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

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.

scholarly journals Soil respiration of alpine meadow is controlled by freeze–thaw processes of active layer in the permafrost region of the Qinghai–Tibet Plateau

2020 ◽  
Vol 14 (9) ◽  
pp. 2835-2848
Author(s):  
Junfeng Wang ◽  
Qingbai Wu ◽  
Ziqiang Yuan ◽  
Hojeong Kang
Keyword(s):  
Soil Respiration ◽  
Active Layer ◽  
Alpine Meadow ◽  
Tibet Plateau ◽  
Permafrost Region ◽  
Permafrost Degradation ◽  
Freeze Thaw ◽  
Thaw Cycle ◽  
Freeze Thaw Cycle ◽  
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 processes affect the Rs dynamics in different stages of the alpine meadow underlain by permafrost in the Qinghai–Tibet Plateau (QTP). We conducted continuous in situ measurements of Rs and freeze–thaw processes of the active layer at an alpine meadow site in the Beiluhe permafrost region of the QTP and divided the freeze–thaw processes into four different stages in a complete freeze–thaw cycle, comprising the summer thawing (ST) stage, autumn freezing (AF) stage, winter cooling (WC) stage, and spring warming (SW) stage. We found that the freeze–thaw processes have various effects on the Rs dynamics in different freeze–thaw stages. The mean Rs ranged from 0.12 to 3.18 µmol m−2 s−1 across the stages, with the lowest value in WC and highest value in ST. Q10 among the different freeze–thaw stages changed greatly, with the maximum (4.91±0.35) in WC and minimum (0.33±0.21) in AF. Patterns of Rs among the ST, AF, WC, and SW stages differed, and the corresponding contribution percentages of cumulative Rs to total Rs of a complete freeze–thaw cycle (1692.98±51.43 g CO2 m−2) were 61.32±0.32 %, 8.89±0.18 %, 18.43±0.11 %, and 11.29±0.11 %, respectively. Soil temperature (Ts) was the most important driver of Rs regardless of soil water status in all stages. Our results suggest that as climate change and permafrost degradation continue, great changes in freeze–thaw process patterns may trigger more Rs emissions from this ecosystem because of a prolonged ST stage.

scholarly journals Importance of active layer freeze-thaw cycles on the riverine dissolved carbon export on the Qinghai-Tibet Plateau permafrost region

PeerJ ◽  
2019 ◽  
Vol 7 ◽  
pp. e7146 ◽  
Author(s):  
Chunlin Song ◽  
Genxu Wang ◽  
Tianxu Mao ◽  
Xiaopeng Chen ◽  
Kewei Huang ◽  
...  
Keyword(s):  
Active Layer ◽  
Carbonic Acid ◽  
Tibet Plateau ◽  
Vegetation Coverage ◽  
Permafrost Region ◽  
Permafrost Degradation ◽  
Carbon Export ◽  
Dissolved Carbon ◽  
Total Runoff ◽  
Qinghai Tibet Plateau

The Qinghai-Tibet Plateau (QTP) is experiencing severe permafrost degradation, which can affect the hydrological and biogeochemical processes. Yet how the permafrost change affects riverine carbon export remains uncertain. Here, we investigated the seasonal variations of dissolved inorganic and organic carbon (DIC and DOC) during flow seasons in a watershed located in the central QTP permafrost region. The results showed that riverine DIC concentrations (27.81 ± 9.75 mg L−1) were much higher than DOC concentrations (6.57 ± 2.24 mg L−1). DIC and DOC fluxes were 3.95 and 0.94 g C m−2 year−1, respectively. DIC concentrations increased from initial thaw (May) to freeze period (October), while DOC concentrations remained relatively steady. Daily dissolved carbon concentrations were more closely correlated with baseflow than that with total runoff. Spatially, average DIC and DOC concentrations were positively correlated with vegetation coverage but negatively correlated with bare land coverage. DIC concentrations increased with the thawed and frozen depths due to increased soil interflow, more thaw-released carbon, more groundwater contribution, and possibly more carbonate weathering by soil CO2 formed carbonic acid. The DIC and DOC fluxes increased with thawed depth and decreased with frozen layer thickness. The seasonality of riverine dissolved carbon export was highly dependent on active layer thawing and freezing processes, which highlights the importance of changing permafrost for riverine carbon export. Future warming in the QTP permafrost region may alter the quantity and mechanisms of riverine carbon export.

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

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

<p>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.</p><p>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°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.</p><p>The volume of ground ice contained in permafrost on QTP is estimated up to 1.27×10<sup>4</sup> km<sup>3</sup> (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.</p><p>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.</p>

scholarly journals Small-Baseline Approach for Monitoring the Freezing and Thawing Deformation of Permafrost on the Beiluhe Basin, Tibetan Plateau Using TerraSAR-X and Sentinel-1 Data

Sensors ◽  
2020 ◽  
Vol 20 (16) ◽  
pp. 4464
Author(s):  
Jing Wang ◽  
Chao Wang ◽  
Hong Zhang ◽  
Yixian Tang ◽  
Xuefei Zhang ◽  
...  
Keyword(s):  
Active Layer ◽  
Surface Deformation ◽  
Residual Deformation ◽  
Dynamic Monitoring ◽  
Tibet Plateau ◽  
Time Lags ◽  
Freezing And Thawing ◽  
Linear Deformation ◽  
Small Baseline ◽  
Qinghai Tibet Plateau

The dynamic changes of the thawing and freezing processes of the active layer cause seasonal subsidence and uplift over a large area on the Qinghai–Tibet Plateau due to ongoing climate warming. To analyze and investigate the seasonal freeze–thaw process of the active layer, we employ the new small baseline subset (NSBAS) technique based on a piecewise displacement model, including seasonal deformation, as well as linear and residual deformation trends, to retrieve the surface deformation of the Beiluhe basin. We collect 35 Sentinel-1 images with a 12 days revisit time and 9 TerraSAR-X images with less-than two month revisit time from 2018 to 2019 to analyze the type of the amplitude of seasonal oscillation of different ground targets on the Beiluhe basin in detail. The Sentinel-1 results show that the amplitude of seasonal deformation is between −62.50 mm and 11.50 mm, and the linear deformation rate ranges from −24.50 mm/yr to 5.00 mm/yr (2018–2019) in the study area. The deformation trends in the Qinghai–Tibet Railway (QTR) and Qinghai–Tibet Highway (QTH) regions are stable, ranging from −18.00 mm to 6 mm. The InSAR results of Sentinel-1 and TerraSAR-X data show that seasonal deformation trends are consistent, exhibiting good correlations 0.78 and 0.84, and the seasonal and linear deformation rates of different ground targets are clearly different on the Beiluhe basin. Additionally, there are different time lags between the maximum freezing uplift or thawing subsidence and the maximum or minimum temperature for the different ground target areas. The deformation values of the alpine meadow and floodplain areas are higher compared with the alpine desert and barren areas, and the time lags of the freezing and thawing periods based on the Sentinel-1 results are longest in the alpine desert area, that is, 86 days and 65 days, respectively. Our research has important reference significance for the seasonal dynamic monitoring of different types of seasonal deformation and the extensive investigations of permafrost in Qinghai Tibet Plateau.

scholarly journals Reduced microbial stability in the active layer is associated with carbon loss under alpine permafrost degradation

2021 ◽  
Vol 118 (25) ◽  
pp. e2025321118
Author(s):  
Ming-Hui Wu ◽  
Sheng-Yun Chen ◽  
Jian-Wei Chen ◽  
Kai Xue ◽  
Shi-Long Chen ◽  
...  
Keyword(s):  
Active Layer ◽  
Tibet Plateau ◽  
Permafrost Degradation ◽  
Soil C ◽  
C Cycling ◽  
Microbial Stability ◽  
The Stability ◽  
Qinghai Tibet Plateau ◽  
Permafrost Regions

Permafrost degradation may induce soil carbon (C) loss, critical for global C cycling, and be mediated by microbes. Despite larger C stored within the active layer of permafrost regions, which are more affected by warming, and the critical roles of Qinghai-Tibet Plateau in C cycling, most previous studies focused on the permafrost layer and in high-latitude areas. We demonstrate in situ that permafrost degradation alters the diversity and potentially decreases the stability of active layer microbial communities. These changes are associated with soil C loss and potentially a positive C feedback. This study provides insights into microbial-mediated mechanisms responsible for C loss within the active layer in degraded permafrost, aiding in the modeling of C emission under future scenarios.

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