Swash-zone morphodynamics     

《Continental Shelf Research》2006,26(5):661-680

Hydrodynamic forcing with respect to sediment transport and morphologic change, paying particular attention to relevant swash asymmetries, is reviewed. The hydrodynamics are categorized into their individual effects: high- and low-frequency motions, bores and turbulence, in/exfiltration, shear stresses and friction coefficients. Individual effects are then related to their potential for driving or influencing sediment transport and morphological change. Additional concepts such as settling/scour lag and sediment advection that have largely been ignored are also discussed. A simple framework is presented for the morphological response of the beachface under swash zone hydrodynamic processes. The framework acknowledges that the beachface cannot be considered in isolation from the surf zone and that the two zones are strongly linked through feedback processes. The swash zone itself is also a morphodynamic system and morphological response occurs as a result of disequilibrium between the beachface gradient and asymmetries in the swash hydrodynamics. Any beachface morphological development in response to such equilibrium will have direct and indirect effects on swash hydrodynamics and sediment transport processes. It is concluded that the two issues requiring most urgent research attention with regards to swash zone sediment transport processes are the roles of sediment advection and longshore swash motion.  相似文献   

The effects of soil type and chemical treatment on nickel speciation in refinery enriched soils: A multi-technique investigation   总被引：1，自引：0，他引：1  

David H. McNear Jr.  Rufus L. Chaney 《Geochimica et cosmochimica acta》2007,71(9):2190-2208

Aerial deposition of Ni from a refinery in Port Colborne, Ontario, Canada has resulted in the enrichment of 29 km² of land with Ni concentrations exceeding the Canadian Ministry of the Environment’s remedial action level of 200 mg kg⁻¹. Several studies on these soils have shown that making the soils calcareous was effective at reducing chemically extractable Ni, as well as alleviating Ni phytotoxicity symptoms in vegetable crops grown in the vicinity of the refinery. Conversely, dolomitic limestone additions resulted in increased uptake of Ni in the Ni hyperaccumulator Alyssum murale ‘Kotodesh’, a plant whose use was proposed as a remediation strategy for this area. In this paper we use multiple techniques to directly assess the role soil type and lime treatments play in altering the speciation of Ni in the Welland loam and Quarry muck soils around the refinery and relate these findings to Ni mobility and bioavailability.Stirred-flow dissolution experiments using pH 4 HNO₃ showed that Ni release from the limed Quarry muck and Welland loam soils was reduced (∼0.10%) relative to the unlimed soils (∼2.0%). Electron microprobe analysis (EMPA) identified approximately spherical NiO and Ni metal particles, which are associated with no other metals, and range from 5 to 50 μm in diameter. Synchrotron micro-X-ray absorption fine structure and X-ray fluorescence spectroscopies showed that Ni and Al layered double hydroxide (Ni-Al LDH) phases were present in both the limed and unlimed mineral soils, with a tendency towards more stable (e.g., aged-LDH and phyllosilicate) Ni species in the limed soil, possibly aided by the solubilization of Si with increasing pH. In the muck soils, Ni-organic complexes (namely fulvic acid) dominated the speciation in both limed and unlimed soils.The results reported herein show that both soil type and treatment have a pronounced effect on the speciation of Ni in the soils surrounding the Port Colborne refinery. We provide the first evidence that Ni-Al LDH phases can form in anthropogenically enriched mineral field soils at circumneutral pH, and can lead to a reduction in Ni mobility. In the organic soils Ni is strongly complexed by soil organic matter; a property enhanced with liming. Interestingly, increased accumulation of Ni by A. murale grown in the limed muck and loam soils indicates that the plant may be capable of removing Ni from those fractions typically considered unavailable to most plants.  相似文献   

Quaternary depositional patterns and sea-level fluctuations, northeastern North Carolina     

Peter R. Parham  Stanley R. Riggs  David J. Mallinson 《Quaternary Research》2007,67(1):83-99

A detailed record of late Quaternary sea-level oscillations is preserved within the upper 45 m of deposits along an eight km transect across Croatan Sound, a drowned tributary of the Roanoke/Albemarle drainage system, northeastern North Carolina. Drill-hole and seismic data reveal nine relatively complete sequences filling an antecedent valley comprised of discontinuous middle and early Pleistocene deposits. On interfluves, lithologically similar marine deposits of different sequences occur stacked in vertical succession and separated by ravinement surfaces. Within the paleo-drainage, marine deposits are separated by fluvial and/or estuarine sediments deposited during periods of lowered sea level. Foraminiferal and molluscan fossil assemblages indicate that marine facies were deposited in a shallow-marine embayment with open connection to shelf waters. Each sequence modifies or truncates portions of the preceding sequence or sequences. Sequence boundaries are the product of a combination of fluvial, estuarine, and marine erosional processes. Stratigraphic and age analyses constrain the ages of sequences to late Marine Isotope Stage (MIS) 6 and younger (∼ 140 ka to present), indicating multiple sea-level oscillations during this interval. Elevations of highstand deposits associated with late MIS 5 and MIS 3 imply that sea level was either similar to present during those times, or that the region may have been influenced by glacio-isostatic uplift and subsidence.  相似文献   

Line-Driven Instability     

Achim Feldmeier  Stanley Owocki 《Astrophysics and Space Science》1998,260(1-2):113-122

Line-driven winds are subject to a strong radiation-hydrodynamic instability. We discuss the linear stability analysis and numerical simulations of the fully developed wind structure. The latter show sequences of strong reverse shocks, and two different families of clouds which mutually collide. Possible applications are the X-ray emission from O stars and the formation of dense clouds in broad absorption line quasars. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

The impact of drilling fluid and well cuttings on polychaete feeding guilds from the US northeastern continental shelf     

Don Maurer  Wayne Leathem  Charles Menzie 《Marine pollution bulletin》1981,12(10):342-347

The effect of recent drilling operations (fluid and well cuttings) on polychaete feeding guilds from the continental shelf off Atlantic City, New Jersey, was examined. Although there were some adverse effects on macrobenthos from 2160 metric tons of cuttings and mud solids discharged into the marine environment, the composition of polychaete feeding guilds remained essentially unchanged. This key trophic relationship between polychaetes and the changing environment due to the drilling operation was apparently uninterrupted. This relationship remains to be examined in other natural and perturbed habitats.  相似文献   

Salinity stress in harpacticoid copepods     

Colin M. Finney 《Estuaries and Coasts》1979,2(2):132-135

Three species of intertidal harpacticoid copepods,Tigriopus japonicus, Tachidius brevicornis andTisbe sp., were tested for their response to salinities ranging from 0‰ to 210‰. At 90‰Tigriopus became dormant, but could be reanimated if placed in 30‰ seawater within 18 hours.Tachidius became dormant at 60‰ but could also be revived if placed in 30‰ seawater.Tisbe died shortly after an exposure to seawater of 45‰. Death was brought about inTigriopus andTachidius by salinities of 150‰. Naupliar, copepodite, and adult stages ofTigriopus withstood the salinities equally well, while egg sacs could tolerate five times the length of exposure of these stages. The respiratory rate ofTigriopus was 3.76 (±1.32) μl 0₂ hr^?1 for active adults and 0.03 (±0.01) nl 0₂ hr^?1 mg dry wt^?1 for adults in the dormant state. The duration of dormancy, with successful revival, appears to be limited to the time before the loss of the vital water content of the tissues due to the high osmotic pressure. The ability to enter dormancy in times of stress may have high survival value to some intertidal copepods.  相似文献   

The Ivory Coast microtektite strewnfield: new data     

B.P. Glass  Peter A. Zwart 《Earth and Planetary Science Letters》1979,43(2):336-342

Ivory Coast microtektites have recently been found in three piston cores from the Atlantic Ocean. In two of these cores, the microtektites occur in a layer above the base of the Jaramillo geomagnetic event indicating that they fell approximately 0.95 m.y. ago. Major element compositions have been obtained for forty-one of the microtektites by electron microprobe and energy-dispersive X-ray analysis. The geographic location, stratigraphic age and major element compositions indicate that these microtektites are part of the Ivory Coast tektite strewnfield. Present data suggest that the Ivory Coast strewnfield may cover an area of about 4.5 million square kilometers and contain about 20 million metric tons of microtektites.  相似文献   

Tests for size and shape dependency in deep-sea mixing     

W.F. Ruddiman  G.A. Jones  T.-H. Peng  L.K. Glover  B.P. Glass  P.J. Liebertz 《Sedimentary Geology》1980,25(4):257-276

Bioturbation is generally not a strongly size-dependent or shape-dependent process in deep-sea sediments. Different sizes of ash (11–250 μm) deposited during a single eruption are usually mixed about equally, although in a few cores we found minor tendencies toward greater mixing of finer ash. Platey volcanic ash and spherical microtektites initially deposited within a few centimeters of each other in the sediment column are mixed with roughly comparable intensity. Radiocarbon dating of three sizes of CaCO₃ near the top of one box core produced ages within the analytical error; this also suggests no size dependency in the mixing process. Another core showed age differences opposite in sense to those that would be predicted if the finer fractions were more intensely mixed than the coarser fractions.The sizes examined (11–250 μm) encompass most of the sedimentary components used in paleoclimatic analyses of deep-sea cores. From these findings, we infer that significant artificial lead/lag offsets in paleoclimatic signals will not be created by size-selective or shape-selective mixing. Mixing models calibrated on one sediment size fraction should be generally applicable to other sizes and kinds of material.  相似文献   

Model Simulations on the Variability of Particulate MSA to Non-Sea-Salt Sulfate Ratio in the Marine Environment     

Veli-Matti Kerminen  Risto E. Hillamo  Anthony S. Wexler 《Journal of Atmospheric Chemistry》1998,30(3):345-370

A box model was constructed to investigate connections between the particulate MSA to non-sea-salt sulfate ratio, R, and DMS chemistry in a clean marine boundary layer. The simulations demonstrated that R varies widely with particle size, which must be taken into account when interpreting field measurements or comparing them with each other. In addition to DMS gas-phase chemistry, R in the submicron size range was shown to be sensitive to the factors dictating sulfate production via cloud processing, to the removal of SO₂ from the boundary layer by dry deposition and sea-salt oxidation, to the entrainment of SO₂ from the free troposphere, to the relative concentration of sub- and supermicron particles, and to meteorology. Three potential explanations for the increase of R toward high-latitudes during the summer were found: larger MSA yields from DMS oxidation at high latitudes, larger DMSO yields from DMS oxidation followed by the conversion of DMSO to MSA at high latitudes, or lower ambient H₂O₂ concentrations at high latitudes leading to less efficient sulfate production in clouds. Possible reasons for the large seasonal amplitude of R at mid and high latitudes include seasonal changes in the partitioning of DMS oxidation to the OH and NO₃ initiated pathways, seasonal changes in the concentration of species participating the DMS-OH reaction pathway, or the existence of a SO₂ source other than DMS oxidation in the marine boundary layer. Even small anthropogenic perturbations were shown to have a potential to alter the MSA to non-sea-salt sulfate ratio.  相似文献   

Ground Water Contaminant Source and Transport Parameter Identification by Correlation Coefficient Optimization   总被引：1，自引：0，他引：1  

P. Sidauruk  A.H-D. Cheng  D. Ouazar 《Ground water》1998,36(2):208-214

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