Buccianti, Antonella

The analysis of trace metals and metalloids, and the Sr-isotopic systematics were applied to 16 must samples from vines growing in the Sesia Val Grande Supervolcano UNESCO Global Geopark in the northern Piedmont Region (Italy), a land worldwide famous for the production of quality Nebbiolo-based red wines. Twenty-four elements were measured in each sample with inductively coupled plasma-mass spectrometry (ICP-MS). The results indicate a wide variability in trace element concentration in musts from the different vineyards. In particular, Rb and Sr reach their maximum at 5110 and 694 µg L−1, respectively, reflecting the geological nature of the magmatic bedrocks. Fe, Cu, Pb and Ba concentrations reach 3118, 1200, 130 and 720 µg L−1, respectively, suggesting a source from iron oxide, Pb–Zn and Ba ores associated to the volcanic activity. The 87Sr/86Sr ratio is in the range 0.711608–0.718160, showing a highly radiogenic signature which is uncommon in must/wine. This is consistent with the high 87Sr/86Sr isotopic ratio of the old rhyolitic bedrocks. Furthermore, the 87Sr/86Sr ratio in musts linearly correlates with the corresponding 87Rb/86Sr ratio, reflecting the Rb and 87Sr release from primary minerals during pedogenesis and matching the initial 87Sr/86Sr ratio of the parent bedrocks magmatic reservoir, thus assuming importance for authenticity assessment.

Anomalous geochemical signals inferred from elemental and isotopic analyses on spring waters and soil degassing are often detected in response to tectonic loading along faults. Recent results highlighted how the geochemical anomalies are closely related to episodes of crustal deformation. In the present study, the carbon dioxide and radon from soil degassing and the geochemical features of springs spatially related to fault zones in the Friuli-Venezia Giulia region (north-eastern Italy), a seismic-prone area, have been coupled with crustal deformation analyses to better define the possible correlations between fluctuations of geochemical parameters and seismicity, with the aim of gaining new information about local geodynamic processes. The natural CO2 and Rn degassing was evaluated by a soil gas survey carried out by a grid of about 100 measuring sites located over the area that had been hit by strong earthquakes, in the past (Gemona – Idrija 1511, Raveo 1700, Tolmezzo 1788 and 1928, Gemona 1976). The results obtained show a significant amount of crustal-originated gases, especially CO2, possibly related to decarbonation reactions and stress accumulation occurring in deep-seated structures. The spring waters show, in some cases, anomalous geochemical transients, in particular concerning the chloride and Rn concentration, that are not related to seasonal changes and interpreted to reflect distinct fluid pressure regimes within the fault zone, yielding the leakage of pore fluids into the country-rock aquifers. In particular, the changes in the chloride content have been tentatively modeled in terms of pore-fluid expulsion from compacting clays during pressure gradients at shallow crustal levels. The flow regimes and chemical evolution have been related to the strain computed at the outlet sites through the Gutenberg–Richter relation parameters and the regional value of the strain rate. The information provided here may be used to start up a long-term geochemical monitoring of this seismically active area able to detect the modifications occurring in the circulating fluids to gain a better insight on the relationships between the geochemistry of the fluids and the activity of the local seismogenic faults.

Gli elementi chimici disciolti nelle acque continentali provengono dall’alterazione della crosta terrestre. L’acqua erode e dissolve i minerali delle rocce attraverso l’alterazione chimica avvalendosi del contributo dei gas presenti in atmosfera o nel sottosuolo. Il nitrato, una delle sostanze responsabili delle più gravi forme di inquinamento delle acque nei paesi in via di sviluppo, è un nutriente essenziale per la crescita delle piante e rappresenta un anello fondamentale del ciclo biogeochimico dell'azoto, in quanto viene prodotto dai batteri a partire dall'azoto atmosferico. In quantità eccessive il nitrato può essere dannoso per gli uomini e per gli animali. Elevati livelli di nitrato nell'acqua sono causati in larga misura dall'uso di fertilizzanti ricchi di nitrato e dal letame. In questo contesto, le condizioni redox delle acque naturali, che controllano la speciazione dei composti dell’azoto, sono altamente variabili perché controllate prevalentemente dall’attività biologica. In particolare, il bilancio fra i due processi dell’attività biologica, la fotosintesi e la respirazione (o decomposizione della sostanza organica), determina la presenza nel sistema di condizioni ossidanti o riducenti. I composti dell’azoto possono quindi essere considerati utili indicatori dello stato di salute di un acquifero superficiale. In questo lavoro sono analizzati i dati relativi ai tenori delle specie dell’azoto NH4 +, NO2 - e NO3 - relativi ad acque di falda campionate nell’area aretina nel corso della realizzazione dell’Atlante Geochimico delle Acque di Falda e di Scorrimento Superficiale del Comune di Arezzo. I dati sono analizzati proponendo nuove metodologie grafiche e numeriche per visualizzare lo stato del territorio nei confronti della pressione antropica come rilevata dal comportamento spaziale e temporale delle specie suddette.

Since 2000 a joint project between the Department of Earth Science of Florence and the Unit of Environment and Health of the Municipality of Arezzo has allowed to geochemically characterise the superficial and ground waters of the municipal territory of Arezzo in order to establish the water quality and to investigate the main natural and anthropic processes responsible of their composition. The available geochemical data-base consists of more than 500 samples sites (90% of which are private wells and 7 and 3% are springs and running waters, respectively) on which physical parameters (temperature and electrical conductivity) and major, minor and trace dissolved species (pH, Ca, Mg, Na, K, NH4, HCO3, SO4, NO3, NO2, Cl, Br, F, heavy metals) have been performed by using the same sampling procedure and analytical methodology in order to have a consistent set of data. Fifteen selected sites have been analysed twice per year to evidence possible seasonal effects. No significant differences have been recorded. The Arezzo Basin, formed since Upper Pliocene, is a structural depression limited to the North and to the East by the Pratomagno and Chianti belts, respectively, and to the South and to the East by two tectonic lineaments (Val d’Arbia-Val Marecchia transversal and Chitignano normal faults). Along these tectonic discontinuities CO2-rich manifestations either seep out or exploited by private companies. Hydrogeologically, three main aquifers are recognised: i) a relatively deep aquifer hosted in Tertiary sandstone formations; ii) an intermediate aquifer hosted in Quaternary fluvio-lacustrine sediments and iii) a shallow aquifer in recent alluvional sediments. The content in Total Dissolved Solids (TDS) allows to classify the Arezzo waters in: oligomineral (69%), medium-mineral (30%) and mineral (1%) and they can be regarded as Ca(Mg)-HCO3 (87 %), Na(K)-HCO3 (7%), Ca(Mg)-SO4 (5%) and Na(K)-Cl (1%). It is noteworthy to point of that the Na(K)-HCO3 waters are aligned along the above mentioned tectonic systems. The quality of Arezzo waters has been referred to the Italian legislation that is addressed to the definition of the Maximum Admissible Concentration (MAC, DPR 236/88, Dlgs 31/01) and the Reference Value (RV, DPR 236/88) in terms of waters for the human consumption. Waters from the northern area of Arezzo overcome MAC for chlorides, sulphates and sodium; if we consider nitrogen species (NH4, NO2, NO3) the values overcome CMA for those waters collected into the city, its peripheral areas and in the south-western suburbs. Thematic maps has been produced, on the basis of the principles of linear Geostatistics, in order to analyse the spatial behaviour of the analysed variables. The aim was to find correlations with lithology, use of the soils, drainage density, pressure of antrophic activities and so on, and to identify sensible areas to monitor in their time evolution. The investigation has been developed starting from a detailed variographic analysis by means of the geochemical behaviour of each variable has been analysed in the different directions of the space while the estimation procedure to obtain the maps has been based on the application of sequential Gaussian simulation procedures.

CO2 geological storage is one of the most promising technologies for reducing atmospheric emissions of greenhouse gas. The results obtained by a new approach applied to a CO2 storage geochemical model at the Weyburn (Saskatchewan, Canada) test site, where since September 2000 5000 t/day of supercritical CO2 are injected, are presented and discussed. The Weyburn oil-pull is recovered from the Midale Beds (at the depth of 1300-1500 m), consisting of Mississippian shallow marine carbonate-evaporites, that is classically subdivided into two units: i) the dolomitic “Marly” and ii) the underlying calcitic “Vuggy”, sealed by an anhydrite cap-rock. Assumptions and gap-acceptance are commonly made to reconstruct the reservoir conditions (pressure, pH, chemistry, and mineral assemblage), although most geochemical parameters of deep fluids are to be computed by a posteriori procedure due to the sampling collection at the well-head, i.e. using depressurised aliquots. On the basis of the available data at Weyburn, such as: a) bulk mineralogy of the Marly and Vuggy reservoirs; b) mean gas-cap composition at the well-heads and c) selected pre- and post-CO2 injection water samples, we have rebuilt the in-situ reservoir chemical composition and the kinetic evolution after CO2 injection. The geochemical modelling has been performed by using the code PRHEEQC (V2.11) software package; the in-situ reservoir composition was calculated by the chemical equilibrium among the various phases at reservoir temperature (62 °C) and pressure (150 bars) via thermodynamic corrections to the code default database. Furthermore, the “primitive” chemical composition of the pre-injection Marly and Vuggy liquid phase was derived by assuming the equilibrium conditions for the mineral assemblage with respect to a Na-Cl (Cl/Na=1.2) water. A comparison between the chemical composition of the “primitive brine” and that measured before the CO2 injection shown an agreement within 10 % for most analytical species. The second step has been that to compute the geochemical impact of three years of CO2 injection (September 2000-2003) by kinetically controlled reactions. In order to statically validated our geochemical model we have compared the computed and measured data by using the Median Test. The results show that the proposed geochemical model is able to reliably describe (within 5% error) the behaviour of pH, HCO3, Cl, Li, Na, Sr, Si and HS+SO4, with the exception of K, Ca and Mg. Finally, the kinetic evolution of the CO2-rich Weyburn brines interacting with the host-rock minerals, performed over 100 years after injection, has also been modelled. The solubility trapping (short/medium-term sequestration) gives an amount of dissolved CO2 of 0.761moles/L and 0.752 moles/L for Marly and Vuggy units, respectively, whereas the mineral trapping, calculated as difference between dissolved (calcite and dolomite) and precipitated carbonate (dawsonite) minerals, is -0.019 and -5.69x10-5 moles/L for Marly and Vuggy units, respectively. The experimental data-set available and the geochemical modelling intrinsic limitation introduce a large uncertainty in the modelled results and in order to evaluate the dependence of the results from the modeling code, a different thermodynamic approach, such as the modelling software GEM (Gibbs Energy Minimization approach), is required.

In this paper thematic maps produced on the basis of the principles of linear geostatistics are described in order to characterise the superficial and ground waters of the municipal territory of Arezzo. The aim is to assess the correlation with lithology, use of soil, drainage density and anthropogenic pressure and identify sensible areas to be periodically monitored in time. This study has used an original geochemical data-base consisting of about 500 water samples. A statistical approach has been used for the identification of anomalous values and homogenous populations. This step was followed by a detailed variographic study in order to analyse the spatial behaviour of the variables. Subsequently, an estimation procedure based on the application of ordinary kriging algorithm and sequential Gaussian simulation methods was applied to obtain the maps.