Stable water isotopes as fundamental tool in karst aquifer studies: some results from isotopic applications in the Apuan Alps carbonatic complexes (NW Tuscany).

The management and protection of water resources in karst environment require detailed knowledge of the aquifer system which can be obtained through a multidisciplinary approach, including not only hydrogeological/structural assessment, but also the use of tools not commonly used in hydrogeology, as the isotope ratios. In the present work some examples of isotopic applications on karst aquifers are discussed in relation to hydrogeological studies carried out in the Carrione Stream, Frigido River, and Versilia River catchments (Apuan Alps, Tuscany). In particular, during such studies the isotopic ratios 18O / 16O and 2H / 1H of the water molecule, mainly, and 13C / 12C of inorganic carbon in solution were used. The isotopic data, and their comparison with the hydrogeological and structural-geological ones, were useful: to obtain information about the hydrodynamic conditions in the aquifer; to define the recharge area of main springs; and to identify different circulation systems drained by closing springs which have similar chemistry. The obtained results confirm that in karst systems, where it is often difficult to carry out conventional hydrogeological surveys, the isotopic instruments have a fundamental role in the study of water circulation.