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1.
Specific processes of delta formation at the Mississippi River mouth are discussed. In the last 7000–8000 years, a series
of large deltaic lobes was formed in succession at the Mississippi River mouth under the condition of high river sediment
runoff and stabilization of the ocean level after its sudden postglacial rise. In the mid-XX century, the formation of a new
deltaic lobe began at the Atchafalaya Branch mouth. Over the last centuries, the processes of delta formation at the Mississippi
River mouth slowed down as a result of the river sediment runoff decrease after flow regulation of the Missouri and Arkansas
tributaries; in some parts of the deltaic plain, these processes gave way to degradation of marshes and seashore erosion under
the impact of intense land subsidence. The current processes of delta formation are under the great influence of local economic
activities. 相似文献
2.
The development of the Sulak River Delta in the 19th and 20th centuries is discussed. It is shown that a drastic reduction in sediment runoff after the establishment of river flow regulation, anthropogenic restructuring of the river channel system in the delta area, and large-scale variations in the Caspian Sea level had an impact on the delta evolution. The processes of delta degradation over the period of the recent sea level rise are analyzed. The dynamics of the Sulak Delta in recent decades is studied using space photographs. 相似文献
3.
Hydrological and Morphological Processes in the Kura River Delta 总被引：1，自引：0，他引：1
Peculiarities of the development of the Kura Delta over the last 200 years are discussed. As shown, changes in the delta were greatly affected by the Caspian Sea level drop during 1929–1977 and its rise during 1978–1995 as well as by natural and human-induced variations in the water and sediment runoff of the river. It was noted that the delta area decreased by nearly 40% as a result of the sea level rise. The following significant changes in the Kura Delta were revealed in recent years using space images: river water rushed through the right mouth spit and, hence, the main Southeastern Branch was devoid of its flow and a new sea spit began its formation in the branch mouth using wave-cut products. 相似文献
4.
珠江三角洲地震活动的若干特点 总被引：1，自引：0，他引：1
分析了二十世纪末30年来珠江三角洲地区地震活动的特征，认为珠江三角洲地区与东南沿海地震带在地震序列分布上总体趋势是一致的。在1970～1997年间，珠江三角洲地区b值滑动时间曲线从1984年起至1986年的高值异常可能是东南沿海地震带1986年开始的活跃幕的中期前兆。地震活动指数A(b)值曲线1988年及1994年的两处低值异常，则可能是本区1989年及1997年两个地震能量释放高峰的中期前兆。从本区及东南沿海地震带地震发生的时间进程上来看，本区很可能是东南沿海地震带区域应力场的调整单元。 相似文献
5.
The interaction among tidal currents, sediment transport, and long-term changes of the sea bottom in the Colorado River Delta
have been investigated applying a two dimensional nonlinear hydrodynamic-numerical finite differences model. The system was
forced by the dominant M
2 tidal component at the open boundary. We carried out calculations to study the morphodynamics of the actual bathymetry caused
by the bedload sediment transport. To investigate the origin of actual morphological features, we performed experiments using
a smoothed bathymetry, in which the islands Montague, Gore, and Pelícano were eliminated. Under the imposed tidal hydrodynamics,
the results indicate that the bedload transport contributes significantly in the genesis of sandbanks and in the formation
and maintaining of the Montague and Gore Islands. 相似文献
6.
Data on water discharges and levels, morphometry of river branches, elevation base, runoff, and granulometric composition of sediments in the Ob Delta over the period of instrumental measurements were analyzed and summarized. The obtained results served as a basis for the delta parameterization. Detailed characteristics of the hydrological regime and quantitative characteristics of reversible fluviomorphological deformations averaged for the deltaic water streams were defined at different water levels in the channel. A many-year trend of these deformations was revealed. It was found that in the period between two cycles of field studies of the Ob Delta, no noticeable changes occured in the distribution of water discharges by the main branches at the delta head. Some secondary water streams in the delta lower reaches, where field observations were carried out over the mentioned period of time, featured a certain decrease in the flow discharged by these water streams along with a simultaneous increase in the water turbidity. The area of possible application of the obtained results was outlined. 相似文献
7.
Specific features of the geomorphology and hydrology of Selenga River delta are considered. Fractal theory is used to evaluate the fractal dimension of the river delta as a branched structure. The fractal dimension of the planar pattern of the Selenga and Volga deltas are evaluated for the first time using three independent methods. The obtained values are 1.38 and 1.72, respectively. 相似文献
8.
Cyclic shear response of channel-fill Fraser River Delta silt 总被引：2，自引：0，他引：2
The cyclic shear response of a channel-fill, low-plastic silt was investigated using constant-volume direct simple shear testing. Silt specimens, initially consolidated to stress levels at or above the preconsolidation stress, displayed cyclic-mobility-type strain development during cyclic loading without static shear stress bias. Liquefaction in the form of strain softening accompanied by loss of shear strength did not manifest regardless of the applied cyclic stress ratio, or the level of induced excess pore water pressure, suggesting that the silt is unlikely to experience flow failure under cyclic loading. The cyclic shear resistance of the silt increased with increasing overconsolidation ratio (OCR) for OCR>1.3. The silt specimens that experienced high equivalent excess cyclic pore water pressure ratios (ru>80%) resulted in considerable volumetric strains (2.5%–5%) during post-cyclic reconsolidation implying potentially significant changes to the particle fabric under cyclic loading. 相似文献
9.
珠江三角洲地区新构造运动 总被引：15，自引：1，他引：15
概述了珠江三角洲地区新构造运动的基本特征：晚第三纪以来的构造运动经历了由强逐渐减弱，晚更新世（约50－30Ka B.P)又重新增强的演变。重点估算了晚第四纪珠江三角洲断块垂直构造运动速率，定量分析了分割断块的断裂构造的活动性。认为斗门断块区和广州－番禺断块区这两个次级断块构造以及围限它们的广州－从化断裂，三水－罗浮断裂，西江断裂，白坭－沙湾断裂的活动性相对较强。从区域地震构造而言 ，珠江三角洲新构造运动远弱于日本－琉球－台湾岛弧，也弱于奥东潮汕和桂东南灵山等强震危险区。但由于其震源浅及松软土层较厚，加上本区经济发达，人口稠密，因此地震造成的破坏和损失仍不可低估，必须加强抗震减灾工作。 相似文献
10.
钻探证实,镇江市谏壁镇长江北岸高桥镇北部埋藏硬粘土层,之上为冰后期松散沉积物。沉积物主要为粉砂、粘土质粉砂、砂泥互层,中部局部夹含细砾中细砂,顶部见淤泥质粘土;夹数十层植物炭屑层;以水平纹理为主,局部见小型交错层理、波状层理。表明冰后期以来该地处于水动力较弱的河湖环境,为多期湖沼相沉积夹汉道河流相沉积,局部有海相沉积物加入。根据碳化植物碎屑^14C年龄,推测冰后期底界年龄约13000aBP,海侵到达该地的时间约为9000aBP,海侵最高位时间约为6500aBP。冰后期平均沉积速率约为4．9m／ka,湖沼相3．4～6m／ka,河流相10～15m／ka。对全新统的底界年龄和海相层的埋藏深度进行了讨论。 相似文献
11.
The peculiarities of the hydrological regime of the delta and near-shore zone of the Po River are discussed. The intrusion of salt seawater into the delta is described. The history of the Po Delta formation has been restored on the basis of the analysis of historical, archeological, and cartographic data. As shown, the peculiarities of hydrological and morphological processes in the Po River mouth are associated with natural and specifically with human-induced variations in sediment runoff of the river, with levee construction along branches, subsidence of deltaic deposits, and eustatic rise of the sea level. 相似文献
12.
Guo-Fang Li Xin-Yi Xiang Yi-Yi Tong Hui-Min Wang 《Stochastic Environmental Research and Risk Assessment (SERRA)》2013,27(7):1683-1693
The Yangtze River Delta region is the region with highest urbanization speed in China. In this study, 6 typical urbanization areas in Yangtze River Delta were selected as the objectives of study. Flood risk assessment index system was established based on the flood disaster formation mechanism, and analytic hierarchy process was utilized to define the weight of indices. The flood hazard, the exposure of disaster bearing body, the vulnerability of disaster bearing body and the comprehensive flood risk corresponding to three typical years in different urbanization stages, 1991, 2001 and 2006 were assessed. The results show that the flood hazard and the exposure of disaster bearing body in the 6 areas are all with an increasing trend in the process of urbanization, among which, the increasing trend of the exposure of disaster bearing body is especially obvious. Though the vulnerabilities of disaster bearing body in the 6 areas are all with decreasing trend owe to the enhancement of flood control and disaster mitigation capability, the comprehensive flood risks in the 6 areas increased as a whole, which would pose a serious threat to urban sustainable development. Finally, effective countermeasures for flood risk management of urbanization areas in Yangtze River Delta were put forward based on the assessment results. 相似文献
13.
Xiaoli Liu Linbao Zhang Liping You Huifeng Wu Jianmin Zhao Ming Cong Fei Li Qing Wang Lianzhen Li Chenghua Li Guangxuan Han Guangmei Wang Chuanhai Xia Junbao Yu 《洁净——土壤、空气、水》2011,39(8):720-727
Plant metabolomics has been well established and applied across multiple fields including medicine, biotechnology, and environmental sciences in the post‐genomic era. The Chenopodiaceae C3 halophyte Suaeda salsa is the most important plant species in the vegetation of saline soil and even intertidal zone in the Yellow River Delta, which is economically consumed as food, widely used as a bioindicator of environmental stresses (salinity, drought, and pollution) and typically applied for the phyto‐remediation of degraded wetland. However, no global studies have been focused on the metabolic profile of this halophyte which is widely applied in environment related research areas. In metabolomics, the first crucial step is the preparation of plant samples. In this work, several strategies of metabolite extraction from this C3 halophytes S. salsa were evaluated and the metabolic profile was characterized by NMR‐based metabolomics. Multiple replicates of plant tissues (approx. 250 mg whole fresh weight of leaves and stems) were homogenized by a high throughput automated Precellys 24 bead‐based homogenizer and then extracted using the following solvent systems of varying polarities: methanol, water, methanol/water, methanol/chloroform/water, and acetonitrile. The hydrophilic metabolites were analyzed using one‐dimensional proton NMR spectroscopy, and the subsequent NMR spectra were evaluated by principal components analysis (PCA). Each extraction protocol revealed unique metabolic profile from S. salsa. Overall, the quality of each extraction protocol was assessed based on the yield, reproducibility, ease, and speed, and we concluded that the solvent of methanol/water was preferable for the metabolite extraction due to its highest reproducibility, ease, and speed, and considerably high yield. Validation of methanol/water (1:1) solvent also showed a high degree of reproducibility with technical variation being considerably lower than biological variation in S. salsa samples. This demonstrated the quality and robustness of the methanol/water extraction method for NMR‐based metabolomics studies. 相似文献
14.
Khazheeva Z. I. Urbazaeva S. D. Bodoev N. V. Radnaeva L. D. Kalinin Yu. O. 《Water Resources》2004,31(1):64-67
The overall concentration of Cu, Pb, Zn, Cr, Mn, and Fe are determined in the water and bottom sediments of the Selenga River delta. The concentration of Cu, Pb, and Zn is found to decrease in the lower course of the river, at the delta outlet. The concentration of Mn and Fe is found to decrease in the downstream direction from the river's upper course along the investigated delta arms, whereas the concentration of Zn and Cr in certain arms exceeds their concentration in the upper section of the delta. 相似文献
15.
珠江三角洲的新构造运动及其与三角洲演化的关系 总被引：4，自引：0，他引：4
综合已有资料。重新对珠江三角洲的新构造运动进行了系统的分析．分析结果表明该地区的新构造运动以断裂活动和断块差异升降运动为主要特征．这些特征在珠江三角洲的演化过程中起着非常重要的作用。大多数在第四纪形成或重新活化的基底断裂把三角洲切割成一系列的断块,并且在垂直运动上以沉降为主导,为珠江三角洲的第四系沉积创造了空间。另外,第四系两期河流相砂砾层分布的差异反映了古河道在晚更新世海侵后、全新世海侵前所发生的变迁。这主要是断裂活动的结果。因此,在珠江三角洲的形成和演化过程中。新构造运动既影响着三角洲的沉积又控制着河道的变迁． 相似文献
16.
Three areas with different trends in water level variations over the period of many years have been distinguished within the Kuban Delta. It was found that the eustatic level rise of the Sea of Azov and soil subsidence on the sea edge of the delta and in the lower reaches of the Protoka Branch were responsible for the noticeable rise in water levels. A considerable water level drop caused by the river runoff regulation and erosion of the lower pool of the Krasnodarskii Waterworks was recorded in the upper part of the delta; in the rest part of the delta, water levels dropped insignificantly, which was partially due to the impact of the tectonic uplift. 相似文献
17.
In this article, by using the daily precipitation data measured at 58 meteorological stations, spatial and temporal variability of daily precipitation including zero rainfall values (called “precipitation”) and without zero rainfall values (called “rain”) and four precipitation extrema (P0, P20, P50, and P100 representing the daily precipitation with the magnitude smaller than 0.1 mm, bigger than 20 mm, 50 mm, and 100 mm per day, respectively) in the Yangtze River Delta (YRD) during 1958–2007 were analyzed, and the effects of urbanization were further investigated. Results indicate that (i) differing from the downward trends in 1958–1985, daily precipitation and rain in 1986–2007 show slowly downward trends in the mid YRD but show upward trends in the northern and southern YRD. (ii) Spatial and temporal variability of the rain is more complex than daily precipitation. Both of them become smaller but show more obvious fluctuations in 1986–2007. (iii) Urbanizations cause not only the urban rainfall island problem but also more obvious fluctuations of rain intensity in the mid YRD, reflecting more uncertainty of daily precipitation variability. (iv) Urbanizations have little effects on the variability of P0 and P100 but cause notable increases of P20 and P50. (v) The spatial variability of daily precipitation and precipitation extrema in 1958–1985 clearly shows a breakpoint at 30°20′N latitude, but the breakpoint disappears afterward because of the effects of urbanization. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
18.
The Ecological Restoration of Heavily Degraded Saline Wetland in the Yellow River Delta 总被引：2，自引：0，他引：2
As a result of discontinuous water flow, agriculture, and increasing urban use of fresh water affecting the natural wetlands of the Yellow River Delta, these areas have experienced significant degradation in the past two decades, ultimately diminishing the overall natural wetland land area in the region. This study aimed to address the issue of decreasing fresh water in the Yellow River Delta by studying the effects of three different approaches to restoration on long‐term wetland recovery. The results of the study demonstrated that soil salt and available Na contents significantly decreased in response to all three restoration treatments. Impacts of the restoration treatments were more significant in 2009 than in 2010, as shown by the high rate of activity in the reed debris group. The highest phosphatase activity of the experimental period was also observed in the reed debris group. Meanwhile, a marked variation in soil nutrient elements (total carbon (TC), total nitrogen (TN), available phosphorus, and available potassium) was observed in the restoration treatment plots throughout the experimental period. TC and TN contents were generally higher in the restoration treatment groups than in the control group. Moreover, urease and phosphatase activity levels were highly correlated with one another, as well as with soil nutrient elements. In 2009, the yield of the Suaeda salsa plant was highest in the reed debris treatment group and lowest in the ploughing treatment group. The S. salsa plant did show a positive response to all of the different restoration treatments. Taken together, these results suggest that restoration approaches that implement ploughing techniques aided in the restoration of degraded saline wetlands. 相似文献
19.
2003年春、夏、秋季对黄河三角洲7座平原型水库进行了4次调查,发现:1)由摇蚊科幼虫和水蚯蚓构成的大型底栖动物,体内磷含量随底泥沉积磷的增加而增加(P<0．000),底柄动物对沉积磷的积累系数亦随沉积磷含量的增加而增加(p<0．000);2)4、5月份摇蚊幼虫在底栖动物体所占不同比例(20％-100％),没有显示与底柄动物体内磷含量任何关系;3)底栖动物含磷量与水层总磷无显著相关关系;4)底柄动物生物量与沉积总磷仅4月份有相关(p<0．10),其中摇蚊幼虫生物量与沉积磷量相关显著(P<0．05),总体上,水库底柄动物最高生物量随沉积磷增加而增加;5)底栖动物生物量与水层总磷无相关关系,但去掉底层鱼产量高的水库后,8月份二者有显著相关关系(p<0．03),且总体底栖动物最高生物量也随水层总磷增加而增加．认为:1)由摇蚊科幼虫和水蚯蚓构成的大型底柄动物对磷的积累以及摇蚊幼虫的生物量均与水体磷负荷有密切关系;2)摇蚊幼虫和水蚯蚓含磷量(干重)差异不明显;3)以摇蚊幼虫为主的底栖动物对磷的积累主要来自沉积磷的影响,受季节的影响相对较弱;4)底栖动物生物量主要受水层总磷的控制,也受鱼类摄食以及摇蚊幼虫个体羽化时间不一致的影响． 相似文献
20.
本文对黄河三角洲Z07孔沉积物进行了系统的磁性地层学和环境磁学研究.通过结合沉积速率和古地磁长期变化数据，我们为该孔建立了较为精确可信的年代框架（1999-03-2006-06 A.D.）.环境磁学结果表明黄河三角洲沉积物与中国黄土的磁学特征相似，主要载磁矿物为单畴（SD）磁铁矿，超顺磁颗粒（SP）含量也较高.整体上，该孔沉积物磁学参数的变化主要受粒度和含量控制.岩芯磁性参数在2003年前后发生了系统变化.我们认为，黄河自2002年起进行调水调沙工程，黄河下游河道冲刷加剧，形成新的物质来源，河流输入的沉积物粒度变粗，输沙量增加，这一新的物质来源是造成Z07钻孔磁性参数发生显著变化的主因. 相似文献