Anthropogenic activities at the scale of a watershed can be very numerous (e.g. agricultural practices, industries, transport, and tourism). These activities generate pressures that result in the input of pollutants to the watercourse (e.g. major elements, organic micropollutants, trace metals). The identification of these sources of pollutants in watercourses remains a challenge to date. Organic matter in its dissolved fraction (DOM) constitutes a complex mixture of molecules whose composition and physicochemical properties depend on its origin, whether natural or anthropogenic, terrigenous or autochthonous, diffuse or point source. Because of its ubiquity, the DOM present in the rivers could be used as a tracer of the anthropic activities and thus of the sources of pollutants at the scale of a catchment. In this context, the objective of this thesis is to identify markers based on physico-chemical properties of DOM (that are characteristic of natural (e.g. terrigenous inputs, autochthonous production) and anthropogenic (e.g. wastewater treatment plant discharges, urban runoff, agriculture and livestock activities) sources at the watershed scale. For this purpose, an original database was built with more than 130 water samples representative of these different sources and analyzed with a wide range of analytical techniques (dissolved organic carbon determination, analysis by UV-Visible spectroscopy and fluorescence excitation-emission, analysis by steric exclusion chromatography coupled with UV and fluorescence detection - HPSEC/UV-fluorescence - , and molecular analysis by liquid chromatography coupled with high resolution mass spectrometry - LC-HRMS - ). The exploitation of the database allowed to improve the characterization of DOM with the identification of new optical (HPSEC/UV-fluorescence) and molecular (LC-HRMS) indicators. A protocol for processing complex data from non-targeted LC-HRMS analysis was developed and validated using quality control in order to extract the most relevant molecular compounds to differentiate DOM sources. This work also validated a sampling methodology specific to land-based diffuse sources in relation to land use to build their footprints at the watershed scale. Finally, the integrated multi-analytical and multi-source approach developed in the framework of the thesis allowed the construction of specific fingerprints of the selected sources of DOM (natural, anthropogenic, diffuse, point). The results of this work clearly show that DOM can be considered as a tracer of the origin of the water masses and the associated pollutions in the rivers.

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Cite the thesis

Mohamed-Amine Boukra. Caractérisation intégrée de la matière organique dissoute : recherche d'empreintes physico-chimiques pour tracer les sources de pollutions anthropiques. Chimie. Université Claude Bernard - Lyon I, 2023. Français. ⟨NNT : 2023LYO10094⟩. ⟨tel-04584694⟩

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