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1.
Aeolian sand landforms in the Yarlung Zangbo River(YZR) valley are a special type of aeolian landform that has attracted the attention of many scholars. However, the spatial distribution as well as the formation mechanism of aeolian sand has rarely been reported with integrated studies. In this paper, for remote sensing interpretation, scanning electron microscopy(SEM), X-ray diffraction(XRD) and particle size distribution(PSD) methods were used to analyze the spatial distribution and the deposition characteristics of aeolian sand. Combined with wind data and topography, the main driving factors and the formation mechanism of aeolian sand landforms were also examined. In the middle reaches of the YZR valley, there is a total of 2324.43 km~2 of aeolian sand, especially on the north bank of the wide valleys. In different wide valleys, the aeolian sand landforms exhibit a decreasing trend from the upstream to the downstream regions in both the area and expansion rate of aeolian sand. The cyclonic vortexes generated by the westerly winds and glacial winds are the main driving factors for transporting alluvial sand to the riverbank areas to form aeolian dunes. There are three main types of sand dunes in the river valley: climbing dunes, lee dunes and circumfluent dunes. Climbing dunes and lee dunes are mostly located west of the Jiacha Gorge, and the circumfluent dunes are mostly located east of the Jiacha Gorge.  相似文献   

2.
Wind and sand control are important factors in combating desertification and protecting oases. An oasis protective system can provide these benefits, but quantitative research on protection effects has been lacking to date. This researchdescribes an oasis protective system in the southeastern border of the Tengger Desert. The system consists of a sand barrier belt, a shrub and herbaceous plant belt, and a farmland shelter belt.The system was compared to a bare dunes area as the control zone. The study investigated windproof effect,sediment transport, and erosion through fieldobservations. Results showed that the roughness of the shrub and herbaceous plant belt, farmland shelter belt, and sand barrier belt were increased compared with bare dunes. The shrub and herbaceous plant belt provided the highest windproof effect values for the same wind velocity measurement height, and the windproof effect values for different protective belts were as follows: shrub and herbaceous plant belt farmland shelter belt sand barrier belt. The sand barrier belt provided effective wind and sand control at heights from 0 to 50 cm above the ground. The total sediment transport for each protective belt is as follows: bare dunes sand barrier belt shrub and herbaceous plant belt farmland shelter belt. The sediment transport decreased exponentially as the height increased. In the bare dunes and protective systems, the sediment transport is mainly within 30 cm of the ground surface. The wind erosion intensity for this protective system was as follows: bare dunes sand barrier belt shrub and herbaceous plant belt farmland shelter belt. This research offers quantitative evidence for how oasis protective systems can effectively intercept sand and prevent erosion in oases. The results of this study can be applied in similar regions.  相似文献   

3.
SahelbioclimaticzonecrossNorthAfricabe-tweenl7oNandl3"Nborders,theSaharaDeserttothenorthandtheSudansavannatothesouth,beinganimportantfragileecologicalzoneintheworld.SincethesevereSudano-Saheliandroughtof1968-l973sandydesertificationhasresultedinaverymiserableconse-quencestolocalpeople,asaSahelcountryinwestAhica,theRepublicofMaliisoneofthecountriesmostseverelyaffectedbydroughtanddesertification,AccordingtotheinvestigationsoftheexpertgroupoftheLanzhouInstituteofDesertResearch,theChineseA-…  相似文献   

4.
Considerable efforts have been dedicated to desertification research in the arid and semi-arid drylands of central Asia. However, there are few quantitative studies in conjunction with proper qualitative evaluation concerning land degradation and aeolian activity in the alpine realm. In this study, spectral information from two Landsat-5 TM scenes (04.08.1994 and 28.07.2009, respectively) was combined with reference information obtained in the field to run supervised classifications of eight landscape types for both time steps. Subsequently, the temporal and spatial patterns of the alpine wetlands/grasslands evolutions in the Zoige Basin were quantified and assessed based on these two classification maps. The most conspicuous change is the sharp increase of ~627 km2 degraded meadow. Concerning other land-covers, shallow wetland increases ~107 km2 and aeolian sediments (mobile dunes and sand sheets) have an increase of ~30 km2. Considering the deterioration, an obvious decrease of ~440 km2 degraded wetland can be observed. Likewise, decrease of deep wetland (~78 km2), humid meadow (~80 km2) and undisturbed meadow (~88 km2) were determined. These entire evolution matrixes undoubtedly hint a deteriorating tendency of the Zoige Basin ecosystem, which is characterized by significantly declined proportion of intact wetlands, meadow, rangeland and a considerable increase of degraded meadow and larger areas of mobile dunes. In particular, not only temporal alteration of the land-cover categories, the spatial and topographical characteristics of the land degradation also deserves more attention. In the alpine rangelands, the higher terraces of the river channels along with their slopes are more liable to the degradation and desertification. This tendency has significantly impeded the nomadic and agriculture activities. The set of anthropozoogenic factors encompassing enclosures, overgrazing and trampling, rodent damaging and exceedingly ditching in the wetlands are assumed to be the main controlling mechanisms for the landscape degradation. A suite of strict protection policies is urgent and indispensable for self-regulation and restoration of the alpine meadow ecosystem. Controlling the size of livestock, less ditching in the rangeland, and the launching of a more strict nature reserve management by adjacent Ruoergai, Maqu and Hongyuan Counties would be practical and efficacious in achieving these objectives.  相似文献   

5.
1INTRODUCTIONOrdosDesertisageneral appellationof Qubqi Desert onthe north, Hedong Sandy Landonthesouthwest and MuUs Desert on the southeast (Fig. 1). It is situated on atransitional zone from arid desert steppe to semi-aridsteppe between ariddesertinNorth…  相似文献   

6.
The survival of Dunhuang Oasis is largely determined by the evolution of sand dunes in the southern edge of the oasis, mainly composed of shield dunes and mega pyramid dunes, which occupy two-thirds and one-third of the area, respectively. However, few studies have focused on dynamics of these dunes, especially in terms of quantification. So the theoretical basis of sand-control engineering is relatively limited. Here we present the characteristics of dune dynamics of a shield dune and mega pyramid dune in the southern edge of Dunhuang Oasis during April 2014–April 2016 based on measurement data of a 3-D laser scanner. Results indicate that the volume of the shield dune decreased during the monitoring period of two years, and the gravity centers of the monitored shield dune moved windward, indicating that sand was transported toward the oasis. Conversely, the dune volume of the mega pyramid dune increased and the gravity center presented no prominent movement, indicating that the mega pyramid dune was relatively stable and its migration toward the oasis was not notable. Thus, compared with mega pyramid dunes, shield dunes in the southern edge of Dunhuang Oasis are identified as a more significant sand source endangering the protection of the oasis, and sand-control engineering should mainly focus on these shield dunes.  相似文献   

7.
Wind erosion, or the transportation and deposition of sand into desert dunes and aeolian loess, is one of the most important aeolian activities. The progression of aeolian landforms expands arid and barren landscapes, leading to the degradation of adjacent areas. The Gonghe Basin, as a typical plateau with abundant sand sources, is highly sensitive to changes in the local climate conditions. In order to quantify the spatial-temporal variations in the aeolian landforms in the Gonghe Basin, we conducted field surveys and also analyzed twelve remote sensing(Landsat5 TM and Landsat8 OLI) images that sample the Gonghe Basin from 1989 to 2019. In the Gonghe Basin, we identified aeolian landforms such as climbing dunes on the windward slopes of the foothills, checkerboard dunes in the southeastern part of the basin, flat dunes, parabolic dunes and crescent dunes on the east and west sides of Longyangxia Reservoir, shrubby sandbanks on the valley slope in Shazhuyu, Tanggemu, and Indel, and sandy thickets at the bottom of the valley near the Dalian Sea, the Longyangxia Reservoir, and the tributaries of the Yellow River. From 1989 to 2005, the area of theaeolian regions expanded by 816.7 km~2, with an annual conversion rate of 0.05%. From 2015 to 2019, the area of the aeolian regions shrunk by 2411.9 km~2, with an annual conversion rate of-0.15%.The number and size of the fixed and semi-fixed dunes(e.g. the shrubby sandbanks on the valley slope and the sandy thickets at the bottom of the valley) were more stable than those of the mobile dunes(e.g. the checkerboard dunes, the flat dunes, the crescent dunes, the parabolic dunes, and the climbing dunes). The fixed and semi-fixed dunes were arranged in an irregular ring shape, and the location of the center of gravity of this ring did not change significantly from 1989 to 2019; in this time, the mobile dunes migrated to the northwest.  相似文献   

8.
 青海三江源区是长江、黄河、澜沧江3大河流的发源地。草地是该区域的主体生态系统,高寒草甸是其主要类型。近30年来,三江源地区草地发生了大面积的退化,不同退化程度的高寒草甸光谱特征是高寒草甸遥感分类和退化监测的重要依据。2009年8月作者在青海省三江源区对高山嵩草、矮嵩草和藏嵩草3种未退化高寒草甸,以及4种不同退化程度的高山嵩草草甸,进行了地面光谱测量和草地样方调查。同时对实测光谱曲线进行了比较,提取和分析了它们在557nm、675nm和760nm处反射率,以及"红边"斜率。结果表明,3种高寒草甸的光谱曲线,以及4种退化程度高寒草甸和未退化高寒草甸的光谱曲线在557nm处的反射率差异较小,在675nm和760nm处的反射率及"红边"斜率存在明显差异,能有效区分高寒草甸,可为高寒草甸遥感自动分类和退化监测提供依据。不同退化程度的高寒草甸地上生物量与其光谱曲线的"红边"斜率和归一化植被指数(NDVI)线性拟合的确定系数分别为0.93和0.87,其相关性较好,可用于高寒草甸地上生物量的估算。本文提取的光谱反射率的"红边"斜率不仅能有效区分3种典型高寒草甸和不同退化程度的高寒草甸,且与高寒草甸地上生物量的关系优于NDVI,对高寒草甸识别分类,退化监测和生物量估算有重要意义。  相似文献   

9.
Widespread aeolian sediments have been found in the middle reaches of the Yarlung Zangbo River, China. The grain-size characteristics of sediments from Cha'er Section in the area were analyzed. The results show that the section include one stratum of paleo-mobile dunes, four strata of paleo-semi-fixed dunes, two strata of paleo-fixed dunes, one stratum of sandy immature soils. The paleo-mobile and paleo-somi-fixed dune sand in this section are similar to modern aeolian sand in either grain-size composition or Mz and σ distribution. Compared the above types of dunes each other, the content of sand substance decreases, while the content of silt and clay increases for palco-fixed dunes and sandy immature soils. Combined with age data for each stratum, the analysis shows that these strata are the products of climate changes and the evolution of aeolian landforms. The evolutionary sequence of the paleoclimate and of acolian activities in the valley since 8600 yr B.P. reveals four stages: 8600-5700 yr B.P., when the paleoclimate was cold and dry, with strong winds, thereby activating dunes; 5700-3600 yr B.P., when it was warm and wet, with weak winds, causing dunes to undergo soil-forming processes; 3600-1900 yr B.P., when climate shifted from cold-dry with strong winds to warm-wet with weak winds, and activated dunes were fixed again; and 1900 yr B.P. -present, when the climate became fine, with weak winds, fixing dunes again.  相似文献   

10.
The interaction between fluvial and aeolian processes can significantly change surface morphology of the Earth. Taking the Horqin Sandy Land as the research area and using Landsat series satellite remote sensing images, this study utilizes geomorphology and landscape ecology to monitor and analyze the aeolian geomorphology characteristics of the Horqin Sandy Land. Results show that the sand dunes of the Horqin Sandy Land are mainly distributed on alluvial plains along the banks of the mainstream and tributaries of the Western Liao River, and the sand dune types tend to simplify from west to east and from south to north. The aeolian geomorphology coverage tend to be decreasing in the past 40 years, with an average annual change rate of 0.31%. While the area of traveling dunes decreased, the area of fixed and semi-fixed dunes increased. The fractal dimensions of various types of sand dune have all remained relatively constant between 1.07 and 1.10, suggesting that they are experiencing a relatively stable evolutionary process. There is a complex interaction between fluvial and aeolian processes of the Horqin Sandy Land, which plays a central role in surface landscape molding. Sand dunes on both sides of different rivers on the Horqin Sandy Land present certain regularity and different characteristics in terms of morphology, developmental scale, and spatial pattern. There are six fluvial-aeolian interaction modes in this area: supply of sand sources by rivers for sand dune development, complete obstruction of dune migration by rivers, partial obstruction of dune migration by rivers, influence of river valleys on dune developmental types on both sides, influence of river valleys on dune developmental scale on both sides, and river diversion due to obstruction and forcing by sand dunes. This study deepens our understanding of the surface process mechanism of the interaction between fluvial and aeolian processes in semi-arid regions, and provides a basis for researches on regional landscape responses in the context of global environmental change.  相似文献   

11.
The average size of the sand of dune in the vicinity of Tumen River is 0.12～0.30 mm, its standard deviation is 0.45～0.99 φ and the frequency cumulative distribution curve is divided into the single peak and the double peak. The Ski of the single peak is negative and the double peak is positive. There are two different areas in the plot of the Ski versus σi* It is shown that the sedimentary environment of the dunes is neritic deposit by the expressions of the grain-size parameters. All of the characters show that the sand dunes in Estuary of Tumen River may be the dunes of sea facies which were changed again by weathering and fluvialaction.  相似文献   

12.
ＳＩＭＵＬＡＴＩＮＧＳＴＵＤＹＯＮＢＡＲＣＨＡＮＤＵＮＥ①ＬｉｎｇＹｕｑｕａｎ（凌裕泉）１ＷｕＺｈｅｎｇ（吴正）２ＬｉｕＳｈａｏｚｈｏｎｇ（刘绍中）３ＬｉＣｈａｎｇｚｈｉ（李长治）１１ＩｎｓｔｉｔｕｔｅｏｆＤｅｓｅｒｔＲｅｓｅａｒｃｈ,ｔｈｅＣｈｉｎ...  相似文献   

13.
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14.
Barchan dune is one of the basic forms of eolian landform, it is usually moulded by high-concentration non-saturated wind-sand flow. The formation process of barchan dune begins from “wave-grain duality” of wind-sand movement, and goes through two developmental stages of sand material accumulating (high-concertration saturated wind-sand flow) and dune form moulding (high-concentration non-saturated wind-sand flow), i.e. the processes of dissipative increase and dispersive decrease. The scattered single barchan dunes on non-sandy bed surface have obvious characteristics of mobility and unstability (not including barchan sand hill). The formation of barchan dune in wind tunnel (its dune scale is one order of magnitude larger than sand ripple scale) is helpful to know the formation mechanism of barchan dunes. One of the series achievements supported by the National Natural Science Fundation of China (No. 49371009)  相似文献   

15.
BASIC FEATURES OF FOREST STEPPE IN THE LOESS PLATEAU OF CHINA   总被引：2，自引：0，他引：2  
ＢＡＳＩＣＦＥＡＴＵＲＥＳＯＦＦＯＲＥＳＴＳＴＥＰＰＥＩＮＴＨＥＬＯＥＳＳＰＬＡＴＥＡＵＯＦＣＨＩＮＡ￥ＺｈｕＺｈｉｃｈｅｎｇ（朱志诚）（ＤｅｐａｒｔｍｅｎｔｏｆＢｉｏｌｏｇｙ．ＮｏｒｔｈｗｅｓｔＵｎｉｖｅｒｓｉｔｙ，Ｘｉａｎ７１００６９，ＰＲＣ）Ａ...  相似文献   

16.
Hurqin Sand Land is regarded as the typical region for studying the problem of desertification.The integra-tion of 3S(GIS,GPS and RS)techniques offer a most helpful method to study and monitor the dynamics of desertification.Based on the data derived from 3 periodsˊmultitemporal Landsat TM imagery of the 1990s,the regional land use and dynamo-ics of desertification in Horqin Sand Land were studied.The main results revealed that :1)as long as the general change tendency was concerned,the desertification of Horqin Sand Land would continue to spread;2)there was a gradual de-crease in the area of both moving sand dunes and semi-stabilized ones,which meant that fruitful progress had been made to control the desertification during the 1990s;3)as a result of unreasonable cultivation,the total area of stabilized sand dunes and grassland in the middle and western region decreased obviously.It suggested that the increasing damage caused by human was leading to the hazard of further desertification.So in the future,it is necessary to take more effect-tive measures to control the spread of desertification and restore the degraded ecosystems for the purpose of optimizing the global eco-environment in Horqin Sand Land.  相似文献   

17.
The oasis-desert ecotone is a fragile ecological zone that is affected both by oasis and desert conditions. To understand the impact of the differences in wind power, and the influence of wind erosion and deposition on the ecotone, meteorological data and con- temporaneous wind erosion and deposition data were collected on the southern margin of Tarim Basin with serious sand-blown hazards. The wind velocity, average wind velocity, sand drift potential （DP）, resultant sand drift potential （RDP）, and sand transportation rate decrease significantly and successively across four landscape types with increasing vegetation coverage （VC）. Flat surfaces and areas of shifting sandy ground experience intense wind erosion with fast movement of mobile sand dunes; semi-fixed sand areas experience ex- tensive wind deposition but only slight wind erosion; and fixed sand areas experience only slight wind erosion and deposition. Volume of wind erosion on bare newly reclaimed farmland is up to 6.96 times that of bare shifting sandy ground. Wind erosion volume per unit area and VC follow an exponential function relationship in natural conditions, while wind deposition volume per unit area does not conform to any functions which has close relationship with vary topography and arrangement patterns of vegetation besides for VC. The results indicate that the volume of wind erosion has a close correlation with VC, and different types and distribution patterns of topog- raphy and vegetation also profoundly influence the wind deposition volume in the field, and underground water tables in different land- scape types control the plant community distribution. Keywords： wind erosion; wind deposition; oasis-desert ecotone; vegetation coverage （VC）; topography; Cele County  相似文献   

18.
1 Introduction The preferential flow tends to result in the loss of irriga- tion water and nutrients. The formation of the preferen- tial flow was caused by various factors, such as soil structure, tillage, worm cavity and root channeling rup- ture (Pot et al., 2005). Besides, frozen rupture can not be ignored in the northeastern China where the lowest tem- perature reaches -40℃ (Wang et al., 1993). There are several types of preferential flow, such as bypass flow, channeling flow and macro…  相似文献   

19.
This paper evaluated the impacts of mounds created by the plateau pika (Ochotona curzoniae) on the vege- tation composition, structure, and species diversity of an alpine Kobresia steppe meadow in Nagqu County, Tibet Autonomous Region, China. Based on mound height or the depth of erosion pit, we defined five stages of erosion and compared the floristic features of communities at these stages with those in undisturbed sites. In the study area, the mounds and pits covered up to 7% of the total area. Lancea tibetica, Lamiophlomis rotata, and Potentilla bifurca were the dominant species in erosion pits, and Kobresia pygmaea, the dominant species in undisturbed sites, became a com- panion species in eroded areas. In the process of erosion, the original vegetation was covered by soil ejected by the pika, then the mounds were gradually eroded by wind and rain, and finally erosion pits formed. The vegetation coverage in- creased with increasing erosion stages but remained significantly lower than that in undisturbed sites. Improved coverage eventually reduced soil erosion, and pit depth eventually stabilized at around 20cm. Aboveground biomass increased with increasing erosion stage, but the proportion of low-quality forage reached more than 94%. The richness index and Shannon-Wiener index increased significantly with increasing erosion stage, but the richness index in mound and pit areas was significantly lower than that in undisturbed sites.  相似文献   

20.
Based on the field surveys and repeated cross-profile observations combined with the comparison of many years’ topog-raphic maps,this study shows the spatial variability and varying patterns of coastal erosion along the west coast of the Taiwan Strait.Regional differentiation in the Meso-Cenozoic coastal tectonics determined the irregular coastline and geological background for large-scale coastal erosion distribution.The intensity of coastal erosion on the west side of the Taiwan Strait is mild in the nort...  相似文献   

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