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Accueil du site → Doctorat → France → 2011 → Quantification de l’érosion éolienne sur des surfaces anthropisées : simulations des flux en masse à l’échelle des zones arides Tunisiennes

Université Paris Diderot - Paris 7 (2011)

Quantification de l’érosion éolienne sur des surfaces anthropisées : simulations des flux en masse à l’échelle des zones arides Tunisiennes

Labiadh, Mohamed Taieb

Titre : Quantification de l’érosion éolienne sur des surfaces anthropisées : simulations des flux en masse à l’échelle des zones arides Tunisiennes

Quantification of wind erosion over agricultural surfaces : simulation of the flux masse on the Southern tunisian arid regions

Auteur : Labiadh, Mohamed Taieb

Université de soutenance : Université Paris Diderot - Paris 7

Grade : Doctorat : Chimie de la pollution atmosphérique et physique de l’environnement : Paris 7 : 2011

The aim of this work is to present a methodology permitting to quantify wind erosion, in particular the fluxes in mass on the southern Tunisian arid regions, A particular attention has been carried to the description and the assessment of the modifications of land use (extension of culture, change of agricultural practices, etc.). An approach combining simulations in laboratory, experiences on parcels and modelling is implemented. Otherwise, this last technique, modelling, is considered like one main tools of investigating permitting to give elements of answer to the final objectives of this work. Some specific parametrisations bas been developed on the laboratory permitting, consequequently to describe the erosion fluxes on agricultural surfaces (Kardous. 2005a, 2005b). These relations, allow to derive solely from the geometric features of the ridged surfaces (the height, RH, and the spacing, RS) the aerodynamic roughness height, the erosion threshold friction velocity and the saltation fluxes. To validate these parametrisation in situ, we had conduct in southern Tunisian arid region three experiences (2003. 2008 and 2009 on parcels plowed by three different tools (the disc, the moulboard and the tiller). These experiences show, on one hand that the model developed on the laboratory’ reproduces very well the experimental results and describes on a satisfying way the saltation fluxes on agricultural surfaces in Tunisian arid zones. On the other hand, theses results indicate also that erosion fluxes are smaller for the mouldboard, intermediate with the tiller and the higher for the disc. To simulate the emission of erosion fluxes the scale of arid and desert Tunisian zones, we used a meso-scale model, the regional Atmospheric Modeling System (RAMS) coupled on line with the Dust production model (DPM) developed by Marticorena and Bergametti (1995) and Laurent (2005). We had, first identified the most frequent and intense simulated zones sources of clust emission, We evaluated also the relative contribution of both natural surfaces and land agricultural uses to the fluxes in mass. The results suggest that the wind erosion stays predominant on the natural surfaces. Finally. a very marked seasonal cycle of the emissions is simulated with a maximum in the spring and in the beginning of the summer. This cycle is mainly due to the high wind speed generally observed on this period of year. Iron dust solubility in atmospheric waters is critical to estimate the effect of its deposition on primary production, especially on global carbon cycle. My PhD studies the effect of atmospheric organic complexation on iron dust dissolution. First of all, I studied the water soluble fraction of collected aerosols in the source region during strong biomass burning event, an important source of organic compounds. Second of all, I performed laboratory experiments with dust particles from different African sources and different organic compounds measured in the atmosphere. This work have highlight that the variability of iron dust solubility could be linked to the organic complexation. Oxalic acid is the most important iron ligand in the atmosphère and is the one with the most important effect on iron solubility, but others organic compounds such as malonic, tartane, glycolic acids or HULIS could enhanced the dissolution of iron. This dissolution, without light, is reductive and lead to the formation of Fe(II). I found a linear dissolution for dust iron in presence of increasing concentration of oxalate and HULIS, but for the other compounds the dissolution seems to be limited. I also found that the mineralogical composition of iron contained in dust is very important, and the dissolution is controlled by me presence of iron from clay minerals rather than iron from (hydr-)oxides.

Mots Clés : Érosion éolienne — Tunisie — — Vents — Vitesse — Rugosité — Simulation, Méthodes de — Cartographie — Quantification des émissions

Présentation : SUDOC

Page publiée le 8 mai 2012, mise à jour le 12 janvier 2018