Does the permeability of gravel river beds affect near‐bed hydrodynamics?          下载免费PDF全文

James R. Cooper  Annie Ockleford  Stephen P. Rice  D. Mark Powell 《地球表面变化过程与地形》2018,43(5):943-955

The permeability of river beds is an important control on hyporheic flow and the movement of fine sediment and solutes into and out of the bed. However, relatively little is known about the effect of bed permeability on overlying near‐bed flow dynamics, and thus on fluid advection at the sediment–water interface. This study provides the first quantification of this effect for water‐worked gravel beds. Laboratory experiments in a recirculating flume revealed that flows over permeable beds exhibit fundamental differences compared with flows over impermeable beds of the same topography. The turbulence over permeable beds is less intense, more organised and more efficient at momentum transfer because eddies are more coherent. Furthermore, turbulent kinetic energy is lower, meaning that less energy is extracted from the mean flow by this turbulence. Consequently, the double‐averaged velocity is higher and the bulk flow resistance is lower over permeable beds, and there is a difference in how momentum is conveyed from the overlying flow to the bed surface. The main implications of these results are three‐fold. First, local pressure gradients, and therefore rates of material transport, across the sediment–water interface are likely to differ between impermeable and permeable beds. Second, near‐bed and hyporheic flows are unlikely to be adequately predicted by numerical models that represent the bed as an impermeable boundary. Third, more sophisticated flow resistance models are required for coarse‐grained rivers that consider not only the bed surface but also the underlying permeable structure. Overall, our results suggest that the effects of bed permeability have critical implications for hyporheic exchange, fluvial sediment dynamics and benthic habitat availability. © 2017 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd.  相似文献   

On the map: American cartography in 2015     

Dierdre Bevington-Attardi  Matthew Rice 《制图学和地理信息科学》2015,42(4):1-5

  相似文献   

Channel-tolerant FH-MFSK acoustic signaling for underseacommunications and networks     

Green  M.D. Rice  J.A. 《Oceanic Engineering, IEEE Journal of》2000,25(1):28-39

  相似文献   

Introducing a hybrid radiative transfer method for smoothed particle hydrodynamics     

Duncan Forgan  Ken Rice  Dimitris Stamatellos  Anthony Whitworth 《Monthly notices of the Royal Astronomical Society》2009,394(2):882-891

A new means of incorporating radiative transfer into smoothed particle hydrodynamics (SPH) is introduced, which builds on the success of two previous methods – the polytropic cooling approximation as devised by Stamatellos et al. and flux-limited diffusion. This hybrid method preserves the strengths of its individual components, while removing the need for atmosphere matching or other boundary conditions to marry optically thick and optically thin regions. The code uses a non-trivial equation of state to calculate temperatures and opacities of SPH particles, which captures the effects of H₂ dissociation, H⁰ ionization, He⁰ and He⁺ ionization, ice evaporation, dust sublimation, molecular absorption, bound-free and free–free transitions and electron scattering. The method is tested in several scenarios, including (i) the evolution of a  0.07 M_⊙  protoplanetary disc surrounding a  0.5 M_⊙  star; (ii) the collapse of a  1 M_⊙  protostellar cloud and (iii) the thermal relaxation of temperature fluctuations in a static homogeneous sphere.  相似文献   

Metavolcanic host rocks,mineralization, and gossans of the Shaib al Tair and Rabathan volcanogenic massive sulphide deposits of the Wadi Bidah Mineral District,Saudi Arabia     

John C. Volesky  Robert J. Stern  Jan M. Peter  Daniel Layton-Matthews  Sarah Rice 《International Geology Review》2017,59(16):1975-2002

The Wadi Bidah Mineral District of Saudi Arabia contains more than 16 small outcropping stratabound volcanogenic Cu–Zn–(Pb) ± Au-bearing massive sulphide deposits and associated zones of hydrothermal alteration. Here, we use major and trace element analyses of massive sulphides, gossans, and hydrothermally altered and least altered metamorphosed host rock (schist) from two of the deposits (Shaib al Tair and Rabathan) to interpret the geochemical and petrological evolution of the host rocks and gossanization of the mineralization. Tectonic interpretations utilize high-field-strength elements, including the rare earth elements (REE), because they are relatively immobile during hydrothermal alteration, low-grade metamorphism, and supergene weathering and therefore are useful in constraining the source, composition, and physicochemical parameters of the primary igneous rocks, the mineralizing hydrothermal fluid and subsequent supergene weathering processes. Positive Eu anomalies in some of the massive sulphide samples are consistent with a high temperature (>250°C) hydrothermal origin, consistent with the Cu contents (up to 2 wt.%) of the massive sulphides. The REE profiles of the gossans are topologically similar to nearby hydrothermally altered felsic schists (light REE (LREE)-enriched to concave-up REE profiles, with or without positive Eu anomalies) suggesting that the REE experienced little fractionation during metamorphism or supergene weathering. Hydrothermally altered rocks (now schists) close to the massive sulphide deposits have high base metals and Ba contents and have concave-up REE patterns, in contrast to the least altered host rocks, consistent with greater mobility of the middle REE compared to the light and heavy REE during hydrothermal alteration. The gossans are interpreted to represent relict massive sulphides that have undergone supergene weathering; ‘chert’ beds within these massive sulphide deposits may be leached wall-rock gossans that experienced silicification and Pb–Ba–Fe enrichment from acidic groundwaters generated during gossan formation.  相似文献   

Mass‐balance modeling of mineral weathering rates and CO2 consumption in the forested,metabasaltic Hauver Branch watershed,Catoctin Mountain,Maryland, USA     

Jason R. Price  Karen C. Rice  David W. Szymanski 《地球表面变化过程与地形》2013,38(8):859-875

Mineral weathering rates and a forest macronutrient uptake stoichiometry were determined for the forested, metabasaltic Hauver Branch watershed in north‐central Maryland, USA. Previous studies of Hauver Branch have had an insufficient number of analytes to permit determination of rates of all the minerals involved in chemical weathering, including biomass. More equations in the mass‐balance matrix were added using existing mineralogic information. The stoichiometry of a deciduous biomass term was determined using multi‐year weekly to biweekly stream‐water chemistry for a nearby watershed, which drains relatively unreactive quartzite bedrock. At Hauver Branch, calcite hosts ~38 mol% of the calcium ion (Ca²⁺) contained in weathering minerals, but its weathering provides ~90% of the stream water Ca²⁺. This occurs in a landscape with a regolith residence time of more than several Ka (kiloannum). Previous studies indicate that such old regolith does not typically contain dissolving calcite that affects stream Ca²⁺/Na⁺ ratios. The relatively high calcite dissolution rate likely reflects dissolution of calcite in fractures of the deep critical zone. Of the carbon dioxide (CO₂) consumed by mineral weathering, calcite is responsible for approximately 27%, with the silicate weathering consumption rate far exceeding that of the global average. The chemical weathering of mafic terrains in decaying orogens thus may be capable of influencing global geochemical cycles, and therefore, climate, on geological timescales. Based on carbon‐balance calculations, atmospheric‐derived sulfuric acid is responsible for approximately 22% of the mineral weathering occurring in the watershed. Our results suggest that rising air temperatures, driven by global warming and resulting in higher precipitation, will cause the rate of chemical weathering in the Hauver Branch watershed to increase until a threshold temperature is reached. Beyond the threshold temperature, increased recharge would produce a shallower groundwater table and reduced chemical weathering rates. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

Testing the locality of transport in self-gravitating accretion discs – II. The massive disc case     

G. Lodato  W. K. M. Rice 《Monthly notices of the Royal Astronomical Society》2005,358(4):1489-1500

We present hydrogen emission-line profile models of magnetospheric accretion on to classical T Tauri stars. The models are computed under the Sobolev approximation using the three-dimensional Monte Carlo radiative-transfer code torus . We have calculated four illustrative models in which the accretion flows are confined to azimuthal curtains – a geometry predicted by magnetohydrodynamic simulations. Properties of the line profile variability of our models are discussed, with reference to dynamic spectra and cross-correlation images. We find that some gross characteristics of the observed line profile variability are reproduced by our models, although in general the level of variability predicted is larger than that observed. We conclude that this excessive variability probably excludes dynamical simulations that predict accretion flows with low degrees of axisymmetry.  相似文献   

Do explicit criteria help in selecting indicators for ecosystem-based fisheries management?   总被引：1，自引：1，他引：1  

Rochet  Marie-Joelle; Rice  Jake C. 《ICES Journal of Marine Science》2005,62(3):528-539

  相似文献   

Toxic contributions of specific drilling mud components to larval shrimp and crabs     

Mark G. Carls  Stanley D. Rice 《Marine environmental research》1984,12(1):45-62

We investigated the toxicities of six drilling muds, toxicities of mud fractions (supernatants and suspensions) and the toxicities of common mud components—barite and bentonite (particulates) and ferrochrome lignosulfonate (soluble)—to the stage I larvae of six species of shrimp and crab. The drilling muds we tested were not very toxic to these larvae: LC₅₀'s for supernatants ranged from 0·6 to 82% (vol/vol). Shrimp larvae were slightly more sensitive than crab larvae.Drilling muds were not rapidly toxic, in contrast to toxicants such as the water-soluble fractions of oil. Supernatants, prepared by centrifuging whole muds, were mildly toxic. Suspensions were more toxic than supernatants and toxicity was greatest when particulates remained suspended: for example, used Cook Inlet mud suspensions were about seven times more toxic than supernatants. The toxicity of used Cook Inlet mud was therefore primarily due to suspended solids (88%) rather than chemical toxicity: ferrochrome lignosulfonate was relatively toxic alone, but accounted for only about 6% of the toxicity of used Cook Inlet mud suspensions. Contributions of particulates to mud toxicities varied considerably. Barite and bentonite were not very toxic when tested alone. The toxicity of one mud was caused by its high alkalinity.  相似文献   

Mycobacteria, but not mercury, induces metallothionein (MT) protein in striped bass, Morone saxitilis, phagocytes, while both stimuli induce MT in channel catfish, Ictalurus punctatus, phagocytes     

Regala RP  Rice CD 《Marine environmental research》2004,58(2-5):719-723

Recent advances in molecular immunology indicate that the expression of inducible pro-inflammatory proteins is increased in vertebrates in response to both infectious disease agents and various xenobiotics. For example, iNOS, COX-2, and CYP1A are induced by both inflammation and AhR ligands. Moreover, the expression of these proteins in response to stimuli varies among individuals within populations. Little is known of the differences among fish in the inducibility of proinflammatory proteins in response to both infectious agents and xenobiotics. Through random screening of a striped bass, Morone saxitilis, peritoneal macrophage cDNA library, a full length metallothionein (MT) gene was cloned and sequenced. MT is a low-molecular weight (6-8 kDa), cysteine-rich metal binding protein. Metals are required by pathogenic bacteria for growth, and by the host defense system by serving as a catalyst for the generation of reactive oxygen intermediates (ROIs) by phagocytes. A recombinant striped bass MT (rMT) was expressed and purified, then used to generate a specific mAb (MT-16). MT protein expression was followed in freshly isolated striped bass and channel catfish, Ictalurus punctatus, phagocytes after in vitro exposure to the naturally occurring intracellular pathogen Mycobacteria fortuitum or to 0.1 and 1 microM mercury (Hg), as HgCl(2). MT expression was increased by 24 h in both channel catfish and striped bass phagocytes as a result of exposure to M. fortuitum cells. On the other hand, MT was induced by Hg in channel catfish cells, but not those of striped bass. These results indicate that metal homeostasis in phagocytes is different between catfish and striped bass. In addition, these data suggest that care should be taken to distinguish between inflammation-induced vs. metal-induced MT when using MT expression as a biomarker of metal exposure.  相似文献