Expanding knowledge about the origin and mixing of deep fluids and the water–rock–gas interactions in aquifer systems can represent an improvement in the comprehension of crustal deformation processes. An analysis of the deep and meteoric fluid contributions to a regional groundwater circulation model in an active seismic area has been carried out. We performed two hydrogeochemical screenings of 15 springs in the San Vittorino Plain (central Italy). Furthermore, we updated the San Vittorino Plain structural setting with a new geological map and cross-sections, highlighting how and where the aquifers are intersected by faults. The application of Na-Li geothermometers, coupled with trace element and gas analyses, agrees in attributing the highest temperatures (>150 °C), the greatest enrichments in Li (124.3 ppb) and Cs (>5 ppb), and traces of mantle-derived He (1–2%) to springs located in correspondence with high-angle faults (i.e., S5, S11, S13, and S15). This evidence points out the role of faults acting as vehicles for deep fluids into regional carbonate aquifers. These results highlight the criteria for identifying the most suitable sites for monitoring variations in groundwater geochemistry due to the uprising of deep fluids modulated by fault activity to be further correlated with crustal deformation and possibly with seismicity.

Microbial activity has been documented in various lacustrine environments, suggesting its fundamental role in mineral precipitation and, therefore, in the formation of organo-deposits such as microbialites. Many studies are currently focused on documenting how the association of microbes and extracellular polymeric substances (EPSs) may influence the authigenesis of Mg-rich clay minerals and the subsequent carbonate precipitation in growing microbialites in lacustrine environments. In this study, we investigate the present-day microbialites of the alkaline Bagno dell’Acqua lake (Pantelleria Island, Italy) using X-ray diffraction (XRD) scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Our results reveal the intimate association of Mg-smectite/carbonate minerals with the EPS and microbes, and, for the first time, we selected microbes belonging to phylum Firmicutes (Bacillus sp.), from natural microbialites, to carry out laboratory experiments that testify their direct role in the precipitation of clay and carbonate minerals.

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 M_w 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.

A key challenge in earthquake hydrogeology is separating hydrogeochemical changes induced by seismic activity from those driven by natural recharge dynamics. This study provides a comprehensive long-term multiparameter analysis of hydrogeochemical parameters and dissolved radon concentrations in groundwater, monitored at four springs in the Matese area (central-southern Italy), fed by carbonate aquifers and located within an active extensional tectonic setting. Discrete monthly hydrogeochemical sampling has been performed at the four sites since December 2017, while continuous radon monitoring has been carried out at Rio Freddo spring (since July 2018) and Grassano spring (since July 2020) using gas-monitoring stations. Principal Component Analysis (PCA) was applied to the discrete hydrogeochemical dataset to identify anomalous sampling campaigns and the dominant geochemical processes controlling groundwater composition at each spring. Seasonal Trend decomposition using LOESS (STL) was applied to the continuous radon measurements, discerning long-term trend, seasonal, and residual components. PCA results highlight discrete sampling campaigns with anomalous enrichment in major ions and/or trace elements, tentatively associated with seismic events or stress-induced permeability changes. STL radon decomposition reveals site-specific trend evolutions and seasonal patterns, with residual variability showing a clear dependence on meteorological forcing. Moreover, residual anomalies exceeding ± 3σ were evaluated against regional seismicity. These findings demonstrate the potential of combined PCA and STL approaches for discriminating between deep-seated fluid contributions to carbonate fractured aquifer and shallow meteorological factors in active extensional settings.