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Response of Soil Moisture in Shallow Depth to Stochastic Rainfall and Biological Crust in Revegetated Sand Dunes in the Tengger Desert, China
Shi Wei, Wang Xinping, Zhang Yafeng
Journal of Desert Research    2018, 38 (3): 600-609.   doi: 10.7522/j.issn.1000-694X.2017.00027
Abstract(221)   PDF (0KB) (11)  
An experiment to measure water balance associated with infiltration events was conducted on the revegetated sand dunes in the Tengger Desert, north-western China. We choose three land cover types (Moss dominated soil crust, Algae dominated soil crust and dune sand) to study the effects of land cover change on infiltration, soil water redistribution and evaporation under different conditions of rainfall events on 8th July and 30th September, 2015, respectively. The results showed that surface soil moisture changed remarkably at the early stage of rainfall occurrence with a sharp increase within three hours, whereas, soil moisture exhibited a slight fluctuation at the later stage of rainfall resulted from the decrease of soil water potential gradient. In general, the presence of moss and algae dominated soil crusts impede the rainfall infiltration, limiting the depth to which rainwater can infiltrate and/or redistribute. Furthermore, biological crust could increase evaporation. We may conclude that the land cover with different biological soil crust had significant effects on soil hydrological processes, inducing more shallow distributed soil water in the revegetated sand dunes.
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The Aerodynamic Roughness Length over Rough Surfaces Derived from Whole Wind Velocity Profiles with the Log Law and Its Spatial Variations
Mei Fanmin, Zhang Ningning, Xi Yuan, Liu Xiuxiu
Journal of Desert Research    2018, 38 (3): 445-454.   doi: 10.7522/j.issn.1000-694X.2017.00052
Abstract(188)   PDF (0KB) (19)  
In terms of wind profiles over 39 surfaces covered with slender, porous and stocky roughness elements respectively at different density that were observed in a blown-sand wind tunnel under wind velocity around 4-20 m·s-1, aerodynamic roughness length is redefined as value estimated from whole wind velocity profile following the log law rather than that from inertial sub-layer so as to understand further drag effect on airflow and to reduce uncertainty of estimation about aerodynamic roughness. These whole wind profiles with the log law (here called as WWPL) extend from 0.1-0.3 h to the top of boundary layer except profiles over stocky roughness elements in wake flows which extend upward from top of the roughness elements, indicating extension of WWPL in street flows being stable in contrast with extension of inertial sub-layer. The trends of aerodynamic roughness lengths to observed heights are viewed as increase-decrease (probability 70%), decrease (21%) and increase types (9%) at the range around 0.01-1 mm. The trends can be explained as variations of wind velocity gradients with height due to dissipation of airflows' momentum at the bottom and restoration above top of roughness elements. As a result, adoption of roughness length from WWPL resulting from vertical average of wind velocity gradient, is necessary for expressing drag effect of roughness surfaces on airflow. Increase of aerodynamic roughness length from WWPL with roughness elements' density as a power function shows further the index being better indicator of the resistance effect compared to the traditional roughness length. On average, aerodynamic roughness length from WWPL in wake flow being about 1-5 times higher than that from WWPL in street flow, indicates aerodynamic roughness from WWPL in street flow is a better parameter for predication saltation threshold.
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Climate Change Revealed by Geochemical Major Elements during Holocene in the Southeastern Mu US Desert
Su Zhizhu, Wu Yujing, Kong Mengyuan, Ma Yijuan, Liang Aimin, Liu Miaomiao, Zhang Caixia
Journal of Desert Research    2018, 38 (3): 516-523.   doi: 10.7522/j.issn.1000-694X.2018.00012
Abstract(133)   PDF (0KB) (11)  
The Mu US Desert located in the semi-arid area of northwest edge of China's monsoon region is typically sensitive to the global climate change, so this area is usually regarded as ideal area for research of climate change and desert evolution. The Jinjie profile (38°44′45″N, 110°09′56″E) of Shenmu County that located in Southeastern of Mu US Desert, has developed representative aeolian sand-paleosoil sedimentary structure. We analyzed sediment in Jinjie profile, based on data of OSL dating, geochemical major element oxides and the ratio of these elements, in combination with magnetic susceptibility and grain size. The result showed that: (1)The sediment of Jinjie profile was mainly composed of SiO2 and Al2O3, with the contents of 69.72%-81.40% and 11.04%-12.71%, the other major element oxides' contents are in order of Na>K>Fe>Ca>Mg. Chemical activity of different geochemical elements in the section showed obvious variability: K, Na and Si were more migrated and leached; while Ca, Mg, Fe, Al were obviously enriched. (2)The geochemical parameters can be used as the sensitive index to indicate the variability of Asian summer monsoon and winter monsoon. (3)The climate change in Southeastern of Mu US Desert since 7.9 ka BP can be classified into 6 stages: 7.9-7.3 ka BP, the paleosoil layer is developed, the summer monsoon was powerful and the climate was warmest and wettest during this period, chemical weathering is strong and indicating accessing to the Holocene Optimum; 7.3-6.8 ka BP, the aeolian sand is developed, and the winter monsoon became stronger and the climate was cold and dry; 6.8-4.3 ka BP, the climate was warm and wet as a whole but still occurs two climatic fluctuations which become dry and cold from warm and wet, more than, there were six aeolian events were recorded at 6.6-6.3 ka BP, 6.1 ka BP, 5.9 ka BP, 5.7-5.5 ka BP, 5.3-5.0 ka BP, 4.7-4.4 ka BP; 4.3-2.5 ka BP, the winter monsoon became stronger again, the cold and dry climate was dominated; 2.5-1.8 ka BP, the climate was warm and humid, but the summer monsoon is weaker than the Holocene Optimum; Since 1.8 ka BP, the climate becomes colder and arider.  The climate change in the study area reflects the strong and weak changes of East Asian monsoon and is coincident with the regional and global climate change.
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Dynamic Mechanism Research on the Secondary Blown Sand Disaster in the 110 MW Photovoltaic Arrays of the Hobq Desert
Guo Caiyun, Han Zhiwen, Li Aimin, Zhong Shuai
Journal of Desert Research    2018, 38 (2): 225-232.   doi: 10.7522/j.issn.1000-694X.2016.00142
Abstract(125)   PDF (3316KB) (267)  
In order to explain the dynamic mechanism of sand erosion and accumulation of sandy surface under the interference of photovoltaic facilities, two cross sections were set in the 110 MW photovoltaic Plant located in the Hopq Desert. MetOne 014A/024A 8 channel anemometer (with CR200X data collection instrument) were used, and the average wind speed of four heights (20 cm, 50 cm, 100 cm, 200 cm) around the photovoltaic panel were observed simultaneously. The variations of wind velocity around the photovoltaic panel were analysed. Results showed that:(1) The photovoltaic facilities resulted in the variations of flow field on both sides of the photovoltaic panels and generated four secondary flow field zones, namely, the conflux accelerating speed-up zone under the panels, the resistance decelerating zone in front and back of the panels, the uplift zone above the panels and the recovery area between the plates; Moreover, there were significant differences in the flow field pattern between the upwind edge region and the area within the photovoltaic plants. (2) The dynamical distribution indicated by develop degree of the flow field pattern was identical with the surface erosion and accumulation situation basically. (3)Vegetation can increase the surface roughness effectively, and reduce the transit speed below 50 cm near surface, and prevent the occurrence and aggravation of the sand erosion. (4) The conflux accelerating zone under the panels and the reverse vortex around the panels were the main dynamic mechanisms of shaping wind erosion ditches (PITS) and sand accumulation belts, respectively.
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Composition and Micro-morphological Characteristics of Aeolian Sand in the Middle of the Mu Us Sandy Land
Chen Guoxiang, Dong Zhibao, Cui Xujia, Xiao Weiqiang, Li Lulu, Yang Junhuai, Shi Weikang
Journal of Desert Research    2018, 38 (3): 473-483.   doi: 10.7522/j.issn.1000-694X.2017.00066
Abstract(123)   PDF (0KB) (15)  
In this paper, the grain size, element and micro-morphological characteristics of mobile dune and fixed/semi-fixed dune in the middle of the Mu Us Sandy Land are analyzed. The results show that both the mobile dune and the fixed/semi-fixed dune are composed of fine sand and medium sand, while the sorting of mobile dune is better, and the sorting of fixed/semi-fixed dune is poor. The transport style of dunes is saltation in a frequent and strong wind activity environment, and the way of transportation is fixed and the power of transportation is stable. Compared with UCC, SiO2 and Na2O are rich in major elements, others are loss, and Co is enriched obviously for trace element. Values of CIA of dunes are close to the average of the upper continental crust, indicating that the dune has experienced a low degree of chemical weathering. The roundness of mobile dune and fixed/semi-fixed dune is poor, and most of them are angular shape or sub-angular shape, and the real round shape is less; The typical mark of the windy environment is dish-shaped pits accounted for a large proportion, and it is inferred that the climate of the Mu Us Sandy Land is relatively dry, the mechanical action occupies a dominant position while the chemical weathering plays a small role.
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Climatic Change Reflected by Geochemical Features in Datong Basin, North China since 220 ka BP
Liu Miaomiao, Su Zhizhu, Kong Mengyuan, Zhang Caixia, Li Jinchang, Wang Guoling, Li Xiang
Journal of Desert Research    2018, 38 (2): 278-285.   doi: 10.7522/j.issn.1000-694X.2017.00104
Abstract(107)   PDF (1974KB) (176)  
The Datong Basin developed thick fluvio-lacustrine sediments in Quaternary period and aeolian loess overlied, which recorded an abundant information on past climatic and environmental changes. To analyze the climate changes, we mainly use the primary oxides as climate proxies to establish the age framework according to stratigraphic dating data, combining formation susceptibility and particle size. The results showed that:(1)The average content of chemical elements of the sediments in the constant formation was SiO2 > Al2O3 > CaO > Na2O > TOFE > K2O > MgO from high to low,the sedimentary facies of different elements are obviously different, reflecting elements vary with climate change. (2) The Datong Basin climate change experienced the following 5 stages:The research area climate was warm-humid during the Middle Pleistocene of 220-199 ka BP, and cold-dry climate occurrenced during the Middle Pleistocene of 199-138 ka BP, and warm-humid climate occurrenced during the last interglacial period of 138-71 ka BP, and cold-dry climate was showed during the last glacial stage of 71-11 ka BP, and the Holocene periodclimate was alternate variationsof warm-wet and cold-dry. However, during each period there is still less-grade climate fluctuation level. (3) These climatic changes is similar with Salawusu River and Inner Mongolia Daihai region roughly in the same latitude, and are well accordant with the global climatic change reflected by the deep-sea oxygen isotope and the polar ice core, showing a consistency in time of climatic change between the study area and the global. The climate change in this area is regional response of global climate change influenced by the East Asian winter and summer monsoon.
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Compilation of Geomorphic Map of the Mu Us Desert
Wen Yanglei, Hao Chengzhi, Tan Lihua, Li Dawei, Fu Tianyang, Zhang Mei, Wu Yongqiu
Journal of Desert Research    2018, 38 (3): 508-515.   doi: 10.7522/j.issn.1000-694X.2017.00030
Abstract(99)   PDF (0KB) (15)  
Desert geomorphic map can provide the basic information for studying deserts. The dune types were complex in the Mu Us Desert, so it was important to divide aeolian landforms in detail and compile a geomorphic map of the Mu Us Desert. The map can help us to study the causes, distribution characteristics and evolution laws of aeolian landforms. The scale of the map was determined to be 1∶250 000, considering the cartographic region to be shown and the required specification of printing paper. 1∶100 000 topographic maps were selected as the basic data and 1∶50 000 topographic maps and 1∶200 000 geologic maps were selected as supplementary. The images provided by landset-8 and Google Earth were selected as the thematic contents. The geomorphic types were classified as aeolian landforms, lacustrine landforms, fluvial landforms, arid landforms, loess landforms and others. Aeolian landforms were the key elements to be manifested in the thematic map. Legend system and hill-shading were used to show the geomorphic types according to the topographical features of the Mu Us Desert. Legend system included many representing methods, such as colours, symbols, codes, notes and so on. Using hill-shading enhanced the stereo sense on the vision and made the map more beautiful.
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Wind Regime and Dune Field Patterns in the Gonghe Basin, Qinghai, China
Chen Zongyan, Dong Zhibao, Wang Qingchun
Journal of Desert Research    2018, 38 (3): 492-499.   doi: 10.7522/j.issn.1000-694X.2017.00014
Abstract(93)   PDF (0KB) (12)  
Based on the wind data collected from automatic meteorological stations of Chaka, Gonghe and Guinan in the Gonghe Basin, this paper analyzed the variation characteristics of wind speed, wind direction and sand drift potential. Combining with high resolution images of Google Earth, the relationship between wind regime and aeolian geomorphology is discussed. The results are as follows: (1) The annual mean wind speed ranges in 1.6-2.7 m·s-1 in the Gonghe Basin. The frequency of threshold wind in northwest region, middle region and southeast region were 7.7%, 3.5% and 0.9%, respectively. The threshold wind mainly occurs in the winter and spring. Its direction is mainly WNW and W. (2) The wind energy is low. The sand activity weakens from northwest to southeast in the Gonghe Basin. The wind direction variability ranges in 0.7-0.96, and wind regime is narrow unimodal or wide unimodal. The wind direction variability belongs to high ratio in northwest region and middle region, but in southeast region, it belongs to intermediate. RDP is almost the same, and its value ranges in 281°-287.1°. (3)Dune field patterns conclude barchans dunes, reticulate dunes, compound dunes chain, mega dunes, longitudinal dunes and parabolic dunes etc. That fits well with wind regime in the Gonghe Basin.
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Biomass Estimation Models for Dominant Sand-fixing Shrubs in Horqin Sand Land
Journal of Desert Research    2018, 38 (3): 553-559.   doi: 10.7522/j.issn.1000-694X.2018.00033
Abstract(93)   PDF (0KB) (15)  
Biomass estimation modelling is essential to rapidly evaluate the productivity of sand-fixing shrub forest. In this study, estimation model of above-ground, root and whole plant biomass was constructed after the proper independent variables were determined for 3 dominant sand-fixing shrubs, Caragana microphylla, Artemisia halondendron, and Salix gordejevii, in Kerqin Sand Land. The optimal models were selected according to the largest determination coefficients (R2), the smallest standard error of estimates (SEE) and significance level (P<0.05). The results showed that shrub canopy volume was the best independent variable of biomass estimation for C. microphylla and S. gordejevii, and shrub canopy area was the best independent variable for A. halondendron. Subsequently, the largest R2 and the smallest SEE were detected in power function equations for above-ground, root and whole plant biomass of 3 shrubs. In addition, prediction precisions of power function equations for 3 shrubs exceeded 93%, suggesting that allometric growth equation was the optimal biomass models for dominant sand-fixing shrubs. These optimal biomass estimation models will be helpful for productivity evaluation of sand-fixing shrub forest, and thereby supply scientific basis for human management and involvement of sand-fixing shrub forest.
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Characteristics of Surface Wind Field  in the Hobq Desert from 1957 to 2014
Xiao Nan, Dong Zhibao, Nan Weige, Cui Xujia, Li Chao, Xiao Weiqiang, Li Lulu
Journal of Desert Research    2018, 38 (3): 628-636.   doi: 10.7522/j.issn.1000-694X.2017.00034
Abstract(93)   PDF (0KB) (16)  
Sandy desertification is greatly influenced by wind, and threshold wind of transporting sand is major power shaping desert landform pattern. We analyzed surface wind field from wind speed, wind direction and sand drift potential by surface wind data from four national basic meteorological stations around the Hobq Desert from 1957 to 2014. The results showed that: (1) The correlation of mean wind speed and frequency of threshold wind of transporting sand is significant in the Hobq Desert. (2) Annual mean wind speed is 2.7 m·s-1, and prevailing wind direction is WNW-NW, and the wind direction variability is intermediate. The resultant drift direction is around 310°. The wind speed is the largest in April with intermediate wind direction variability; the wind speed is relatively little in August with high wind direction variability and the wind speed is the least in January with low wind direction variability. The wind speed is the largest from March to June with intermediate wind direction concentration; the wind speed is relatively large from November to February with high wind direction concentration and the wind speed is the least from July to October with low wind direction concentration. (3) There is a great tendency change for the wind speed, the frequency of threshold wind of transporting sand and sand drift potential in mid and late 1980s and around 2007, and there is a trend from decrease to increase around 2007. (4) It is the change of atmospheric circulation and surface roughness length that significantly changes surface wind field in the Hobq Desert.
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