[en] The IAEA, through the Technical Cooperation Project (RLA8036), supports the application of isotope tools as part of a large international project which addresses a number of key questions in hydrolgeology and groundwater uses of the Guarani Aquifer. Groundwater constitutes around 95% of all the planet's fresh and liquid water. It is used by more than two billion people in the world and is considered as the greatest strategic reserve for the next decades. About 26% of the available freshwater in the world is in South America, and more than 50% of its population is supplied by groundwater. Low vulnerability to short climate variations places groundwater in a privileged position when societies' sustainability is evaluated. In spite of this importance, in many of our countries, groundwater resources have not received, nor receive, the attention deserved. During the last decade, the interest in South America about groundwater has grown but the few available management schemes operating in most countries are no longer adequate. As a result of a lack of adequate management schemes, ground pollution and inadequate well-head protection measures, some overexploitation (greater water extraction than the aquifer's potential) and pollution signs have been observed in some aquifers. If actions are not taken to ensure the preservation of these resources and correction measures are not adopted in critical areas, we will place at risk public and private water supply schemes, mainly in urban centres. The actions to be adopted will depend on the existing technical knowledge of the aquifers an on the countries' initiatives

[en] Groundwater form Esmeralda-Pica-Matilla region was analysed using environmental isotopes. Difference in the origin of groundwater from adjacent areas of Canchones and Esmeralda was found. This implies that an increase of the groundwater extraction at Esmeralda will not affect the pumping station of Canchones. At Pica-Matilla two different groundwater bodies were characterized, one seems to be connected with the Quisma creek and the other, related to the springs at Pica with the precipitation between the Huasco and Coposa salars. (Author)

[en] Reconstruction of lakewater oxygen isotope histories, based on stratigraphic analysis of finely disseminated sediment cellulose, provides insight into Holocene palaeohydrological changes in the remote and largely unstudied tundra landscape of northern Russia. Oxygen and hydrogen isotope evaluation of local meteorite waters and frozen pore waters from nearby peatlands has enabled speculative deconvolution of the isotopic composition of precipitation from evaporative isotopic enrichment in the lakewater records. These collective data suggest that the western Taimyr Peninsula was wetter, and the lower Lena River basin probably drier, during the climatic warming of the mid-Holocene, perhaps because of incursions of southerly air masses having different moisture characteristics. Since the establishment of modern tundra vegetation, c. 3500 a BP, these two regions have apparently experienced highly variable yet regionally similar changes in moisture conditions. (author)

[en] Changes in the oxygen and hydrogen isotopic composition of wood cellulose primarily reflect changes in the isotopic composition of meteoric water taken up by trees and the subsequent evapotranspirative enrichment of plant water. Therefore, cellulose based isotope palaeoclimatic interpretations are possible owing to the strong relationships between the mean annual temperature and meteoric water isotopic composition and between relative humidity and evapotranspirative enrichment. The empirical 'cellulose model' allows for the quantitative estimation of δ¹⁸Omw and h values from δ²D and δ¹⁸O measurements on wood cellulose. 5 refs, 1 fig

[en] Methane is a major contaminant in the groundwater from a regional confined aquifer located in southern Ontario, Canada. The aquifer is a major source of water for several cities located in this area. This poster presents data from research whose main objectives were the evaluation of (a) the origin and distribution of methane; (b) the geochemistry of dissolved organic carbon (DOC) and dissolved inorganic carbon (DIC). The last objective was to study the potential of ¹⁴C-DOC analyses as an alternative to the use of conventional ¹⁴C-DIC for groundwater dating in an aquifer affected by methanogenesis. The geochemical characterization of DOC is also intended to provide information on carbon sources for methane. 3 refs

[en] This report informs the preliminary results of a study on tree leaves undertaken in various areas of Santiago, aired at evaluating the pollution levels reached by combustion of fossil fuels, using carbon - 14 and carbon - 13 as natural tracers. (Author)

[en] Inferred records of lake water oxygen isotope (δ¹⁸O) composition, acquired through analysis of sediment cellulose, have generated novel insights into Holocene palaeohydrology near the forest/tundra - tundra ecotonoe in central Canada. Supplemented by results from ongoing modern hydrological studies, both rapid and long term hydrological change have been interpreted from three lacustrine sediment records. 5 refs, 2 figs

[en] The origin of dissolved organic carbon (DOC) in groundwater is a key element for the application of ¹⁴C analyses of DOC fractions as a dating tool in groundwater systems. This paper discusses chemical and carbon isotopic data on DOC collected in a regional confined aquifer affected by methanogenesis. These data clearly illustrate the soil zone and organic rich aquifer sediments as the main sources of DOC in groundwater in the study aquifer. This research approach demonstrates the advantage of the combined use of chemical and isotopic tools to understand the origin and nature of DOC in groundwater systems

[en] The identification of contaminant sources is one of the key aspects that consultants and environmental agencies have to deal with when investigating groundwater contamination providing the basis for assignment responsibility for groundwater remediation. Environmental isotopes offer a unique approach for fingerprinting sources of organic contaminants in groundwater. This paper presents the first novel application of the combined use of ³⁷Cl and ¹³C to evaluate the contribution of two sources to trichloroethene (TCE) contamination. The first source consists of an on-site TCE source, the second of an off-site TCE source producing TCE by biodegradation. The site is located in Pleasant Hill, California and the contamination is located in unconfined to semi-confined sand stringers within a fairly tight silty clay matrix aquifer and a deeper confined aquifer consisting of sand beds. The stable isotope data showed a very distinct and significantly different isotopic fingerprint for the primary source of TCE compared to the off-site source. The different signatures make it possible to relate downgradient contamination to the respective sources and clearly demonstrate that the off-site source contributes to TCE contamination at the site. These results demonstrate the great potential of the combined use of ³⁷Cl and ¹³C for fingerprinting organic contaminant sources in groundwater. (author)

[en] A hydrogeological conceptual model of the Eastern margin of the Salar de Atacama (Chile) is proposed taking into account climatic, geological, geomorphological, piezometric, chemical and isotopic data. The study establishes the processes that explain the hydrochemical evolution of waters from salty groundwater in the alluvial aquifer located in eastern part of basin until brines at the saline aquifer of the Salar. The main processes associated with this hydrochemical evolution are evaporation and mixing, but water-crust interaction in the discharge areas of the alluvial aquifer associated with the saline wedge also modifies groundwater composition, and plays a role in the dynamics of the evaporitic crusts in the Salar. The existence of low permeability materials near the surface explains the existence of the permanent surface water bodies in the study area. Based on the data collected in the study three different mechanisms are proposed regarding the main sources of water to the lagoons: (1) discharge of saline groundwater from the detrital and volcanic aquifers of the E margin, (2) discharge of surface waters associated to the N area (Burro Muerto channel), and (3) a combination of both previous mechanisms. (Author).