Research in Cold and Arid Regions最新文献

Under global warming, permafrost around the world is experiencing degradation which is especially so on the Third Pole, the Qinghai-Tibet Plateau (QTP), China. Retrogressive thaw slump (RTS) is one of the thermokarst features caused by rapid degradation of ice rich permafrost, which transforms landforms and threatens infrastructures, and even affects the terrestrial carbon cycle. In this work, vegetation communities surrounding a RTS in the Fenghuoshan Mountains of the interior portion of the Qinghai-Tibet Plateau have been investigated to examine the impact from RTS. This investigation indicates that the occurrence of RTS influences the vegetation community by altering their habitats, especially the soil water content, which forces the vegetation community to evolve in order to adapt to the alterations. In the interior part of RTS where it has been disturbed tremendously, alterations have produced a wider niche and richer plant species. This favors species of a wet environment in a habitat where it was a relatively dry environment of alpine steppe prior to the occurrence of RTS. This study adds to limited observations regarding the impact of RTS to vegetation community on the QTP and helps us to reach a broader understanding of the effects of permafrost degradation as well as global warming.

The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations. The construction process and the hydration heat of cast-in-place (CIP) pile foundations affect the thermal stability of permafrost. In this paper, temperature data from inside multiple CIP piles, borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations. The following conclusions are drawn from the field observation data. (1) The early temperature change process of different CIP piles is different, and the differences gradually diminish over time. (2) The initial concrete temperature is linearly related with the air temperature, net radiation and wind speed within 1 h before the completion of concrete pouring; the contributions of the air temperature, net radiation, and wind speed to the initial concrete temperature are 51.9%, 20.3% and 27.9%, respectively. (3) The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center. It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.

The amount of rainfall varies unevenly in different regions of the Qinghai-Tibet Plateau, with some regions becoming wetter and others drier. Precipitation has an important impact on the process of surface energy balance and the energy-water transfer within soils. To clarify the thermal-moisture dynamics and thermal stability of the active layer in permafrost regions under wet/dry conditions, the verified water-vapour-heat coupling model was used. Changes in the surface energy balance, energy-water transfer within the soil, and thickness of the active layer were quantitatively analyzed. The results demonstrate that rainfall changes significantly affect the Bowen ratio, which in turn affects surface energy exchange. Under wet/dry conditions, there is a positive correlation between rainfall and liquid water flux under the hydraulic gradient; water vapour migration is the main form under the temperature gradient, which indicates that the influence of water vapour migration on thermal-moisture dynamics of the active layer cannot be neglected. Concurrently, regardless of wet or dry conditions, disturbance of the heat transport by conduction caused by rainfall is stronger than that of convection by liquid water. In addition, when rainfall decreases by 1.5 times (212 mm) and increases by 1.5 times (477 mm), the thickness of the active layer increases by 0.12 m and decreases by 0.21 m, respectively. The results show that dry conditions are not conducive to the preservation of frozen soil; however, wet conditions are conducive to the preservation of frozen soil, although there is a threshold value. When this threshold value is exceeded, rainfall is unfavourable for the development of frozen soil.

Nitraria tangutorum Bobr., a typical xero-halophyte, can be used for vegetation restoration and reconstruction in arid and semiarid regions affected by salinity. However, global climate change and unreasonable human activity have exacerbated salinization in arid and semi-arid regions, which in turn has led to the growth inhibition of halophytes, including N. tangutorum. Arbuscular mycorrhizal fungi (AMF) and plant growth-promoting rhizobacteria (PGPR) have the potential to improve the salt tolerance of plants and their adaptation to saline soil environments. In this study, the effects of single and combined inoculations of AMF (Glomus mosseae) and PGPR (Bacillus amyloliquefaciens FZB42) on N. tangutorum were evaluated in severe saline soil conditions. The results indicate that AMF and PGPR alone may not adapt well to the real soil environment, and cannot ensure the effect of either growth promotion or salt-tolerance induction on N. tangutorum seedlings. However, the combination of AMF and PGPR significantly promoted mycorrhizal colonization, increased biomass accumulation, improved morphological development, enhanced photosynthetic performance, stomatal adjustment ability, and the exchange of water and gas. Co-inoculation also significantly counteracted the adverse effect of salinity on the soil structure of N. tangutorum seedlings. It is concluded that the effectiveness of microbial inoculation on the salt tolerance of N. tangutorum seedlings depends on the functional compatibility between plants and microorganisms as well as the specific combinations of AMF and PGPR.

Heavy metal pollution of soil has become one of the most common hazards in human development. The artificial freezing method, especially the progressive freezing method, can reduce heavy metal pollutants in the soil and promises to be an effective in-situ treatment of contaminated sites. This study analyzes the freezing purification mechanism of heavy metal contaminants in saturated sand and identifies three main factors that impact the effects of purification: freezing rate, initial concentration, and diffusion coefficient. Moreover, one-dimensional freezing tests are carried out by different freezing modes. The experimental results show that the heavy metal chromium could only be removed effectively with a slow freezing rate. By optimizing the freezing mode and freezing rate, a long section of soil was frozen and purified, with the maximum purification rate reaching 65.8%. This study shows that it is feasible to treat contaminated saturated sand by a gradual-cooling freezing method.

China's Northwest Arid Region (NAR), with dry and cold climate conditions and glaciers widely developed in the high mountains, provides vital water resources for Asia. The consecutive cold, warm, dry and wet days have much higher impacts on the water cycle process in this region than extreme temperature and precipitation events with short durations but high intensities. Parametric and nonparametric trend analysis methods widely used in climatology and hydrology are employed to identify the temporal and spatial features of the changes in the consecutive cold, warm, dry and wet days in the NAR based on China's 0.5° × 0.5° meteorological grid datasets of daily temperature and precipitation from 1961 to 2018. This study found that (1) the consecutive cold days (Cold Spell Duration Indicator, CSDI), and the consecutive dry days (CDD) decreased, while the consecutive warm days (Warm Spell Duration Indicator, WSDI), and the consecutive wet days (CWD) increased from 1961 to 2018, (2) and the eastern Kunlun Mountains were the hot spots where all of these consecutive climate indices changed significantly, (3) and the changes in these consecutive climate indices were highly correlated with the rise in the Global Mean Land/Ocean Temperature Index. The results indicated that winters tended to warmer and dryer and summer became hotter and wetter during 1961–2018 in the NAR under the global warming, which can lead to the sustained glacier retreat and the increase in summer runoff in this region, and the eastern Kunlun Mountains are the area where could face high risks of water scarcity and floods if the changes in these climate indices continue in the future. Given the vulnerability of the socio-economic systems in the NAR to a water shortage and floods, it is most crucial to improve the strategies of water resources management, disaster prevention and risk management for this region under climate change.

Straw checkerboard sand barriers with a porous structure that consists of a pervious upper portion and a dense lower portion are widely used to achieve great sand control effect. Considering this, and resolving the serious earth surface undercutting problem after HDPE sandbreak net checkboard barriers setting, the authors used HDPE (high-density polyethylene) materials to prepare new sandbreak materials with a similar porous structure. Through wind tunnel simulations and field sand control monitoring, we compared the sand control effect of three HDPE sandbreak nets with different porosity structure. Compared to the sandbreak net with uniform porosity structure, the three types of HDPE sandbreak nets with different porosity structure had poorer effect on reducing sand transport rates, but had longer effective protection distance before sandbreak nets at low wind velocity conditions (<12 m/s), longer effective protection distance at high wind velocity (>14 m/s) and longer effective protection distance between sandbreak nets at all experimental wind velocity conditions. Wind and sand control effect characteristics of HDPE sandbreak nets with different porosity structure provide an ideal material on semi-buried checkerboard sand barriers for sand stabilization. By contrast, uniform-type sandbreak nets are used as materials on high upright sand fences for sand blocking. These HDPE sandbreak nets can be used to replace traditional sandbreak materials and have a very high potential for widespread and popular application in aeolian sand disaster control.

The freezing-thawing variation of permafrost active layer increases the complexity of rainfall-runoff processes in alpine river basins, Northwest China. And alpine meadow is the prominent ecosystem in these basins. This study selected a small alpine meadow watershed in the upper reaches of the Shule River Basin, China. We investigated alpine rainfall-runoff processes, as well as impacts of summer thaw depth of active layer, soil temperature and moisture variation on streamflow based on in-situ observations from July 2015 to December 2020. Some hydrologic parameters or indices were calculated using statistical methods, and impacts of permafrost change on river runoff were assessed using the variable infiltration capacity model (VIC). In the alpine meadow, surface soil (0–10 cm depth) of the active layer starts to freeze in mid-October each year, and begins to thaw in early April. Also, the deeper soil (70–80 cm depth) of the active layer starts to freeze in late October, and begins to thaw in late June. Moisture content in shallow soils fluctuates regularly, whereas deeper soils are more stable, and their response to rainstorms is negligible. During active layer thawing, the moisture content increases with soil depth. In the alpine meadow, vertical infiltration only occurred in soils up to 40 cm deep, and lateral flow occurred in 0–20 and 60–80 cm deep soils at current rainfall intensity. Summer runoff ratios were 0.06–0.31, and runoff floods show lags of 9.5–23.0 h following the rainfall event in the study area. The freeze–thaw process also significantly impacts runoff regression coefficients, which were 0.0088–0.0654 per hour. Recession coefficient decrease negatively correlates with active layer thawing depth in summer and autumn. Alpine river basin permafrost can effectively increase peak discharge and reduce low flow. These findings are highly significant for rainfall–runoff conversion research in alpine areas of inland rivers.

The vibration of underground or buried piping during construction and long-term operation causes secondary disasters, and becomes more complex when tubes are buried in cold regions. The interface between saturated frozen soil and lining is regarded as a thin spring-like layer whose thickness could be negligible. In this paper, the dynamic response of saturated frozen soil is studied in frequency domain by using the Helmholtz composition and Fourier transform to obtain analytical solutions of the radial and axial displacement, as well as expressions of the stiffness coefficient (K_r) and damping coefficient (C_r) of the spring-like interface. Numerical results indicate that K_r and C_r are related to physical properties of the lining and its surrounding soil, and the coefficients of the spring-like model could be changed by adjusting lining parameters to improve structure stability under the same load conditions. Also, the viscoelastic contact surface of the spring-like model is considered to have less effect on the surrounding soil than that when the lining has complete contact with the soil under load. The degree of soil freezing significantly affects the axial and radial displacement of the soil when the interface between lining and unsaturated frozen soil is taken into consideration.

Research on the stability of soil slopes in seasonally frozen regions has mainly focused on slope failures during the thawing window. There are few studies on slope stability during the freezing window and its subsequent influence on slope failure in the next thawing window. In this paper, soil strength was tested during freezing and thawing to obtain temperature-dependent strength parameters for the simulation of slope stability. Then, the slope's temperature field over an entire year was accurately simulated so that characteristics of the frozen layer could be determined at any time. Based on the above results, the progressive failure modes of frozen soil slopes are discussed. The results show that: 1) during the freezing window, depth of the frozen soil layer increases, as does the slope's safety factor, while a yield zone propagates towards the slope shoulder. (2) During the thawing window, the frozen soil layer shrinks in depth while the yield zone continuously expands, which decreases the safety factor. Comprehensive analysis of these results indicate that the frozen layer provides a “toe-locking effect” that increases the safety factor during the freezing window, while it also provides a “dragging effect” that propagates the yield zone towards the slope shoulder. During the thawing window, the “toe-locking effect” gradually diminishes; a continuous sliding surface is formed, which lead to a landslide. The frozen soil layer of the freezing window accelerates the slope sliding in the thawing window.