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1.
《中国科学:地球科学》2017,(4)
在全球高差最大的巴丹吉林沙漠发现了沙山斜坡上的表层径流物理沉积及化学沉积、沙山洼地罕见的地表超渗径流和沙山底部泉水溪流.根据电镜观察、能谱分析、入渗实验、含水量测定和粒度分析等资料,研究了表层径流化学沉积物的矿物和化学组成、物理沉积物的粒度组成、沙山区水分平衡、大气降水对地下水与湖水的补给条件和补给机制.超渗径流与表层径流的存在表明,该区存在能够为地下水提供补给来源的较强有效降雨过程.各种表层径流物理沉积与化学沉积、泉水溪流、超渗径流与含量为3~6%的重力水等8项科学证据十分可靠地从深层次上证明,该区降水通过入渗达到了沙山的底部,已经对地下水构成了补给.新生方解石和石膏等径流化学沉积物和灰黑色物理沉积物以及径流沉积扇形地演化的阶段性均指示该区大气降水对地下水的补给不是偶然的降水事件造成的,具有长期补给性.细粒层的隔水性是该区地下径流出露于地表的原因.沙山区具有一定有效降水能够提供水分补给源、沙层的高入渗率能够将大气降水快速转化沙层水、植被稀少蒸腾量少、沙层受蒸发影响深度小降低了蒸发对水分的消耗、沙层含有运移较快的重力水是该区水分出现正平衡和大气降水能够补给地下水的5个因素,这5个因素的共同作用构成了该区大气降水向地下水的补给机制,为地下水和湖泊提供了水分补给来源.本文对国内外沙漠区水循环、地下水补给条件、补给动力和补给机制的研究具有重要参考意义. 相似文献
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鄱阳湖是我国最大的淡水湖泊.每年秋冬枯水期,在赣江和修水入湖三角洲前缘,由草滩-泥滩-积水洼地组成的湿地生态环境为越冬候鸟提供了良好的栖息条件。调查表明,高程12-13m低地最适宜候鸟越冬生存。三峡建坝后,10月份水库蓄水长江下泄流量减少,引起鄱阳湖的提前退水和滩地提前显露,虽使动物性饵料略有减少,但对食草候鸟影响不大.人类提前对草滩资源利用和利用下限的扩大,使候鸟隐蔽条件变差. 相似文献
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海南岛三亚小东海发育有美丽的岸礁,岸礁礁坪环境向海延伸数十米,珊瑚礁生态沉积分带明显,从陆地向海依次为海滩岩、大块礁珊瑚带、礁坪内带、礁坪外带和礁坪前缘斜坡带,不同的分带有不同的碳酸盐沉积和造礁珊瑚生态群落.海滩岩的成分主要有珊瑚骨骼、藻类、腹足类、瓣鳃类和底栖有孔虫等生物砂颗粒;石英砂颗粒含量较少,成岩作用主要表现为早期胶结作用.小东海的礁坪是一种向海进积类型的,礁坪靠海滩岩一侧为大块珊瑚带,平顶、原地、且已死亡的块状珊瑚分布其中,大块珊瑚周围是生物砂粒和灰泥沉积;礁坪内带以死亡的珊瑚居多,表面包有生物颗粒和灰泥沉积物,活珊瑚都以块状复体为主,枝状和其他生态类型的几乎没有.群落动态变化统计分析显示,礁坪外带强波浪作用带是造礁珊瑚生长最繁盛和分布最密集区域,除块状复体的珊瑚大量繁盛外,枝状的伞房鹿角珊瑚也大量发育,由于波浪强烈的冲刷作用,生物颗粒和灰泥沉积物极少.微生物碳酸盐沉积一般发育在海滩岩的孔穴、珊瑚骨骼空腔和生物颗粒上,而以后面二者居多;从海滩岩到礁坪外带的波浪和水流作用变化,决定了小东海珊瑚礁的生态沉积分带,微生物碳酸盐沉积一般不在波浪作用强烈和沉积物受冲刷的礁坪外带发育. 相似文献
4.
南黄海表层沉积物粒度端元反演及其对沉积动力环境的指示意义 总被引：2，自引：0，他引：2
《中国科学:地球科学》2015,(10)
应用端元分析模型对南黄海表层沉积物粒度数据进行了反演,分离出四个端元.根据各端元频率分布曲线及平面分布特征,结合南黄海沉积动力格局,分析了各端元与研究区物源和水动力环境的对应关系.端元1和端元2反映了海洋动力过程对陆源沉积物的输运和分选,端元3和端元4反映了海洋动力对残留砂的改造.南黄海海洋锋面主要对陆源较粗颗粒沉积物的输运有影响,陆源较粗颗粒沉积物基本不能跨越山东外海海洋锋面.陆源细颗粒沉积物受海洋锋面影响较小,并在潮汐动力条件较弱的南黄海中部大量沉降,构成南黄海中部泥质区主体.南黄海中部细颗粒沉积物可能有西北和西南两个不同物源方向,其北部沉积物主要来自沿岸流输运跨越锋面后的黄河沉积物的细颗粒部分,西南部沉积物主要来自跨越苏北海洋锋面具有长江和黄河混合物源的苏北沿岸沉积物的细颗粒部分.和直接利用沉积物粒度数据研究沉积动力环境的传统方法相比,利用沉积物粒度端元分析方法分离出的沉积物不同端元分析区域沉积动力环境效果更好. 相似文献
5.
筑坝拦截对黑河河道沉积物粒度空间分布的影响 总被引：2，自引：1，他引：1
河流沉积物对流域环境变化具有敏感响应，其粒度参数能反映沉积环境中物质来源和水动力环境.本文以黑河流域上中游为研究区域，探究河流沉积物粒度对流域环境变化的响应.从黑河上中游干流22个主要控制断面采集河床沉积物样品，采用筛分法和吸管法对沉积物样品粒度参数进行测定，并分析其空间分布规律对筑坝拦截为主的环境改变响应.研究结果表明：受梯级水库建设影响，黑河上中游泥沙粒径大小差异显著.干流库区泥沙粒径较自然河段明显减小，分选很好，呈正偏或极正偏尖锐分布，而且在库区不同沉积高度上表现出分层沉积特征；坝下游河段因遭受强烈冲刷，较自然河段泥沙粒径粗化显著，分选变差，偏态趋向极正偏，峰态尖锐化；水库回水区受水库壅水及下泄清水的双重制约，泥沙粒度参数介于自然河段和坝下游河段之间，整体分选中等，呈极正偏尖锐分布；沉积环境分析表明，上游支流河段沉积物粒度特征受泥沙供给和物源特征的影响较水动力条件显著，干流河段沉积物粒度特征主要受水动力条件控制.研究结果既符合河流上中游沉积物粒度分布规律，也反映了河流环境变化对沉积物粒度组成的影响. 相似文献
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汉源大树剖面厚11.2m,光释光测年结果显示其地质时代为中更新世晚期-晚更新世中期.频率曲线有两峰a型、三峰b型和带粗尾巴的三峰c型三种类型,具有1-2Φ、3-4Φ、4-5Φ、5-6.5Φ、6.5-8Φ、10-11Φ等6个众数,各众数在地层纵向各层段上变化趋势明显;具有a型频率曲线特征的沉积物反映湖水较深,而其余的则可能指示了水体较浅的滨浅湖相.粒度组成以粉砂为主,分选性较好,中值粒径平均为18.12μm.粘土与细粉砂、粉砂含量曲线呈正相关关系;中值粒径与砂、粗粉砂含量曲线也呈正相关关系,并与粘土含量曲线呈负相关关系.大树剖面粒度组成可分为八个沉积阶段,构成从细到粗的三个沉积旋回,各沉积阶段分别指示了不同的水动力条件. 相似文献
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对太湖西北部主要入湖河流、河口及近岸湖区64个表层沉积物样品进行粒度分析,结合粒度参数计算和聚类分析,探讨了表层沉积物的粒度分布特征及其沉积类型.研究结果表明:研究区沉积物平均粒径介于4.0~58.7μm之间,粒级组分为黏土、粉砂和砂,其含量的均值分别为7.19%、81.81%和11.00%.太湖西北部表层沉积物以粉砂和砂质粉砂为主;研究区粒度总体呈南粗北细的分布特征,太湖西部沿岸区距离物源区较近且水动力条件复杂,沉积物粒度较粗.太湖北部入湖河流沉积物的频率曲线峰形较宽,峰值位于细粒级;西岸入湖河道多呈单峰态,粒径偏粗;河口区沉积物粒径较河道偏粗,粗颗粒含量高.Q型聚类分析结果表明,研究区可分为4类沉积区,其中3类沉积区有典型特征:第1类沉积区主要分布在太湖西部沿岸,其沉积物粒度相对较粗;第2类沉积区主要位于入湖河流河口,沉积物粒度最粗;第3类沉积区位于蓝藻频发的梁溪河,其沉积物黏土含量极高,表明沉积物粒度特征可能与污染状况有一定的联系. 相似文献
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苏州澄湖湖底主要由硬粘土组成,同时残留有湖沼洼地和古河道,古河道大致呈NNW-SSE延伸,与历史文献所载"古三江"之一的东江基本一致.保存着硬粘土平原形成后从河流到湖泊环境演化的良好沉积记录,通过对湖心区古河道SC7孔2cm间隔取样和AMS14C测年、粒度、磁化率等测试分析,初步探讨了该孔的沉积粒度特征及古环境意义,研究结果表明,沉积物粗粉砂含量极少或不含,中-细粉砂和粘土分别占53%-65.8%和19.7%-40.1%;与河床硬粘土相比,粉砂含量较低,粘土含量较高,平均粒径较小,为正偏(硬粘土为极正偏),磁化率也明显较高,多种粒度指标和磁化率指标均表明,澄湖的形成具有河流、河流-湖泊过渡到湖泊的阶段性演化特点,为太湖平原湖荡区湖泊的河泛成因提供了新的证据,现代澄湖则明显受到人类活动的扰动影响. 相似文献
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测量表明,哈纳斯湖最大水深达188.5m,平均水深达120.1m,优质淡水容量达53.78×10~8m~3,均在我国湖泊中居突出地位。横断面为罕见的典型箱形,断陷作用仍在强烈进行之中。湖底表层沉积物粒度参数之分布主要受纵向搬运作用控制,局部受横向搬运作用影响。沉积物的矿物学特征与元素分布特征明显受沉积环境控制。沉积物中营养元素含量总体偏低。~(210)Pb法测得平均沉积速率为0.52mm/a,难以补偿断陷作用,湖盆将继续加深。 相似文献
11.
Thomas Vijverberg Johan Christian Winterwerp Stefan Gert Jan Aarninkhof Hans Drost 《Ocean Dynamics》2011,61(2-3):187-202
Lake Markermeer is a large (680?km2), shallow body of water in the middle of the Netherlands, with a mean water depth of 3.6?m. One of the major problems in the lake is its decreasing ecological value which is, among other reasons, caused by a gradual increase of suspended sediment concentration and associated increase of light attenuation in the water column. A thorough understanding of fine sediment dynamics in the lake is a prerequisite for solving this problem. This paper addresses the 3D nature of near-bed sediment dynamics in Lake Markermeer, based on data sampled from a 1-month field experiment in autumn 2007. The campaign involved the collection of 71 bed samples across the lake. At each location, dual-frequency echo soundings were carried out to assess the thickness of the silt layer, and sediment concentration throughout the water column was measured with an Optical Backscatter Sensor (OBS). Moreover, 2-week time series of wave height, water level, current velocities, and near-bed sediment concentration were collected at a single location. The time series of sediment concentration were measured with a regular OBS and an Argus Surface Meter IV (ASM). During the measurement period, flow velocities ranged between 2 and 15?cm/s, wave heights up to 1.2?m were observed and turbidity levels varied between 40?mg/l to more than 300?mg/l. The ASM data generally showed uniform concentration profiles. However, profiles with steep concentration gradients near the bed were found for wave heights above 0.5?m. The field experiments further revealed pronounced 3D structures near the bed during discrete storms. The results are generalized for a wider range of conditions and across the full water depth through application of a 1DV point model, using a two-fraction representation of the grain size distribution. The fine and coarse fractions are found to resuspend rapidly for wind speeds above 5?m/s and 10??2?m/s, respectively, forming a uniform concentration profile if these wind conditions persists. High-concentration (???g/l) layers near the bed, containing the coarse sediment fraction, only occur at the onset and towards the end of a storm, when wind speed changes rapidly. It is under these conditions that horizontal gradients in layer density or thickness can transport considerable fine sediment. This transport provides an additional mechanism for the infill of, for instance, silt traps and navigation channels. 相似文献
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Tsunami Sediment Characteristics at the Thai Andaman Coast 总被引：1，自引：0，他引：1
This paper describes and summarizes the 2004 Indian Ocean tsunami sediment characteristics at the Thai Andaman coast. Field investigations have been made approximately 3 years after the 2004 Indian Ocean tsunami event. Seven transects have been examined at five locations. Sediment samples have been collected for grain-size analyses by wet-sieve method. Tsunami sediments are compared to three deposits from coastal sub-environments. The mean grain-size and standard deviation of deposits show that shoreface deposits are fine to very fine sand, poorly to moderately well sorted; swash zone deposits are coarse to fine sand, poorly to well sorted; berm/dune deposits are medium to fine sand, poorly to well sorted; and tsunami deposits are coarse to very fine sand, poorly to moderately well sorted. A plot of deposit mean grain-size versus sorting indicates that tsunami deposits are composed of shoreface deposits, swash zone deposits and berm/dune deposits as well. The tsunami sediment is a gray sand layer deposited with an erosional base on a pre-existing soil (rooted soil). The thickness of the tsunami sediment layer is variable. The best location for observation of the recent tsunami sediment is at about 50–200 m inland from the coastline. In most cases, the sediment layer is normally graded. In some cases, the sediment contains rip-up clasts of muddy soils and/or organic matter. The vertical variation of tsunami sediment texture shows that the mean grain-size is fining upward and landward. Break points of slope in a plot of standard deviation versus depth mark a break in turbulence associated with a transition to a lower or higher Reynolds number runup. This can be used to evaluate tsunami sediment main layer and tsunami sediment sub layers. The skewness of tsunami sediment indicates a grain size distribution with prominent finer-grain or coarse-grain particles. The kurtosis of tsunami sediment indicates grain-size distributions which are flat to peak distribution (or multi-modal to uni-modal distribution) upward. Generally, the major origins of tsunami sediment are swash zone and berm/dune zone sands where coarse to medium sands are the significant material at these locations. The minor origin of tsunami sediment is the shoreface where the significant materials are fine to very fine sands. However, for a coastal area where the shoreface slope is mild, the major origin of tsunami sediment is the shoreface. The interpretation of runup number from tsunami sediment characteristics gets three runups for the 2004 Indian Ocean tsunami at the Thai Andaman coast. It corresponds to field observations from local eyewitnesses. The 1st runup transported and deposited more coarse particles than the following runups. Overall, the pattern of onshore tsunami sediment transportation indicates erosion at swash zone and berm/dune zone, followed by dynamic equilibrium at an area behind the berm/dune zone and after that deposition at inland zone until the limit of sediment inundation. The total deposition is a major pattern in onshore tsunami sediment transportation at the deposition zone which the sediment must find in the direction of transport. 相似文献
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洪泛湿地是位于水生系统和陆生系统之间的过渡带，在河流和陆地之间的水文生态方面起着纽带作用，受气候变化和人类活动的叠加影响，其水文过程改变很大程度上影响了湿地生态系统循环、结构和功能的稳定。本文以鄱阳湖洪泛区湿地为研究区，应用湖泊水动力和洪泛区地下水数值模型，评估鄱阳湖拟建水利枢纽工程对洪泛区地下水系统的影响。模拟结果表明，拟建水利枢纽工程将会遵循调度方案使得湖泊水位明显提高，但同时导致洪泛区地下水位的整体抬升，且东部主湖区附近的地下水位受到的影响（约1～3 m）要明显强于洪泛区其它区域（约小于1 m）。地下水位的变化同时导致不同典型时期洪泛区地下水流速的减小及地下水流向的改变，表现为枢纽建设后地下水流向的逆转和流速基本小于0.1 m/d。鄱阳湖涨水-丰水期总体为湖水补给洪泛区地下水模式，枯水-退水期主要为地下水补给湖水模式，但水利枢纽可能导致洪泛区地下水系统水均衡状态发生转变，影响了地下水系统的补给和排泄状态，最终形成了长期稳定的湖泊补给地下水的作用模式。从地下水-生态系统响应变化的角度分析，拟建水利枢纽建设引起的地下水位上升，可能会给湿地生物地球化学元素的迁移转化、植被群落的演变与退... 相似文献
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Size and Fourier-shape characteristics of quartz sand grains were determined by computerized image analysis in order to distinguish between aeolian and fluvial soil parent materials in the Dallol Bosso in Niger. Factor analysis of grain-size distributions gave four sand end-members that can be related to fluvial transport dynamics operating when the sediments were initially deposited. The medium to fine (and more angular shaped) sand fractions are being reworked by wind. Aeolian deposits were well sorted whereas fluvial deposits were poorly sorted in both size and shape. Although gross-shape characteristics (lower harmonics of Fourier series expansion) indicated a common source rock for all sands, the aeolian sands were well rounded whereas the fluvial sands tended to be more angular (upper harmonics of Fourier series). 相似文献
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Floodplain wetlands are dynamic systems undergoing frequent hydro-sedimentological changes. Tropical/subtropical wetlands have even more pronounced climatic and biological influences on the sediment dynamics. In the current study, a protected subtropical wetland in Bihar(India) has been assessed for its sedimentary and mineralogical status. Sediment characteristics and associated granulometric parameters are discussed to highlight the wetland’s hydrogeomorphic character, energy dimension, and th... 相似文献
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Miguel Angel de Lucas Pardo Marieke Bakker Thijs van Kessel Francesco Cozzoli Johan Christian Winterwerp 《Ocean Dynamics》2013,63(9-10):1137-1150
The Markermeer is a large and shallow man-made freshwater lake in the Netherlands, characterized by its high turbidity. As part of a study aiming to mitigate this high turbidity, we studied the water–bed exchange processes of the lake’s muddy bed. The upper centimeter’s–decimeter’s of the lake bed sediments mainly consists of soft anoxic mud. Recent measurements have proved the existence of a thin oxic layer on top of this soft anoxic mud. This oxic layer, which is much easier to be eroded than the anoxic mud, is believed to be related with Markermeer’s high-turbidity levels. Our hypothesis is that the thin oxic layer develops from the anoxic mud, enhanced by bioturbation. Actually, we will demonstrate that it is the bioturbated state of the bed that increases its erodability, and not the oxidation state of the sediments. In particular, we will refer to bioturbation caused by meiobenthic fauna. The objective of this study is therefore to determine the influence of the development of the thin oxic layer on the water–bed exchange processes, as well as to establish the role of bioturbation on those processes. This is done by quantifying the erosion rate as a function of bed shear stresses, and at different stages of the development of the oxic layer. Our experiments show that bioturbation increases the rate at which Markermeer sediments are eroded by almost an order of magnitude. The short-term fine sediment dynamics in Markermeer are found to be driven by the complex and highly dynamic interactions between physics, chemistry, and biology. Finally, the long-term fine sediment dynamics are driven by the erosion of the historical deposits in the lake’s bed, which is only possible after bioturbation, and which leads to an increase of the stock of sediments in the lake’s muddy bed. 相似文献
18.
基于实测和数值模拟方法分析了台风“摩羯”和“温比亚”过境巢湖流域时的影响.台风“摩羯”和“温比亚”过境时,在巢湖产生较大的风速和风浪过程,其中对东巢湖的影响最大,中巢湖次之,西巢湖最小.东巢湖、中巢湖、西巢湖在台风“摩羯”过境时出现了0.68、0.67和0.48 m的最大有效波高和2.25、2.33和1.95 s的最大平均波周期;而台风“温比亚”过境时则最大有效波高可达1.50、1.47和1.18 m,最大平均波周期可达2.99、3.04和2.74 s.影响较大的区域位于东巢湖与中巢湖连接的湖心水域,总体对东巢湖的影响最为显著,中巢湖次之,西巢湖最小.不同湖区湖心水域由于水深、风区长度大,往往是出现最大风浪强度的区域. 相似文献
19.
The evolution of barchan-to-parabolic dunes can be driven by vegetation establishment, which may be linked to climate change and/or human activity. However, little is known of the impact of changes in wind strength on vegetation development and the resulting impacts on the evolution of dune morphology and sedimentological characteristics. To address this issue, we studied the morphology and grain-size characteristics of barchan, barchan-to-parabolic and parabolic dunes in the Mu Us Desert in north China, which was combined with an analysis of changes in normalized difference vegetation index (NDVI) and climatic variables during 1982–2018. The results reveal a trend of increasing growing-season NDVI which was related to a significant decrease in drift potential (DP). Therefore, we suggest that the initiation of dune transformation was caused by the reduced wind strength which favored the establishment and development of vegetation. To reveal the response of sedimentological reorganization during the processes of dune transformation, grain-size characteristics along the longitudinal profile of the three different types of dunes were examined. The decreasing wind strength led to the transport of fine sands on the upper part of the windward face of the dunes, resulting in a progressive coarsening of the grain-size distribution (GSD) and a reduction in dune height at the crest area. No distinct trend in sorting and mean grain-size was observed on the windward slope of the barchan-to-parabolic dune, indicating that the sand in transit had little influence on the GSD. Conversely, progressive sorting and coarsening of the sand occurred towards the crest of the parabolic dune. This indicates that vegetation development limited the transport of sand from upwind of the dune, and affected a shift in the dune source material to the underlying source deposits, or to reworked pre-existing aeolian deposits, and resulted in the trapping of sand in the crest area. © 2020 John Wiley & Sons, Ltd. 相似文献