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Project: Environmental isotope applications in Latin America and the Caribbean region This Special Issue illustrates the use of environmental isotopes in studying and assessing hydrogeological and ecohydrological issues in the Latin America and the Caribbean (LAC) region. The issue includes twenty selected papers, which have been peer-reviewed in Isotopes in Environmental and Health Studies. Although the LAC region concentrates a third of the world’s freshwater resources [1], access to safe water supplies and sanitation remains unevenly distributed, with water scarcity affecting most arid and semiarid areas and serious water quality issues across the region [2]. About 82% of the LAC population lives in urban centres, including some megacities, creating major challenges to water authorities [3]. Water security is often compromised due to a fast-growing water demand near urban centres (i.e. domestic supply, irrigation and industrial uses) along with the expected impacts of climate change [4] on both water availability and quality [5–7]. In many parts of the LAC region, groundwater resources have become the main or the only source of water to cover basic human needs and the maintenance of ecosystems [8–10]. This rapid increase of water demand is generally translated into intensive and unsustainable exploitation of water resources, having a profound impact on local hydrological cycles. In order to assess the availability of local resources for the near future and adopt sustainable management practices, sound and precise hydrological information is required. Este número especial ilustra el uso de isótopos ambientales en el estudio y evaluación de problemas hidrogeológicos y ecohidrológicos en la región de América Latina y el Caribe (ALC). El número incluye veinte artículos seleccionados, que han sido revisados ​​por pares en Isotopes in Environmental and Health Studies. Aunque la región de ALC concentra un tercio de los recursos de agua dulce del mundo [1], el acceso al suministro de agua potable y al saneamiento sigue distribuido de manera desigual, con la escasez de agua que afecta a la mayoría de las áreas áridas y semiáridas y graves problemas de calidad del agua en toda la región [2]. Aproximadamente el 82% de la población de ALC vive en centros urbanos, incluidas algunas megaciudades, lo que crea grandes desafíos para las autoridades del agua [3]. La seguridad hídrica a menudo se ve comprometida debido al rápido crecimiento de la demanda de agua cerca de los centros urbanos (es decir, el suministro doméstico, el riego y los usos industriales) junto con los impactos esperados del cambio climático [4] tanto en la disponibilidad como en la calidad del agua [5-7]. En muchas partes de la región de ALC, los recursos hídricos subterráneos se han convertido en la principal o única fuente de agua para cubrir las necesidades humanas básicas y el mantenimiento de los ecosistemas [8-10]. Este rápido aumento de la demanda de agua se traduce generalmente en una explotación intensiva e insostenible de los recursos hídricos, con un profundo impacto en los ciclos hidrológicos locales. Para evaluar la disponibilidad de recursos locales para el futuro cercano y adoptar prácticas de gestión sostenible, se requiere información hidrológica sólida y precisa. Universidad Nacional, Costa Rica Escuela de Química

The Guaraní Aquifer System (SAG) is the largest transboundary aquifer in Latin America, extending beneath parts of Brazil, Paraguay, Argentina, and Uruguay. This paper presents the results of recent hydrogeological studies in the southern portion of the SAG. Locally, the abundance of surface water bodies precluded the use of conventional hydrological tools to characterize groundwater flows. Geological, hydrochemical and environmental isotope investigations were integrated to postulate a revised hydrogeological conceptual model. The revised geological model has provided a better definition of the geometry of the aquifer units and outlined the relevance of regional faults in controlling flow patterns. The new potentiometric map is consistent with groundwater flow from the SAG outcrops to the centre of the Corrientes Province, where upwards flows were identified. Hydrochemical and isotope data confirmed the widespread occurrence of mixing. Noble gas isotopes dissolved in groundwater (

The use of stable isotopes (δ2H and δ18O) is widespread in water resources studies. In the Latin America and the Caribbean (LAC) region, the application of isotope techniques has increased in the p...

Rationale Tritium (3H) is an important hydrological tracer that has been commonly used for over 60 years to evaluate water residence times and water dynamics in shallow/recent groundwaters, streams, lakes and the ocean. We tested the analytical performance of 78 international laboratories engaged in low‐level 3H assays for water age dating and monitoring of environmental waters. Methods Seven test waters were distributed by the IAEA to 78 international tritium laboratories. Set 1 included a tritium‐free groundwater plus three ultra‐low 3H samples (0.5–7 TU) for meeting groundwater dating specifications. Set 2 contained three higher 3H‐content samples (40–500 TU) suitable for testing of environmental monitoring laboratories. Results Seventy of the laboratories used liquid scintillation counting with or without electrolytic enrichment, seven utilized 3He accumulation and mass spectrometry, and one used gas‐proportional counting. Only ~50% of laboratories demonstrated the ability to generate accurate 3H data that was precise enough for water age dating purposes. Conclusions The proficiency test helped identify recurrent weaknesses and potential solutions. Strategies for performance improvements of 3H laboratories include: (a) improved quantification of 3H detection limits and analytical uncertainty, (b) stricter quality control practices in routine operations along with care and recalibration of 3H standards traceable to primary NIST standards, (c) annual assessment of tritium enrichment factors and instrumental performance, and (d) for water age dating purposes the use of electrolytic enrichment systems having the highest possible 3H enrichment factors (e.g. >50×).

Tritium (3H) is an essential tracer of the Earth's water cycle; yet widespread adoption of tritium in hydrologic studies remains a challenge because of analytical barriers to quantification and det...

2013-2017: International Atomic Energy Agency, Vienna, Austria, Project CRP 17947: Stable isotopes in precipitation and paleoclimatic archives in tropical areas to improve regional hydrological and climatic impact models Costa Rica is located on the Central American Isthmus, which receives moisture inputs directly from the Caribbean Sea and the Eastern Pacific Ocean. This location includes unique mountainous and lowland microclimates, but only limited knowledge exists about the impact of relief and regional atmospheric circulation patterns on precipitation origin, transport, and isotopic composition. Therefore, the main scope of this project is to identify the key drivers controlling stable isotope variations in daily-scale precipitation of Costa Rica. The monitoring sites comprise three strategic locations across Costa Rica: Heredia (Central Valley), Turrialba (Caribbean slope), and Caño Seco (South Pacific slope). Sporadic dry season rain is mostly related to isolated enriched events ranging from −5.8‰ to −0.9‰ δ18O. By mid-May, the Intertropical Convergence Zone reaches Costa Rica resulting in a notable depletion in isotope ratios (up to −18.5‰ δ18O). HYSPLIT air mass back trajectories indicate the strong influence on the origin and transport of precipitation of three main moisture transport mechanisms, the Caribbean Low Level Jet, the Colombian Low Level Jet, and localized convection events. Multiple linear regression models constructed based on Random Forests of surface meteorological information and atmospheric sounding profiles suggest that lifted condensation level and surface relative humidity are the main factors controlling isotopic variations. These findings diverge from the recognized ‘amount effect’ in monthly composite samples across the tropics. Understanding of stable isotope dynamics in tropical precipitation can be used to a) enhance groundwater modeling efforts in ungauged basins where scarcity of long-term monitoring data drastically limit current and future water resources management, b) improve the re-construction of paleoclimatic records in the Central American land bridge, c) calibrate and validate regional circulation models. Costa Rica está ubicada en el Istmo Centroamericano, que recibe aportes de humedad directamente del Mar Caribe y del Océano Pacífico Oriental. Esta ubicación incluye microclimas montañosos y de tierras bajas únicas, pero solo existe un conocimiento limitado sobre el impacto del relieve y los patrones de circulación atmosférica regional sobre el origen, el transporte y la composición isotópica de las precipitaciones. Por lo tanto, el alcance principal de este proyecto es identificar los impulsores clave que controlan las variaciones de isótopos estables en la precipitación a escala diaria de Costa Rica. Los sitios de monitoreo comprenden tres ubicaciones estratégicas en Costa Rica: Heredia (Valle Central), Turrialba (vertiente del Caribe) y Caño Seco (vertiente del Pacífico Sur). La lluvia esporádica de la estación seca se relaciona principalmente con eventos enriquecidos aislados que van desde −5,8 ‰ a −0,9 ‰ δ18O. A mediados de mayo, la Zona de Convergencia Intertropical llega a Costa Rica, lo que resulta en un notable agotamiento de las proporciones de isótopos (hasta −18,5 ‰ δ18O). Las trayectorias de retroceso de la masa de aire de HYSPLIT indican la fuerte influencia en el origen y transporte de la precipitación de tres mecanismos principales de transporte de humedad, el chorro de bajo nivel del Caribe, el chorro de bajo nivel de Colombia y los eventos de convección localizados. Múltiples modelos de regresión lineal construidos a partir de bosques aleatorios de información meteorológica de superficie y perfiles de sondeo atmosférico sugieren que el nivel de condensación elevado y la humedad relativa de la superficie son los principales factores que controlan las variaciones isotópicas. Estos hallazgos difieren del "efecto de cantidad" reconocido en muestras compuestas mensuales en los trópicos. La comprensión de la dinámica de isótopos estables en la precipitación tropical se puede utilizar para a) mejorar los esfuerzos de modelado de aguas subterráneas en cuencas no calibradas donde la escasez de datos de monitoreo a largo plazo limita drásticamente la gestión actual y futura de los recursos hídricos, Puente terrestre centroamericano, c) calibrar y validar modelos de circulación regional. Escuela de Química

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.

We introduce a new online global database of riverine water stable isotopes (Global Network of Isotopes in Rivers, GNIR) and evaluate its longer-term data holdings. Overall, 218 GNIR river stations were clustered into three different groups based on the seasonal variation in their isotopic composition, which was closely coupled to precipitation and snowmelt water runoff regimes. Sinusoidal fit functions revealed phases within each grouping and deviations from the sinusoidal functions revealed important river alterations or hydrological processes in these watersheds. The seasonal isotopic amplitude of δ18O in rivers averaged 2.5 ‰, and did not increase as a function of latitude, like it does for global precipitation. Low seasonal isotopic amplitudes in rivers suggest the prevalence of mixing and storage such as occurs via lakes, reservoirs, and groundwater. The application of a catchment-constrained regionalized cluster-based water isotope prediction model (CC-RCWIP) allowed for direct comparison between the expected isotopic compositions for the upstream catchment precipitation with the measured isotopic composition of river discharge at observation stations. The catchment-constrained model revealed a strong global isotopic correlation between average rainfall and river discharge (R2 = 0.88) and the study demonstrated that the seasonal isotopic composition and variation of river water can be predicted. Deviations in data from model-predicted values suggest there are important natural or anthropogenic catchment processes like evaporation, damming, and water storage in the upstream catchment.

Tritium (

Rationale Water stable isotope ratios (δ2 H and δ18 O values) are widely used tracers in environmental studies; hence, accurate and precise assays are required for providing sound scientific information. We tested the analytical performance of 235 international laboratories conducting water isotope analyses using dual-inlet and continuous-flow isotope ratio mass spectrometers and laser spectrometers through a water isotope inter-comparison test. Methods Eight test water samples were distributed by the IAEA to international stable isotope laboratories. These consisted of a core set of five samples spanning the common δ-range of natural waters, and three optional samples (highly depleted, enriched, and saline). The fifth core sample contained unrevealed trace methanol to assess analyst vigilance to the impact of organic contamination on water isotopic measurements made by all instrument technologies. Results For the core and optional samples ~73 % of laboratories gave acceptable results within 0.2 ‰ and 1.5 ‰ of the reference values for δ18 O and δ2 H, respectively; ~27 % produced unacceptable results. Top performance for δ18 O values was dominated by dual-inlet IRMS laboratories; top performance for δ2 H values was led by laser spectrometer laboratories. Continuous-flow instruments yielded comparatively intermediate results. Trace methanol contamination of water resulted in extreme outlier δ-values for laser instruments, but also affected reactor-based continuous-flow IRMS systems; however, dual-inlet IRMS δ-values were unaffected. Conclusions Analysis of the laboratory results and their metadata suggested inaccurate or imprecise performance stemmed mainly from skill- and knowledge-based errors including: calculation mistakes, inappropriate or compromised laboratory calibration standards, poorly performing instrumentation, lack of vigilance to contamination, or inattention to unreasonable isotopic outcomes. To counteract common errors, we recommend that laboratories include 1-2 'known' control standards in all autoruns; laser laboratories should screen each autorun for spectral contamination; and all laboratories should evaluate whether derived d-excess values are realistic when both isotope ratios are measured. Combined, these data evaluation strategies should immediately inform the laboratory about fundamental mistakes or compromised samples.

Tritium concentrations in river and stream waters from different locations can be compared by normalizing them using the ratio of tritium concentrations in precipitation and surface water (Cp/Cs) in the study area. This study uses these ratios in a hydrological residence time context to make regional- and global-scale comparisons about river basin dynamics. Prior to the advent of nuclear weapons testing, the Cp/Cs ratio was greater than or equal to 1 everywhere because of the decay of tritium in the watershed after it was deposited by precipitation. After an initial increase in the ratios during the bomb peak, the ratio dropped to less than 1 for most surface waters in the following years. This post-bomb change in the ratio is due to the retention of the bomb-pulse water in watersheds on timescales that are long relative to the residence time of tritium in the atmosphere. Ratios were calculated for over 6500 measurements of tritium in river and stream waters compiled by the International Atomic Energy Agency. These measurements span the post-nuclear era (1940s to present) and include many long-term datasets, which make it possible to examine residence times of waters in watersheds on a global basis. Plotting Cp/Cs versus time shows that ratios tended to reach a minimum in approximately one to two decades after the bomb peak for most locations. This result suggests that changes affecting quantity and quality of river flows need to be assessed on a multi-decadal timescale. These long lag times have significant implications for assessing climate or land-use change impacts on a large number of river systems around the world. The continuing value of tritium in studying surface water systems for both the Southern and Northern Hemisphere is also demonstrated. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

A regionalized cluster-based water isotope prediction (RCWIP) approach, based on the Global Network of Isotopes in Precipitation (GNIP), was demonstrated for the purposes of predicting point- and large-scale spatio-temporal patterns of the stable isotope composition (δ2H, δ18O) of precipitation around the world. Unlike earlier global domain and fixed regressor models, RCWIP predefined 36 climatic cluster domains and tested all model combinations from an array of climatic and spatial regressor variables to obtain the best predictive approach to each cluster domain, as indicated by root-mean-squared error (RMSE) and variogram analysis. Fuzzy membership fractions were thereafter used as the weights to seamlessly amalgamate results of the optimized climatic zone prediction models into a single predictive mapping product, such as global or regional amount-weighted mean annual, mean monthly, or growing-season δ18O/δ2H in precipitation. Comparative tests revealed the RCWIP approach outperformed classical global-fixed regression–interpolation-based models more than 67% of the time, and clearly improved upon predictive accuracy and precision. All RCWIP isotope mapping products are available as gridded GeoTIFF files from the IAEA website (www.iaea.org/water) and are for use in hydrology, climatology, food authenticity, ecology, and forensics.

Uptake of atmospheric CO2 during sample collection and analysis, and consequent lowering of estimated ages, has rarely been considered in radiocarbon dating of groundwater. Using field and laboratory experiments, we show that atmospheric CO2 can be easily and rapidly absorbed in hyperalkaline solutions used for the extraction of dissolved inorganic carbon, resulting in elevated 14C measurements. Kinetic isotope fractionation during atmospheric CO2 uptake may also result in decrease of δ13C, leading to insufficient corrections for addition of dead carbon by geochemical processes. Consequently, measured 14C values of groundwater should not be used for age estimation without corresponding δ13C values, and historical 14C data in the range of 1 to 10% modern Carbon should be re-evaluated to ensure that samples with atmospheric contamination are recognized appropriately. We recommend that samples for 14C analysis should be collected and processed in the field and the laboratory without exposure to the atmosphere. These precautions are considered necessary even if 14C measurements are made with an accelerator mass spectrometer.

Helium-4 is produced in the Earth’s crust and degassed to the atmosphere. Measurements of 4He and 81Kr dating in an aquifer in Brazil suggest that most crustal 4He reaches the atmosphere by the discharge of deep groundwater at the surface.

Tropical and midlatitude precipitation is fundamentally of two types, spatially-limited and high-intensity convective or widespread and lower-intensity stratiform, owing to differences in vertical air motions and microphysical processes governing rain formation. These processes are difficult to observe or model and precipitation partitioning into rain types is critical for understanding how the water cycle responds to climate changes. Here, we combine two independent data sets – convective and stratiform precipitation fractions, derived from the Tropical Rainfall Measuring Mission satellite or synoptic cloud observations, and stable isotope and tritium compositions of surface precipitation, derived from a global network – to show that isotope ratios reflect rain type proportions and are negatively correlated with stratiform fractions. Condensation and riming associated with boundary layer moisture produces higher isotope ratios in convective rain, along with higher tritium when riming in deep convection occurs with entrained air at higher altitudes. Based on our data, stable isotope ratios can be used to monitor changes in the character of precipitation in response to periodic variability or changes in climate. Our results also provide observational constraints for an improved simulation of convection in climate models and a better understanding of isotope variations in proxy archives, such as speleothems and tropical ice.

Recent commercially available laser spectroscopy systems enabled us to continuously and reliably measure the δD and δ18O of atmospheric water vapor. The use of this new technology is becoming popular because of its advantages over the conventional approach based on cold trap collection. These advantages include much higher temporal resolution/continuous monitoring and the ability to make direct measurements of both isotopes in the field. Here, we evaluate the accuracy and precision of the laser based water vapor isotope instrument through a comparison of measurements with those found using the conventional cold trap method. A commercially available water vapor isotope analyzer (WVIA) with the vaporization system of a liquid water standard (Water Vapor Isotope Standard Source, WVISS) from Los Gatos Research (LGR) Inc. was used for this study. We found that the WVIA instrument can provide accurate results if (1) correction is applied for time-dependent isotope drift, (2) normalization to the VSMOW/SLAP scale is implemented, and (3) the water vapor concentration dependence of the isotopic ratio is also corrected. In addition, since the isotopic value of water vapor generated by the WVISS is also dependent on the concentration of water vapor, this effect must be considered to determine the true water vapor concentration effect on the resulting isotope measurement. To test our calibration procedure, continuous water vapor isotope measurements using both a laser instrument and a cold trap system were carried out at the IAEA Isotope Hydrology Laboratory in Vienna from August to December 2011. The calibrated isotopic values measured using the WVIA agree well with those obtained via the cold trap method. The standard deviation of the isotopic difference between both methods is about 1.4‰ for δD and 0.28‰ for δ18O. This precision allowed us to obtain reliable values for d-excess. The day-to-day variation of d-excess measured by WVIA also agrees well with that found using the cold trap method. These results demonstrate that a coupled system, using commercially available WVIA and WVISS instruments can provide continuous and accurate isotope data, with results achieved similar to those obtained using the conventional method, but with drastically improved temporal resolution.

Physical-chemical, chemical and isotopic data of spring water, groundwater and river water from the Actopan basin, central Veracruz were analyzed with the purpose of determining the origin and flow of groundwater. Spring water temperature between 9.6 °C and 18.3 °C, and low electrical conductivity ( 10 mg/L allow the identification of anthropogenic sources. Hydrogen and oxygen isotope results fit reasonable well with the Global Meteoric Water Line (GMWL, δ2H = 8 δ18O + 10) indicating that their recharge derives from local precipitation. On the basis of the observed isotope gradient with altitude (Z), (δ18O = -2.1 (Z km) - 5.56), three main groups of groundwater have been identified: 1) Evaporated water related to the precipitation in the dry season; 2) water, located on the line defined for the regional isotopic gradient, recharged during the rainy season; and 3) water recharged at levels slightly higher than its theoretical value of recharge, showing a component of deep flow and recharge from river water in the coastal plain.

The stable isotopes of oxygen and hydrogen incorporated in the water molecule ( 18 O and 2 H) have become an important tool not only in Isotope Hydrology, routinely applied to study the origin and dynamics of surface and groundwaters, but also in studies related to atmospheric circulation and palaeoclimatic investigations. A proper understanding of the behaviour of these tracers in the water cycle is required for a meaningful use of these tools in any of these disciplines. Our knowledge of the vertical distribution and the factors controlling the stable isotope ratios of oxygen and hydrogen in atmospheric moisture derives from a limited number of observations and vertical profiles in the atmosphere. An international programme jointly operated by the International Atomic Energy Agency (IAEA) and the World Meteorological Organization (WMO), and operational since 1961. has resulted in the development of a dedicated database to monitor isotope ratios in precipitation in more than 500 meteorological stations world-wide. The main features of the spatial and temporal variations of stable isotope ratios of oxygen and hydrogen in precipitation and atmospheric moisture at the global scale are presented based on the analysis of limited data on water vapour, data obtained by the Global Network for Isotopes in Precipitation IGNIP) and the few observations at high latitudes.

Spatial and temporal variability of the stable isotope composition of precipitation in the southeast Asia and western Pacific region is discussed, with emphasis on the China territory, based on the database of the International Atomic Energy Agency/World Meteorological Organization Global Network Isotopes in Precipitation and the available information on the regional climatology and atmospheric circulation patterns. The meteorological and pluviometric regime of southeast Asia is controlled by five different air masses: (1) polar air mass originating in the Arctic, (2) continental air mass originating over central Asia, (3) tropical-maritime air mass originating in the northern Pacific, (4) equatorial-maritime air mass originating in the western equatorial Pacific, and (5) equatorial-maritime air mass originating in the Indian Ocean. The relative importance of different air masses in the course of a given year is modulated by the monsoon activity and the seasonal displacement of the Intertropical Convergence Zone (ITCZ). Gradual rain-out of moist, oceanic air masses moving inland, associated with monsoon circulation, constitutes a powerful mechanism capable of producing large isotopic depletions in rainfall, often completely overshadowing the dependence of δ 18 O and δ 2 H on temperature. For instance, precipitation at Lhasa station (Tibetan Plateau) during rainy period (June-September) is depleted in 18 O by more than 6 ‰ with respect to winter rainfall, despite of 10°C higher surface air temperature in summer. This characteristic isotopic imprint of monsoon activity is seen over large areas of the region. The oceanic air masses forming the two monsoon systems, Pacific and Indian monsoon, differ in their isotope signatures, as demonstrated by the average δ 18 O of rainfall, which in the south of China (Haikou, Hong Kong) is about 2.5‰ more negative than in the Bay of Bengal (Yangoon). Strong seasonal variations of the deuterium excess values in precipitation observed in some areas of the studied region result from a complete reversal of atmospheric circulation over these areas and changing source of atmospheric moisture. High d-excess values observed at Tokyo and Pohang during winter (15-25‰) result from interaction of dry air masses from the northern Asian continent passing the Sea of Japan and the China Sea and picking up moisture under reduced relative humidity. The isotopic composition of precipitation also provides information about the maximum extent of the ITCZ on the continent during summer.

Uptake of atmospheric CO₂ during sample collection and analysis, and consequent lowering of estimated ages, has rarely been considered in radiocarbon dating of groundwater. Using field and laboratory experiments, we show that atmospheric CO₂ can be easily and rapidly absorbed in hyperalkaline solutions used for the extraction of dissolved inorganic carbon, resulting in elevated ¹⁴C measurements. Kinetic isotope fractionation during atmospheric CO₂ uptake may also result in decrease of δ¹³C, leading to insufficient corrections for addition of dead carbon by geochemical processes. Consequently, measured ¹⁴C values of groundwater should not be used for age estimation without corresponding δ¹³C values, and historical ¹⁴C data in the range of 1 to 10% modern Carbon should be re-evaluated to ensure that samples with atmospheric contamination are recognized appropriately. We recommend that samples for ¹⁴C analysis should be collected and processed in the field and the laboratory without exposure to the atmosphere. These precautions are considered necessary even if ¹⁴C measurements are made with an accelerator mass spectrometer.

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.

Although shallow groundwater (

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.

[1] We present a new approach based on atmospheric moisture residence time (RT) to interpret precipitation stable isotope ratio variations in all climate regimes, including tropical and polar, on monthly or inter-annual time scales.δ18O and ln RT are positively correlated and a single regression line describes variations in δ18O and RT anomalies, overcoming limitations of existing Rayleigh distillation-based approaches for tracing moisture dynamics and precipitation processes. We use this approach to characterize changes in tropical precipitation during El Nino events and suggest that increased precipitation in a warmer climate may occur with higherδ18O values, contrary to assumptions made in interpreting proxy climate records in speleothems and other archives. Our results will allow the use of isotopes to monitor climate change impacts on the character and intensity of precipitation and to improve the performance of climate models by providing a direct means to calibrate model results.

Isotopes of light elements constitute a set of powerful and widely used environmental tracers that often provide unique information about hydrological, climatological, and ecological processes. Environmental isotopes are extensively used in groundwater and surface water hydrology, palaeoclimatic reconstructions, atmospheric circulation processes, ocean dynamics, archaeology, palaeontology, anthropology, ecology, food webs, forensics and food authentication. Basic data on spatial and temporal distribution of isotopes at varying scales in the different components of the water cycle are required for a meaningful application of these tracers. A major source of isotope data on a global scale has been provided since the 1960s by the International Atomic Energy Agency (IAEA), which collects and disseminates isotope data and related hydrological information obtained as part of global or regional monitoring programmes and isotope hydrology studies. Available isotope data are gathered and compiled through global networks such as the global network of isotopes in precipitation (GNIP); global network of isotopes in rivers (GNIR); and moisture isotopes in biosphere and atmosphere (MIBA) network. In addition, global isotope data from surface waters and groundwaters are also being compiled. Other important hydrological isotope databases not covered by these networks are the Global Seawater Oxygen-18 Database; and GNIP-Antarctica, an extensive data set containing isotope composition of samples collected in Antarctic snow pits and ice cores. This chapter reviews the current status of and the basic information provided by global isotope networks and databases, and includes some examples of how such data are used to understand regional- to global-scale processes.

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.

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.

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.