Water storage and transfer in the epikarst of karstic systems during high flow periods L. Aquilina a, * , B. Ladouche b , N. Do ¨rfliger b a CAREN – Ge ´osciences Rennes, UMR 6118 CNRS-Univ. Rennes1, Campus Beaulieu, 35000 Cedex Rennes, France b BRGM Service Eau, 1039 rue de Pinville, 34000 Montpellier, France Received 24 August 2004; received in revised form 21 November 2005; accepted 24 November 2005 Summary A monitoring of spring and rain waters in the South of France during two hydrolog- ical cycles is presented. Rain waters were sampled after each precipitation event at 3 rain-gauge stations. Four karstic springs located in the same area have also been daily (high discharge events) to monthly (low flow periods) sampled. This paper focuses on compositional changes in the Cl  and Br  ions and the oxygen-18 (d18O) and hydrogen (dD) isotopes during the high discharge events. The responses of the different karstic systems are quite homogeneous and reflect the hydro- logical state of the system. The waters discharged during the major autumn and winter high discharge events originate from the epikarstic reservoir and show characteristics chemical vari- ations related to residence in the unsaturated zone close to the surface. Their residence time in the order of 1–3 months. Correlations between the composition of the spring-water and the rainwater during three successive high discharge events during the summer of 1998 indicate that the water for high discharge event ‘‘n’’ is derived from water from precipitation event ‘‘n  1’’ via a piston-type mechanism with residence time of 2 weeks. These results are interpreted as an indication of the major role of the epikarst reservoir in the karst recharge functioning. The similar behaviour of the four springs, although located in different geological contexts allows to think that the epikarst role could be more important than previously thought. ª 2005 Elsevier B.V. All rights reserved. KEYWORDS Karst; Epikarst; Recharge processes; High discharge event; Oxygen isotopes; Hydrogen isotopes; Mass balance Introduction Karstic systems exhibit highly heterogeneous drainage due to uneven permeability development through carbonate dis- solution. Karst aquifers can thus be subdivided into three main parts (Mangin, 1974a,b, 1975). 0022-1694/$ - see front matter ª 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jhydrol.2005.11.054 * Corresponding author. E-mail address: luc.aquilina@univ-rennes1.fr (L. Aquilina). Journal of Hydrology (2006) 327, 472– 485 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/jhydrol