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1.
Variable vegetation cover and episodic sand movement on longitudinal desert sand dunes 总被引：6，自引：0，他引：6
Longitudinal (linear) sand dunes of the Simpson and Strzelecki dunefields in eastern central Australia present a paradox. Low levels of activity today stand in contrast to luminescence dating which has repeatedly shown deep deposits of sand on dune crests dating to within the late Holocene. In order to investigate the nature of dune activity in the Simpson–Strzelecki dunefield, vegetation and sand mobility were investigated by detailed vegetation survey and measurement of rippled area and loose sand depth of dunes at three sites along a climatic gradient. The response of both vegetation and sand movement to inter-annual climate variability was examined by repeat surveys of two sites in drought and non-drought conditions. Projected plant cover and plant + crust cover were found to have inverse linear relationships with rippled area and the area of deep loose sand. No relationship was found between these measures of sand movement and the plant frontal area index. A negative exponential relationship between equivalent mobile sand depth on dune surfaces and both vascular plant cover and vascular + crust cover was also found. There is no simple threshold of vegetation cover below which sand transport begins. Dunes with low perennial plant cover may form small dunes with slip faces leading to a positive feedback inhibiting ephemeral plant growth in wet years and accelerating sand transport rates. The linear dunefields are largely within the zone in which plant cover is sufficient to enforce low sand transport rates, and in which there is a strong response of vegetation and sand transport to inter-annual variation in rainfall. Both ephemeral plants (mostly forbs) and crust were found to respond rapidly to large (> 20 mm/month) rainfall events. On millennial time-scales, the level of dune activity is controlled by vegetation cover and probably not by fluctuations of wind strength. Land use or extreme, decadal time-scale, drought may destabilise dunes by removing perennial plant cover, accelerating wind erosion. 相似文献
2.
图们江下游圈河流域河岸沙丘动态变化 总被引：1，自引：1，他引：0
以图们江下游跨国界地区圈河流域河岸沙丘为研究对象,运用遥感与GIS技术,结合遥感影像、地形图等资料,分析该区1984~2015年河岸沙丘空间分布与格局演变,计算河岸沙丘分维值与稳定性指数。结果表明：该区河岸沙丘主要分布在弯曲型河道东岸,呈WNW-ESE向带状展布,面积15.71 km2。近31 a沙丘面积总体呈减少态势,净减少0.09 km2,其中,较少有人类活动的A区,沙丘面积呈减少趋势,减少幅度为8.21%;而受人类活动影响较大的B区,沙丘面积持续增加,尤其近5 a增幅达32%。河岸沙丘分维值虽总体高于内陆沙漠沙丘,但变化不显著,说明河岸沙丘处于相对稳定的发育演化过程中。该研究为图们江下游跨国界地区生态环境可续持发展提供科学依据。 相似文献
3.
As a contribution to understanding the morphogenesis of the Australian continental dunefield, maps are presented of the main types of dunes, their orientation and mean spacing using the best available sources of data. Major features on previous maps of the Australian dunefield are verified and new information has been obtained. The anticlockwise whorl of dunes has been found to close on both its eastern and western ends. Dunes extend as far north as 16°S and over large parts of the far south‐west of Western Australia. Distributions of dune types are related to former vegetation cover, climate, supply of sand and directional variability of formative winds. Previously documented relationships between dune spacing, height, equivalent sand thickness (EST) and the texture of surfaces over which sand is transported are used to partially explain the map of mean dune spacings. The spatial distribution of EST, and mineralogic and sedimentologic evidence show that aeolian sediment in the Australian dunefield has travelled only short distances. 相似文献
4.
库姆塔格沙漠北部三垄沙地区风成沉积物粒度特征 总被引：4，自引：3，他引：1
对位于库姆塔格沙漠北部的三垄沙地区,迄今尚未开展详细的风沙地貌研究。对该区域地表沉积物样品进行粒度分析,旨在探讨不同区域、不同沙丘类型以及沙丘不同地貌部位的沉积物特征差异。结果表明:三垄沙地区地表沉积物以中沙和细沙为主,二者平均含量之和为63.20%,平均粒径为0.95~1.89Φ,分选系数为0.55~1.55,粗于库姆塔格沙漠和塔克拉玛干沙漠,与世界其他沙海沙物质相比属于偏粗粒径。三垄沙地区的主要沙丘类型为新月形沙丘或沙丘链,其北部发育有线形沙丘;这两种沙丘表层沉积物平均粒径均属于中沙范围,且从沙丘底部到丘顶平均粒径变大、分选变好,最粗的沙粒出现在沙丘顶部,平均粒径分别为1.64Φ和0.71Φ,不同于其他地区沙丘顶部沉积物最细的分布模式。从概率累积曲线来看,流动沙丘多为二段或三段式,风成沙砾浪和剥蚀残丘多为三段或四段式,表明后者经历的分选过程较短。本区地表沉积物的平均粒径沿主导风向有变小的趋势,其中,新月形沙丘和线形沙丘的这一特征最为明显。 相似文献
5.
Climate data from 339 meteorological stations collected from the 1950s to the early 2000s was employed to discuss aeolian activity in arid and semiarid northern China. The results show that at decadal time scales, erosivity varied greatly in this region. Most of arid and semiarid northern China was characterised by environments with moderate to low wind energy. After the 1980s, the erosivity was only 20 to 50% of that beforehand, and this difference had a significant impact on the environmental changes observed during the two periods. The dune mobility index was consistent with the observed dune activity. After the 1980s dune activity decreased and in some deserts with vegetated dune systems during the 1970s most of the dune plinths were active until the 1980s, after which only the crests were active. Some mobile dunes that had developed at the margins of mobile deserts were replaced by semi-anchored or anchored dunes. Because most desert areas with vegetated dune systems in arid and semiarid northern China are used for farming or grazing, the results of our monitoring show that the desertification trends were consistent with the trends in erosivity and dune activity in this region. Desertification was controlled much more by climatic changes than has previously been acknowledged, and especially by fluctuations in wind energy. 相似文献
6.
小冰期福建海岸沙丘的沉积环境 总被引：2，自引：2，他引：0
选取福建东南沿海典型海岸沙丘——东海沙丘,运用GPR（Ground Penetrating Radar）技术探测海岸沙丘内部构造,辅助天然剖面和人工探槽观测,进行系统的年代采样与OSL（Optically Stimulated Luminescence）测年,并选择物理意义明确的粒度参数作为主要环境代用指标,获得了亚热带季风区砂质海岸带典型海岸沙丘的沉积年代和沉积结构。结果表明：（1）东海沙丘是由若干灌丛沙丘组成的横向沙丘,0～6 m主要是～0.45 ka BP以来形成的海岸风成沙丘,可以划分为～0.45 ka BP和0.22～0.12 ka BP两个阶段。（2）东海沙丘沉积过程是多因素共同作用的结果,冷干的气候环境是沙丘发育的适宜条件,入境台风频率增加可能加快了风沙的沉积过程。对比历史文献资料发现,气候异常期往往与社会动荡期、重要历史事件相对应。 相似文献
7.
Measurements and numerical simulations of the degree of activity and vegetation cover on parabolic dunes in north-eastern Brazil 总被引：3，自引：0，他引：3
In this work we present measurements of vegetation cover over parabolic dunes with different degrees of activation along the north-eastern Brazilian coast. We extend the local values of the vegetation cover density to the whole dune by correlating measurements with the relative brightness index C of high resolution QuickBird panchromatic satellite images of the dune field. We then introduce the vegetation data into a continuous model for vegetated dunes, coupling sand erosion and vegetation growth, and perform simulations of the evolution of the morphology and vegetation cover of parabolic dunes. Finally, from the comparison of both, the measurements and the simulation results, we show that the model is able to predict the dune shape and the vegetation distribution of real parabolic dunes as result of the evolution of a blow-out. 相似文献
8.
基于遥感的中国北方风沙地貌类型分析 总被引：7，自引：0，他引：7
风沙地貌在我国有广泛的分布,特别在北方,对区域生态安全、社会经济发展有重大影响。为了了解我国风沙地貌最新状况,通过解译2000~2002年的Landsat7 ETM影像,建立了我国风沙地貌类型数据库。对北方风沙地貌的分析表明:1.我国北方风沙地貌主要分布在新疆、内蒙古、青海、宁夏、甘肃、陕西、吉林、黑龙江8省区,其中以新疆、内蒙古的面积最广、地貌类型最丰富;2.类型多样性上,干旱区沙漠的地貌类型远比半干旱区的沙地丰富,其中有些类型分布普遍,还有些类型仅仅局限于特定区域,是在特定的风力、风向、植被等作用下形成的;3.沙丘动态上,沙漠除古尔班通古特与乌兰布和沙漠以固定、半固定为主外其他都以流动为主,沙地沙丘则以固定、半固定状态占优势。本文从沙丘形态类型角度分析了我国风沙地貌的最新特征,具有定位、定量特点,所建数据库不仅能用于风沙地貌的定期遥感监测,还能对沙丘形态演化进行定位监测研究。 相似文献
9.
沙丘的形态变化与移动蕴含区域风沙环境和地貌演化的关键信息,是风沙地貌研究的重要内容。以腾格里沙漠南缘的长格状和方格状沙丘为研究对象,利用风况资料和Google Earth卫星影像,监测2009—2020年两种格状沙丘的形态变化并分析其移动特征。结果表明：(1)腾格里沙漠西南缘和东南缘的主风向均为西北风,长格状沙丘分布区的次风向为东南风,方格状沙丘分布区次风向为东风和东南风,都属于低风能环境、中变率风况。西南部风能环境大于东南部,研究区近10年风动力呈衰减趋势。(2)格状沙丘的主副梁长度和间距在增加,其中,长格状沙丘高度增加,方格状沙丘高度在降低。沙丘主梁向东偏移,副梁向南偏移,形态整体保持稳定。(3)长格状沙丘平均移动速率为1.57～1.71 m·a-1,方格状沙丘平均移动速率为1.63～2.01 m·a-1,沙丘平均移动方向与合成输沙方向基本一致,沙丘的体积是造成移动速率差异的主因。 相似文献
10.
Based on systematically monitoring plants on dune ridges in the southern part of the Gurbantunggut Desert in 2002, this paper, from the angle of dune stabilization by vegetation, describes the temporal and spatial distribution patterns of ephemeral plants on isolated sand dunes, analyses the natural invasion processes of ephemeral plants on human-disturbed sand surface and expounds the importance of ephemeral plants in stabilizing sand dune surface. A total of 45 plant species were identified in the study area, 29 of which are ephemeral plants. Ephemeral plants sprouted in early April and completed their life-circle within about two months. Just as aeolian sand activities came to the strongest stage from April to June in desert regions of northern Xinjiang, the total coverage of trees, shrubs and herbs of long vegetational period on most dune ridges was less than 10%, while the mean coverage of ephemeral plants reached 13.9% in April, 40.2% in May and 14.1% in June. Therefore ephemeral plants acted as the major contributor to dune surface stabilization in the Gurbantunggut Desert. Investigations of vegetation restoration on engineering-disturbed dune surface show that ephemeral plants first recolonized the disturbed dune surface. 相似文献
11.
古尔班通古特沙漠短命植物分布及其沙面稳定意义 总被引：7，自引：3，他引：4
Based on systematically monitoring plants on dune ridges in the southern part of the Gurbantunggut Desert in 2002, this paper, from the angle of dune stabilization by vegetation,describes the temporal and spatial distribution patterns of ephemeral plants on isolated sand dunes,analyses the natural invasion processes of ephemeral plants on human-disturbed sand surface and expounds the importance of ephemeral plants in stabilizing sand dune surface. A total of 45 plant species were identified in the study area, 29 of which are ephemeral plants. Ephemeral plants sprouted in early April and completed their life-circle within about two months. Just as aeolian sand activities came to the strongest stage from April to June in desert regions of northern Xinjiang, the total coverage of trees, shrubs and herbs of long vegetational period on most dune ridges was less than 10%, while the mean coverage of ephemeral plants reached 13.9% in April, 40.2% in May and 14.1% in June. Therefore ephemeral plants acted as the major contributor to dune surface stabilization in the Gurbantunggut Desert.Investigations of vegetation restoration on engineering-disturbed dune surface show that ephemeral plants first recolonized the disturbed dune surface. 相似文献
12.
古尔班通古特沙漠纵向沙垄植被空间异质性 总被引：5，自引：3，他引：2
在古尔班通古特沙漠南部纵向沙垄上按5 m×10 m的网格测度植被样方100个,采集浅层风沙土样品184件。调查发现,乔灌木层片和草本层片的分布及相互关系明显受沙垄地形影响,并且在干旱环境下种群间的竞争和空间上的互补使两层片生态优势度具有显著的相关性。地统计分析结果显示,纵向沙垄上植被空间异质性表现为木本层片的物种多样性呈斑块状分布,草本层片物种多样性呈现平行沙垄的带状结构和斑块结构叠加的特点,而植被盖度则在垂直沙垄走向的方向上具有强烈的梯度性变化。和沙垄土壤理化性质空间格局特征相对比,植被盖度及物种多样性与风沙土浅层含水量在自相关空间（变程）及空间异质性程度上比较接近。这是纵向沙垄小生态系统中草本植物和浅层土壤水分耦合关系在空间上的反映,也是木本植物对水分和土壤资源在小尺度（m）上竞争及中小尺度（10～100 m）上互补的结果。 相似文献
13.
沙丘内部沉积构造保存了沙丘动力演变过程的重要信息。以古尔班通古特沙漠西南缘固定、半固定新月形沙丘区为研究区域,利用探地雷达在春、秋两季对固定、半固定新月形沙丘内部构造进行探测,获取了不同规模形态的固定、半固定新月形沙丘深约8 m的内部构造图像信息。通过图像增益处理、解译和对比分析表明：（1） 古尔班通古特沙漠固定、半固定新月形沙丘共有5种沙丘内部构造雷达相,即高倾角斜层理、楔状交错层理、上凸形交错层理、低倾角-近水平层理和块状层理,其中前4种主要分布在3~5 m的浅层,而块状层理主要分布在4~5 m以下的深度。（2） 高倾角斜层理、楔状交错层理主要分布在高大新月形沙丘（链）的迎风坡上部和丘顶地带,前者为背风坡前积层埋藏而成,反映高大新月形沙丘迎风坡上部和丘顶风沙活动较频繁,沙丘“固身缩顶”后埋藏的前积纹层因风蚀而出露,后者为迎风坡风蚀坑和风蚀槽中由风沙流充填而成的构造或在丘顶风向的季节性变化形成的构造。（3） 与灌丛沙丘相关的上凸形交错层理广泛分布在新月形沙丘的迎风坡中下部,在背风坡也有局部出现,表明灌丛沙丘在沙丘表层的风沙过程中占有重要地位;而深部的块状层理可能是早期风积层受到强烈的生物扰动,原生层理消失而产生。（4） 以上沙丘内部构造的类型与组合分布特点,反映了研究区新月形沙丘总体上趋于稳定或衰退状态,这与现代沙丘“固身缩顶”的地貌变化特征相一致。例如,迎风坡中上部和丘顶常见风蚀槽,背风坡因坡度变缓、前积层发育趋缓,现代风沙活动主要集中于新月形沙丘的上部和丘顶等。由此可见,研究区固定、半固定新月形沙丘内部构造及其组合分布特征异于流动新月形沙丘,也与半个多世纪以来北疆沙漠气候变暖变湿、平均风速减弱、植被盖度增加的区域自然地理环境变化趋势有一定的吻合性。 相似文献
14.
新月形沙丘顶部稳定性是风沙地貌学尚未解决的科学问题。研究新月形沙丘的顶部稳定性,对于绿洲边缘风沙运动规律揭示、防沙工程建设和沙区生态环境保护等具有重要的现实意义。选择民勤沙区新月形沙丘,通过测定沙丘各部位风速、风蚀风积和粒度等,分析了新月形沙丘顶部稳定机理。主风向（NW）作用是新月形沙丘最高点与沙脊线重合、沙丘前移和高度降低的过程;反向风（SE）作用是沙丘最高点与沙脊线分离、沙丘背风坡风蚀与沙丘增高的过程。由于研究区以NW风为主,新月形沙丘沿NW-SE方向前移,SE风只能风蚀减缓沙丘背风坡的坡度。人为干预将会阻止或减少从迎风坡向沙丘顶部输送沙量,使得新月形沙丘背风坡尤其是背风坡上部风蚀过程增强,新月形沙丘逐渐过渡为抛物线形沙丘。 相似文献
15.
巴丹吉林沙漠与腾格里沙漠分别为中国面积第二、第三大流动性沙漠,对两大沙漠连接带新月形沙丘的动态监测可以揭示该地区沙丘形成演化规律,为沙漠连接带风沙地貌发育研究提供科学支撑。通过Google Earth高清历史影像对巴丹吉林沙漠与腾格里沙漠连接带的新月形沙丘带进行监测,分析了两大沙漠交界处沙丘的移动速率和形态变化。结果表明:巴丹吉林沙漠与腾格里沙漠连接带沙丘移动速率范围5.88-19.55 m·a^(-1),平均移动速率10.03 m·a^(-1);移动方向范围109°-135°,平均移动方向122°。风况为沙丘移动提供动力条件,合成输沙方向与沙丘移动方向吻合。受NW、WNW方向输沙影响,新月形沙丘南翼在移动速率增加的同时长度不断伸长,显著区别于北翼。沙丘移动受控于沙丘本身形态,沙丘各形态参数(迎风坡长度、高度、宽度、周长、底面积)与移动速率呈现显著负相关关系(P<0.01)。植被覆盖以及沙丘密度的差异导致了研究区沙丘移动速率的差异。沙丘移动前后,形态参数变化具有复杂性,而沙源丰富度差异以及丘间地灌丛沙包对沙丘形态的改变,是沙丘形态变化复杂性的主要原因。两大沙漠连接带年输沙通量170-521 t·m^(-1),均值为301 t·m^(-1)。 相似文献
16.
Complex systems in aeolian geomorphology 总被引：6，自引：1，他引：6
Aeolian geomorphology provides a rich ground for investigating Earth surface processes and landforms as complex systems. Sand transport by wind is a classic dissipative process with non-linear dynamics, while dune field evolution is a prototypical self-organisation phenomenon. Both of these broad areas of aeolian geomorphology are discussed and analysed in the context of complexity and a systems approach. A feedback loop analysis of the aeolian boundary-layer-flow/sediment-transport/bedform interactions, based on contemporary physical models, reveals that the system is fundamentally unstable (or at most meta-stable) and likely to exhibit chaotic behaviour. Recent field-experimental research on aeolian streamers and spatio-temporal transport patterns, however, indicates that sand transport by wind may be wholly controlled by a self-similar turbulence cascade in the boundary layer flow, and that key aspects of transport event time-series can be fully reproduced from a combination of (self-organised) 1/f forcing, motion threshold, and saltation inertia. The evolution of various types of bare-sand dunes and dune field patterns have been simulated successfully with self-organising cellular automata that incorporate only simplified physically-based interactions (rules). Because of their undefined physical scale, however, it not clear whether they in fact simulate ripples (bedforms) or dunes (landforms), raising fundamental cross-cutting questions regarding the difference between aeolian dunes, impact ripples, and subaqueous (current) ripples and dunes. An extended cellular automaton (CA) model, currently under development, incorporates the effects of vegetation in the aeolian environment and is capable of simulating the development of nebkhas, blow-outs, and parabolic coastal dunes. Preliminary results indicate the potential for establishing phase diagrams and attractor trajectories for vegetated aeolian dunescapes. Progress is limited, however, by a serious lack of appropriate concepts for quantifying meaningful state variables at the landscape scale. State variables currently used in the bare-sand models are far from capturing the rich 3D topography and patterns and are not sufficiently discriminative to distinguish different attractors. The vegetation component in the extended model, and indeed ecogeomorphic systems in general, pose even graver challenges to establishing appropriate state variables. A re-examination of older concepts, such as landscape entropy, perhaps complemented by recent developments in information theory, may be a potentially fruitful avenue for research, although the outlines of such an implementation are still rather vague. 相似文献
17.
Wisconsin's Central Sand Plain east of the Wisconsin River is composed of eolian sand forming high-relief dunes surrounded by sand sheets and scattered low-relief dunes. To establish a maximum age for dune formation, three samples for optical dating were taken from glacial Lake Wisconsin lacustrine sediment that underlies eolian sand. These age estimates range from 19.3 to 13.6ka. Age estimates taken from within or at the base of the dunes range from 14.0 to 10.6ka. Samples taken from < 2m of the ground surface were slightly younger, indicating dunes were stabilized between 11.8 and 5.5ka. The younger ages near the surface of some dunes were most likely the result of pedoturbation or localized problems with applying the optical dating method. The majority of the optical age estimates from dunes (18 of 21) indicated that most of the dunes were active between 14 and 10ka and that most dune activity ended by 10ka. These ages suggest that localized activity on dune crests may have occurred in the Holocene but would have been limited to < 1m of sand accumulation. The timing of dune activity and the lack of any significant Holocene reactivation suggest that dune activation in this setting cannot be attributed solely to changes in aridity. Instead, we attribute dune formation to changes in sediment availability from either sand inputs from the Wisconsin River or the melting of permafrost. 相似文献
18.
Claire Kain Christopher Gomez Patrick Wassmer Franck Lavigne Deirdre Hart 《New Zealand geographer》2014,70(3):165-178
The 2004 tsunami transformed the coast of Indonesia. This research investigates a sand dune area in Lampuuk, Sumatra, that was scoured by tsunami flow. We assessed geomorphology one‐year post‐event and examine the timescale of vegetation recovery. Ground Penetrating Radar (GPR) evidence shows an eroded succession of thin dipping units, overlain by aeolian layers 0 to 50 cm thick. Incipient dunes were absent, indicating limited dune rebuilding at one‐year post‐tsunami, possibly resulting from channelised airflow and the absence of vegetation. Recolonisation by vegetation was initially limited but progressed rapidly between 2005 and 2011, highlighting the temporal non‐linearity of recovery processes. 相似文献
19.
沙坡头铁路防护体系内风沙沉积的粒度特征 总被引：4，自引：2，他引：4
包兰铁路沙坡头段铁路防护体系内,由于下垫面性质发生变化,流沙区至人工植被带地表沉积物中表层土壤的黏粒和粉沙含量显著增大,平均粒径减小,颗粒分选性显著变差。防护体系内表层沉积物中的粉沙含量与地表相对高程反相关,黏粒含量与地形起伏没有直接关系,颗粒平均粒径、分选性与地表相对高程正相关。在土层垂直方向上,表层0~5cm内土壤粉沙含量较高,颗粒分选性差;5cm以下深度内土壤粉沙含量减少,颗粒分选性变好。在防护体系内沙丘地貌的不同部位,沙尘沉积速率不同。据此估算表明防护体系内固定沙丘迎风坡顶部沉积速率为0.147 cm/a左右;背风坡和丘间地平均堆积速率大于0.588cm/a。 相似文献
20.
东部沙区表土有机质和速效养分与风沙环境关系初探 总被引：2，自引：0，他引：2
东部沙区表土有机质、速效养分含量普遍较低。按照库布齐沙漠、毛乌素沙地、浑善达克沙地、科尔沁沙地和呼伦贝尔沙地的次序,有机质和速效K含量逐渐增大,这种分布格局与区域风沙环境性质、风沙活动方式密切相关;各沙漠/沙地内部,表土有机质和速效K含量分别与植被盖度、颗粒平均粒径、分选系数之间存在较好的相关性。速效N和速效P含量未表现出上述变化规律。可见有机质和速效K含量对风沙环境的变化较为敏感,因而其在表土中的再分配可以在一定程度上反映局地风沙环境的变化,而速效N和速效P对风沙环境的指示意义不明显。东部沙区表土有机质、速效N及速效P含量普遍高于西部沙区,而速效K含量明显偏低。 相似文献