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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(99)   PDF (3316KB) (241)  
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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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(78)   PDF (0KB) (0)  
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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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(71)   PDF (1974KB) (159)  
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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Variations of the Components of Radiation in Desert Wetland of Dunhuang, China
Yin Daiying, Qu Jianjun, Yu Ye, Zhao Suping, Li Fang, Xiao Jianhua
JOURNAL OF DESERT RESEARCH    2018, 38 (1): 172-181.   doi: 10.7522/j.issn.1000-694X.2016.00112
Abstract(56)   PDF (6273KB) (258)  
The characteristics of radiation on the Xihu wetland ecosystem of Dunhuang are analyzed by radiation data from the measurements of observation system in 2013. The results show that the daily variations of the radiation components are different under different weathers. The daily variation curves are smooth on sunny day, but on cloudy day and dust the curves become irregular. The diurnal variations of the radiation flux are unimodal type, but the radiation components volume variances are different and the extremes appear in different times. The seasonal variation characteristics of monthly total downward shortwave radiation, downward long-wave radiation, upward long-wave radiation and net radiation are obvious:the maximum value appears in summer, and the minimum value appears in winter. However, the seasonal variation characteristics of monthly total upward shortwave radiation are not obvious. The daily mean of downward shortwave radiation, upward shortwave radiation downward long-wave radiation, upward long-wave radiation and net radiation has seasonality:the maximum value appears in June or July and the minimum value appears in January or December. The surface albedo in the growing season is lower than in the non-growing season. The diurnal variation of surface albedo is "U" shape, with the maximum value in the morning and evening.
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Aeolian Sediment Transport in the Sanlongsha Area to the North of Kumtagh Desert
Yang Zhuanling, Qian Guangqiang, Dongzhibao, Luo Wanyin, Zhang Zhengcai, Lu Junfeng, Li Jiyan
JOURNAL OF DESERT RESEARCH    2018, 38 (1): 58-67.   doi: 10.7522/j.issn.1000-694X.2016.00132
Abstract(55)   PDF (5442KB) (270)  
The development of aeolian geomorphology is controlled by near surface sand movement, whereas the current research pays more attention to the short period (a few minutes to a few hours) and single direction (facing the main direction) of the blowing sand structure characteristics, and it is difficult to relate the results to the long-term geomorphological processes. Thus, we conducted a whole year field observation of aeolian sediment transport from May 2014 to May 2015 in the Sanlongsha Area of the Northern Kumtagh Desert, adopting the eight-directional four layer gradient sand trap (SEDST). After continuous observation of six periods, totally obtained 192 sand samples from different directions and different heights. Observation results show that the total weight of the captured sediments is 405.2 kg within 1 m above the ground and 75.3% of them are transported within 0-0.2 m, reflecting the characteristics of near surface sediment transport. The average sediment transport rate is 55.2 kg·5m-1·5d-1, with sediments mainly from the N, NE and NW directions, and there is significant diversity in different seasons, and the maximum transport rate in spring is 2.5 times of the annual average value, followed by summer and winter minimum. The annual average sediment flux profile (blowing sand structure) shows exponential decline trend, part of the flux profile has presented the "trunk effect" over the gobi surface. The annual mean net flux is 1.159 kg·5m-1·5d-1, along with the increase of the height decreased, and the variation of net flux with altitude at different time periods is consistent with that of the whole year; the annual mean resultant sediment transport direction is 193.2, and the direction of sediment transport increases with the increase of the height from the northeast to the north. In conclusion, the sediment transport intensity reaches the strongest in the spring, and the main sediment transport direction is N, NE and NW, with a secondary sediment transport direction, S direction, in spring and summer, respectively. The study has great significance for the further understanding aeolian sediment transport of Sanlongsha area and revealing the material sources of Kumtagh desert.
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Spatial Distribution of Grain Size in Aeolian Flow in Nylon Net Checkerboard Barrier
Li Xiaojuan, Zhou Zhibin, Li Ning, Lu Jingjing, Ding Xinyuan, Zhu Hai, Wang Lijie
JOURNAL OF DESERT RESEARCH    2018, 38 (1): 76-84.   doi: 10.7522/j.issn.1000-694X.2016.00110
Abstract(55)   PDF (4824KB) (241)  
The research on grain size is of great importance in aeolian geomorphology. On one hand, grain size characteristics of the surface sediments not only reflects the wind for transporting and sorting but also records the wind strength formation of the aeolian process. On the other hand, it embodies that terrain and other obstacles have made a big change on the sand flow transport processes. Thus, studying the spatial distribution of grain size in aeolian flow in the hinter land of Taklimakan Desert is extremely important. To reveal spatial distribution of grain size in aeolian flow, two kinds underlying surface, bare sandy land and nylon net checkerboard barrier, were selected in this study. Using two kinds of sand collectors (one was set to observe sand flow in the vertical height, the other was set to observe sand flow in the horizontal direction) to measure sediment runoff of sand flow in 2-100 cm and 16 directions. And then the grain size of sand samples was analyzed by BT-2001 Laser grain size analyzer. The results show that the shape of frequency distribution curves of grain size is unimodal. In the vertical height, the average grain size of sand grains at the L1 and L2 decreases with the increase of height. At L3 average grain size increase before it is stable. With the degree of depth in the sand barrier, sorting is worse; skewness increase, kurtosis reduces. With the decreasing of mean grain size, sorting is deteriorating. The thin tail of frequency distribution curves becomes more and more obvious. Grain size distribution is narrowed at the L1 and L2. At L1 the change rate of mean grain-size to standard deviation, skewness, kurtosis is greater than at L2. In the horizontal direction, the average grain size of sand have the first increase after a decrease during T1-T2-T3. At T2, sorting is the best, skewness and kurtosis are minimum. Size parameters and the average particle diameter have no significant correlation in the three points.
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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(55)   PDF (0KB) (0)  
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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Water Sources of Typical Desert Riparian Plants in the Lower Reaches of Tarim River
Wang Yuyang, Chen Yapeng, Li Weihong, Wang Rizhao, Zhou Yingying, Zhang Jianpeng
JOURNAL OF DESERT RESEARCH    2017, 37 (6): 1150-1157.   doi: 10.7522/j.issn.1000-694X.2016.00103
Abstract(54)   PDF (2349KB) (295)  
The Lower Reaches of the Tarim River is featured with an extraordinary dry and hot climate.Vegetation here has a harsh environment to survival, and water is the most crucial ecological factor. The research of water sources used by desert plants in the growing season helps to understand the water use strategy of the desert plants, which will be useful to vegetation reconstruction in the Lower Reaches of Tarim River. In this study, the stable oxygen isotope (δ18O) of stem water of four dominant plant species, groundwater and soil water in the lower reaches of Tarim River were measured in May, July, August and September, 2015. And then we used the Multi-source mixed liner model (IsoSource) to analyze the probable contribution of potential water sources used by these dominant desert plants. In addition, we use the proportional similarity index (PSI) to analyze the water use relationship between different desert plants. The result indicated that: (1) in the Lower Reaches of Tarim River, Populus euphratica oliv (young and mature) and Tamarix ramosissima can hardly use soil water stored at 0-50 cm depth, but mainly uptook deep soil water stored below 200 cm depth and groundwater, Glycyrrhiza inflata and Alhagi spar folia mainly acquired soil water stored at 50-200 cm depth. (2) During growing season, P. euphratica oliv (young and mature) and T. ramosissima had a fierce water competition, except for individual months. lycyrrhiza inflata and Alhagi spar folia also had a strong water competition, however, P. euphratica oliv (young and mature) and T. ramosissima had a weak water competition with G. inflata and A. spar folia. (3) In order to adapt extremely drought environment, P. euphratica oliv (young and mature) and T. ramosissima had a stable water sources, and the feasible proportion of water sources used by different plants had a slight fluctuation in the Lower Reaches of Tarim River.
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Population Structure Characteristics of Population euphratica in the Lower Reaches of Tarim River
Zhou Yingying, Chen Yaning, Zhu Chenggang, Chen Yapeng, Chen Xiaolin
Journal of Desert Research    2018, 38 (2): 315-323.   doi: 10.7522/j.issn.1000-694X.2017.00103
Abstract(54)   PDF (2537KB) (227)  
Population structure characteristics can reflect the living conditions and future trends of one population. In this paper, we investigated the living status of Populus euphratica in the lower reaches of Tarim River, after years of ecological water conveyances to restore the ecosystem. The population density, age structure, sex ratio structure and spatial structure of P. euphratica were analyzed based on field investigation. The results indicated that the pattern of age structure of P. euphratica in the lower reaches of Tarim River followed the "inverted pyramid" pattern. The population dynamics index, population density, had similar patterns with that of the age structure, indicating the declining trend of P. euphratica will continue. The P. euphratica was significantly male-biased, and this deviation increased with the deterioration of habitats. The distribution pattern of P. euphratica showed a significant cluster distribution with no intensity difference among them. After 18 years, ecological water conveyances, the degradation trends of the P. euphratica distributed far from the river have not yet completely reversed although the ecological conditions near the river have improved. The ecological water conveyances along a natural river channel created a too narrow flooded area to improve the population regeneration rates. Therefore, during the processes of ecological water conveyances, artificial measures are suggested to be taken to extend the flooded area to provide conditions for the reproduction and regeneration of the P. euphratica.
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Self-organization Process of Sand-fixing Plantation in A Desert-oasis Ecotone, Northwestern China
Zhao Wenzhi, Zheng Ying, Zhang Gefei
JOURNAL OF DESERT RESEARCH    2018, 38 (1): 1-7.   doi: 10.7522/j.issn.1000-694X.2017.00091
Abstract(52)   PDF (2187KB) (370)  
The two-phase mosaics of vegetation alternating with bare ground, was frequently observed in arid ecosystem. Theoretical studies suggest that this range of spatial patterns is the result of self-organization as a consequence of resource redistribution. On the basis of the review of self-organized process of vegetation, the spatial patterns and self-thinning process of Haloxylon ammodendron plantation for more than 40 years were analyzed in an oasis-desert ecotone in the Hexi Corridor. Results showed that a self-organized process of sand-fixing plantation would also take place in arid areas especially where precipitation is less than 200 mm. The overall spatial pattern of H. ammodendron shifted from initially uniform distribution to clustered, the landscape patches are becoming fragmented. But the self-thinning process of H. ammodendron plantation don't follow the natural order of the developmental stages, it is most relevant to the distance between the habitats of H.ammodendron and oasis marginal, and the groundwater depth in the habitats of H.ammodendron plantation. Ecosystem may abruptly shifted from one alternative stable state to another one, accompanied with great changes, under climate change and exacerbated human disturbance, the research of threshold range of vegetation pattern regime shift should be strengthened in the future, and the research of self-organized process of the sand-fixing plantation in the arid areas should also be strengthened.
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