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Theses

Étangs et qualité des cours d’eau de têtes de bassins versants agricoles : impact sur le devenir des pesticides et leurs produits de transformation

Abstract : In Lorraine, many fishponds are located at the head of the watershed. These fishponds have the direct effect of breaking the ecological continuum. Their impact on water quality has been shortly studied and remains largely unknown. studies on this matter has shown that, according to fish farming practices, emptying can be an important export phase for nutrients while retention can be expected during the fish production phase. As a result of this work, good management practices (eg not removing water during the passage of the nets, not leaving the sediments exposed during heavy rainfall) have been recommended to producers. In the same way, it was observed during the periods of pesticide application on the upstream watershed, a reduction of the concentrations (dissolved transport) in mother molecules in the stream downstream of the ponds. In view of these results, it is necessary: - to quantify the impact of ponds on dissolved but also particulate fluxes of pesticides; - to evaluate whether the reduction of concentrations downstream of the ponds results in the rejection of metabolites or a true retention / degradation of pesticides within the water bodies; - to assess the retention of phytosanitary products in the sedimentary compartment (in order to anticipate and quantify potential phytosanitary discharges during oil changes and to recommend management practices favorable to the preservation of downstream watercourses); - to appreciate the accumulation in the flesh of the fish to determine the piscicultural practices favorable to the production of fish of quality (even labeled 'Bio') and the preservation of the masses of water. Based on the previous work and supported by bibliographic data, we have established a list of potential pesticides and potentially formed metabolites. After having finalized the development of the analytical methods necessary for the monitoring of water, particulate, sedimentary and fish matrices, the inflow and outflow of ponds will be studied during the whole of an annual cycle of fish exploitation. The sediments will be sampled to determine the periods of accumulation or release by the sedimentary matrix. In order to ensure the safety of the fish produced and to appreciate the links between the quality of the environment and the biota, the accumulation in the fish flesh will be monitored. All the results obtained should allow: - to determine the occurrence of pesticides and their metabolites at the head of agricultural catchment; To appreciate the dissolved and particulate fluxes of these molecules during an annual cycle; - to assess the accumulation of phytosanitary products in sedimentary matrices in order to anticipate the risks of downstream discharges and to recommend management practices that minimize downstream impact; - to evaluate the accumulation of pesticides in fish in order to determine the practices favorable to a good sanitary quality of the fish and the preservation of the environment; - establish in water bodies the links between contaminations of abiotic matrices (ie water, sediments, particles) and biotic matrices (fish).
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Submitted on : Wednesday, April 6, 2022 - 4:55:37 PM
Last modification on : Thursday, April 7, 2022 - 3:37:51 AM

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DDOC_T_2021_0195_LE_COR.pdf
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  • HAL Id : tel-03633053, version 1

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François Le Cor. Étangs et qualité des cours d’eau de têtes de bassins versants agricoles : impact sur le devenir des pesticides et leurs produits de transformation. Sciences de l'environnement. Université de Lorraine, 2021. Français. ⟨NNT : 2021LORR0195⟩. ⟨tel-03633053⟩

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