Contributions of the International Atomic Energy Agency to the development and practice of isotope hydrology

Abstract

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