Karst Recharge Areas Identified by Combined Application of Isotopes and Hydrogeological Budget

The identification of recharge areas in karst aquifers allows us to perform sustainable management of these groundwater resources. Stable isotopes (δ18O and δ2H) have been largely used to provide information about recharge elevation in many mountainous regions. In this paper, an improved version of a recent “isotope-driven model”, for the identification of recharge areas, was applied to Capodacqua di Spigno Spring (south of the Latium region). The model upgrade consists of a preliminary check procedure to estimate the degree of influence of the rainfall’s isotopic variability on the spring water. This additional procedure gives us an indication of the reliability of the model and its applicability conditions. Moreover, the dataset of the spring was updated to analyze the degree of reliability of the isotope-driven model. The purpose of this study was to combine the previously mentioned isotope-driven model with hydrogeological tools. A quantitative study of the basin, based on the estimation of the average monthly infiltration volume, was performed by using the inverse hydrogeological water budget. In this way, the qualitative model for the recharge areas’ estimation was validated by a quantitative hydrogeological tool. Both models show that, for karst mountain basins, the recharge areas decrease as the average recharge elevations increase, including areas at high altitudes.