering the Meteorological Sensitivity of Net Carbon Exchanges of Arctic Tundra

et al. 2018

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The climate sensitivity of carbon (C) cycling in Arctic terrestrial ecosystems is a major unknown in the Earth system. There is a lack of knowledge about the mechanisms that drive the interactions between photosynthesis, respiration, and changes in C stocks across full annual cycles in Arctic tundra. We use a calibrated and validated model (soil-plant-atmosphere; SPA) to estimate net ecosystem exchange (NEE), gross primary production (GPP), ecosystem respiration (R eco ), and internal C processing across eight full years. SPA's carbon flux estimates are validated with observational data obtained from the Greenland Ecosystem Monitoring program in West Greenland tundra. Overall, the model explained 73%, 73%, and 50% of the variance in NEE, GPP, and R eco , respectively, and 85% of the plant greenness variation. Flux data highlighted the insensitivity of growing season NEE to interannual meteorological variability, due to compensatory responses of photosynthesis and ecosystem respiration. In this modelling study, we show that this NEE buffering is the case also for full annual cycles. We show through a sensitivity analysis that plant traits related to nitrogen are likely key determinants in the compensatory response, through simulated links to photosynthesis and plant respiration. Interestingly, we found a similar temperature sensitivity of the trait-flux couplings for GPP and R eco , suggesting that plant traits drive the stabilization of NEE. Further, model analysis indicated that wintertime periods decreased the C sink by 60%, mostly driven by litter heterotrophic respiration. This result emphasizes the importance of wintertime periods and allows a more comprehensive understanding of full annual C dynamics.

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Toward a statistical description of methane emissions from arctic wetlands

Cited by 22 publications

References 42 publications

Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems

Sensitivity of Methane Emissions to Later Soil Freezing in Arctic Tundra Ecosystems

Methane Efflux Measured by Eddy Covariance in Alaskan Upland Tundra Undergoing Permafrost Degradation

Plant Traits are Key Determinants in Buffering the Meteorological Sensitivity of Net Carbon Exchanges of Arctic Tundra

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