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China prioritizes ecological civilization construction and embraces the concept of "lucid waters and lush mountains are invaluable assets." Great achievements have been made in ecological protection and restoration through implementing a series of policies and projects. This paper reviews the history of ecological restoration in China and the current development of the "integrated protection and restoration project of mountains, rivers, forests, farmlands, lakes, grasslands, and deserts (IPRP)." Furthermore, the characteristics of IPRP were systematically elaborated from the perspectives of the ecological civilization thought, the policy management, and the key scientific issues. Also, the current achievements were summarized in the fields of national ecological space management, biodiversity conservation, and ecological protection and restoration. Existing challenges in management policy, scientific issues, and engineering practices were highlighted. Future perspectives include ecological space control, nature-based Solutions, biodiversity big data platform, modern techniques, and value realization mechanisms of ecological products. [ABSTRACT FROM AUTHOR]

In seismic data processing, low-frequency random noise with non-Gaussian and non-stationary characteristics heavily contaminates the reflected signals in Tarim area, which brings great difficulties in interpretation of seismic records in northwest China. To achieve more satisfied resolution, more greater fidelity, together with much higher increased signal-to-noise ratio (SNR), this paper proposes a SNR enhancement method based on the combination of variational mode decomposition (VMD) and Semi-soft Go Decomposition (Semi-Soft GoDec), named VMD-SSGoDec, which can realize the simplification of low-rank extraction in time–frequency representation (TFR) domain. Firstly, each trace of the rough seismic record is decomposed into several modes to reconstruct a component matrix by VMD. Due to the semi-low rank or approximate low-rank character of the desert low-frequency noise component matrix in TFR domain, secondly, we apply the Semi-soft GoDec, a low-rank matrix estimation to extract the low-frequency random noise components from the VMD results obtained in the first step. Repeating the above single-trace procedure to each trace rather than decomposing the entire record but use low-rank estimation once can lead to a more reduced dimension of the component matrix, and thus simplify the low-rank selection in Semi-soft GoDec. Finally, with the extracted random noise results in the second step, we can obtain the denoised record by making a difference with the original input. The proposed algorithm is tested by both synthetic record and field desert seismic data. Experimental results show outstanding advantages in low-frequency noise attenuation comparing with those of f-x deconvolution and SSWT-OptShrink. Both low-frequency random noise and surface waves are almost thoroughly attenuated by the proposed method, while the reflected signals are left nearly intact, revealing a significant enhancement in SNR. [ABSTRACT FROM AUTHOR]

Seismic exploration is an essential way for stratigraphic information acquisition and resource exploitation. However, the unique near surface conditions of the desert region in northwest China pose a special problem. On the one hand, compared with Gaussian noise, desert noise concentrates in the low-frequency band, which is seriously overlapped with those of the effective signals; On the other hand, its nonstationary, nonlinear, and non-Gaussian characteristics seriously affect the accuracy of weak signal recovery and increase the difficulty of noise suppression. In the collected field data, effective signals are often submerged by the intense low-frequency noise. Considering that traditional denoising methods have some limitations on this kind of noise, a new multi-scale dense connection feature fusion (MS-DCFF) denoising convolution neural network is presented in this paper. This denoising network can adaptively learn the potential features of effective signals through multi-scale feature fusion techniques and increase the degree of information exchange by utilizing the dense connections between different blocks. Moreover, we construct relatively complete training dataset containing an effective signal dataset and a noise dataset for desert low-frequency noise suppression, thereby boosting the feasibility of the network for desert noise suppression. Both simulation and field data prove that the superior performance of the proposed MS-DCFF in the aspect of low-frequency noise (mainly includes random noise and surface waves) suppression and effective signal recovery, compared with band-pass filtering, f-x filtering, and DnCNNs. [ABSTRACT FROM AUTHOR]

Desertification is one of the major challenges facing humanity. However, there is no effective way to effectively control desertification. China is experiencing serious desertification, and to alleviate this trend, China has implemented a series of major ecological projects since 1978 and has achieved good results. Remote sensing can record changes in surface processes over a long period of time and can play an active role in desertification monitoring and governance. However, there is no systematic remote sensing monitoring method for desertification. In response to this problem, this paper takes a demonstration and reconstruction project of the United Nations desertification in the Kubuqi Desert in China as an example. By using the 30-year time series Landsat data, we propose a new remote sensing monitoring method for the impact of ecological restoration engineering of desert to monitor the spatial and temporal evolution pattern of the Kubuqi Desert in the past 30 years and the impact of the human ecological reconstruction project on the location of land use types in the Kubuqi Desert. In addition, the method analyzes the impact of the Kubuqi Desert Reconstruction Project on the local ecological environment changes from time and space perspectives. The results show the following: (1) During 1991–2017, the Kubuqi Desert Reconstruction Project improved the cultivated land, afforestation, and the Yellow River Drainage to control the sand and in conjunction with other renovation projects improved the ecological environment. The area of the sandy land decreased from 45.76% to 28.66%, while the areas of the waters wetland and artificial forest (shrub), urban construction land, and agricultural land increased; (2) There are obvious time and space differences in the transformation, and the vegetation cover increases as a whole. The obvious change areas are mainly distributed in the riverbank irrigation area of the Yellow River section of the Kubuqi Desert and the torrents such as the Maobula Kong, Buer Taigou and Heilaigou and other mountain gully areas. The relevant experience of the Kubuqi Desert Reconstruction Project in China has important reference significance for world desertification transformation. [ABSTRACT FROM AUTHOR]

Currently, fire in building is one of the most serious disasters. With the increase of basic construction items in western China, ordinary medium sand resource no longer met with the need of engineering. Compressive strength experiments of concrete produced with desert sand after elevated temperature were carried out in this paper. The effects of desert sand replacement rate (DSRR), temperature and cooling regime on the mechanical performances of concrete produced with desert sand were analyzed. XRD and SEM experiments were also conducted to study the microstructure of concrete produced with desert sand after elevated temperature. Experimental results showed that the cubic compressive strength of concrete produced with desert sand increased firstly, and then declined with temperature. Whereas, the prismatic compressive strength and elasticity modulus of concrete produced with desert sand under static compression declined with temperature. With the enhancement of DSRR, the elasticity modulus under static compression, cubic compressive strength and prismatic compressive strength of concrete produced with desert sand after elevated temperature increased firstly, and then declined, the maximum value of which was reached when DSRR amounted to 40%. Regression models were established to predict the mechanical performances of concrete produced with desert sand after elevated temperature, which were in good agreement with experimental results. [ABSTRACT FROM AUTHOR]

As one of the major regions of carbonate rock oil–gas exploration in western China, Tazhong area of the Tarim Basin has severe environment and complex ground surface conditions, hence the signal to noise ratio (SNR) of the field seismic data is extremely low. To improve the SNR of desert seismic data is a crucial step in the following work. However, the random noise in desert seismic characterizes by non-stationary, non-gaussian, non-linear and low frequency, which are very different from the random Gaussian noise. In addition, the effective signals of desert seismic generally share the same frequency band with strong random noise. These all make some traditional denoising methods cannot suppress it well. Therefore, a new noise suppression framework based on improved PSO–SVM is proposed in this paper. First, we extract the correlation of noisy desert seismic data to form feature vector. Subsequently, the model of improved PSO–SVM was built to classify the extracted feature, thereby identifying the position of the seismic events. Finally, second-order TGV filter was applied for obtaining denoised results. We perform tests on synthetic and field desert seismic record and the denoising results show that the proposed method can effectively preserve effective signals and eliminate random noise. [ABSTRACT FROM AUTHOR]

Spatiotemporal patterns of column-averaged dry air mole fraction of CO2 (XCO2) have not been well characterized on a regional scale due to limitations in data availability and precision. This paper addresses these issues by examining such patterns in China using the long-term mapping XCO2 dataset (2009–2016) derived from the Greenhouse gases Observing SATellite (GOSAT). XCO2 simulations are also constructed using the high-resolution nested-grid GEOS-Chem model. The following results are found: Firstly, the correlation coefficient between the anthropogenic emissions and XCO2 spatial distribution is nearly zero in summer but up to 0.32 in autumn. Secondly, on average, XCO2 increases by 2.08 ppm every year from 2010 to 2015, with a sharp increase of 2.6 ppm in 2013. Lastly, in the analysis of three typical regions, the GOSAT XCO2 time series is in better agreement with the GEOS-Chem simulation of XCO2 in the Taklimakan Desert region (the least difference with bias 0.65±0.78 ppm), compared with the northern urban agglomeration region (−1.3±1.2 ppm) and the northeastern forest region (−1.4±1.4 ppm). The results are likely attributable to uncertainty in both the satellite-retrieved XCO2 data and the model simulation data. [ABSTRACT FROM AUTHOR]

The changes and influencing factors of soil inorganic carbon (SIC) and organic carbon (SOC) on precipitation gradients are crucial for predicting and evaluating carbon storage changes at the regional scale. However, people's understanding of the distribution characteristics of SOC and SIC reserves on regional precipitation gradients is insufficient, and the main environmental variables that affect SOC and SIC changes are also not well understood. Therefore, this study focuses on the Alxa region and selects five regions covered by three typical desert vegetation types, Zygophyllum xanthoxylon (ZX), Nitraria tangutorum (NT), and Reaumuria songarica (RS), along the climate transect where precipitation gradually increases. The study analyzes and discusses the variation characteristics of SOC and SIC under different vegetation and precipitation conditions. The results indicate that both SOC and SIC increase with the increase of precipitation, and the increase in SOC is greater with the increase of precipitation. The average SOC content in the 0–300cm profile is NT (4.13 g kg−1) > RS (3.61 g kg−1) > ZX (3.57 g kg−1); The average value of SIC content is: RS (5.78 g kg−1) > NT (5.11 g kg−1) > ZX (5.02 g kg−1). Overall, the multi-annual average precipitation (MAP) in the Alxa region is the most important environmental factor affecting SIC and SOC. [ABSTRACT FROM AUTHOR]

This paper presents the environmental history and its responses to palaeoclimatic changes since the start of the Holocene in the eastern portion of the desert belt (sand seas and sandy lands) in northern China by comparing the aeolian sandpalaeosol sequences and their palaeoclimatic proxies. The optically stimulated luminescence (OSL) ages of the aeolian sandpalaeosol sedimentary sequences and a series of palaeoenvironmental proxies show that: (1) The large-scale dune landscape currently in the Kubuqi Sand Sea was formed during the Holocene in general; and the palaeosol was generally developed during the period of 4–2 ka, indicating conditions favorable for vegetation growth, soil development, and organic carbon accumulation due to increased precipitation or effective moisture and weakened aeolian activities; the large-scale expansion of dunes in the recent 2 ka is closely linked to human activities. The variable discharge of the Yellow River with diversions for irrigation may have resulted in a more consistent supply of aeolian particles for dune field expansion. (2) The dune landscape of the Hunshandake Sandy Land was likely formed around 12 ka, and before this, the western part of the Hunshandake Sandy Land would have been covered by a single large lake; it was obviously wetter than today in the sandy land during the period of 9.6–3 ka and the palaeosols were developed at the same time. But the aeolian activities have not been completely dormant in this long-lasting wetter epoch; because the Holocene wetter period was likely time-transgressive across the region. (3) The palaeosol of the Hulunbuir Sandy Land began to develop as early as 14.5 ka, probably continuing until the last 2 ka. The palaeosol development of various dune fields in the eastern portion of the desert belt (sand seas and sandy lands) in northern China is spatially heterogeneous, and even the palaeosol development time in different locations within each sandy land is inconsistent. During the middle Holocene (especially the 7.5–3.5 ka), all the sandy lands were stabilized in general and the intensity of aeolian activities was significantly weakened. The number of palaeoenvironmental records in the eastern portion of the desert belt (sand seas and sandy lands) in northern China has increased rapidly in the past decade, but the amount of published data still does not match the vast extent of the dune fields. It does require much more in-depth palaeoenvironmental studies for a full understanding of the relationship between aeolian activities and climate change in northern China. [ABSTRACT FROM AUTHOR]

Deserts and sandylands that are located in the semi-arid and arid regions in the middle latitudes of the Northern Hemisphere are usually regarded as environmentally sensitive change belts which respond to global climatic change. In northern China, activation or immobilization of sand dunes is mainly influenced by humid and dry variation and is related to stronger or weaker Asian monsoons. In this paper, the history of Holocene millennial-scale climatic and environmental change is reconstructed by the systematic analysis of the geochemical element contents and parameters, along with the OSL and C chronologies, from the different lithologies of the palaeosol-aeolian sand sequence in the south-eastern Mu Us Desert, northern China. Our results indicate that the region was dominated by a dry climate with intensive aeolian activity before 7.2 ka BP, and there was an optimal humid climate and fixed desert in 7.2-4.6 ka. Afterwards, the dune fields became mobile again as the effective humidity declined. Additionally, six dry events were discovered with times of ~7.2, 7.0-6.8, 6.6-5.7, 4.6-4.1, 3.7-3.5, and 3.3-2.5 ka, which were not only coincident with the intervals of millennial-scale weaker Asian summer monsoons, but also accordant with the cold events evidenced in the ice cores and deep-sea deposits of the high latitudes in the Northern Hemisphere. In general, the Holocene climatic and environmental changes had the characteristics of the 'monsoonal mode' and 'abrupt millennial-scale oscillation' in the Mu Us Desert. [ABSTRACT FROM AUTHOR]

Soil water is the key abiotic limiting factor in desert areas and hydrological processes determine the vegetation composition, patterns and processes in desert regions. The hydrological processes can be altered by vegetation succession. In this paper, we review the major advances in ecohydrological research and their potential impact on plant-water relations in revegetated desert communities. The major advances in ecohydrological research over the past 50 years in desert areas were analyzed using a case study that investigated the long-term ecosystem effects of sand-binding vegetation in the Tengger Desert. Key challenges and opportunities for ecohydrology research in the future are also discussed in the context of the major scientific issues affecting sand binding vegetation. [ABSTRACT FROM AUTHOR]

The unique linear dunes in the northern Kumtagh Desert of northwest China have inspired enthusiastic debate among aeolian geomorphologists over their origins and classification. Their uniqueness lies not only in their morphology, but also in their geomorphological patterns. In this paper, the geomorphological patterns and ages of the linear dunes in the northern Kumtagh Desert are analyzed using the pattern analysis method that was recently adopted by geomorphologists. The analysis suggests that these linear dunes have developed since 13 ka BP, during the late part of the most recent deglaciation stage, when the region's dry climate was favorable for dune formation. The differences in dune construction time within this region result from the complex factors that control their formation and spatial variations in the local environment, but these factors were not strong enough to prevent us from estimating the dune age recorded by the geomorphological patterns with acceptable precision. It is also suggested that the pattern analysis method can be used to estimate dune ages in the absence of more reliable dating methods. [ABSTRACT FROM AUTHOR]

TD-2 structure is located in the eastern part of the Central Uplift zone of the Tarim Basin, China. It is a basement-uplift anticline-type structure confirmed by seismic and gravity prospecting, and it is expected to have good potential for oil and gas according to the analysis of regional geological evolution history. But further exploration such as drilling is suspended because of lacking direct geochemical information. Therefore, multi-parametric geochemical surveys, such as free hydrocarbons (C-C), acid hydrocarbons (C-C) and ΔC, Hg of soil, were conducted. It is concluded in this paper that free hydrocarbons are obviously better than other geochemical parameters and could be used for evaluation of oil and gas potential of TD-2 structure in the desert area. Shapes of near-surface geochemical anomalies and geochemical characteristic parameters suggested that TD-2 structure was a dry gas-bearing structure at the early-middle dissipation stage. So TD-2 structure should have some promising potential for oil-gas. Multi-parametric geochemical survey provided important information for further drilling exploration. [ABSTRACT FROM AUTHOR]

The sustained development of an artificial oasis depends critically on the stability of the natural oasis associated with it. This work theoretically investigates the most suitable ratio of natural oasis area to artificial oasis area in oasis ecosystems, as quantified by the percentage of artificial oasis (PAO). Based on data from oases observed in Xinjiang Province, China, this paper analyzes the PAO distribution for these oases via fractal theory. The results allowed us to draw the following conclusions. (1) The PAO distribution possesses fractal characteristics, and the fractal dimension of the PAO decreases as the oasis evolves. (2) The interval of the fractal dimension of the PAO is 0–1.7068, and the interval of the expectation of the PAO is 0–85.01%. This indicates that the natural oasis should occupy at least around 15% of the total oasis area. (3) The fractal dimension and the expectation of the PAO for the ecosystem of oases in Xinjiang Province, China, are currently 0.5369 and 53.51%, respectively. These results show that the development of artificial oases in Xinjiang Province should continue, although the corresponding natural oases should also be maintained and developed at the same time. [ABSTRACT FROM AUTHOR]

In this study, the land desertification of transitional zones of desert loess in the Yulin region (China) is studied from TM images in a geographical information system (GIS). It is found that the desertification in Yulin is still severe. The desertified land accounts for 67.7% of the total land areas. The distribution of desertified land shows obvious spatial imbalance, with severe desertification in northwestern regions and slight desertification in southeastern regions. This imbalance is related to the difference in physical factors and land-use pattern. The process of desertification in Yulin areas shows a steady and even reversed trend between 1987 and 1999, as a result of positive efforts. At the end of the paper the cause of desertification is discussed. It is believed that the interaction and confliction between the natural process and human activities may lead to the development of desertification. [ABSTRACT FROM AUTHOR]

Deserts cover a vast area of the world's land surface, but the study of desert climate has been impeded by the lack of ground meteorological observations. In recent years, the climate reanalysis products provide an important data source to investigate climate change in observation-limited areas. However, their accuracy in desert regions has been poorly investigated. Here, we evaluated the performance of the latest ERA5 reanalysis datasets for the climatic conditions over the deserts of northern China (DNC), including temperature and precipitation variations, climate extremes, and detection skills of daily precipitation. The results show that ERA5 well captures the observed pattern of annual and seasonal temperatures, as well as the warming trend during the past four decades in DNC, compared to the ground observations. However, both annual and seasonal precipitations are greatly overestimated over DNC, and large uncertainties exist in precipitation trends. In addition, the variability of interannual precipitation, precipitation intensity, maximum 1-day precipitation, and the number of continuous dry days are underestimated by ERA5. The bias of precipitation estimates may be traced to the overestimation of rainfall occurrence in ERA5. Comparing to other reanalysis (such as MERRA2, NCEP/NCAR, and NOAA-20C), the ERA5 outperforms them for precipitation and precipitation extremes over DNC, although its performance is not as good as gridded gauge-based precipitation datasets (such as CPC). Overall, this study provides references for the use of ERA5 over DNC and facilitates the applications of ERA5 over other observation-limited desert regions. [ABSTRACT FROM AUTHOR]

In this study, to reduce the consumption of natural sand and improve the utilization rate of desert sand in western China, while preparing 14 groups of samples, desert sand is used to replace natural sand by the ratio of 20%, 40%, and 60%, and steel fiber is mixed with volume fraction 0.5%, 1.0%, 1.5%, and 2.0%. The mechanical properties of the specimens, including compressive strength, splitting tensile strength, and axial compressive strength were tested. Besides, the microstructures of the samples were analyzed by SEM, XRD, and acoustic emission detection technologies to identify the damage process. The results show that the desert sand can refine the microstructure and fill the pores, and it has good comprehensive properties at a 40% substitution rate. The compression properties of specimens are not apparently improved, but the tensile strength and deformation properties are significantly improved. The steel fiber with 1.5 vol% content behaves better, and the 28d compressive strength of the optimized group reaches 58.7 MPa. As a result, the polynomial fitting degree of total AE hits and stress level receives a more incredible goodness (R2) value than 0.96. The strength characteristics of steel fiber-desert sand concrete (SFDSC) can meet the demands of C40 concrete, and this research can provide a reference for engineers using desert sand in their designs. [ABSTRACT FROM AUTHOR]

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Periodic wetting is an inherent feature of many monsoon marginal region deserts. Previous studies consistently demonstrate desert wetting during times of Earth's high orbital eccentricity and strong summer monsoon. Here we report the first evidence demonstrating desert wetting during Earth's low orbital eccentricity from the late Miocene strata of the northwestern Tarim Basin of northern China, which is commonly thought to be beyond the range of Asian monsoon precipitation. Using mechanisms for modern Tarim wetting as analogs, we propose that East Asian summer monsoon weakening enhanced westward moisture transport and caused opposite desert wetting pattern to that observed in monsoon marginal region deserts. This inference is supported by our model simulations. This result has far-reaching implications for understanding environmental variations in non-monsoonal deserts in the next few thousands of years under high atmospheric CO2 content and low eccentricity. The late Miocene Tarim desert experienced periodic wetting and greening in eccentricity minimum and East Asian summer monsoon weakening [ABSTRACT FROM AUTHOR]

Leaf functional traits are important for characterizing plant nutrient strategies. The C:N:P stoichiometric balance in soils and plants, which could indicate types of nutrient limitation, is altered under changing precipitation patterns. However, whether such alterations affect leaf functional traits remains unclear. We conducted a three-year simulated precipitation experiment in a desert steppe in northwestern China to determine changes in leaf photosynthetic traits and nutrient conservation traits in five plant species and tested the relationships of these traits with soil and leaf C:N:P stoichiometry. The five species showed few changes in their leaf traits under drought conditions, but they adjusted these traits (especially P traits) under extremely wet conditions (50% increase in precipitation). Improved leaf photosynthetic N and P use, lowered leaf P uptake, and enhanced leaf N resorption might help Lespedeza potaninii to rely less on soil nutrients in extremely wet environments than other species do. Leaf photosynthetic traits were regulated primarily by soil and leaf C:N:P stoichiometry. Leaf nutrient conservation traits were controlled by both leaf C:N:P stoichiometry and soil properties (i.e., enzyme activity and microbial biomass), a condition especially true for P traits. The results suggest that precipitation-induced alteration in the C:N:P stoichiometric balance might have important influences on plant nutrient use strategies and even on the nutrient cycling of desert steppes. [ABSTRACT FROM AUTHOR]

Ephemeral plants are a crucial vegetation component in temperate deserts of Central Asia, and play an important role in biogeochemical cycle and biodiversity maintenance in desert ecosystems. However, the nitrogen (N) and phosphorus (P) status and interrelations of leaf-root-soil of ephemeral plants remain unclear. A total of 194 leaf-root-soil samples of eight ephemeral species at 37 sites in the Gurbantunggut Desert, China were collected, and then the corresponding N and P concentrations, and the N:P ratio were measured. Results showed that soil parameters presented no significant difference among the eight species. The total soil N:P was only 0.116 (geomean), indicating limited soil N, while the available soil N:P (4.896, geomean) was significantly larger than the total N:P. The leaf N (averagely 30.995 mg g−1) and P (averagely 1.523 mg g−1) concentrations were 2.64–8.46 and 0.93–3.99 times higher than the root N (averagely 8.014 mg g−1) and P (averagely 0.802 mg g−1) concentrations, respectively. Thus, leaf N:P (averagely 21.499) was 1.410–2.957 times higher than root N:P (averagely 11.803). Meanwhile, significant interspecific differences existed in plant stoichiometric traits. At the across-species level, N content scaled as the 3/4-power of P content in both leaves and roots. Leaf and root N:P ratios were mainly influenced by P; however, the leaf-to-root N or P ratio was dominated by roots. Leaf and root N, P contents and N:P were generally unrelated to soil nutrients, and the former presented lower variation than the latter, indicating a strong stoichiometric homeostasis for ephemerals. These results demonstrate that regardless of soil nutrient supply capacity in this region, the fast-growing ephemeral plants have formed a specific leaf-root-soil stoichiometric relation and nutrient use strategy adapting to the extreme desert environment. [ABSTRACT FROM AUTHOR]

Aims: Desert regions are regarded as highly sensitive to climatic changes. In arid and semi-arid desert, photosynthetic organisms from biological soil crusts are poikilohydric and sensitive to fluctuations in precipitation. How do physiological properties such as concentration of biochemical constituents and enzymes respond to a precipitation gradient from semi-arid to arid desert regions? Methods: We sampled cyanobacteria and moss crusts from four desert regions with distinctly different amounts of annual rainfall. Subsequently, the contents of photosynthetic pigments, malondialdehyde (MDA), osmotic adjustment substances, and antioxidative enzyme activities were correlated with the means of annual precipitation, evaporation, and temperature at the various sites. Results: Crust type, precipitation level, and their interaction had significant influences on many physiological properties (photosynthetic pigments, proline, soluble sugar, and superoxide dismutase). The contents of soluble protein, proline, and soluble sugar of cyanobacteria/moss crusts decreased with increasing precipitation level. Superoxide dismutase and catalase activities of cyanobacteria crusts decreased significantly with increasing annual precipitation. No significant variations in MDA were observed between different precipitation regions in the two crusts. Conclusions: Among the environmental variables tested, the annual amount of precipitation had the strongest effect on the physiological properties of moss/cyanobacteria crusts in different regions. Crust type combined with particular precipitation level influenced the physiological properties of crusts. Moreover, both moss and cyanobacteria crusts exhibited strong physiological adaptability to changes in precipitation. This result needs to be incorporated into future ecological models, which will help in understanding the function and vulnerability of biocrusts in the face of climate change. [ABSTRACT FROM AUTHOR]

Limited knowledge about the variation patterns of bacterial community composition in the sand and vegetative ecosystems confines our understanding regarding the contribution of the sand dune to desert areas. In this study, 454 pyrosequencing platforms were adopted to determine the community structure of bacteria and diversity of sand dunes in northeastern Qinghai-Tibet Plateau, China: 50 cm deep, rhizosphere, physical crusts, and biological crusts representing sand and vegetative ecosystems, respectively. The findings revealed significant variation in bacterial diversities and the structure of communities in the sand and vegetative ecosystems. The dominant bacterial phyla of sand and vegetative ecosystems were Firmicutes (47%), Actinobacteria (21%), Proteobacteria (16%), and Bacteroidetes (13%), while Lactococcus (50%) was found to be the dominant genus. Furthermore, samples with high alpha-diversity indices (Chao 1 and Shannon) for the vegetative ecosystem have the lowest modularity index and the largest number of biomarkers, with some exceptions. Redundancy analysis exhibited that environmental factors could explain 72% (phyla) and 67% (genera) of the bacterial communities, with EC, TC, and TOC being the major driving factors. This study expands our understanding of bacterial community composition in the desert ecosystem. The findings suggest that variations in the sand and vegetative ecosystems, such as those predicted by environmental factors, may reduce the abundance and diversity of bacteria, a response that likely affects the provision of key ecosystem processes by desert regions. [ABSTRACT FROM AUTHOR]

The significance of aeolian–fluvial interactions in controlling the geomorphology of the landscape in semi-arid desert dune fields has long been appreciated, but limited field data are available to examine how these modern aeolian–fluvial processes interact with the desert channel. In this study, based on desert channel changes and flash flood monitoring during a field survey, we characterize the responses of the desert channel to interactions between fluvial and aeolian processes in an ephemeral desert river in the ten kongduis region in the Hobq Desert in the Ordos Plateau (China). We find that the desert channel is the key place for interactions between aeolian and fluvial processes and has a significant impact on erosion and sediment yield. The pattern of aeolian–fluvial interactions in this area is that aeolian processes can move dunes and narrow the channels in the dry season, but storm floods can cause hyper-erosion of dune-covered banks and widen the channels, which are characterized by hyper-concentration flows during the flood season. Based on the cross-sections, the results show that the channel cross-section accretion area in the dry season was 0.4 times and 0.2 times the channel erosion area in the flood seasons of 2011 and 2012, respectively, of which the left bank accretion area in the dry season was 0.3 times and 0.1 times the left bank erosion in the flood seasons of 2011 and 2012, respectively. In the flood season, the dune-covered left bank erosion and sediment yield were 3.5 times those of the right bank on average. For channel lateral movement, the channel narrowing width caused by aeolian dune accretion in the dry season was 1/6 of the channel widening induced by storm-flood erosion in the flood season. Therefore, aeolian–fluvial interactions control the landform and landscape evolution in this desert area. [ABSTRACT FROM AUTHOR]

The operation and power generation of utility-scale solar energy infrastructure in desert areas are affected by changes in surface erosion processes resulting from the construction of solar photovoltaic (PV) power stations. However, few studies have addressed the interactions between solar PV arrays and aeolian erosion processes. In this study, wind flow field characteristics and the vertical distribution of sediments were investigated in the near-surface transport layer at three different locations with respect to the solar PV arrays in a 200 WM-p PV power station in the central Hobq Desert, northwestern China. The results indicate that the sediment transport varied around the panels, with the greatest transport occurring between the panels, followed by behind and in front of the panels. The sediment fluxes of all of the observation sites obey an exponential function. The secondary flow field zones formed around the PV panels: the conflux accelerating zone between the panels, the resistance decelerating zone of the under panels, and the transition zone of the rapid velocity increase in front of and behind the panels. This resulted in a greater shear force in front of the panels under the downward flow diversion effect of PV panels, and the wind erosion depressions were finally formed here. The results of this study provide information for planning better technical schemes for wind-sand hazards at solar PV power stations, which would ensure operational stability and safety in desert areas. [ABSTRACT FROM AUTHOR]

Purpose: Gobi deserts are a major source of natural and anthropogenic aerosols in China. However, the characteristics of the sand flow and dust emission processes are still an open question. This study intends to accurately describe the characteristics of the sand flow and dust emission and to determine the relationship between the sand transport rate and the vertical dust flux above a gobi surface. Materials and methods: In this study, a field observation was conducted over a gobi (gravel) desert surface (Yangguan Gobi Desert, Gansu Province, China). We investigated the wind velocity, sand flux, and concentration of particles smaller than 10 μm (PM10) by using cup anemometers, a sonic anemometer, sand traps, and DustTrak. Results and discussion: We found that (1) piecewise regression described the vertical sand flux profiles; the upper part of the profile (above 17 cm) should be described by a power function and the lower part should be described by a Gaussian function. (2) An empirical model based on the modified Owen equation could predict the sand transport rate accurately. (3) The vertical dust flux was described well by Fv∝u*3 and the dust emission above the gobi surface should follow Aρu*t (u*2 − u*t2), where A is an empirical regression coefficient. (4) The efficiency of saltation bombardment (Fv/Q) was linearly related to the ratio u*t/u*. Conclusions: The results of this study show that the characteristics of the sand flow and dust emission above a gobi surface were highly different from those of bare sandy surface. In future research, it will be necessary to account for the effect of surface characteristics, and particularly the characteristics of the gravel, to improve the predictive ability of our model. [ABSTRACT FROM AUTHOR]

Obtaining surface albedo of high accuracy and analyzing spatial and temporal characteristics are essential for detecting change mechanism and influencing factors of surface albedo in deserts. Surface albedo from the Operational Land Imager (OLI) was assimilated into black-sky short-wave albedo (BSA) with an ensemble Kalman filter (EnKF) algorithm, to retrieve the surface albedo of high accuracy in Badain Jaran Desert. The results show that the average relative error decreases from 14.813% to 8.530% when surface albedo based on OLI is assimilated into BSA with the EnKF, and assimilated value can accurately describe the spatial and temporal distribution of surface albedo. The surface albedo has an obvious seasonal difference and presents a U-shape curve in a year, with the highest albedo in winter and lowest in summer. Owing to snow cover in some high-altitude areas, surface albedo is the highest and the spatial difference reaches maximum (variation coefficient=0.14) in winter. The Structure Similarity in surface albedo increases from the hinterland of desert (0.40–0.70) to the outer areas (0.70–0.90), as dune number decreases and distance between dunes increases. Compared with mobile and semi-mobile dunes, the minimum surface albedo of semi-fixed and fixed dunes postpones one month due to lag effect of the vegetation response to precipitation. [ABSTRACT FROM AUTHOR]

Dust has a variety of significant impacts on geochemical cycles, climate change and human health. The emission, deposition, grain size distribution and geochemical composition of aeolian dust in the eastern Kumtag Desert were studied. The aeolian dust mainly came from the Kumtag sandy and gravel deserts based on grain size and geochemical composition data. The horizontal aeolian sediment flux per unit width in the study area was 385.12 kg m−1 year−1. The calculated dust emission rates for PM10, PM20 and PM63 were 0.39, 0.61 and 1.72 t ha−1 year−1, respectively. The mean dust deposition rate was 1.08 t ha−1 year−1. Dust deposited in the study region contained P, Fe, Mg, Ca, Na and K at rates of 0.07, 3.16, 1.81, 6.17, 2.65 and 1.47 g m−2 year−1, respectively, which are very important for regional ecosystems. The above results provide an important scientific basis for quantitative evaluations of the impacts of dust and sandstorm disaster prevention. [ABSTRACT FROM AUTHOR]

Based on the analysis of particle size mechanical composition and parameter distribution of surface sediments in the Hobq Desert (HD), the Ulan Buh Desert (UBD) and the northern part of the Mu Us Desert (MUD) in western Inner Mongolia, and combining the sedimentary environment discrimination method and the particle size lognormal fitting method, this research compares and explores the particle size characteristics and the significance of sensitive components in the sedimentary environment to the provenance in the three deserts. The results are shown as follows: (1) Sediment samples in the HD are dominated by fine sand (48.9%), in the UBD by fine sand and medium sand (41.10% and 42.90%, respectively) and in the MUD by medium sand (41.62%). (2) σ 1 and S K 1 in the HD and the UBD are well sorted and symmetric, but are averagely sorted and show highly positive skewness in the MUD. (3) The sediment samples in the HD and the UBD are mainly aeolian sediments, with lacustrine sediments being secondary. By contrast, the sediment samples in MUD is largely made up of lacustrine deposits. (4) By fitting the particle size frequency curves of all samples, five components, namely C1, C2, C3, C4 and C5 ranging from fineness to coarseness, are obtained. It is also indicated that the sediments in the study area do not undergo a wide range of mixing, but mainly experience in situ sedimentation. The most of these sediments may belong to lakeshore deposits that have been modified by wind for a long time, and are accompanied by long-distance westerly dust, weathered debris from bedrock, and active paleosand dunes of riverbed sediments. [ABSTRACT FROM AUTHOR]

The characteristics of eolian sand activity are greatly influenced by the wind regime, and wind regimes have been changing around the world in response to climate change. This has also been true in the desert area of northwestern China since 1965, and these changes have changed the region's landforms, sandstorm frequency, and desertification. In this study, we analyzed the temporal and spatial variation of the region's near-surface wind field since 1965. We found an average annual wind speed during this period of 1.7 m s−1, with a decreasing trend from 1965 to 2000 and an increasing trend from 2000 to 2015. The maximum rate of decrease occurred in the spring and in the eastern Taklimakan Desert. The variation of the average wind speed depended on the frequency of winds strong enough to entrain sand (with a wind speed > 6 m s−1). We also found that variations of the drift potential were primarily controlled by three prevailing wind groups (winds from the northwest, north, and northeast), but showed complex changes between seasons and regions. The wind direction in the Taklimakan Desert is characterized by two characteristics of branch and steering, the branch line is swinging in the direction of the east and the west (81.5° E~84° E). The changes in wind speed were mainly caused by a decreased frequency of strong winds, precipitation, and urban development. However, the variation of wind speed had less impact on the desert environment than the variation of wind direction. [ABSTRACT FROM AUTHOR]

Mineral dust released from the desert is one of the important components of atmospheric aerosols. Arid and semi-arid deserts, sandy lands in northern China and their adjacent Gobi Desert lands in northern China and neighboring Mongolia (hereinafter referred to as Gobi) are potential sources of mineral dust in Asia. However, there is currently a lack of systematic studies on the characteristics of major elements in the potential mineral dust source area. This study investigates the major elements of 310 surficial sand samples in the stabilized and semi-stabilized dune fields from 12 deserts/sandy land and Gobi in northern China and southern Mongolian Gobi and compiles published data. We identify four regions with distinct geochemical characteristics: (1) Taklimakan, Kumtag and Qaidam deserts in western China; (2) Badain Jaran, Tengger, Hobq, and Mu Us deserts in the central and western regions of northern China; (3) Hulun Buir, Onqin Daga and Horqin sandy lands in northeast China; and (4) Gobi and Gurbantunggut deserts. The spatial distributions of the SiO2 and CaO contents in Chinese deserts are highly variable. The average content of SiO2 generally reflects an increasing trend from west to east, while the average content of CaO shows a decreasing trend from west to east. We demonstrate that the spatial variation of major elements is likely controlled by two key scenarios: the composition of source rocks and the mineral maturity caused by the supply of fresh materials. The SiO2/(Al2O3+K2O+Na2O) ratio of desert sediments is relatively lower in western China and may be caused by high ferric-magnesia and high carbonate minerals; this ratio is relatively higher in the northeast sandy lands and may be linked to a lack of fresh material supply and the presence of high K-feldspar minerals in source rocks. The deserts can be further distinguished by ternary diagrams with SiO2/10-CaO-Al2O3, (K2O+Na2O)-CaO-Fe2O3 and CaO-Na2O-K2O. The comparison of major elements between desert sediments and loess suggests that the western and/or central deserts in China may be the potential provenances of loess on the Loess Plateau. [ABSTRACT FROM AUTHOR]

Rapid and extensive social and economic development has caused severe soil contamination by heavy metals in China. The spatial distribution, pollution levels, and health risks of metals were identified in an oasis-desert zone of northwest China. The mean concentrations of six heavy metals exceeded their corresponding background contents, and each metal concentration in farmland samples was higher than that in Gobi samples. Moreover, these heavy metals followed a similar spatial pattern and showed significant positive correlations with each other, indicating that they have the same sources. The contamination features of heavy metals and ecological risks were calculated using several quality indicators, and their health risks for population groups were quantified. The results showed that the Gobi and farmland soils were uncontaminated to moderately contaminated by heavy metals, and that farmland pollution was more serious than that of Gobi. The Gobi and farmland soils posed low ecological risks. As a whole, the non-carcinogenic risk which was caused by heavy metals was low for local residents, and the carcinogenic risk was within an acceptable level. Comparatively speaking, children were the more vulnerable population to health risks. The Zn and Cu pollution was relatively serious, and Cr and V were major contributors to health risks.ᅟ [ABSTRACT FROM AUTHOR]

The development of the atmospheric boundary layer is closely connected with the exchange of momentum, heat, and mass near the Earth’s surface, especially for a convective boundary layer (CBL). Besides being modulated by the buoyancy flux near the Earth’s surface, some studies point out that a neutrally stratified residual layer is also crucial for the appearance of a deep CBL. To verify the importance of the residual layer, the CBLs over two deserts in northwest China (Badan Jaran and Taklimakan) were investigated. The summer CBL mean depth over the Taklimakan Desert is shallower than that over the Badan Jaran Desert, even when the sensible heat flux of the former is stronger. Meanwhile, the climatological mean residual layer in the Badan Jaran Desert is much deeper and neutrally stratified in summer. Moreover, we found a significant and negative correlation between the lapse rate of the residual layer and the CBL depth over the Badan Jaran Desert. The different lapse rates of the residual layer in the two regions are partly connected with the advection heating from large-scale atmospheric circulation. The advection heating tends to reduce the temperature difference in the 700 to 500-hPa layer over the Badan Jaran Desert, and it increases the stability in the same atmospheric layer over the Taklimakan Desert. The advection due to climatological mean atmospheric circulation is more effective at modulating the lapse rate of the residual layer than from varied circulation. Also, the interannual variation of planetary boundary layer (PBL) height over two deserts was found to covary with the wave train. [ABSTRACT FROM AUTHOR]

The sandy land in the southern region of the Tengger Desert is adjacent to cities and towns, and land desertification poses a threat to the livelihood and production of local residents. To determine dynamic changes in local desertification, five periods (1973, 1987, 1992, 2001, and 2009) of remote sensing data are studied by remote sensing (RS) and geographic information system (GIS). The desert contraction area is primarily centered around three units (Wuwei, Gulang, and Jingtai) and nearby regions of Zhongwei City. The primary desert expansion areas include the west side of Helan Mountain (WSHM), the Central Mountainous Area (CMA), and the eastern and western Zhongwei units far from towns. From 1973 to 2009, the degree of change in the contracting part of the primary desert expansion unit showed an increasing trend; in brief, most of the desert (especially after 2001) has been developing in a direction in which desertification has been gradually controlled. The primary desert expansion areas are less affected by human activity, but they are primarily controlled by natural factors (especially wind and terrain). The desert contraction areas occur around the towns and nearby regions with frequent human activity; desertification is primarily controlled by human factors. With rapid economic development (especially after 2000), the scale of the cultivated area, town, and ecological protection engineering has gradually expanded, and the latter two are primarily built on a previous desert, which is the root cause of the reduction in the desert areas around the towns and the shrinkage toward north of border. Therefore, reasonable and effective human activity in the southern region of the Tengger Desert is playing a crucial role in preventing desertification. [ABSTRACT FROM AUTHOR]

Effects of biological soil crusts (BSCs) on soil evaporation is quite controversial in literature, being either facilitative or inhibitive, and therein few studies have actually conducted direct evaporation measurements. Continuous field measurements of soil water evaporation were conducted on two microlysimeters, i.e., one with sand soil collected from bare sand dune area and the other with moss-crusted soil collected from an area that was revegetated in 1956, from field capacity to dry, at the southeastern edge of the Tengger Desert. We mainly aimed to quantify the diurnal variations of evaporation rate from two soils, and further comparatively discuss the effects of BSCs on soil evaporation after revegetation. Results showed that in clear days with high soil water content (Day 1 and 2), the diurnal variation of soil evaporation rate followed the typical convex upward parabolic curve, reaching its peak around mid-day. Diurnal evaporation rate and the accumulated evaporation amount of moss-crusted soil were lower (an average of 0.90 times) than that of sand soil in this stage. However, as soil water content decreased to a moderately low level (Day 3 and 4), the diurnal evaporation rate from moss-crusted soil was pronouncedly higher (an average of 3.91 times) than that of sand soil, prolonging the duration of this higher evaporation rate stage; it was slightly higher in the final stage (Day 5 and 6) when soil moisture was very low. We conclude that the effects of moss crusts on soil evaporation vary with different evaporation stages, which is closely related to soil water content, and the variation and transition of evaporation rate between bare soil and moss-crusted soil are expected to be predicted by soil water content. [ABSTRACT FROM AUTHOR]

Soil crusts commonly form in arid and semi-arid desert regions once shifting sand dunes stabilize. The crusts affect soil properties such as texture and fertility. However, the role of crusts depends on the species composition, their physiological activity, and their stage of evolution, and varies with precipitation and season. In this study, the soil properties of physical and biological crusts in different rainfall zones of the arid and semi-arid desert regions of northern China were analyzed. More developed crusts had finer soil texture. The impact on chemical properties was greater in areas with higher precipitation. Contents of soil organic carbon (SOC), total nutrients, available N, and exchangeable ions did not vary among crust types in a hyperarid region. SOC, total N and P, and available N increased with crust development at 150-400 mm rainfall. Soil crusts increased available P during the initial stage of development. Crust development increased available K at 300-400 mm precipitation, but not at ≤250 mm precipitation. CaCO changes were related to windblown dust and soil moisture in the crust. Electrical conductivity and total salinity varied in response to variation of soil nutrients and aeolian salt accumulation. The pH did not vary greatly between crust types and sites. Crust development was accompanied by soil alkalization. Ca was more abundant than other cations. Crust development did not influence Cl, but increased HCO and Na. During crust development, SO and K contents decreased, and Mg increased, in regions with ≤250 mm precipitation. The opposite changes occurred at 300-400 mm precipitation. [ABSTRACT FROM AUTHOR]

In the arid inland river basins of northwestern China, human activities control almost all the surface hydrologic processes. The potential effects of these altered hydrologic processes are gradually becoming clear, especially since the 2000 implementation of the integrated water resources management projects in the Shiyang River, the Heihe River, the Tarim River, and the Shuler River. While the appearance of these eco-hydrology changes and consequent environmental effects in the oasis has attracted broad attention, related research is still lacking. Eco-hydrological process changes in the desert-oasis ecotone were investigated in the Pingchuan irrigation district in the middle reaches of the Heihe River. The results showed that the annual average amount of surface water irrigation during the past 20 years has decreased by 1.498×10 m, while the annual average amount of well irrigation has increased by 1.457×10 m, since 2000, when the State Council of China approved the water diversion scheme for the Heihe River Basin. The groundwater depth before the water diversion scheme generally varied between 2.44-3.19 m (average 2.73±0.24 m), while that after the water diversion scheme has varied between 3.08-4.01 m (average 3.79±0.62 m). The distribution area of <3 m groundwater depth decreased from 3612 to 394 hm; while the distribution area of >3 m groundwater depth increased from 853 to 3843 hm. However, although the hydrologic processes changed dramatically, no significant effects on vegetation productivity in the desert-oasis ecotone were detected during the study period. [ABSTRACT FROM AUTHOR]

Climate plays a crucial role in controlling vegetation distribution and climate change may therefore cause extended changes. A coupled biogeography and biogeochemistry model called BIOME4 was modified by redefining the bioclimatic limits of key plant function types on the basis of the regional vegetation-climate relationships in China. Compared to existing natural vegetation distribution, BIOME4 is proven more reliable in simulating the overall vegetation distribution in China. Possible changes in vegetation distribution were simulated under climate change scenarios by using the improved model. Simulation results suggest that regional climate change would result in dramatic changes in vegetation distribution. Climate change may increase the areas covered by tropical forests, warm-temperate forests, savannahs/dry woodlands and grasslands/dry shrublands, but decrease the areas occupied by temperate forests, boreal forests, deserts, dry tundra and tundra across China. Most vegetation in east China, specifically the boreal forests and the tropical forests, may shift their boundaries northwards. The tundra and dry tundra on the Tibetan Plateau may be progressively confined to higher elevation. [ABSTRACT FROM AUTHOR]

In groundwater-dependent ecosystems, groundwater circulation controls the overall water quality and ecosystem dynamics. Groundwater and vegetation across a 30-km groundwater transect linking oasis, desert and river in an extremely arid area were investigated with a series of soil profiles drilled into the unsaturated zone to understand groundwater circulation and its control on groundwater quality and surface vegetation in the extremely arid Lower Tarim River, NW China. Measurements have included water-table depth, water chemistry and water isotopes (H, O, H) for 15 water samples, soil moisture and chloride content for 11 soil profiles, and vegetation investigation. Results show that the groundwater in desert zone is characterized by slow recharge rate (pre-modern water), great water-table depth (6.17-9.43 m) and high salinity (15.32-26.50 g/L), while that in oasis (uncultivated land) and riparian zone is characterized by relatively fast recharge rate (modern water), small groundwater-table depth (3.56-8.36 m) and low salinity (1.25-1.95 g/L). Stable isotopes show that secondary evaporation takes place during irrigation in oasis. The vegetation characteristics (coverage, richness, evenness and number of plants) are closely related to soil moisture and water-table depth. Groundwater recharge from irrigation in oasis and from river in riparian zone sustains a better ecosystem than that in the desert area, where lateral and vertical groundwater recharge is limited. The more evapotranspirative enrichment may occur in the vegetated and water-rich riparian zone as compared to desert. This study also demonstrates the effectiveness of environmental tracers in studying ecohydrological processes in arid regions. [ABSTRACT FROM AUTHOR]

The Last Glacial Maximum (LGM, c. 26-16 ka) and the Holocene Optimum (HO, c. 9-5 ka) were characterized by cold-dry and warm-wet climates respectively in the recently geological Earth. How Chinese deserts and sand fields responded to these distinctive climatic changes is still not clear, however. To reconstruct environments of the deserts and sand fields during the LGM and HO is helpful to understand the forcing mechanisms of environment change in this arid region, and to test paleoclimatic modeling results. Through our long-term field and laboratory investigations, 400 optically stimulated luminescence (OSL) ages and more than 100 depositional records in the Chinese deserts and sand fields were obtained; on the basis of these data, we reconstruct spatial distributions of the deserts and sand fields during the LGM and HO. Our results show that the sand fields of Mu Us, Hunshandake, Horqin and Hulun Buir in northern and northeastern China had expanded 25%, 37%, 38% and 270%, respectively, during the LGM; the sand fields of Gonghe in the northeastern Qinghai-Tibetan Plateau had expanded 20%, and the deserts of Badain Jaran, Tengger in central northern China had expanded 39% and 29% separately during the LGM; the deserts of Taklimakan, Gurbantünggüt and Kumtag in northwestern China had expanded 10%-20% respectively, compared to their modern areas. On the other hand, all of the sand fields were nearly completely covered by vegetation during the HO; the deserts in northwestern and central northern China were reduced by around 5%-20% in area during this time. Lakes in this arid region were probably expanded during the HO but this conclusion needs more investigation. Compared with the geological distributions of deserts and sand fields, human activity has clearly changed (expanded) the area of active sand dunes at the present time. Our observations show that environmental conditions of Chinese deserts and sand fields are controlled by regional climate together with human activity. [ABSTRACT FROM AUTHOR]

Tongwan City is one of the most famous and best-researched archaeological sites in China. By using palaeoclimatology proxy records from China over the last 2,000 years and archaeological/historical documents, we analyse the possible effect of climate on the collapse of Tongwan City, an ancient urban city of the Daxia state (AD 407-427). During Tongwan City's existence (AD 413-994), two severe cold and drought stages were recorded by both natural proxy data and the synthesis compiled from the historical documents. The first cold and drought stage occurred at about AD 420-550, with the lowest point centred at about AD 500. The second cold and drought stage occurred at about AD 780-950. These periods correspond to the times of climate deterioration, especially weak summer monsoons, which eventually resulted in the intensive desertification and collapse of Tongwan City. [ABSTRACT FROM AUTHOR]

The velocities in front of five topographic obstacles with windward slope angles between 45° and 80° were measured using ultrasonic anemometers in the field at the southeastern margin of the Tengger Desert. The characteristics of the horizontal and vertical velocities indicated that the airflow pattern was significantly influenced by the obstacle's windward slope angle. The horizontal flow decelerated but the vertical flow accelerated upwind of the obstacles when the windward slope was less than 60°, but a reversed flow formed in front of steeper obstacles. The size of the area occupied by the reversed horizontal component increased with increasing windward slope, but the region of reversed vertical velocity became narrower and taller. Airflow turbulence was strengthened as the wind approached the obstacle, and low-frequency high-energy velocity fluctuations were observed upwind of the obstacle, and could affect the entrainment and saltation processes of sand particles. Turbulence intensities for both the horizontal and vertical components of the airflow increased with increasing windward slope and with decreasing distance from the obstacle. The deceleration and downward movement of airflow upwind of the obstacle would result in supersaturation of the air-sand flow, leading to deposition of moving sand, and these deposited grains would become the material basis for the formation of echo dunes. The reversed airflow would both determine the initial position of the echo dune and provide the necessary motive power to subsequently shape the echo dune. [ABSTRACT FROM AUTHOR]

Water availability is one of the most important factors limiting photosynthetic assimilation of carbon dioxide and growth of individual plants in terrestrial ecosystems. Water use efficiency (WUE) of plants has been widely assessed using ecological methods in field measurements; however, approaches for remotely sensing WUE are still lacking, particularly in arid ecosystems. In this study, a comprehensive analysis of diurnal WUE via spectral indices in arid ecosystems was assessed. Analyses were conducted on a native dominant desert shrub, Tamarix ramosissima, in its original habitat on the southern periphery of the Gurbantunggut Desert, China. Based on diurnal measurements of spectral reflectance, photosynthesis, and micrometeorological variables, simple and useful spectral indices for estimating diurnal WUE at the assimilative organ scale were explored. From six types of spectral indices, ranging from simple to sophisticated, the best wavelength domains for a given type of index were determined by screening all combinations using correlation analysis. The coefficient of determination ( R), ranging from 0.19 to 0.60, for WUE was calculated for all indices derived from spectra taken from the assimilative organs. With only two wavelengths and a significant correlation coefficient ( R = 0.60, P < 0.001), the simple ratio (SR) type index was the most sensitive to WUE among all of the indices. Furthermore, SR is a useful indicator to determine the dynamic and diurnal processes of photosynthesis and transpiration of T. ramosissima. Although it has a few weaknesses, SR serves as a simple and robust indicator of WUE in arid ecosystems. [ABSTRACT FROM AUTHOR]

Feathered sand ridges in the northeastern Kumtagh Desert in China cover an area of 4016 km and consist of crescent sand ridges and interridge tongue-shaped dunes. Differences in grain size, mineral composition and albedo between crescent sand ridges and tongue-shaped dunes, and between windward and leeward slopes of tongue-shaped dunes, result in their feathery appearance in aerial and satellite imagery. Measurements of the sand drift potential in the region show that the sand-moving wind for feathered sand ridges can be divided into three sectors; i.e. north-northeasterly, easterly and east-northeasterly sectors roughly corresponding to the southeast, northwest and southwest slip faces. Our findings suggests that the crescent sand ridges resulting from the connection of barchan dunes along the prevailing wind direction are longitudinal dune ridges rather than transverse ones. Tongue-shaped dunes and quasi-dune shapes have obvious distinctions and are new transverse dune types. According to McKee's dune shape classification, the feathered sand ridges are not a deformation dune type but a complex one. According to Wu's dune morphological and genetic classification, they are not dune ridges or compound dune ridges that form under the action of unidirectional winds or two winds intersecting at an acute angle, but are complex dune ridges that form under the action of three winds intersecting at an acute angle. [ABSTRACT FROM AUTHOR]

The height profile of sand-dust flux at 0-2.0-m has been well studied. However, there have been very few experimental studies in the 0-50-m layer. In this study, the height profile of sand-dust flux at 0-50-m was observed by using three sandstorm observation towers (50 m in height) in 2006. The towers were located at three sites with different vegetation conditions (desert, edge of an oasis, and oasis) in the Minqin region, a typical desert-oasis area in China. At the same time, the features of the underlying vegetation were investigated. Results indicated that in the 0-50-m layer, sand-dust flux decreased rapidly as height rose at the desert and the edge of oasis sites, whereas it increased slightly as height rose in the oasis site. At the three sites sand-dust fluxes at each height increased with wind velocity, and there was a fairly good exponential relationship among them. In 2006, a total of 19 sandstorms occurred. The annual sand-dust that passed through a 1-m-wide, 50-m-high section was 9,169 kg at the desert site, 5,318 kg at the edge of oasis site, and 2,345 kg at the oasis site. Compared with the desert site, the annual sand flux was lower by 42% at the edge of oasis site and 74% at the oasis site. Vegetation had a significant effect in reducing the sand-dust flux. [ABSTRACT FROM AUTHOR]

The complicated desert vegetation pattern and its links to soil conditions in the Manas River basin where the natural landscape and human land-use history are representative for NW China and even central Asia are quantitatively investigated in this study. Vegetation and soil of 47 remnant desert and 22 cropland stands along the Manas River were sampled. Soil features, including Total Organic Carbon (TOC), total and individual ( $${\text{HCO}}_3^ - $$ , $${\text{CO}}_3^{2 - } $$ , Cl−, $${\text{SO}}_4^{2 - } $$ , K+, Na+, Ca2+, Mg2+) salt content, and physical components of both remnant desert and cropland stands were analyzed in a laboratory. In total, eight types of desert and lowland marsh communities are distinguished. Topographical conditions are found to strongly affect soil features. The topsoil is also distinguishable from the subsoil, particularly in clay content. Statistical analyses demonstrate that both silt percentage and total salt content in the soil are significant for the distribution of plant communities. Discriminant functions for the main desert and lowland marsh types were established based on their subsoil features, with accuracy up to 83%. The vegetation patterns prior to massive cultivation of 22 cropland plots were reliably interpreted from the cropland subsoil features using these discriminant functions. Twenty of them coincide very well with topological conditions, place names and records in literature, further confirming that the subsoil features have not substantially changed in the shifting from desert to cropland. [ABSTRACT FROM AUTHOR]

There have been significant variations in wind activity over the past five decades in arid and semiarid areas in China. High wind activity occurred from the 1960s to the 1970s, but wind activity has decreased continuously from the 1980s to the present; as a result, the potential sand transport during the latter period was only 20%-50% of the values during the 1960s and 1970s. Phases of high wind activity were highly consistent with the trends in desertification over the past five decades in arid and semiarid areas in China, but spring precipitation was also a significant factor: rapid desertification during the 1960s and 1970s was due to high wind activity, generally combining with low spring precipitation; subsequent rehabilitation since the 1980s has resulted from the combined effects of low wind activity and higher spring precipitation. Therefore, although modern desertification and rehabilitation processes are being more or less affected by human activities, both processes appear to be more strongly controlled by climate change. [ABSTRACT FROM AUTHOR]

In the present research, the authors measured parameters of richness, cover and importance value of ephemeral and ephemeroid plants on south-north and east-west transects in the Gurbantünggüt Desert in early spring, and investigated and analyzed the microhabitats, such as terrain, geomorphology, soil physical-chemical properties and crusts. By comparison, the regional differences in the ephemeral distribution in the desert were revealed. The species of ephemeral plants in the south and center are the richest and those in the west are the poorest in the desert. The cover of ephemeral plants in the mid-south is higher than that in the north, and that in the mid-east is higher than that in the west. The response of ephemeral plants to the spatial variation of the desert habitat forms the population-habitat gradient of ephemeral plants. The characteristics are: (1) In the habitat with higher terrain, coarser textured soil with poorer sorting and correspondingly higher organic matter and lower alkali-saline contents, Carex physoides and Eremopyrum orientale are the dominant ephemeral plants; (2) In the dry habitat with lower terrain, looser textured soil, some organic matter, alkali-saline soil, and developed crust, the ephemeral plants Alyssum linifolium and Erodium oxyrrhynchum are of characteristic of drought and alkali-saline tolerance; (3) In the habitat with lower terrain, some water and more alkali- saline soil, the ephemeral plants Neotorularia torulosa and Hypecoum parviflorum being of alkali-saline tolerance are mainly developed. However, most ephemerals are distributed in a habitat order of higher terrain, some organic, and less alkali-saline soil on the above-mentioned ephemeral population-habitat gradient. The spatial gradient of variation in desert microhabitats is small, and as a whole, the physiological character of mesophytism is represented by the desert ephemerals. [ABSTRACT FROM AUTHOR]

Properties of the soil and sand-binding vegetation were measured at five sites plus a control on dunes of the Tengger Desert stabilized for periods of up to 50 years. In the topsoil, fine particles, total N, P, K and organic matter increased significantly with increasing site age. However, there were no significant changes in deeper soil profiles (>0.4 m depth). Soil pH, calcium carbonate content, and total salt content tended to increase with age. Soil water in the topsoil changed little with increasing age, but was closely related to rainfall during the 50-year period. For deeper soil layers (0.4–3.0 m) soil water decreased significantly with age. After revegetation, the number of herbaceous species increased up to 30 years and then levelled off to 12–14 species, whereas the number of shrub species decreased from the 10 initial sand-binding species to only 3 species. Shrub cover decreased from a highest average of about 33% to the current 9%, whereas cover and biomass of herbaceous species increased throughout succession from 1956 to 2006. The development of soil and cryptogamic crusts on the surface of stabilized dunes enhanced the colonization and establishment of herbaceous plants due to increasing water availability, clay and silt content and soil nutrients. We propose that changes in properties of the surface soil led to increased interception of water, favoring shallow rooted grasses and forbs over perennial shrubs. [ABSTRACT FROM AUTHOR]

Located in the Junggar Basin in Xinjiang, the Gurbantonggut Desert is the second largest desert in China. Microbiotic crusts consisting of animalcule, lichen, moss, and algae species develop extensively in the region. Their formation, species composition and distribution pattern are closely related to the environmental conditions along the different parts of sand dune. Analysis of microbiotic crust distribution and relationship to environmental factors shows that average microbiotic crust thickness is 0.05–0.1 cm at the tops dunes, 0.2–1.5 cm in the upper part, 1.5–2.5 cm in middle and lower parts of dunes, and 1.5–5.0 cm in interdune areas, while areal coverage is 30.5, 48.5, 55.5, and 75.5%, respectively. Microbiotic crust differentiation along dune slopes is a result of the development stage and converse-succession resistance of the different microbiotic crusts. The numbers of species, thickness and degree of development of microbiotic crusts increase from the upper part to the middle and lower parts of dune slopes. The development and differentiation of microbiotic crusts at various dune slope positions are a reflection of the ecological expression of the comprehensive adaptability and natural selection of different microbiotic crust species to the local environmental conditions, and are closely related to such ecological conditions as the physiochemical properties of soils and topsoil textural stability. [ABSTRACT FROM AUTHOR]