Characterizing multiple water-rock interaction in the critical zone through Sr-isotope tracing of surface and groundwater.

International audienceHere, we report on both Sr isotope and major ions data, from shallow and deep groundwater from catchments located on granite and schist around the world. This extensive approach of Sr isotope tracing, initiated in France on areas impacted by intensive agricultural activities, was enlarged to Africa (granite-gneiss and schists 2200-700Ma of the Congo Basin), French Guiana (Archaen gneiss 3400-2700Ma and granite-gneiss rocks 2300-1900Ma) and India (Archean granites 2500Ma and Palaeoproterozoic granodiorite and schists 3100-1600Ma). The Sr content is well correlated with Mg and both are partly related to agricultural and weathering inputs. The relationship between Sr- isotope and Mg/Sr ratios allows defining the relative impact on surface and groundwater of processes occurring in the Critical Zone, mainly rain, agricultural practice and water-rock interactions