Variabilités des temps de résidence de l’eau et du débit dans les rivières et les nappes phréatiques : implications sur la qualité de l’eau : inférence, modélisation et prédiction des temps de transit de l’eau dans les bassins versants

Abstract : Groundwater travel time controls contaminant transport, weathering processes and biogeochemical cycles. Groundwater travel time is a fundamental descriptor characterizing the transit time of water inside the catchment, from precipitation events to the streams. Quantifying these transit times is pivotal to predict the impact of anthropogenic pressure and assess freshwater ecosystems resilience. However, streamwater and groundwater are a mixture of water of different ages (the transit time and the residence time distribution), which vary according to climatic forcings. This makes difficult its characterization and prediction. Here we infer residence times with geochemical tracers and data-driven models. We show how this can be constrained by silicate weathering at the catchment scale. We then develop a novel process-based framework, which can model discharge and transit time seasonal and interannual variabilities. We identify water table fluctuations, its interaction with permeable soil layers and the resulting subsurface stormflow generation as a key process for seasonal water quality variations described by dissolved silica measurements. Finally, we draw a reactivity framework to represent biogeochemical processes. Indeed, evaluating reactive solute degradation is needed to assess the efficiency of reducing fertilizer loads, to predict the long term evolution of in stream solute concentrations and the eutrophication potential of freshwater bodies. Modeling the reactivity at the catchment scale is the missing link to understand, quantify and predict the effect of anthropogenic pressure on the critical zone.
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https://tel.archives-ouvertes.fr/tel-02096703
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Jean Marçais. Variabilités des temps de résidence de l’eau et du débit dans les rivières et les nappes phréatiques : implications sur la qualité de l’eau : inférence, modélisation et prédiction des temps de transit de l’eau dans les bassins versants. Sciences de la Terre. Université Rennes 1, 2018. Français. ⟨NNT : 2018REN1B025⟩. ⟨tel-02096703⟩

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