An understanding of soil microbial communities is crucial in roadside soil environmental assessments. The 16S rRNA sequencing of a stressed microbial community in soil adjacent to the Qinghai-Tibet Highway (QTH) revealed that the accumulation of heavy metals (over about 10 years) has affected the diversity of bacterial abundance and microbial community structure. The proximity of a sampling site to the QTH/Qinghai-Tibet Railway (QTR), which is effectively a measure of the density of human engineering, was the dominant factor influencing bacterial community diversity. The diversity of bacterial communities shows that 16S rRNA gene abundance decreased in relation to proximity to the QTH and QTR in both alpine wetland and meadow areas. The dominant phyla across all samples were Actinobacteria and Proteobacteria. The concentration of Cr and Cd in the soil were positively correlated with proximity to the QTH and QTR (MC/WC sampling sites), and Ni, Co, and V were positively correlated with proximity to the QTH and QTR (MA/WA sampling sites). The results presented in this study provide an insight into the relationships among heavy metals and soil microbial communities, and have important implications for assessing and predicting the impacts of human-induced activities from the QTH and QTR in such an extreme and fragile environment.
The original landform along the China-Russia Crude Oil Pipeline (CRCOP, line 2) was disturbed during installation of pavement for the pipeline. Forest and vegetation coverage is dense, and runoff develops along the pipe. Since the operation of the CRCOP (line 2) began in 2018, ponding has appeared on both sides of the pipeline. If there is no drainage, ponding can hardly dissipate, due to the low permeability of the permafrost layer. With the supply of surface flow and the transportation of oil at positive temperatures, ponding promotes an increase in temperature and changes the boundary thermal conditions of the pipeline. Meanwhile, when the ponding freezes and thaws, frost heave threatens operational safety of the pipeline. Furthermore, the ponding can affect the thermal condition of line 1. In this paper, the distribution of ponding along the CRCOP was obtained by field investigation. The type and cause of ponding were summarized, and the catchment and stream order were extracted by the Digital Elevation Model (DEM). According to the statistical results in attributes for topographic factors, it is known that ponding along the pipeline is relative to elevation, slope, aspect, and the Topographic Wetness Index (TWI). Water easily accumulates at altitudes of 300-450 m, slopes within 3°-5°, aspect in the northeast or south, TWI within 13-16, flow direction in north-east-south, and flow length within 90-150 km. This paper proposes a theoretical basis for the cause and characteristics of ponding along the pipeline.
A series of directional shear tests on remolded frozen soil was carried out at -10 °C by using a hollow cylinder apparatus to study failure criterion under a directional shear-stress path. Directional shear tests were conducted at five shear rates (10, 20, 30, 40, and 50 kPa/min) and five intermediate principal stress coefficients (b=0, 0.25, 0.5, 0.75, and 1), with the mean principal stress (p=4.5 MPa) kept constant. The results show that the torsional strength and the generalized strength both increase with the increase of the shear rates. According to the failure modes of frozen soil under different shear rates, the specimens present obvious plastic failure and shear band; and the torsional shear component dominates the failure modes of hollow cylindrical specimens. A shear rate of 30 kPa/min is chosen as the loading rate in the directional shear tests of frozen soil. The shape of the failure curve in the π plane is dependent on the directional angles α of the major principal stress. It is reasonable to use the strain-hardening curves to define the deviatoric stress value at γg =15% (generalized shear strain) as the failure criterion of frozen soil under a directional shear-stress path.
Hydrology of the high glacierized region in the Tianshan Mountains is an important water resource for arid and semiarid areas of China, even Central Asia. The hydrological process is complex to understand, due to the high variability in climate and the lack of hydrometeorological data. Based on field observations, the present study analyzes the meteorological and hydrological characteristics of the Koxkar Glacier River Basin during 2008-2011; and the factors influencing climate impact on glacier hydrology are discussed. The results show that precipitation at the terminus of the glacier was 426.2 mm, 471.8 mm, 624.9 mm, and 532 mm in 2008, 2009, 2010, and 2011, respectively. Discharge increases starting in May, reaches its highest value in July and August, and then starts to decrease. The mean annual discharge was 118.23×106 m3 during the four years observed, with 87.0% occurring in the ablation season (May-September). During the study period, the runoff in August accounted for 29% of total streamflow, followed by July (22%) and June (14%). The runoff exhibited obviously high interannual variability from April to September, induced by drastic changes in climate factors. Discharge autocorrelations are very high for all the years. The climate factors show different influences on discharge. The highest correlation R between daily temperature and discharge was for a time lag of 2-3 days on the Koxkar Glacier (0.66-0.76). The daily depth of runoff to daily temperature and daily water vapor pressure had an R 2 value of 0.56 and 0.69, respectively, which could be described by an exponential function. A closer relationship is found between runoff and either temperature or water vapor pressure on a monthly scale; the R 2 values are 0.65 and 0.78, respectively. The study helps us to understand the mechanisms of the hydrological-meteorological system of typical regional glaciers and to provide a reference for glacier-runoff simulations and water-resource management.
Vegetation plays a significant role in global terrestrial ecosystems and in combating desertification. We analyzed vegetation change in Inner Mongolia of northern China using the Normalized Difference Vegetation Index (NDVI) from 1998 to 2013, which is an important composite of Chinese National Ecological Security Shelter. The correlation between vegetation growth and drought quantified using the Standardized Precipitation Evapotranspiration Index (SPEI) was also explored. Results show that vegetation in most of the study area has been rehabilitated to various degrees, especially in regions such as most of the Horqin Sandy Land, eastern Ordos Plateau, Hetao Plain, as well as the middle-northern Da Hinggan Ling Mountains. Vegetation improvement in spring was significant in most of the study area. Vegetation degradation was centrally distributed in Xilingol grassland close to the Sino-Mongolia border and abandoned croplands in Ulanqab Meng. Vegetation change trends and seasonal differences varied among different vegetation types. The biggest vegetation variation in the growing season was the belt-like distribution along those grasslands close to the precipitation isoline of 200 mm and the Sino-Mongolia border, but also variation in summer and autumn exist in obvious spatial differences between grasslands and forests. Drought largely influenced vegetation change of Inner Mongolia at 6-month scale or 12-month scale, except for forests of eastern Hunlun Buir Meng and deserts or gobi deserts of western Alxa Meng. Moreover, drought in the previous winter and early spring seasons had a lag effect on growing-season vegetation. Desert grassland was the most easily affected by drought in the study area. Anthropogenic activities have made great progress in improving local vegetation under the lasting drought background.
In this study, in-situ soil moisture measurements are used to evaluate the accuracy of three AMSR-E soil moisture products from NASA (National Aeronautics and Space Administration), JAXA (Japanese Aerospace Exploration Agency) and VUA (Vrije University Amsterdam and NASA) over Maqu County, Source Area of the Yellow River (SAYR), China. Results show that the VUA soil moisture product performs the best among the three AMSR-E soil moisture products in the study area, with a minimum RMSE (root mean square error) of 0.08 (0.10) m3/m3 and smallest absolute error of 0.07 (0.08) m3/m3 at the grassland area with ascending (descending) data. Therefore, the VUA soil moisture product is used to describe the spatial variation of soil moisture during the 2010 growing season over SAYR. The VUA soil moisture product shows that soil moisture presents a declining trend from east south (0.42 m3/m3) to west north (0.23 m3/m3), with good agreement with a general precipitation distribution. The center of SAYR presents extreme wetness (0.60 m3/m3) during the whole study period, especially in July, while the head of SAYR presents a high level soil moisture (0.23 m3/m3) in July, August and September.
Spatial and temporal variations in moisture conditions across monsoon Asia were investigated using 347 Monsoon Asia Drought Atlas (MADA) grid points and 100 Chinese historical documents sites during the years 1470-2000. We applied Rotated Empirical Orthogonal Function (REOF) analysis to evaluate spatial moisture variability during the past 530 years. The first 13 principal components together explained 61.35% of the total variance, with the First Principal Component (PC1) accounting for 14.1%. After varimax rotation to the first 13 EOFs, we obtained new time series and spatial patterns. These patterns divided monsoon Asia into 13 regions with coherent moisture variability. Drought events were analyzed within these 13 regions. The results indicate that there has been a prominent drying trend in eastern and central Mongolia, Southeast Asia and east China during the last 50 years. Conversely, India and the Tibetan Plateau show a significant increase in moisture around the late 20th century. We found four drought periods, A.D. 1625-1644, A.D. 1710-1729, A.D. 1920s, and A.D. 1975-1999 occurred widely across monsoon Asia during the past 530 years. On inter-annual time scales, moisture variations in the northwest region of monsoon Asia, the Indian subcontinent and Southeast Asia are influenced by the El Ni?o-Southern Oscillation (ENSO). Thirty-year running correlation coefficient diagnostic analysis revealed that moisture variability in monsoon Asia is associated with the Pacific Decadal Oscillation (PDO).
