INTRODUCTION

Isotope tracers are an important tool for quantifying the age, origin and pathway of water to streams in headwater catchments. While used regularly in temperate and high latitude areas, applications of isotope tracer techniques in the humid tropics have been minimal to date. In the developing world, finances and logistics often preclude the use of traditional hydrometric measures of streamflow, groundwater dynamics and soil water recharge. Thus, isotopic tracers and isotopic hydrograph separations (IHSs) can serve as a valuable tool for extending our understanding of streamflow generation in poorly gauged areas (Shuttleworth, 2002), particularly in humid low latitude regions. They can also provide complementary information on water sources and pathways that are often required in order to draw conclusions about streamflow generation (reviewed by Bonell, this volume), effects of disturbance on tropical forest ecosystems (Bruijnzeel, 1990), or the closure of nutrient cycles in tropical forest ecosystems (Elsenbeer et al., 1995).

The aim of this chapter is to provide an overview of what has been accomplished in isotope tracing studies (mainly in mid-latitude environments to date) as an impetus for those working in the humid tropics to consider the merits of this approach. While we do not advocate use of this technique exclusively in research settings, we argue that it can be a valuable approach in the ‘toolkit’ of land managers and catchment scientists working on hydrological processes related to land use change in humid tropical areas.