The efficient and coordinated development of industrialization,urbanization,informatization and agricultural modernization(so called "Sihua Tongbu" in China,and hereinafter referred to as "four modernizations") is not only a practical need but also an important strategic direction of integrating urban-rural development and regional development in recent China.This paper evaluated the comprehensive,coupling and coordinated developmental indices of "four modernizations" of China's 343 prefecture-level administrative units,and calculated their efficiency of "four modernizations" in 2001 and 2011.The efficiency evaluation index system was established.The efficiencies and their changing trend during the period 2001-2011 were investigated using the data envelopment analysis(DEA) model.Spatial-temporal pattern of the efficiency of China's prefecture-level units was explored by using exploratory spatial data analysis(ESDA).Finally,the main influencing factors were revealed with the aid of geographically weighted regression(GWR) model.Results indicate that the comprehensive,coupling and coordinated developmental indices and efficiency of "four modernizations" of China's prefecture-level administrative units have obvious spatial differences and show diverse regional patterns.Overall,the efficiency is relatively low,and only few units with small urban populations and economic scale are in DEA efficiencies.The efficiency changing trends were decreasing during 2001-2011,with a transfer of high efficiency areas from inland to eastern coastal areas.The difference between urban and rural per capita investment in fixed assets boasts the greatest influence on the efficiency.
Maximum frost heave of unsaturated frost-susceptible soils, in conjunction with a high water table, is an important consideration for the design of foundations in seasonally frozen regions. Therefore, it is necessary to evaluate accurately and efficiently the maximum frost heave for a given soil. For this purpose, a series of one-sided freezing experiments was conducted on unsaturated silty clay in an open system. Multistage cooling of sufficient duration was applied to the soil sample's top, while constant above-zero temperatures were maintained at the bottom. Then, a simple methodology for calculating maximum frost heave at a given cooling temperature was derived utilizing information obtained within the limited time allotted for each stage. On this basis, an empirical equation for defining maximum frost heave as a function of cooling temperature and overburden pressure was determined. Overall, this study provides a simple and practical procedure that is applicable to the evaluation of maximum frost heave of unsaturated frost-susceptible soils.
Land use change has a profound impact on biodiversity and ecological processes, and is closely related to changes in landscape patterns. This paper introduces the theory and method of land economic niche into landscape ecology, which provides a new method for spatial characterization of urban and rural spatial landscape patterns. Based on this theory, this paper analyzes the landscape pattern of Ganzhou District by using Landsat images as data source in 1995, 2000, 2005, 2010 and 2015. We calculated the land economic niche by applying the niche potential theory. Combined with the theory of landscape ecology, we explored the effects of the land economic niche change on the landscape pattern at a county scale. The results show that economic niche of construction land, watershed and farmland increased during 1995-2015, and grassland declined significantly. The economic niche of farmland, construction land, watershed and grassland show a negative correlation with the number of patches (NP), fragmentation index (FN) and the fractal dimension index (FD), and had a positive correlation with the aggregation index (AI). There was no significant correlation between the forest land economic niche and landscape metrics. The change of land economic niche has a driving effect on the landscape pattern of the county, which can represent the economic development direction of Ganzhou District. The land economic niche is closely related to the landscape type which can directly obtain an economic benefit.
Dissolved organic matter (DOM) is an important component of ice cores but is currently poorly characterized. DOM from one Holocene sample (HS, aged at 1600-4500 B.P.) and one Last Glacial Maximum sample (LS, aged at 21000-25000 B.P.) from the North Greenland Eemian Ice Drilling (NEEM) ice core were analyzed by ultra-high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). CHO compounds contributed 50% of the compounds identified in negative-ionization mode in these two samples, with significant contributions from organic N, S, and P compounds, likely suggesting that marine DOM was an important source in these samples. Overall, the chemical compositions are similar between these two samples, suggesting their consistent DOM sources. However, subtle differences in the DOM between these two samples are apparent and could indicate differences in source strength or chemistry occurring through both pre- and post-depositional processes. For example, higher relative amounts of condensed carbon compounds in the HS DOM (5%), compared to the LS DOM (2%), suggest potentially important contributions from terrestrial sources. Greater incorporation of P in the observed DOM in the LS DOM (22%), compared to the HS DOM (13%), indicate more active microbiological processes that likely contribute to phosphorus incorporation into the DOM pool. Although these two samples present only a preliminary analysis of DOM in glacial/interglacial periods, the data indicate a need to expand the analysis into a broader range of ice-core samples, geographical locations, and glacial/interglacial periods.
The soil-freezing characteristic curve (SFCC), which represents the relationship between unfrozen water content and sub-freezing temperature (or suction at ice-water interface) in a freezing soil, can be used for understanding the transportation of heat, water, and solute in frozen soils. In this paper, the soil freezing process and the similarity between the SFCC of saturated frozen soil and soil-water characteristic curve (SWCC) of unfrozen unsaturated soil are reviewed. Based on similar characteristics between SWCC and SFCC, a conceptual SFCC is drawn for illustrating the main features of soil freezing and thawing processes. Various SFCC expressions from the literature are summarized. Four widely used expressions (i.e., power relationship, exponential relationship, van Genuchten 1980 equation and Fredlund and Xing 1994 equation) are evaluated using published experimental data on four different soils (i.e., sandy loam, silt, clay, and saline silt). Results show that the exponential relationship and van Genuchten (1980) equation are more suitable for sandy soils. The simple power relationship can be used to reasonably best-fit the SFCC for soils with different particle sizes; however, it exhibits limitations when fitting the saline silt data. The Fredlund and Xing (1994) equation is suitable for fitting the SFCCs for all soils studied in this paper.
The simulation of soil temperature on the Tibetan Plateau (TP) plays a dominant role in the performance of both global climate and numerical weather forecast models. To improve the simulation of soil temperature on the TP, the Johansen soil thermal conductivity parameterization scheme was introduced into Community Land Model 3.5 (CLM3.5) and Regional Climatic Model 4 (RegCM4). The improved CLM3.5 and RegCM4-CLM were utilized to conduct offline and regional simulation experiments on the TP. Comparison of the new and old schemes revealed that CLM3.5 provides high thermal conductivity parameters of mineral soil solid on the TP. The Johansen scheme is more practical for the TP than the soil thermal conductivity parameterization in CLM3.5. The simulation of soil temperature and liquid water content was improved in offline experiment. The improved parameterization scheme can also reduce the simulation error of soil temperature in winter throughout the entire TP.
Expansive soils located in cold regions can easily endure the action of frost heaving and cyclic freezing–thawing. Cracking can also occur in expansive clayey soils under freeze–thaw cycles, of which little attention has been paid on this issue. In this study, laboratory experiment and cracking analysis were performed on an expansive soil. Crack patterns were quantitatively analyzed using the fractal concept. The relationships among crack pattern, water loss, number of freeze–thaw cycles, and fractal dimension were discussed. It was found that crack patterns on the surface exhibit a hierarchical network structure that is fractal at a statistical level. Cracks induced by freeze–thaw cycles are shorter, more irregularly oriented, and slowly evolves from an irregularly rectilinear pattern towards a polygonal or quasi–hexagonal one; water loss, closely related to specimen thickness, plays a significant role in the process of soil cracking; crack development under freeze-thaw cycles are not only attributed to capillary effect, but also to expansion and absorption effects.
The objective of this project was to characterize the freeze-thaw properties of recycled concrete (RCA) and asphalt (RAP) as unbound base and to assess how they behaved in the field for nearly 8 years. This paper includes an examination of existing information, laboratory studies of freeze-thaw behavior, and evaluation of data from MnROAD field-test sections in a seasonally cold region, i.e., in Minnesota, USA. Test sections were constructed using recycled materials in the granular base layers at the MnROAD test facility. One test section included 100% RAP, another 100% RCA, a third one a 50/50 blend of RCA/natural aggregate, and a fourth one only natural aggregate (Class 5) as a control. The stiffness (i.e., elastic modulus) was monitored during construction and throughout the pavement life by the Minnesota Department of Transportation, along with the variation of temperatures and moisture regimes in the pavement to determine their effects on pavement performance. The resilient modulus of each material was determined by bench-scale testing in accordance with NCHRP 1-28a, as well as by field-scale tests incorporating a falling-weight deflectometer. Specimens were subjected to as many as 20 cycles of freeze-thaw in the laboratory, and the change in their resilient modulus was measured. In the field-test sections constructed with the same materials as the base course, temperature, moisture, and field modulus (from falling-weight deflectometer tests) were monitored seasonally for nearly 8 years. From the temperatures in the base course layer, the number of freeze-thaw cycles experienced in the field was determined for each test section. Inferences were made relative to modulus change versus freeze-thaw cycles. Conclusions were drawn for long-term field performances of the recycled base (RAB) in comparison to natural aggregate.
A pile foundation is commonly adopted in geotechnical engineering to support structures, and its application has been extended to cold-regions engineering. In past decades, a host of scholars investigated pile behaviors and proposed design guidelines for seasonally frozen ground or permafrost. This paper reviews the research with respect to pile performance and engineering practice in cold regions, organized as follows: (1) creep tests and bearing capacity, (2) frost-jacking hazards, (3) laterally loaded piles, (4) dynamic responses, (5) refreezing due to concrete-hydration heat, and (6) improved countermeasures and design methods. We first summarize previous research and recent progress; then, predict the development trend of pile foundations in cold regions and recommend further research.
The spatial distributions of lead, arsenic, and copper (Pb, As, and Cu, respectively) in surface snow along the transect from the Zhongshan Station to Dome A, East Antarctica, are presented. The mean concentrations of Pb, As, and Cu are 1.04±1.56 pg/g, 0.39±0.08 pg/g, and 11.2±14.4 pg/g, respectively. It is estimated that anthropogenic contributions are dominant for Pb, As, and Cu. Spatially, Pb concentrations show an exponentially decreasing trend from the coast inland, while a moderate decreasing trend is observed for Cu concentrations in the coastal area (below 2,000 m above sea level (a.s.l.)). In the intermediate area (2,000-3,000 m a.s.l.), the concentrations and enrichment factors of all these elements show high variability due to the complicated characteristics of climate and environment. On the inland plateau (above 3,000 m a.s.l.), the high concentrations of As and Pb are induced by high deposition efficiency, the existence of polar stratospheric precipitation, and the different fraction deposition to East Antarctica. The extremely high concentrations with maximum values of 9.59 pg/g and 69.9 pg/g for Pb and Cu, respectively, are suggested to result mainly from local human activities at the station. Our results suggest that source, transport pathway, and deposition pattern, rather than distance from the coast or altitude, lead to the spatial distributions of Pb, As, and Cu; and it is further confirmed by spatial variations of the three metals deposited over the whole continent of Antarctica.
An increasing number of studies in recent years has elucidated distinguishable effects of stemflow on hydrology and biogeochemistry within a variety of ecosystems. Nonetheless, no known studies have investigated the temporal variability of stemflow volume within discrete rainfall events for xerophytic shrubs. Here, stemflow was monitored at 5-min intervals using a tipping-bucket rain gage during the 2015 growing season for a xerophytic shrub (Caragana korshinskii) within a water-limited arid desert ecosystem of northern China. We characterized the stemflow temporal variability, along with rainfall, and found the temporal heterogeneity of rainfall clearly affected the timing of stemflow inputs into basal soil within discrete rainfall events. The rainfall threshold value for stemflow generation is not a constant value but a range (0.6~2.1mm, with an average of 1.1 mm) across rainfall events and is closely associated with the antecedent dry period. Time lags existed between the onset of rainfall and the onset of stemflow, and between rainfall peaks and stemflow peaks. Our findings are expected to be helpful for an improved process-based understanding of the temporal stemflow yield of xerophytic shrubs within water-limited arid desert ecosystems.
The degree-day model is one important method to estimate glacier melt, which is based on the specific relationship between glacial melting and the sum of daily mean temperatures above the melting point. According to the observation data on the Koxkar Glacier (KG) from 2005 to 2010, we analyzed the temporal and spatial variation of degree-day factors (DDF) and its influential factors. The results indicate that the average value of DDF was 7.2~10.4 mm/(℃·d) on the KG from 2005 to 2010. It showed a decreasing trend between 3,700 m and 4,200 m, and the deceasing trend was more obvious in the upper part of the KG. On a spatial scale, the DDF increased evidently with increasing altitude. The DDF ranged from 3.6 to 9.3 mm/(℃·d) at 3,700 m a.s.l., with the average value of 9.3 mm/(℃·d). It varied from 6.9 to 13.0 mm/(℃·d) at 4,000 m a.s.l., with the average value of 10.2 mm/(℃·d). During the period of ablation, the fluctuation of DDF was not significant at the lower altitude (3,700 m a.s.l.), but it decreased at the higher altitudes (4,000 m a.s.l. and 4,200 m a.s.l.). The debris changes the transmission of heat, which accelerates the melting of a glacier; and the DDF showed high value. This paper will provide the reference for temporal-spatial parameterization schemes of DDF on Tuomuer glaciers of the Tianshan Mountains.
The active-layer soils overlying the permafrost are the most thermodynamically active zone of rock or soil and play important roles in the earth-atmosphere energy system. The processes of thawing and freezing and their associated complex hydrothermal coupling can significantly affect variation in mean annual temperatures and the formation of ground ice in permafrost regions. Using soil-temperature and -moisture data obtained from the active layer between September 2011 and October 2014 in the permafrost region of the Nanweng'he River in the Da Xing'anling Mountains, the freeze-thaw characteristics of the permafrost were studied. Based on analysis of ground-temperature variation and hydrothermal transport characteristics, the thawing and freezing processes of the active layer were divided into three stages: (1) autumn-winter freezing, (2) winter freeze-up, and (3) spring-summer thawing. Variations in the soil temperature and moisture were analyzed during each stage of the freeze-thaw process, and the effects of the soil moisture and ground vegetation on the freeze-thaw are discussed in this paper. The study's results show that thawing in the active layer was unidirectional, while the ground freezing was bidirectional (upward from the bottom of the active layer and downward from the ground surface). During the annual freeze-thaw cycle, the migration of soil moisture had different characteristics at different stages. In general, during a freezing-thawing cycle, the soil-water molecules migrate downward, i.e., soil moisture transports from the entire active layer to the upper limit of the permafrost. In the meantime, freeze-thaw in the active layer can be significantly affected by the soil-moisture content and vegetation.
Differential Interferometric Synthetic Aperture Radar (D-InSAR) has been widely used to measure surface deformation over the Tibetan Plateau. However, the accuracy and applicability of the D-InSAR method are not well estimated due to the lack of in-situ validation. In this paper, we mapped the seasonal and long-term displacement of Tanggula (TGL) and Liangdaohe (LDH) permafrost regions with a stack of Sentinel-1 acquisitions using the Small Baseline Subset InSAR (SBAS-InSAR) method. In the TGL region, with its dry soils and sparse vegetation, the InSAR-derived surface-deformation trend was consistent with ground-based leveling results; long-term changes of the active layer showed a settlement rate of around 1 to 3 mm/a due to the melting of ground ice, indicating a degrading permafrost in this area. Around half of the deformation was picked up on monitoring, in contrast with in-situ measurements in LDH, implying that the D-InSAR method remarkably underestimated the surface-deformation. This phenomenon may be induced by the large soil-water content, high vegetation coverage, or a combination of these two factors in this region. This study demonstrates that surface deformation could be mapped accurately for a specific region with Sentinel-1 C-band data, such as in the TGL region. Moreover, although the D-InSAR technology provides an efficient solution for broad surface-deformation monitoring in permafrost regions, it shows a poor performance in the region with high soil-water content and dense vegetation coverage.
In seasonally frozen regions, freezing-and-thawing action is the main cause responsible for the destruction of canals, which is closely linked to the temperature gradient and water transport. To investigate the behaviour of soils under freezing-and-thawing actions, many numerical models have been established that consider the important coupling of moisture transport and temperature evolution; but they contain excessive parameters, some of which are rather difficult to determine. Based on the well-known Harlan's theory, a simple moisture-heat coupling model was recently proposed to quantify the coupled moisture-heat transport performance of soils in terms of the central temperature and porosity. The mathematical module of COMSOL Multiphysics was further employed to solve the governing equations numerically. To validate our model, a thorough experimental scheme was carried out in our lab. The measured temperature distribution was found to be consistent with the predicted results.
Snow covers the road embankments in winter in high latitude permafrost zones. The effect of snow cover on embankments was simulated based on field measurements of boundary conditions and initial ground temperature profile in Mohe, China. The effect of thermosyphons on the embankment warmed by snow cover was evaluated by numerical simulations as well. The results indicate that the difference of thermal regimes between non-thermosyphon and thermosyphon embankments reaches to 22 m in depth below the ground surface. It is much warmer in the non-thermosyphon embankment body in winter. Affected by the snow cover, heat flux gradually spreads into the deep ground of the subgrade over time. The permafrost table under the slope toe of a thermosyphon embankment is 1.2 m higher than that of a non-thermosyphon embankment in the 20th year. In addition, the permafrost table at the slope toe of a thermosyphon embankment is 26 cm deeper over 20 years. These results indicate that thermosyphons can greatly weaken the warm effect of snow cover. However, thermosyphons cannot avoid the degradation of permafrost under the scenarios of snow cover. Therefore, composite measures need to be adopted to keep embankment stability in snowy permafrost zones.
This study is devoted to the numerical simulation of the artificial ground freezing process in a fluid-saturated rock mass of the potassium salt deposit. A coupled model of nonstationary thermal conductivity, filtration and thermo-poroelasticity, which takes into account dependence of the physical properties on temperature and pressure, is proposed on the basis of the accepted hypotheses. The considered area is a cylinder with a depth of 256 meters and diameter of 26.5 meters and includes 13 layers with different thermophysical and filtration properties. Numerical simulation was carried out by the finite-element method. It has been shown that substantial ice wall formation occurs non-uniformly along the layers. This can be connected with geometry of the freezing wells and with difference in physical properties. The average width of the ice wall in each layer was calculated. It was demonstrated that two toroidal convective cells induced by thermogravitational convection were created from the very beginning of the freezing process. The effect of the constant seepage flow on the ice wall formation was investigated. It was shown that the presence of the slow flow lead to the delay in ice wall closure. In case of the flow with a velocity of more than 30 mm per day, closure of the ice wall was not observed at all in the foreseeable time.
To study the distribution characteristics and variation regularity of the temperature field during the process of seepage freezing, a simulated-freezing test with seepage of Xuzhou sand was completed by using a model test developed in-house equipment. By means of three group freezing tests with different seepage velocities, we discovered the phenomenon of the asymmetry of the temperature field under the influence of seepage. The temperature upstream was obviously higher than that downstream. The temperature gradient upstream was also steeper than that downstream. With a higher seepage velocity, the asymmetry of the temperature field is more pronounced. The asymmetry for the interface temperature profile is more strongly manifest than for the main surface temperature profile. The cryogenic barrier section is somewhat "heart-shaped". With the increasing velocity of the seepage flow, the cooling rate of the soil decreases. It takes much time to reach the equilibrium state of the soil mass. In our study, seepage flow velocities of 0 m/d, 7.5 m/d, and 15 m/d showed the soil-cooling rate of 4.35℃/h, 4.96℃/h, and 1.72℃/h, respectively.
The operation of a railway track in cold regions results in the premature deformation of subgrade soils caused by significant temperature fluctuations and ecological imbalance. Identification and calculation of the thawing degree of permafrost soils, frost heaving of clays, and groundwater flooding require careful engineering and geological surveying. The paper describes the unique, long-standing experience of the university scientists connected with maintaining the Russian East-Siberian and Trans-Baikal Railways' facilities. Specific features of and requirements for the surveying, depending on the geological and climatic conditions, are identified.
Soil pollution significantly reduces environmental quality. In this study, farmland soil samples were collected from 25 sites in Baghrash County, Northwest China; and the concentrations of eight heavy-metal elements (arsenic, As; cadmium, Cd; chromium, Cr; copper, Cu; manganese, Mn; nickel, Ni; lead, Pb; zinc, Zn) were determined by standard methods. The spatial distribution, contamination level, and ecological risk stature of heavy metals were analyzed based on GIS technology, the Geo-accumulation Index (Igeo), the Pollution Load Index (PLI), and the Potential Ecological Risk Index (RI). Results indicated that (1) The average concentrations of Cd exceeded 12.12 times the allowed national standard for soil environmental quality of China. The average concentrations of Cd, Cr, Ni, Pb, and Zn exceeded the background values of irrigation soils in Xinjiang by 60.58, 1.25, 1.50, 4.95, and 5.10 times, respectively. (2) The pollution order of the average value of Igeo for heavy metals was ranked as Cd > Zn > Pb > Ni > Cr > Cu > As > Mn. The individual potential ecological risk index for heavy metals was ranked in the order of Cd > As > Ni > Cu > Pb > Cr > Zn. The average PLI for the study area showed a heavy pollution level, while the average RI showed a considerable ecological risk stature, as compared to the classification standard. (3) The spatial distribution patterns of eight heavy metal elements were substantially heterogeneous. The moderately polluted areas with moderate potential ecological risks were distributed in the southern parts of the study area, whereas the heavily polluted areas with considerable potential ecological risks were distributed in the northern parts. Overall, it was observed that Cd contributed most to the PLI and RI of the farmland soils in Baghrash County. The pollution risk of Cd should be a major concern, and human activities in the region should be cautious.