L'utilizzo degli isotopi stabili da reti pluviometriche per la definizione degli areali di ricarica delle acque sorgive: problemi e possibili soluzioni da casi di studio nell'Appennino settentrionale

The water stable isotopes are widely exploited in hydrogeology to define the recharge area of mountain springs. In almost all cases, pre-existing relationships linking the isotopic contents of meteoric water that were collected in several rain gauges located at different altitudes are used. Although such approach is straightforward, it assumes that the water aliquots collected in the raingauges fully recharge the groundwater. From the hydrogeological point of view, this assumption does not take into account the water balance equation, as it neglects evapotranspiration and runoff. This manuscript deals on the preliminary comparison of water stable isotopes in meteoric water (1 raingauge) and groundwater (2 springs) from the northern Apennines of Italy. Results highlight that the pre-existing isotopic relationships commonly used in northern Apennines largely overestimate the mean altitudes of recharge of springs. This fact may be only in part due to the evapotranspiration processes taking place during summer period so that isotopic gradients obtained from weighting procedure linking effective rainfall with isotopic contents in raingauges are still not recommended. To date, isotopic gradients obtained from ephemeral springs fed by reduced surficial deposits seem to be the most reliable tool.