Le partenariat économique et financier euro-méditerranéen.

Au moment où la France, soutenue par l’Italie et l’Espagne, propose la création d’une Union pour la Méditerranée, le bilan économique et financier des douze années du partenariat de Barcelone entre l’Union européenne et les pays du pourtour méditerranéen reste mitigé.intégration régionale, banques centrales, Union européenne, pays partenaires méditerranéens, PPM, transferts des migrants, Alena, commerce international, investissement, IDE.

Synthèse des impacts écologiques des feux et des coupes forestières sur les lacs de l'écozone boréale au Québec

Cet article présente une première synthèse comparative des impacts des feux et des coupes forestières sur la qualité des eaux et les communautés aquatiques des lacs de l'écozone boréale de l'est du Canada. La recherche a été réalisée de 1996 à 1998 dans le cadre d'un projet du Réseau de centre d'excellence sur la gestion durable des forêts (RCE-GDF) et porte sur 38 lacs du Bouclier Canadien du Québec. Les changements dans la qualité de l'eau ainsi que dans la diversité, la biomasse et la structure des communautés de plancton et de poissons ont été suivis pendant trois ans dans 20 lacs dont les bassins versants étaient non perturbés, dans 9 lacs qui avaient subit des coupes forestières et dans 9 lacs qui avaient subit des feux de forêt.Notre étude montre que les feux et les coupes ont des impacts significatifs qui diffèrent selon le type de perturbation. En général, les lacs affectés par les coupes et les feux ont des concentrations de phosphore 2 à 3 fois plus élevées que les lacs de référence. Toutefois, les lacs affectés par les feux montrent des concentrations en nitrates beaucoup plus élevées tandis que les lacs affectés par les coupes sont moins transparents et ont des eaux plus colorées, très riches en carbone organique dissous. Les feux et les coupes affectent aussi de façon différente la minéralisation des eaux et les concentrations des ions majeurs. Les feux et les coupes n'ont pas d'effet sur la biodiversité des communautés planctoniques, sauf dans les lacs ayant un grand bassin versant et plus de 40 % de perturbation. Aucune différence n'a été observée entre les lacs de référence et les lacs perturbés au niveau de l'occurrence, l'abondance et la croissance des espèces de poissons. En revanche, les feux et les coupes affectent la production et la structure des communautés aquatiques. Dans les lacs affectés par les feux, l'enrichissement en azote et phosphore provoque une hausse de la concentration en chlorophylle a, et de la biomasse du phytoplancton et du limnoplancton (seston > 53 µm), en particulier des diatomées, des rotifères et des gros crustacés, pendant deux à trois années après les feux. En revanche, dans les lacs affectés par les coupes, l'enrichissement en phosphore n'entraîne qu'une augmentation très faible et limitée à un an de la biomasse des algues et pas de changement dans les biomasses du limnoplancton, en raison de la forte couleur et de la transparence réduite des eaux, qui limite la production biologique. Les coupes ont un impact négatif sur les copépodes calanoïdes, un groupe de zooplancton caractéristique des lacs oligotrophes et transparents. Une diminution significative de la proportion des individus de petite taille a été observée chez les populations de perchaude et de meunier noir des lacs perturbés (lacs de coupe et de feux formant un seul groupe). Les impacts observés dans la qualité des eaux et la production du plancton augmentent avec l'importance relative des perturbations au niveau du bassin versant. Cependant, la variabilité dans les caractéristiques des bassins versants et des lacs, en particulier le rapport de drainage et le temps de résidence des eaux, a des effets confondants sur les réponses des écosystèmes lacustres aux perturbations par les feux et les coupes.This paper presents a comparative review on ecological impacts of wildfires and harvesting on water quality and aquatic community attributes of boreal lakes in eastern Canada. This project was carried out from 1996 to 1998, as part of the research program of the Sustainable Forest Management Network Centre of Excellence (NCE-SFM), on 38 lakes of the Boreal Canadian Shield (Québec, Canada). Changes in water quality, and in diversity, biomass and community structure of pelagic plankton and fish populations were monitored for 3 years in 20 reference lakes, 9 cut lakes and 9 burnt lakes.Our study shows that wildfires and logging have significant impacts on water quality as well as primary and secondary producers in boreal lakes. However, fire and logging does not have similar impacts. In general, cut and burnt lakes showed higher concentrations of total phosphorus (TP: 2-3 folds) than reference lakes. However nitrates concentrations (NO3-) were higher in burnt lakes than in reference and cut lakes, whereas dissolved organic carbon (DOC), light extinction coefficient (e PAR) and water colour were higher in cut lakes than in reference lakes, burnt lakes showing intermediate values. Wildfire and logging also affect ionic composition of lake water. Both burnt and cut lakes had higher concentrations of potassium (K+), chloride (Cl-) and calcium (Ca2+) than reference lakes, while sulphates (SO42-) and magnesium (Mg2+) increased only in burnt lakes. The observed increases in organic and mineral elements reflect their export from the watershed and were related to the drainage ratio. As mobile ions are rapidly flushed from the perturbed watersheds, ionic water composition returned to normal levels within three years after the perturbation. In contrast, some changes in water quality (P and N enrichment in perturbed lakes; DOC increase in cut lakes) seems to be on longer term and might have a more important effect on limnological features of lakes such as thermal stratification, mixed and euphotic depth, plankton biomass and bioaccumulation of mercury in zooplankton and fish.Wildfires and logging do not have significant impacts on species richness of planktonic communities, except for lakes with large drainage basins and those where the perturbation was higher than 40% of the watershed area. However, wildfires and logging affect biomass of plankton communities. In burnt lakes, the nutrient enrichment induced important increases in Chl. a concentration and phytoplankton biomass, and a small increase in limnoplankton biomass (seston > 53 µm). Diatoms, rotifers and large crustaceans showed significant increases. In burnt lakes, increases in phytoplankton were observed during the three years of the survey and were highest in the first 2 years after fires. Limnoplankton increases lasted only 2 years and were highest the second year after fires. In cut lakes, nutrient enrichment was not reflected in a proportional increase in plankton production due to increase in DOC concentrations and lake water colour that reduced water transparency. Phytoplankton slightly increased only the first year after logging and no increase was observed for limnoplankton and zooplankton. Logging negatively affect calanoids, a zooplankton group characteristic of clear and oligotrophic lakes. No significant differences were observed in the occurrence, abundance and growth of fish populations among reference and perturbed lakes. However, the proportion of small yellow perch and white sucker were significantly lower in populations of impacted lakes (burned and logged lakes pooled). In most cases, impacts on water quality and plankton communities were related to the intensity of fire or logging, when expressed as the percent area of watershed harvested or burnt divided by the lake surface or volume. Simple models may then be developed and help to predict the effect of harvesting practices on lake ecosystems. However, environmental variation in watershed and lakes characteristics, especially drainage ratio and lake water residence time, are important confounding factors in the responses of lakes to watershed perturbations by fire or logging. Lakes with drainage ratio > 4 and with more of 30% of their watershed perturbed are the most sensitive to fire and logging. These factors should be considered when developing lake management models in the boreal forest impacted by fire and logging

Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {\guillemotright}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO3 layers, especially in view of their integration in devices.Comment: In press in J. Appl. Phy

The ecology of sexual dimorphism in size and shape of the freshwater blenny Salaria fluviatilis.

Sexual selection is considered the major cause of sexual dimorphism, but recent observations suggest that natural selection may play a more important role in the evolution of sex differentiation than previously recognized. Therefore, studying the trade-offs between natural selection and sexual selection is crucial to a better understanding of the ecology underlying the evolution of sexual dimorphism. The freshwater blenny Salaria fluviatilis, a fish inhabiting lakes and rivers around the Mediterranean Sea, displays strong sexual dimorphism in size, shape, and behavior (i.e., larger body and head size for males and higher swimming requirements for females during the reproductive period). We tested for differences in sexual dimorphism in size and shape between the populations from lake and river habitats with the goal of identifying the trade-offs between natural and sexual selection that underlie variations in sexual dimorphism in this species. Our results show i) differences in sexual size dimorphism (SSizeD) in accordance to Rensch's rule (i.e., larger individuals in rivers associated with higher SSizeD), and ii) a decrease in shape differentiation between males and females in lake populations. Together, this suggests that the different environmental conditions between lake and river habitats (e.g., resource limitations, predation pressure, water velocity) affect the relative importance of sexual selection in the display of sexual dimorphism within the species. This study highlights the importance of considering the environmental conditions to which populations are exposed to better understand the ecology underlying the evolution of sexual dimorphism

Measuring movement fluency during the sit-to-walk task

Restoring movement fluency is a key focus for physical rehabilitation; it's measurement, however, lacks objectivity. The purpose of this study was to find whether measurable movement fluency variables differed between groups of adults with different movement abilities whilst performing the sit-to-walk (STW) movement. The movement fluency variables were: (1) hesitation during movement (reduction in forward velocity of the centre of mass; CoM), (2) coordination (percentage of temporal overlap of joint rotations) and (3) smoothness (number of inflections in the CoM jerk signal)

Transport and Magnetic Properties of R1-xAxCoO3 (R=La, Pr and Nd; A=Ba, Sr and Ca)

Transport and magnetic measurements have been carried out on perovskite Co-oxides R1-xAxCoO3 (R=La, Pr, and Nd; A=Ba, Sr and Ca; 0<x<0.5: All sets of the R and A species except Nd1-xBaxCoO3 have been studied.). With increasing the Sr- or Ba-concentration x, the system becomes metallic ferromagnet with rather large magnetic moments. For R=Pr and Nd and A=Ca, the system approaches the metal- insulator phase boundary but does not become metallic. The magnetic moments of the Ca-doped systems measured with the magnetic field H=0.1 T are much smaller than those of the Ba- and Sr-doped systems. The thermoelectric powers of the Ba- and Sr-doped systems decrease from large positive values of lightly doped samples to negative ones with increasing doping level, while those of Ca-doped systems remain positive. These results can be understood by considering the relationship between the average ionic radius of R1-xAx and the energy difference between the low spin and intermediate spin states. We have found the resistivity-anomaly in the measurements of Pr1-xCaxCoO3 under pressure in the wide region of x, which indicates the existence of a phase transition different from the one reported in the very restricted region of x~0.5 at ambient pressure [Tsubouchi et al. Phys. Rev. B 66 (2002) 052418.]. No indication of this kind of transition has been observed in other species of R.Comment: 9 pages, 8 figures. J. Phys. Soc. Jpn. 72 (2003) No.

Determination of the cation site distribution of the spinel in multiferroic CoFe2O4 / BaTiO3 layers by X-ray photoelectron spectroscopy

International audienceThe properties of CoFe2O4/BaTiO3 artificial multiferroic multilayers strongly depend on the crystalline structure, the stoichiometry and the cation distribution between octahedral (Oh) and tetrahedral (Td) sites (inversion factor). In the present study, we have investigated epitaxial CoFe2O4 layers grown on BaTiO3, with different Co/Fe ratios. We determined the cation distribution in our samples by X-ray magnetic circular dichroism (XMCD), a well accepted method to do so, and by X-ray photoelectron spectroscopy (XPS), using a fitting method based on physical considerations. We observed that our XPS approach converged on results consistent with XMCD measurements made on the same samples. Thus, within a careful decomposition based on individual chemical environments it is shown that XPS is fully able to determine the actual inversion factor