Composition, transfert et dynamique de la matière organique dissoute (MOD) dans les eaux fluviales et estuariennes : impact des activités agricoles

Abstract : In watersheds under strong agricultural pressure, manuring activities, particularly animal farming, are the main source of dissolved organic matter (DOM). However, the composition, the role and the fate of this DOM have been poorly studied. This study focuses on the sources, dynamics and transformation of the DOM and its constituents in riverine and estuarine systems affected by different agricultural practices. The analysis of DOM was performed using two recent and innovative analytical techniques: (i) an electrochemical method (DP-CSV), allowed us to characterize simultaneously three dissolved organic compounds: glutathione (GSH-like), thioacetamide (TA-like), and fulvic acids (FA-like), (ii) a size exclusion liquid chromatography coupled to an carbon, nitrogen and UV detector (LC-OCD-OND-UVD) allowed the DOM pool to be subdivided into 6 major sub-fractions. Relative to the pristine river, concentrations of organic compounds were found to be 1.5 to 4 times higher in impacted systems. These anomalies are related to the agricultural pressure and also to the type of livestock. Our results also showed that the seasonal variations were controlled by different processes: soil washing-out during high precipitation events for FA-like compounds which represent the major part of DOM, formation in deep horizons then rising of groundwater for TA-like compounds and a pedogenic and aquatic origin for GSH-like compounds. Along the salinity gradient, GSH-like and FA-like displayed a conservative behaviour whereas TA-like do not behave conservatively with important removals.
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Lauriane Marie. Composition, transfert et dynamique de la matière organique dissoute (MOD) dans les eaux fluviales et estuariennes : impact des activités agricoles. Chimie analytique. Université de Bretagne occidentale - Brest, 2016. Français. ⟨NNT : 2016BRES0101⟩. ⟨tel-01543508⟩

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