Strontium isotopes as tracers of water-rocks interactions, mixing processes and residence time indicator of groundwater within the granite-carbonate coastal aquifer of Bonifacio (Corsica, France)

S Santoni; F Huneau; E Garel; L Aquilina; V Vergnaud-Ayraud; T Labasque; H Celle-Jeanton

doi:10.1016/j.scitotenv.2016.08.087

Strontium isotopes as tracers of water-rocks interactions, mixing processes and residence time indicator of groundwater within the granite-carbonate coastal aquifer of Bonifacio (Corsica, France)

Sci Total Environ. 2016 Dec 15:573:233-246. doi: 10.1016/j.scitotenv.2016.08.087. Epub 2016 Aug 24.

Authors

S Santoni¹, F Huneau², E Garel², L Aquilina³, V Vergnaud-Ayraud³, T Labasque³, H Celle-Jeanton⁴

Affiliations

¹ Université de Corse Pascal Paoli, Faculté des Sciences et Techniques, Laboratoire d'Hydrogéologie, Campus Grimaldi, BP 52, F-20250 Corte, France; CNRS, UMR 6134, SPE, F-20250 Corte, France. Electronic address: santoni7@univ-corse.fr.
² Université de Corse Pascal Paoli, Faculté des Sciences et Techniques, Laboratoire d'Hydrogéologie, Campus Grimaldi, BP 52, F-20250 Corte, France; CNRS, UMR 6134, SPE, F-20250 Corte, France.
³ OSUR, Géosciences Rennes, UMR 6118, CNRS/Université Rennes-1, F-35042 Rennes, France.
⁴ Université de Bourgogne Franche-Comté, UFR Sciences et Techniques, CNRS UMR 6249 Chrono-Environnement, 16 route de Gray, F-25 030 Besançon Cedex, France.

PMID: 27565532
DOI: 10.1016/j.scitotenv.2016.08.087

Abstract

This study aims at identifying the water-rock interactions and mixing rates within a complex granite-carbonate coastal aquifer under high touristic pressure. Investigations have been carried out within the coastal aquifer of Bonifacio (southern Corsica, France) mainly composed of continental granitic weathering products and marine calcarenite sediments filling a granitic depression. A multi-tracer approach combining physico-chemical parameters, major ions, selected trace elements, stable isotopes of the water molecule and ⁸⁷Sr/⁸⁶Sr ratios measurements is undertaken for 20 groundwater samples during the low water period in November 2014. 5 rock samples of the sedimentary deposits and surrounding granites are also analysed. First, the water-rock interactions processes governing the groundwater mineralization are described in order to fix the hydrogeochemical background. Secondly, the flow conditions are refined through the quantification of inter aquifer levels mixing, and thirdly, the kinetics of water-rock interaction based on groundwater residence time from a previous study using CFCs and SF₆ are quantified for the two main flow lines. A regional contrast in the groundwater recharge altitude allowed the oxygene-18 to be useful combined with the ⁸⁷Sr/⁸⁶Sr ratios to differentiate the groundwater origins and to compute the mixing rates, revealing the real extension of the watershed and the availability of the resource. The results also highlight a very good correlation between the groundwater residence time and the spatial evolution of ⁸⁷Sr/⁸⁶Sr ratios, allowing water-rock interaction kinetics to be defined empirically for the two main flow lines through the calcarenites. These results demonstrate the efficiency of strontium isotopes as tracers of water-rock interaction kinetics and by extension their relevance as a proxy of groundwater residence time, fundamental parameter documenting the long term sustainability of the hydrosystem.

Keywords: Corsica; Hydrogeochemistry; Kinetics; Strontium isotopes; Water-rocks interaction.