Problems in the application of environmental isotopes to the hydrogeology of high mountain aquifers

In the present work some issues have been analysed, concerning the application of environmental isotopes to hydrogeology problems. Furthermore, a local meteoric water line for central Apennines has been proposed, and an isotope altitude gradient, valid for central Apennines, has been calculated by monthly rain samples. The studied areas are located in central Apennines, and belong to the Meso-cenozoic limestone ridge The main problems were related to the effect of orography and climate on isotopic contents, and to the hydrogeological complexity. In fact, in such zones the orography led to meteoric precipitations having a peculiar isotope content. Moreover, the occurrence of snowpack (especially in the Mt. Sibillini area, at south), persistent even until late spring, caused the aquifers to be recharged mainly by snowmelt; this fact brought to actual variations in the isotopic contents of springs. For these reasons, the sampling procedure and the location of rain and snow samplers took on particular importance. Finally, an application of isotopic data to some springs in Umbria and Marche regions has been made and presented at the end of the paper, to assess the suitability of the calculated gradient to define the recharge elevation of aquifers. The obtained results underlined the suitability of isotopes techniques for hydrogeologic purposes, especially where the relationships among aquifers, the karstification and the structural setting were quite complex but defined. In other cases, with an even more complex hydrogeological setting a good interpretation of the isotopic data is very hard. Further investigations will be necessary to define the effectiveness of isotope techniques in such complicated conditions.