科尔沁沙地沙丘-草甸相间地区1986-2013年湖泊演变   总被引：1，自引：1，他引：0  

贾恪  刘廷玺  雷慧闽  段利民  罗艳云  张圣微  童新  孙丽 《中国沙漠》2015,35(3):783-791

湖泊变化敏感地记录着气候变化的信息。以科尔沁沙地沙丘-草甸相间地区为研究区,利用多时相TM/ETM+遥感影像,基于遥感和GIS技术提取研究区1986-2013年湖泊个数与面积信息,分析其变化规律及空间分异特征。在此基础上,联系降水量、蒸发量等气候要素和以人类活动影响为主的时间因子t,采用多元统计分析方法对研究区湖泊面积进行了模拟分析。结果表明:(1)研究区小型湖泊近30年间面积和个数均发生了不同程度的变化,其变化趋势与降水量呈现很强的正相关,与蒸发量呈较强的负相关,人类活动对小型湖泊面积的影响不太显著,随着时间的推移,研究区湖泊面积趋于萎缩,这种萎缩主要归因于气候的干化;(2)研究区t年湖泊面积A_t与前一年湖泊面积A_t-1、t年降水量P_t和蒸发量E_t存在较强的相关关系;(3)1986-2013年研究区典型湖泊--王巴哈嘎湖泊总体上呈萎缩状态,但不同方向上既有萎缩也有扩张,Ⅰ、Ⅱ、Ⅴ、Ⅵ区域(以北向为0°,顺时针每45°一个区域,并顺序标记为Ⅰ~Ⅷ区域)萎缩,其他区域扩张,其中以Ⅱ、Ⅲ、Ⅷ、Ⅳ区域为主导变异方向,Ⅵ方向次之,其他方向变化缓滞。研究成果不仅为科尔沁沙地生态系统的健康维持提供技术支撑,对其他同类地区湖泊环境的研究也具有指导作用。  相似文献   

Natural and anthropogenic influences in the northeastern coast of the Nile delta,Egypt   总被引：4，自引：0，他引：4  

Mahmoud M. El Banna  Omran E. Frihy 《Environmental Geology》2009,57(7):1593-1602

Landsat enhanced thematic mapper imagery (ETM) of 2002 and aerial photography of 1955, combined with published charts and field observations were used to interpret coastal changes in the zone between Kitchener drain and Damietta spit in the northeastern Nile delta, previously recognized as a vulnerable zone to the effects of any sea level rise resulting from global warming. The interpretation resulted in recognition of several changes in nine identified geomorphological land types: beach and coastal flat, coastal dunes, agricultural deltaic land, sabkhas, fish farms, Manzala lagoon, saltpans, marshes and urban centers. Reclamation of vast areas of the coastal dunes and of Manzala lagoon added about 420 km2 to the agricultural deltaic land. About 48 km2 of backshore flats, marshes, salt pans and Manzala lagoon have been converted to productive fish farms. The main urban centers have expanded; nearly 12.1 km² have been added to their areas, and new urban centers (Damietta harbor and the New Damietta city) with total area reach of ~35.3 km² have been constructed at the expense of vast areas of Manzala lagoon, coastal dunes, and backshore flats. As a consequence of human activities, the size of Manzala lagoon has been reduced to more than 65%. Shoreline changes have been determined from beach profile survey (1990–2000), and comparison of 1955 aerial photographs and ETM satellite image of 2002 reveal alongshore patterns of erosion versus accretion. The short-term rate of shoreline retreat (1990–2000) has increased in the downdrift side of Damietta harbor (≃14 m/year), whereas areas of accretion exist within the embayment of Gamasa and in the shadow of Ras El Bar detached breakwaters system, with a maximum shoreline advance of ~15 m/year. A sandy spit, 12 km long, has developed southeast of Damietta promontory. These erosion/accretion patterns denote the natural processes of wave-induced longshore currents and sediment transport, in addition, the impact of man-made coastal protection structures.  相似文献   

The effects of surface moisture on aeolian sediment transport threshold and mass flux on a beach   总被引：1，自引：0，他引：1  

Robin G. D. Davidson‐Arnott  Yanqi Yang  Jeff Ollerhead  Patrick A. Hesp  Ian J. Walker 《地球表面变化过程与地形》2008,33(1):55-74

This paper presents results from a study designed to explore the effects of beach surface moisture and fetch effects on the threshold of movement, intensity of sand transport by wind and mass flux. The experiment was carried out over a period of five weeks at Greenwich Dunes, Prince Edward Island, Canada in May and June 2002. Moisture content was measured with a Delta‐T moisture probe over a 50 m by 25 m grid established on the beach. Measurements of wind speed and direction were made with arrays of cup anemometers and a two‐dimensional sonic anemometer. Transport intensity was measured at a height of 2–4 cm above the bed using omnidirectional saltation probes which count the impact of saltating grains on a piezoelectric crystal. Anemometers and saltation probes were sampled at 1 Hz. Sand transport was measured with vertical integrating sand traps over periods of 10–20 minutes. Results show that where there is a considerable supply of dry sand the saltation system responds very rapidly (1–2 s) to fluctuations in wind speed, i.e. to wind gusts. Where sand supply from the surface is limited by moisture, mean transport rates are much lower and this reflects in both a reduction in the instantaneous transport rate and in a transport system that becomes increasingly intermittent. Threshold wind speed is significantly correlated with an increase in surface moisture content near the upwind end of the beach fetch, but the relationship is not significant at the downwind end where sediment transport is initiated primarily by saltation impact from upwind. Mass flux increases with increasing fetch length and the relationship is described best by a power function. Further work is necessary to develop a theoretical function to predict the increase in transport with fetch distance as well as the critical fetch distance. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

塔克拉玛干沙漠中部地区线形沙丘表面动力学过程   总被引：10，自引：3，他引：7  

张家武陈广庭  陈发虎王建民 《中国沙漠》1999,19(2):41

通过野外观测与室内风洞实验模拟,结合研究区气象资料统计分析,研究了塔克拉玛干沙漠中部地区线形沙丘表面动力学过程。结果表明,塔克拉玛干沙漠中部地区的线形沙丘与主风向的夹角为１２．５°,与年合成输沙方向（ＲＤＤ）的夹角为４．８°。年合成风向与主风向一致,但风向变率较大。风洞模拟实验揭示,当风向与线形沙丘的夹角较小时,沙丘背风侧均有旁侧气流存在,且随夹角增大而减弱。气流与输沙势分解结果显示,由于平行于沙丘的输沙分量显著大于垂直于沙丘的输沙分量,使线形沙丘纵向移动较快,约为１０ｍ·ａ－１。整体侧向移动不明显,但因风向变率较大,沙丘基座以上局部侧向移动频繁;平行于沙丘的气流分量大于垂直于沙丘的分量,加上背风侧旁侧气流盛行,使沙粒的总体运动方向平行于沙丘的走向方向,从而使线形沙丘在快速纵向移动的过程中保持形态基本不变。  相似文献   

毛乌素沙地沙障环境下的沙丘迎风坡植被及土壤养分变化     

石麟  赵雨兴  哈斯额尔敦null  张萍  许映军  王卓然 《中国沙漠》2021,41(5):140-146

沙障在固定流沙、促进植被恢复和改良土壤等生态建设方面起着重要作用。对毛乌素沙地设置沙柳（Salix psammophila）沙障6、8、10、11、12年的沙丘迎风坡（裸露沙丘地作为对照）开展了植被调查和土壤养分测试分析。结果显示：设障8年后的沙丘迎风坡0—30 cm深度内的土壤有机质、全氮含量显著（P<0.05）高于流动沙丘,且设障10—11年沙丘迎风坡植被盖度、0—80 cm深度内土壤有机质和全氮含量达到最大,但全磷和全钾含量无明显的变化,所有样地间和3个深度层间的全磷、全钾含量均无显著性差异;植被总盖度、0—80 cm深度内土壤有机质含量及全氮含量相互之间存在极显著线性正相关关系（P<0.01）,而且土壤pH值随有机质含量增加而线性降低。沙柳沙障固沙地的植被盖度、土壤有机质和全氮相互之间存在趋同性,且布设10年的沙障土壤改良和植被恢复成效达到最大,之后表现出下降趋势。据此建议活体沙柳沙障在维持其固沙功效的前提下以10年为限需进行平茬处理。  相似文献   

Coversand and Pleistocene palaeosols in the Landes region,southwestern France     

Pascal Bertran  Giselle Allenet  Thierry Gé  Filipa Naughton  Philippe Poirier  Maria F. Sanchez Goñi 《第四纪科学杂志》2009,24(3):259-269

New sections in the coversand of the Landes region, southwestern France, show at least two main depositional phases corresponding to the Upper Pleniglacial and the Lateglacial, which are separated by palaeosols. The lower palaeosol, a gleyic to histic cryosol overlying a net of sand wedges and dated to ca. 23 ¹⁴C ka BP, testifies to a short occurrence of permafrost. Impeded drainage due to the frozen subsoil is assumed to be the main factor involved in lowered aeolian transport and soil formation. Pollen analysis indicates a shrub tundra‐type environment. The overlying coversand unit is associated with small transverse ridges or sheet‐like deposits, and corresponds to the maximal extension of the sands, Upper Pleniglacial in age. An incipient podzol developed on the dunes under a boreal pine forest, and has been dated to 11.5–12 ¹⁴C ka BP, i.e. to the Allerød period. This has been buried by the second coversand unit during the Younger Dryas, typified by abundant denivation features and root imprints. Although preliminary, the chronology of sand deposition in the Landes region appears thus to be roughly similar to that found for the other European coversands, showing that all were the result of similar western European climatic changes, i.e. repeated episodes of increasing aridity related to the Upper Pleniglacial and the Younger Dryas episode. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

Aeolian dune interactions and dune‐field pattern formation: White Sands Dune Field,New Mexico     

RYAN C. EWING  GARY A. KOCUREK 《Sedimentology》2010,57(5):1199-1219

Pattern formation is a fundamental aspect of self‐organization in fields of bedforms. Time‐series aerial photographs and airborne light detection and ranging show that fully developed, crescentic aeolian dunes at White Sands, New Mexico, interact and the dune pattern organizes in systematically similar ways as wind ripples and subaqueous dunes and ripples. Documented interactions include: (i) merging; (ii) lateral linking; (iii) defect repulsion; (iv) bedform repulsion; (v) off‐centre collision; (vi) defect creation; and (vii) dune splitting. Merging and lateral linking are constructive interactions that give rise to a more organized pattern. Defect creation and bedform splitting are regenerative interactions that push the system to a more disorganized state. Defect/bedform repulsion and off‐centre collision cause significant pattern change, but appear to be neutral in overall pattern development. Measurements of pattern parameters (number of dunes, crest length, defect density, crest spacing and dune height), dune migration rates, and the type and frequency of dune interactions within a 3500 m box transect from the upwind margin to the core of the dune field show that most pattern organization occurs within the upwind field. Upwind dominance by constructive interactions yields to neutral and regenerative interactions in the field centre. This spatial change reflects upwind line source and sediment availability boundary conditions arising from antecedent palaeo‐lake topography. Pattern evolution is most strongly coupled to the pattern parameters of dune spacing and defect density, such that spatially or temporally the frequency of bedform interactions decreases as the dunes become further apart and have fewer defects.  相似文献   

Late Quaternary history of the coastal Wahiba Sands,Sultanate of Oman     

Frank Preusser  Dirk Radies  Frauke Driehorst  Albert Matter 《第四纪科学杂志》2005,20(4):395-405

Continental sediments and geomorphological features of the coastal Wahiba Sands, Sultanate of Oman, reflect environmental variability in southeastern Arabia during the late Quaternary. Weakly cemented dune sands, interdune deposits and coastal sediments were dated by luminescence methods to establish an absolute chronology of changes in sedimentary dynamics. The dating results confirm previous assumptions that during times of low global sea level sand was transported by southerly winds from the exposed shelf onto the Arabian Peninsula. Two prominent phases of sand accumulation in the coastal area took place just before and after the last glacial maximum (LGM). A final significant period of dune consolidation is recognised during the early Holocene. However, no major consolidation of dunes appears to have occurred during the LGM and the Younger Dryas. In the northern part of the Wahiba Sands, these two periods are characterised by substantial sand deposition. This discrepancy is explained by the lack of conservation potential for dunes in the coastal area, probably caused by a low groundwater table due to low sea level and decreased precipitation. While the times of aeolian activity reflect arid to hyper‐arid conditions, lacustrine and pedogenically altered interdune deposits indicate wetter conditions than today caused by increased monsoonal circulation during the Holocene climatic optimum. Copyright © 2005 John Wiley & Sons, Ltd.  相似文献   

The effect of asymmetric dune roughness on tidal asymmetry in the Weser estuary     

Gerald Herrling  Marius Becker  Alice Lefebvre  Anna Zorndt  Knut Krämer  Christian Winter 《地球表面变化过程与地形》2021,46(11):2211-2228

The bed of estuaries is often characterized by ripples and dunes of varying size. Whereas smaller bedforms adapt their morphological shape to the oscillating tidal currents, large compound dunes (here: asymmetric tidal dunes) remain stable for periods longer than a tidal cycle. Bedforms constitute a form roughness, that is, hydraulic flow resistance, which has a large-scale effect on tidal asymmetry and, hence, on hydrodynamics, sediment transport, and morphodynamics of estuaries and coastal seas. Flow separation behind the dune crest and recirculation on the steep downstream side result in turbulence and energy loss. Since the energy dissipation can be related to the dune lee slope angle, asymmetric dune shapes induce variable flow resistance during ebb and flood phases. Here, a noncalibrated numerical model has been applied to analyze the large-scale effect of symmetric and asymmetric dune shapes on estuarine tidal asymmetry evaluated by residual bed load sediment transport at the Weser estuary, Germany. Scenario simulations were performed with parameterized bed roughness of symmetric and asymmetric dune shapes and without dune roughness. The spatiotemporal interaction of distinct dune shapes with the main drivers of estuarine sediment and morphodynamics, that is, river discharge and tidal energy, is shown to be complex but substantial. The contrasting effects of flood- and ebb-oriented asymmetric dunes on residual bed load transport rates and directions are estimated to be of a similar importance as the controls of seasonal changes of discharge on these net sediment fluxes at the Lower Weser estuary. This corroborates the need to consider dune-induced directional bed roughness in numerical models of estuarine and tidal environments.  相似文献   

Runoff generation and sediment yield on homogeneous dune slopes: scale effect and implications for analysis   总被引：1，自引：0，他引：1  

Giora J. Kidron 《地球表面变化过程与地形》2011,36(13):1809-1824

Data concerning runoff and sediment yield in arid zones is of prime importance for hydrologists, geomorphologists, pedologists, ecologists and landscape engineers. For data comparison and extrapolations, runoff and sediment yield are often presented in mass per unit area. Runoff and sediment yield collected on dune slopes over a wide range of plot sizes during 1990–1994 in the Negev Desert, Israel, showed that the contributing area was mainly confined to a narrow belt at the bottom of the slopes. It was therefore hypothesized that the very short rain bursts, capable of runoff generation, may result in a scale effect (SE). Indeed, average duration of duration of consecutive medium and high rain intensities which are potentially above the surface infiltration rate ranged between 2.2 and 3.0 minutes, implying that flow connectivity is largely limited. Based on the intermittent character of the rain spells capable of runoff generation it is argued that SE is an inherent outcome of the rain properties. Yet, it is further argued that the magnitude of the SE is surface‐dependent. As a result, it is argued that the conventional way for runoff and sediment yield presentation as mass per unit area implies theoretical misconceptions and may cause gross overestimation in extrapolation and the presentation of runoff and sediment yield in mass per unit width of the slope is suggested. The accuracy of the two extrapolation methods are compared to the actual runoff and sediment yield collected in the field. The data show that extrapolation based on runoff (or sediment) yield per plot width deviates from the actual amounts collected by a factor of 1·1 to 1·3 only while deviating by a factor of 4·2 to 5·6 and 10·7 to 11·8 if the extrapolation is based on large and small plots, respectively. Theoretical and practical reasons for presentation of runoff and sediment yield as mass per unit width are discussed. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献