Locally modified surface winds on linear dunes as derived from directional raingauges     

David Sharon  Adina Margalit  Simon M. Berkowicz 《地球表面变化过程与地形》2002,27(8):867-889

The study deals with local airflow patterns induced by 12–16 m high, partly vegetated dunes, under various prevailing wind conditions. Detailed empirical data were derived by means of an unconventional use of directional raingauges. The utility and accuracy of the method have been previously tested in a combined empirical and numerical study over ridges on a similar scale. Results are presented on the nature, extent and intensity of locally modified patterns of surface flow and on their dependence on wind conditions and slope inclination. Results may serve to verify or refine existing perceptions or models of the flow affecting sand movement over dunes. For example, deflected surface wind flow and even stationary vortices were found to form under winds with resultant angles of incidence of only 5–10° relative to the axes of the dunes, and on slopes inclined only 12–15°, i.e. lower angles than often assumed in previous studies of dune morphology. Various effects of the resulting surface flow on the dune ecosystem are also referred to, e.g. the distribution of settling dust and seed dispersal. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

Sand Dunes Fixation in Baiji District,Iraq     

AyadMohammedFadhil 《中国地质大学学报(英文版)》2002,13(1):67-72

This study was carried out at Sand Dunes Stabilization Researches Station in Baiji district (230km north of Baghdad,Iraq) to evaluate the effects of local soil conditioners manufactured from oil derivatives and plant residuals on sand dunes fixation as the first step for sand dunes stabilization.The results indicate that the fuel oil has the first place in improving wind erosion parameters in the study area,such as increasing mean weight diameter,dry aggregates percentage,the needed time for complete disaggregation by dry sieving,and decreasing the disaggregation rates.Bitumen emulsion occupies the second place ,while the plant residuals occupies the third place and has slight effects on the studied pa-rameters.Effects of conditioners on natural vegetation cover are negative in oil derivatives treatments,while positive in plants residuals treatments.  相似文献   

Reconstructing the geomorphic evolution of large coastal dunes along the southeastern shore of Lake Michigan   总被引：1，自引：0，他引：1  

Alan F. Arbogast  Edward C. Hansen  Martin D. Van Oort 《Geomorphology》2002,46(3-4)

Coastal dunes are common along the eastern shore of Lake Michigan, with the most common being large (>30 m high), parabolic dunes that mantle lake terraces south of Manistee, MI. Although these dunes are an important resource in Michigan, and thus intensely managed by various state agencies, their geomorphic history is poorly understood. This study examines four sites near Holland, MI, through stratigraphic and radiocarbon analyses and is the most detailed geomorphic reconstruction conducted of coastal parabolic dunes in the region. Results from this study could benefit the environmental agencies in their management of the coastal dune ecosystem.Deposition of Eolian sand apparently began 5500 cal. years BP (i.e., during the Nipissing high stand). Most (75%) dune building occurred between 4000 and 2500 cal. years BP but was punctuated by brief periods of stability that resulted in the development of Entisols (A/C horizonation). Entisol burial occurred because the sand supply apparently increased during both the receding and rising lake levels. Subsequently, each dune stabilized for 2000 years, allowing the formation of Inceptisols (i.e., A/E/Bs/C horizonation). This interval of dune stability correlates with sites south of Holland and occurred while Lake Michigan fluctuated slowly and the beach potentially prograded. These combined variables of slow fluctuation and potential beach progradation hypothetically protected the dunes from wave erosion. Dunes near Holland became active again 1000–500 cal. years BP and grew both vertically and laterally. This activity intensified in the past 500 cal. years BP and hypothetically occurred due to recession of the lake shore such that wave erosion at the modern bluff base resumed. Results from this study indicate that coastal dunes along Lake Michigan are similar to many coastal dunes around the world, including those along the intermediate beaches in SE Australia.  相似文献   

Embryo dune development on a large,actively accreting macrotidal beach: Calais,North Sea coast of France     

Edward J. Anthony  Stéphane Vanhée  Marie‐Hélène Ruz 《地球表面变化过程与地形》2007,32(4):631-636

Sediment budget data from an 18‐month topographic survey were analysed with data from brief experiments on wind parameters, beach moisture contents, bedforms and sand mobilization in order to monitor conditions and patterns of embryo dune development over a flat 150–1000 m wide accreting upper beach. The surface conditions over the upper beach locally affect aeolian transport, but net dune development over time depends on sustained strong winds and their orientation. Incoming marine sand supplied by storms and onshore winds is reorganized by the dominant offshore to longshore winds into elongated embryo dunes over this upper beach, imprinting a regional morphology of long‐term longshore dune ridge development. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Last glacial megafaunal death assemblage and early human occupation at Lake Menindee, southeastern Australia     

Matthew L. Cupper  Jacqui Duncan 《Quaternary Research》2006,66(2):332-341

The Tedford subfossil locality at Lake Menindee preserves a diverse assemblage of marsupials, monotremes and placental rodents. Of the 38 mammal taxa recorded at the site, almost a third are of extinct megafauna. Some of the bones are articulated or semi-articulated and include almost complete skeletons, indicating that aeolian sediments rapidly buried the animals following death. New optical ages show the site dates to the early part of the last glacial (55,700 ± 1300 yr weighted mean age). This is close to the 51,200-39,800 yr Australia-wide extinction age for megafauna suggested by Roberts et al. [2001, Science 292:1888-1892], but like all previous researchers, we cannot conclusively determine whether humans were implicated in the deaths of the animals. Although an intrusive hearth at the site dating to 45,100 ± 1400 yr ago is the oldest evidence of human occupation of the Darling River, no artifacts were identified in situ within the sub-fossil-bearing unit. Non-anthropogenic causes, such as natural senescence or ecosystem stress due to climatic aridity, probably explain the mortality of the faunal assemblage at Lake Menindee.  相似文献   

高精度光释光测年揭示的晚第四纪毛乌素和浑善达克沙地沙丘的固定与活化过程   总被引：13，自引：3，他引：13  

周亚利  鹿化煜  张家富  周力平  苗晓东  MASON J A 《中国沙漠》2005,25(3):342-350

利用光释光测年技术对毛乌素沙地和浑善达克沙地7个地点的沉积剖面进行了年代测试,结合地层特征,获得了最近60kaBP以来两个沙地沙丘固定与活化时间的年代学控制60kaBP以来毛乌素沙地的固定期分别为距今37.71ka、8.54ka、8.32ka、7.93ka、7.77ka、7.57ka、7.39ka和2.39ka以后;活化的时间分别为距今57.08ka、52.50ka、13.65ka、13.13ka、7.20ka前后、2.39ka以前和0.29ka以来。在10.97kaBP、10.04kaBP、9.81kaBP和8.67kaBP前后沙地处于气候干湿交替时期。全新世期间,浑善达克沙地在距今8.74～8.72ka、7.79ka前后,沙丘活化;5.69kaBP、4.25kaBP、2.75kaBP、1.53kaBP和0.71kaBP前后,沙丘处于相对固定阶段,0.15kaBP以来,沙丘处于半固定状态。晚第四纪气候千年至百年尺度的变化可能是两个沙地沙丘活化与固定的主导因素。  相似文献   

The morphodynamics of fluvial sand dunes in the River Rhine, near Mainz, Germany. II. Hydrodynamics and sediment transport   总被引：1，自引：0，他引：1  

Carling  Williams  Gölz  & Kelsey 《Sedimentology》2000,47(1):253-278

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粒子图像测速(PIV)技术在风沙环境风洞中的应用     

钱广强  董治宝  王洪涛  罗万银 《中国沙漠》2006,26(6):890-893

粒子图像测速技术是一种全新的非接触、瞬时、全场流速测量方法,广泛应用于流体力学实验中。笔者将其引入风沙运动研究是一个尝试,旨在为风沙物理和防沙工程研究提供新的测量手段。通过分析一系列的风洞实验结果,我们认为,在风沙流中颗粒速度分布、浓度分布、风沙地貌形成演化、防沙工程原理及应用方面,粒子图像测速技术具有一定优势,可以克服传统测量手段的某些不足。  相似文献   

沙坡头地区固定沙丘一年生植物小画眉草种群动态研究   总被引：17，自引：9，他引：8  

张景光  李新荣  王新平  王刚  李金贵  王宗灵 《中国沙漠》2001,21(3):232-235

通过对一年生草本植物小画眉草(Eragrostis poaeoides)种群动态的研究,可以看到小画眉草的萌发和生长以及数量动态对于降水的强烈依赖,使得草本植物的萌发具有成批性,小画眉草有4批出苗。开始出苗后由于连日高温干旱,致使第一批苗全部死亡。之后,由于降水较多且相对较集中,出苗、生长发育与自疏死亡成连续过程,观察到的是其净结果。由于水分对种群的制约,种群间对水分的竞争必然导致自疏现象。一年生草本植物的存活曲线属于C型,生活史对策明显表现为r-对策。r-对策种群往往出现在群落演替的早期阶段。  相似文献   

Transgressive dunefield landforms and vegetation associations,Doña Juana,Veracruz, Mexico     

Patrick Hesp  Marisa Martinez  Graziela Miot da Silva  Natalia Rodríguez‐Revelo  Erika Gutierrez  Adriana Humanes  Daniela Laínez  Irene Montaño  Verónica Palacios  Agustín Quesada  Lorena Storero  Gabriela González Trilla  Carolina Trochine 《地球表面变化过程与地形》2011,36(3):285-295

Transgressive dune fields often comprise a multiplicity of landforms where vegetation processes largely affect landform dynamics, which in turn, also affect vegetation processes. These associations have seldom been studied in detail. This paper examines four separate landform types in a complex coastal transgressive dunefield located in the central Gulf of Mexico, in order to assess the relationships between dunefield habitat, local environmental factors, vegetation associations and landform evolution. Topographic surveys using tape and clinometer were conducted in conjunction with vegetation survey transects at four locations across the Doña Juana dunefield. Vegetation surveys allowed the estimation of relative plant cover of each plant species found along the transects. A large variety of landforms were found at the Doña Juana Dunefield: deflation plains, gegenwalle (counter) ridges, transverse dune trailing ridges, blowouts and parabolic dunes, aklé (fish‐scale shaped) dunefields and precipitation ridges, with plant species associations developing on these different landforms equally variable. Flood tolerant species were located in the lower parts (deflation plain and gegenwalle ridges) whereas the older and dryer parts were covered by coastal matorral shrubs. Burial‐tolerant species were dominant in the most mobile areas (blowouts and aklé dunefield and margin). The dune trailing ridge, with relatively milder conditions, showed the highest richness, with no dominant species. A dual interaction was found such that colonizing species both create and affect topography, and in turn, topography determines vegetation association and succession patterns. In coastal dunes, the vegetation and abiotic environment (namely the different landforms and the inherent micronevironmental variability) interact tightly and generate a complex and highly dynamic biogeomorphic system where substrate mobility and colonization processes reinforce one another in positive feedback. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献