Suelos volcanicos endurecidos

The tepetates of Mexico Highlands are indurated horizons with fragipan pr0perties. Tepetates appear among pyroclastic deposits (T1, T2, T3). A soil profile located near Texcoco, Mexico, including tepetate layers was studied. Mineralogical and microscopical features of this profile were studied using a series of methods. This report the main results of the study. Tepetates were characterized by several features: first, the nature of their parent material; second, a close matrix microstructure and third, their colloidal fraction. The latter is conformed mainly by laminated 1:1 to 2:1 mixed layer minerals made of flaky layers. These features can explain the fragipan properties of tepetates and most of their mechanical behaviour. (Résumé d'auteur)

Model testing of radioactive contamination Cs-137 of soils and bottom sediments in the Romachka river (Tomsk region, Russia)

This paper presents results of testing models for the radioactive contamination of river water and bottom sediments by 137Cs. The scenario for the model testing is based on data from the Romashka River, which was contaminated as a result of accidents at the Siberian Chemical Combine (Russia, Region of Tomsk). The input data include the following: estimates of inventories of 137Cs in the floodplain of the downstream part of Romashka River; the estimated annual runoff of 137Cs from the downstream part of Romachka River; data on the precipitation, hydrological and hydrochemical characteristics of the river. The endpoints of the scenario are model predictions of the activity concentrations of 137Cs in water and bottom sediments along the Romachka River in 2012-2013. Calculations for the Romashka scenario were performed by the Institute of radioprotection and nuclear safety (model CASTEAUR and HAMSTER. As a whole, the radionuclide predictions for137Cs for all considered models. At the same time the CASTEAUR model estimate the activity concentrations of 137Cs and in water more precisely than in bottom sediments

Andosols of the Canary Islands (X). Vitrandepts. Mineralogical characteristics. Their interpretation and classification

12 páginas, 8 gráficas.Interpretation, classification and mineralogical characteristics of Vitrandepts are given by the authors. The soils of this group are typically andosoils, with a littie differenciated profil developed on very recent vitric pyroclastic materials. Primary minerals, and volcanic glasses are very abundant in the gross and fine fractions of this soil. Secondary minerals are mainly allophane. Techniques used for mineralogical identifications include X-Ray, Infrared and electron-Microscope.Peer reviewe

Impact of Climate, Agriculture and Vegetation in the Sahel in the recent past : the CAVIARS Projet. [P-3330-53]

The semi-arid regions of the Earth are particularly vulnerable to wind erosion. The Sahelian region experienced contrasted climatic conditions during the last decades, with severe drought in the 70's and 80's and a relative re-greening in the recent years. Over the same period, changes in land use have occurred with an increase of the cultivated surfaces leading to a decrease of fallows and rangelands. As a result, a significant proportion of the land is bare or sparsely vegetated, and thus is not efficiently protected from the erosive action of wind. In this region, wind erosion tends to decrease the productive capacity of the soils whose fertility is already very low. In addition, the impact of wind erosion is expected to increase significantly in the near future (1) in relation with the expected changes in climate (in particular the modifications of precipitation and surface wind) and (2) in response to the increasing land use due to population increase and the related food needs. The aims of the CAVIARS project (Climate, Agriculture and Vegetation: Impacts on Aeolian ERosion in the Sahel) are to develop an integrated modeling tool to describe the evolution of wind erosion in the Sahel in connection with climatic and land use changes, to validate this tool in the current period by making the best possible use of the numerous data sets acquired in recent years over West Africa, and to test its ability to reproduce specific events (such as the drought in the Sahel) of the recent past (about the last 50 years). This project is based on a modeling approach of this recent past (hindcasts) that is justified by the need to ensure the robustness of the simulations with different forcings prior to any simulation of future scenarios. The proposed strategy is (1) to develop or optimize reliable modeling tools for quantifying the various terms (land use, changes in aridity...) responsible for changes in the intensity of wind erosion (2) to synthesize quality checked observations, that can be used as direct or indirect indicators of wind erosion (precipitation time series, changes in vegetation cover, atmospheric dust load,...) (3) to implement a validation strategy based on the quantification of wind erosion both locally, measured on grazed and cultivated plots, and at the regional and continental scales. (Texte intégral