Some applications of geochemical and isotopic techniques to hydrogeology of the caves after research in two sites (Nerja Cave-S Spain, and Fourbanne system-French Jura)

Abstract : Caves constitute privileged sampling spots to investigate the hydrochemical behaviour of infiltration, but the representative nature of samples can limit their reach. Taking this into account many results can be obtained from chemistry of water sampled in the caves. Carbonate tracers enable to reconstruct the 'history' of drip water water, including rainfall and temperatures. Moreover, permanent drip waters prove durability of water stored in the unsaturated zone over the cave, and lags between rain inputs and drip output enable to evaluate transit time through the unsaturated zone. The comparison of input/output concentrations can also contribute to estimate the local water balance of the site.Finally, providing an access to the water table of the saturated zone, caves allow a calculation of mixing rates of infiltration water with water stored in the saturated zone.