Do the shallow‐water habitats of a hypersaline tropical estuary act as nursery grounds for fishes?          下载免费PDF全文

Natalice dos Santos Sales  Alexandra Sofia Baptista Vicente Baeta  Lidiane Gomes de Lima  André Luiz Machado Pessanha 《Marine Ecology》2018,39(1)

Fish assemblages were studied in a hypersaline tropical estuary in Northeastern Brazil. A total of 104 species were collected by beach seine during the dry and rainy seasons of 2012. Two families, Atherinopsidae and Gerreidae, were numerically dominant in all zones of the estuary; juveniles of Atherinella brasiliensis, Eucinostomus argenteus, Lile piquitinga, Ulaema lefroyi, Lutjanus analis and Sphoeroides greeleyi contributed 77% of the total catch. The factors that best explained the fish abundance pattern were salinity and depth, which were related to spatial segregation. Species richness was lowest in the upper zone, an area with high salinity and shallow depth. The distinct roles of structurally different habitats (submerged macrophyte beds and mangrove prop‐roots) and the influence of physicochemical conditions in the middle zone of the estuary may influence taxonomic diversity. The middle zone of the estuary is the one most attractive to juveniles of reef species (Lutjanidae and Serranidae). The fish assemblages are clearly dominated by marine estuarine dependent species, highlighting the importance of the ecosystem as a nursery ground for marine species of the Brazilian coast.  相似文献   

Escape route analysis after water inrush from the working face during submarine tunnel excavation     

S. C. Li  J. Wu  Z. H. Xu  B. Zhang  X. Huang 《Marine Georesources & Geotechnology》2018,36(4):379-392

More and more deep-seated long submarine tunnels are under construction, which greatly promotes the development of tunneling technology. The complex geological conditions and frequent geological disasters have become great challenges during submarine tunnel excavation. Among them, casualties and economic losses caused by water inrush are on the top levels in all kinds of tunnel geological disasters. Escape routes after water inrush from the working face during submarine tunnel excavation are investigated and optimized in the present study. Numerical simulations are performed using the FLUENT software to probe water flow characteristics after inrush. Two common cases of water inrush during double-line submarine tunnel excavation are researched. The variation rules of velocity and pressure in the tunnels after inrush are analyzed and discussed. The optimized escape routes are achieved. Finally, the water movement laws after inrush from the working face under different excavation situations are further discussed by comparing the two case studies. Water inrush of high velocity occurs on one working face of the double-line submarine tunnel, and the research results are as follows: (1) The velocity close to the tunnel side wall is the minimum, while it is the maximum in the middle position. (2) The pressure changes greatly at the intersection area of the cross passage and the tunnels. (3) The velocity and pressure nearby the working face without water inrush are both small. (4) The velocity at the high location of the cross passage is relatively small.  相似文献   

浅地震反射剖面揭示地震小区划覆盖层厚度及隐伏断裂——以九江芳兰规划区为例     

林松  蔡永建  雷东宁  王秋良  杨钢 《大地测量与地球动力学》2018,38(9):881-885

以九江芳兰规划区为例,利用浅层地震反射方法获取小区划工区的覆盖层厚度,并查明周边隐伏断裂位置及特征。结合钻孔资料对比解译,对地震小区划工作提供基础地震地质信息,同时为该区的活断层探测和地震危险性评价提供参考资料。  相似文献   

地下隧道-土体系地震反应分析的有限元与无限元耦合法   总被引：9，自引：1，他引：8  

姜忻良  徐余  郑? 《地震工程与工程振动》1999,19(3):22-26

本文采用有限元－无限元耦合法进行地下隧道－土相作用分析,阐述了有无限与无限元耦合模式的基本原理,耦合分析方法具有精度高,省机时的特点。  相似文献   

ACCURACY AND STABILITY OF FINITE DIFFERENCE EQUATIONS FOR SHALLOW WATER FLOWS IN ORTHOGOPNAL COORDINATES     

CHEN Jianwu  SHAO Xuejun 《国际泥沙研究》1999,(2)

IINTRODUCTIONNumericalmethodsasatooltosimulateflowsandpollutanttransportareincreasinglyimportantinhydraulicandenvironmentalengineering.AveryusefulapplicationofthenumericalmethodologyinengineeringproblemswouldbetosolvethesystemofZDdepth-integratedshallowwaterequations.ManysolutionsofthegoverningequationsarederivedusingtraditionalfinitedifferencemethodonCartesianregulargrids.ThedisadvantageofthismethodseemstobetheinflexibilityofCartesiangridstocomplywithirregularorcurvedperimeterswhichsur…  相似文献   

几种化学固沙材料抗风蚀的风洞实验研究   总被引：21，自引：0，他引：21  

胡英娣 《中国沙漠》1997,17(1):103-106

以几种常用的化学固沙材料为研究对象,对其固结层与风蚀量关系进行了风洞实验。为指导现场施工提供了依据。  相似文献   

利用MVDR算法削弱多波束测深声纳的隧道效应   总被引：1，自引：0，他引：1  

魏玉阔  陈宝伟  李海森 《海洋测绘》2011,31(1):28-31

分析了海底多波束测深声纳中存在的隧道效应及其产生机理,指出旁瓣干扰是引起隧道效应的重要因素,隧道效应的出现导致多波束测深声纳把相对平坦的海底误测成凹面向上的水平半圆柱面海底地形。研究了基于GSC结构的自适应波束形成算法,推导提出了MVDR算法的连续自适应实现方案,并利用该算法对多波束测深声纳湖试数据中存在的隧道效应进行处理,结果表明该算法能够有效削弱多波束测深数据边缘波束中存在的旁瓣干扰。  相似文献   

Imaging shallow structure with active-source surface wave signal recorded by distributed acoustic sensing arrays          下载免费PDF全文

Zhenghong Song  Xiangfang Zeng  Clifford H. Thurber  Hebert F. Wang  Dante Fratta 《地震科学（英文版）》2018,31(4):208-214

Distributed acoustic sensing (DAS) is one recently developed seismic acquisition technique that is based on fiber-optic sensing. DAS provides dense spatial spacing that is useful to image shallow structure with surface waves. To test the feasibility of DAS in shallow structure imaging, the PoroTomo team conducted a DAS experiment with the vibroseis truck T-Rex in Brady’s Hot Springs, Nevada, USA. The Rayleigh waves excited by the vertical mode of the vibroseis truck were analyzed with the Multichannel Analysis of Surface Waves (MASW) method. Phase velocities between 5 and 20 Hz were successfully extracted for one segment of cable and were employed to build a shear-wave velocity model for the top 50 meters. The dispersion curves obtained with DAS agree well with the ones extracted from co-located geophones data and from the passive source Noise Correlation Functions (NCF). Comparing to the co-located geophone array, the higher sensor density that DAS arrays provides help reducing aliasing in dispersion analysis, and separating different surface wave modes. This study demonstrates the feasibility and advantage of DAS in imaging shallow structure with surface waves.  相似文献   

Hummock corridors in the south‐central sector of the Fennoscandian ice sheet,morphometry and pattern          下载免费PDF全文

Gustaf Peterson  Mark D. Johnson 《地球表面变化过程与地形》2018,43(4):919-929

Subglacial conditions strongly influence the flow of ice‐sheets, in part due to the availability of melt water. Contemporary ice sheets are retreating and are affected by increased melting as climate warms. The south Swedish uplands (SSU) were deglaciated during the relatively warm Bølling‐Allerød interval, and by studying the glacial landforms there it is possible to increase the understanding of the subglacial environment during this period of warming. Across the study area, vast tracts of hummocks have long been recognized. However, recent mapping shows a pattern of elongated zones of hummocks radially oriented, hereafter referred to as ‘hummock corridors’. Morphometric parameters were measured on the hummock corridors using a 2 m horizontal resolution digital elevation model. Corridor width varies between 0.2 and 4.9 km and their length between 1.5 and 11.8 km. A majority of hummock corridors are incised in drumlinised till surfaces. The pattern of hummock corridors shows a clear relation to the overall ice‐flow. Further, hummock corridors do not follow topographic gradients, and in at least one place an esker overlies hummocks on the corridor floor. The lateral spacing of hummock corridors and corridor morphology are similar to tunnel valleys, eskers and glaciofluvial corridors reported elsewhere. Such relationships support a subglacial genesis of the corridors in the SSU by water driven by the subglacial hydraulic gradient and that hummock corridors are forms that can be identified as tunnel valleys and glaciofluvial corridors (GFC). Ages were assigned to hummock‐corridor cross‐sections from a deglacial reconstruction of the Fennoscandian Ice Sheet. By comparing the frequency of corridors per age interval with climate variations from a Greenland ice core, we hypothesize that an increase in the number of corridors is related to the Bølling‐Allerød warming, indicating a higher rate of delivery of surface melt water to the bed at this time. Copyright © 2017 John Wiley & Sons, Ltd.  相似文献   

大型浅水湖泊水体对流混合速率分析     

肖启涛  段洪涛  张弥  刘寿东  胡正华  李旭辉 《湖泊科学》2020,32(4):1189-1198

湖泊水体的对流混合是最基本的物理过程,其能显著影响湖泊生态系统温室气体等循环,但浅水湖泊水体对流混合的研究鲜有报道.本研究基于太湖(面积2400 km2,平均水深1.9 m)中尺度通量网的原位、高频、连续和多点的观测数据,分析该大型浅水湖泊水体对流混合速率w*的时空特征.结果表明太湖水体w*的均值为2.49 mm/s,因太湖的风速、水温和辐射等物理参数无空间变化,w*也无明显的空间变化.但是研究表明w*呈现显著的昼夜变化和季节变化,且昼夜变化幅度强于季节变化.总体上夜间w*是白天的4倍多,冬季w*(均值1.79 mm/s)明显低于春季(均值2.42 mm/s)、夏季(均值2.91 mm/s)和秋季(均值2.82 mm/s).太湖w*主要受风速和能量收支影响,白天风速是主要驱动因子,夜晚能量收支是主要驱动因子.  相似文献