Consumption of atmospheric methane by the Qinghai–Tibet Plateau alpine steppe ecosystem

Abstract. The methane (CH4) cycle on the Qinghai–Tibet Plateau (QTP), the world's largest high-elevation permafrost region, is sensitive to climate change and subsequent freezing and thawing dynamics. Yet, its magnitudes, patterns, and environmental controls are still poorly understood. Here, we report results from five continuous year-round CH4 observations from a typical alpine steppe ecosystem in the QTP permafrost region. Our results suggest that the QTP permafrost region was a CH4 sink of -0.86±0.23 g CH4-C m−2 yr−1 over 2012–2016, a rate higher than that of many other permafrost areas, such as the Arctic tundra in northern Greenland, Alaska, and western Siberia. Soil temperature and soil water content were dominant factors controlling CH4 fluxes; however, their correlations changed with soil depths due to freezing and thawing dynamics. This region was a net CH4 sink in autumn, but a net source in spring, despite both seasons experiencing similar top soil thawing and freezing dynamics. The opposite CH4 source–sink function in spring versus in autumn was likely caused by the respective seasons' specialized freezing and thawing processes, which modified the vertical distribution of soil layers that are highly mixed in autumn, but not in spring. Furthermore, the traditional definition of four seasons failed to capture the pattern of the annual CH4 cycle. We developed a new seasonal division method based on soil temperature, bacterial activity, and permafrost active layer thickness, which significantly improved the modeling of the annual CH4 cycle. Collectively, our findings highlight the critical role of fine-scale climate freezing and thawing dynamics in driving permafrost CH4 dynamics, which needs to be better monitored and modeled in Earth system models.

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Consumption of atmospheric methane by the Qinghai–Tibetan Plateau alpine steppe ecosystem

10.5194/tc-2017-264 ◽

2017 ◽

Author(s):

Hanbo Yun ◽

Qingbai Wu ◽

Qianlai Zhuang ◽

Anping Chen ◽

Tong Yu ◽

...

Keyword(s):

Tibetan Plateau ◽

Soil Temperature ◽

Critical Role ◽

High Elevation ◽

Active Layer Thickness ◽

Permafrost Region ◽

Atmospheric Methane ◽

Alpine Steppe ◽

Environmental Controls ◽

Steppe Ecosystem

Abstract. Methane (CH4) cycle on the Qinghai–Tibetan Plateau (QTP), the world's largest high-elevation permafrost region, is sensitive to climate change and subsequent cryoturbation dynamics. Yet its magnitudes, patterns, and environmental controls are still poorly understood. Here we report results from five continuous year-round CH4 observation from a typical alpine steppe ecosystem in the QTP permafrost region. Results suggested the QTP permafrost region was a CH4 sink of −0.86 ± 0.23 g CH4–C m-2 yr1 over 2012–2016, a rate higher than that of many other permafrost areas such as Arctic tundra in northern Greenland, Alaska, and western Siberia. Soil temperature and soil water content were dominant factors controlling CH4 fluxes and their correlations however changed with soil depths due to cryoturbation dynamics. This region was a net CH4 sink in autumn, but a net source in spring, despite both seasons experienced similar top soil thawing and freeze dynamics. The opposite effect was likely caused by their season–specialized cryoturbation processes, which modified the vertical distribution of soil layers that are highly mixed like a multi–layer hamburger in autumn, but not in spring. Furthermore, the traditional definition of four seasons failed to capture the pattern of annual CH4 cycle. We developed a new season division method based on soil temperature, bacteria activities, and permafrost active layer thickness, which significantly improved the modelling of annual CH4 cycle. Collectively, our findings highlight the critical role of fine–scale climate and cryoturbation in driving permafrost CH4 dynamics, which needs to be better monitored and modelled in Earth system models.

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Freeze-thaw processes of active layer regulate soil respiration of alpine meadow in the permafrost region of the Qinghai-Tibet Plateau

10.5194/tc-2019-214 ◽

2019 ◽

Author(s):

Junfeng Wang ◽

Qingbai Wu ◽

Ziqiang Yuan ◽

Hojeong Kang

Keyword(s):

Soil Respiration ◽

Active Layer ◽

Alpine Meadow ◽

Water Status ◽

Tibet Plateau ◽

Permafrost Region ◽

Permafrost Degradation ◽

Freezing And Thawing ◽

Freeze Thaw ◽

Qinghai Tibet Plateau

Abstract. Freezing and thawing action of the active layer plays a significant role in soil respiration (Rs) in permafrost regions. However, little is known about how the freeze-thaw process regulates the Rs dynamics in different stages for the alpine meadow underlain by permafrost on the Qinghai-Tibet Plateau (QTP). We conducted continuous in-situ measurements of Rs and freeze-thaw process of the active layer at an alpine meadow site in the Beiluhe permafrost region of QTP to determine the regulatory mechanisms of the different freeze-thaw stages of the active layer on the Rs. We found that the freezing and thawing process of active layer modified the Rs dynamics differently in different freeze-thaw stages. The mean Rs ranged from 0.56 to 1.75 μmol/m2s across the stages, with the lowest value in the SW stage and highest value in the ST stage; and Q10 among the different freeze-thaw stages changed greatly, with maximum (4.9) in the WC stage and minimum (1.7) in the SW stage. Patterns of Rs among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative Rs to annual total Rs were 61.54, 8.89, 18.35, and 11.2 %, respectively. Soil temperature (Ts) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as the climate warming and permafrost degradation continue, great changes in freeze-thaw process patterns may trigger more Rs emissions from this ecosystem because of prolonged ST stage.

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Using MODIS Land Surface Temperatures for Permafrost Thermal Modeling in Beiluhe Basin on the Qinghai-Tibet Plateau

Sensors ◽

10.3390/s19194200 ◽

2019 ◽

Vol 19 (19) ◽

pp. 4200 ◽

Cited By ~ 1

Author(s):

Anyuan Li ◽

Caichu Xia ◽

Chunyan Bao ◽

Guoan Yin

Keyword(s):

Surface Temperature ◽

Land Surface ◽

Ground Surface ◽

Tibet Plateau ◽

Active Layer Thickness ◽

Permafrost Region ◽

Thermal Dynamics ◽

Near Surface ◽

Warm Bias ◽

Qinghai Tibet Plateau

It is essential to monitor the ground temperature over large areas to understand and predict the effects of climate change on permafrost due to its rapid warming on the Qinghai-Tibet Plateau (QTP). Land surface temperature (LST) is an important parameter for the energy budget of permafrost environments. Moderate Resolution Imaging Spectroradiometer (MODIS) LST products are especially valuable for detecting permafrost thermal dynamics across the QTP. This study presents a comparison of MODIS-LST values with in situ near-surface air temperature (Ta), and ground surface temperature (GST) obtained from 2014 to 2016 at five sites in Beiluhe basin, a representative permafrost region on the QTP. Furthermore, the performance of the thermal permafrost model forced by MODIS-LSTs was studied. Averaged LSTs are found to strongly correlated with Ta and GST with R2 values being around 0.9. There is a significant warm bias (4.43–4.67 °C) between averaged LST and Ta, and a slight warm bias (0.67–2.66 °C) between averaged LST and GST. This study indicates that averaged MODIS-LST is supposed to be a useful data source for permafrost monitoring. The modeled ground temperatures and active-layer thickness have a good agreement with the measurements, with a difference of less than 1.0 °C and 0.4 m, respectively.

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Impacts of changes in vegetation cover on soil water heat coupling in an alpine meadow of the Qinghai-Tibet Plateau, China

Hydrology and Earth System Sciences ◽

10.5194/hess-13-327-2009 ◽

2009 ◽

Vol 13 (3) ◽

pp. 327-341 ◽

Cited By ~ 10

Author(s):

W. Genxu ◽

H. Hongchang ◽

L. Guangsheng ◽

L. Na

Keyword(s):

Heat Flux ◽

Soil Temperature ◽

Soil Water ◽

Vegetation Cover ◽

Alpine Meadow ◽

Root Zone ◽

Frozen Soil ◽

Tibet Plateau ◽

Permafrost Region ◽

Qinghai Tibet Plateau

Abstract. Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau, and the transmission of coupled soil water heat is one of the most crucial processes influencing cyclic variations in the hydrology of frozen soil regions, especially under different vegetation covers. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different vegetation covers (30, 65, and 93%) on both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by the changes in vegetation cover. The decrease in vegetation cover of an alpine meadow reduced the difference between air temperature and ground temperature (ΔTa−s), and it also resulted in a decrease in Ts at which soil froze, and an increase in the temperature at which it thawed. This was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With the increase in vegetation cover, the surface heat flux decreased. Soil heat storage at 20 cm in depth increased with increasing vegetation cover, and the heat flux that was downwardly transmitted decreased. The soil property varied greatly under different vegetation covers, causing the variation of heat conductivity and water-heat hold capacity in topsoil layer in different vegetation cover. The variation of heat budget and transmitting in soil is the main factor that causes changes in soil thawing and freezing processes, and θv−Ts coupling relationship under different vegetation fractions. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also would slow down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau.

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Vegetation Mapping in the Permafrost Region: A Case Study on the Central Qinghai-Tibet Plateau

Remote Sensing ◽

10.3390/rs14010232 ◽

2022 ◽

Vol 14 (1) ◽

pp. 232

Author(s):

Defu Zou ◽

Lin Zhao ◽

Guangyue Liu ◽

Erji Du ◽

Guojie Hu ◽

...

Keyword(s):

Thermal State ◽

Vegetation Type ◽

Confusion Matrix ◽

Kappa Coefficient ◽

Tibet Plateau ◽

Landsat 8 ◽

Permafrost Region ◽

Vegetation Map ◽

Alpine Steppe ◽

Qinghai Tibet Plateau

An accurate and detailed vegetation map is of crucial significance for understanding the spatial heterogeneity of subsurfaces, which can help to characterize the thermal state of permafrost. The absence of an alpine swamp meadow (ASM) type, or an insufficient resolution (usually km-level) to capture the spatial distribution of the ASM, greatly limits the availability of existing vegetation maps in permafrost modeling of the Qinghai-Tibet Plateau (QTP). This study generated a map of the vegetation type at a spatial resolution of 30 m on the central QTP. The random forest (RF) classification approach was employed to map the vegetation based on 319 ground-truth samples, combined with a set of input variables derived from the visible, infrared, and thermal Landsat-8 images. Validation using a train-test split (i.e., 70% of the samples were randomly selected to train the RF model, while the remaining 30% were used for validation and a total of 1000 runs) showed that the average overall accuracy and Kappa coefficient of the RF approach were 0.78 (0.68–0.85) and 0.69 (0.64–0.74), respectively. The confusion matrix showed that the overall accuracy and Kappa coefficient of the predicted vegetation map reached 0.848 (0.844–0.852) and 0.790 (0.785–0.796), respectively. The user accuracies for the ASM, alpine meadow, alpine steppe, and alpine desert were 95.0%, 83.3%, 82.4%, and 86.7%, respectively. The most important variables for vegetation type prediction were two vegetation indices, i.e., NDVI and EVI. The surface reflectance of visible and shortwave infrared bands showed a secondary contribution, and the brightness temperature and the surface temperature of the thermal infrared bands showed little contribution. The dominant vegetation in the study area is alpine steppe and alpine desert. The results of this study can provide an accurate and detailed vegetation map, especially for the distribution of the ASM, which can help to improve further permafrost studies.

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Response of freeze-thaw processes to experimental warming in the permafrost regions of the central Qinghai-Tibet Plateau

10.5194/tc-2016-80 ◽

2016 ◽

Cited By ~ 1

Author(s):

Shengyun Chen ◽

Wenjie Liu ◽

Qian Zhao ◽

Lin Zhao ◽

Qingbai Wu ◽

...

Keyword(s):

Soil Moisture ◽

Soil Moisture Content ◽

Tibet Plateau ◽

Active Layer Thickness ◽

Experimental Warming ◽

Freeze Thaw ◽

Alpine Steppe ◽

Steppe Ecosystems ◽

Qinghai Tibet Plateau ◽

Permafrost Regions

Abstract. Assessing quantitatively effect of climate warming on freeze/thaw index (FI/TI), soil freeze-thaw processes and active layer thickness (ALT) is still lacking in the permafrost regions of the Qinghai-Tibet Plateau (QTP) until now. Experimental warming was manipulated using open top chambers (OTCs) in alpine swamp meadow and alpine steppe ecosystems in the permafrost regions of the central QTP during 2009–2011. Under OTCs treatment, air temperature (Ta) significantly increased in the daytime and decreased in the nighttime, diurnal and annual Ta range significantly enhanced, and mean annual Ta increased by 1.4 °C. Owing to the experimental warming, mean annual soil temperature at the depths from 5 cm to 40 cm was increased by 0.2 ~ 0.7 °C in alpine swamp meadow and 0.3 ~ 1.5 °C in alpine steppe. Mean annual soil moisture content at 10 cm depth decreased by 1.1 % and 0.8 %, and mean annual soil salinity at 10 cm depth significantly increased by 0.3 g L-1 and 0.1 g L-1 in alpine swamp meadow and alpine steppe, respectively. Further, FI was significantly decreased by 410.7 °C d while TI was significantly increased by 460.7 °C d. Likewise, the onset dates of shallow soil thawing at 5–40 cm depths were advanced by 9 days and 8 days while the onset dates of freezing were delayed by 10 days and 4 days in alpine swamp meadow and alpine steppe, respectively. Moreover, soil frozen days were significantly decreased by 28 days and 16 days, but thawed days were increased by 18 days and 6 days, and frozen-thawed days were significantly increased by 10 days and 10 days in alpine swamp meadow and alpine steppe, respectively. Furthermore, ALT would be significantly increased by ~ 6.9 cm and ~ 19.6 cm in alpine swamp meadow and alpine steppe ecosystems, respectively.

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Impacts of changes in vegetation cover on soil water heat coupling in an alpine meadow, Qinghai-Tibet Plateau, China

Hydrology and Earth System Sciences Discussions ◽

10.5194/hessd-5-2543-2008 ◽

2008 ◽

Vol 5 (4) ◽

pp. 2543-2579

Author(s):

W. Genxu ◽

H. Hongchang ◽

L. Yuanshou ◽

W. Yibo

Keyword(s):

Heat Flux ◽

Soil Temperature ◽

Soil Water ◽

Vegetation Cover ◽

Alpine Meadow ◽

Root Zone ◽

Frozen Soil ◽

Tibet Plateau ◽

Permafrost Region ◽

Qinghai Tibet Plateau

Abstract. Alpine meadow is one of the most widespread grassland types in the permafrost regions of the Qinghai-Tibet Plateau. The transmission of coupled soil water heat is one of the most important processes influencing cyclic variations in the hydrology of frozen soil regions, especially under conditions of changing vegetation cover. The present study assesses the impact of changes in vegetation cover on the coupling of soil water and heat in a permafrost region. Soil moisture (θv), soil temperature (Ts), soil heat content, and differences in θv−Ts coupling were monitored on a seasonal and daily basis under three different densities of vegetation cover (30, 65, and 93%) upon both thawed and frozen soils. Regression analysis of θv vs. Ts plots under different levels of vegetation cover indicates that soil freeze-thaw processes were significantly affected by changes in vegetation cover. With decreasing vegetation cover upon an alpine meadow, the difference between air temperature and ground temperature (ΔTa−s) also decreased. A decrease in vegetation cover also resulted in a decrease in the Ts at which soil froze and an increase in the temperature at which it thawed; this was reflected in a greater response of soil temperature to changes in air temperature (Ta). For ΔTa−s outside the range of −0.1 to 1.0°C, root zone soil-water temperatures showed a significant increase with increasing ΔTa−s; however, the magnitude of this relationship was dampened with increasing vegetation cover. At the time of maximum water content in the thawing season, the soil temperature decreased with increasing vegetation. Changes in vegetation cover also led to variations in θv−Ts coupling. With increasing vegetation cover, the surface heat flux increased, along with the amplitude of its variations. Soil heat storage at 20 cm depth also increased with increasing vegetation cover, and the downward transmitted of heat flux decreased. In addition to providing insulation against soil warming, vegetation in alpine meadows within the permafrost region also slows down the response of permafrost to climatic warming via the greater water-holding capacity of its root zone. Such vegetation may therefore play an important role in conserving water in alpine meadows and maintaining the stability of engineering works constructed within frozen soil of the Qinghai-Tibet Plateau.

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Status, Changes and Impacts of Permafrost on Qinghai-Tibet Plateau

10.5194/egusphere-egu2020-6246 ◽

2020 ◽

Author(s):

Lin Zhao ◽

Guojie Hu ◽

Defu Zou ◽

Ren Li ◽

Yu Sheng ◽

...

Keyword(s):

Organic Carbon ◽

Soil Organic Carbon ◽

Active Layer ◽

Climate Warming ◽

Global Climate ◽

Tibet Plateau ◽

Active Layer Thickness ◽

Permafrost Region ◽

Permafrost Degradation ◽

Qinghai Tibet Plateau

Due to the climate warming, permafrost on the Qinghai-Tibet Plateau (QTP) was degradating in the past decades. Since its impacts on East Asian monsoon, and even on the global climate system, it is fundamental to reveal permafrost status, changes and its physical processes. Based on previous research results and new observation data, this paper reviews the characteristics of the status of permafrost on the QTP, including the active layer thickness (ALT), the spatial distribution of permafrost, permafrost temperature and thickness, as well as the ground ice and soil carbon storage in permafrost region.The results showed that the permafrost and seasonally frozen ground area (excluding glaciers and lakes) is 1.06 million square kilometters and 1.45 million square kilometters on the QTP. The permafrost thickness varies greatly among topography, with the maximum value in mountainous areas, which could be deeper than 200 m, while the minimum value in the flat areas and mountain valleys, which could be less than 60 m. The mean value of active layer thickness is about 2.3 m. Soil temperature at 0~10 cm, 10~40 cm, 40~100 cm, 100~200 cm increased at a rate of 0.439, 0.449, 0.396, and 0.259&#176;C/10a, respectively, from 1980 to 2015. The increasing rate of the soil temperature at the bottom of active layer was 0.486 oC/10a from 2004 to 2018.The volume of ground ice contained in permafrost on QTP is estimated up to 1.27&#215;104 km3 (liquid water equivalent). The soil organic carbon staored in the upper 2 m of soils within the permafrost region is about 17 Pg. Most of the research results showed that the permafrost ecosystem is still a carbon sink at the present, but it might be shifted to a carbon source due to the loss of soil organic carbon along with permafrost degradation.Overall, the plateau permafrost has undergone remarkable degradation during past decades, which are clearly proven by the increasing ALTs and ground temperature. Most of the permafrost on the QTP belongs to the unstable permafrost, meaning that permafrost over TPQ is very sensitive to climate warming. The permafrost interacts closely with water, soil, greenhouse gases emission and biosphere. Therefore, the permafrost degradation greatly affects the regional hydrology, ecology and even the global climate system.

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ACTIVE LAYER THICKNESS RETRIEVAL OVER THE QINGHAI-TIBET PLATEAU FROM 2000 TO 2020 BASED ON INSAR-MEASURED SUBSIDENCE AND MULTI-LAYER SOIL MOISTURE

ISPRS - International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences ◽

10.5194/isprs-archives-xliii-b3-2021-437-2021 ◽

2021 ◽

Vol XLIII-B3-2021 ◽

pp. 437-442

Author(s):

T. Chang ◽

J. Han ◽

Z. Li ◽

Y. Wen ◽

T. Hao ◽

...

Keyword(s):

Soil Moisture ◽

Layer Thickness ◽

Active Layer ◽

Surface Deformation ◽

Tibet Plateau ◽

Active Layer Thickness ◽

Permafrost Region ◽

Radar Images ◽

Soil Moisture Data ◽

Qinghai Tibet Plateau

Abstract. Active layer thickness (ALT) is an important index to reflect the stability of permafrost. The retrieval of ALT based on Interferometric Synthetic Aperture Radar (InSAR) technology has been investigated recently in permafrost research. However, most of such studies are carried out in a limited extend and relatively short temporal coverage. The combination of temporal-spatial multi-layer soil moisture data and multi-temporal InSAR is a promising approach for the large-scale characterization of ALT. In this study, we employed Small Baseline Subset Interferometry (SBAS-InSAR) technology to obtain the seasonal surface deformation from radar images of Envisat and Sentinel-1 in a permafrost region of Qinghai-Tibet Plateau (QTP). We attempt to verify and calibrate the temporal-spatial multi-layer soil moisture product in combination with the in-situ data. Based on the land subsidence data and the temporal-spatial multi-layer soil moisture data, we further improve method to retrieve the ALT information. This paper describes the progress so far and point out the future work.

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Permafrost Deformation Monitoring Along the Qinghai-Tibet Plateau Engineering Corridor Using InSAR Observations with Multi-Sensor SAR Datasets from 1997–2018

Sensors ◽

10.3390/s19235306 ◽

2019 ◽

Vol 19 (23) ◽

pp. 5306 ◽

Cited By ~ 5

Author(s):

Zhengjia Zhang ◽

Mengmeng Wang ◽

Zhijie Wu ◽

Xiuguo Liu

Keyword(s):

Human Activities ◽

Ground Deformation ◽

Deformation Monitoring ◽

Tibet Plateau ◽

Deformation Model ◽

Permafrost Region ◽

Infrastructure Development ◽

Freezing And Thawing ◽

Qinghai Tibet Plateau ◽

Observation Period

As the highest elevation permafrost region in the world, the Qinghai-Tibet Plateau (QTP) permafrost is quickly degrading due to global warming, climate change and human activities. The Qinghai-Tibet Engineering Corridor (QTEC), located in the QTP tundra, is of growing interest due to the increased infrastructure development in the remote QTP area. The ground, including the embankment of permafrost engineering, is prone to instability, primarily due to the seasonal freezing and thawing cycles and increase in human activities. In this study, we used ERS-1 (1997–1999), ENVISAT (2004–2010) and Sentinel-1A (2015–2018) images to assess the ground deformation along QTEC using time-series InSAR. We present a piecewise deformation model including periodic deformation related to seasonal components and interannual linear subsidence trends was presented. Analysis of the ERS-1 result show ground deformation along QTEC ranged from −5 to +5 mm/year during the 1997–1999 observation period. For the ENVISAT and Sentinel-1A results, the estimated deformation rate ranged from −20 to +10 mm/year. Throughout the whole observation period, most of the QTEC appeared to be stable. Significant ground deformation was detected in three sections of the corridor in the Sentinel-1A results. An analysis of the distribution of the thaw slumping region in the Tuotuohe area reveals that ground deformation was associated with the development of thaw slumps in one of the three sections. This research indicates that the InSAR technique could be crucial for monitoring the ground deformation along QTEC.

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