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91.
Nguyen Tai Tue Hideki Hamaoka Atsushi Sogabe Tran Dang Quy Mai Trong Nhuan Koji Omori 《Environmental Earth Sciences》2011,64(5):1475-1486
In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red
River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment.
In addition, mangrove leaves and particulate organic matter were collected and measured for δ13C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ13C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ13C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ13C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ13C values in mangrove sediments. However, the shifts of δ13C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with
values of C/N > 12 and δ13C < −25‰, and C/N < 12 and δ13C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ13C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be
reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ13C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ13C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ13C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem. 相似文献
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In many geotechnical systems, such as reinforced slopes and embankments, soil-structure interfaces are often unsaturated. Shear behaviour of unsaturated interfaces is strongly dependent on their matric suctions, as revealed by the results of extensive laboratory tests. So far, constitutive models for unsaturated interfaces are very limited in the literature. This paper reports a new bounding surface model for saturated and unsaturated interfaces. New formulations were developed to incorporate suction effects on the flow rule and plastic modulus. To examine the capability of the proposed model, it was applied to simulate suction- and stress-controlled direct shear tests on unsaturated soil–cement, soil–steel and soil–geotextile interfaces. Measured and computed results are well matched, demonstrating that the proposed model can well capture key features of the shear behaviour of unsaturated interfaces, including suction-dependent dilatancy, stress–strain relation and peak and critical state shear strengths. 相似文献
94.
湿地执法管理是湿地保护的重要手段,探讨了九段沙湿地执法管理的3种模式:单一执法、联合执法、综合执法。根据九段沙湿地现状,认为综合执法是九段沙湿地保护和管理的最佳模式,它将为上海市的国际化生态城市的建设和经济的可持续发展起到积极作用。 相似文献
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城市游憩场点系统结构分形及优化——以苏州市区为例 总被引:4,自引:0,他引:4
以苏州市区为例,采用Zipf分维数、空间关联维数以及交通长度-半径维数三个指标,分别对城市游憩场点系统的等级结构、空间结构及交通网络通达性进行分维刻画。研究发现:首先,苏州游憩场点系统及其交通道路支持系统都具有较好的分形特性;其次,各分维指标能够准确地刻画城市游憩场点系统及交通道路支持系统的结构分异,可以为游憩场点系统的结构优化提供标准依据并指明方向;其三,苏州游憩场点系统的等级结构和空间结构均呈现出一种核心松散、外围紧致的结构递变趋势,自组织能力的离心化现象比较突出;最后,从分形几何和系统论的角度揭示、证实了游憩场点系统和旅游景点系统在结构分形及自组织演化上存在着显著差异。 相似文献
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99.
Shear-wave splitting in the crust: Regional compressive stress from polarizations of fast shear-waves 下载免费PDF全文
When propagating through anisotropic rocks in the crust, shear-waves split into faster and slower components with almost orthogonal polarizations. For nearly vertical propagation the polarization of fast shearwave (PFS) is parallel to both the strike of the cracks and the direction of maximum horizontal stress, therefore it is possible to use PFS to study stress in the crust. This study discusses several examples in which PFS is applied to deduce the compressive stress in North China, Longmenshan fault zone of east edge of Tibetan plateau and Yunnan zone of southeast edge of Tibetan plateau, also discusses temporal variations of PFS orientations of 1999 Xiuyan earthquake sequences of northeastern China. The results are consistent to those of other independent traditional stress measurements. There is a bridge between crustal PFS and the crustal principal compressive stress although there are many unclear disturbance sources. This study suggests the PFS results could be used to deduce regional and in situ principal compressive stress in the crust only if there are enough seismic stations and enough data. At least, PFS is a useful choice in the zone where there are a large number of dense seismic stations. 相似文献
100.
据博斯腾湖流域1958-2010年期间主要河流开都河、黄水沟、清水河、孔雀河的逐年流量资料,结合焉耆盆地降水、蒸发要素的同期观测资料,对大湖区的逐年水量收支进行计算,并依据水量平衡原理对博湖大湖区残差水量进行了逐年分析。结果表明:(1)1958-2010年期间年均入湖水量14.34×108 m3/a,其中入湖河水约占95%;年均输出水量13.96×108 m3/a,其中大湖区输入孔雀河水量约占43%,湖面蒸发耗水量占57%;湖区年均蓄水量71.57±3.92×108 m3108 m3/a,湖水年均水位为1 047.01±0.94 m;(2)极端水文年度水量平衡分析指出:1986年为最枯年份,入湖河水是多年平均值的62%,而出湖河水量是多年平均值的153%,导致年内湖区水位下降0.94 m;2002年最丰年份入湖河水是多年平均值的2.6倍,致使年内水位上升0.80 m;(3)残差水量逐年“正负”变化指出,湖水与地下水之间存在互补关系,过去53 a间湖水补给地下水的年均水量为0.87×108 m3/a。 相似文献