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971.
Gabriele La Mesa Andrea Molinari Silvia Gambaccini Leonardo Tunesi 《Marine Ecology》2011,32(1):104-114
Variability of fish assemblages across habitat structures can depend on spatial scales. A hierarchical sampling design was used to assess the spatial variability of temperate fish assemblages in different habitats and at multiple scales. Underwater visual censuses were carried out along the coasts of Elba Island (NW Mediterranean) on Posidonia oceanica beds, rocky algal reefs and sandy habitat at three spatial scales, namely tens of metres (individual replicates), hundreds of metres (sites) and tens of kilometres (locations). At the assemblage level, there was a clear relationship between fish and habitat type and the observed habitat‐related differences were largely dependent on species identity. Fish assemblages on P. oceanica beds and rocky reefs shared a high number of species, whereas overlap with sandy assemblages was negligible. Multivariate analyses revealed significant differences in fish assemblages among habitats, although there was also a significant habitat × site interaction. These differences relied mainly upon assemblage composition and species richness. Assemblages on rocky reefs and P. oceanica meadows usually harboured a higher number of species and individuals compared with sandy assemblages. Nevertheless, the patterns of habitat‐related differences in species richness and, especially, in the total number of fish, changed significantly from site to site. Eight species showed significant differences over habitats, but they were not consistent due to the interaction of habitat with site. Predictability of fish at both assemblage and population levels decreased with the scale of observation, and the spatial pattern of fish observed at the smallest scale was likely dependent on factors other than habitat type. 相似文献
972.
This paper presents two comparisons or tests for a Lagrangian model of zooplankton dispersion:numerical schemes and time steps.Firstly,we compared three numerical schemes using idealized circulations.Results show that the precisions of the advanced Adams-Bashfold-Moulton(ABM) method and the Runge-Kutta(RK) method were in the same order and both were much higher than that of the Euler method.Furthermore,the advanced ABM method is more efficient than the RK method in computational memory requirements and time consumption.We therefore chose the advanced ABM method as the Lagrangian particle-tracking algorithm.Secondly,we performed a sensitivity test for time steps,using outputs of the hydrodynamic model,Symphonie.Results show that the time step choices depend on the fluid response time that is related to the spatial resolution of velocity fields.The method introduced by Oliveira et al.in 2002 is suitable for choosing time steps of Lagrangian particle-tracking models,at least when only considering advection. 相似文献
973.
974.
Spectral mapping of rock weathering degrees on granite using hyperspectral DAIS 7915 spectrometer data 总被引:1,自引:0,他引:1
Asuncin Riaza Peter Strobl Ulrich Beisl Andrea Hausold Andreas Müller 《International Journal of Applied Earth Observation and Geoinformation》2001,3(4):345
Rocks are weathered by chemical and physical processes into a mixture of loose material that produces soil. Mineralogical and textural changes are involved, which can be detected by imagery through digital image processing based on rock spectral behaviour as recorded by ground and laboratory spectrometers. Different densities of vegetation cover can be mapped qualifying further evolution of the area in terms of erosion, transport and sedimentation. Hyperspectral imagery helps to map the weathering front and different degrees of weathering on granite rock through mineralogical and textural associations related to the geomorphological processes in the area on various granitic facies. Abundance of feldspar and porfidic texture on the fresh rock are the critical parameters conditioning intensity of weathering in the area. Maps spectrally elaborated gather information on lithologies, mineralogical changes produced by geomorphological processes associated to landforms, topography and climate. Such maps contribute to estimating the spatial controls of erosion, suggesting soil particle size distribution, soil aggregation, soil depth, and consequently, helping to elaborate soil loss and soil conservation maps. 相似文献
975.
Andrea Tribe 《地球表面变化过程与地形》1992,17(5):437-454
Valley recognition methods given in the literature fail to produce valley networks suitable for locating valley heads for one of two main reasons: (a) they are based on the concept of [higher than] or (b) they are based on contributing area thresholds. In this paper a new method for recognizing valley bottoms is presented. This is based on two improvements of Carroll's (1983) method, and produces a network that reflects the topography well. The network is used to locate valley heads. Once located, the valley heads are delineated using criteria suggested by geomorphologists and hydrologists. The resultant valley heads are generally well recognized although two problems are evident: (a) there are a number of commission errors; and (b) the valley heads recognized by the method are too small. 相似文献
976.
977.
978.
Fragmented water governance arrangements complicate sustainable water management in the western U.S. where local water management organizations (LWMOs), including municipalities and irrigation groups, directly manage water conveyance systems. LWMOs make critical decisions that determine water delivery and management, but have traditionally not collaborated with one another. Our research examines the ways in which LWMOs are increasingly interconnected within a context of widespread urbanization. We draw on three years of qualitative research on LWMOs in Utah, including interviews and in-depth qualitative case studies, to analyze the conditions under which collaborations between LWMOs emerge, or have not yet occurred. Our findings indicate that historically fragmented LWMOs are engaging in cooperative efforts based on their extensive water infrastructure connections. LWMOs did not transform cooperative efforts into collaborations unless such a collaboration protected internal interests. LWMOs engaged in collaborations primarily to reduce their liabilities in the instance of infrastructure failure. 相似文献
979.
Geological structure and kinematics of normal faults in the Otway Basin,Australia, based on quantitative analysis of 3‐D seismic reflection data 下载免费PDF全文
Jennifer Ziesch Chiara M. Aruffo David C. Tanner Thies Beilecke Tess Dance Andreas Henk Bastian Weber Eric Tenthorey Andrea Lippmann Charlotte M. Krawczyk 《Basin Research》2017,29(2):129-148
The Otway Basin in the south of Victoria, Australia underwent three phases of deformation during breakup of the southern Australian margin. We assess the geometry and kinematics of faulting in the basin by analysing a 3‐D reflection seismic volume. Eight stratigraphic horizons and 24 SW‐dipping normal faults as well as subordinate antithetic faults were interpreted. This resulted in a high‐resolution geological 3‐D model (ca. 8 km × 7 km × 4 km depth) that we present as a supplementary 3‐D PDF (Data S1). We identified hard‐ and soft‐linking fault connections over the entire area, such as antithetic faults and relay ramps, respectively. Most major faults were continuously active from Early to Late Cretaceous, with two faults in the northern part of the study area active until at least the Oligocene. Allan maps of faults show tectonic activity continuously waned over this time period. Isopach maps of stratigraphic volumes quantify the amount of syn‐sedimentary movement that is characteristic of passive margins, such as the Otway Basin. We show that the faults possess strong corrugations (with amplitudes above the seismic resolution), which we illustrated by novel techniques, such as cylindricity and curvature. We argue that the corrugations are produced by sutures between sub‐vertical fault segments and this morphology was maintained during fault growth. Thus, they can be used to indicate the kinematics vector of the fault movement. This evidences, together with left‐stepping relay ramps, that 40% of the faults had a small component (up to 25°) of dextral oblique slip as well as normal (dip‐slip) movement. 相似文献
980.
Andrea C. Riao Juan C. Reyes Luis E. Yamín Jacobo Bielak Ricardo Taborda Doriam Restrepo 《地震工程与结构动力学》2021,50(1):155-176
Bogotá, the capital city of Colombia, is mostly located on a lacustrine soil deposit surrounded by hills in a central plateau of the eastern cordillera of the Colombian Andes. This highly populated urban area is exposed to a significant seismic hazard from local and regional fault systems. In addition, the potential ground motion amplification during earthquakes due to the presence of soft soil deposits, along with the effects of the surface and subsurface topography, can strongly influence the seismic hazard and consequently the seismic risk to the city. This study aims to develop a physics‐based framework to generate synthetic ground records that can help better understand the seismic response of the basin and other amplification effects during strong earthquake shaking in the region, and to incorporate these effects into the estimation of seismic risk. To this end, a set of simulations were first conducted on Hercules, the wave propagation octree‐based finite element simulator developed by the Quake Group at Carnegie Mellon University, to identify the impacts of hypothetical strong earthquakes scenarios. Then, the results from these simulations were integrated with the exposure and vulnerability information previously developed for the main building constructions in the city to assess the seismic risk in the region under different conditions of analysis. Results from this more detailed model are compared with previously published results from simplified models. Sensitivity analyses help identify critical aspects that should be considered in the future to improve the seismic risk assessment of infrastructure. 相似文献