Dispersion Statistics and Sample Size Estimates for Three Fish Species (Symphodus ocellatus,Serranus scriba and Diplodus annularis) in the Lavezzi Islands Marine Reserve (South Corsica,Mediterranean Sea)

For the correct management of the future International Marine Park of Bonifacio, a sampling strategy must be adopted to follow the population fluctuations of certain species of fish. This sampling will be carried out by SCUBA visual census using the fixed point method. The information to be gleaned using this method will include estimates of biomass. These data will subsequently be used to perform both spatial comparisons between sites and temporal comparisons over periods of several years. In order to reveal the existence of statistically significant differences, the sampling strategy adopted must allow accurate means to be obtained which possess relatively low coefficients of variability. The calculation of this optimum sampling depends on the spatial distribution of the species examined. The Taylor law (s² = a ×x ^b), which represents a much utilized mean-variance relationship, will be used to compare the aggregation of three species of fish (Symphodus ocellatus,Serranus scriba and Diplodus annularis) on two different substrate types (Posidonia oceanica meadows and rocks) and for four sites in the Lavezzi Islands. The goodness of fit of this law to the biomass data will allow an optimum sampling strategy to be determined for each species with coefficients of variability of 10 and 25%.     

Supracrustal faults of the St. Lawrence rift system, Québec: kinematics and geometry as revealed by field mapping and marine seismic reflection data

The St. Lawrence rift system from the Laurentian craton core to the offshore St. Lawrence River system is a seismically active zone in which fault reactivation is believed to occur along late Proterozoic to early Paleozoic normal faults related to the opening of the Iapetus ocean. The rift-related faults fringe the contact between the Grenvillian basement to the NW and Cambrian–Ordovician rocks of the St. Lawrence Lowlands to the SE and occur also within the Grenvillian basement. The St. Lawrence rift system trends NE–SW and represents a SE-dipping half-graben that links the NW–SE-trending Ottawa–Bonnechère and Saguenay River grabens, both interpreted as Iapetan failed arms. Coastal sections of the St. Lawrence River that expose fault rocks related to the St. Lawrence rift system have been studied between Québec city and the Saguenay River. Brittle faults marking the St. Lawrence rift system consist of NE- and NW-trending structures that show mutual crosscutting relationships. Fault rocks consist of fault breccias, cataclasites and pseudotachylytes. Field relationships suggest that the various types of fault rocks are associated with the same tectonic event. High-resolution marine seismic reflection data acquired in the St. Lawrence River estuary, between Rimouski, the Saguenay River and Forestville, identify submarine topographic relief attributed to the St. Lawrence rift system. Northeast-trending seismic reflection profiles show a basement geometry that agrees with onshore structural features. Northwest-trending seismic profiles suggest that normal faults fringing the St. Lawrence River are associated with a major topographic depression in the estuary, the Laurentian Channel trough, with up to 700 m of basement relief. A two-way travel-time to bedrock map, based on seismic data from the St. Lawrence estuary, and comparison with the onshore rift segment suggest that the Laurentian Channel trough varies from a half-graben to a graben structure from SW to NE. It is speculated that natural gas occurrences within both the onshore and offshore sequences of unconsolidated Quaternary deposits are possibly related to degassing processes of basement rocks, and that hydrocarbons were drained upward by the rift faults.     

The effect of heterogeneity of diffusion parameters on chloride transport in low-permeability argillites

Understanding flow and transport in low-permeability media is very important in the context of nuclear waste disposal, oil and gas reservoirs and long term evolution of groundwater systems. In low-permeability media, transport by diffusion is often the most important mass transport process. This study investigates the effect of the heterogeneity of diffusion parameters on mass transport in low-permeability media. A geostatistical approach for integrating heterogeneity of diffusion parameters in groundwater flow and transport models is proposed and applied to the Toarcian argillites in France which are studied in the framework of feasibility of storing radioactive waste in deep clayey massifs. Stochastic fields of the diffusion parameters of the Toarcian argillites (France) are generated based on 64 measured values of diffusion coefficient and diffusion accessible porosity and used as input for a 3D local-scale groundwater flow and transport model. The chloride concentrations computed by these heterogeneous models are compared to the measured chloride concentrations and to concentrations calculated with a model in which the Toarcian argillites are subdivided into several homogeneous zones. The heterogeneous simulations result in a slightly better correspondence between measured and calculated values and have the additional advantage that the measured diffusion coefficient values in the Toarcian are perfectly honored in the model. This study shows that small-scale variability of diffusion parameters has a significant effect on solute concentrations and omitting this heterogeneity may be a problem in transport calculations in low-permeability media, depending on the specific setting and objectives of the study.     

GIS-based hydrogeological databases and groundwater modelling

Reliability and validity of groundwater analysis strongly depend on the availability of large volumes of high-quality data. Putting all data into a coherent and logical structure supported by a computing environment helps ensure validity and availability and provides a powerful tool for hydrogeological studies. A hydrogeological geographic information system (GIS) database that offers facilities for groundwater-vulnerability analysis and hydrogeological modelling has been designed in Belgium for the Walloon region. Data from five river basins, chosen for their contrasting hydrogeological characteristics, have been included in the database, and a set of applications that have been developed now allow further advances. Interest is growing in the potential for integrating GIS technology and groundwater simulation models. A "loose-coupling" tool was created between the spatial-database scheme and the groundwater numerical model interface GMS (Groundwater Modelling System). Following time and spatial queries, the hydrogeological data stored in the database can be easily used within different groundwater numerical models. Electronic Publication     

Dynamics and fluxes of organic carbon and nitrogen in two Guiana Shield river basins impacted by deforestation and mining activities

Deforestation and mining activities have proven to be very damaging to rivers because these activities disturb the environmental characteristics of rivers. Thus, the concentrations of dissolved organic carbon (DOC), particulate organic carbon (POC), particulate nitrogen (PN), and Chlorophyll‐a (Chl‐a) were measured monthly during 2 hydrological years in the Maroni and Oyapock Rivers to assess the dynamics and fluxes of organic carbon and nitrogen in these 2 Guiana Shield basins, which have been strongly (Maroni) and weakly (Oyapock) impacted by deforestation and mining activities. The 2‐year time series show that DOC, POC, PN, and Chl‐a concentrations vary seasonally with discharge in both rivers, indicating a hydrologically dominated control. Temporal patterns of DOC, POC, and PN indicate that these variables show maximum concentrations in rising waters due to the yield of organic matter and nitrogen accumulated in soils, which are incorporated into the rivers during rainfall. However, the Chl‐a concentrations were at a maximum during low‐water stages. The C/N and C/Chl‐a ratios also showed a seasonal trend, with lower values during the low water periods due to an increase in algal biomass. During high water, the POC in both rivers is the result of terrestrial organic matter, whereas during low‐water autochthonous organic matter can reach up to 34% of the POC. The mean annual fluxes of TOC and PN were higher (4.56 × 10⁵ tonC year^?1 and 1.77 × 10⁴ tonN year^?1, respectively) in the Maroni River than those (1.84 × 10⁵ tonC year^?1 and 0.54 × 10⁴ tonN year^?1, respectively) in the Oyapock River. However, the specific fluxes of DOC, POC, and PN from both basins were nearly the same. Although gold mining activities are performed in both basins, there is no conclusive evidence regarding the impact of these activities on the dynamics of organic matter and particulate nitrogen in the Maroni and Oyapock Rivers.     

Total atmospheric ozone measured by ground based high resolution infrared spectra-comparison with dobson measurements

Total atmospheric ozone has been measured at the “Observatoire de Haute-Provence”, Chiran Station, 1905 m high with a ground based, high resolution i.r. spectrometer, using the Sun as a source. Results are compared with a Dobson spectrophotometer which has been calibrated and intercompared with a standard. Total ozone values found with Dobson are 4% lower than values given by i.r. measurements. In addition, a negative correlation between total ozone and tropopause height has been found.     

Low-frequency transfer of seismic energy by superficial soil deposits and soft rocks

Recordings of recent strong earthquakes obtained on alluvial sites show that the maximum horizontal accelerations tend towards a limit of about 0.45 to 0.50g, associated with large displacements. by contrast, vertical accelerations do not appear to be subject to such a limit (1.7g for the 1979 Imperial Valley earthquake). Theoretical linear elasticity models, when applied to superficial layers of low strength, seem to be inadequate for the prediction of near-field ground motions in alluvial deposits. A good approximation for the horizontal component of certain Imperial Valley records was, however, obtained through a non-linear approach, using local soil properties together with a reasonable hypothesis for motion at the base of the superficial layers in question that included large values of acceleration for high-frequency shear waves.     

Chemical and structural control of the partitioning of Co, Ce, and Pb in marine ferromanganese oxides

The oxidation state and mineral phase association of Co, Ce, and Pb in hydrogenetic, diagenetic, and hydrothermal marine ferromanganese oxides were characterized by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) spectroscopy and chemical extraction. Cobalt is trivalent and associated exclusively with the Mn oxide component (vernadite). Cerium is tetravalent in all genetic-type oxides (detection limit for Ce(III) ∼ 5 at. %), including Fe-rich areas (ferrihydrite) of hydrogenetic oxides, and is associated primarily with vernadite. Thus, the extent of a Ce anomaly does not result from variations in redox conditions, but appears to be kinetically controlled, decreasing when the growth rate increases from hydrogenetic to diagenetic to hydrothermal oxides. Lead is divalent and associated with Mn and Fe oxides in variable proportions. According to EXAFS data, Pb is mostly sorbed on edge sites at chain terminations in Fe oxide and at layer edges in Mn oxide (ES complex), and also on interlayer vacancy sites in Mn oxide (TCS complex). Sequential leaching experiments, spectroscopic data, and electrochemical considerations suggest that the geochemical partitioning in favor of the Mn oxide component decreases from Co to Ce to Pb, and depends on their oxidative scavenging by Mn and Fe oxides.     

Two-phase, partially miscible flow and transport modeling in porous media; application to gas migration in a nuclear waste repository

We derive a compositional compressible two-phase, liquid and gas, flow model for numerical simulations of hydrogen migration in deep geological repository for radioactive waste. This model includes capillary effects and the gas high diffusivity. Moreover, it is written in variables (total hydrogen mass density and liquid pressure) chosen in order to be consistent with gas appearance or disappearance. We discuss the well possedness of this model and give some computational evidences of its adequacy to simulate gas generation in a water-saturated repository.     

Maris Gullying: canonical analysis of erosion and sedimentation sequences (Baronnies - France)

Abstract

The gullying action on Jurassic and Cretaceous marls in the Baronnies is observed, warm season after cold season, thanks to a network of measuring stakes arranged in 12 gullies. The climate, characterized by summer heath, rather cold but luminous winters, and quite heavy rain, can be classified as mountainous-mediterranean. Seasonal ablation/sedimentation measures have been carried out upon 119 stakes five times within two years (768 days): two in automn, two in early spring (april), and one at end-of-spring.

Ablation and sedimentation sequences are described among the stakes population by Correspondance Factor Analysis (CFA), and their covariations in space and time are explained by Canonical Correspondance Analysis (CCA) according to biophysical environment variables.

Axis 1 of the CFA opposes ground level variations according to their amplitude, high or moderate, regardless of the direction of variation and of measurement date. Axis 2 presents a temporal variation, opposing, on one side, sedimentation sequences at post-winter terms and ablation sequences at postsummer terms, to their converse on the other side.

The CCA indicates that talwegs in their medium and lower parts are more likely to undergo hard gullying or strong accumulation, especially on steep, or conversely flat, vegetationfree slopes of oxfordian marls; on the contrary, interfluve ridges and Gonson moderate gentle to moderate slopes on cenomanian marls, possibly with some vegetation are less dynamic (canonical axis 1). This result allows to extend former observations on rythmic, contrasted variations of gullies bottoms, well different of interfluves and gonson, progressive, regular, ones.

Owing to their varied reactions to seasonal erosive agents (cryoclasty, concentrated run-off), upper parts of talwegs and lower parts of gully slopes and interfluves (canonical axis 2) originate seasonal contrasts revealed by CFA’s axis 2. However, to insure this point of view, more sampling is needed.