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排序方式: 共有192条查询结果,搜索用时 15 毫秒
1.
Daniel Bernard Jamal El Khattabi Emilie Lefevre Hani Serhal Sabine Bastin-Lacherez Isam Shahrour 《Environmental Geology》2008,53(5):1129-1138
In the north of France, high registers of nickel are sometimes recorded within the chalk aquifer. In a confined context, the
presence of pyrite in the covering clays or in the marcasite nodules encrusted in the clay may constitute a natural source
of trace metals. With an objective of sanitary control, the limits of chemical contents regulating the quality of water destined
for human consumption have been lowered by the European Framework Directive in the field of water policy (2000/60/EC). As
a result, nickel limits have been reduced from 50 to 20 μg/l. The analyses, carried out on three water catchment fields in
our area of study, were centred on variable parameters (Eh, O2(d), pH, Conductivity, T°), major elements (SO4, NO3) and metals (Fe, Ni, Mn, Co). The acquired data enabled us to identify from one hand, the conditions which are presented
within the site, special thanks to the evolution of nitrate and iron contents and on the other hand, the natural origin (geological)
of nickel for two of the three sites studied based essentially on the evaluation of the Nickel/Cobalt ratio. Thus, on the
first site, the evolution of nickel content and nitrate content showed the influence of the phenomenon of denitrification
on the re-mobilisation of the nickel. Whereas on the second site, a high variation of total iron content and oxygen dissolved
in solution highlighted a particular phenomenon of oxidation of the pyrite through molecular oxygen. Finally, the correlation
with the sulphates clearly showed behaviour of the nickel, once released, that was entirely dependent on the phenomenon of
adsorption on the iron and manganese hydroxides. 相似文献
2.
3.
Variation in glycogen concentration, condition index (CI) and filtration activity were measured in the bivalve Macoma balthica buried in sediment and experimentally exposed to cadmium (Cd). The stress due to elevated but sub-lethal concentrations (300 ppb Cd) affected the overall fitness of the organism as all parameters monitored responded significantly. Lower concentrations tested (10, 30 and 100 ppb) only induced a significant decrease in filtration activity, which may play a protective role, enabling the organism to slow down its metabolic activity and preserving the integrity of its reserves (reflected by stable CI and glycogen levels). Hence, the various endpoints selected show different thresholds. Our results also demonstrate that under high exposure, small individuals loose proportionally more glycogen per unit of weight than larger ones, thus confirming the higher sensitivity of small individuals to metal contamination. Furthermore, exposure to intermediate concentration (30 ppb) seems to be beneficial to the small individuals as indicated by their high CI values compared to the control. These results showed thus that non-sigmoidal concentration-response relationship and sizes of individuals should be considered in monitoring programmes and risk assessment. 相似文献
4.
Sauveur Belviso Grard Thouzeau Sabine Schmidt Marit Reigstad Paul Wassmann Elena Arashkevich Jacqueline Stefels 《Estuarine, Coastal and Shelf Science》2006,68(3-4):473
In April 1997 and 1998 the significance of sedimentation as a sink for epipelagic dimethylsulphoniopropionate (DMSP) production and as a source for marine sediments was reassessed using a newly designed sediment trap. The behaviour of the traps in immersion was monitored continuously and the collection efficiency was evaluated with 234Th measurements. Net DMS(P) fluxes were corrected for some physical and biological losses during the whole sedimentation process providing reliable estimates of gross DMSP fluxes. It is shown that daily losses by sedimentation account for between 0.1% and 16% of seawater particulate DMSP (DMSPp) standing stocks, and between 3% and 75% of daily DMSPp production. In the Malangen fjord we observed temporal increases of DMSP production and standing stocks which resulted also in increases of DMSP vertical fluxes and DMS(P) concentrations at the sediment surface. This result illustrates how tight the coupling can be between pelagos and benthos, and confirms that DMS(P) concentration in the sediment was a reliable diagnostic indicator of vertical export from overlying waters in Malangen fjord. In Ullsfjord, however, DMS(P) concentrations in the sediment were poorly indicators of Phaeocystis pouchetii export during the early stage of growth of a bloom. The high load of DMS(P) in Balsfjord's sediments could neither be attributed to local vertical sedimentation nor to short-term lateral advection of fresh DMSP-containing phytoplanktonic material, and provides indication that this tracer sometimes also can be misleading. The highest loads of DMS(P) in sediments and the fastest rates of sedimentation occurred in the Southern Bight of the North Sea. 相似文献
5.
Th sorption and export models in the water column: A review 总被引:2,自引:3,他引:2
Nicolas Savoye Claudia Benitez-Nelson Adrian B. Burd J. Kirk Cochran Matthew Charette Ken O. Buesseler George A. Jackson Matthieu Roy-Barman Sabine Schmidt Marc Elskens 《Marine Chemistry》2006,100(3-4):234
Over the past few decades, the radioisotope pair of 238U / 234Th has been widely and increasingly used to describe particle dynamics and particle export fluxes in a variety of aquatic systems. The present paper is one of five review articles dedicated to 234Th. It is focused on the models associated with 234Th whereas the companion papers (same issue) are focused on present and future methodologies and techniques (Rutgers van der Loeff et al.), C / 234Th ratios (Buesseler et al.), 234Th speciation (Santschi et al.) and present and future applications of 234Th [Waples, J.T., Benitez-Nelson, C.R., Savoye, N., Rutgers van der Loeff, M., Baskaran, M., Gustafsson, Ö., this issue. An Introduction to the application and future use of 234Th in aquatic systems. Marine Chemistry, FATE special issue]. In this paper, we review current 234Th scavenging models and discuss the relative importance of the non-steady state and physical terms associated with the most commonly used model to estimate 234Th flux. Based on this discussion we recommend that for future work the use of models should be accompanied by a discussion of the effect that model and data uncertainty have on the model results. We also suggest that future field work incorporate repeat occupations of sample sites on time scales of 1–4 weeks in order to evaluate steady state versus non-steady state estimates of 234Th export, especially during high flux events (> ca. 800 dpm m− 2 d− 1). Finally, knowledge of the physical oceanography of the study area is essential, particularly in ocean margins and in areas of established upwelling (e.g., Equatorial Pacific). These suggestions will greatly enhance the application of 234Th as a tracer of particle dynamics and flux in more complicated regimes. 相似文献
6.
Sabine Attinger 《Computational Geosciences》2003,7(4):253-273
This paper focuses on heterogeneous soil conductivities and on the impact their resolution has on a solution of the piezometric
head equation: owing to spatial variations of the conductivity, the flow properties at larger scales differ from those found
for experiments performed at smaller scales. The method of coarse graining is proposed in order to upscale the piezometric
head equation on arbitrary intermediate scales. At intermediate scales large scale fluctuations of the conductivities are
resolved, whereas small scale fluctuations are smoothed by a partialy spatial filtering procedure. The filtering procedure
is performed in Fourier space with the aid of a low-frequency cut-off function. We derive the partially upscaled head equations.
In these equations, the impact of the small scale variability is modeled by scale dependent effective conductivities which
are determined by additional differential equations. Explicit results for the scale dependent conductivity values are presented
in lowest order perturbation theory. The perturbation theory contributions are summed up with using a renormalisation group
analysis yielding explicit results for the effective conductivity in isotropic media. Therefore, the results are also valid
for highly heterogeneous media. The results are compared with numerical simulations performed by Dykaar and Kitanidis (1992).
The method of coarse graining combined by a renormalisation group analysis offers a tool to derive exact and explicit expressions
for resolution dependent conductivity values. It is, e.g., relevant for the interpretation of measurement data on different
scales and for reduction of grid-block resolution in numerical modeling.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
7.
Sabine Gaudzinski Felix Bittmann Wolfgang Boenigk Manfred Frechen Thijs Van Kolfschoten 《Quaternary Research》1996,46(3):319-334
The Kärlich–Seeufer archaeological site in Germany's central Rhineland was excavated between 1980 and 1992. The site provides evidence for hominid activity during a Middle Pleistocene interglaciation known up to now only from the Kärlich clay pit and therefore defined as the Kärlich Interglaciation, which is considered to be post-Cromer IV and pre-Holstein (sensu stricto) in age. The site is characterized by Acheulean artifacts, a fauna dominated byElephas (Palaeoloxodon) antiquus,and a unique and outstanding preservation of wooden and other palaeobotanical remains. Assuming all finds are associated, the site previously was interpreted as an elephant hunting camp with a wooden structure, together with wood and bone implements preservedin situ.Recent analysis of the same features has shown that the site can also be interpreted as a reworked archaeological sample. Hominid occupation occurred in the vicinity of a small lake with prevailing meso-oligotrophic conditions. Expanding boreal forests and fen vegetation characterized the landscape. 相似文献
8.
Ana-Voica Bojar Harald Fritz Sabine Kargl Wolfgang Unzog 《Journal of African Earth Sciences》2002,34(3-4)
To constrain the post-Pan-African evolution of the Arabian–Nubian Shield, macro-scale tectonic studies, paleostress and fission track data were performed in the Eastern Desert of Egypt. The results provide insights into the processes driving late stage vertical motion and the timing of exhumation of a large shield area. Results of apatite, zircon and sphene fission track analyses from the Neoproterozoic basement indicate two major episodes of exhumation. Sphene and zircon fission track data range from 339 to 410 Ma and from 315 to 366 Ma, respectively. The data are interpreted to represent an intraplate thermotectonic episode during the Late Devonian–Early Carboniferous. At that time, the intraplate stresses responsible for deformation, uplift and erosion, were induced by the collision of Gondwana with Laurussia which started in Late Devonian times. Apatite fission track data indicate that the second cooling phase started in Oligocene and was related to extension, flank uplift and erosion along the actual margin of the Red Sea. Structural data collected from Neoproterozoic basement, Late Cretaceous and Tertiary sedimentary cover suggest two stages of rift formation. (1) Cretaceous strike-slip tectonics with sub-horizontal σ1 (ENE/WSW) and σ3 (NNW/SSE), and sub-vertical σ2 resulted in formation of small pull-apart basins. Basin axes are parallel to the trend of Pan-African structural elements which acted as stress guides. (2) During Oligocene to Miocene the stress field changed towards horizontal NE–SW extension (σ3), and sub-vertical σ1. Relations between structures, depositional ages of sediments and apatite fission track data indicate that the initiation of rift flank uplift, erosion and plate deformation occurred nearly simultaneously. 相似文献
9.
This article provides a refined technique to measure and interpret variables associated with the quality of an inspection—be it port state control or vetting inspections towards the probability of a very serious, serious or less serious casualty. It concentrates on filtering out the effect of variables such as detention, the port state control regime that inspected the vessel, time in-between inspections, deficiencies found during an inspection and the effect of vetting inspections. The consensus amongst policy makers in the shipping industry is that data cannot be combined to target vessels. While this article does demonstrate that the decrease in the probability of casualty is stronger for the South American Region, the Indian Ocean Region and Australia versus North Europe, North America or the Caribbean, it also demonstrates that the data can be combined to target vessels for inspections. Since the time in-between inspections and detention is mostly not significant towards decreasing the probability of casualty, these results reflect the lack of coordination amongst port state control regimes and industry inspections. Due to this lack of coordination and trust, a ship might be inspected in several regimes during a relative short time period where the benefit of an inspection can be easily saturated. Our recommendation on direct policy implication is to promote the harmonization of inspection databases across port state control regimes, preferably with the coordination of the development of the Global Integrated Ship Information System (GISIS) of the International Maritime Organization (IMO), to review the policy of a release of a vessel from detention and to increase cooperation amongst regimes with respect to the follow up of the rectification of deficiencies. 相似文献
10.
The topic of ship recycling has obtained considerable attention during the last two decades for a variety of reasons with the likelihood of the adoption of a new international convention under the auspices of the International Maritime Organization (IMO). This study applies econometric modeling to a unique data set to provide insight into the dynamics of the ship recycling market. The data set contains information on 51,112 ships over 100 gt and includes 748,621 events over a period of 29 years. The analysis confirms a negative relationship of earnings and a positive relationship of scrap prices for all locations while Bangladesh seems to be more sensitive to changes in earnings than the other locations and more likely demolishes larger and older vessels. The results for flag and ownership vary across scrapping locations with Malta and Cyprus indicating potential importance from a registry perspective. The overall safety profile of a vessel seems to be less important towards the probability of a ship being scrapped. Possible implementation of the convention at EU level will mostly likely affect Turkey while non-ratification of one of the major flags will most likely affect China or Bangladesh. 相似文献