Flux de CO2 consommé par altération chimique continentale : influences du drainage et de la lithologie = CO2 flux consumed by chemical weathering of continents : influences of drainage and lithology

The flux of atmospheric/soil CO2 consumed by chemical weathering of the continents (FCO2) can be estimated from bicarbonate concentrations in surface water. Using data from the bibliography for 232 small monolithologic watersheds, relationships between FCO2 and the runoff (Q) have been determined For the major rock types outcropping on the continents. The models fitted to these relationships are then applied to the Garonne and Congo river basins, in order to calculate the mean CO2 flux consumed in these basins. The results obtained are close to previous estimates bosed on field measurement

Worldwide distribution of continental rock lithology: Implications for the atmospheric/soil CO2 uptake by continental weathering and alkalinity river transport to the oceans

The silicate rock weathering followed by the formation of carbonate rocks in the ocean, transfers CO2 from the atmosphere to the lithosphere. This CO2 uptake plays a major role in the regulation of atmospheric CO2 concentrations at the geologic timescale and is mainly controlled by the chemical properties of rocks. This leads us to develop the first world lithological map with a grid resolution of 1 1. This paper analyzes the spatial distribution of the six main rock types by latitude, continents, and ocean drainage basins and for 49 large river basins. Coupling our digital map with the GEM-CO2 model, we have also calculated the amount of atmospheric/soil CO2 consumed by rock weathering and alkalinity river transport to the ocean. Among all silicate rocks, shales and basalts appear to have a significant influence on the amount of CO2 uptake by chemical weatherin

Enhanced chemical weathering of rocks during the last glacial maximum: a sink for atmospheric CO2?

It has been proposed that increased rates of chemical weathering and the related drawdown of atmospheric CO2 on the continents may have at least partly contributed to the low CO2 concentrations during the last glacial maximum LGM.. Variations in continental erosion could thus be one of the driving forces for the glacialrinterglacial climate cycles during Quaternary times. To test such an hypothesis, a global carbon erosion model has been applied to a LGM scenario in order to determine the amount of CO2 consumed by chemical rock weathering during that time. In this model, both the part of atmospheric CO2 coming from silicate weathering and the part coming from carbonate weathering are distinguished. The climatic conditions during LGM were reconstructed on the basis of the output files from a computer simulation with a general circulation model. Only the predicted changes in precipitation and temperature have been used, whereas the changes in continental runoff were determined with an empirical method. It is found that during the LGM, the overall atmospheric CO2 consumption may have been greater than today by about 20%., mainly because of greater carbonate outcrop area related to the lower sea level on the shelves. This does not, however, affect the atmospheric CO2 consumption by silicate weathering, which alone has the potential to alter atmospheric CO2 on the long-term. Silicate weathering and the concomitant atmospheric CO2 consumption decreased together with a global decrease of continental runoff compared to present-day both by about 10%.. Nevertheless, some uncertainty remains because the individual lithologies of the continental shelves as well as their behavior with respect to chemical weathering are probably not well enough known. The values we present refer to the ice-free continental area only, but we tested also whether chemical weathering under the huge ice sheets could have been important for the global budget. Although glacial runoff was considerably increased during LGM, weathering under the ice sheets seems to be of minor importance

The use of performance enhancing substances by adolescent male athletes in selected Johannesburg boys' high schools

MSc (Med), Biokinetics, Faculty of Health Sciences, University of the WitwatersrandIntroduction: Performance enhancing substance (PES) use is a major concern currently facing adolescent sport. The youth have become more competitive in sport, with some using substances and supplements to improve their performance. Unfortunately, some of these adolescent athletes are using substances that are both harmful to their health and prohibited. Aim of study: To establish the attitudes and perceptions towards and the use of PES, including prohibited substances and food supplements, by adolescent male athletes, in selected Johannesburg boys’ high schools. Method: The study design was a cross-sectional study using a self-administered questionnaire. Male adolescent high school learners involved in 1st and 2nd team competitive high school sport in seven Johannesburg boys’ high schools were invited to volunteer to participate in the study. Questionnaires were completed under conditions similar to an examination, where participants were not allowed to communicate with each other. Demographic data was analysed using descriptive statistics. Results: The sample size was 100. Results indicated that the prevalence of PES use amongst the participants was 30%. The use of prohibited substances was found, including growth hormone (5%), anabolic androgenic steroids (4%), and adrenaline (4%). Food supplement use was also found in this sample, including creatine (32%), protein (61%), carbohydrate (54%), caffeine (57%) and vitamin (61%) supplementation. Most of the participants (83%) that used PES started using them when they were over 15 years old. The majority of the participants (42%) played rugby as their main high school sport. Conclusion: The findings indicate that there was generally a low prevalence of ergogenic substance use in Johannesburg boys’ high school sport for performance enhancement. Substances such as anabolic androgenic steroids (4%) and growth hormone (5%) were found to be used by the learners. The anti-doping attitude of the learners may be improved by education programmes, which aim to decrease the prevalence of prohibited PES use in adolescent sport

Scale effects on the response of composite structures under impact loading

For several years, composite materials have taken a significant part in the realization of structures designed for transport (aeronautical, nautical, automotive. . .). In order to qualify the behavior of such structures, preliminary validation tests have to be done. These specific tests are often very expensive and difficult to set up, especially when the structure dimensions are large (fuselages of aircraft, ship hulls. . .). An alternative way is then to employ small-scale models. The use of these reduced scale structures requires the identification of similitude models allowing the extrapolation of the small-scale model behavior to the real structure. Although largely developed in the case of homogeneous materials, such similitude techniques are not clearly identified for composite materials taking into account the damage evolution during an impact. The purpose of this article is firstly to present existing similitude techniques making it possible to predict the composite structure behaviour from the knowledge of small-scale model response. Secondly, experiments were done on two scale of samples carried out by stratification of unidirectional carbon/epoxy plies. These results were finally compared with the analytical predictions of similitude laws currently used. The aim of this paper is to contribute to similitude laws development applied to composite structures. These laws permit to extrapolate the small-scale model behavior to the real scale one. Existing approaches have been established following two different methods. They are summarized in this paper and applied to impact loadings on two laminated plate scales. In order to complete data collected by ‘‘conventional’’ instrumentation (force transducer, displacement sensor, accelerometer.. .), optical device such as an high-velocity CCD camera, associated with optical techniques for the monitoring of markers, were used. These techniques make possible to compare displacement lines corresponding to each scale. It is shown that existing similitude laws, used for elastic materials, do not allow to simulate the behavior of the real scale when this one is damaged

Factors associated with obesity and metabolic syndrome in an ageing cohort of black women living in Soweto, Johannesburg (study of women in and entering endocrine transition [sweet])

A thesis submitted to the Department of Paediatrics Faculty of Health Sciences University of the Witwatersrand In fulfilment of the requirements for the Degree of Doctor of Philosophy Johannesburg, 2016Background: Black South African women living in urban settings have the highest prevalence of obesity in the sub–Saharan African region, and consequently a high prevalence of cardiometabolic diseases. The risk factors for obesity and the metabolic syndrome are not well studied in this population group, and the inter–relationship between diseases risk factors for metabolic syndrome is poorly understood, in addition to whether one factor predominates. Aim: The aim is three–fold: (i) To assess the physical activity patterns of middle–aged, urban black South African women, and if these patterns are associated with metabolic outcomes; (ii) To examine the association between lifestyle and psycho–social factors and changes in body composition over 10 years in this population; and (iii) To identify risk factors for the various components of metabolic syndrome. Methods: Drawing on the longitudinal Birth to Twenty Plus cohort (a longitudinal study of the health and development of children and their families) data collected in 2003 and 2013 was used to address the respective aims of the thesis. In particular, data on (i) anthropometry; (ii) body composition; (iii) blood pressure; (iv) cardiometabolic markers; (v) environmental factors (physical activity, smoking and smokeless tobacco consumption, and alcohol consumption); (vi) psycho–social factors; (vii) socio–economic status; and (viii) education status was used. Analytical methods comprised of descriptive, correlations, comparisons, multivariable regression, and logistic regression. Paper 1 described the patterns, levels and correlates of physical activity in 977 African women. Paper 2 was a longitudinal study of the role of environmental and psycho–social factors in predicting changes in body composition over 10 years (N=430). Body composition from ultrasound and DXA analyses, blood pressure, cardiometabolic and demographic factors were measured in 702 black African women from Soweto, Johannesburg for paper 3, which was a descriptive, cross–sectional study using data from the 2011/13 wave of data collection. Results: The prevalence of obesity (48.0% (baseline) to 67.8% (follow–up)) and metabolic syndrome (40.0% (baseline) to 49.6% (follow–up) increased significantly over ten years. The majority of the population were classified as “active” according to global physical activity questionnaire criteria, and the domain that contributed most to overall weekly physical activity was walking for travel. Sitting time (mins/wk) was not different between the activity groups, but was positively associated with triglyceride levels and diastolic blood pressure. Total physical activity was inversely associated with fasting insulin, and physical activity in the work domain was associated with fat–free, soft–tissue mass. Two distinct groups of overweight/obese females were identified using body–size dissatisfaction and body–size discrepancy scores: one that was content with their body–size and one that wished to be leaner. Vigorous physical activity at baseline was inversely associated with absolute changes in all measures of adiposity. In subjects who underestimated their body–size at baseline (74.0 % of the study population) changes in total and peripheral levels of body fat were less than in subjects who correctly identified their body–size. In the group that underestimated body–size, more women wanted to be leaner than in the group who knew their body–size (60.1 % vs 47.5 %, p < 0.05). Logistic regression analysis demonstrated that adiponectin (odds ratio [95% CIs]: 0.84 [0.77, 0.92], p<0.0005) and abdominal subcutaneous fat (0.56 [0.39, 0.79], p=0.001) reduced metabolic syndrome risk whilst insulin resistance (1.31 [1.16, 1.48], p<0.0005) and trunk fat–free, soft–tissue mass (1.34 [1.10, 1.61], p=0.002) increased risk. Within this group of risk factors, the relationship of adiponectin with metabolic syndrome risk, when analysed across adiponectin hexiles, was the least affected by adjustment for the other risk factors. Conclusions: The findings of this thesis show that the majority of urban black South African women have a high prevalence of obesity and cardiometabolic disease risk factors despite being classified as ‘physically active’. However, the intensity of the respective domains of physical activity is unknown. As walking as a means of travel/transport is a major contributor to physical activity, future research should attempt to determine whether the intensity of this activity plays a role in the prevention of cardiometabolic diseases. It was also demonstrated that an underestimation of body–size is common and is associated with a lower gain in total body adiposity and a desire to lose weight in most of the participants. Finally, this thesis observed that adiponectin has a significant protective role against metabolic syndrome that is independent of other risk factors. The protective and augmentive effects of abdominal subcutaneous fat and lean trunk mass, respectively, on metabolic syndrome risk demonstrate the existence of novel interactions between body composition and cardiometabolic disease.MT201

Atmospheric CO2 consumption by continental erosion : present-day controls and implications for the last glacial maximum

The export of carbon from land to sea by rivers represents a major link in the global carbon cycle. For all principal carbon forms, the main factors that control the present-day fluxes at the global scale have been determined in order to establish global budgets and to predict regional fluxes. Dissolved organic carbon fluxes are mainly related to drainage intensity, basin slope, and the amount of carbon stored in soils. Particulate organic carbon fluxes are calculated as a function of sediment yields and of drainage intensity. The consumption of atmospheric/soil CO2 by chemical rock weathering depends mainly on the rock type and on the drainage intensity. Our empirical models yield a total of 0.721 Gt of carbon (Gt C) that is exported from the continents to the oceans each year. From this figure, 0.096 Gt C come from carbonate mineral dissolution and the remaining 0.625 Gt C stem from the atmosphere (FCO2). Of this atmospheric carbon, 33% is discharged as dissolved organic carbon, 30% as particulate organic carbon, and 37% as bicarbonate ions. Predicted inorganic carbon fluxes were further compared with observed fluxes for a set of 35 major world rivers, and possible additional climatic effects on the consumption of atmospheric CO2 by rock weathering were investigated in these river basins. Finally, we discuss the implications of our results for the river carbon fluxes and the role of continental erosion in the global carbon cycle during the last glacial maximum

Impact of nitrogen fertilizers on the natural weathering-erosion processes and fluvial transport in the Garonne basin

Knowledge of the impact of N-fertilizers on the weathering-erosion processes of soils in intensively cultivated regions is of prime importance. Nitrification of NH4− fertilizers produces HNO3 in the basin of the Garonne river, enhancing soil degradation. Their influence on the weathering rates was determined by calculating the consumption rate of atmospheric/soil CO2 by soil weathering and erosion, and its contribution to the total dissolved riverine HCO3−. This contribution was found to be less than 50% which corresponds normally to a complete carbonate dissolution by carbonic acid, suggesting that part of the alkalinity in the river waters is due to carbonate dissolution by an acid other than carbonic acid, probably HNO3

Sources et cheminements des polluants

Dans l’environnement, un ensemble complexe de processus chimiques, physiques, biologiques et géologiques régule le cycle des éléments et des composés chimiques. La composition des eaux, qui résulte de ces processus, est naturellement contrôlée par l’altération des minéraux qui consomme du CO2 atmosphérique et l’activité des organismes vivants. Les activités anthropiques génèrent des contaminants véhiculés dans les différents compartiments interdépendants: eaux, biosphère, atmosphère, sol et roches). Pour comprendre le cheminement des composés dans les eaux, il faut tenir compte du trajet des eaux dans chaque compartiment et des relations entre les compartiments. Les processus physico-chimiques sont associés aux échanges entre les phases dissoutes et solides particulaires , aux interactions avec les organismes, ainsi qu’aux processus physiques. Ceux-ci sont plus ou moins fortement perturbés par les activités humaines, dont l’expansion et l’intensification accroissent la dispersion des polluants dans les milieux naturels. Il en est ainsi des flux de certains polluants qui peuvent être très largement supérieurs aux flux d’éléments naturels libérés par l’érosion chimique et les interactions avec les organismes