Key drivers for copepod assemblages in a eutrophic coastal brackish lake

The copepod assemblages and abiotic parameters were investigated at 11 stations in a large coastal lake (Lake Manzalah, Nile Delta) from 2009-2010 in order to verify any impacts of eutrophication and salinity on the copepod species composition. The environmental conditions and the copepod assemblages appeared to have changed in comparison with previous studies, possibly because of increasing eutrophication and invasions of non-indigenous species (NIS). The aim of the present study was the identification of species which can be used as ecological indicators of high trophic status. Among the nine copepod species of Lake Manzalah, Acartia tonsa, Mesocyclops ogunnus, and Apocyclops panamensis were reported for the first time. Acartia tonsa, a well-known NIS for the Mediterranean, numerically dominated the copepod assemblages in some portions of the lake. The distribution of Acanthocyclops trajani and Thermocyclops consimilis was insensible to eutrophication because they can stand high levels of nutrients and hypoxia. Compared with previous reports, the copepod assemblage of Lake Manzalah was richer in species. The invasions of NIS, in addition to the heterogeneous progress of eutrophication in the lake, created an environmental mosaic with many species in total, but with single areas suitable for only a small number of them

Application des modèles de Langmuir et Freundlich aux isothermes d'adsorption des métaux lourds par l'argile purifiée

Bentonite, which consist essentially of clay minerals belonging to the smectite group, have a wide range of chemical and industrial uses. The structure chemical composition, exchangeable-ion type and small crystal size of smectite are responsible for several properties, including a large chemically active surface area, a high cation-exchange capacity and interlamellar surface having usual hydratation characteristics. A sample collected from Zaghouan (North East Tunisia, North Africa) is studied through some physico-chemical methods. Results from X-ray diffraction, chemical analysis, infrared spectroscopy, thermogravimetric analysis (TGA) and differential thermal analysis (DTA), cation exchange capacities, specific and total surfaces, confirm the general smectite character of the sample. The adsorption capacity of this clay was tested out using three metallic ions (Pb$^{2+}$, Zn$^{2+}$, Ni$^{2+}$). The results showed that, in all cases, adsorption can be illustrated by Freundlich or Langmuir isotherms. However, for 10$^{-3}$M Pb$^{2+}$ the low value of the correlation coefficient (R$^{2}$) indicated that the experimental data for the adsorption didn't fit to any linear form of the Langmuir equation. Metal adsorbed onto Zaghouan clay varied in the decreasing order PbPb$^{2+}$ > Zn$^{2+}$ > Ni$^{2+}$ and fitted in satisfactorily with the uptake capacity. For Pb$^{2+}$ the amount of adsorbed ions remained higher than the CEC (cation exchange capacity) of the clay fraction. This result may be due to adsorption of hydroxy lead complex in addition to sorption of bivalent lead form which explains the high amount of Pb$^{2+}$ removed from aqueous solution

Solution solide d’apatites de plomb, d’argent et de sodium : synthèse, caractérisation structurale et propriétés électriques

A continuous solid solution of Pb$_8$Na$_{\rm 2-x}$Ag$_x$(PO$_4$)$_6$ (0$\leq$ x $\leq$2) crystallizing in the anionic-deficient apatite structure was obtained by solid-state reaction. The samples were characterized by using X-ray diffraction, infrared absorption spectroscopy, Raman scattering spectroscopy, $^{31}$P MAS-NMR and chemical analysis. The electrical conductivity versus x measured in a wide range of temperature increases with silver content. For each composition, conductivity values obey the Arrhenius law. Correlations between electrical and structural properties are established

Retention and swelling properties of a calcareous soil during leaching by zinc solutions

International audienc

Préparation et étude des propriétés de conduction ionique des polyphosphate mixtes de type MI^{\rm I}MIII^{\rm III}(PO3_3)4_4, (MI^{\rm I} = Li, K et MIII^{\rm III} = Y, Bi)

The field of research related to ionic transport in the solid electrolytes has passed through very fast evolution during the last years. The main importance here has the discovery of many ionic conducting compounds which are characterized by the nature of the ion responsible for the ionic transport, by the temperature range, and the dimensionality of the conducting phase. The materials with high ionic conductivity have various applications in the energetics, the analysis and the electronics fields. In particular, the compounds with Li$^+$ cations are of a great interest in connection with production of electrochemical generators of high energy density. Nevertheless the study of materials with low ionic conductivity remains interesting to specify some mechanisms of transport. Within the confines of the systematic study of a new long chain polyphosphates containing monovalent and yttrium cations, appearing in the M$^{\rm I}$PO$_3$ – M$^{\rm III}$(PO$_3$)$_3$ systems with (M$^{\rm I}$ = Li, K and M$^{\rm III}$ = Y). We have described the chemical preparations and the structural studies of these mixed polyphosphates of type M$^{\rm I}$M$^{\rm III}$(PO$_3$)$_4$ with (M$^{\rm I}$ = Li, K and M$^{\rm III}$ = Y). These incongruent melting compounds were identifie by X-ray diffraction and the infra-red spectroscopy. Both these two intermediate compounds and the LiBi(PO$_3$)$_4$ polyphosphate were the subject of the ionic study of conductivity with use of the impedance spectroscopy. The values of ionic conductivity as well as the energies of activation were given at various temperatures

Stabilisation des phases monocristallines quadratique et cubique dans BaTiO3_3

Single crystals of Ba$_{\rm 1-x}$Yb$_x$TiO$_3$ and Ba$_{\rm 1-x}$Sr$_x$TiO$_3$ with tetragonal structure were grown by the floating zone (FZ) method using an LHPG (Laser Heated Pedestal Growth) technique. The grown crystals, typically 1 mm in diameter and 8 mm in length, were yellowish transparent. Substitution of more than 2.5 at % Sr for Ba in BaTiO3 and addition of 3 to 5 at % Ln (Ln= Yb, Eu), were effective in preventing the formation of the hexagonal phase. The Eu$^{3+}$ emission spectra recorded at room temperature demonstrate a significant intensity enhancement of the $^{5}$D$_0$ → $^{7}$F$_1$ magnetic dipolar transition compared to the $^{5}$D$_0$ → $^{7}$F$_2$ electric dipolar transition.Les fibres monocristallines de Ba$_{\rm 1-x}$YbxTiO$_3$ et Ba$_{\rm 1-x}$Sr$_x$TiO$_3$ de structure quadratique ont été préparées par la méthode de la zone flottante (FZ) en utilisant la technique LHPG (Laser Heated Pedestal Growth). Les échantillons élaborés, de dimensions 1mm x 8 mm, sont jaunâtres et transparentes. La substitution du baryum par plus de 2,5 mol% de Sr dans BaTiO$_3$ et le dopage de 3 à 5 mol% de Ln (Ln = Yb, Eu) évitent la formation de la phase hexagonale. Le spectre d’émission de Eu$^{3+}$ enregistré à température ambiante montre le changement de structure traduit par la forte intensité de la transition dipolaire magnétique $^{5}$D$_0$ → $^{7}$F$_1$ comparée à celle de la transition dipolaire électrique $^{5}$D$_0$ → $^{7}$F$_2$