Changes in Methane Flux along a Permafrost Thaw Sequence on the Tibetan Plateau

Yang, Guibiao; Peng, Yunfeng; Olefeldt, David; Chen, Yongliang; Wang, Guanqin; Li, Fēi; Zhang, Dianye; Wang, Jun; Yu, Jianliang; Liu, Li; Qin, Shuqi; Sun, Tianyang; Yang, Yuanhe

doi:10.1021/acs.est.7b04979

Cited by 53 publications

(42 citation statements)

References 58 publications

(113 reference statements)

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“…Local wetting trends including general increases in wetness in high latitudes (Zhang et al, ) can delay soil freezing (Hinkel et al, ), which our results suggest could increases the fall CH 4 emissions due to the higher rates of CH 4 efflux before the soil freezes. Recent studies in more upland thermokarst regions agree with our assumptions and data as well showing a 3.5 times higher rate of CH 4 efflux under thermokarst degradation leading to wetter ecosystems (Yang et al, ). Therefore, we suggest that understanding and predicting hydrological changes in the Arctic is of critical importance to forecast the future of carbon budgets and specifically the role CH 4 will play with changing climate.…”

Section: Discussionsupporting

confidence: 91%

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: Discussionsupporting

confidence: 91%

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

et al. 2019

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“…We chose our path analysis model based on our prior knowledge of how biophysical factors may affect GPP, R eco , and CH 4 fluxes (Gomez‐Casanovas et al, ; Lee et al, ; Reichstein et al, , ; Turetsky et al, ) and based on findings from the multiple regression analysis as described previously (Fan et al, ; Lee et al, ; Ouyang et al, ; Song et al, ; Yang et al, ). In our path analysis model, we considered temperature, water table, VPD, and PAR to be the primary factors driving GPP.…”

Section: Methodsmentioning

confidence: 99%

Seasonal Controls of CO₂ and CH₄ Dynamics in a Temporarily Flooded Subtropical Wetland

Gomez‐Casanovas

DeLucia

et al. 2020

JGR Biogeosciences

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Subtropical and tropical wetlands play a prominent role in the global carbon (C) cycle; yet factors that influence their C fluxes remain uncertain. We collected measurements from a temporarily flooded subtropical wetland over 3 years to investigate environmental drivers impacting CO2 and CH4 fluxes. The wetland was a sink of CO2 (−469 to −380 g C‐CO2 · m−2 · year−1) and a source of CH4 (25.1 to 32.1 g C‐CH4 · m−2 · year−1) to the atmosphere. Dry season CH4 emissions represented 41 to 49% of the annual budget, reflecting the importance of continuous CH4 flux measurements. Gross primary productivity (GPP) increased with temperature and radiation, and the influence of VPD on GPP varied with soil inundation. Higher water tables decreased Reco and increased GPP, and a higher GPP in turn lead to enhanced Reco likely through enhancements of GPP on autotrophic respiration. This suggests that the impact of the water table on Reco depends on the cancelling effects of hydrology and GPP. Emissions of CH4 increased with soil temperature, water table, and GPP until soils were inundated at which point temperature and GPP became the main drivers. Water table and temperature influenced GPP and CH4 fluxes, and increases in GPP directly enhanced CH4 emissions. In addition to impacting C fluxes directly through water table depth, hydrology also determined the hierarchy of the dominance of factors controlling C fluxes and their response. The positive climate forcing of subtropical wetlands may be dictated by plant‐mediated and climate interactions, with hydrological factors playing a major role in determining the greenhouse gas sink or source strength of subtropical wetlands.

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“…The soil C and N concentrations at a depth of 0–15 cm are 145.2 and 13.0 g kg −1 , respectively (Liu, Chen, Zhang, et al, ). The average active‐layer thickness in nonthermokarst areas is estimated at ~0.9 m. Thermokarst landscapes, that is, thermo‐erosion gullies, develop in this permafrost region, with the depth of the active layer within the gully exhibiting no significant difference from that of the nonthermokarst areas (Yang, Peng, Marushchak, et al, ; Yang, Peng, Olefeldt, et al, ).…”

Section: Methodsmentioning

confidence: 99%

“…One site in the undisturbed grassland without ground collapse, which was 5 m away from the gully, represented the control; the other three sites in the gully, with 50 to 90‐m interval between adjacent sites, referred to various permafrost thaw stages (Chen et al, ). The specific age of the selected site in the gully was obtained by dividing the distance between a specific site and the gully head by the extend speed, and the speed was acquired using Google Earth images (2007–2013) and repeated field surveys (2014–2016; Yang, Peng, Olefeldt, et al, ). Based on this calculation, the ages of these three sites in the gully were identified as 1, 10, and 16 years since collapse and were considered as the early, middle, and late thaw stages, respectively (Figure S1).…”

Section: Methodsmentioning

confidence: 99%

Trajectory of Topsoil Nitrogen Transformations Along a Thermo‐Erosion Gully on the Tibetan Plateau

et al. 2019

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Permafrost thaw, especially thermokarst formation, that is, ground collapse due to thawing of ice‐rich permafrost, is expected to alter soil gross nitrogen (N) transformations, which can regulate plant productivity and ecosystem carbon cycle. However, it remains unclear how thermokarst formation modifies soil N processes in permafrost ecosystems. Here 15N pool dilution techniques were used to evaluate changes in topsoil gross N transformations during various thaw stages (early, middle, and late stages) along a thermo‐erosion gully on the Tibetan Plateau. Structural equation modeling was then conducted to explore the relative importance of biotic and abiotic factors in affecting soil gross N transformations. The results showed that topsoil gross N mineralization (GNM) decreased at the three stages, reflecting declined inorganic N production after permafrost collapse. In contrast, topsoil gross nitrification increased only during the early stage. Additionally, the ratio of microbial N immobilization to GNM was enhanced during the middle and late stages, indicating a stronger microbial N limitation after thermokarst formation. The structural equation modeling analysis revealed that soil moisture played an important role in modulating gross N transformations. For GNM, decreased soil moisture had inhibiting effects via regulating the microbial biomass, microbial community, and enzyme activities along the thaw sequence. For gross nitrification, declined soil moisture exerted facilitating effects directly by improving oxygen availability and indirectly by modulating the abundances of ammonia‐oxidizing archaea and bacteria during the early stage. Overall, these results demonstrated that thermokarst formation altered soil N processes, potentially triggering interactions between ecosystem N and carbon cycles after permafrost thaw.

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Changes in Methane Flux along a Permafrost Thaw Sequence on the Tibetan Plateau

Cited by 53 publications

References 58 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

Seasonal Controls of CO₂ and CH₄ Dynamics in a Temporarily Flooded Subtropical Wetland

Trajectory of Topsoil Nitrogen Transformations Along a Thermo‐Erosion Gully on the Tibetan Plateau

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Changes in Methane Flux along a Permafrost Thaw Sequence on the Tibetan Plateau

Cited by 53 publications

References 58 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

Seasonal Controls of CO2 and CH4 Dynamics in a Temporarily Flooded Subtropical Wetland

Trajectory of Topsoil Nitrogen Transformations Along a Thermo‐Erosion Gully on the Tibetan Plateau

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Seasonal Controls of CO₂ and CH₄ Dynamics in a Temporarily Flooded Subtropical Wetland