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Dynamique spatio-temporelle des flux naturels et anthropiques vers les hydrosystèmes littoraux tributaires des eaux souterraines : Investigations isotopiques et géochimiques pour la compréhension des interactions aquifères-lagune sur le site de Biguglia (Haute-Corse)

Abstract : The exacerbated anthropization of coastal hydrosystems poses a significant threat to groundwater and ecosystems that depend on it, then called "groundwater-dependent ecosystems". Like the Biguglia hydrosystem (Corsica, France), rapid and disorganized urbanization, as well as industrial and agricultural activities developed on the Marana plain are major sources of groundwater degradation. This strategic resource, used for the drinking water supply of the Bastia urban area, presents the markers of multiple and diffuse contaminations. In addition to being problematic for human water needs, the groundwater qualitative degradation of the Marana aquifer also constitutes a threat to the fragile ecosystem of the Biguglia lagoon and the sustainability of the ecosystem services it provides. In this context of increasing pressures, a strong knowledge of the Biguglia hydrosystem behavior is essential to ensure sustainable management of water resources. To this end, a multi-tracer geochemical and isotopic approach has been developed in order to better constrain the state of the groundwater resource, the hydrodynamic conditions and the nature of aquifer-river-lagoon interactions. The study of the stable isotopes of the water molecule (18O, 2H) has highlighted the recharge complexity. The Marana aquifer benefits from an indigenous recharge through direct infiltration of precipitation on the plain and an allochthonous recharge through precipitation from the schistous reliefs. The infiltration of river water from the Bevincu and Golu rivers and the lateral contribution of water from the schistous reliefs also contribute to the aquifer recharge. The developed mixing model (18O, Cl- and HCO3-) allowed a semi-quantitative estimation of the mixing processes. It demonstrates the complex aquifer behavior, with a significant difference in the contribution of schistous groundwater depending on the location and depth of the resource. It is also clear that the Biguglia lagoon is partially dependent on groundwater. The Marana plain is subject to qualitative degradation due to the excessive presence of nitrates (NO3-) and organic micropollutants. According to the NO3- (15N-NO3-, 18O-NO3-) and Boron (11B) isotopes, the main sources of nitrogen are soil and wastewater. The correlation between NO3- concentrations and water residence time (3H and CFCs) highlighted the storage and the groundwater archiving capacity. With regard to the evolution of land use, the progressive modification of the nitrogen sources recorded in the aquifer made it possible to trace the socio-environmental trajectory of the Biguglia hydrosystem. The contemporary degraded state of the resource mainly results from the pollution legacy linked to historical human activities. The conceptual model developed provides new elements that can help towards the implementation of relevant management strategies, to ensure the sustainability of water resources and associated ecosystem services.
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Submitted on : Friday, July 31, 2020 - 10:55:49 AM
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Mélanie Erostate. Dynamique spatio-temporelle des flux naturels et anthropiques vers les hydrosystèmes littoraux tributaires des eaux souterraines : Investigations isotopiques et géochimiques pour la compréhension des interactions aquifères-lagune sur le site de Biguglia (Haute-Corse). Hydrologie. Université de Corse Pasquale Paoli (UCPP), 2020. Français. ⟨tel-02909784v1⟩

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