Phytoplankton associations with the variable nepheloid layer on the Texas continental shelf     

Daniel Kamykowski  Jerry L. Bird 《Estuarine, Coastal and Shelf Science》1981,13(3):317-326

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大青山地区金地球化学特征     

江淑娥 《国土资源》1988,(3)

大青山地区出露地层主要是侏罗系中统兰旗组安山岩、安山质角砾熔岩、凝灰岩等;侵入岩为晚侏罗世二长花岗岩;断裂发育,岩石蚀变强烈。金地球化学特征表明,金主要富集在侏罗系中统兰旗组火山岩中。金的原生晕、次生晕异常特征和分布表明,破碎蚀变岩带就是金矿化蚀变带。通过野外地质调查已在三道盘—马家窝铺的安山岩和二长花岗岩中发现了5条金矿化带和29条金银矿脉。实践证明,在大青山地区进行金矿普查运用地球化学方法是有效的。  相似文献   

Transverse structures in the central part of the Red Sea and implications on early stages of oceanic accretion     

A. Y. Izzeldin 《Geophysical Journal International》1989,96(1):117-129

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Macrofaunal involvement in the sublittoral decay of kelp debris: the detritivore community and species interactions     

A.P. Bedford  P.G. Moore 《Estuarine, Coastal and Shelf Science》1984,18(1):97-111

The fauna associated with sea-bed accumulations of decomposing Laminaria saccharina has been studied by year-round SCUBA diving at two sites in the Clyde Sea area. Seasonal changes in density of 64 species are reported. In the autumn, large quantities of kelp are detached by storms. This weed carries with it to the sea bed a large part of its normal fauna. Additional species settle onto the weed from the plankton whilst others migrate onto it from the surrounding sea bed. Peak densities of associated species were recorded in autumn. Litter bag experiments in situ showed that, except during the summer, weed is lost from sea-bed accumulations at a faster rate when macrofaunal animals are excluded. The macrofauna therefore inhibits decomposition. The relative importance of interactive cropping by three macrodetritivores, Psammechinus miliaris (Echinodermata), Platynereis dumerilii (Polychaeta) and Gammarus locusta (Amphipoda) was studied by in situ containment of different species combinations. The presence of Gammarus with Psammechinus resulted in less weed being lost than when Psammechinus was isolated. This is because Gammarus selectively crops rotting weed, retarding frond disintegration by microbes. Platynereis retards microbial colonization of frond tissues ruptured during its feeding by repeated cropping of the same region. Weed would decompose very rapidly were it not for macrofaunal cropping. Macroalgal decay thus differs profoundly from that of vascular plants.  相似文献   

Pyroclastic Flow Hazard at Volcán Citlaltépetl     

Sheridan  Michael F.  Hubbard  Bernard  Carrasco-núñez  Gerardo  Siebe  Claus 《Natural Hazards》2004,33(2):209-221

Volcán Citlaltépetl (Pico de Orizaba) with an elevation of 5,675 m is the highest volcano in North America. Its most recent catastrophic events involved the production of pyroclastic flows that erupted approximately 4,000, 8,500, and 13,000 years ago. The distribution of mapped deposits from these eruptions gives an approximate guide to the extent of products from potential future eruptions. Because the topography of this volcano is constantly changing computer simulations were made on the present topography using three computer algorithms: energy cone, FLOW2D, and FLOW3D. The Heim Coefficient (), used as a code parameter for frictional sliding in all our algorithms, is the ratio of the assumed drop in elevation (H) divided by the lateral extent of the mapped deposits (L). The viscosity parameter for the FLOW2D and FLOW3D codes was adjusted so that the paths of the flows mimicked those inferred from the mapped deposits. We modeled two categories of pyroclastic flows modeled for the level I and level II events. Level I pyroclastic flows correspond to small but more frequent block-and-ash flows that remain on the main cone. Level II flows correspond to more widespread flows from catastrophic eruptions with an approximate 4,000-year repose period. We developed hazard maps from simulations based on a National Imagery and Mapping Agency (NIMA) DTED-1 DEM with a 90 m grid and a vertical accuracy of ±30 m. Because realistic visualization is an important aid to understanding the risks related to volcanic hazards we present the DEM as modeled by FLOW3D. The model shows that the pyroclastic flows extend for much greater distances to the east of the volcano summit where the topographic relief is nearly 4,300 m. This study was used to plot hazard zones for pyroclastic flows in the official hazard map that was published recently.  相似文献   

植被发育斜坡非饱和带大孔隙   总被引：4，自引：0，他引：4  

张家明  徐则民  裴银鸽 《山地学报》2012,30(4):439-449

在气候温湿的滑坡灾害易发区,根系通道、动物通道、干裂缝、管道及团聚体间的结构性孔隙等大孔隙普遍存在于斜坡非饱和带中.采用微观观察、化学分析和现场试验方法并结合相关学科的研究成果,分析大孔隙界定、大孔隙类型和主控因素、大孔隙三维空间结构及大孔隙时效稳定.不同测量方法的差异和大孔隙密度时空变异性是目前大孔隙定义缺乏统一性的原因.大孔隙尺寸不能作为唯一标准界定大孔隙,必须考虑其三维几何形态.多因素控制大孔隙的成因和类型,其中根系通道、裂缝和结构性孔隙对优先流有显著贡献.需从三维几何学和拓扑学方面进一步研究大孔隙三维结构.枯枝落叶层是大孔隙抵御环境因素扰动的重要屏障,但大孔隙域与周围基质域水量交换对大孔隙时效稳定是不利的.深入研究以上问题对植被发育斜坡优先流模型的改进和发展是重要的.  相似文献   

江苏省开发区土地集约利用的分层线性模型实证研究   总被引：5，自引：1，他引：4  

赵小风  黄贤金  钟太洋  彭佳雯  赵雲泰  吕晓 《地理研究》2012,31(9):1611-1620

本文构建了分层线性模型以揭示不同层次因素对工业用地集约利用的影响。研究表明,开发区土地集约度的差异有63.96%是开发区本身的差异造成的,有36.04%是区域之间的差异造成的;开发区成立年限、开发区入驻企业数量和开发区土地政策强度在区域之间存在明显的变异,开发区区位和开发区级别对开发区土地集约度的关系不依赖于区域环境的变化;区域工业产值和区域城市化率两个变量对开发区成立年限和开发区土地集约度的正向关联影响不显著;区域工业产值会强化开发区入驻企业数量和开发区土地集约度之间的正向关联,而区域城市化率则弱化了开发区入驻企业数量和开发区土地集约度之间的正向关联;开发区土地政策强度和开发区土地集约度之间的正向关系受区域工业产值的影响不大,而区域城市化率会强化开发区土地政策强度和开发区土地集约度之间的正向关系;区域层次变量解释了18.18%的开发区入驻企业数量与开发区土地集约度之间的相关,解释了11.27%的开发区土地政策强度与开发区土地集约度之间的相关。  相似文献   

Outside the boundary - Land use changes in the surroundings of urban nature reserves     

S. Borgström  S.A.O. CousinsR. Lindborg 《Applied geography (Sevenoaks, England)》2012,32(2):350-359

The importance of the landscape surrounding a protected area for sustaining its values is frequently discussed in conservation literature. Studies on the interactions of urbanisation and nature conservation at the global scale suggest that protected nature attracts urbanisation, and that this in turn might negatively impact the area. However, studies specifically addressing such land use dynamics at city scale are largely missing. In this study we examine the change in proportion of built up area in two zones (500 m and 1000 m) surrounding 15 urban nature reserves in southern Sweden. By using comprehensive maps from the last 50 years, we compared the zones to the overall urbanisation in the cities to reveal discrepancies in land use surrounding the nature reserves. We found that the amount of built up area in the buffer zones surrounding nature reserves followed the same trend as the corresponding cities and this relation was stable over time, although the positive relationship was not significant. The establishment of nature reserves had no detectable effect on surrounding land use, however two distinguished groups of reserves were identified with either more or less built up area in buffers zones compared to cities. These differences were related to specific local drivers such as land ownership, land use history and nature reserve location. In contrast to earlier studies at global scale, our study did not show that nature reserves attract urbanisation. Instead, we stress that the great variety of contextual factors at the city scale makes quantitative analysis of this kind extremely difficult. However, a general neglect from planning and nature conservation agencies to recognise nature reserves’ dependence on the surrounding landscape configuration could be detrimental to sustain their values in the long-term. Hence we suggest that zones surrounding nature-protected areas should be planned and managed according to local land use history and current landscape conditions to enable and enhance necessary cross-boundary interactions.  相似文献   

Mechanism of the Anlesi landslide in the Three Gorges Reservoir, China   总被引：5，自引：0，他引：5  

Wenxing Jian  Zhijian Wang  Kunlong Yin 《Engineering Geology》2009,108(1-2):86-95

Many gentle dip translational rock slides have taken place in the Three Gorges Reservoir, China. In order to study the mechanism of these translational rock slides, the authors use the Anlesi landslide as a typical case study to investigate in detail. Field investigations show that the slip zones of the Anlesi landslide were formed from a white mudstone in Jurassic red strata. X-ray diffraction and infrared ray analysis showed that the main mineral components of the slip zones are montmorillonite, illite, feldspar and quartz. Laboratory tests indicate that the slip zone soils are silty clay, of medium-swelling potential, the shear strength decreasing significantly as the slip zone attracts water and saturates.The main factors contributing to the Anlesi landslide are recent tectonic activity, incompetent beds, and intensive rainfall. Recent tectonic activity had caused shear failure along the incompetent beds, and joints within the sandstone. With the effect of intensive rainfall, water percolates to the incompetent beds along tectonic fissures, resulting in swelling of the soil material and high groundwater pressures within fissures in the strata. As a consequence, the Anlesi slope is prone to slide along these incompetent beds.Flac3D software was used to simulate the mechanism of the Anlesi landslide considering the rheological properties of soil and rock. The simulation results demonstrate that the stress, displacement and failure area changes with simulated creep time. The maximum displacement in the X direction reaches 7.59 m after 200-year simulated creep. Therefore, the mechanism of the Anlesi landslide can be illustrated considering the rheological properties of Jurassic red strata.  相似文献   

Deformation during exhumation of medium‐ and high‐grade metamorphic rocks in the Variscan chain in northern Sardinia (Italy)     

Rodolfo Carosi  Chiara Frassi  Chiara Montomoli 《Geological Journal》2009,44(3):280-305

The Anglona and SW Gallura regions represent key places to investigate the tectonic evolution of medium‐ and high‐grade metamorphic rocks cropping out in northern Sardinia (Italy). From south to north we distinguish two different metamorphic complexes recording similar deformation histories but different metamorphic evolution: the Medium Grade Metamorphic Complex (MGMC) and the High Grade Metamorphic Complex (HGMC). After the initial collisional stage (D1 deformation phase), both complexes were affected by three contractional deformational phases (D2, D3 and D4) followed by later extensional tectonics. The D2 deformation phase was the most significant event producing an important deformation partitioning that produced localized shearing and folding domains at the boundary between the two metamorphic complexes. We highlight the presence of two previously undocumented systems of shear belts with different kinematics but analogous orientation in the axial zone of Sardinia. They became active at the boundary between the MGMC and HGMC from the beginning of D2. They formed a transpressive regime responsible for the exhumation of the medium‐ and high‐grade metamorphic rocks, and overall represent a change from orthogonal to orogen‐parallel tectonic transport. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献