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821.
Paul-Désiré Ndjigui Paul Bilong Dieudonné Bitom 《Journal of African Earth Sciences》2009,53(1-2):59-69
Strong negative cerium anomalies are developed in the saprolite zone of two serpentinite lateritic profiles in the Mada region of the Kongo–Nkamouma massif in the Lomié ultramafic complex (South-East Cameroon).The total lanthanide contents increase strongly from the parent rock (1.328 ppm) to the weathered materials (ranging from 74.32 to 742.18 ppm); the highest value is observed in the black nodules from the western weathering profile and the lowest one in the top of the clayey surface soil from the same profile. The lanthanide contents, except cerium, are highest in the saprolite and decrease along the profile. The light REE contents are very high compared to those of the heavy REE (LREE/HREE ranging from 3.21 to 44.37). The lanthanides normalized with respect to the parent rock reveal: (i) strong negative Ce anomalies with [Ce/Ce1] ranging from 0.006 to 0.680 in the saprolite zone; (ii) strong positive Ce anomalies with [Ce/Ce1] ranging from 1.23 to 23.96 from the top of the saprolite to the clayey surface horizon; (iii) positive Eu anomalies with [Eu/Eu1] ranging from 2.09 to 2.41 in all the weathered materials.Mass balance evaluation shows that, except cerium, lanthanides have been highly accumulated in the saprolite zone and moderately concentrated in the upper part of both profiles. Cerium has been highly accumulated in the nodules of the West Mada profile. The presence of negative Ce anomalies is confirmed by its low degree of accumulation whereas the positive ones are related to its high degree of accumulation. 相似文献
822.
José R. Martínez Catalán Ricardo Arenas Jacobo Abati Sonia Sánchez Martínez Florentino Díaz García Javier Fernández Suárez Pablo González Cuadra Pedro Castiñeiras Juan Gómez Barreiro Alejandro Díez Montes Emilio González Clavijo Francisco J. Rubio Pascual Pilar Andonaegui Teresa E. Jeffries James E. Alcock Rubén Díez Fernández Alicia López Carmona 《Comptes Rendus Geoscience》2009,341(2-3):114-126
Ophiolites of different Paleozoic ages occur in North-West (NW) Iberia in a rootless suture representing the remnants of the Rheic Ocean. Associated allochthonous terranes in the hanging- and foot-walls of the suture derive from the former margins, whereas the relative autochthon corresponds to the Paleozoic passive margin of northern Gondwana. The Paleozoic tectonic evolution of this part of the circum-Atlantic region is deduced from the stratigraphical, petrological, structural and metamorphic evolution of the different units and their ages. The tectonic reconstruction covers from Cambro-Ordovician continental rifting and the opening of the Rheic Ocean to its Middle to Upper Devonian closure. Then, the Variscan Laurussia–Gondwana convergence and collision is briefly described, from its onset to the late stages of collapse associated with the demise of the orogenic roots. 相似文献
823.
Dennis F. Whigham Jos T. A. Verhoeven Vladimir Samarkin Patrick J. Megonigal 《Estuaries and Coasts》2009,32(5):926-936
The responses of dwarf black mangroves (Avicennia germinans) and components of the microbial community to the addition of nitrate over a 2-year period were examined. The field study
was conducted in the Indian River Lagoon (Florida) in a mangrove-dominated impoundment that was established for purposes of
mosquito control. The responses of mangroves to the regular addition of nitrate were insignificant or relatively minor compared
to responses of the components of the microbial community. Denitrification rates, measured in the field and laboratory, increased
significantly in fertilized plots and nitrous oxide emission rates were almost six times higher in fertilized plots. Nitrogen
fixation was significantly lower in fertilized plots. Results suggest that mangrove systems in the N-limited Indian River
Lagoon are likely to be long-term sinks for any increases in N loading. 相似文献
824.
Eleazar Padrón Gladys Melián Rayco Marrero Dácil Nolasco José Barrancos Germán Padilla Pedro A. Hernández Nemesio M. Pérez 《Pure and Applied Geophysics》2008,165(1):95-114
Significant changes in the diffuse emission of carbon dioxide were recorded in a geochemical station located at El Hierro,
Canary Islands, before the occurrence of several seismic events during 2004. Two precursory CO2 efflux increases started thirteen and nine days before two seismic events of magnitude 2.3 and 1.7, which took place near
El Hierro Island, Canary Islands, on March 23 and April 15, reaching a maximun value of 51.1 and 46.2 g m−2 d−1, respectively, five and eight days before the two seismic events. Other similar increases started thirteen and five days
before the occurrence of two seismic events of magnitude 1.3 and 1.5 which took place on October 15 and 21 respectively, reaching
the maximum values four and one day before the earthquakes. These changes were not related to variations in atmospheric or
soil parameters. The Material Failure Forecast Method (FFM), which analyzes the rate of precursory phenomena, was successfully
applied to forecast the first seismic event that took place in El Hierro Island in 2004. 相似文献
825.
The study of bedload transport processes is constrained by an inability to monitor the mass, volume and grain size distribution of sediment in transport at high temporal frequencies. Building upon a previously published design, we have integrated a high‐resolution (1392 × 1024 pixels) video camera with a light table to continuously capture images of 2–181 mm material exiting a flume. The images are continuously recorded at a rate of 15 to 20 frames per second and are post‐processed using LabView(?) software, yielding continuous grain‐size‐specific transport information on a per second basis. The video capture rate is sufficient to record multiple images of each grain leaving the flume so that particle velocities can be measured automatically. No manual image processing is required. After calibration the method is accurate and precise for sediment in the 2 mm through to 45 mm grain size classes compared with other means of measuring bedload. Based on a set of validation samples, no statistically significant difference existed between the D10, D16, D25, D50, D75, D84, D90 and D95 determined by sieving captured samples and the Di values determined with the system. On average the system overpredicted transport by 4 per cent (n = 206, SD = 42%). This error can be corrected easily by simply weighing the mass of sediment that leaves the flume. The technology is relatively inexpensive and provides high‐resolution data on coarse sediment transport out of a flume. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
826.
This study is part of a project aiming to validate the use of the intertidal shanny Lipophorys pholis as a sentinel species in pollution monitoring in NW European marine ecosystems. To this end, a characterisation of acethylcholin (AChE), butyrylcholin (BChE) and propionylcholin (PrChE) esterases in L. pholis muscle was performed and the results indicated that AChE was predominant. Furthermore, the use of eserine sulphate and BW284c51 (0.64–800 μM), and iso-OMPA (0.08–16 mM), confirmed the measurement of true cholinesterases (ChEs) as well as the presence of pseudocholinesterases. The field application of these markers to L. pholis, sampled in seven locations along the Portuguese coast, revealed that fish were likely to be affected by neurotoxic compounds. This was indicated by the significant depletion of AChE (p < 0.05) in animals collected at urban and industrialised sites, compared with those from reference locations. The inclusion of a marker of effect, measured as lipid peroxidation levels in muscle tissue, also revealed the existence of site differences. Overall, the study further validates the utility of L. pholis in pollution monitoring studies. 相似文献
827.
Thébault H Rodriguez Y Baena AM Andral B Barisic D Albaladejo JB Bologa AS Boudjenoun R Delfanti R Egorov VN El Khoukhi T Florou H Kniewald G Noureddine A Patrascu V Pham MK Scarpato A Stokozov NA Topcuoglu S Warnau M 《Marine pollution bulletin》2008,57(6-12):801-806
The common mussel Mytilus galloprovincialis was selected as unique biomonitor species to implement a regional monitoring programme, the CIESM Mediterranean Mussel Watch (MMW), in the Mediterranean and Black Seas. As of today, and upon standardization of the methodological approach, the MMW Network has been able to quantify (137)Cs levels in mussels from 60 coastal stations and to produce the first distribution map of this artificial radionuclide at the scale of the entire Mediterranean and Black Seas. While measured (137)Cs levels were found to be very low (usually < 1 Bq kg(-1) wet wt) (137)Cs activity concentrations in the Black Sea and North Aegean Sea were up to two orders of magnitude higher than those in the western Mediterranean Basin. Such effects, far from representing a threat to human populations or the environment, reflect a persistent signature of the Chernobyl fallout in this area. 相似文献
828.
829.
From break-bulk to containers: the transformation of general cargo handling and trade 总被引:1,自引:0,他引:1
André Vigarié 《GeoJournal》1999,48(1):3-7
The era of containerisation has brought about considerable changes in maritime transport. This paper describes how general
cargo handling and port operationss have been transformed in the wake of unitisation. It stresses that the changes have had
far-reaching effects on port labour and upon the social and physical character of port cities. From places of intense labour
activity, docks and their adjacent communities have been fundamentally re-structured. The bonds that produced vibrant communities
characterised by strong social and political activism have been destroyed. The modern port city is shaped by technological
developments that take place on sites far removed from the former docklands.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
830.
An overview of recent changes in salinity in the surface waters of the Aral sea basin is given. Total dissolved salts (salinity)
in most waters are higher than admissible values for drinking water, and ionic composition has changed with time. Salinity
of the ‘Big Sea’ of the Aral was 48 g L−1 in 1998, but has decreased to below 21 g L−1 in the ‘Small Sea’ due to the building of a new dam between the two parts of the Aral Sea. 相似文献