Laser spectroscopic analysis of stable isotopes in natural waters: a low-cost, robust technique for the use of environmental isotopes in hydrological and climate studies

Stable isotopes of oxygen and hydrogen in natural waters have proven to be effective tracers for the origin and movement of water on earth. An extensive analysis of isotopes in precipitation, surface water and groundwater potentially can provide unique insights into hydrological and climatic processes at a regional scale such as the role of groundwater in rivers and lakes, groundwater recharge, sources of moisture in precipitation, and recycling and transport of atmospheric moisture. The widespread use of isotope techniques by hydrologists in general has been limited by the relatively high operational skill and cost of mass spectrometers used for measuring isotope ratios. Less expensive and easy-to-use spectroscopic methods using lasers have been developed for some time but have lacked the ability to provide results with sufficient precision necessary for hydrological applications. In this presentation, we will report on the analysis of natural water samples using a telemetric laser. The instrument has been extensively tested using a number of secondary standards calibrated on the VSMOW scale and natural water samples. The technique uses a cavity with high-reflectivity mirrors to generate path lengths of several kilometres, resulting in clear separation of different masses. Results show that stable isotope ratios can be measured with a precision of one per mil for hydrogen and 0.3 per mil for oxygen-18 (on the delta scale).