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The investigated mantle bodies from the External Ligurians (Groppo di Gorro and Mt. Rocchetta) show evidences of a complex evolution determined by an early high temperature metasomatism, due to percolating melts of asthenospheric origin, and a later metasomatism at relatively high temperature by hydrothermal fluids, with formation of rodingites. At Groppo di Gorro, the serpentinization and chloritization processes obliterated totally the pyroxenite protolith, whereas at Mt. Rocchetta relics of peridotite and pyroxenite protoliths were preserved from serpentinization. The rodingite parageneses consist of diopside ​+ ​vesuvianite ​+ ​garnet ​+ ​calcite ​+ ​chlorite at Groppo di Gorro and garnet ​+ ​diopside ​+ ​serpentine ​± ​vesuvianite ​± ​prehnite ​± ​chlorite ​± ​pumpellyite at Mt. Rocchetta. Fluid inclusion measurements show that rodingitization occurred at relatively high temperatures (264–334 ​°C at 500 ​bar and 300–380 ​°C at 1 ​kbar). Garnet, the first phase of rodingite to form, consists of abundant hydrogarnet component at Groppo di Gorro, whereas it is mainly composed of grossular and andradite at Mt. Rocchetta. The last stage of rodingitization is characterized by the vesuvianite formation. Hydrogarnet nucleation requires high Ca and low silica fluids, whereas the formation of vesuvianite does not need CO2-poor fluids. The formation of calcite at Groppo di Gorro points to mildly oxidizing conditions compatible with hydrothermal fluids; the presence of andradite associated with serpentine and magnetite at Mt. Rocchetta suggests Fe3+-bearing fluids with fO2 slightly higher than iron-magnetite buffer. We propose that the formation of the studied rodingite could be related to different pulses of hydrothermal fluids mainly occurring in an ocean-continent transitional setting and, locally, in an accretionary prism associated with intra-oceanic subduction.

Knowing water quality at larger scales and related ground and surface water interactions impacted by land use and climate is essential to our future protection and restoration investments. Population growth has driven humankind into the Anthropocene where continuous water quality degradation is a global phenomenon as shown by extensive recalcitrant chemical contamination, increased eutrophication, hazardous algal blooms, and faecal contamination connected with microbial hazards antibiotic resistance. In this framework, climate change and related extreme events indeed exacerbate the negative trend in water quality. Notwithstanding the increasing concern in climate change and water security, research linking climate change and groundwater quality remain early. Additional research is required to improve our knowledge of climate and groundwater interactions and integrated groundwater management. Long-term monitoring of groundwater, surface water, vegetation, and land-use patterns must be supported and fortified to quantify baseline properties. Concerning the ways climate change affects water quality, limited literature data are available. This study investigates the link between climate change and groundwater quality aquifers by examining case studies of regional carbonate aquifers located in Central Italy. This study also highlights the need for strategic groundwater management policy and planning to decrease groundwater quality due to aquifer resource shortages and climate change factors. In this scenario, the role of the Society of Environmental Geochemistry is to work together within and across geochemical environments linked with the health of plants, animals, and humans to respond to multiple challenges and opportunities made by global warming.

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 (&gt, 150 °C), the greatest enrichments in Li (124.3 ppb) and Cs (&gt, 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.

Hydrogeochemical changes before Mw ≥ ∼5.0 earthquakes are hoped to be applicable as seismic precursors. It is now necessary to pass from single experiences to structured networks, systematically monitoring large seismic areas for long periods. Our aim is to provide a pilot methodological experience for how such networks could be realized and the types of results they could deliver. We present the method and some initial results to document the method’s applicability. In 2017, we started the HydroQuakes project in seismically active central Italy, with the Sulmona and Matese areas selected as the two monitoring nodes. Each node includes 5–6 monitored springs, and for each spring, we performed laboratory analyses of major and trace elements and some isotopes. We installed in situ probes for continuous monitoring. Between December 2017 and January 2020, the most energetic earthquakes were three events with Mw of 3.9, 4.1, and 4.4. They were not preceded by significant hydrogeochemical anomalies, except for the Mw 4.1 event. Despite its low Mw, this earthquake occurred over a large normal fault at a great depth in the crust (∼17 km) and was preceded by weak but detectable hydrogeochemical anomalies of boron and δ11B that were similar but milder than the hydrogeochemical anomalies before the 2016 Mw 6.0 earthquake in the central Apennines. This and previous evidence show the B and δ11B hydro-seismo-sensitivity and indicates that pre-seismic hydrogeochemical anomalies could arise mostly before Mw ≥ ∼5.0 earthquakes, with weak exceptions occurring in specific conditions such as long and deep faults.

We analysed temporal variations of trace element concentrations in groundwater from a 101 m-deep borehole (HA01) in northern Iceland during 2010-2018 and compared them with seismic and volcanic events that occurred in the same period to identify potential hydrogeochemical precursors. An increase of B, Al, V, Li and Mo concentrations started from eight months to one month before the 2014 Barðarbunga eruption (~115 km from HA01), a major rifting event in central Iceland, while Ga and V concentrations began to increase one day and one month after the onset of the event, respectively. We also found that concentrations of some trace elements (Li, B, Ga, Mo, Sr, Rb and Fe) significantly increased before an Mw 5.0 earthquake that occurred ~80 km from the borehole in 2018. However, other notable hydrogeochemical changes were detected during the monitoring period without apparent correlation with the seismic and volcanic events in the region. This study shows that the systematic long-term hydrogeochemical monitoring in seismic and volcanic areas is critical to advance the science of seismic and eruptive precursors. Furthermore, the use of statistical tools, such as Principal Component Analysis (PCA) and Change Point (CP) detection can help identify the most useful chemical elements and validate the trend variability of those elements in the time series, reducing arbitrary choices of pre-seismic and pre-volcanic hydrogeochemical anomalies as potential precursors.

The complex Djibouti volcanic aquifer system was studied to improve understanding of the recharge conditions of the Awrlofoul low-enthalpy geothermal system located in the middle of the aquifer. Forty-four thermal and non-thermal groundwater samples were analyzed to determine their major chemical compositions, trace element compositions, and multi-isotopic compositions (δ2H(H2O), δ18O(H2O), δ18O(SO4), δ34S(SO4), δ13C(DIC), 14C, 87Sr/86Sr, δ11B, δ15N(NO3−), and δ18O(NO3−)). Statistical analysis (Hierarchical Cluster Analysis and Principal Component Analysis) of chemical composition identified three main water groups, two affected by salinization (C1 and C2) and one fresh water group useful for drinking (C3). The latter group includes thermal water from the Awrlofoul geothermal field. This separation into three different water groups is also clear on a Langelier-Ludwig plot and is confirmed by analysis of historical chemical data over the last 30 years. The main causes of salinization are contamination of the fresh groundwater either by recent seawater intrusions (C2) or mixing with Ca-Cl fossil saline water (C1). The C1 waters are also highly affected by Mg/Ca-Na clay exchange. As expected, the 11B/10B isotope ratio of the intruded salt water, both recent and fossil, was much higher than that of seawater (δ11B up to +55‰). Unexpectedly, groundwater of meteoric origin (i.e., unaffected by a seawater intrusion), also showed a δ11B higher than that of seawater (46.3‰ To estimate the temperature of the Awrlofoul low-enthalpy geothermal system, a multi-method geothermometric approach was applied. Chemical (mainly SiO2) and isotope (sulfate-water oxygen fractionation) geothermometers were employed together with multiple mineral equilibria. These different geothermometric approaches estimated a temperature range of 102 °C–140 °C for the geothermal reservoir, with a mean temperature of about 110 °C. Finally, a conceptual model was proposed for the Awrlofoul low-enthalpy geothermal system on the basis of the geochemical and isotopic data of the thermal and non-thermal groundwaters combined with the geology and hydrogeology of the study area.

The examination of past and new chemical–isotopic data (2H/1H–18O/16O, 11B/10B and 87Sr/86Sr ratios) shows the meteoric origin of the Sawa Lake (Muthanna Governorate, Iraq) and its connection with the local aquifers, which feed the lake via the groundwater emerging from its floor through fault systems. The chemical and isotopic evaporation models are traced by geochemical computer codes by using a different composition of some potential inflows to the lake (e.g., the Euphrates River and Dammam aquifer). The main product of the chemical evaporation models is gypsum, as confirmed by the mineralogical examination of the sediment and the surrounding outcrops. A strong 18O–2H enrichment is a consequence of the evaporation effect in arid regions; δ18O–Cl models and δ11B = + 23.4‰ exclude the contribution of any seawater-derived fluids. This latter value along with 87Sr/86Sr = 0.707989 suggests a mixed origin from the Eocene–Miocene aquifers. The isotope and chemical evaporation paths from the meteorically recharged sources match the lake composition. However, compositional switches from NaCl toward MgCl2 occurred in the last decade and are related to post-drought periods, showing that the interaction of the recharging waters with the local soils (Na–Mg exchange and/or the leaching of the top layer salts) have a role in the chemical composition. This demonstrates that the lake is significantly influenced by climatic variations.

In this study, the thermodynamic data of some lithium (Li) minerals (bikitaite, cookeite, elbaite, ephesite, hectorite, lepidolite, Li-mica, petalite, polylithionite, taeniolite, zinnwaldite) are revised. Despite the economic importance of lithium worldwide and the availability of some standard thermodynamic parameters of lithium minerals, a reluctance persists to include solubility data at different temperatures (logK) in hydrogeochemical calculation codes. The previously published standard thermodynamic data are reviewed, averaged and/or recalculated. Thereafter, the logK values are calculated and formated to be included into the thermodynamic dataset of two hydrogeochemical codes (The Geochemist's Workbench; PHREEQC). The interested reader has the possibility of reviewing and reworking them for other specific software. Finally, understanding the lithium geochemistry and geothermometry of the geothermal waters from El Tatio (northern Chile) and South Crofty Mine (Cornwall, UK) are discussed.

Within the East African Rift System (EARS), the complex Ali-Sabieh aquifers system, located in the south of the Republic of Djibouti, was overexploited and subjected to anthropogenic and/or geogenic pollution with high concentrations of dissolved nitrate (up to 181 mg/l) and sulfates (up to 1540 mg/l). This study is the first undertaken on the hydrochemistry of this aquifer system, combining geochemical tools and multi-isotope - δ2H(H2O), δ18O(H2O), δ18O(SO4), δ34S(SO4), δ15N(NO3), δ18O(NO3), δ13C(DIC), and 14C- was used to decipher the origin and fate of different nitrate and sulfate sources to groundwater. The groundwater samples of the region show a chemical evolution from fresh Ca(Na)-bicarbonate to brackish Na-Cl , mainly due to water-rock interaction. The combined chloride and water isotope data show that evaporation and transpiration are present, with the latter occurring primarily in the shallow alluvial aquifer waters. Inspection of δ15N(NO3) vs. δ18O(NO3) and NO3/Cl vs. Cl diagrams show that dissolved nitrates are primarily of anthropogenic origin. In particular, higher nitrate concentrations may be related to animal manure used as organic fertilizers during agricultural activities. Sulfates are from a natural origin related to the interaction of water with gypsum of hydrothermal or sedimentary origin. SO4/Cl ratio and isotopic composition show that dissolved sulfates in saline and ancient groundwater of the Cretaceous sandstone aquifer (between 7.4 ± 2.2 and 5.8 ± 1.4 k-years before the present) are generated by interaction with gypsum from oxidation of pre-existing (Jurassic?) sulfides. This work highlight that isotopic ratios of the two molecules -δ18O(SO4), δ34S(SO4), δ15N(NO3), δ18O(NO3)- are not sufficient for tracing the origin of nitrate and sulfates in groundwater, but that a complete hydrogeochemical study is needed. In the absence of this, the relatively high concentration of chloride and sulfates could be wrongly linked to the anthropogenic source of nitrate (manure or sewage).

The Na-Cl waters from NW Tuscany (central Italy) record similar water isotopic and major chemical compositions, which demonstrate their meteoric origin and interactions with Upper Triassic evaporites and the metamorphic units of the Paleozoic basement. Slight differences are found in the deep temperature-pressure conditions of the Lunigiana graben (39–42 °C/143–145 bar) and the Garfagnana graben (73–78 °C/250–256 bar). In particular, the thermal fluids outpouring from Garfagnana are probably related to a common deep reservoir or interconnected fluids. Their differences are mainly evidenced by strontium isotopic ratio data (87Sr/86Sr), which combined with previously published sulfur isotope ratios (34S/32S) demonstrate the involvement of vein barites in water-rock interactions. Most likely, these minerals formed during Upper Oligocene-Miocene tectogenesis due to the mixing of fluids from the Verrucano Group and Upper Triassic units. The results of this hydrogeochemical study of the deep Na-Cl fluids could better clarify the distribution of the Verrucano Group within this area and the related discrepancies in the stratigraphic interpretations of the Palaeozoic-Mesozoic transition. Furthermore, the possible presence of an interconnected reservoir could be used to help interpret data produced by the local geochemical monitoring of seismic activity.

The chemical and isotope compositions of slab dehydration fluids from convergent margins have been theorized by many authors who have adopted several approaches. A direct collection of natural water is possible only in an oceanic environment, despite several difficulties in estimating the deepest component due to the mixing with seawater or hydrothermal fluids from the ridge. Accordingly, the study of melt inclusions is a valuable alternative. However, the latter mainly represents high temperature/pressure conditions in deep magmatic or metamorphic settings. Here, we present new H, O, Li and B isotope along with a revision of previously published chemical data from a potential natural example of slab dehydration water, sampled in a forearc region and affected by low-temperature metamorphism and serpentinization processes (Aqua de Ney, Northern California). Its extreme composition challenges the understanding of its origin and deep temperature, but this work is a further step on a topic of increasing interest for several scientists from different academic disciplines.

Fractured volcanic aquifers are the main water resources in the arid climate of the Republic of Djibouti. Nonetheless, these strategic reservoirs are overexploited and their comprehensive understanding is therefore a pre-requisite for a sustainable use. A geochemical and isotopic survey, including major ion chemistry, 2H, 18O, 13C, 3H, 87Sr/86Sr, 15N was performed and combined with existing 14C data to study recharge, contamination processes and groundwater flow patterns inside and between the compartments of a complex aquifer system composed by basaltic rocks and by alluvium located in Petit Bara, Grand Bara, and Mouloud areas (Southwest of Djibouti). A main feature was the common trend from a fresh Na-Cl-HCO3 water type (alluvium groundwaters) to an intermediate water type (alluvium and basalt groundwaters) and finally to a Na-Cl-SO4 water type (most mineralized basalt groundwater). Elementary and isotopic nitrate evidenced and located anthropogenic and geogenic origins of nitrate. Alluvium groundwaters had δ2H and δ18O signature of modern precipitation while basalt groundwaters were significantly depleted and enriched in δ13C due to water-rock interactions. Modern radiocarbon and tritium were evidenced in the alluvium groundwaters, while recalculated radiocarbon ages located recharge of the basalt groundwaters in the early to mid-Holocene. These features revealed a common evolutionary pattern, with a recharge from wadi-rivers to the alluvium and a downward circulation to the basalt through major faults, combined with a mixing with a more geochemically evolved groundwater. Accordingly, highly saline groundwater at the outlet of the Petit Bara plain was found to be diluted by modern recharge in the alluvium. Two major basaltic aquifer compartments were found to be connected (Grand Bara and Mouloud), revealing a global northeastward flowpath below the endorheic Grand Bara plain.

The aim of this work is to provide a methodology for the investigation of seismic precursors starting from hydrogeological, hydrogeochemical, and seismic study of the territory. Hydrological effects originated during the seismic cycle (particularly prior to and during strong earthquakes) have long been observed and documented, as they are among the most outstanding coseismic phenomena that can be even observed over great distances. Moreover, since a few decades, geochemical changes of groundwater prior to intermediate and/or strong (Mw ≥ 5.0) earthquakes have started to be a concrete hope and, at the same time, a big scientific and technological challenge for geoscientists working in the field of seismic precursors. Deformation and stress perturbation during the seismic cycle can cause changes in deep fluid migration eventually leading to changes in shallower groundwater circulation and geochemistry. As monitoring sites, we identified the Sulmona and Matese areas in the central-southern Apennines. These two areas were affected in the past by Mw > 5.5 earthquakes. Each study area includes 5-6 monitored springs and boreholes. Groundwaters are mainly calcium-bicarbonate type or secondarily sulphate-calcium-bicarbonate type. Continuous monitoring and monthly sampling of the two study areas started in December 2017, although in the Sulmona area they had already started in 2014 for a previous project, whose results have been published in previous papers. In an attempt to identify potential seismic precursors, we carried out, for each monitored spring, analyses of major and trace elements and analyses of isotopes of the water molecule, boron, and strontium. During these years of monitoring (2018-2019), there were no high magnitude earthquakes. The three seismic events with the highest magnitude were indeed the 2019 Collelongo (Mw 4.1, January 1st), Balsorano (Mw 4.4, November 7th), and San Leucio del Sannio (Mw 3.9, December 16th) earthquakes. The most interesting result is that these earthquakes (except Collelongo) were not substantially preceded by hydrogeochemical anomalies. This evidence suggests that this type of pre-seismic anomalies could arise substantially only with intermediate and strong earthquakes (Mw≥5.0); however, it is also true that the Collelongo earthquake, which occurred on a very large Apennine normal fault (the fault that generated the great Avezzano earthquake of 1915, Mw 7.0) at great depths - about 16-17 km -, was preceded by very weak hydrogeochemical anomalies of Li, B, and Sr in most monitored springs. These weak anomalies could be related to pre-seismic breakages at great crustal depths along a very large fault. We also describe the monitoring stations as well as the used instrumentations, procedures, and analyses. We propose some preliminary results that emphasize the importance of collecting data from a widespread network of monitoring stations over a seismic territory and for long time. HydroQuakes provides new evidence for the importance of building a national hydrogeochemical network for the identification of seismic precursors. Future possible implementations as well as further societal uses for such a network are also addressed. The HydroQuakes Project is funded by Fondazione ANIA to CNR-IGAG.

The Cabezo Negro de Tallante volcano (SE Spain) is well known in literature for the presence of abundant mantle and crustal xenoliths in basaltic lithologies. Here we report field, petrographic, mineralogical and geochemical data of a poorly investigated pyroclastic deposit (breccia) and provide evidence for the presence of a primary magmatic carbonatite component. The matrix of the pyroclastic breccia contains carbonate and silicate portions. The carbonate portion is made up of calcitic ash with micro-lapilli of fine-grained carbonate, while globules and clasts of basaltic composition represent the silicate portion. A liquid immiscibility relationship between the carbonate and silicate portions is indicated by the presence of sharp, curved menisci between them, the presence of carbonate globules in silicate glass (and vice-versa) and the overall appearance as emulsion texture with bulging and pinch-off shapes. Carbonate globules in fresh silicate glass are also present as inclusions within xenolith crystals and bimodal carbonate mineralogy, consisting of either calcite (plus Mg-calcite) and dolomite, was observed in quenched liquids within mantle xenoliths. The whole-rock composition of the carbonate portion is within the compositional range of the carbonatitic rocks, but shows low concentrations of Sr, Ba, Nb, P and LREE if compared with typical carbonatite magmas. REE profiles of the carbonate portion are parallel to the patterns of associated alkaline basalts and fall in the range of both intraplate and convergent margin carbonatites. The carbonate portion shows high δ18O compared to primary igneous carbonates, a feature common to many extrusive carbonatites and plots slightly towards higher 87Sr/86Sr for a given 143Nd/144Nd in the Nd-Sr isotopic trend described by the associated rocks (alkaline basalts and mantle xenoliths) suggesting a contribution from crustal subducted material. These results support a magmatic origin for the carbonate portion and a contemporaneous eruption of carbonatic and silicatic magmas. The CO2 produced by the transformation of dolomitic melt into Mg-calcitic melt was the principal propellant in the high-energy explosive eruption at the Cabezo Negro de Tallante volcano.

In this study, a revision of the previously published data on hydrogen (2H/1H) and oxygen (18O/16O) stable isotope ratio of precipitation in northern Chile is presented. Using the amount-weighted mean data and the combined standard deviation (related to both the weighted mean calculation and the spectrometric measurement), the equation of the local meteoric line calculated by error-in-variables regression is as follows: Northern Chile EIV-LMWL: &delta, 2H = [(7.93 &plusmn, 0.15) &delta, 18O] + [12.3 &plusmn, 2.1]. The slope is similar to that obtained by ordinary least square regression or other types of regression methods, whether weighted or not (e.g., reduced major axis or major axis) by the amount of precipitation. However, the error-in-variables regression is more accurate and suitable than ordinary least square regression (and other types of regression models) where statistical assumptions (i.e., no measurement errors in the x-axis) are violated. A generalized interval of &delta, 2H = &plusmn, 13.1&permil, is also proposed to be used with the local meteoric line. This combines the confidence and prediction intervals around the regression line and appears to be a valid tool for distinguishing outliers or water samples with an isotope composition significantly different from local precipitation. The applicative examples for the Pampa del Tamarugal aquifer system, snow samples and the local geothermal waters are discussed.

Eighty-six sodium bicarbonate to sodium chloride hot springs and four water wells in the Tadjourah Region of Djibouti were investigated for major, minor (B, Br, F, Sr, Li) chemistry and isotope composition of water and dissolved components (87Sr/86Sr, 11B/10B, 13C/12C and 14C of DIC, 34S/32S and 18O/16O of sulfate). The deep saline Na-Cl reservoir at 143 °C shows affinity with the shallow geothermal water from the “active” Asal rift. Asal water is a diluted and recycled seawater component with the major cation composition obliterated by equilibration with Stratoid basalt. Locally, the deep reservoir is differentiated in term of recharge, and re-equilibration with rocks and mixing. In particular, two spring groups reveal contributions from evaporites typical of the “passive” graben setting of the Afar. A model on 34S/32S and 18O/16O demonstrates the isotope imprint of magmatic SO2 disproportionation on dissolved and solid sulfate, whose values probably persists in a sedimentary environment without trace of seawater. On the other hand a seawater signature, modified by mixing and secondary fractionation effects, is partially maintained according to the boron isotope composition (up to + 27.4‰). Temperature estimation in low-enthalpy geothermal reservoirs is notoriously difficult, especially where mixing with fluids of differing genesis and/or conduction cooling take place. From a geothermometric point of view, the multi-method approach followed in this study (up-to-date theoretical and thermodynamic equations, ad-hoc silica geothermometers inferred from local rocks, checking of the results on a 18Oαsulfate-water vs. temperature diagram) provides some insights and perspectives on how to tackle the problem.

Free water and water in emulsion with oil from hydrocarbon wells onshore–offshore Lake Maracaibo were extracted and analyzed. The use of classical and new chemical diagrams evidenced that Na–HCO3 and Na–Cl are the main chemical facies, whereas Na–SO4 facies was rare and revealed only in faulted areas in which shallow groundwater was involved in deep circulation. Cretaceous Ca–Cl waters were not revealed, but their imprint on some samples was traced and evidenced by Langelier–Ludwig, Brine-Differentiation and Caexcess vs. Nadeficit diagrams. These square plots, allowing a discrimination between the water contributions from the different source rocks, should be more exploited as hydrogeochemical tools in hydrocarbon exploration. Original data on monocarboxylic anions showed acetate concentration higher than ten times that of formate at sampling conditions, but speciation under deep conditions indicated a reversed activity dominance. Calculation of saturation indexes and kinetic modeling showed an active precipitation of chalcedony, kaolinite and clays, especially where the temperature was lower (T < 100 °C). Formation waters and lake water showed quite similar chloride concentration and hydrogen isotope composition. However, thermodynamic calculations at the oilfield P-T conditions revealed chlorite and illite, produced during previous diagenetic stages of Misoa sandstones, recrystallization to smectite and vermiculite in present-day stage. The diagenetic water produced in these reactions could have enriched the δ18O isotopic composition of approximately +2‰. This isotope diagenetic effect was more evident in Na–HCO3 waters, which also showed a decrease in chloride at constant boron concentration as a consequence of clay dewatering. In this regard, a new boron geothermometer useful for formation waters is also proposed: T°C=[5.1364×ln(1/B)mg/1]+5.728(±0.180)−0.164(±0.012)

This paper focuses on the geochemical composition and isotope geochemistry of brines in the Cenomanian–Turonian carbonate Mishrif reservoir of southern Iraq. Main dissolved constituents, trace elements, δ2H and δ18O, 87Sr/86Sr, mineral saturation indices and thermodynamic calculations were investigated in formation waters from the Mishrif Formation to obtain a better understanding of brine evolution and diagenetic effects over geological time. Previous published δ11B data were also reinterpreted as a geothermometer tool. The results are compared with previous published data for local oilfields and coeval formations in the Arabian Gulf. The Mishrif brine has a marine origin and is diagenetically modified to Ca-excess and Na-deficit. Formation waters are quartz supersaturated and are in equilibrium with chalcedony and calcite-dolomite in the temperatures range of 50–75 °C, which is also confirmed by calcite-water oxygen isotope fractionation and δ11B geothermometer. The potential role of clays in conditioning brine chemistry during diagenetic processes was highlighted by activity diagrams; in particular, their adsorption/exchange effect on sodium could explain the lower temperature obtained by the Na/Li geothermometer (42 ± 6 °C). The δ2H and δ18O values show that oxygen isotope composition of the brines was isotopically more affected by interaction with limestone during diagenesis than seawater evaporation. The main effect is an 18O-enrichment on the brine starting from the SMOW value. Locally, dilution by present-day meteoric water was also detected (Rumaila South), which is shifted towards the local meteoric water line. The strontium isotope ratios range from 0.707713 to 0.707749 and correspond to a marine strontium of late Cenomanian–early Maastrichtian age, except for the Majnoon sample, which shows a more radiogenic value (0.708043). Radiogenic strontium and gypsum and anhydride saturation indices of the Majnoon sample could indicate the contribution of calcium and sulphate from the strontium-rich sulphate minerals of the Cambrian salt domes occurring in the oilfields of southern Iraq. The higher manganese concentration (4 mg/l) and the slightly higher temperature inferred by geothermometers (up to 74 °C) in comparison with present-day could indicate that the Majnoon brine is a hot fluid, probably related to a deeper structure such as the Zagros Foredeep Fault.

Water from ten thermal springs, five drinking-water boreholes and one hand-dug well from Hanle-Gaggade grabens has been analyzed for major-minor hydrogeochemical parameters and multi-isotope composition: δ2H(H2O), δ18O(H2O), δ18O(SO42−), δ34S(SO42−), δ13C(DIC), 14C(DIC), and δ11B. The interaction of the thermal water with both silicic (basaltic) and sedimentary rocks and its low enthalpy (T ≤ 150 °C) regime make this area an optimal site for testing chemical and isotope geothermometers and optimizing them for similar difficult cases. In this study, the use of radiogenic carbon (14C) reveals that the age of the deep aquifer is between 12,500 and 8700 years ago (late Pleistocene/early-to-mid Holocene), which places it within the East African Humid Period. The oxygen and hydrogen stable isotope ratios of the water molecules, δ2H(H2O), δ18O(H2O), show common characteristics between the groundwater from this area and that of groundwater from nearby local lakes (Asal-Abhe) and palaeolakes (Sakalol-Hanle-Gaggade-Dobi), which were interconnected during that period to form the terminal Awash River Basin. The comparison of these aquifers within the transboundary aquifer located between northeast Ethiopia and Djibouti helps to reconstruct both the palaeoenvironmental history and the hydrogeochemical characteristics of this regional aquifer. At present, these data are poorly defined, but it is of fundamental importance for the constructive use of water resources in arid areas. Finally, a conceptual model was proposed for the Hanle-Gaggade low-enthalpy geothermal system on the basis of the geochemical and isotope data on the thermal and non-thermal groundwaters combined with geological and tectonic information and the results of recent geophysical studies.

Drinking water is scarce in Djibouti because of the hot desert climate. Moreover, seawater intrusion or fossil saltwater contamination of the limited number of freshwater aquifers due to groundwater overexploitation affect those who live close to the coastline (~80% of the population). Despite this, the geothermal potential of the country&rsquo, s plentiful hot springs could resolve the increasing electricity demand. Strontium isotopes (87Sr/86Sr) are routinely used to determine sources and mixing relationships in geochemical studies. They have proven to be useful in determining weathering processes and quantifying endmember mixing processes. In this study, we summarise and reinterpret the 87Sr/86Sr ratio and Sr concentration data of the groundwater collected to date in the different regions of the Djibouti country, trying to discriminate between the different water sources, to evaluate the water/rock ratio and to compare the data with those coming from the groundwater in the neighbouring Main Ethiopian Rift and the Red Sea bottom brine. New preliminary data from the groundwater of the Hanl&eacute, Gaggad&eacute, plains are also presented.

The Lake Abhe Geothermal Field is located in the South-Western region of the Republic of Djibouti, on the border with Ethiopia. The Lake Abhe geothermal system occurs within a rift basin filled with Pliocene-Quaternary volcanic (mainly basalt) and lacustrine sediments. The thermal water in Lake Abhe geothermal field discharges as hot springs at the bottom of hydrothermal carbonate chimneys distributed along the main faults. Hot springs of Lake Abhe geothermal field as well as ground- and surface waters were sampled and major elements, trace elements, and isotopic (18O/16O, 2H/1H, 3H, 34S/32S, 87Sr/86Sr) compositions were analyzed. Hydrochemical features of the hot springs are dissimilar from those of warm waters: the former are mainly Na–Cl dominated whereas the latter were mostly Na–HCO3–Cl–SO4 and Na–HCO3–Cl. The isotopic composition of sulfur and oxygen in dissolved sulfates suggests equilibrium with anhydrite as the major source of sulfates in the thermal waters. Chemical (mainly Na/K and SiO2), isotope (bisulfate- and anhydrite- water), and multiple mineral equilibrium approaches were applied to estimate the reservoir temperature of the hot springs in the Lake Abhe geothermal field. These different geothermometric approaches estimated a temperature range of the deep geothermal reservoir of 120–160 °C. In spite of the relatively wide range, the three different approaches led to a same mean of about 135 °C. The hot spring and warm borehole waters from the southwestern part of the Republic of Djibouti showed a possible mixing with hydrothermal waters from the local rift. The negligible tritium content and the low deuterium values (δ2H − 10‰).

This paper examines the hydrochemical features of the waters from the Obock coastal geothermal field. As the submarine waters at the ridge, their chemical and isotope composition shows affinities with sea water–basalt interactions at hydrothermal temperature. Moreover, good linear correlations were obtained between hot springs and of sea water sample points when plotting normalized concentrations of elements to chloride (Mg/Cl, SO 4 /Cl, K/Cl, Ca/Cl, SiO 2 /Cl) versus concentration of Li/Cl. This would indicate that two end members exist (seawater and reservoir fluid). After extrapolation of the Mg and SO 4 concentrations to zero, the obtained value of SiO 2 corresponding to the reservoir fluid end member was used to estimate the reservoir temperature by quartz geothermometers. The obtained temperature of 187 °C is in good agreement with that obtained from multiple mineral equilibrium approach (180–200 °C), cationic geothermometers (172–191 °C) and by the evaluation of isotopic equilibrium between water and sulfate molecule (207 °C). Summarizing all the employed approaches, a mean temperature of 197 ± 10 °C has been estimated. The isotopic δ 34 S(SO 4 ) signature of the dissolved sulfates in Obock thermal waters confirms that these waters result from the mixture of a hot seawater-derived fluid (absence of sulfates) with cold seawater. However, water isotope data did not exclude the presence of a small contribution from fresh groundwater.

Messinian evaporates are widely distributed in the Mediterranean Sea as outcropping sediments in small marginal basins and in marine cores. Progressive filling of subbasins led to the formation of complex aquifer systems in different regions where hypersaline and fresh water coexist and interact in different manner. It also generates a significant diversification of groundwater hydrochemical signature and different microbial communities. In the case study, the hydrogeology and hydrochemistry of the whole system are influenced by good hydraulic connection between the shallower pyroclastic horizon and the underlying evaporate-bearing fine-grained Messinian succession. This is demonstrated by the merge of hydrogeological, chemical, isotopic, and microbiological data. No mixing with deep ascending waters has been observed. As shown by geophysical, hydraulic, and microbiological investigations, the hydraulic heterogeneity of the Messinian bedrock, mainly due to karstified evaporitic interstrata/lenses, causes the hydraulic head to significantly vary with depth. Somewhere, the head increases with the depth’s increase and artesian flow conditions are locally observed. Moreover, the metagenomic investigations demonstrated the existence of a poor hydraulic connection within the evaporate-bearing fine-grained succession at metric and decametric scales, therefore leading to a patchwork of geochemical (and microbiological) subenvironments.

An understanding of the origin and migration pathways of geofluids in an active seismic area is of paramount importance in terms of societal challenges such as mitigation of seismic hazards. This study investigates the relationship between the stable isotope ratio 13C/12C of deep CO2 and geothermometry in selected groundwater samples located close to extensional faults in central Italy. The temperature range is inferred from an equation based on the Na/Li ratio and chemical geothermal modelling: 113–130 °C. Globally, the calculated temperature range agrees with that resulting from deep boreholes in the Northern Apennines. An alternative method is also included to better evaluate the difference in isotopic composition between the aqueous and gaseous δ13C(CO2) at deep condition. A review of previously published data shows that monitoring of the isotopic composition of the dissolved inorganic carbon (DIC) in springs fed by meteoric origin located in seismically active areas must take into account mass and isotopic balance to correctly evaluate the component, and the role, of deep fluid during seismic events. In particular, the coupled (and corrected) isotope and geothermometrical monitoring of the springs could help to distinguish between deep gas or deep fluid contributions to shallow aquifers. The results of this study indicate that faults play a crucial role in controlling the migration of crustal fluids. In addition, they reveal that possible evaluation of potential seismic precursors mandatorily requires a long period of monthly monitoring.

The boron stable isotope ratio δ11B of 12 water samples representative of three chemical facies (fresh Na-bicarbonate, brackish Na-chloride, saline, and brine Ca-chloride) has been analyzed. Interpretation of the δ11B data, along with the chemical compositions, reveals that Na-carbonate waters from the Northern Apennine are of meteoric origin, with boron contributions from clay desorption and mixing with seawater-derived fluids of Na-chloride or Ca-chloride compositions. The comparison of our new results with the literature data on other sedimentary basins of Mediterranean, and worldwide, confirms the contribution of Na-bicarbonate waters to the genesis of mud volcano fluids. The Na-chloride sample of Salvarola (SAL), which may represent the end-member of the mud volcanoes, and the Ca-chloride brine water from Salsomaggiore (SM) indicate boron release from clays compatible with the diagenetic process. The empirical equation: δ11B=[5.1364×ln(1/B)mgl−1]+44.601 relating boron concentration and the stable isotope composition of the fluids observed in this study and the literature is proposed to trace the effect of diagenesis in sedimentary basins. A geothermometer associated to the diagenetic equation is also proposed: T∘C=[δ11B−38.873(±1.180)]/[−0.164(±0.012)] The application of this equation to obtain reservoir temperatures from δ11B compositions of waters should be carefully evaluated against the results obtained from other chemical and isotopic geothermometers from other basins around the world.

Chemical and water isotope ratios data for groundwaters from the Pozzo del Sale area in the Irpinia sector of the Southern Apennines are presented. The water chemistry of the aquifer system may initially be regarded as the result of easy and common, low temperature interaction between meteoric water and Late Messinian evaporites, which produce Ca-bicarbonate and Na-chloride passing through Ca-sulfate waters. However, a closer inspection reveals a more complicated geochemical setting consisting of: (1) two further Na-sulfate and Ca(Mg)-sulfate waters; (2) the existence of different meteoric recharge areas; (3) the mixing between the different groundwaters and allochthonous fluids from terrestrial mud volcanoes. The salinization mechanism and the local mineralogy were inferred by classical and novel ternary and binary diagrams. The presence of MgSO4- and Na2SO4-bearing minerals of non-marine or mixed origin other than gypsum and halite within the local evaporites suggests a mineralogical heterogeneity within the local Messinian evaporites. The paleoenvironment of this sector of the Gessoso–Solfifera Formation might have been composed of relatively small playa-lakes fed by seawater but also large amounts of continental waters of meteoric origin.

Spring waters issuing from serpentinized ultramafic rocks of the Taro-Ceno Valleys (Northern Apennine, Emilia-Romagna region, Italy) were analyzed for major element, trace element and dissolved gas concentrations and ?11B, ?7Li, ?18O(H2O), ?2H(H2O), ?13C(CH4) and ?2H(CH4) isotope compositions. Similar to other springs worldwide that issue from serpentinites, the chemical composition of the waters evolves with water-rock interaction from Ca-HCO3, through Mg-HCO3 and ultimately to a hyperalkaline Na-(Ca)-OH composition. Most of the Ca- and Mg-HCO3 springs have ?11B ranging between +16.3? and +23.7?, consistent with the range of low P-T serpentinites. Very high ?11B in two springs from Mt. Prinzera (PR10: +39?; PR01: +43?) can be related to isotopic fractionation during secondary phase precipitation, as also inferred from ?7Li values. In contrast to typical abiogenic isotope signatures of CH4 from serpentinized rocks, dissolved CH4 from the Taro-Ceno hyperalkaline springs has an apparent biotic (thermogenic and/or mixed thermogenic-microbial) signature with ?13C(CH4) ranging from -57.5? to -40.8?, which is similar to that of hydrocarbons from production wells and natural seeps in adjacent hydrocarbon systems. The data suggest that CH4 in the hyperalkaline springs investigated in this study may derive from organic matter of the sedimentary (flysch and arenaceous) formations underlying the ophiolite unit. However, small amounts of H2 were detected in one hyperalkaline spring (PR10), but for two springs with very low CH4 concentrations (PR01 and UM15) the ?2H value could not be measured, so the occurrence of some abiotic CH4 cannot be excluded. The occurrence of thermogenic CH4 in ophiolites may be a widespread phenomenon, and thus the characterization of serpentinization-related gases requires accurate evaluation of the regional context including a careful knowledge of the relationships with surrounding sedimentary rocks and their hydrocarbon potential.

In natural resource exploration, Ca–Cl basinal brines are important for understanding the origin and spatial and temporal distribution of hydrocarbons and sedimentary ore deposits. Little attention has been paid to the possible connection between fossil basinal brines and paleo-seawaters and to the implications for reconstructing paleo-seawater compositions. Secular variations of Ca/Mg and Ca/Sr ratios in seawater have been documented mainly using fluid inclusions in halite, calcareous fossils and mineral analyses. However, brines and other sedimentary records connected to paleo-seawater or its evaporated residues may be chemically affected by burial diagenesis or the effects of continental waters of meteoric origin, thus complicating interpretations of the analytical results. To investigate these effects on fluids and minerals related to the Messinian salinity crisis of the Mediterranean basin, we re-evaluate published data from: (1) brackish-to-brine waters from onshore (Northern Apennine foredeep; Levantine basin) and offshore (porewaters from the Deep Sea Drilling Project); (2) Messinian parental seawater deduced from calcareous fossils, fluid inclusions and sulfate minerals; (3) meteoric waters dissolving evaporites. The compositional trends related to seawater evaporation, diagenesis and mixing that affect the Ca/Mg and Ca/Sr molar ratios of the basinal brines are effectively discriminated on a binary plot depicting the proper fields for seawater and meteoric-derived fluids. Brines showing stronger dolomitization start from Ca/Mg and Ca/Sr molar ratios of Messinian seawater deduced from the published analysis of fluid inclusions and open ocean fossils, that are therefore here validated ex post.

Serpentinization of ultramafic rocks is considered a major process of production of abiotic methane (CH4) and hydrogen (H2) on Earth, and it may be responsible for CH4 occurrence on other planets. While serpentinization and CH4 synthesis have been widely studied and modeled in high temperature hydrothermal conditions, such as on submarine mid-ocean ridges, the increasing number of discoveries of abiotic CH4 in ophiolites on continents shows the importance of present-day (meteoric water driven) serpentinization in low temperature (

Albano is a typical maar lake showing mainly a bicarbonate-alkali geochemical facies. However, chemical monitoring shows a switch toward an alkaline earth composition in the deeper layers. Water isotope compositions of the lake from this study are compared with lake and groundwater data from the literature and are used to infer meteoric recharge and humidity variations. Enhanced evaporation is inferred, and in conjunction with a reduction in lake volume, is linked to a global relative humidity drop of about 3% by our model, which agrees with the ground level measurements during the last 20 years.

Since approximately forty years ago, the equation relating the oxygen isotope fractionation between bisulfate and water has been extensively used as a geothermometer for acidic and high-enthalpy hydrothermal systems (T > 150 °C). Its application to near-neutral or basic, low-enthalpy (T < 150 °C) systems was considered to be unreliable. Recently, empirical and theoretical geothermometric equations were formulated for the (SO42 −–H2O) oxygen isotope system, opening new perspectives on isotope geochemistry applied to geothermal research. In the present paper, these geothermometers are applied while revisiting a variety of hydrological case studies. In addition to the equilibrium fractionation, isotopic effects on geothermometric estimates due to mixing–dilution, salinity, sulfide oxidation, sulfate reduction, standardization of the analytical results and aqueous speciation are also discussed.

Classical chemical classification plots that use major anions and cations can discern between different water facies but they do not offer sufficient discriminatory power for salt waters from sedimentary basins, whose origin is therefore frequently misunderstood. The Brine Differentiation Plot (BDP) was proposed by Hounslow (1995) in order to investigate the brine genesis, principally evaporite dissolution, alkali lakes and oilfield brines. However, its diagnostic potential has been undervalued so far. In this paper, the potential of BDP was tested and compared with the classical Langelier–Ludwig plot using concentration of major dissolved constituents of fresh to brine waters from different sedimentary basins (Northern Apennine Foredeep, Italy; Provence Basin, Western Mediterranean; Caucasus; Trinidad). Mixing processes between different water types as evaluated by these diagrams would seem to be constrained by the boron–chloride plot.

The salt waters from the Emilia-Romagna sector of the Northern Apennine Foredeep have been investigated using major and trace element and stable isotope (δ2H, δ18O, δ37Cl, δ81Br and 87Sr/86Sr ratio). Ca, Mg, Na, K, Sr, Li, B, I, Br and SO4 vs. Cl diagrams suggest the subaerial evaporation of seawater beyond gypsum and before halite precipitation as primary process to explain the brine’s salinity, whereas saline to brackish waters were formed by mixing of evaporated seawater and water of meteoric origin. A diagenetic end-member may be a third component for mud volcanoes and some brackish waters. Salinization by dissolution of (Triassic) evaporites has been detected only in samples from the Tuscan side of the Apennines and/or interacting with the Tuscan Nappe. In comparison with the seawater evaporation path, Ca–Sr enrichment and Na–K–Mg depletion of the foredeep waters reveal the presence of secondary processes such as dolomitization–chloritization, zeolitization–albitization and illitization. Sulfate concentration, formerly buffered by gypsum-anhydrite deposition, is heavily lowered by bacterial and locally by thermochemical reduction during burial diagenesis. From an isotopic point of view, data of the water molecule confirm mixing between seawater and meteoric end-members. Local 18O-shift up to +11‰ at Salsomaggiore is related to water–rock interaction at high temperature (≈150°C) as confirmed by chemical (Mg, Li, Ca distribution) and isotopic (SO4–H2O) geothermometers. 37Cl/35Cl and 81Br/79Br ratios corroborate the marine origin of the brines and evidence the diffusion of halogens from the deepest and most saline aquifers toward the surface. The 87Sr/86Sr ratio suggests a Miocene origin of Sr and rule out the hypothesis of a Triassic provenance of the dissolved components for the analyzed waters issuing from the Emilia-Romagna sector of the foredeep. Waters issuing from the Tuscan side of the Apennines and from the Marche sector of the foredeep show higher 87Sr/86Sr ratios because of the interaction with siliciclastic rocks.

Trace element geochemistry of the Arno River and its main tributaries was investigated on the basis of two sampling campaigns carried out in November 1996 and June 1997. By analyzing filtered and unfiltered water samples, Fe and Al are found in solution mainly as colloidal particles of size lower than 0.45 μm. In June (lower flow rate), Fe and Al are enriched in the filtered waters from the main river, and this feature was interpreted in terms of higher water temperature promoting the formation of smaller particles, thus reducing their aggregation properties. Iron and Al show perfectly synchronous downstream profiles along the Arno River, correlate quite well each to other, and display abrupt concentration increases near to Florence, where the lithology of the catchment changes from siliciclastic dominated to clay-sand (lacustrine-marine)-dominated. The same behaviour is shown by most of the other trace elements in the river, thus supporting a general lithological control. Trace elements in the final part of the Arno River are influenced by flocculation processes in addition to mixing. Adsorption phenomena on oxy-hydroxides are denoted by good elemental correlations with Fe (and Al). Sporadic anomalous concentration values, possibly related to anthropogenic contributions, may prevent such correlations. Referring to the quality of waters for potable use and fish life, toxic elements are below the acceptable limits of current European regulations, with few exceptions for Hg exceeding guideline values. Multivariate analysis groups trace elements according to geochemical affinities and natural or anthropogenic sources, thus distinguishing contaminated from uncontaminated samples. The results achieved in this work will help regional and national Authorities for compliance with the EU water policy, especially in assessing the water quality at the river basin scale and its vulnerability to human activities.

The purpose of this study was to investigate the possibility of identifying oil source areas by means of simple measurements on the natural samples avoiding time-consuming sample treatments. The oxygen and carbon isotopic values of 150 samples of extra-virgin olive oil from eight different Italian regions and from three different years of production were measured according to well-established techniques. Statistical treatments of the results obtained show a very good correlation of the δ18O of oil with latitude, mean annual temperature, and mean relative humidity at the collection site. No correlation is found with elevation and mean annual precipitation. The shift of the oil δ18O per degree centigrade of the mean annual temperature is quantitatively close to that calculated for atmospheric precipitation in continental areas. Accordingly, in our measurements, the year of oil production can be identified on the basis of the δ18O value (mean 2004 temperatures were higher than 2005 temperatures). On the contrary, the oil δ13C values show no correlation with the above variables but only with latitude and, consequently, are less suitable for discriminating the geographic origin of oil. However, the δ13C values are suitable to indicate biological differentiation while the δ18O values are not. Copyright © 2009 John Wiley & Sons, Ltd.

article i nfo In the area of the Taro-Ceno Valleys (Northern Apennine, Emilia-Romagna region, Italy), waters of meteoric origin interact with ophiolite rocks of the External Ligurides. Fresh water springs issuing from basalts have a Ca-HCO3 composition, whereas freshwater springs from ultramafites vary in composition from Ca-HCO3 or Mg-HCO3 to Na-OH or Na-SO4 types and in pH values from 7.3-8.8 up to pH 11, respectively. In addition, the boron content of the alkaline waters is up to 13 mg/L, which is unusually high for freshwaters in general and ultramafites that have undergone oceanic serpentinisation in particular and gives a boric alkalinity to the waters. The springs waters show evidence of recent low-temperature continental serpentinisation and the process is modeled by reaction paths using an updated geochemical thermodynamic database, consistent with the local primary and secondary serpentinite paragenesis. For the model, bicarbonate waters evolve to alkaline waters supersaturated in Ca-(Mg)-carbonate, based on the assumption that the dissolution of serpentinite results in supersaturation with respect to kaolinite, ferrihydrite, vermiculite, Fe 2+ -Mg 2+ - saponite, and poorly crystalline serpentine. The alkaline composition and the chloride content of the waters suggest a prolonged interaction with the rocks at depth that led to dissolution of albite and leaching of olivine-hosted fluid inclusions. A similar evolution is also proposed for the more developed springs issuing from the ultramafic rocks of the Voltri Group (Liguria region), where solutions are supersaturated in brucite and are in equilibrium with enstatite and/or chlorite.

The Serchio River and its tributaries in northern Tuscany were investigated for the chemical and isotopic compositions of waters and bed sediments. Bedrocks are mostly limestone/dolomite and siliciclastics, thermal spring systems are present in the catchment, and the main industrial activity is represented by paper-mills. Main results obtained are: (1) major ions in solution appear to be basically controlled by precipitation and lithology, as well as subordinately by direct inputs of thermal springs, (2) human influence on metals in the waters along the main Serchio and Lima rivers is indicated at a number of sites by increases in concentration compared to the chemical composition of upstream tributaries, (3) S and O isotope compositions delineate two main sources for aqueous SO 4 2 - , that is dissolution of Triassic evaporite (directly or via thermal springs) and oxidation of sulfide dispersed in siliciclastic rocks. Anthropogenic contributions are probable, but they cannot be quantitatively assessed. Only SO 4 2 - in the notoriously polluted Ozzeri tributary is suspected to be largely anthropogenic, and (4) the chemical composition of bed sediments is mainly influenced by lithology, apart from a number of technogenic elements in the upper part of the Serchio River and in some tributaries. Contamination possibly occurs at other sites, but geochemical indications are weak.

Within the hydrologic balance of the River Arno catchment (northern Tuscany), the Rivers Elsa and Era are important tributaries entering the main river from the left bank in the lower part of the watershed. Waters and bed sediments were sampled in June 2000 during low discharges in the Rivers Elsa and Era, as well as in major tributary streams. Water samples were analysed for major chemistry and sulphur isotope composition of sulphate, and sediment samples were analysed for major composition and selected trace elements of environmental concern (Zn, Cu, Pb, Cr and Ni). The main results for the waters are: (1) Na and Cl in solution show consistent downstream positive trends in the main rivers, thus supporting progressive contributions of anthropogenic salts; the highest concentration values are observed in tributaries; (2) as shown by sulphur isotopes, sulphate in solution is mainly controlled by dissolution of evaporites (Elsa basin) or oxidation of reduced organic/biogenic sulphur (Era basin), with anthropogenic contributions in most streams not higher than 10% in both the basins. A δ34S signature in the range −2 to +3‰ is estimated for pollutant sulphate in the basins studied. The main results for the sediments are: (1) major chemistry is essentially controlled by the lithotypes drained by the waters; (2) pollution by heavy metals does not reach high levels; (3) compared with local fine-grained rocks, copper is more frequently anomalous, whereas lead and zinc show only occasional anomalies; (4) local high concentrations of chromium and nickel can be attributed to upstream occurrences of ophiolites. Copyright © 2006 John Wiley & Sons, Ltd.

Na-carbonate (NaCW) waters are not concentrated in well defined areas, but usually widespread in areas where other water types (e.g., Ca-carbonate) are dominant. NaCW are the product of long-term water-rock interaction with dissolution of Na-silicates in presence of phyllosilicates, silica phases, and calcite. NaCW circulating in calcite-bearing sediments very probably have a Ca-carbonate parent with moderate to low PCO2, which changes its composition assuming increasing Na character as the water-rock interaction proceeds. However, the moderate to low PCO2 values of the potential parent Ca-carbonate waters do not account for the high Na content of many NaCW. The higher PCO2 required may be due to oxidation of organic matter of the sediments and, perhaps, to further addition of CO2 coming from deeper crustal levels, from the mantle, or from other sources. Na-Ca exchange involving a Na-exchanger could be an alternative genetic hypothesis. At present, however, at least for some areas (e.g., Northern Apennines, Italy), this hypothesis is not supported by mineralogical evidence.

The water resources in the Guanahacabibes Peninsula are distributed in two areas. The northeastern area is characterized by swamps, wetlands and lagoons, with a low contribution of seawater, whereas the area in the southwestern plain shows a considerable development of the karst structures that limits the existence of superficial waters but permits the ingression of the surrounding seawater. In this latter area, the groundwater showed a marked increase in salinity with the depth. In particular, groundwater with a seawater fraction of 0.1 had the lowest Ca-(Mg)-carbonates saturation indexes calculated by modeling the mixing between freshwater and seawater using different software, thermodynamic databases and equations for activity coefficients. Generally, seawater and groundwaters with an added seawater fraction above 0.60–0.65 showed similar oversaturated indexes in high-Mg calcites and pure Ca-carbonates (calcite and aragonite). Differently, in the groundwater that showed carbonates undersaturation (generally with a seawater fraction between 0.02 and 0.60), the saturation indexes in high-Mg calcites were 0.2 lower than pure Ca-carbonates. Locally, the bacterial reduction of the dissolved sulfate enhanced the dissolution of the limestone, contributing to the increased development of the karst structures and the seawater intrusion. Finally, the presence near the coastline of fresh Ca- and Na-bicarbonate waters was in accordance with the upward flow of the shallow freshwater during the formation of the saline wedge. However, the oxygen and hydrogen stable isotope composition of the waters showed a probable contribution to the area from a deep aquifer that is recharged in the highest reliefs of the province (Cordillera de Guaniguanico).