Characterization of natural colloids from a river and spring in a karstic basin

 Colloids are known to transport contaminants over long distances in natural media. Despite this potentially harmful effect, very few studies have been undertaken in subsurface aquifers. This paper presents the first results of a study of natural colloids and particles in a karstic aquifer. The site was chosen for its coverage by clay layers and peat which deliver various and numerous particle types in water. The methodological part describes three methods used for size determination and sample fractionation of surface water and spring water. These methods have been adapted for the treatment of multiple samples due to the rapid discharge variation typical of karstic aquifers. The analysis of many particle size distributions (PSD) shows that they can be described by a Pareto law. The variation of the slope of the PSD at the spring is mainly dependent on discharge. This behavior is interpreted as a washing of the karstic drains during the first phase of high flow events. Fractionation of the samples allowed application of various characterization techniques to particle size classes. X-ray diffraction (XRD) patterns showed that most of the mineral particles originated from Quaternary deposits and limestones. However the use of scanning electron micrsocopy with energy-dispersive spectrometer (SEM-EDS) detailed the composition of individual particles and revealed particles not found by XRD. These techniques also showed the high complexity of the natural particles and the important place of coprecipitation in their formation. Consequences on the fluxes of particulate matter and its potential role as a carrier of contaminants are discussed. Received: 28 October 1996 · Accepted: 7 July 1997     

A Compilation of Silicon and Thirty One Trace Elements Measured in the Natural River Water Reference Material SLRS-4 (NRC-CNRC)

The natural river water certified reference material SLRS-4 (NRC-CNRC, National Research Council-Conseil National de Recherches Canada) has been routinely analysed for major and trace elements by six French laboratories. Most measurements were made using inductively coupled plasma-mass spectrometry. For silicon and thirty one trace elements (rare earth elements, Ag, B, Br, Cs, Ga, Ge, Li, P, Pd, Rb, Se, Th, Ti, Tl, W, Y and Zr), no certified values are assigned by NRC-CNRC. We propose some compilation values and related uncertainties according to the results obtained by the different laboratories.     

Climatic variability during the last 90 ka of the southern and northern Levantine Basin as evident from marine records and speleothems

The influence of the northern Atlantic and tropical monsoonal systems, as recorded by the River Nile, on the climate variability of the southeastern Mediterranean was studied in two cores taken by the R/V Marion Dufresne: one core taken SE of Cyprus representing the northern Levantine Basin (core 9501, 980 m water depth) and the other located ˜380 km further south, represents the southeastern Levantine Basin in an area influenced by the River Nile plume (core 9509, 884 m water depth). The study was performed at relatively high resolution using several proxies: δ¹⁸O of Globigerinoides ruber, sediment characteristics and index colour parameters in core sections representing the last 86 ka. A low-resolution alkenone sea surface temperature record was also measured. The time frame in both cores was mostly constrained by ‘wiggle’ matching with the nearby well-dated δ¹⁸O and δ¹³C record of the Soreq Cave, which is mainly influenced by the eastern Mediterranean water vapor. The sedimentary record of the southern core is strongly influenced by the River Nile contribution throughout the last 86 ka, as evidenced by the higher sedimentation rates compared with the northern core (20 cm/ka vs. 5 cm/ka), continuously darker sediment colour, and higher TOC values (0.6–0.9 vs. 0.25 wt% not including sapropels). During sapropels S1 and S3, present in both cores, the influence of the River Nile became more widespread, reaching as far as Cyprus. Yet, the influence of the River Nile remained stronger in the south, as evident by the higher TOC values in the southern core throughout the entire 90 ka period and the longer duration of S1 in the southern core. An anomalous low δ¹⁸O interval that is not recorded in western Mediterranean occurred between 58 and 49 ka in the Levantine Basin and is more developed in the northern core. This period correlates with D-O interstadial 14 and maximum northern hemisphere insolation during the lastglacial cycle, suggesting that the warming mainly impacted the northern Levant.The Eastern Mediterranean Sea and land area was considerably warmer than the western Mediterranean throughout the LGM – Holocene transition, and the δ¹⁸O_{G. ruber} drop of 4.5‰ is significantly greater than the 3‰ shift found for the western Mediterranean δ¹⁸O_{G. bulloides}, both differences reflecting an increased continental effect from the western to eastern Mediterranean. Comparison between the marine and the land δ¹⁸O records suggests that the origin of rain over the land is composed of mixed signal from the southern and northern Levantine Basin. The study of Δδ¹⁸O_sea–land variations demonstrates that various factors have influenced the sea–land relationship during the last 90 ka. The ‘amount effect’ has an important influence on rainfall δ¹⁸O during interglacial periods (particularly sapropel periods), whereas during glacial periods, increased land distances and elevation differences arising from decrease in sea level may have brought about decrease in δ¹⁸O of rainfall due to Rayleigh distillation processes. These influences were superimposed on those of sea surface water δ¹⁸O changes brought about by continental ice melting, and the strong effects felt in the southern Levantine Basin of the high River Nile input during periods of enhanced monsoonal activity.     

Structural investigations of (Ca,Sr)ZrO<Subscript>3</Subscript> and Ca(Sn,Zr)O<Subscript>3</Subscript> perovskite compounds

(Ca _x ,Sr_1?x )ZrO₃ and Ca(Sn _y ,Zr_1-y )O₃ solid solutions were synthesized by solid-state reaction at high temperature before to be studied by powder X-ray diffraction and Raman Spectroscopy. Diffraction data allow the distortion of the ABO₃ perovskite structure to be investigated according to cations substitution on A and B-sites. It is shown that distortion, characterized by Φ, the tilt angle of BO₆ octahedra, slightly increases with decreasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds and strongly decreases with decreasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds. Such results are discussed in view of the relative A and B cation sizes. Raman data show that vibrational spectra are strongly affected by the cation substitution on A-site; the frequencies of most vibrational modes increase with increasing x content in (Ca _x ,Sr_1?x )ZrO₃ compounds, i.e. with the decreasing mean size of the A-cation; the upper shift is observed for the 358 cm^?1 mode (?ν/?r = ?60.1 cm^?1/Å). On the other hand, the cation substitution on B-sites, slightly affect the spectra; it is shown that in most cases, the frequency of vibrational modes increases with increasing y content in Ca(Sn _y ,Zr_1?y )O₃ compounds, i.e. with the decreasing mean size of the B-cation, but that two modes (287 and 358 cm^?1) behave differently: their frequencies decrease with the decreasing mean size of the B-cation, with a shift respectively equal to +314 and +162 cm^?1/Å. Such results could be used to predict the location of different elements such as trivalent cations or radwaste elements on A- or B-site, in the perovskite structure.     

Trace metal pollution and its influence on the community structure of soft bottom molluscs in intertidal areas of the Dar es Salaam coast, Tanzania

The influence of trace metal pollution on the community structure of soft bottom molluscs was investigated in intertidal areas of the Dar es Salaam coast. Significant enrichment of As, Mn, Mo, Sb, and Zn in sediments was recorded. Redundancy analysis indicated that trace metal pollution contributed 68% of the variation in community structure. Monte Carlo permutation test showed that As and Sb contributed significantly to variation in species composition. T-value biplots and van Dobben circles showed that the gastropods Acteon fortis, Assiminea ovata, and Littoraria aberrans, were negatively affected by As and Sb, while the bivalve Semele radiata and the gastropod Conus litteratus were only negatively affected by As. Bioaccumulation of As, Cd, Cu, Mo and Zn occurred in the bivalve Mactra ovalina and the gastropod Polinices mammilla. This calls for regular monitoring and management measures.     

Nutrient fluxes between water column and sediments: Potential influence of the pearl oyster culture

This study quantifies benthic nutrient fluxes and sedimentation rates in the Ahe Atoll lagoon (French Polynesia), in two stations located under pearl oyster frames, and two control stations away from the pearl culture facility. Dissolved inorganic nitrogen fluxes ranged between 2 and 35μmolNm(-2)h(-1) and Soluble Reactive Phosphorus varied between -3 and 8.2μmolPm(-2)h(-1). Particulate sedimentation rates beneath the oysters were approximately five times higher than in the control zone and the percentage of small particles (?63μm) were about the twice. In contrast, sediment composition was similar under and outside the direct influence of oyster frames. In this ecosystem, where primary production is dependent on the available nitrogen, our study revealed that, while highly variable, benthic fluxes could sometimes contribute up to 28% of the nitrogen demand for primary production.     

A search for Chandler and nearly diurnal free wobbles using Liouville equations

Summary. The basic equations describing the dynamical effects of the Earth's fluid core (Liouville, Navier-Stokes and elasticity equations) are derived for an ellipsoidal earth model without axial symmetry but with an homogeneous and deformable fluid core and elastic mantle.
We develop the balance of moment of momentum up to the second order and use Love numbers to describe the inertia tensor's variations. The inertial torque takes into account the ellipticity and the volume change of the liquid core. On the core—mantle boundary we locate dissipative, magnetic and viscous torques. In this way we obtain quite a complete formulation for the Liouville equations.
These equations are restricted in order to obtain the usual Chandler and nearly diurnal eigenfrequencies.
Then we propose a method for calculating the perturbations of these eigenfrequencies when considering additional terms in the Liouville equations.