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Evaporation of water from the oceans and terrestrial environment governs the global water cycle and climate. Heavy isotope (H-2, O-18, O-17) enrichment during evaporation led to the development of the well-known Craig-Gordon (C-G) model for quantifying evaporation. Several variables control the H and O isotopic composition of evaporating water including; the isotopic composition of the water, temperature, relative humidity, ambient vapor isotopic composition, diffusion and/or mixing at the water-air interface, and the thermodynamic activity (salinity) of water. Previous C-G modeling efforts considered these controlling variables separately; here we propose a newly unified C-G analytical model that allows for simultaneous quantification of all controlling variables in the evaporation of fresh and saline waters. Our unified model accurately predicted the results of laboratory water evaporation experiments conducted under a variety of molecular diffusion and turbulent diffusion conditions. We demonstrate the general applicability of the model by successfully predicting historical O and H isotope data for fresh and saltwater evaporation obtained from the scientific literature. The unified C-G model allows for improved estimates environmental parameters controlling the H and O isotope fractionation during water evaporation under natural conditions and can be used to better inform modeling efforts in regional and large-scale water balance studies. (C) 2018 Elsevier Ltd. All rights reserved.

The International Atomic Energy Agency (IAEA) has played a crucial role in promoting and expanding the use of isotopes in hydrology over the last five decades to gain unique insights into the functioning of terrestrial and atmospheric water cycles. In this essay, an historical perspective of IAEA activities is provided, along with some of the achievements and recent initiatives. When the IAEA was formally established in 1957, radioactive fallout from atmospheric thermonuclear testing, particularly tritium, and its impact on human health and the environment posed serious societal concerns. This led the IAEA to initiate a global project to measure tritium concentrations in precipitation. Brian Payne, first Head of the Isotope Hydrology Section of IAEA, convened a scientific advisory committee in 1959 to define the scope of hydrological aspects of tritium monitoring in precipitation. The committee of three eminent scientists — Fritz Begemann, Erik Eriksson and Hans E. Suess — emphasized that, based on contemporary publications, tritium and stable isotopes of oxygen and hydrogen in precipitation would be useful for studying many watercycle processes, including water-residence time and evaporation losses from lakes and reservoirs, groundwater age and aquifer dynamics, continental water balance, age of hot spring water, and mixing time of the oceans (e.g. Friedman 1953; Epstein and Mayeda 1953; Dansgaard 1953; Urey et al. 1951; Libby 1953). The IAEA’s precipitation monitoring efforts began in 1960, and were later expanded to a global scale in 1961 by collaboration with the World Meteorological Organisation (WMO). This expanded network became known as the IAEA-WMO Global Network for Isotopes in Precipitation (GNIP). The number of operational GNIP stations has varied over the years. Originally 161 stations were in operation. By 1963–1964 there was a maximum of about 220 stations, and currently 185 stations in 53 countries contribute samples. In its 50 years of existence, the GNIP database has gained about 120,000 monthly records of stable oxygen and hydrogen isotopes and tritium from more than 900 meteorological stations worldwide. Dansgaard (1964) conducted a comprehensive analysis of stable isotope data from the GNIP and proposed key relationships between precipitation isotopes and climate. In particular, isotope correlations between surface air temperature and amount of precipitation were crucial to interpreting palaeoclimate records preserved in proxy archives such as ice cores, lake sediments, groundwater, tree rings and speleothems. Stable isotope data from the GNIP continue to be extensively utilized in climate research. Most general circulation models currently in use have been expanded to simulate precipitation isotopes (Joussaume et al. 1984; Jouzel et al. 1997; Hoffmann et al. 2000) and GNIP data provide a means to validate these models. A number of IAEA publications have reported on the statistical evaluations of precipitation isotope distributions (e.g., Yurtsever and Gat 1981; Rozanski et al. 1991, 1993; Aggarwal et al. 2010). Figure 1 shows all GNIP stations past and present, and a global map of interpolated stable oxygen isotope data (1961–2004) using active and inactive stations. The continuous operation of GNIP has also been critical for the use of tritium in hydrology, hydrogeology, and hydrometeorology. In addition to tritium in precipitation, tritium in rivers, lakes and groundwater has yielded invaluable information on the dynamic aspects of the water cycle such as the residence time of water in the different hydrologic reservoirs and hydrograph separation in stream flow. Similarly, stable isotope data in precipitation, surface water and groundwater were invaluable for characterizing the role of groundwater in streams, rivers and lakes, the geographic and temporal origin of groundwater recharge and its effect on the water balance of hydrologic systems, especially in wetlands and evaporation prone areas. Due to the very nature of the methodology, isotope hydrology’s emphasis has been Received: 4 March 2010 /Accepted: 28 August 2010 Published online: 24 September 2010

The (11)B/(10)B ratio exhibits wide variations in nature; thus, boron isotopes have found numerous applications in geochemistry, hydrology, and environmental studies. The main analytical techniques used are as follows: positive thermal ionisation mass spectrometry is the most precise (about 0.2 per thousand of the boron isotope ratio), but requires complex and laborious sample preparation; negative thermal ionisation mass spectrometry is less precise (about 0.5 per thousand), but rapid and suitable for water samples, whereas total evaporation-NTIMS allows for identification of the precise boron isotope composition of marine carbonates. It is expected that multi-collection system inductively coupled plasma mass spectrometry (MC-ICPMS) will eventually combine high precision with simple analytical procedures. Secondary ion mass spectrometry and laser ablation (LA)-MC-ICPMS allow in situ determinations on solid samples, but require the availability of calibration materials which are chemically and mineralogically similar to samples. These features of boron isotope measurement techniques were confirmed by the results of the first inter-laboratory comparison of measurements, organised by the Istituto di Geoscienze e Georisorse in Pisa. Finally, two examples of boron isotope applications in groundwater investigations are reported.

The Cornia Plain alluvial aquifer, in Tuscany, is exploited intensely to meet the demand for domestic, irrigation and industrial water supplies. The B concentration of groundwater, however, is often above the European limit of 1 mg L(-1), with the result that exploitation of these water resources requires careful management. Boron and Sr isotopes have been used as part of a study on the origin and distribution of B dissolved in groundwater, and indirectly as a contribution to the development of appropriate water management strategies. The geochemistry of the Cornia Plain groundwater changes from a HCO(3) facies in the inland areas to a Cl facies along the coastal belt, where seawater intrusion takes place. The B concentration of groundwater increases towards the coastal areas, while the (11)B/(10)B ratio decreases. This indicates that there is an increasing interaction between dissolved B and the sediments forming the aquifer matrix, whose B content is in the order of 100 mg kg(-1). Adsorption-desorption exchanges take place between water and the sediment fine fraction rich in clay minerals, with a net release of B from the matrix into the groundwater, and a consequent delta(11)B shift from positive to negative values. The aquifer matrix sediments therefore seem to be the major source of B dissolved in the groundwater. The groundwater-matrix interactions triggered by the ionic strength increase caused by seawater intrusion can also be detected in the Ca-Na ion exchanges. Dissolved Sr follows a trend similar to that of Ca, while the (87)Sr/(86)Sr ratio is equal to that of the exchangeable Sr of the aquifer matrix and therefore does not change significantly. These results have helped to define a new strategy for groundwater exploitation, with the final objective of reducing B concentration in the water extracted from the aquifer.

The wide boron isotopic variations occurring in natural waters mainly are derived from the 20‰ fractionation between dissolved boric acid and borate anions, associated with the preferential removal from the system of 11 B depleted borate ions by adsorption and/or minerals formation. Typical adsorbants of boron dissolved in groundwater are clay minerals of the aquifer matrix. Boron (and strontium) isotopes were used in investigating two alluvial aquifers in Tuscany, where boron concentration is often above 1 mg L − 1 and may attain 8 mg L − 1 . The isotopic results indicate that, in the first case (Cecina River basin), the boron contamination is anthropogenic and derives from past discharge into streams of boron-rich industrial wastes. In the second case (Cornia Plain), the dissolved boron is released by boron-rich clayey sediments of the aquifer matrix and has, therefore, a natural origin.

The origin of carbon-bearing compounds (CO 2 , CH 4 , C 2 –C 4 saturated hydrocarbons) and helium in the geothermal fluid of Larderello is investigated by means of the variations in concentration and isotopic composition. The CO 2 ( δ 13 C from −1.4 to −7.1‰ versus V-PDB) is mainly of crustal origin. The carbon isotopes of methane ( δ 13 C from −20.9 to −31.7‰) and other hydrocarbons indicate a complex thermogenic origin. The temperatures obtained with the CH 4 –CO 2 isotope geothermometer are in rough agreement with those observed in deeper geothermal wells. The CH 4 /C 2 H 6 ratios show a tendency towards partial equilibrium with increasing temperature. He isotopes ( R / R A from 0.5 to 3) indicate that although the major part of helium derives from crustal sources, a significant fraction of mantle helium is also present. Helium contamination by air, deducted from He/Ne ratios, is generally negligible.

From March 1997 to March 1999, sequential rainwater samples were collected during 12 rainfalls at Avignon, Southern France, with the objective of investigating how the formation conditions affect the isotopic composition of the most frequent rain types occurring in the western Mediterranean region. Three major isotopic trends were identified: (i) a descending δ18O trend, produced when a cold front penetration causes the rise of warm and humid air masses, accompanied by adiabatic cooling and precipitation. The temperature variation is the predominant feature of frontal rainfalls; (ii) an L-shaped δ18O trend, which can be produced by convective rains, with an initial rapid decrease followed by a stationary value; (iii) a V-shaped trend, in which the final phase of precipitation obeys a different mechanism from the first phase. Frontal and convective rainfalls may produce this trend. Three heavy rainfalls were selected for applying a numerical Rayleigh condensation model to describe their isotopic trends. Some irregularities in the generally monotonously decreasing isotopic trend were attributed to inputs of new air masses, which were often recorded by chemical variations as well. The numerical model indicates that about 80, 60 and 45% of the vapour initially present was condensed. The lowest fraction corresponds to the most abundant rainfall, and it is due to the convective nature of the latter implying a continuous supply of condensable vapour.

The kinetics of isotopic exchange between dissolved inorganic carbon (DIC) of groundwater and calcite of the matrix of karst aquifers of Cyrenaica, Libya, can be deduced from 13 C and 14 C data. The aquifers are mostly confined, and the majority of the wells do not show any occurrence of modern recharge: in 1976–1980, in fact, the tritium content was below 1 tritium unit (TU) in most sites. Assuming that the isotopic exchange takes place through a first order reaction such as 14 C radioactive decay, it can be shown that a linear correlation occurs between ln A and ln( δ M − δ − e P ), where A is the 14 C activity, δ M and δ are the 13 C contents of matrix calcite and DIC, respectively, and e P is the 13 C enrichment in CaCO 3 precipitation. The slope of the correlation provides the half-life of the isotopic exchange process. For Cyrenaica karst groundwater, a half-life of about 11,000 years is obtained, i.e. about double that of 14 C radioactive decay. The isotopic exchange kinetics also depends on the ratio between groundwater volume and the calcite surface exposed to the exchange process. Thus, other aquifers will show different exchange half-life values. The Cretaceous chalk aquifers of the Paris Basin, France and Lagerdorf, Germany give a half-life of about 4000 years, much shorter than that of Cyrenaica, which may be due to the high porosity, i.e. to the large surface available for the isotope exchange process. The Berkshire Chalk aquifer, UK, gives a half-life of about 10,000 years. Much higher half-lives, above 20,000 years, are obtained for two sandy aquifers in Flevoland, The Netherlands, and Texas, USA, which could be explained by the low CaCO 3 content of the aquifer matrix. The highest half-life value, about 40,000 years, is obtained in an artesian limestone aquifer in Florida, USA.

The Istituto di Geoscienze e Georisorse (IGG), on behalf and with the support of the International Atomic Energy Agency (IAEA), prepared eight geological materials (three natural waters and five rocks and minerals), intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials were distributed to twenty seven laboratories - virtually all those performing geochemical boron isotope analyses in the world -which agreed to participate in the intercomparison exercise. Only fifteen laboratories, however, ultimately submitted the isotopic and/or concentration results they obtained on the intercomparison materials. The results demonstrate that interlaboratory reproducibility is not well reflected by the precision values reported by the individual laboratories and this observation holds true for both boron concentration and isotopic composition. The reasons for the discrepancies include fractionations due to the chemical matrix of materials, relative shift of the zero position on the δ11B scale and a lack of well characterized materials for calibrating absolute boron content measurements. The intercomparison materials are now available at the IAEA (solid materials) and IGG (waters) for future distribution. L'Istituto di Geoscienze e Georisorse (IGG), pour le compte et avec le soutien de l'Agence Internationale de l'Energie Atomique (AIEA), a prepare huit materiaux geologiques (trois eaux naturelles et cinq roches et mineraux) destines a la conduite d'une comparaison en aveugle des mesures de composition isotopique et de concentration du bore entre differents laboratoires. Vingt-sept laboratoires -pratiquement tous ceux qui travaillent sur les isotopes du bore en geochimie - ont accepte de participer a cette intercomparaison, mais quinze seulement ont finalement envoye leurs donnees de composition isotopique et/ou de concentration du bore. Les resultats demontrent que la precision des valeurs indiquee par les laboratoires reflete mal la reproductibilite entre laboratoires des mesures de composition isotopique comme de concentration du bore. Les raisons de ces discordances peuvent comprendre l'existence de fractionnements isotopiques dus aux matrices chimiques des materiaux, un deplacement relatif du zero de l'echelle de δ11B, ainsi que le manque de materiaux bien caracterises pour calibrer les mesures de concentration du bore. Les materiaux utilises pour l'intercomparaison des mesures sont maintenant a disposition a l'AIEA (materiaux solides) et l'IGG (eaux) pour etre distribues.

The International Atomic Energy Agency (IAEA), in cooperation with the World Meteorological Organization (WMO), has been conducting a world-wide survey of hydrogen (H/'H) and oxygen (O/O) isotope composition of monthly precipitation since 1961. At present, 72 IAEA/WMO network stations are in operation. Another 82 stations belonging to national organizations continue to send their results to the IAEA for publication. The paper focuses on basic features of spatial and temporal distribution of deuterium and O in global precipitation, as derived from the IAEA/WMO isotope database. The internal structure and basic characteristics of this database are discussed in some detail. The existing phenomenological relationships between observed stable isotope composition of precipitation and various climate-related parameters such as local surface air temperature and amount of precipitation are reviewed and critically assessed. Attempts are presented towards revealing interannual fluctuations in the accumulated isotope records and relating them to changes of precipitation amount and the surface air temperature over the past 30 years.

The vacuum distillation method of extracting soil water for stable isotope analysis was tested for three different types of soil characterized by high water content: (1) pure sand, (2) cambisol with high organic matter content, developed on calcareous sandstone under temperate climatic conditions (Austria), and (3) tropical latosol poor in organic matter, developed on sandy clay sediment (Brazil). The method yields accurate and reproducible results for sand, provided that more than 98% of the original soil water is extracted. The time required for complete extraction is a function of sample size and the applied extraction temperature. Column experiments with the clayey soils revealed existence of a weakly bound, easily exchangeable pool of water which is isotopically different from the mobile water. The experiments showed that the extracted soil water is depleted in both deuterium and oxygen-18 by 5–10% and 0.3–0.5%, respectively, when compared with the percolate (mobile water). This depletion depends strongly on the soil type. The reproducibility for replicate extractions of soil water from clayey soils is around ±3% and 0.3% for δD and δ 18 O, respectively.

The 11B/10B ratio exhibits wide variations in nature; thus, boron isotopes have found numerous applications in geochemistry, hydrology, and environmental studies. The main analytical techniques used are as follows: positive thermal ionisation mass spectrometry is the most precise (about 0.2‰ of the boron isotope ratio), but requires complex and laborious sample preparation; negative thermal ionisation mass spectrometry is less precise (about 0.5‰), but rapid and suitable for water samples, whereas total evaporation-NTIMS allows for identification of the precise boron isotope composition of marine carbonates. It is expected that multi-collection system inductively coupled plasma mass spectrometry (MC-ICPMS) will eventually combine high precision with simple analytical procedures. Secondary ion mass spectrometry and laser ablation (LA)-MC-ICPMS allow in situ determinations on solid samples, but require the availability of calibration materials which are chemically and mineralogically similar to samples. The...

Stable isotopic compositions of meteoric and geothermal waters indicate that the Palinpinon geothermal system of Southern Negros is fed by a parent water that originated from a mixture of local meteoric (80%) and magmatic (20%) waters. The meteoric water has an isotopic concentration of −8.5‰ and −54‰ in 18O and 2H, respectively, which corresponds to an average infiltration altitude of about 1000 m above sea level. With exploitation of the system and injection of wastewaters to the reservoir, the stable isotopic composition became heavier due to significant mixing of geothermal fluids with injection waters. Incursion of cooler meteoric waters, which is confirmed by the presence of tritium, also leads to the formation of acid-sulfate waters. Stable isotopes are effective as “natural tracers” to determine the origin and mixing of different fluids in the reservoir.

Fluids in the Greater Tongonan geothermal system exhibit a large positive {sup 18}O shift from the Leyte meteoric water line. However, there is also a significant shift in {sup 2}H. The {delta}{sup 2}H-{delta}{sup 18}O plot shows that the geothermal fluids may be derived by the mixing of meteoric water with local magmatic water. The most enriched water in the Greater Tongonan system, in terms of {delta}{sup 18}O, {delta}{sup 2}H and Cl, is comprised of approximately 40% magmatic water. Baseline isotope results support a hydrogeochemical model in which there is increasing meteoric water dilution to the southeast, from Mahiao to Sambaloran and towards Malitbog. The Cl-{delta}{sup 18}O plot confirms that the geothermal fluid in Mahanagdong, further southeast, is distinct from that of the Mahiao-Sambaloran-Malitbog system.

Temporal and spatial variations of tritium in the global atmosphere during the past three decades are discussed, with emphasis on the tritium content of monthly precipitation, as derived from the database of the IAEA/WMO global network 'Isotopes in Precipitation'. Whereas the tritium levels in precipitation have, in recent years, returned close to natural, pre-bomb values in most parts of the world, the technogenic emissions of tritium are becoming more and more visible. The most important sources of technogenic tritium are nuclear facilities as well as manufacturing and disposal of luminous consumer products. Examples of local and regional scale contamination of the lower troposphere due to ground-level tritium releases are presented.

We briefly present here the environmental isotope intercalibration programs of the International Atomic Energy Agency (IAEA). In fact, the IAEA has implemented two parallel programs during the last 20 years: for stable isotopes of light elements and for a radioactive isotope of hydrogen, tritium. This IAEA activity resulted in the preparation of a number of reference and intercomparison materials of various types, now stored in the Agency and available upon request.

The groundwater B concentration in the alluvial aquifer of the upper Cecina River basin in Tuscany, Italy, often exceeds the limit of 1 mg L−1 set by the European Union for drinking water. On the basis of hydrogeological and geochemical observations, the main source of the B contamination of groundwater has been attributed to past releases into streams of exhausted, B-rich geothermal waters and/or mud derived from boric acid manufacturing in Larderello. The releases were discontinued 25–30 years ago. This study confirms that the B dissolved in groundwater is anthropogenic. In fact, the δ11B values of groundwater B match the range −12.2‰ to −13.3‰ of the Turkish B mineral (colemanite) processed in boric acid manufacturing, in the course of which no significant isotopic effects have been observed. This isotopic tracing of the Cecina alluvial aquifer occurs just below the confluence of the Possera Creek, which carries the B releases from Larderello. Strontium isotope ratios support this conclusion. At about 18 km from the Possera Creek confluence, the groundwater δ11B drops to much more negative values (−22‰ to −27‰), which are believed to be produced by adsorption–desorption interactions between dissolved B and the aquifer matrix. The δ11B of B fixed in well bottom sediments shows a similar variation. At present, desorption is prevailing over adsorption because the releases of B-rich water have ceased. A theoretical model is suggested to explain the isotopic trends observed. Thus, B isotopes appear to be a powerful tool for identifying the origin of B contamination in natural waters, although isotopic effects associated with adsorption–desorption processes may complicate the picture, to some extent.

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In 1999 the Istituto di Geoscienze e Georisorse (IGG), with the support of the International Atomic Energy Agency (IAEA), undertook the collection, preparation and distribution of eight geological materials intended for a blind interlaboratory comparison of measurements of boron isotopic composition and concentration. The materials came from Italian sources and consist of three natural waters (Mediterranean seawater and two groundwaters) and five rocks and minerals (tourmaline, basalt, obsidian, limestone and clay). The solid materials were crushed, milled and mixed, in preparation for distribution. Extensive assays performed at the IGG on these materials demonstrated that their boron isotopic and chemical compositions are homogeneous. Additional homogeneity tests were carried out on solid material fragments at the GeoForschungsZentrum Potsdam, with the specific objective of investigating the suitability of some of them for the calibration in situ of micro-analytical techniques. Two materials, B4 (tourmaline) and B6 (obsidian), proved to be isotopically homogeneous and may become excellent references for in situ microanalyses of boron isotopes. The materials described here were used as the basis of a major laboratory intercomparison study and are now available for further distribution from either the IAEA (solid materials) or the IGG (waters). L'Istituto di Geoscienze e Georisorse (IGG), avec le soutien de l'Agence Internationale de l'Energie Atomique (AIEA), a entrepris en 1999 la recolte, la preparation et la distribution de huit materiaux geologiques dans le but de conduire une comparaison en aveugle des mesures de composition isotopique et de concentration du bore entre differents laboratoires. Les materiaux, qui derivent tous de sites italiens, comprennent trois eaux naturelles (une eau de la Mer Mediterranee et deux eaux souterraines) et cinq roches et mineraux (tourmaline, basalte, obsidienne, calcaire et argile). Pour la distribution, les materiaux solides ont ete reduits en fragments, broyes et melanges et leur homogeneite de composition isotopique et chimique du bore a ete verifiee par des essais exhaustifs. D'autres essais d'homogeneite ont ete effectues au GeoForschungsZentrum Potsdam sur des fragments des materiaux solides avec le but particulier d'etudier la possibilite d'utilisation de ces materiaux pour la calibration in situ des techniques microanalytiques. Deux materiaux, le B4 (tourmaline) et le B6 (obsidienne), se sont reveles isotopiquement homogenes et donc peuvent devenir d'excellents materiaux de reference pour les microanalyses isotopiques in situ du bore. Les materiaux, qui sont decrits dans cette note, ont ete utilises pour une etude d'intercomparaison des mesures isotopiques et chimiques du bore entre differents laboratoire. Ils sont maintenant a disposition a l'AIEA (materiaux solides) et a l'IGG (eaux) pour leur distribution ulterieure.

Data on the Isotopic composition of yearly and monthly precipitation samples collected at various altitudes on Mount Cameroon, Africa, and in two transects from the Amazon to the Altiplano in Bolivia, South America, are presented. In Bolivia, the 2H/1H and 18O/16O ratios show seasonal variations, with lower values in the summer rainy months with respects to the winter dry ones. The δ2H and δ18O values are linearly correlated with a slope of 7.5 in all seasons, but the intercept is higher in winter than in summer. The δ-gradient vs. altitude is larger in rainy periods. The isotopic data are fitted by using a numerical model based on Rayleigh adiabatic condensation process. Model simulations show that the δ–altitude relationship slightly deviates from linearity, because the slope increases with altitude due to the lowering of temperature and the consequent increase of the condensation rate of atmospheric vapour. The parameters which most affect the shape of δ–altitude relationships are the temperature vertical gradient (lapse rate) and the initial relative humidity of the ascending air masses, while a change of the initial isotopic composition of water vapour determines a shift of the curve along the δ-axis. In addition, the model explains the observed increase of the deuterium excess with altitude.

Publisher Summary The concentration of stable isotopes in groundwater depends mainly on the origin of the water. The concentration of radioactive isotopes and dissolved compounds in groundwater depends on the initial concentration and residence time of groundwater in the aquifer. These two factors determine the amount of radioactive isotope(s) decayed, removed, or added during water-rock processes. As geochemical tools, stable and radioactive environmental isotopes provide information on the geochemical processes operating on groundwater and on the hydrogeological characteristics of aquifers. Information provided by environmental isotopes is also useful in modeling groundwater systems. This chapter discusses the scientific background of applications of environmental isotope techniques to groundwater hydrology. The stable isotope composition of groundwater reflects that of the precipitation in the recharge area that seeps through the soil and the unsaturated zone to reach the water table. Stable isotopes are often used to identify groundwater recharge by rivers and lakes. These water bodies frequently have isotopic compositions different from that of precipitation over the study area.

In order to better understand the hydric behaviour of the Bort-les-Orgues reservoir, physico-chemical studies, as well as isotopic studies were carried out in 1996 and 1997. The physical results show that the lake is monomictic, with thermic stratification from June to September–October. The high values of pH in the surface water during summer reveal an active development of biological production starting in June. Isotopic values of 18O show evaporation at the water-atmosphere interface. The 13C of the dissolved total inorganic carbon is governed both by atmospheric exchange and biologic activity. Information about the internal dynamics of the reservoir such as a water current, an upstream water column renewal (by ‘piston effect’), and a downstream sediment resuspension can thus be obtained.

Stable isotope ratios of oxygen ((18)O/(16)O) and hydrogen (D/H) in water have long been considered powerful indicators of paleoclimate. However, quantitative interpretation of isotope variations in terms of climate changes is hampered by a limited understanding of physical processes controlling the global isotope behavior. Analysis was conducted of time series of (18)O content (delta (18)O) of monthly precipitation and surface air temperature available through the International Atomic Energy Agency-World Meteorological Organization global network, "Isotopes in Precipitation." This study indicates that long-term changes of isotopic composition of precipitation over mid-and high-latitude regions during the past three decades closely followed long-term changes of surface air temperature with the average 8180-temperature coefficient around 0.6 per mil per degree Celsius.

Corner stones keep a building safe, give confidence and character to the architectural site. In isotope research, one of those corner stones is the isotope fractionation accompanying the phase chan...

The isotopic compositions of the waters discharged from Parbati Valley geothermal areas indicate a higher altitude meteoric origin, with discharge temperatures reflecting variations in the depth of penetration of the waters to levels heated by the existence of a ‘normal’ geothermal gradient. On the basis of mixing models involving silica, tritium, discharge temperatures and chloride contents, deep equilibration temperatures of 120–140°C were obtained for Manikaran, possibly reaching 160°C at even greater depth. Geothermometers based on sulfate-water 18O exchange and gas reactions point to similar temperatures. Exceptionally high helium contents of the discharges correspond to apparent crustal residence times of the waters in the order of 10–100 Ma; relative nitrogen-argon contents support a largely meteoric origin of the waters with a possible fossil brine, but no detectable magmatic component.

The variations in the 18 O/ 16 O, D/H, 13 C/ 12 C, 34 S/ 32 S isotopic ratios and in the tritium concentrations of several components of geothermal fluids have been used widely in the hydrological study of thermal systems. The recharge areas, as well as the mixing phenomena between different fluids and the circulation times, can all be evaluated satisfactorily with the help of these techniques. Of great diagnostic value are the effects of the high temperatures at depth in the geothermal fields on the isotopic exchange reactions between the fluids and the reservoir rocks and on the fractionation factors between the compounds that coexist in the fluid. The latter phenomenon in particular has permitted us to use many isotopic geothermometers that provide useful indications on the temperatures of the main reservoirs. This paper gives a detailed description of their main applications and present limits, together with some indications as to future development of field research with regard to isotopic methods applied to exploration and study of geothermal areas.

The isotopic composition of the atmospheric water vapour over the Leman Lake changes regularly with the distance from the water surface. This fact indicates that the vapour results from a mixing of the vapour generated by the lake with the regional atmospheric vapour. The fractions of these two vapours of different origin are evaluated in each sample on the basis of the isotopic data. The method allows to estimate the climatic zone of influence of the lake in the atmosphere.

Resume The evolution of the water isotopic composition of two basins having no outlet in the North-Western Sahara (Gara Diba Guelta and el Melah Sebkha) has been studied. A regular sampling taken during the whole drying process of these basins (4 months for the Guelta and 6 months for the Sebkha) showed a considerable isotopic enrichment (more than 30% for oxygen-18 and more than 100% for deuterium) due to the low relative humidity. The last samples collected in the Sebkha show an inversion in the isotopic enrichment, due to a decrease of the solvent activity. The piot of δ D against δ 18 O gives a straight line with a 4.6 slope and whose intersection with the meteoritic waters straight line gives the isotopic composition of the rainfalls which fed the basins. A theoretical model giving an account of the experimental values was developed for the Guelta evaporating water. It provided us with an estimate of the amount of water evaporated between the rainfall and the sampling and of the amount of salts dissolved by ground leaching.

O18/O16 ratios have been measured along a firn profile extending from the surface to a depth of 16 meters in the shelf ice of King Baudouin station (East Antarctica, 70°26′S, 24°19′E). Periodical variations are found which are believed to reflect the seasonal variations in the O18/O10 ratio of precipitations. They allow the identification of annual layers following the method suggested by Epstein and Sharp. The oxygen isotope variations are compared with the stratigraphic features of the same profile. The notion ‘winter’ or ‘summer’ layers is shown to be meaningless when the layers are derived from stratigraphie criteria only. Very often the fine-grained unmetamorphosed layers (generally called ‘winter’ layers) are made up of snow with high O18 content which must represent summer precipitation. On the other hand, the coarse-grained recrystallized layers (‘summer’ layers) often display a minimum O18 content and are composed of snow that fell in the winter. Identification of annual layers involves a similar degree of uncertainty from personal interpretation in the stratigraphic method as well as in the isotope ratio method, but the two methods are complementary, being affected differently by natural circumstances. A good agreement is found between the average accumulation rates deduced from both methods.

Measured oxygen isotope variations for determining net accumulation rates in three sections of snow and ice core from a drilling project, at King Baudouin Station on Princesse Ragnhild Coast, Antarctica, are reported and discussed. Results of this investigation show that the 6.10-m surface core section was deposited during 7.5 years, with a yearly mean accumulation of 38.5 cm of water. The intermediate section, from 43.70- to 52.26-m depth, was deposited during 16 to 18 years (depending on interpretation), with a yearly mean accumulation of 41.5 to 36.9 cm of water. The deepest section, from 98.70- to 101.60-m depth, was deposited during 10 years, with a yearly mean accumulation of 24.6 cm of water. The decrease of the mean yearly accumulation measured in the deepest section is probably due to the plastic deformation of the expanding shelf and possibly to a different accumulation rate in the past. The differences among the mean δ values in the three sections are attributed to climatic change and are consistent with the temperature increase observed in Antarctica during the last 60 years.

About a hundred gas samples were collected and studied from different wells in a multilayer gas field of Southern Italy. The reservoir is constituted by alternating sand an clay layers of Pliocene age. The total volume of gas accumulated in the sand traps is on the order of several billions cubic meters.

THE work recorded here is a continuation of that reported in Nature 1,2 on the isotopic composition of Antarctic snows. © 1963 Nature Publishing Group., SCOPUS: ar.j, info:eu-repo/semantics/published

SINCE the fundamental paper by Craig1 on the geochemistry of the stable carbon isotopes, much work has been done on the determination of carbon isotope distribution in different materials.

THE relative abundance of oxygen isotopes in atmospheric precipitation being closely related to temperature, it has been suggested that the variations of the ratio oxygen-18/oxygen-16 in snow should be used in glaciological studies of polar regions1,2. It has been recently announced that very promising results have been already obtained by analysing cores of old ice from deep bore holes in Greenland3. © 1959 Nature Publishing Group.

The Massaciuccoli palustrine marsh is amongst the most important wetlands in Tuscany. It is a coastal lagoon of fresh to brackish water, which drains a total basin area of about 112 km2 and opens to the sea by way of an artificial channel, known as Burlamacca.In the palustrine area there are old quarries (30 m max depth and 2.5 km2 total area) which have been left by the previous sand extraction activity. Sewage, wastewaters of reclamation lands and wastewaters of cattle-breeding and of a food-industry are the main polluting sources. Within the basin, there are two landfills and several agricultural farming activities.This research, attempts to study 1) the anthropogenic impact on water chemistry; 2) the seawater inflow, the groundwater infiltration and the evaporation rate; 3) the role of the excavation area and 4) the function of the biotic processes, by applying geochemical techniques and chemical (Br, B, Cl and nutrients) and isotopic (δ18O, δ11B, δ2H, δ13C, δ34SSO4 and δ18OSO4) tracers.This study highlighted some important methodological aspects concerning:1-the role of biotic processes to regulate the contents of several dissolved chemical compounds2-the application of isotopes to trace the chemical-physical processes, taking place at the interface between the different compartments, to establish the origin of the elements and to get dating.In particular we point out:i. the distribution in the system of trace elements depends on the presence and intensity of biotic activityii. the importance of isotope geochemistry to trace the origin of water and active, chemical-physical processesiii. the increase in the radiocarbon activity of the sedimentary organic matter, corresponding to the atomic experiments carried out during the 60's, at different depths in the sediments from different sites in the lake.We can conclude that geochemical research allowed us to underline the influence of agricultural activity on the chemical composition of lake water, the hydrodynamic equilibrium and superficial sediment composition.The quarries, because of their high water volume, represent a hydraulic barrier for seawater intrusion into the lake. They act also as a sink for nutrients and they have a positive hydraulic function to prevent lake contamination. However, in future, they will become a serious problem if the stratification (chiefly due to chemical stability) disappears or if they are filled up.iv, Le marais de Massaciuccoli est la plus importante zone humide de la Toscane septentrionale. C'est une lagune côtière qui draine un bassin d'environ 112 km2 de surface totale et qui est caractérisée par des eaux à salinité très variable. Cette zone est reliée à la mer par un canal artificiel, appelé « Burlamacca ».Dans cette zone palustre, on retrouve de vieilles carrières (profondeur maximum : 30 m., superficie totale : 2,5 km2 ), témoignage d'une ancienne activité d'extraction de sable siliceux. Les principales sources polluantes sont représentées par les déchets urbains et industriels et par les eaux de drainage agricole ; au sein du bassin, il y a en effet 2 décharges et plusieurs entreprises agricoles.Ce projet de recherche se propose d'étudier : 1) l'impact anthropique sur la chimie des eaux du bassin du lac de Massaciuccoli ; 2) l'apport de l'eau de mer, l'infiltration des eaux souterraines et le taux d'évaporation du lac ; 3) le rôle exercé par les anciennes carrières, et 4) le rôle des processus biologiques.Les résultats ont été obtenus en appliquant des techniques géochimiques et en utilisant des traceurs chimiques (Br, B, Cl et des éléments nutritifs) et isotopiques (δ18O, δ11B, δ2H, δ13C, δ34SSO4 et δ18OSO4).L'étude a mis en évidence des aspects méthodologiques importants, concernant :1. l'influence des processus biologiques sur le contenu des composés chimiques dissous dans les eaux2. l'application des techniques isotopiques qui, non seulement, a permis de suivre les processus chimiques et physiques qui se développent à l'interface entre les différents compartiments, mais qui a permis aussi d'établir l'origine des divers éléments et d'effectuer des datations.Notamment, on a mis en évidence les points suivants:a. la distribution des éléments dans le système étudié est fonction de la présence et de l'intensité de l'activité biologiqueb. la géochimie est importante pour tracer l'origine des eaux et des processus chimiques et physiques.c. Les datations effectuées sur la matière organique des sédiments avec le 14C mettent en évidence la présence d'un pic de l'activité radioactive, qui correspond aux essais atomiques effectués dans les années '60. La profondeur, à laquelle on peut trouver ces évidences, varie selon les différents sites échantillonnés.En conclusion, ce travail a permis de mettre en évidence l'influence de l'activité agricole sur la composition chimique de l'eau du lac, sur l'équilibre hydrodynamique et sur la composition du sédiment superficiel. En outre, les carrières, en relation à leur extension et profondeur, représentent une barrière hydraulique à l'intrusion de l'eau marine dans le lac ; la disparition de la stratification des eaux des carrières ou un éventuel remplissage de ces dernières pourrait devenir un problème très sérieux pour l'équilibre de l'écosystème palustre.vi