Silver fluxes to the Gironde Estuary - Eleven years (1999-2009) of monitoring at the watershed scale

Although Ag has long been recognized as highly toxic to aquatic organisms and as an efficient tracer of urban wastewater inputs, there are very few data available on Ag levels and fluxes in rivers and estuaries. Due to anomalously high Ag concentrations in oysters from the estuary mouth, dissolved (Ag_D) and particulate Ag (Ag_P) concentrations in rivers of the Gironde Estuary watershed were studied. Using daily discharge, Suspended particulate matter (SPM) data and monthly measured Ag_D and Ag_P, the respective fluxes were estimated at the three main entries of the Gironde Estuary and at selected key sites at the outlets of different sub-watersheds for multiple years of the past decade. Dissolved and particulate Ag concentrations were 0.5 ng/L (detection limit) to 5.7 ng/L and 0.13-13.9 mg/kg in all rivers, except for the Riou-Mort River (up to 1260 ng/L and 261 mg/kg) that has been heavily polluted by former Zn ore treatment and remaining waste tailings. At all sites Ag transport mainly (73-100%) occurred in the particulate phase, i.e. strongly depended on hydrological parameters. Comparing Th-normalised (i.e. grain size independent) Ag_P levels at the different sites including one remote site showed that the regional background is best described by Ag_P/Th_P = 0.026. The anthropogenic components in Ag_P levels and fluxes ranged from 24% to 90% at all sites, except for the Riou-Mort River (81-99%). Although this former ore treatment site still is an evident Ag source to the Lot-Garonne fluvial-estuarine system, its contribution to Ag fluxes at the main entry of the Gironde Estuary (i.e. 0.33-2.44 t/a at the La Reole site) is <11%. This clearly suggests that other sources such as rock weathering and erosion (0.057-0.817 t/a), urban wastewater inputs (0.042-0.057 t/a) and cloud-seeding (0.030-0.063 t/a) contribute the major parts of the fluvial Ag budget in this watershed. The estimated anthropogenic surface- and population-specific Ag fluxes in the studied system were 1.14-682 g/km²/a and 0.028-6.05 g/person/a, respectively. The results obtained suggest that the Gironde fluvial-estuarine system is contaminated by Ag inputs from various sources, but further work is necessary to (i) identify and quantify the major sources and (ii) produce comparable data for other systems, which would be useful for the evaluation of Ag contamination at a larger scale.     

Overview of the subsurface structural pattern of the Paris Basin (France): Insights from the reprocessing and interpretation of regional seismic lines

The study presents the methodology used by the French Geological Survey (BRGM) for the building, reprocessing and interpretation of selected regional seismic lines in the Paris intracratonic basin (France): the 14 constructed E-W and N-S regional transects represent a total of 2,516 km length, and are based on the merge of 240 seismic single profiles recorded by petroleum operators between 1971 and 1995. The regional lines have been selected to cross the main oil fields of the Paris Basin, as well as high potential areas for oil exploration. A first difficulty was to recover the raw data necessary to build-up the regional transects. The signal reprocessing, harmonization and merge of the single seismic lines, constituent of the regional transects, are then described; these operations represent the cornerstone of the study. We put the emphasis on the primary static corrections, as the targeted structures are commonly spatially associated with large seismic velocity variations in the upper Cretaceous chalk and Tertiary sedimentary cover.The interpreted regional transects definitely give complementary information to the existing studies, which generally lack seismic (and therefore structural) data: we give an overview of the main structural and geometrical features of the Paris Basin: inversion structures, major unconformities, as well as Permo-Carboniferous basins. We also describe the structural pattern, and show the close relationships between the faults geometry, the faults density, and the geological evolution of the Paris Basin: we distinguish (1) few large-scale polyphase faults, with a Variscan origin, representing the first order structural frame of the Paris Basin; (2) monophase normal faults, with strike-slip features, representing the subsurface prolongation of Cenozoic grabens cropping out in the neighbourhood; (3) deep normal faults, sealed by the base Calcareous Dogger sequence, related to the Permo-Liassic extensional tectonic regime. This large-scale view of the Paris Basin has highlighted several potential exploration targets.     

Molecular evidence for life in the 3.5 billion year old Warrawoona chert

The biological origin of organic matter in the oldest siliceous sediments (cherts) is still debated. To address this issue, the insoluble organic matter (kerogen) was isolated from a chert of the Warrawoona group. The chemical structure of the kerogen was investigated through a combination of analytical techniques including solid-state ¹³C nuclear magnetic resonance and pyrolysis. Although dominated by aromatic hydrocarbons, the pyrolysate comprises a homologous series of long chain aliphatic hydrocarbons characterized by odd-over-even carbon number predominance. This distribution is only consistent with a biological origin. As kerogen must be contemporaneous of the solidification of the chert, this observation should be regarded as an evidence for the presence of life on Earth, 3.5 By ago.     

Microstructural Inhomogeneity and Mechanical Anisotropy Associated with Bedding in Rothbach Sandstone

This study present the result of conventional triaxial tests conducted on samples of Rothbach sandstone cored parallel, oblique (at 45 degrees) and perpendicular to the bedding at effective pressures ranging from 5 to 250 MPa. Mechanical and microstructural data were used to determine the role of the bedding on mechanical strength and failure mode. We find that samples cored at 45 degrees to the bedding yield at intermediate level of differential stress between the ones for parallel and perpendicular samples at all effective pressures. Strain localization at high confining pressure (i.e., in the compactive domain) is observed in samples perpendicular and oblique to the bedding but not in samples cored parallel to the bedding. However, porosity reduction is comparable whether compactive shear bands, compaction bands or homogeneous cataclastic flow develop. Microstructural data suggest that (1) mechanical anisotropy is controlled by a preferred intergranular contact alignment parallel to the bedding and that (2) localization of compaction is controlled by bedding laminations and grain scale heterogeneity, which both prevent the development of well localized compaction features.     

Rotational Properties of Cometary Nuclei

We review several techniques used to retrieve rotational parameters from observations. The spin period of a dozen of comets retrieved with these techniques are summarized. We describe how the spin period of comet Hale-Bopp (C/1995 O1) has been calculated with a high accuracy (11.30–11.34 h). Although several authors converged to a spin axis orientation at (α,δ) = (275 ± 15°, -55 ± 5°), detailed studies indicate that the dust jets morphology in 1996–1997 may be incompatible with this orientation. Comet 19P/Borrelly has been recently observed by the Deep Space 1 spacecraft. At the same time, its spin axis orientation and period have been determined by several authors to be respectively (α,δ) = (225 ± 15°, -10 ± 10°)and 26h. These two comets are likely to be in (or close to) a principal axis spin state. We discuss new modeling of the spin state of comet 46P/Wirtanen, the target of the Rosetta mission. The model involves a three-dimensional shape and thermal model, from which the torque of the non gravitational force is calculated at each time step. The moments of inertia are computed for each irregular shape. The results from numerical integrations show that this comet can remain in a principal axis spin state during more than 10 orbits if the spin period does not get above～6 h. If the spin period increases, its nucleus gets rapidly into excited spin states. It shows that even small and very active short-period comets are not necessarily in non principal axis spin states. In the last section, the consequences of recent observations and modeling of the rotational parameters of comet nuclei are discussed, and unsolved problems are presented.     

Effects of the Upstream-Flow Regime and Canyon Aspect Ratio on Non-linear Interactions Between a Street-Canyon Flow and the Overlying Boundary Layer

Large-scale structures within a rough-wall boundary layer generated over a cube array have recently been linked to small-scale fluctuations close to the roughness through a dynamical mechanism similar to amplitude modulation. Demonstrating the existence of this mechanism for different roughness types is a crucial step towards the development of a generic model for wind fluctuations in the urban canopy. Here the influence of the upstream roughness geometry (two-dimensional (2D) and three-dimensional (3D)) and planform packing density (\( \lambda_{p} \)) and street-canyon aspect ratio on the non-linear interactions between large-scale momentum regions and the small scales induced by the presence of the roughness is studied within a wind tunnel using combined particle-image velocimetry and hot-wire anemometry. A multi-time delay linear stochastic estimation is used to decompose the flow into large scales that participate in modulation and the remaining small scales. Using three different upstream roughness configurations composed of either 3D cubes or 2D rectangular blocks it is shown that the upstream roughness configuration has an influence on the non-linear interactions in the rough-wall boundary layer. Analysis of the turbulence skewness decomposition shows a change in the location of the maximum of the term \( \overline{{u_{L}^{\prime} u_{S}^{\prime 2}}} \), which represents the influence of the large-scale momentum regions on the small scales, whilst the temporal correlation shows a modification of the interaction located closer to the roughness with a change from 3D to 2D roughness. Furthermore, a two-point spatio–temporal correlation demonstrates that the non-linear relationship is significantly modified in the wake-interference-flow regime compared to the skimming-flow regime. Through skewness decomposition and temporal correlations the canyon aspect ratio is shown to have no influence on the non-linear interactions, indicating that the mechanism depends only on the flow developing upstream. Finally, although the upstream roughness configuration is shown to influence the non-linear interactions, the nature of the mechanism remains the same in all configurations.     

Mobility of arsenic in West Bengal aquifers conducting low and high groundwater arsenic. Part I: Comparative hydrochemical and hydrogeological characteristics

The present study demonstrates the importance of hydrogeochemical characteristics (groundwater flow and recharge) of an aquifer in the release of As to groundwater. The study area (∼20 km²) is located in Chakdaha block, Nadia district, West Bengal, which hosts groundwaters of variable As content. The spatial distribution pattern of As is patchy with areas containing groundwater that is high in As (>200 μg L⁻¹) found in close vicinity to low As (<50 μg L⁻¹) groundwaters (within 100 m). The concentration of groundwater As is found to decrease with depth. In addition, the data shows that there is no conspicuous relationship between high groundwater As concentration and high groundwater abstraction, although the central cone of depression has enlarged over 2 a and is extending towards the SE of the study area. The river Hooghly, which forms the NW boundary of the study site, shows dual behaviour (effluent and influent during pre- and post-monsoon periods, respectively), complicating the site hydrogeology. The observed groundwater flow lines tend to be deflected away from the high As portion of the aquifer, indicating that groundwater movement is very sluggish in the As-rich area. This leads to a high residence time for this groundwater package, prolonging sediment–water interaction, and hence facilitating groundwater As release.     

Northern marine transportation corridors: Creation and analysis of northern marine traffic routes in Canadian waters

The concept of the Northern Marine Transportation Corridors (NMTC) initiative was developed under the Government of Canada World‐Class Tanker Safety System Initiative (WCTSS). The NMTC is an interdepartmental Arctic initiative within the Department of Fisheries and Oceans Canada (DFO), through the Canadian Coast Guard (CCG) and the Canadian Hydrographic Service (CHS), in collaboration with Transport Canada (TC). The NMTC initiative was developed to strengthen the safety of marine navigation in the Arctic, and to offer an efficient planning guide for present and future Arctic investments. Transportation corridors identified through this initiative will provide the Government of Canada the framework needed to better prioritize and deliver on its programs and services, including: nautical charts and products; aids to navigation; icebreaking services; and marine safety regulations. The corridors were generated and analyzed with a Geographic Information System (GIS) using two main data sources: the Automated Identification System (AIS) and CHS's nautical charts and publications. The geographic extent of the NMTC is defined as the Northern Canada Vessel Traffic Service Zone (NORDREG Zone) and the Mackenzie River. With close to 4 million km² of water in the Arctic and 162,000 km of coastline, surveying the Arctic to modern standards represents an enormous challenge to CHS. By adopting a corridor‐based approach, CHS and other government programs can prioritize their efforts on 12% of the Canadian Arctic waters. CHS currently has 32% of the NMTC adequately surveyed, with an additional 3% surveyed to modern standards.     

Geometry and kinematics of extension in Alpine Corsica

The geometry of the most recent deformation in Alpine Corsica is discussed in terms of reactivation of thrusts as normal faults and crustal extension, following crustal thickening in late Cretaceous and Eocene time. A cross section interpreted in terms of obduction in previous works is shown here to be a result of ductile and brittle extension in late Oligocene and Early Miocene time. This new interpretation is based on field observations of the brittle and ductile structures and their relations to the metamorphic history in the Tenda-col de Teghime and Centuri regions, as well as additional observations in other parts of Alpine Corsica. The following geological features are observed: (1) The recent deformation was partly achieved during a top-to-the-east ductile shear close to the brittle-ductile transition and was later superimposed by brittle shear indicating a transition in time from ductile to brittle regime. (2) Extensional brittle structures in the Early Miocene Saint Florent limestone and sense of tilt are compatible with the eastward sense of shear observed in the ductile rocks. (3) The movement along major “thrust” contacts is associated with retrograde metamorphism which overprinted the early high-P-low-T paragenesis at less severe P-T conditions. They also bring tectonic units with contrasted metamorphic evolutions into close contacts. (4) There is a regional correlation between retromorphosis and recent deformation since the high-P-low-T paragenesis are better preserved in southern of Alpine Corsica where the recent deformation is less pervasive. (5) Highly non-coaxial deformation is localized along east-dipping shear zones close to brittle normal faults which bounds tilted Miocene basins; in between the geometry is more symmetric and the finite strain therefore more coaxial. (6) Late extensional brittle structures are observed at many sites in the metamorphic rocks. In the present paper we discussed these first-order observations and describe the geometry of crustal extension in Alpine Corsica. We analyze the progressive formation of a crustal-scale tilted block in Cap Corse and propose that the normal faults are localized by asymmetric boudinage of the crust. The asymmetry of this crustal-scale boudinage is controlled by the position of early thrust planes.     

Study of inorganic ligand-chromium(III)-surface ternary complexes by ESR spectroscopy

Cr(III) sorbed at the solid/water interface of latex and hectorite was studied by ESR spectroscopy in the presence of different inorganic ligands. The ESR spectra of the surface obtained in the presence of selenite, phosphate and fluoride can be explained in terms of ternary surface complex formation. This is contrasted by the behaviour of sulfate and selenate ions which were found to have no effect on the ligand field of Cr(III), either in the adsorbed state or in solution.