149 research outputs found
Carence en vitamine D et risque de pré-éclampsie : existe-t'il un lien ?
No full textMédecineLa carence en vitamine D est un problème de santé publique. Elle touche approximativement un milliard de personnes dans le monde et les femmes enceintes ne sont pas épargnées. L'hypovitaminose D gravidique peut avoir des conséquences telles qu'une augmentation de l'incidence de la prématurité, du diabète gestationnel et de l'hypertension, ayant ainsi des répercussions sur l'évolution de la grossesse. La pré-éclampsie, qui se caractérise par une hypertension et une protéinurie, est responsable de 50 000 à 70 000 morts maternelles par an dans le monde. De ce fait, une carence en vitamine D peut-elle augmenter le risque de développer une pré-éclampsie pendant la grossesse ? Afin de répondre à cette interrogation, notre mémoire s'est basé sur une lecture critique de quatre articles, puis d'une discussion autour de l'ensemble des données actuelles de la littérature scientifique. Une étude a conclu qu'une concentration en 25 OH D inférieure à 50 nmol/L entre 24-26 semaines d'aménorrhées (SA) augmenterait de 3,2 fois le risque de développer une pré-éclampsie. Il a aussi été observé que la concentration en 25 OH D entre 15 et 20 SA était de 23% plus basse chez la femme développant une pré-éclampsie sévère. Il a également été établi que les femmes à carnation foncée, résidant dans des zones faiblement ensoleillées et à de hautes latitudes sont des populations plus à risque de carence en vitamine D et de pré-éclampsie. La carence en vitamine D et le risque de pré-éclampsie sont très certainement liés. Les mécanismes physiopathologiques permettant de comprendre comment le manque de vitamine D favoriserait le développement de la pré-éclampsie restent encore non élucidés à ce jour mais de nombreuses pistes émergent et s'orientent vers une implication de la vitamine D au niveau vasculaire, immunitaire, et surtout génétique. Une des solutions, selon certains experts, pour diminuer l'incidence de la prééclampsie est la supplémentation en vitamine D mais les recommandations actuelles ne sont pas adaptées et la plupart des femmes enceintes sont en insuffisance voire en carence. Une augmentation de la dose actuellement prescrite permettrait d'assurer un statut vitaminique normal et donc par ce biais, de diminuer l'incidence de la pré-éclampsie. Un changement des recommandations et des pratiques serait nécessaire dans les années à veni
d13C pattern of dissolved inorganic carbon in a small granitic catchment: the Strengbach case study (Vosges mountains, France)
No full textThe transfers and origins of dissolved inorganic carbon DIC. were studied for a year in a soil–spring–stream system in
the Strengbach catchment, Vosges mountains, France. This 80 ha experimental research basin is located on the eastern side
of the mountains, at an altitude ranging from 883 to 1146 m.a.s.l. and is mainly covered by spruce 80%.. Brown acid and
podzolic soils developed on a granitic basement, and, as a result, the DIC originates solely from CO2 generated by oxidation
of soil organic matter. The d13CDIC. in catchment waters is highly variable, from about y22‰ in the springs and
piezometers to about y12‰ in the stream at the outlet of the catchment. In the springs, pronounced seasonal variations of
d13C exist, with the DIC in isotopic equilibrium with the soil CO that has estimated d13DIC 2 C of about y24‰ in winter and
y20‰ in summer. These seasonal variations reflect an isotopic fractionation that seems only induced by molecular
diffusion of soil CO2 in summer. In stream water, seasonal variations are small and the relatively heavy DIC y12‰ on
average. is a result of isotopic equilibration of the aqueous CO2 with atmospheric CO2
Evidence of hydrological control of Sr behavior in stream water (Strengbach catchment, Vosges mountains, France)
No full textStrontium and particularly 87Sr/86Sr ratios in stream water have often been used to calculate weathering rates in catchments. Nevertheless, in the literature, discharge variation effects on the geochemical behavior of Sr are often omitted or considered as negligible. A regular survey of both Sr concentrations and Sr isotope ratios of the Strengbach stream water draining a granite (Vosges mountains, France) has been performed during one year. The results indicate that during low water flow periods, waters contain lower Sr concentrations and less radiogenic Sr isotope ratios (Sr=11.6 ppb and 87Sr/86Sr=0.7246 as an average, respectively) than during high water flow periods (Sr= 13 ppb and 87Sr/86Sr=0.7252 as an average, respectively). This is contrary to expected dilution processes by meteoric waters which have comparatively lower Sr isotopic ratios and lower Sr concentrations. Furthermore, 87Sr/86Sr ratios in stream water behave in 3 different ways depending on moisture and on hydrological conditions prevailing in the catchment. During low water flow periods (discharge < 9 l/s), a positive linear relationship exists between Sr isotope ratio and discharge, indicating the influence of radiogenic waters draining the saturated area during storm events. During high water flow conditions, rising discharges are characterized by significantly less radiogenic waters than the recession stages of discharge. This suggests a large contribution of radiogenic waters draining the deep layers of the hillslopes during the recession stages, particularly those from the more radiogenic north-facing slopes. These results allow one to confirm the negligible instantaneous incidence of rainwater on stream water chemistry during flood events, as well as the existence in the catchment of distinct contributive areas and reservoirs. The influence of these areas or reservoirs on the fluctuations of Sr concentrations and on Sr isotopic variations in stream water depends on both moisture and hydrological conditions. Hence, on a same bedrock type, 87Sr/86Sr ratios in surface waters can be related to flow rate. Consequently, discharge variations must be considered as a pre-requisite when using Sr isotopes for calculating weathering rates in catchments, particularly to define the range of variations of the end-members
Modelling weathering processes at the catchment scale: The WITCH numerical model
No full textA numerical model of chemical weathering in soil horizons and underlying bedrock (WITCH) has been coupled to a numerical model of water and carbon cycles in forest ecosystems (ASPECTS) to simulate the concentration of major species within the soil horizons and the stream of the Strengbach granitic watershed, located in the Vosges Mountains (France). For the first time, simulations of solute concentrations in soil layers and in the catchment river have been performed on a seasonal basis. The model is able to reproduce the concentrations of most major species within the soil horizons, as well as catching the first-order seasonal fluctuations of aqueous calcium, magnesium and silica concentrations. However, the WITCH model underestimates concentrations of Mg2+ and silica at the spring of the catchment stream, and significantly underestimates Ca2+ concentration. The deficit in calculated calcium can be compensated for by dissolution of trace apatite disseminated in the bedrock. However, the resulting increased Ca2+ release yields important smectite precipitation in the deepest model layer (in contact with the bedrock) and subsequent removal of large amount of silica and magnesium from solution. In contrast, the model accurately accounts for the concentrations of major species (Ca, Mg and silica) measured in the catchment stream when precipitation of clay minerals is not allowed. The model underestimation of Mg2+ and H4SiO4 concentrations when precipitation of well crystallized smectites is allowed strongly suggests that precipitation of well crystallized clay minerals is overestimated and that more soluble poorly crystallized and amorphous materials may be forming. In agreement with observations on other watersheds draining granitic rocks, this study indicates that highly soluble trace calcic phases control the aqueous calcium budget in the Strengbach watershed
Hydrograph separation using isotopic, chemical and hydrological approaches (Strengbach catchment, France)
No full textThe streamflow components were determined in a small catchment located in Eastern France for a 40 mm rain event using isotopic and chemical tracing with particular focus on the spatial and temporal variations of catchment sources.
Precipitation, soil solution, springwater and streamwaters were sampled and analysed for stable water isotopes (18O and 2H), major chemical parameters (SO4, NO3, Cl2, Na1, K1, Ca21, Mg21, NH4, H1, H4SiO4, alkalinity and conductivity), dissolved organic carbon (DOC) and trace elements (Al, Rb, Sr, Ba, Pb and U). 18O, Si, DOC, Ba and U were finally selected to assess the different contributing sources using mass balance equations and end-member mixing diagrams.
Isotopic hydrograph separation shows that the pre-event water only contributes to 2% at the beginning of the stormflow to 13% at the main peak flow. DOC associated to Si and U to Ba allow to identify the different contributing areas (upper layers of the saturated areas, deep layers of the hillslope and rainwater). The streamflow (70%) originates from the deep layers of the hillslope, the remaining being supplied by the small saturated areas.
The combination of chemical (both trace and major elements) and isotopic tracers allows to identify the origin of water
pathways. During the first stage of the storm event, a significant part of the runoff (30±39%) comes from the small extended saturated areas located down part of the basin (overland runoff then groundwater ridging). During the second stage, the contribution of waters from the deep layers of the hillslope in the upper subcatchment becomes more significant. The final state is characterised by a balanced contribution between aquifers located in moraine and downslopes.
Indeed, this study demonstrates the interest of combining a variety of hydrometric data, geochemical and isotopic tracers to identify the components of the streamwater in such conditions
Hydrological behaviour of the granitic Strengbach catchment (Vosges massif, Eastern France) during a flood event
No full textA field campaign combining monitoring devices and determination of isotopes and chemical elements has been performed during a summer thunderstorm in the small granitic Strengbach catchment (Vosges, France). The collected ground data were used in a hydrological modelling exercise including two conceptual rainfallrunoff models (GR4, TOPMODEL). The predominant role in flood generation of pre-event water coming from the superficial layers of the water saturated area has been shown and a conceptual scheme has been proposed derived from the field observations. The two tested modelling structures and assumptions are not able to take into account fully the complexity of the physical processes involved in flood generation
Chromosomes in early human embryo development: incidence of chromosomal abnormalities, underlying mechanisms and consequences for development
No full textChromosomes in early human embryo development: incidence of chromosomal abnormalities, underlying mechanisms and consequences for development
No full textThe impact of vegetation on fractionation of rare earth elements(REE) during water–rock interaction
No full textPrevious studies on waters of a streamlet in the Vosges mountains (eastern France) have shown that Sr and rare earth elements (REE) principally originate from apatite dissolution during weathering. However, stream water REE patterns normalized to apatite are still depleted in light REE (LREE, La–Sm) pointing to the presence of an additional LREE depleting process. Speciation calculations indicate that complexation cannot explain this additional LREE depletion. In contrast, vegetation samples are strongly enriched in LREE compared to water and their Sr and Nd isotopic compositions are comparable with those of apatite and waters. Thus, the preferential LREE uptake by the plants at the root–water–soil (apatite) interface might lead to an additional LREE depletion of the waters in the forested catchment. Mass balance calculations indicate that the yearly LREE uptake by vegetation is comparable with the LREE export by the streamlet and, therefore, might be an important factor controlling the LREE depletion in river waters
The Strengbach catchment (Vosges massif, Eastern France): a field laboratory and a multidisciplinary researches site
No full text- …
