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61.
Composition and flux of suspended organic matter in the middle and lower reaches of the Changjiang (Yangtze River) — impact of the Three Gorges Dam and the role of tributaries and channel erosion 下载免费PDF全文
To investigate the sources of particulate organic matter (POM) and the impact of Three Gorges Dam (TGD), two large lakes and erosion processes on determining the composition and flux of POM in low water discharge periods along the middle and lower Changjiang, suspended particulate samples were collected along the middle and lower reaches of the Changjiang (Yangtze River) in January 2008. Organic geochemistry of bulk sediment (particulate organic carbon, organic carbon to nitrogen molar ratio (C/N), stable carbon isotope (δ13C) and grain size) and biomarker of bulk sediment (lignin phenols) were measured to trace the sources of POM. The range of C/N ratios (6.4–8.9), δ13C (?24.3‰ – ?26.2‰) and lignin phenols concentration Λ8 (0.45 mg/100 mg OC‐2.00 mg/100 mg OC) of POM suggested that POM originated from the mixture of soil, plant tissue and autochthonous organic matter (OM) during the dry season. POM from lakes contained a higher portion of terrestrial OM than the mainstream, which was related to sand mining and hydropower erosion processes. A three end‐member model based on δ13C and Λ8 was performed. The results indicated that soil contributed approximately 50% of OM to the POM, which is the dominant OM source in most stations. POM composition was affected by total suspended matter (TSM) and grain size composition, and the direct OM input from two lakes and channel erosion induced OM. The lower TSM concentration in January 2008 was mainly caused by seasonal variations; the impact from the TGD in the dry season was relatively small. A box model indicated that more than 90% of the terrestrial OM transported by the Changjiang in January 2008 was from the middle and lower drainage basins. Channel erosion induced OM, and contributions from Poyang Lake were the major terrestrial OM sources in the dry season. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
62.
针对矢量推进模式下的 AUV 水动力性能和操纵性能,开展了 AUV 矢量推进水动力 CFD 计算, 对矢量推进水平回转操纵性进行了评估,加工了矢量推进样机,并进行湖上操纵性验证。理论计算和试验数据表明:矢量推进具备极高的低速操纵性,该研究为矢量推进在 AUV 上的应用提供了理论和技术基础。 相似文献
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64.
基于水利益共享的跨境流域水资源多目标分配研究——以澜沧江-湄公河为例 总被引:2,自引:1,他引:1
以水利益共享代替分水的理念有利于充分发挥水资源效益和减少区域矛盾冲突,但由于缺乏具体可实施的分配模式一直停留在设想阶段。基于水利益共享理念,建立跨境流域水资源多目标分配指标体系,并结合澜沧江-湄公河流域跨境水资源利用现状及需求,提出澜沧江-湄公河流域跨境水资源多目标分配模型。为基于水利益共享的跨境水资源多目标分配提供了具有充分可操作性的指标体系和分配模型,有助于推进跨境流域水利益共享的实施,实现区域双边或多边在水资源利用上的共赢和发展目标。 相似文献
65.
Hydrological cycle and water balance estimates for the megadune–lake region of the Badain Jaran Desert,China 下载免费PDF全文
Yan‐Dong Ma Jing‐Bo Zhao Xiao‐Qing Luo Tian‐Jie Shao Zhi‐Bao Dong Qi Zhou 《水文研究》2017,31(18):3255-3268
The hydrology and water balance of megadunes and lakes have been investigated in the Badain Jaran Desert of China. Field observations and analyses of sand layer water content, field capacity, secondary salt content, and grain size reveal 3 types of important natural phenomenon: (a) vegetation bands on the leeward slope of the megadunes reflect the hydrological regime within the sandy vadose zone; (b) seepage, wet sand deposits, and secondary salt deposits indicate the pattern of water movement within the sandy vadose zone; (c) zones of groundwater seeps and descending springs around the lakes reflect the influence of the local topography on the hydrological regime of the megadunes. The seepage exposed on the sloping surface of the megadunes and gravity water contained within the sand layer confirm the occurrence of preferential flow within the vadose zone of the megadunes. Alternating layers of coarse and fine sand create the conditions for the formation of preferential flows. The preferential flows promote movement of water within the sand layer water that leads to deep penetration of water within the megadunes and ultimately to the recharging of groundwater and lake water. Our results indicate that a positive water balance promotes recharge of the megadunes, which depends on the high permeability of the megadune material, the shallow depth of the surface sand layer affected by evaporation, the occurrence of rainfall events exceeding 15 mm, and the sparse vegetation cover. Water balance estimates indicate that the annual water storage of the megadunes is about 7.5 mm, accounting for only 8% of annual precipitation; however, the shallow groundwater per unit area under the megadunes receives only 3.6% of annual precipitation, but it is still able to maintain a dynamic balance of the lake water. From a water budget perspective, the annual water storage in the megadunes is sufficient to serve as a recharge source for lake water, thereby enabling the long‐term persistence of the lakes. Overall, our findings demonstrate that precipitation is a significant component of the hydrological cycle in arid deserts. 相似文献
66.
Natural ecosystems in the region of the lower Tarim River in northwestern China strongly deteriorated since the 1950s due to an expanding desertification. As a result, the downstream Tarim River reaches became permanently dry land. This historical evolution in land‐use change is typically the result of the anthropogenic impact on natural ecosystems. On the basis of a spatially distributed hydrological catchment model bidirectionally linked with a fully hydrodynamic MIKE11 river model, land‐use changes characterized by historical changes in leaf area index (LAI) of vegetation, as well as the evolution of irrigated surface areas, can be causally related to changes in water resources (groundwater storage and surface water resources). An increased surface area of irrigated (agricultural) land, together with a majority of inefficient irrigation methods, did lead to a strong increase of water resources consumption of the farmlands located in the upper Tarim River area. Evidently, this evolution influenced available water resources downstream in the Tarim basin. As a result, farmland has been gradually relocated to the upstream regions. This has led to reduced flows from the upper Tarim stream, which subsequently accelerated the dropping of the groundwater level downstream in the basin. This study moreover demonstrates that land surface biomass changes (cumulative LAI) along the lower Tarim River are strongly related to the changes in groundwater storage. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
67.
68.
在已有先导连接参数化方案的基础上,选取近地面层为研究区域,保持方案中其他基本参量不变,通过改变闪电的空间形态,在同一建筑分布的背景下进行多次闪电模拟。研究多个建筑之间的屏蔽作用以及建筑雷击保护距离与建筑相关特征参数之间的关系,结果表明:高建筑对矮建筑具有屏蔽作用,并存在一个临界保护距离,当高、矮建筑高度分别为190 m和165 m,宽度均为20 m时,建筑之间的距离在12 m以内,矮建筑受高建筑完全保护不遭受雷击;建筑之间的距离超过12 m,矮建筑遭雷击次数明显增多。 相似文献
69.
胶东型金矿:与壳源重熔层状花岗岩和壳幔混合花岗闪长岩有关的金矿 总被引:1,自引:0,他引:1
胶东型金矿是与壳源重熔形成的层状岩浆活动和壳幔混合岩浆活动有关的金矿床,由于成矿时所处构造位置和容矿构造不同而表现为不同的类型,涵盖破碎带蚀变岩型、石英脉型等胶东地区所有金矿床类型。玲珑花岗岩是壳源物质长期处于高温高压下且熔融形成的多物质来源层状岩体,其析出的高温碱性热液溶解金等成矿物质形成初始含矿热液。岩体抬升过程中在其边部往往容易形成拆离带,在岩体中形成脆性断裂构造,均为成矿结构面。后期壳幔混合成因的郭家岭花岗闪长岩,侵入于玲珑层状花岗岩中并一起隆升,使郭家岭花岗闪长岩附近区域的成矿结构面进一步扩大,矿液浓度进一步增大,当上升到特定深度时形成金矿体。玲珑花岗岩和郭家岭花岗闪长岩共同构成成矿地质体,重熔的玲珑层状岩体是成矿基础地质体,郭家岭花岗闪长岩加强了金矿的成矿作用。该认识对开辟胶东新的找矿思路和找矿靶区有很好的指导作用,据此初步预测新的大型拆离带是金矿集中成矿区域,可能成为将来有望取得重大突破的矿集区。 相似文献
70.
基于页岩孔隙系统的特殊性,讨论了FESEM-QEMSCAN、FIB-FESEM、NANO-CT、氮气吸附法、小角中子散射等几种页岩孔隙系统研究方法的特点和适用范围。指出场发射扫描电镜以及与之结合的能谱和矿物定量评价系统(FESEM-QEMSCAN)是研究页岩纳米级孔隙类型、大小、形态以及矿物分布的基础手段;聚焦离子束扫描电镜、微纳米CT可刻画页岩孔隙系统在三维空间的展布特征,利用获得的三维数据体进行数值模拟,可进一步计算孔隙度、渗透率等物性参数;氮气吸附法可对小于100nm的极微孔隙的孔径、形态进行求算;小角中子散射则可利用孔隙中存在的气体分子,获得孔隙系统连通性等重要参数。最后从页岩岩石组构的角度,探讨了页岩孔隙控制因素,指出有机质含量与成熟度,黏土矿物类型、含量,碎屑颗粒的含量以及成岩强度是影响页岩孔隙系统的主要因素。 相似文献