Recharge processes in karstic systems at different time scales
Résumé
In karstic systems, the heterogeneity of the transfer processes within the different compartments of the
critical zone (soil, epikarst, and saturated zones) controls the recharge -discharge relationship. The
MEDYCYSS observatory (Multi scalE observatory of flooD dYnamiCs and hYdrodynamicS in karSt,
belonging to OSU OREME and SNO Karst network) has been set up to better understand these
transfers under a Mediterranean climatic context. On the Lez karst catchment (South of France), being
part of MEDYCYSS, a 333 m deep borehole has been equipped with the PMPS Multi-level monitoring
system (SolExperts) in the framework of the CRITEX project. The borehole is located 100 m from an
intermittent river and 500 m from the main outlet (Lez Spring) of the aquifer where an intense pumping
is performed. Continuous pressure and temperature monitoring is realized at 5 depth levels, isolated
by packers, where discrete water sampling are also regularly achieved. The main objective of this
monitoring is to assess the different mechanisms of the recharge process at various time scales. The
collected data implement the existing spatio-temporal monitoring of the hydrodynamic and
geochemical variations followed in bore-holes, karst features (caves and sink-holes), perennial and
temporal springs of the karstic aquifer. In this study, we aim at specifying the contribution of the
different karst compartments, from the recharge zone towards the main outlets. The results obtained
during a one year monitoring show a contrasted hydrodynamic response and underline a pressure
transfer between compartments, surface water and karst flow. Assessed by temperature monitoring,
the hydrochemistry shows a stable water composition for each compartment of the bore-hole, in
contrast with the high variability and water mixing identified at the Lez spring. These new data are
essential to better assess the recharge processes and specify the role of the vadose zone in the flow
organization at short and long timescale.