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A 15-month study of zooplankton ingestion by farmed mussels (Mytilus edulis) in Bantry Bay, Southwest Ireland 总被引：4，自引：1，他引：4
There is a growing body of evidence to suggest that bivalve molluscs routinely ingest zooplankton. To elucidate further these observations, a 15-month study of zooplankton ingestion by farmed mussels was conducted using mussel long-lines in Bantry Bay, Ireland. Stomach content analysis of the mussels showed that there was evidence of zooplankton ingestion throughout the sampling period, but that highest mean numbers of zooplankters were ingested by mussels in the spring and summer months. Various zooplankton species were present in mussel stomachs. Harpacticoid copepods were found more often in stomach contents than calanoid copepods, probably due to their proximity to the bivalves' inhalent siphons. Barnacle cyprids featured in large numbers in stomach contents, but only for a period of 3 months which broadly corresponded with their pelagic phase. Sizes of ingested zooplankton ranged from 126 μm to 6 mm, but more of the smaller zooplankters (e.g. crustacean nauplii) were ingested. When lengths of ingested copepods were compared with those found in plankton net samples, it was found that the net-sampled copepods were significantly larger than those found in mussel stomachs, suggesting that mussels select for smaller categories within the zooplankton available to them. Soft bodied zooplankton was rarely found in mussel stomachs but their absence may be due to rapid digestion or they may have been destroyed in the preservation process. Ingestion of zooplankton by bivalves is discussed in the context of the impacts mussel farms have on resident zooplankton populations. 相似文献
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Javier Caraveo‐Patiño Yiqun Wang Luis A. Soto Kebreab Ghebremeskel Catherine Lehane Michael A. Crawford 《Marine Ecology》2009,30(4):437-447
The radiation of the mammalian land species that became the baleen whales happened about 27–34 Mya. Mammals require omega 6 fatty acids for reproduction. With this long exposure to the omega 3‐rich marine food chain, the Gray whale (Eschrichtius robustus) might be expected to have lost its requirement for omega 6 fatty acids. We report an unexpectedly high content of omega 6 arachidonic acid (ArA) in the Gray whale liver and muscle lipids. This whale migrates 10,000 km from the cold polar, omega 3 oil‐rich food chain to that of the breeding lagoons of the tropical waters. The food web of tropical waters is a source of omega 6 fatty acids, which are hardly present in the cold polar food web. We suggest the reason for this longest of migrations from cold to warm waters is to meet the requirement for omega 6 fatty acids for mammalian reproduction and brain growth. This extreme conservation of omega 6 fatty acids in Gray whale biology has critical implications for mammalian biology and especially for whale conservation. 相似文献
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A range of geotechnical applications require measurement of shear strength at effective stresses below those commonly employed in conventional shear testing devices. Of these devices, the shear box testing apparatus is the oldest and remains the most popular for determining the shear strength characteristics of granular materials. The apparatus is, however, generally considered inadequate when testing at low normal stresses because second order frictional effects become significant at these stresses and lead to large errors in the inferred shear and normal loads on the plane of shearing. A number of new, more elaborate, devices have been employed to measure the frictional characteristics of clays at low stress levels (e.g. the Cam-shear and tilt table tests), but these require a high level of expertise to use correctly, and are not readily available in laboratories around the world. In this paper, statics principles are employed to develop a simple means of correcting for the mechanical friction in a shear box. The applicability of the corrections proposed is examined using data obtained in two different shear boxes for three separate sands over a large range of normal stresses. It is demonstrated that these corrections can be used to determine the peak and critical friction angles of granular materials at low stress levels in a shear box apparatus. 相似文献
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为了揭示黏土中静压沉桩的宏观力学特性,采用西澳大学的梁式离心机压桩系统,通过在双层高岭黏土中进行一系列1g重力场情况下的T-bar触探测试试验、静压沉桩试验、桩拉伸试验和压缩试验,对比分析了T-bar分别在均质软质黏土和双层黏土中随贯入深度变化测得的不排水剪切强度的特性;研究了桩体在贯入过程中沉桩阻力、桩端阻力以及桩侧摩阻力的发展规律;并对桩身径向总应力在沉桩过程中的变化规律进行了探讨;此外,还揭示了不同桩型沉桩终压力与桩承载力之间的关系。结果表明：在黏土中沉桩时,桩侧摩阻力在整个沉桩阻力中发挥主要的作用;对于同一土层而言,当桩超过土层分界面以下2D（D为桩径）范围后,桩端阻力并不受相邻土层性质的影响;随着压桩后时间的推移,桩侧摩阻力对承载力的时效影响较桩端阻力大。 相似文献
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The paper presents observations made in CPTs performed under controlled laboratory conditions in normally consolidated clay–sand mixtures at various penetrations. These results are combined with data from field tests to develop a relationship for CPT data in young normally consolidated soils that combines end resistance and friction sleeve data. This relationship can be used to assist assessment of soil type and CPT parameters for un-aged normally consolidated soils as well as allowing judgements to be made in relation to likely levels of under-consolidation, structure and over-consolidation in any given soil deposit.
相似文献6.
The Strain Path Method (SPM) is an approximate framework for simulating the disturbance caused by piles or penetrometers in soil. The key conceptual assumption of the SPM is that the deformation and strain fields caused during these penetration processes are strongly kinematically constrained (especially during undrained penetration of clays) and can be estimated independently from the actual constitutive properties of the surrounding soil. Previous applications of SPM have estimated strain fields for a variety of penetrometer geometries using velocity fields of ideal inviscid fluids. This paper refines the strain field for penetrometers with 60° conical tips using numerically computed velocity fields in viscous fluids with a variety of boundary conditions imposed on the penetrometer shaft. Following a parametric study, a set of flow conditions is selected which provides a best fit between computed soil deformations and physical displacement measurements made in three separate experiments. The approach is simple and rapid and, while highlighting some of the inaccuracies associated with the existing SPM solution, may also be used for comparative purposes to assist the development of other approaches to the deep penetration problem. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
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Following automation of lighthouses around the coastline of Ireland, reports of accelerated deterioration of interior granite stonework have increased significantly with an associated deterioration in the historic structure and rise in related maintenance costs. Decay of granite stonework primarily occurs through granular disintegration with the effective grusification of granite surfaces. A decay gradient exists within the towers whereby the condition of granite in the lower levels is much worse than elsewhere. The lower tower levels are also regions with highest relative humidity values and greatest salt concentrations. Data indicate that post-automation decay may have been triggered by a change in micro-environmental conditions within the towers associated with increased episodes of condensation on stone surfaces. This in turn appears to have facilitated deposition and accumulation of hygroscopic salts (e.g. NaCl) giving rise to widespread evidence of deliquescence in the lower tower levels. Evidence indicates that the main factors contributing to accelerated deterioration of interior granite stonework are changes in micro-environmental conditions, salt weathering, chemical weathering through the corrosive effect of strongly alkaline conditions on alumino-silicate minerals within the granite and finally, the mica-rich characteristics of the granite itself which increases its structural and chemical susceptibility to subaerial weathering processes by creating points of weakness within the granite. This case study demonstrates how seemingly minor changes in micro-environmental conditions can unintentionally trigger the rapid and extensive deterioration of a previously stable rock type and threaten the long-term future of nationally iconic operational historic structures. 相似文献
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The paper compares the soil structure interaction effects predicted using a finite element (FE) program with those observed during a bored tunnel project conducted in Perth, Western Australia. Both the measured data and geotechnical characteristics of the subsoils are described before presenting comparisons between measurements and analyses. The measured settlement data for two buildings are seen to be dependent on the structural stiffness. It is shown that, in keeping with observations by others, FE predictions of tunnelling induced movement patterns are not predicted to a satisfactory level of accuracy. However, it is also shown that FE analyses of the type described may be employed to provide qualitative information on soil-structure interaction effects. 相似文献
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Acta Geotechnica - Large diameter, short monopiles are the preferred foundation type for offshore wind turbines. These piles demonstrate a rigid response with significant rotation of the pile base... 相似文献
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Bryan A. McCabe Brian G. Sexton Barry M. Lehane 《Geotechnical and Geological Engineering》2013,31(1):183-197
Although finite element packages facilitating coupled consolidation analyses are increasingly in use, many practitioners still favour linear uncoupled analysis out of familiarity with the use of coefficients of consolidation. However, coefficients of consolidation measured by any single means tend to exhibit significant variation, with mean results from different laboratory and field tests also varying widely, leaving uncertainty over the correct values to apply to field problems. In this paper, a finite difference approach is used to back-calculate operational coefficients of consolidation from pore pressure measurements pertinent to a pile group driven in clay–silt. The research shows that this method is capable of successfully capturing the process of pore pressure dissipation, and that the operational coefficient of consolidation around the pile group is higher than that derived from piezocone dissipation tests in the same material. 相似文献
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