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951.
A sharp decrease in total suspended solids (TSS) concentration has occurred in the Mekong River after the closure of the Manwan Dam in China in 1993, the first of a planned cascade of eight dams. This paper describes the upstream developments on the Mekong River, concentrating on the effects of hydropower dams and reservoirs. The reservoir-related changes in total suspended solids, suspended sediment concentration (SSC), and hydrology have been analyzed, and the impacts of such possible changes on the Lower Mekong Basin discussed. The theoretical trapping efficiency of the proposed dams has been computed and the amount of sediment to be trapped in the reservoirs estimated. The reservoir trapping of sediments and the changing of natural flow patterns will impact the countries downstream in this international river basin. Both positive and negative possible effects of such impacts have been reviewed, based on the available data from the Mekong and studies on other basins. 相似文献
952.
953.
福建沿海盆地第四纪构造运动模式与动力学环境 总被引:2,自引:0,他引:2
对福建省福州、泉州、漳州、厦门等城市所在盆地沉积和断裂的研究表明,自漳州地区向北东和向南西各盆地起始沉积、沉积间断和全新世海侵等事件是时间上依次发生的序列沉积事件,漳州及其以北各第四纪盆地构成向南西掀斜的箕状盆地。基于上述规律性,提出了自漳州向北东和向南西依次扩展的第四纪以来地壳隆张的运动模型。分析了菲律宾板块与欧亚板块的接触关系和相互作用,认为菲律宾板块的作用是该区第四纪构造运动的主要驱动力,巴士系构造是该区地壳运动的触发构造。 相似文献
954.
Ming Chee Yeung Sze Chung Lee Bit Hon Lun Peter A. Tanner 《Atmospheric Research》2007,86(3-4):241-248
During the summer monsoon period in south-east Asia marine airstreams normally prevail at the south China coast. However, when tropical cyclones approach then polluted airmasses from south-eastern China can impart high ionic concentrations and high acidity to rainwater. This is illustrated by two examples and the small-scale horizontal variations in rainwater composition are minor during these episodes. Since long-term quality-assured studies of the composition of rainwater in south-east Asia are scarce, the results at three sampling sites in Hong Kong during summer monsoon periods are compared with previous data from the same season. The results for the mid- to end-1990's show a similar trend to those for the ambient concentrations of sulphate and nitrate in aerosol in Hong Kong, which show flattened trends from 1995 to 1999. A marked increase in acidity is found in the summer monsoon period of 2004 which is attributed to the greater proportion of approaching cyclone weather systems in the dataset, reflecting both the increased local emission sources and the burgeoning economic growth of the Pearl River Delta Region. Comparison of the rainwater composition with that at other south-east Asian cities during the summer monsoon period shows that it is most acidic in Hong Kong. 相似文献
955.
辽宁张强盆地聚煤与构造特征 总被引:2,自引:1,他引:2
张强盆地是辽宁晚中生代半地堑式断拗盆地,呈萁状。同生构造控制了盆地的形成、沉积及演化。湖滨三角洲平原聚煤环境、湖泊环境的成油、富煤区与古构造、古气候、占地理的演化紧密相关。与邻区协尔苏盆地、三台子盆地沉积上有相似性及差异性。通过对沉积特征的分析,对今后找矿工作有一定的指导意义。 相似文献
956.
本文使用中国科学院常熟和鹰潭生态实验站和气象站的观测资料,应用区域酸沉降模式系统(RegADMS)和大叶阻力相似模型来研究华东地区不同下垫面条件上的大气硫沉降问题,定量估计了农田下垫面上大气硫化物的沉降通量。SO2和硫酸盐的干沉降速率使用大叶阻力相似模型来估计,使用与降水量有关的参数化方案来确定湿沉降系数。结果表明,常熟地区农田下垫面的大气硫沉降通量为19.0gm^-2 a^-1,其中干沉降占42%;而位于江西红壤地区的鹰潭站的大气硫沉降通量为10.4gm^-2a^-1,其中干沉降占83%。比较发现,两地硫干沉降通量绝对值相差不大,但其在总沉降通量中所占的份额有较大差异;常熟站的硫湿沉降通量比鹰潭站要大9.23gm^-2a^-1,该差异是由两地污染状况和气象条件的不同造成。华东地区的年硫沉降总量为1.88Mt(1Mt=10^6t),其中72.8%沉降在农田下垫面上。硫沉降中43%是干沉降,57%是湿沉降。 相似文献
957.
The presence of ?ne sediment in river gravels is widely recognized as being detrimental to salmonid habitat quality. In order to facilitate quanti?cation of sand presence at larger scales, this paper presents an application of image processing allowing for rapid and accurate assessments of super?cial sand presence in dry exposed ?uvial gravels. Images for the process are acquired with a 35 mm SLR ?lm camera and then scanned with a desktop scanner. Texture‐based segmentation is then applied to differentiate between sand and clast areas. Results show that the method is accurate and therefore it offers an alternative to bulk sampling in cases where rapid assessments of sand presence are required. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
958.
959.
The Dongting Lake is located in the south beach of the middle reaches of the Yangtze River. Its catchment, with an area of 262,823 km2 or about 12% of the total Yangtze River catchment, is situated between 28o43?29o32扤 and 112o54?113o8扙, and crosses Hubei and Hunan provinces in administrative division. The main tributaries include Xiangjiang, Zishui, Yuanjiang, Lishui rivers (4 Tributaries) and some local rivers, such as Miluo River, Xinqiang River and other little streams. In the nor… 相似文献
960.