Hydrogeological Analysis of a Mountain Spring in the Aosta Valley (NW Italy): Insights from Harmonic and Isotopic Approaches

Mountain aquifers are among the most significant sources in northern Italy, playing a crucial role in meeting the population’s water demands. However, in recent decades, various hydrogeological issues have emerged across the Italian Alps, including the drying up of springs and the transition of formerly perennial springs into seasonal ones. The study is conducted in the Aosta Valley, a region characterized by a strong dependence on spring water resources, which account for approximately 80% of the total water supply. Since 2010, the Politecnico di Torino has operated a regional monitoring network, generating long-term hydrological time series. Water probes recording water level, temperature, and electrical conductivity at hourly intervals were installed at the Promise, Entrebin, Gabiet, and Promiod springs, located in distinct mountainous catchments. Complementary meteorological data were supplied by the Centro Funzionale Regionale VDA. To investigate recharge mechanisms, Fast Fourier Transform (FFT) analysis was applied to hydrograph signals, enabling the identification of relationships among flow rate, temperature, and precipitation. In parallel, stable isotope analyses (δ¹⁸O and δ²H, referenced to V-SMOW2) were performed to characterize recharge sources and groundwater flow paths. The integration of harmonic and isotopic analyses improved the understanding of spring recharge sources and dynamics. Springs supplying drinking water generally exhibit relatively stable discharge patterns, suggesting well-buffered aquifer systems capable of sustaining baseflow during dry periods. However, significant interannual fluctuations underline the sensitivity of these systems to climate variability. Overall, the results demonstrate that continuous monitoring, combined with advanced analytical approaches, represents a key tool for assessing groundwater vulnerability and supporting adaptive, sustainable water resource management in Alpine regions under increasing climatic stress.