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This study aims at evaluating sources and processes affecting NO 3 − concentrations in the Oglio River. Five sampling campaigns considered the main watercourse, tributaries, point pollution sources, springs, and groundwater. Physico-chemical parameters, N forms, B, Sr 2 + , stable isotopes (δ 2 H H 2 O , δ 18 O H 2 O , δ 15 N NO 3 , δ 18 O NO 3 , δ 11 B) and discharge were measured. Hydrological modelling was performed using mass balance and End Member Mixing Analysis equations. During the irrigation period, in the upstream reach, up to 90% of the natural river flow is diverted for irrigation and industrial purposes; excess water drained from agricultural fields is returned to river in the downstream reach. Results evidenced, in the middle reach, a large input of NO 3 − -rich groundwater which could be quantified using hydrological modelling. Groundwater inputs are responsible for the sharp, tenfold increase in NO 3 − in the river water, from 2.2–4.4 up to 33.5 mg L − 1 , and are more evident in summer, when discharge is lower. Nevertheless, river water preserves its natural B isotopic composition, indicating that the two tracers do not have a common origin and are not co-migrant. In the lower plain, surface–groundwater interconnections and human disturbances in the water cycle favour the recycling of the compounds in the environment, and lead to a similarity in composition of the different water bodies (Oglio River, tributaries and groundwater). The long lasting agronomical practices have profoundly modified the surface–groundwater equilibrium and chemical characteristics, resulting in a highly buffered system. Infiltrating irrigation water leaches down NO 3 − which is subsequently denitrified; when returned to the Oglio River, groundwater modifies the river water composition by dilution, in the case of NO 3 − , or by addition, for other constituents (e.g. Cl − , B). The results of this study indicate that, in order to reduce the NO 3 − transport towards the Adriatic Sea, groundwater contamination should be addressed first, with expected long recovery times.

Stable isotopes of dissolved nitrates and boron represent a powerful tool, complementary to existing monitoring data, enabling the identification of nitrate sources, the assessment of their relative contribution to nitrate pollution and the quantification of nitrate transport and removal processes. This contribution aims to present groundwater isotope data obtained in an area of 15 000 km2 of the western Po plain. Nitrate isotope data show that synthetic fertilisers and anthropogenic organic matter are the main sources of contamination. ?11B allows the discrimination between manure derived and sewage derived contamination. Results indicate that even in agricultural areas, contamination from sewage exists. Samples from the suburban area of Milan, where sewage was considered the most likely source of contamination, show instead a ?11B typical for cattle manure. This study demonstrates that the attribution of the contamination to a source based solely on present-day land use may lead to inappropriate conclusions.

Multivariate statistical analysis is a useful method for supporting the interpretation of experimental data, particularly in the case of large datasets. In the present study, cluster analysis and factor analysis are used to support the hydrochemical characterization of groundwater and surface water in an area located in the Oglio River basin (N Italy). During a field survey performed in Fall 2015, 58 groundwater, 20 river (Oglio River and its main tributaries), 1 Lake Iseo and 7 spring samples were collected for chemical analysis. Results of multivariate statistical analysis led to the identification of the following 5 main clusters which characterize the hydrological system: (1) higher plain groundwater and springs, characterized by an oxidized hydrofacies with higher NO3, (2) lower plain groundwater, characterized by a reduced hydrofacies with higher As, Fe and Mn, (3) Oglio River, (4) Oglio River tributaries and (5) outliers. This characterization will bear the improvement of the hydrogeological conceptual model of the area, also oriented to groundwater/surface water interactions, that, in turn, will support the numerical flow modeling of the system

Understanding thefactors that control As concentrations in groundwater is vital for supplying safe groundwaterin regions with As-polluted aquifers. Despite much research, mainly addressing Holocene aquifers hosting young (12,000 yrs) groundwatersare not yet fully understood and so are assessed here through an evaluation of the redox properties of the system in a type locality, the PoPlain (Italy).Analyses of redox-sensitive species and major ions on 22 groundwater samples from the Pleistocene arsenic-affected aquifer in the Po Plain shows that groundwater concentrations of As are controlled by the simultaneous operation of several terminal electron accepters. Organic matter, present as peat, is abundant in the aquifer, allowing groundwater to reach a quasi-steady-state of highly reducing conditions close to thermodynamic equilibrium. In this system, simultaneous reduction of Fe-oxide and sulfate results in low concentrations of As (median 7 μg/L) whereas As reaches higher concentrations (median of 82 μg/L) during simultaneous methanogenesis and Fe-reduction. The position of well-screens is an additional controlling factor on groundwater As: short screens that overlap confining aquitards generate higher As concentrations than long screens placed away from them. A conceptual model for groundwater As, applicable worldwidein other Pleistocene aquifers with reducible Fe-oxides andabundant organic matter is proposed: As may have two concentration peaks, the first after prolonged Fe-oxide reduction and until sulfate reduction takes place, the second during simultaneous Fe-reduction and methanogenesis.

The Riardo basin hosts groundwater exploited for the production of high quality, naturally sparkling, bottled water (e.g., Ferrarelle water), and circulating in a system constituted by highly fractured Mesozoic carbonates, overlain by more impervious volcanic rocks of the Roccamonfina complex. The two formations are locally in hydraulic connection and dislocated by deep-rooted faults. The study aimed at elucidating groundwater origin and circulation, using isotopic tracers (δ18O, δ2H, δ11B and 87Sr/86Sr) coupled to groundwater dating (Tritium, CFCs and SF6). Besides recharge by local precipitation over the Riardo hydrogeological basin, stable isotope ratios in water indicated an extra-basin recharge, likely from the elevated surrounding carbonate reliefs (e.g., Maggiore and Matese Mts.). The mineralization process, promoted by the deep CO2 flux, controls the B and Sr contents. However, their isotopic ratios did not allow discriminating between circulation in the volcanic and in the carbonate aquifers, as in the latter the isotopic composition differed from the original marine signature. Groundwater model ages ranged from ~ 30 years for the volcanic endmember to > 70 years for the deep, mineralized end-member, with longer circuits recharged at higher elevations. Overall, the results of this study were particularly relevant for mineral water exploitation. A recharge from outside the hydrogeological basin could be evidenced, especially for the more mineralized and valuable groundwater, and an active recent recharge was detected for the whole Riardo system. Both findings will contribute to the refinement of the hydrogeological model and water budget, and to a sustainable development of the resource.

The successful management of carbon in the Earth's crust is critical for mitigating the increase of anthropogenic CO2 in the atmosphere. Carbon Capture and Storage (CCS) requires an understanding of the behavior of carbon in the crust and the development of robust monitoring techniques to constrain the movement, mechanisms, and pathways for any potential CO2 leakage. Here, we examine an aquifer from the Riardo Plain (Campania Region, southern Italy), which serves as a suitable natural analogue for CO2 migration to the critical zone (i.e., shallow crust and aquifers) and as a case study to evaluate the geochemical processes that occur when CO2-saturated fluids mix with freshwater in shallow aquifers. We investigate the behavior of various geochemical constituents (major and trace elements, δ18O–H2O, δ13C-DIC, and Rn content). Water from this area has a high degree of mineralization (EC 2500–3000 μS/cm), high HCO3- (~2.5 g/L), is saturated with respect to CaCO3, and is enriched in alkali ions (e.g., Na+ + K+). The high degree of mineralization occurs in groundwater that discharges from the basal aquifer of the Roccamonfina volcanic edifice (~6 km NW), with vast CO2 inputs that promote host rock leaching. Superficial volcanic aquifers are recharged by fresh meteoric precipitation when groundwater flows from carbonates at the edge of the plain to aquifers hosted in the southeastern slope of the Roccamonfina volcano. The presence of normal faults in this area permits natural upwelling of CO2-rich groundwater, which locally mixes with shallow freshwater present within the upper volcanic succession. Significant (R > 0.8) linear correlations between conservative elements suggest that groundwater geochemistry is dominated by a mixture of two main endmembers: (i) deep/mineralized waters and (ii) shallow/diluted waters. The intrusion of freshwater to volcanic aquifers induces oxidation, leading to adsorption of select elements (e.g., As and Ba) onto Fe-oxyhydroxide precipitates within these aquifers. Geochemical modeling suggests that CO2 saturation approaches 3 g/L, which agrees with direct measurements of CO2 flux. We conclude that our conceptual geochemical model helps to constrain mixing of CO2 with freshwater and to diagnose the secondary geochemical processes that influence aqueous geochemistry within CO2-influenced groundwater.

For several hundred years, farming in the Po Plain of Italy (46,000 km2, 20 million inhabitants) has been supported by intensive surface irrigation with lake and river water. Despite the longevity of irrigation, its effects on the quality and quantity of groundwater is poorly known and so is investigated here through seasonal measurements of hydraulic heads and water quality in groundwaters, rivers, lake, springs and rainwaters. In the north of the study region, an unconfined coarse-grained alluvial aquifer, infiltration of surface irrigation water, sourced from the Oglio River and low in NO3, contributes much to aquifer recharge (up to 88%, as evidenced by a δ2H-Cl/Br mixing model) and has positive effects on groundwater quality by diluting high concentrations of NO3 (decrease by 17% between June and September). This recharge also helps to maintain numerous local springs that form important local micro-environments. Any increase in water-use efficiency in irrigation will reduce this recharge, imperil the spring environments, and lessen the dilution of NO3 leading to increasing NO3 concentrations in groundwater. These findings can be extended by analogy to the entire Po Plain region and other surface-water-irrigated systems worldwide where inefficient irrigation methods are used and similar hydrogeological features occur.

Located on the north-western border of the Inle lake basin, the Khaung Daing hot spring outflows at ca. 70°C. Temperature at depth, calculated with chemical geothermometers is probably less than 150°C, therefore classifying it as a medium-low enthalpy geothermal resource. Geochemical and isotopic results also demonstrate that the hot spring is fed by local groundwater, equilibrated with the carbonate rocks but without isotopic exchange with the matrix. Trace elements, particularly As (119 µg/L), display high concentrations, raising some concern about potential environmental and health effects.

In aquifers 160 to 260 m deep that used for public water-supply in an area ~ 150 km2 around the town of Cremona, in the Po Plain of Northern Italy, concentrations of arsenic (As) are increasing with time in some wells. The increase is due to drawdown of As-polluted groundwater (As ≤ 144 μg/L) from overlying aquifers at depths 65 to 150 m deep in response to large-scale abstraction for public supply. The increase in As threatens drinking-water quality locally, and by inference does so across the entire Po Plain, where natural As-pollution of groundwater (As > 10 μg/L) is a basin-wide problem. Using new and legacy data for Cl/Br, δ18O/δ2H and other hydrochemical parameters with groundwater from 32 wells, 9 surface waters, a sewage outfall and rainwater, we show that the deep aquifer (160–260 m below ground level), which is tapped widely for public water-supply, is partly recharged by seepage from overlying aquifers (65–150 m below ground level). Groundwater quality in deep aquifers appears free of anthropogenic influences and typically < 10 μg/L of As. In contrast, shallow groundwater and surface water in some, not all, areas are affected by anthropogenic contamination and natural As-pollution (As > 10 μg/L). Outfalls from sewage-treatment plants and black water from septic tanks firstly affect surface waters, which then locally infiltrate shallow aquifers under high channel-stages. Wastewater permeating shallow aquifers carries with it NO3 and SO4 which suppress reduction of iron oxyhydroxides in the aquifer sediments and so suppress the natural release of As to groundwater.

An analysis of 70 wells that tap groundwater from depths of up to 260 m in and around the town of Cremona, N. Italy, shows that 50 of them contain more than 10 μg/L of arsenic. Concentrations of As >10 ppb are accompanied by concentrations of Fe ranging from