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排序方式: 共有374条查询结果,搜索用时 31 毫秒
111.
Nadia Mzoughi Fayçal Hellal Mohamed Dachraoui Jean-Pierre Villeneuve Chantal Cattini Stephen J de Mora Amor El Abed 《Comptes Rendus Geoscience》2002,334(12):893-901
The marine environment is very complex, with several important chemical, biological, and sedimentological interactions. Sediments constitute a reservoir for numerous pollutants, including polycyclic aromatic hydrocarbons (PAHs). PAHs are known by their mutagenic and/or carcinogenic effect. This study evaluates contamination levels in Bizerte Lagoon with respect to PAHs. The extraction efficiency of PAHs from sediment has been evaluated using Soxhlet or ultrasonic procedures, based on the recovery of an internal standard (9,10-dihydroanthracene). Several PAHs were found, including sixteen that are reported in the priority list of pollutants of the US Environmental Protection Agency (EPA). PAHs analysis was carried out by GC–FID and GC–MS for 16 samples sampled in two seasons: summer and winter. Results permit an assessment of PAHs pollution in the Bizerte Lagoon. To cite this article: N. Mzoughi et al., C. R. Geoscience 334 (2002) 893–901. 相似文献
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114.
Sabine Castelle Jörg SchäferGérard Blanc Stéphane AudryHenri Etcheber Jean-Pierre Lissalde 《Applied Geochemistry》2007
Contaminated fluvial sediments represent both temporary sinks for river-borne pollutants and potential sources in case of natural and/or anthropogenic resuspension. Reservoir lakes play a very important role in sediment dynamics of watersheds and may offer great opportunities to study historical records of river-borne particles and associated elements transported in the past. The fate and potential environmental impact of Hg depends on its abundance, its carrier phases and its chemical speciation. Historical Hg records and solid state Hg speciation were compared in sediments from two contrasting reservoirs of the Lot River (France) upstream and downstream from a major polymetallic pollution (e.g. Cd, Zn) source. Natural (geochemical background) and anthropogenic Hg concentrations and their relationships with predominant carrier phases were determined. The results reveal important historical Hg contamination (up to 35 mg kg−1) of the downstream sediment, reflecting the historical evolution of industrial activity at the point source, i.e. former coal mining, Zn ore treatment and post-industrial remediation work. Single chemical extractions (ascorbate, H2O2, KOH) suggest that at both sites most (∼75%) of the Hg is bound to organic and/or reactive sulphide phases. Organo-chelated (KOH-extracted) Hg, representing an important fraction in the uncontaminated sediment, shows similar concentrations (∼0.02 mg kg−1) at both sites and may be mainly attributed to natural inputs and/or processes. Although, total Hg concentrations in recent surface sediments at both sites are still very different, similar mono-methylmercury concentrations (up to 4 μg kg−1) and vertical distributions were observed, suggesting comparable methylation-demethylation processes. High mono-methylmercury concentrations (4–15 μg kg−1) in 10–40 a-old, sulphide-rich, contaminated sediment suggest long-term persistence of mono-methylmercury. Beyond historical records of total concentrations, the studied reservoir sediments provided new insights in solid state speciation and carrier phases of natural and anthropogenic Hg. In case of sediment resuspension, the major part of the Hg historically stored in the Lot River sediments will be accessible to biogeochemical recycling in the downstream fluvial-estuarine environment. 相似文献
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116.
Description and first results of an explicit electrical scheme in a 3D cloud resolving model 总被引:2,自引:0,他引:2
The three-dimensional non-hydrostatic mesoscale model MésoNH of the French community offers the numerical environment to develop a cloud electrification scheme in a consistent way with the original mixed phase microphysical scheme. The charge separation mechanisms are entirely due to non-inductive processes and result from elastic ice–snow, ice–graupel and snow–graupel collisions. The electric charges carried by each of the five hydrometeor categories are transported along the airflow and are exchanged according to the various microphysical mass transfer rates but assuming a power law distribution of the individual charges as a function of the particle size. The electric field is diagnosed at each time step after integrating the electric potential induced by a net charge density in the Poisson equation. Finally, a lightning ash is triggered when the electric field locally steps over a given threshold. It propagates in two opposite directions until the magnitude of the electric field falls below a prescribed value. A fractal branching algorithm is then activated to extend lightning streamers away from the main channel and toward cloudy regions where substantial charge densities are present. Charges are neutralized along the tortuous lightning path with a simple procedure that preserves total charge conservation.The complete electrification scheme tested for an ideal case of vigorous supercellular storm shows an intense electrical activity all along its lifecycle. We show that the model is able to produce a direct tripolar structure of the charges as the result of a temperature charge reversal of − 10 °C and of the different sedimentation rates of the hydrometeors. 相似文献
117.
Elisabeth Haza Philippe Gotteland Jean-Pierre Gourc 《Geotechnical and Geological Engineering》2000,18(4):243-267
This paper presents a method for the design of geosynthetic reinforced soil structures, adapted for the case of a local surcharge load. The load has an important influence on the mechanical behaviour of the reinforcement. The basic calculation method is described and a design calculation method is proposed for the case of a locally loaded structure. This new approach is validated on the basis of experimental results obtained on several full-scale embankments, locally loaded to failure. These experimental results are compared to the results of calculation with partial safety factors from Eurocode 7. 相似文献
118.
Jean Riotte Laurent Ruiz Stéphane Audry Benjamin Baud Jean-Pierre Bedimo Bedimo Laurie Boithias Jean-Jacques Braun Bernard Dupré Jean-Louis Duprey Mikael Faucheux Christelle Lagane Jean-Christophe Marechal Hemanth Moger Mandalagiri Subbarayappa Mohan Kumar Harshad Parate Olivier Ribolzi Emma Rochelle-Newall Buvaneshwari Sriramulu Murari Varma Muddu Sekhar 《水文研究》2021,35(5):e14196
Despite the importance of tropical ecosystems for climate regulation, biodiversity, water and nutrient cycles, only a few Critical Zone Observatories (CZOs) are located in the tropics. Among these, most are in humid climates, while very few data exist for semi-arid and sub-humid climates, due to the difficulty of estimating hydro-geochemical balances in catchments with ephemeral streams. We contribute to fill this gap by presenting a meteorological and hydro-geochemical dataset acquired at the Mule Hole catchment (4.1 km2), a pristine dry deciduous forest located in a biosphere reserve in south India. The dataset consists of time series of variables related to (i) meteorology, including rainfall, air temperature, relative humidity, wind speed and direction, and global radiation, (ii) hydrology, including water level and discharge at the catchment outlet, (iii) hydrogeology, including manual (monthly) and/or automated (from 15 min to hourly) groundwater levels in nine piezometers and (iv) geochemistry, including suspended sediment content in the stream and chemical composition of rainfall (event based), groundwater (monthly sampling) and stream water (storm events, 15 min to hourly frequency with an automatic sampler). The time series extend from 2003 to 2019. Measurement errors are minimized by frequent calibration of sensors and quality checks, both in the field and in the laboratory. Despite these precautions, several data gaps exist, due to occasional access restriction to the site and instrument destruction by wildlife. Results show that large seasonal and interannual variations of climatic conditions were reflected in the large variations of stream flow and groundwater recharge, as well as in water chemical composition. Notably, they reveal a long-term evolution of groundwater storage, suggesting hydrogeological cycles on a decadal scale. This dataset, alone or in combination with other data, has already allowed to better understand water and element cycling in tropical dry forests, and the role of forest diversity on biogeochemical cycles. As tropical ecosystems are underrepresented by Critical Zone Observatories, we expect this data note to be valuable for the global scientific community. 相似文献
119.
Pierre Bouilhol Urs Schaltegger Massimo Chiaradia Maria Ovtcharova Andreas Stracke Jean-Pierre Burg Hamid Dawood 《Chemical Geology》2011,280(3-4):243-256
The combination of age determination and geochemical tracers allows understanding the source evolution during magmatism. We studied the Sapat Complex, in the exhumed Cretaceous Kohistan Paleo-Island Arc, to reconstruct the formation of the juvenile lower arc crust and the evolution of the mantle source during arc magmatism. High precision ID-TIMS U/Pb dating on zircon, shows that a protracted period of magmatic accretion formed the Sapat Complex between 105 and 99 Ma. Since continued melt percolation processes that formed the lower crust obscured the original bulk rock Nd–Pb–Sr isotopic composition, we rely on the Hf isotopic composition of zircons of different ages to unravel the source evolution. Nd and Pb bulk isotopic compositions coupled with Hf isotopic composition on zircons allow reconstructing a geodynamical scenario for the Sapat Complex, and the Cretaceous history of the Arc. We suggest that trenchward migration of the hot mantle source at 105 Ma explains the small heterogeneous εHf signal between + 14 and + 16. This heterogeneity vanished within ca. 2 million years, and the εHf of the source evolved from + 16 to + 14 at 99 Ma. Integrated to the Kohistan Cretaceous history, which has a baseline of εHf ≈ 14, these data pinpoint two geodynamical events, with slab retreat and the formation of the Sapat Complex followed by splitting of the Kohistan island arc at 85 Ma. 相似文献