Impacts of Groundwater Flow on Evolution of a Thermokarst Lake in the Permafrost Region on the Qinghai-Tibet Plateau

Thermokarst lakes and permafrost degradation in the Qinghai-Tibet Plateau (QTP) resulting from global warming have been considerably affected the local hydrological and ecological process in recent decades. Simulation with coupled moisture-heat models that follows talik formation in the Beiluhe Basin (BLB) in the hinterland of permafrost regions on the QTP provides insight into the interaction between groundwater flow and freezing-thawing process. A total of 30 modified SUTRA schemes have been established to examine the effect of hydrodynamic forces, permeability and climate. The simulated results show that the hydrodynamic conditions impact the permafrost degradation surrounding the lake, thereby further affecting groundwater flow and late-stage freezing-thawing process. The thickness of the active layer varies with time and location under different permeability conditions, which significantly influences the occurrence of a breakthrough of the lake bottom. Warmer climate accelerates thawing and decreases the required time of formation of the breakthrough zone. Overall, these results indicate that explicit consideration of hydrologic process is critical to improve the understanding of environmental and ecological changes in cold regions.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.2025321118 ◽

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

The Cryosphere ◽

10.5194/tc-14-2835-2020 ◽

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.

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

PeerJ ◽

10.7717/peerj.7146 ◽

2019 ◽

Vol 7 ◽

pp. e7146 ◽

Cited By ~ 5

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.

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Effect of highway construction on plant diversity of grassland communities in the permafrost regions of the Qinghai - Tibet plateau

The Rangeland Journal ◽

10.1071/rj07016 ◽

2007 ◽

Vol 29 (2) ◽

pp. 161 ◽

Cited By ~ 4

Author(s):

Zheng Gang Guo ◽

Rui Jun Long ◽

Fu Jun Niu ◽

Qing Bo Wu ◽

Yu Kun Hu

Keyword(s):

Plant Diversity ◽

Highway Construction ◽

Tibet Plateau ◽

Permafrost Region ◽

Study Region ◽

Β Diversity ◽

Grassland Type ◽

Grassland Communities ◽

Qinghai Tibet Plateau ◽

Permafrost Regions

During 2002–2004, a broad-scale survey on the plant diversity of grassland communities along a natural elevation gradient in the permafrost regions of the Qinghai–Tibet plateau, China, was conducted to investigate the effect of highway construction nearly 30 years ago. Richness index was not significantly different among undisturbed communities (Kobresia pygmaea meadow, K. humilis meadow, Stipa purpurea steppe, Carex moorcroftii steppe), but significant differences (P < 0.05) were observed for evenness and diversity indices among four undisturbed communities. Three indices significantly decreased from communities 100 m (lightly disturbed communities), 200 m (undisturbed communities), and 50 m (severely disturbed communities) from the Qinghai–Xicang Highway, and three indices of severely disturbed communities were similar to that of 30 m communities (extremely-severely disturbed communities). Diversity and richness indices peaked at intermediate elevations of 4720 m in undisturbed communities and lightly disturbed communities, but were uniform in the severely disturbed communities and extremely-severely disturbed communities along with the increase of elevation. β-Diversity decreased in communities at 30, 50, and 100–200 m distance from the highway. This indicated that β-diversity of communities was enhanced with the increase of disturbance for each grassland type in the study region. Both undisturbed and disturbed communities showed the same changeable bell-shaped trend with elevation increase, increasing from 4320–4620 m, decreasing from 4720 to 4920 m, and peaking at 4620 to ~4720 m, indicating that elevation from 4620–4720 m was a transition zone in permafrost region.

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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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Analysis of Raindrop Size Distribution Characteristics in Permafrost Regions of the Qinghai–Tibet Plateau Based on New Quality Control Scheme

Water ◽

10.3390/w11112265 ◽

2019 ◽

Vol 11 (11) ◽

pp. 2265 ◽

Cited By ~ 1

Author(s):

Ma ◽

Zhao ◽

Yang ◽

Xiao ◽

Zhang ◽

...

Keyword(s):

Particle Size ◽

Quality Control ◽

Rain Rate ◽

Tibet Plateau ◽

Frozen Ground ◽

Fall Velocity ◽

Raindrop Size Distribution ◽

Raindrop Size ◽

Qinghai Tibet Plateau ◽

Permafrost Regions

Raindrop size distribution (DSD) can reflect the fundamental microphysics of precipitation and provide an accurate estimation of its amount and characteristics; however, there are few observations and investigations of DSD in cold, mountainous regions. We used the second-generation particle size and velocity disdrometer Parsivel2 to establish a quality control scheme for raindrop spectral data obtained for the Qinghai–Tibet Plateau in 2015. This scheme included the elimination of particles in the lowest two size classes, particles >10 mm in diameter and rain rates <0.01 mm∙h−1. We analyzed the DSD characteristics for different types of precipitation and rain rates in both permafrost regions and regions with seasonally frozen ground. The precipitation in the permafrost regions during the summer were mainly solid with a large particle size and slow fall velocity, whereas the precipitation in the regions with seasonally frozen ground were mainly liquid. The DSD of snow had a broader drop spectrum, the largest particle size, the slowest fall velocity, and the largest number of particles, followed by hail. Rain and sleet shared similar DSD characteristics, with a smaller particle size, slower velocity, and smaller number of particles. The particle concentration for different classes of rain rate decreased with an increase in particle size and decreased gradually with an increase in rain rate. Precipitation with a rain rate >2 mm∙h−1 was the main contributor to the annual precipitation. The dewpoint thresholds for snow and rain in permafrost regions were 0 and 1.5 °C, respectively. The dewpoint range 0–1.5 °C was characterized by mixed precipitation with a large proportion of hail. This study provides valuable DSD information on the Qinghai–Tibet Plateau and can be used as an important reference for the quality control of raindrop spectral data in regions dominated by solid precipitation.

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