KARSTIC CONTRIBUTION CHARACTERIZATION BY SR ISOTOPES APPLICATION TO COMPS WELL-FIELD

Flow from karst influences the quantity and quality of surface waters which collects it. Geochemistry of major (particularly Cl), and trace elements and measurement of isotopic ratio of Sr (87/86)Sr suggest cle arly two poles (karstic and surface waters) and allow quantification o f the mixing proportions. This karstic contribution identification met hod was applied to the Comps well-field (Gard, France) located in the Rhone river alluvia. It is mainly fed by surface waters, but karstifie d aquifer limestones located along the alluvial terrace may also contr ibute more than 50% in some wells.