Combined impact of climate and seismic activity on groundwater hydrogeochemistry in the Eastern Southern Alps, Italy

Groundwater systems can be perturbed by natural events such as climatic extremes and earthquakes, two complex phenomena that may also interact. This multidisciplinary study investigates their combined effect on groundwater in the Eastern Southern Alps (Italy), an active compressional zone, using hydrogeological, hydrogeochemical, and seismological data. Between May 2022 and May 2024, thirteen springs were monitored annually, with five sampled monthly for chemical-physical parameters, major and trace ions. Most springs show a Ca-HCO₃ facies, indicative of shallow karst circulation, whereas two (Canal and Colesei) exhibit a Ca-SO₄ facies, characterized by elevated Na, Cl, and temperatures, suggesting contributions from deeper sources. Stable isotopes of water and dissolved gases confirm meteoric origin for all springs, while 87Sr/86Sr, trace elements, and geothermometers further support deep inputs at Canal and Colesei. Statistical analyses (Principal Component Analysis and Change Point Detection) identified geochemical anomalies possibly linked to (i) prolonged drought, which reduced aquifer recharge and enhanced ion concentrations, and (ii) seismicity, notably a Mw 5.8 earthquake ∼245 km away, potentially varying mixing between shallow and deep systems. These results highlight the outstanding need for integrated monitoring to understand and manage groundwater resources, particularly in tectonically active and densely populated areas facing climate change and extreme events.