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Seismic precursors are an as yet unattained frontier in earthquake studies. With the aim of making a step towards this frontier, we present a hydrogeochemical dataset associated with the 2016 Amatrice-Norcia seismic sequence (central Apennines, Italy), developed from August 24 th , with an M w 6.0 event, and culminating on October 30 th , with an M w 6.5 mainshock. The seismic sequence occurred during a seasonal depletion of hydrostructures, and the four strongest earthquakes (M w  ≥ 5.5) generated an abrupt uplift of the water level, recorded up to 100 km away from the mainshock area. Monitoring a set of selected springs in the central Apennines, a few hydrogeochemical anomalies were observed months before the onset of the seismic swarm, including a variation of pH values and an increase of As, V, and Fe concentrations. Cr concentrations increased immediately after the onset of the seismic sequence. On November 2016, these elements recovered to their usual low concentrations. We interpret these geochemical anomalies as reliable seismic precursors for a dilational tectonic setting.

How large earthquakes are triggered is a key question in Earth science, and the role played by fluid pressure seems to be crucial. Nevertheless, evaluation of involved fluid volumes is seldom investigated, if not unaccounted for. Moreover, fluid flow along fault zones is a driving factor for seismicity migration, episodic heat and chemical transport. Here we show that time repeated (4D) seismic tomography resolves changes of V p and V p /V s during the Mw6.2 2009 L’Aquila normal faulting sequence, that indicate a post-failure fluid migration from hypocentral depths to the surface, with a volume estimated between 5 and 100 × 10 6 m 3 rising at rates up to 100 m/day. This amount inferred by tomograms is surprisingly consistent with the about 50 × 10 6 m 3 surplus water volume additionally measured at spring discharge, spread in time and space along the 700 km 2 -wide regional carbonate fractured aquifer. Fluids were pushed-up within a huge volume across the fault and expelled from the area of large coseismic slip. Such quantities of fluids liberated during earthquakes add unprecedented constraints to the discussion on the role of fluids during and possibly before earthquake, as well as to the potential impact on the pristine high-quality drinkable groundwater, possibly affecting the biodiversity of groundwater dependent ecosystems too.

Hydrogeological perturbations in response to earthquakes are widely described worldwide. In carbonate aquifers, a post-seismic discharge increase is often attributed to an increase of bulk permeability due to co-seismic fracturing and the attention on the role of faults to explain the diversion of groundwater is increasing. We focus on the reaction of carbonate hydrogeological basins to extensional seismicity, taking as an example the effects of the Central Italy 2016–2017 seismic sequence, on the Basal aquifer of the Sibillini Mountains area. Geo-structural, seismological and ground deformation data were collected and merged with artificial tracer tests results and with a 4-years discharge and geochemical monitoring campaign. The main NNW-directed groundwater flow was diverted to the west and a discharge deficit was observed at the foot-wall of the activated fault system with a relevant discharge increase, accompanied by geochemical variations, at the fault system hanging-wall. The observed variations are consistent with the combined action of a permeability increase along the activated fault systems, which modified the predominant pre-seismic along-strike regional flow, and with hydraulic conductivity increase due to fracturing, determining a fast aquifers emptying. We show that the prevailing mechanism depends on the aquifer systems position with respect to the activated faults.

The combination of several factors related both to human pressure as well as natural issues could lead to a marked alteration of the groundwater budget terms and a decrease in groundwater availability. The basal aquifer of the Sibillini Mts. is a strategic resource of drinking water in the central sector of Apennine (Italy). The seismic sequence that occurred in this area in 2016 induced transient and sustained modifications in the aquifer settings. Springs located on the western side of the Sibillini Mts. were characterized by an increased discharge, while in contrast, the eastern springs suffered an intense drop in their groundwater discharge. In 2017, a drought period started immediately after the exhaustion of the seismic sequence effect. The comparison between the recharge and discharge of the major springs in the 2000–2020 period allowed the definition of the different responses of the aquifer to the co-occurrence of earthquakes and climatic events. The hydrodynamic alteration triggered by the earthquake induced a huge depletion of the groundwater stored in the eastern sector of the basal aquifer (at least 50 × 106 m3). The scarce recharge occurring in the following drought period (more than 30% of the average annual value) was not enough to restore the groundwater resources, causing a serious drinking water supply crisis in the main tapped springs in the eastern sector of the aquifer.

Light nonaqueous phase liquids (LNAPLs), due to their low solubility, dissolve slowly, acting as a long-term source of water contamination, and consequently they represent an important environmental issue. In the subsoil, more than 99% of spilled LNAPL remains as adsorbed and free phase; therefore, the volume estimation of free phase, obtained in this case through two different conceptual models (Pancake Model and Vertical Equilibrium Model), is considered a fundamental step for a correct site remediation. According to the first model, the LNAPL floating on the water table and its saturation is up to 100%; instead, according to the second one, the LNAPL can penetrate below the water table and the coexistence of LNAPL, water, and air in the pore fraction, leads to a lower LNAPL saturation, variable with the depth. Actually, in subsoil LNAPL and water saturations vary with depth due to the influence of capillarity, leading to the inaccuracy of Pancake Model assumption. Despite the evident limitation of Pancake Model, both models were applied, coupled with area calculations with Thiessen polygons and grid at regular mesh, to roughly estimate the free LNAPL volume existing in a contaminated site. The volume estimation carried out, considering the LNAPL type and its features, the soil type, and relative effective porosity, provides estimates of volumes having differences up to thousands of cubic meters. The results analysis shows that this estimation has several critical points such as area definition and the lack of site-specific data (e.g., porosity). Indeed, the sensitivity analysis for porosity shows that a reduction of this parameter provides a 20% reduction of estimated volume.

Hydrogeochemical properties and groundwater quality assessment are very important for the effective management of water resources in arid and semiarid regions. The present investigation is a spatiotemporal analysis of groundwater quality using both chemical analysis and water quality indices (WQIs) in the Mornag Basin in northeastern Tunisia. The results exhibit that the Mornag shallow aquifer is dominated by chloride–sodium–potassium water facies, which progress over time toward chloride–sulfate–calcium and magnesium water facies. This may highlight that the mineralization of groundwater, which increases in the direction of groundwater flow, is primarily controlled by a natural process resulting from the dissolution of evaporative minerals and cation exchange with clay minerals relatively abundant in the study area. The anthropogenic activities represented by the return flow of irrigation water, the recharge by wastewater, and climate change also have a key role in groundwater contamination. The temporal evolution in %Na and SAR over the last three years in the Mornag aquifer shows an increasing trend that makes them unsuitable for irrigation. These findings highlight the need for assessing water quality in mapping local water resource vulnerability to pollution and developing sustainable water resources management.

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.

Superlative levels of arsenic (As) in groundwater and sediment often result from industrial pollution, as is the case for a coastal aquifer in Southern Italy, with a fertilizer plant atop. Understanding conditions under which As is mobilized from the sediments, the source of that As, is necessary for developing effective remediation plans. Here, we examine hydrogeological and geochemical factors that affect groundwater As concentrations in a contaminated coastal aquifer. Groundwater has been subject to pump-and-treat at a massive scale for more than 15 years and is still ongoing. Nevertheless, As concentrations (0.01 to 100 mg/L) that are four orders of magnitude more than Italian drinking water standard of 10 μg/L are still present in groundwater collected from about 50 monitoring wells over three years (2011, 2016, and 2018). As was quantified in three different locations by sequential extractions of 29 sediment cores in 2018 (depth 2.5 m to −16.5 m b.g.l.), combined with groundwater As composition, the aqueous and solid partitioning of As were evaluated by partition coefficient (Kd) in order to infer the evolution of the contaminant plumes. Most sediment As is found in easily extractable and/or adsorbed on amorphous iron oxides/hydroxides fractions based on sequential extractions. The study shows that As contamination persists, even after many years of active remediation due to the partitioning to sediment solids. This implies that the choice of remediation techniques requires an improved understanding of the biogeochemical As-cycling and high spatial resolution characterization of both aqueous and solid phases for sites of interest.

Understanding natural variations of Rn (222Rn) concentrations is the fundamental prerequisite of using this radioactive gas as a tracer, or even precursor, of natural processes, including earthquakes. In this work, Rn concentrations in groundwater were continuously measured over a seven-month period, during 2017, in the Giardino Spring, Italy, together with groundwater levels in a nearby well installed into a fractured regional aquifer. Data were processed to reduce noise, and then analyzed to produce the Fourier spectra of Rn concentrations and groundwater levels. These spectra were compared with the spectrum of tidal forces. Results showed that diurnal and semidiurnal cycles of Rn concentrations, and filtered oscillations of groundwater levels, in the nearby well, are correlated with solar and luni-solar components of tidal forces, and suggested no correlation with the principal lunar components. Therefore, influencing factors linked to solar cycles, such as daily oscillations of temperature and atmospheric pressure, and related rock deformations, may have played a role in Rn concentrations and groundwater levels. An open question remains regarding the correlation, which is documented elsewhere, of Rn concentrations and groundwater levels with the lunar components of the solid Earth tides.

Despite the close attention springs have received from a hydrologic perspective and as biodiversity hotspots, the multiple dimensions of spring meiofaunal assemblage diversity are still poorly investigated. Knowledge of beta diversity patterns and drivers can inform and improve management decisions on biodiversity conservation. Here, we analyzed beta diversity of copepod assemblages in karst springs in Central Italy by focusing on: 1) relative contributions of turnover and nestedness components to taxonomic and phylogenetic beta diversity; 2) temporal variation of species richness and beta diversity within and between the target springs in conjunction with models of the influence of physical-chemical parameters on within-spring diversity changes; 3) expected risk of habitat loss due to variation in groundwater recharge under climate change. To this end, we gathered data from 168 samples collected in four karst springs from 2004 to 2016. Overall, we found 48 copepod species, 22 of which are obligate groundwater dwellers while the remaining 26 usually occur in surface freshwaters. All springs showed significant changes in taxonomic and phylogenetic beta diversity over time. Total beta diversity was high for both the taxonomic and phylogenetic dimensions, and turnover was the main component. Inter-site variability in dissolved oxygen explained a noticeable part of temporal variation in beta diversity, likely reflecting the role of microhabitat heterogeneity in shaping site-specific assemblages. However, most of the temporal variation in species richness and beta diversity remained unexplained, suggesting a major role of other factors, such as seasonal discharge variations. Modelling of recharge rates for all the four springs over 2001–2020 suggested a potential >40% recharge deficit under dry conditions. Moreover, Cellular Automata-based modelling of rainfall over the Gran Sasso-Sirente hydrogeologic unit (feeding three of the four springs) predicted an overall precipitation decrease in the 2081–2095 period. Such changes could produce severe effects on springs’ microhabitats and related communities. Our results indicate that partitioning beta diversity, monitoring its temporal changes and assessing its environmental drivers are critical to evidence-based conservation of springs. Particularly, the high species turnover we have observed suggests that conservation strategies should seek to preserve as many microhabitats as possible within and among karst springs.