Role of suspended sediments on the distribution of PCB in the Seine Estuary (France)     

Alain Abarnou  Jacques Avoine  Jean Paul Dupont  Robert Lafite  Serge Simon 《Continental Shelf Research》1987,7(11-12)

PCB (polychlorinated biphenyls) contamination and its relationship to SPM (suspended particulate material) have been studied in the Seine Estuary, which is heavily polluted by these persistent and hydrophobic man-made chemicals. Two sampling cruises have been performed during different freshwater discharge conditions. PCB and SPM concentrations, as well as grain-size distributions in the particulate material have been determined. Water samples have been collected at fixed positions during a tidal cycle, and along transects within the estuary.PCB concentrations vary from 2 ng 1⁻¹ in the marine zone to 250 ng 1⁻¹ within the estuary, and reach 1.3 × 10³ ng 1⁻¹ in the turbidity maximum zone. During a tidal cycle, low PCB concentrations are observed at high water, and are in the same range in February as in July. High PCB contamination is observed at low water, but PCB concentrations are about five times higher in February. SPM and PCB variations are well correlated in both periods of observations. Higher PCB contamination during February is explained by higher SPM inputs, mainly due to particles of riverine origin. The transport of PCB within the estuary depends on the quantity and the grainsize composition of suspended material, which varies according to freshwater discharge and tidal amplitude.  相似文献   

Partage du nickel entre serpentine et brucite au cours de la serpentinisation du péridot     

Alain Perruchot 《Contributions to Mineralogy and Petrology》1973,42(3):229-234

When nickeliferous peridot is submitted to a serpentinisation reaction with formation of brucite, the peridotic nickel is partitioned between the two minerals (serpentine and brucite) with a distribution coefficient K=[(Ni/Mg) brucite]/[(Ni/Mg)] serpentine=1,63 (at 350°C and 1 kbar), in favour of brucite.  相似文献   

Field evidence of hydraulic connections between bedrock aquifers and overlying granular aquifers: examples from the Grenville Province of the Canadian Shield   总被引：1，自引：0，他引：1  

Sandra K. Richard  Romain Chesnaux  Alain Rouleau  Roger Morin  Julien Walter  Silvain Rafini 《Hydrogeology Journal》2014,22(8):1889-1904

Field evidence of hydraulic connections between a bedrock aquifer and an overlying granular aquifer in the Canadian Shield (Grenville Province) is presented. This issue is rarely considered and investigated despite its important hydraulic and chemical consequences and its widespread occurrence worldwide. The methodology employed is based on complementary field tests conducted at specific experimental sites instrumented both in the rock and in the overlying deposits. One of the bedrock sites revealed a natural hydraulic connection with the overlying granular aquifer caused by the weathered surface of the uppermost bedrock. Another site revealed an artificial hydraulic connection between the bedrock and the granular aquifer created by an improperly sealed casing. A regional study showed that hydraulic connections yield an erroneous interpretation of the true hydraulic properties of the tested aquifer. The detection of hydraulic connections is therefore essential to properly define well-capture areas and contamination conditions. It is recommended to practitioners that pumping tests be performed as well as hydrochemical comparisons of each existing aquifer unit. Falling-head permeability tests are also helpful in verifying the quality of the seal at the bedrock–casing contact. More effective procedural controls and better well-construction practices are necessary to reduce the risks of cross-contamination induced by defective seals.  相似文献   

A literature review of Algerian salt lakes: values,threats and implications     

Fatma Demnati  Boujéma Samraoui  Farid Allache  Alain Sandoz  Lisa Ernoul 《Environmental Earth Sciences》2017,76(3):127

Chotts are salt lakes located in the arid regions of Northern Africa. These unique wetlands are recognized for their role in the migration and breeding of waterbirds and economic values generated from mineral extraction, agriculture and tourist activities. Despite their importance for flora and fauna biodiversity, they continue to face important threats due to human activities. This article consolidates a literature review of Algerian chotts from global to local importance. An in-depth view demonstrates the changes in land use of two large chotts in the southeastern region of Algeria: Chotts Merouane and Melghir. Land use images highlight a net expansion of agricultural lands, a decrease in grazing area around the lakes and a decrease of salt lake surface area. The local focus highlights the threats and changes of Algerian and Northern African chotts and proposes some perspectives for the future.  相似文献   

Characterization of Mediterranean magnetotactic bacteria     

Lefèvre Christopher 《中国海洋大学学报(英文版)》2007,6(4):355-359

Magnetotactic bacteria are a diverse group of motile prokaryotes that are ubiquitous in aquatic habitats and cosmopolitan in distribution. In this study, we collected magnetotactic bacteria from the Mediterranean Sea. A remarkable diversity of morphotypes was observed, including multicellular types that seemed to differ from those previously found in North and South America. Another interesting organism was one with magnetosomes arranged in a six-stranded bundle which occupied one third of the cell width. The magnetosome bundle was evident even under optic microscopy. These cells were connected together and swam as a linear entire unit. Magnetosomes did not always align up to form a straight linear chain. A chain composed of rectangle magnetosomes bent at a posi- tion with an oval crystal. High resolution transmission electron microscopy analysis of the crystal at the pivotal position suggested uncompleted formation of the crystal. This is the first report of Mediterranean magnetotactic bacteria, which should be useful for studies of biogeochemical cycling and geohistory of the Mediterranean Sea.  相似文献