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Nature et rôle des matières solides en suspension dans la dynamique du transfert des éléments polluants

Abstract : In order to characterize the nature and the role of fine and colloidal particles (FCP) in subsurface environments, a time-monitoring of FCP from atmospheric deposition and soil infiltration water and the determination of key factors controlling the distribution of the FCP were performed. The methodology is essentially based on in situ observations and consists on month-scale sampling of the FCP from atmospheric deposition (under a forest and over a vineyard) and soil infiltration water (in the vineyard). TEM/EDX study of individual FCP permitted a typological and physical-chemical characterization as well as the study of their abundance and reactivity facing contaminants. Moreover knowing the environmental parameters of each sampling sites and detailed statistical study of FCP evolution permitted to propose a conceptual model of the dynamic evolution (distribution, reactivity) of the FCP in the sampled environments. Microscopic observations showed that the majority of particles have a diameter inferior to 0.45 µm. Systematic investigations on the samples using TEM and EDX permitted to characterize particles and differentiate several recurrent types in the distinct environments. Then FCP are (i) mineral-types composed of automorphous and altered clays, oxi-hydroxides and salts (sulphur and chlorine) including rare tectosilicates and carbonates, or (ii) organic-types composed of bacteria and non-living organic matter (bacterial products and altered organic matter), or (iii) association of organic and mineral types forming organo-mineral micro-aggregates. Additionally, the characterization of physical and chemical properties of the different types of FCP permitted to identify their source, abundance and reactivity. The study of the time-distribution of the atmospheric FCP combined with the knowledge of environmental factors on the two sampling sites permitted to determine the key-factors that control the FCP distribution. Then, it appears that the amount and the intensity of the rain are the primarily factors. However, geographical position and occupation mode of the soils also have an influence by modifying, before the sources and after the rain action. Indeed, even if the study of the dynamic of the atmospheric FCP shows a strong influence of the rain, both sites have a different answer. The main actor controlling FCP from atmospheric deposition is the rain, modify by the vegetal cover which lead to a chemical enrichment and aggregation onto the leaves. The main actor controlling FCP from the soil infiltration water is the hydrological properties of the soil and so the fluctuation of the saturated state according to depth leading to aggregation processes. Finally, this work highlighted three important results: (i) the development of an efficient methodology, (ii) the evidence of an essential and often neglected contaminant vector, which are bacteria, via in situ observations and batch experiments, and (iii) the importance of the micro-aggregation processes in the transport of the FPC.
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Submitted on : Monday, December 3, 2012 - 10:11:13 PM
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Nicolas Perdrial. Nature et rôle des matières solides en suspension dans la dynamique du transfert des éléments polluants. Géochimie. Université Louis Pasteur - Strasbourg I, 2007. Français. ⟨tel-00760435⟩

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