Channelled erosion through a marine dump site of dredge spoils at the mouth of the Puyallup River, Washington State, USA     

Neil C. Mitchell   《Marine Geology》2005,220(1-4):131-151

Channels are relatively common on river-mouth deltas, but the process by which they arise from river sediment discharge is unclear because they can potentially be explained either by negatively buoyant (hyperpycnal) flows produced directly from the river outflow or by flows generated by repeated failure and mobilisation of sediment rapidly deposited at the delta front. Channels eroded through a dump site of dredge spoils are described here from multibeam and older sonar data collected in Commencement Bay, at the mouth of the Puyallup River. Shallow channels on the seaward upper surface of the dump site, away from any flows that could have been produced by delta front failures, suggest that at least some hyperpycnal flows were produced directly from the positively buoyant river outflow up to 200 m from the edge of the river mouth platform. The form of channel bed erosion is revealed by the longitudinal shape of the main eroded channel compared with the adjacent dump site profile. It suggests that the channel evolved by its steep front retreating, rather than by simple vertical entrenchment or diffusive-like evolution of the profile, a geometry interpreted as evidence that repeated failure of the bed occurred in response to shear stress imposed by bottom-travelling flows. Model calculations based on shear strengths back-calculated from the geometry of channel wall failures suggest that, if the main channel were eroded solely by hyperpycnal flows, their generation was remarkably efficient in order to create flows vigorous enough to cause channel bed failure. Besides the sediment concentration and discharge characteristics that have been considered to dictate the ability of rivers to produce hyperpycnal flows, it is suggested that the timing of floods with respect to the tidal cycle should also be important because extreme low tides may be needed to ensure that coarse sediment is transferred vigorously to the edge of river mouth platforms.  相似文献   

Probing molecular-level transformations of dissolved organic matter: insights on photochemical degradation and protozoan modification of DOM from electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry     

Elizabeth B. Kujawinski  Rossana Del Vecchio  Neil V. Blough  Geoffrey C. Klein  Alan G. Marshall   《Marine Chemistry》2004,92(1-4):23

Molecular-level characterization of natural organic matter (NOM) has been elusive due to the inherent complexity of natural organic mixtures and to the fact that individual components are often polar and macromolecular. Electrospray ionization (ESI) is a “soft” ionization technique that ionizes polar compounds from aqueous solution prior to injection into a mass spectrometer. The highest resolution and mass accuracy of compounds within NOM have been achieved when ESI is combined with an ultrahigh-resolution mass spectrometer such as the Fourier transform ion cyclotron resonance mass spectrometer (FT-ICR MS). With this technique, individual molecules within a variety of natural organic mixtures can be detected and their elemental composition can be determined. At low mass-to-charge (m/z) ratio, the resolution is high enough to assign exact molecular formulas allowing specific components of these mixtures to be identified. In addition to molecular identification, we can now use ESI FT-ICR MS to examine molecular-level changes in different organic mixtures as a function of relevant geo-processes, such as microbial alterations and photochemistry. Here we present the results from the application of ESI FT-ICR MS to two geochemical questions: (1) the effect of photoirradiation on the molecular composition of fulvic acids and (2) the role of protozoan grazers in the modification of DOM in aquatic systems.  相似文献   

Risk-based decision-making for drilling waste discharges using a fuzzy synthetic evaluation technique   总被引：5，自引：0，他引：5  

Rehan Sadiq  Tahir Husain  Neil Bose 《Ocean Engineering》2004,31(16):1929-1953

Offshore petroleum drilling wastes contain toxic substances that are potentially harmful to the marine ecosystem. Despite environmentally benign characteristics, wastes associated with synthetic-based fluids still contain a certain amount of pollutants due to contamination with formation oil and the presence of trace heavy metals in barite, which may pose risk when discharged into the marine environment. A framework is presented here for a decision support system for the selection of the best drilling waste discharge option. Uncertainties in the quantification of risk, cost and technical feasibility are expressed by fuzzy numbers. An analytical hierarchy process with a technique called fuzzy synthetic evaluation is employed to determine the best management alternative (discharge scenario).  相似文献   

Assessment of cytochrome P450 1A in harbour seals (Phoca vitulina) using a minimally-invasive biopsy approach     

Miller KA  Assunção MG  Dangerfield NJ  Bandiera SM  Ross PS 《Marine environmental research》2005,60(2):153-169

Biomarkers of organochlorine exposure, such as the induction of cytochrome P450 1A (CYP1A), can be used to assess the impact of environmental contaminants on the health of free-ranging marine mammal populations. The objective of the present study was to measure CYP1A in skin and liver biopsies obtained from live harbour seals (Phoca vitulina). Twelve harbour seal pups, aged three to five weeks, were captured from the Fraser River estuary, British Columbia, Canada, and temporarily held in captivity. Skin ( approximately 60 mg) and liver ( approximately 40 mg) biopsies, obtained while seals were under general anaesthesia, yielded sufficient tissue for the measurement of CYP1A by immunoblot analysis and ethoxyresorufin O-deethylase activity. A short-term exposure experiment, in which harbour seals (n=3) were treated orally with beta-naphthoflavone (BNF), resulted in increased hepatic and cutaneous CYP1A protein levels, consistent with observations in other mammals. This study is the first to measure CYP1A in skin and liver biopsies from live harbour seals and to report in vivo BNF-associated CYP1A induction in a marine mammal. The results demonstrate that microsamples collected using minimally-invasive techniques can provide toxicologically-relevant information form marine mammals.  相似文献   

Observations of resuspended diatoms in the turbid tidal edge     

Cathy H. Lucas 《Journal of Sea Research》2003,50(4):301-308

Observations of resuspended diatoms in the shallow waters (<60 cm) of the turbid tidal edge are described for single sites on two tidal flats–the Molenplaat in the Westerschelde estuary, and the Hond in the Ems-Dollard estuary, The Netherlands. High concentrations of chlorophyll-a (chl-a) were observed in the trailing edge of the ebbing tide in water depths of <20 cm, after which concentrations decreased markedly. Peak mean values were 19 μg chl-a l⁻¹ in 10 cm of water at the Molenplaat, and 45 μg chl-a l⁻¹ in 5 cm of water at the Hond. Similar trends were observed on the flooding tide, although peak values were far less pronounced (6 and 30 μg chl-a l⁻¹ respectively). Microscopic examination of the diatom community within the turbid tidal edge at the Molenplaat revealed that peaks in biomass were caused by suspended benthic diatoms, as well as the large centric diatom Coscinodiscus sp., particularly on the ebb tide. Planktonic diatoms other than Coscinodiscus sp. were more randomly distributed and did not appear to follow any particular trend. It would seem that as the tide recedes, resuspended benthic diatoms and large Coscinodiscus sp. cells become concentrated in the shallow water. However, the virtual absence of Coscinodiscus sp. from the leading edge of the flooding tide suggests that most of the resuspended cells do not settle to the seabed, but are washed away into the channels. The small peak of benthic diatoms at the leading edge of the flood tide is most likely resuspended locally from the sediment, along with large numbers of diatom frustules.  相似文献   

Interferometric observations of HCN and CN towards carbon stars     

M. Lindqvist  R. Lucas  H. Olofsson  A. Omont  K. Eriksson  B. Gustafsson 《Astrophysics and Space Science》1995,224(1-2):501-502

Using the IRAM interferometer we have observed four carbon stars (U Cam, CIT6, Y CVn, IRC+40540) in the HCN(J=1 0) and CN(N=1 0) lines. Here we present some results for CIT6 and U Cam.  相似文献   

Present day serpentinization in New Caledonia,Oman and Yugoslavia     

Ivan Barnes  J.R O&#x;Neil  J.J Trescases 《Geochimica et cosmochimica acta》1978,42(1):144-145

Geochemical evidence for modern low-temperature serpentinization has been found in three new localities. Apparently the low-temperature reactions are a common mode of formation of the lizardite-chrysotile and brucite assemblage. Possibly the ¹⁸O content of serpentine formed at low temperatures is in part inherited from the pyroxene and olivine.  相似文献   

Deformation mechanisms, microstructure and rheology of rocks in nature and experiment     

Neil S. Mancktelow  Luigi Burlini  Stefan M. Schmalholz  Karsten Kunze   《Tectonophysics》2006,427(1-4)

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Investigating the scale of structural controls on chlorinated hydrocarbon distributions in the fractured-porous unsaturated zone of a sandstone aquifer in the UK     

Adrian Lawrence  Marianne Stuart  Colin Cheney  Neil Jones  Richard Moss 《Hydrogeology Journal》2006,14(8):1470-1482

Contaminant migration behaviour in the unsaturated zone of a fractured porous aquifer is discussed in the context of a study site in Cheshire, UK. The site is situated on gently dipping sandstones, adjacent to a linear lagoon historically used to dispose of industrial wastes containing chlorinated solvents. Two cores of more than 100 m length were recovered and measurements of chlorinated hydrocarbons (CHCs), inorganic chemistry, lithology, fracturing and aquifer properties were made. The results show that selecting an appropriate vertical sampling density is crucial both to providing an understanding of contaminant pathways and distinguishing whether CHCs are present in the aqueous or non-aqueous phase. The spacing of such sampling should be on a similar scale to the heterogeneity that controls water and contaminant movement. For some sections of the Permo-Triassic aquifer, significant changes in lithology and permeability occur over vertical distances of less than 1 m and samples need to be collected at this interval, otherwise considerable resolution is lost, potentially leading to erroneous interpretation of data. At this site, although CHC concentrations were high, the consistent ratio of the two main components of the plume (tetrachloroethene and trichloroethene) provided evidence of movement in the aqueous phase rather than in dense non-aqueous phase liquid (DNAPL).  相似文献   

Tectonics and distribution of gold deposits in China – an overview   总被引：20，自引：0，他引：20  

Taihe Zhou  Richard J. Goldfarb  Neil G. Phillips 《Mineralium Deposita》2002,37(3-4):249-282

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