Permafrost Regions Of Qinghai-Tibet Plateau Research Articles

Seasonal dynamics of suprapermafrost groundwater and its response to the freeing-thawing processes of soil in the permafrost region of Qinghai-Tibet Plateau

The suprapermafrost groundwater in permafrost region not only is an important component of the water cycle and land surface process, but also is closely associated with the charges of ecological environment in cold region. However, the seasonal dynamics, driving factors, and mechanism of suprapermafrost groundwater are not well understood. Based on observation at slope scale on suprapermafrost groundwater dynamics of typical alpine meadows in the Qinghai-Tibet Plateau, the seasonal dynamics, spatial distribution and driving factors of suprapermafrost groundwater were analyzed. The results showed that there were close relationships between the seasonal dynamics of suprapermafrost groundwater and the freezing-thawing processes of active soil in permafrost region. The seasonal dynamics of suprapermafrost groundwater and its slope distribution pattern were controlled by soil temperature of active layers. The phase and range of the suprapermafrost groundwater dynamics are determined by deep soil (below 60 cm depth) moisture and groundwater recharging sources. The relationship between active soil temperatures and dynamics of suprapermafrost groundwater levels was better described by Boltzmann functions. However, the influencing thresholds of soil temperature on groundwater dynamics varied at different depths of active layers and in different slope positions, which resulted in the significant spatial heterogeneity of suprapermafrost groundwater dynamics in slope scale. Land cover change and global warming certainly altered the dynamics of suprapermafrost groundwater and the hydraulic interaction between groundwater and rivers, and consequently altered the overall hydrologic cycle of watershed scale.

Modeling hydrothermal transfer processes in permafrost regions of Qinghai-Tibet Plateau in China

Hydrothermal processes are key components in permafrost dynamics; these processes are integral to global warming. In this study the coupled heat and mass transfer model for (CoupModel) the soil-plant-atmosphere-system is applied in high-altitude permafrost regions and to model hydrothermal transfer processes in freeze-thaw cycles. Measured meteorological forcing and soil and vegetation properties are used in the CoupModel for the period from January 1, 2009 to December 31, 2012 at the Tanggula observation site in the Qinghai-Tibet Plateau. A 24-h time step is used in the model simulation. The results show that the simulated soil temperature and water content, as well as the frozen depth compare well with the measured data. The coefficient of determination (R 2) is 0.97 for the mean soil temperature and 0.73 for the mean soil water content, respectively. The simulated soil heat flux at a depth of 0–20 cm is also consistent with the monitored data. An analysis is performed on the simulated hydrothermal transfer processes from the deep soil layer to the upper one during the freezing and thawing period. At the beginning of the freezing period, the water in the deep soil layer moves upward to the freezing front and releases heat during the freezing process. When the soil layer is completely frozen, there are no vertical water exchanges between the soil layers, and the heat exchange process is controlled by the vertical soil temperature gradient. During the thawing period, the downward heat process becomes more active due to increased incoming shortwave radiation at the ground surface. The melt water is quickly dissolved in the soil, and the soil water movement only changes in the shallow soil layer. Subsequently, the model was used to provide an evaluation of the potential response of the active layer to different scenarios of initial water content and climate warming at the Tanggula site. The results reveal that the soil water content and the organic layer provide protection against active layer deepening in summer, so climate warming will cause the permafrost active layer to become deeper and permafrost degradation.

Effective thermal conductivity of thermokarst lake ice in Beiluhe Basin, Qinghai-Tibet Plateau

Abstract Effective thermal conductivity (ETC) of thermokarst lake ice (TLI) is a key factor in simulating the ice processes in permafrost regions of Qinghai-Tibet Plateau (QTP). Typical TLI blocks sampled from central QTP were prepared to measure their ETC in vertical and horizontal directions at various temperatures. The ETC values of TLI are ranging between 1.60 and 2.10 W/(mK). The ETC values in both directions are very close, and change obviously along the ice depth. The ETC of TLI increases monotonously with decreasing ice temperature between 0 and 25 °C. Both the theoretical modeling and experimental results demonstrate the effects of gas pore structures on ETC of TLI. The temperature-averaged ETC decreases gradually as the porosity increases. A simple linear combination of two structural models is proposed for predicting the ETC against the porosity by introducing an empirical coefficient. This coefficient is controlled by the gas pore size, content, shape and configuration.

Changes in the thermal and hydraulic regime within the active layer in the Qinghai-Tibet Plateau

The change trends of air temperature, precipitation and evaporation from 1999 to 2008 shows that the climate in the Qinghai-Tibet Plateau permafrost region had become warmer. The analysis of the systematic active-layer data monitoring network along the Qinghai-Tibet Highway indicated that the active-layer thickness had been increasing and the soil temperature was rising. The soil temperature was rising in winter but not at the end of spring or during the entire summer. With thickening and warming of the active layer, the liquid water content of the active layer had an obvious downward migration and liquid water content in the top horizons decreased, but in the deeper horizons it increased.

Thermal hazards zonation and permafrost change over the Qinghai–Tibet Plateau

The Qinghai–Tibet Plateau is the largest permafrost region at low latitude in the world. Climate warming may lead to permafrost temperature rise, ground ice thawing and permafrost degradation, thus inducing thermal hazards. In this paper, the ARCGIS method is used to calculate the changes of ground ice content and active layer thickness under different climate scenarios on the Qinghai–Tibet Plateau, in the coming decades, thus providing the basis for hazards zonation. The method proposed by Nelson in 2002 was used for hazards zonation after revision, which was based on the changes of active layer thickness and ground ice content. The study shows that permafrost exhibits different degrees of degradation in the different climate scenarios. The thawing of ground ice and the change from low-temperature to high-temperature permafrost were the main permafrost degradation modes. This process, accompanied with thinning permafrost, increases the active layer thickness and the northward movement of the permafrost southern boundary. By 2099, the permafrost area decreases by 46.2, 16.01 and 8.5% under scenarios A2, A1B and B1, respectively. The greatest danger zones are located mainly to the south of the West Kunlun Mountains, the middle of the Qingnan Valley, the southern piedmont of the Gangdise and Nyainqentanglha Mountains and some regions in the southern piedmont of the Himalayas. The Qinghai–Tibet Plateau permafrost region is in the low-risk category. Climate warming exacerbates the development of thermal hazards. In 2099, the permafrost region is mainly in the middle-risk category, and only a small portion is in the low-risk category.

Analysis of deformation over permafrost regions of Qinghai-Tibet plateau based on permanent scatterers

The surface displacement by seasonally freezing bulge and thawing subsidence are the main hazards for engineering construction in permafrost regions, especially for the Qinghai-Tibet railway. One of the main problems is how to monitor the frozen ground's displacement in the process of construction and protection of the Qinghai-Tibetan railway. The technology of Permanent Scatterers (PS) has been successfully used to detect the long-term subsidence at urban areas. For detecting the subsidence of the frozen earth on Qinghai-Tibet Plateau, this paper extended the capability of the technology of PS to investigate deformation phenomena in vegetated area. The paper analyses an interferometric phase model, and presents improved PS algorithms for separating different components in interferometric phase. The proposed technique is implemented using ENVISAT ASAR images to detect the deformation over permafrost region of Qinghai-Tibet Plateau. The results are in concordance with results provided by a traditional ground levelling, which encourages future development using the Permanent Scatterers method to analyse deformation of the frozen earth on Qinghai-Tibet Plateau.

Water regime shifts in the active soil layer of the Qinghai–Tibet Plateau permafrost region, under different levels of vegetation

Soil moisture and water cycling in a permafrost active layer are affected in a synergistic manner by both the sequence of soil temperature and changes in vegetative cover. Between 2004 and 2007, the dynamics of soil water content and water movement in the active layer of alpine meadow soils were monitored at sites located in the permafrost region of the Qinghai–Tibetan Plateau, China for four years to examine the synergistic effects of freeze–thaw cycles and levels of vegetation cover. The analysis of variations in monthly and seasonal soil moisture, soil-desiccation index, and soil available indicated that soil moisture exhibited a relatively stable and consistent pattern over the growing season (July–September), independent from the vegetation cover. Greater soil moisture was present in the upper root zone and at the bottom of the soil profile, whereas lower moisture levels occurred in the middle portion of the profile. Irrespective of soil depth, the lower the vegetation cover, the quicker the increase in soil liquid water during the thaw initiation period (May and June), and the quicker its decrease during the freeze initiation period (October and November). In addition, the greater the vegetation cover, the greater the available water content of the upper root zone and the less the water content of the soil layer at 0.60−0.70 m depth below the root zone. Both the soil hydraulic parameters and the spatiotemporal distribution of the water content were subject to the synergistic action of the freeze–thaw cycle and the extent of vegetation cover. The variances in active soil heat transmission and heat-water coupling relationship under the different vegetation covers were considered the main driving factors in the distribution and dynamics of the active soil water regime. The permafrost supports the development of alpine frost meadow ecosystems, and well-ordered, high-cover alpine meadow vegetation favors the protection of permafrost from degradation.

Effects of permafrost thawing on vegetation and soil carbon pool losses on the Qinghai–Tibet Plateau, China

Bearing a total organic carbon (TOC) content of 9.3–10.7 kg C/m 2, alpine grassland soils of the Qinghai–Tibet plateau's permafrost region bear a greater organic carbon pool than do grassland soils in other regions of China or than tropical savannah soils. The easily released light fraction organic carbon (LFOC) accounts for 34–54% of the TOC and is particularly enriched in the topsoil (0–0.10 m). The LFOC in the organic carbon pool of alpine cold meadow and alpine cold steppe soils decreased at exponential and quadratic rates, respectively, as the vegetative cover decreased. When the vegetative cover of alpine cold meadows decreased from > 80 dm 2/m 2 to 60 dm 2/m 2, the topsoil TOC and LFOC dropped by 20.4% and 38.4%, respectively. Similarly, when the vegetative cover of alpine cold meadow decreased from 50 dm 2/m 2 to 30 dm 2/m 2 and < 15 dm 2/m 2, the topsoil LFOC content dropped by 60% and 86.7%, respectively. Under climatic warming, the degradation of permafrost and vegetation have resulted in serious soil organic carbon (SOC) loss from the carbon pool. Land cover changes that occurred between 1986 and 2000 are estimated to have resulted in a 1.8 Gg C (120 Mg C/yr) loss in SOC, and a concomitant 65% decrease in the LFOC, in the 0–0.30 m soil layer in the Qinghai–Tibet plateau's permafrost regions. Since the region's ecosystems are quite sensitive to global climate changes, if global warming persists, alpine cold grassland ecosystems are expected to further degrade. Hence, the influence of global climatic change on soil carbon emissions from alpine grasslands should receive more attention.

Phylogenetic diversity of bacteria isolates from the Qinghai-Tibet Plateau permafrost region

The Qinghai-Tibet Plateau in east Asia is a unique and important permafrost environment. However, its microbiology remains largely unexplored to date. In this study, sediment samples were collected from the Qinghai-Tibet Plateau permafrost region, bacteria isolation procedures were performed 8 times, and the samples incubated at 4 degrees C for nearly 3 months. The number of colony forming units (cfu) ranged from 0 to 10(7)/(g dry soil). The quantity of culturable bacteria grew exponentially within the first few weeks, and then slowed gradually to a plateau. Phylogenetic analyses indicated that all the isolates fell into 6 categories: high G+C Gram-positive bacteria, low G+C Gram-positive bacteria, alpha-Proteobacteria, beta-Proteobacteria, gamma-Proteobacteria, and Cytophaga-Flavobacterium-Bacteroides group bacteria. The isolates belong to 19 genera, but the genera Arthrobacter and Pseudomonas were predominant. With the increase in incubation time, the isolated populations changed in terms of both species and their respective quantities. Of the 33 analyzed isolates, 9 isolates related to 8 genera might be new taxa. These results suggest that the Qinghai-Tibet Plateau permafrost region is a specific ecologic niche that accommodates an original microbial assemblage.