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[en] Tritium/³He measurements yield quantitative information on the age of young groundwater. Such measurements provide an important element in the use of groundwater flow systems as archives of environmental records. The general principles of tritium/³He dating of natural waters for this purpose are briefly discussed. This is followed by case studies in which tritium/³He dating is applied to groundwater flow systems of different complexity with respect to (1) the hydrogeological setting, (2) the presence of terrigenic helium (crustal and mantle sources) complicating separation of the tritiogenic ³He component and (3) the presence of tritium from sources other than natural production and (surface) tests of nuclear devices. The case studies include simple, sandy aquifers and more complicated sites such as fractured bedrock. They show that under most circumstances, tritium/³He data, if interpreted in the proper hydrogeological context, can provide reliable, quantitative age information. (author)

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[en] During the last 35 years, the joint programme of the International Atomic Energy Agency and the World Meteorological Organization (WMO) devoted to the systematic measurement of oxygen-18, deuterium and tritium in precipitation on a global scale has compiled a database with more than 100,000 isotope measurements. The survey, known as the Global Network for Isotopes in Precipitation or GNIP, provides basic data on the spatial and temporal distribution of these isotopes. This has been recognized as the major reference of isotope data in precipitation for hydrological applications. For more than a decade, the oxygen-18 and deuterium records have also been used to validate atmospheric global circulation models and to calibrate isotope records in paleoclimatic archives, especially in continental areas, such as ice cores, lake sediments, tree rings, speleothems and groundwater. The paper briefly reviews the main fields in the earth sciences that benefit from the GNIP database and describes the new requirements and challenges of the programme to create, reactivate or maintain some of the co-operating meteorological stations. (author)

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[en] The accumulation and release of salinity from near surface environments takes place naturally as a result of climatic cycles and environmental change. Salinity stratification, both in the saturated and unsaturated zones of aquifers, may be used in certain circumstances to record past recharge events and periods of drought. Chloride, in conjunction with the stable isotopes δ¹⁸O, δ²H and other chemical and stable or radioactive indicator parameters, enables the origins of salinity and the timing of these events to be determined. Salinity may be used as a practical tool in water resource investigation to estimate recharge and discharge, to investigate palaeohydrology and in the understanding and management of groundwater in coastal regions. Human impacts have severely disturbed the natural salinity balance, especially in the past 100 years, and examples of human intervention are presented relating to dryland salinity, irrigation effects and overexploitation. (author)

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