Contribution of isotopic and nuclear tracers to study of groundwaters

Abstract

The application of environmental isotopes in hydrology dates back to 1935, when oxygen isotope ratios were first measured on Lake Michigan water by Dole (1935). However, the first substantive scientific papers on the application of stable isotopes of oxygen and hydrogen to natural waters had to wait until after the second world war (Epstein and Mayeda, 1953; Friedman, 1953). Then, the first systematic application of these isotopes in natural waters was spurred by the classic paper by Craig (1961) which showed systematic differences in the isotopic composition of different waters. This gave the basis for their use in tracing water movement and origins in groundwaters as well as surface waters. The first paper specifically referring to groundwaters was by Münnich (1957) dealing with the possibility of radiocarbon dating. This step was greatly assisted by the injection of tritium (and other radioisotopes) into the global water cycle from thermonuclear weapons testing in the 1950s and early 1960s. In subsequent decades the wider scientific community, notably hydrogeologists and geochemists, took up the development of isotope techniques in groundwater studies. At the present day, and after 40 years of research, stable and radio-isotope techniques have become embedded in hydrogeological curricula and applications, where they are essential in defining conceptual models, establishing groundwater circulation processes, evolution of water quality, tracing the origins of both water and solutes, groundwater residence time studies and palaeohydrology. Several excellent reviews of the application of environmental isotopes in hydrogeological studies have been published (Fritz and Fontes 1980; Clark and Fritz, 1997; Cook and Herczeg, 1999; Geyh, 2000). These texts more than adequately summarize the systematics as well as the applications of isotope techniques applied to groundwaters, as well as demonstrating the very wide range of isotope tools now available. Many of the developments and first applications in isotope hydrology are contained in the proceedings of symposia of IAEA, which form an essential archive for following developments in the science over 4 decades. In this paper some of the key papers of the past 40 years' work are used to illustrate how isotope applications have changed ways of thinking about, and understanding groundwater systems. © 2005 IEA.