Making use of new opportunities and technologies for the measurement of environmental tracers

Full text: The range of environmental tracers available for use today is wide and varied. In many cases the technologies that we use are adapted from other fields and the key insights are in recognising their potential utilisation in examining processes in the hydrosphere. Examples of this include the use of Rn to measure groundwater inflows to streams, where much of the technology has been adapted from the monitoring programs of Rn in air. The atmospheric nuclear test program drove the development of tritium measurements, the IAEA tritium facility was set up in 1958 following recognition that the elevated tritium in the 1950's would be an ideal tracer of hydrosphere residence times. Likewise the technology developed for monitoring of CFC's and SF6 in the atmosphere has allowed these traces to be applied to solving hydrogeological problems. Perhaps the most exciting current trend is the ability to measure tracers continuously to capture transient events. The improvement in sensor technology means that a range of analytes may be measured continuously and data retrieved in real time. In addition, continuous measurements of stable isotopes (via cavity ring-down spectroscopy) and Rn (via Rn-in-air detectors) are becoming more common. Much of this equipment is lightweight, portable, and has modest power consumption, which makes it ideal for autonomous field deployment. The ability to generate time series of data allows geochemical tracers to be integrated with other continuous datasets (such as rainfall, temperature, heads, or streamflow). While we have many tools, the toolbox might not be full and the next development may well exist but being used to answer a different question. (author)