Isotope Tracer Applications in Groundwater Hydrology: A Review of Indian Scenario

Applications of stable and radioactive isotopesin groundwater hydrologyhave a legacy of over five decades in India. Isotope hydrologybegan in India around 1973, concurrently with the worldwide programme of the International HydrologicalDecade (1965–1974) launched by UNESCO. The main thrust of isotopeapplications initially was the groundwater age estimation and understanding recharge process in alluvial terrain assuming piston-flow approach, followed by, in hard rock terrain, to understand the preferential flow for groundwater recharge. It began with application of environmental and injected tritium but gradually a suite of other radioactive and stable isotopeswere employed in groundwater hydrology. Actually, it encompassed examination of the entire hydrologicalcontinuum from atmosphere to surface to subsurface components of hydrologicalcycle rather than just the groundwater age estimation and groundwater rechargeprocesses. Initially, the isotopeanalyses capabilities were restricted only to a few national laboratories but a few other research and academic institutions also developed these capabilities and initiated isotope hydrologyprogramme. The acquisition of correct basic temporal and spatial data is of paramount importance in preparing groundwater resource management policies and development projects of widely different kinds. This can be achieved only when isotopeexpertise is transported from leading research institutions to numerous state and central water resource agencies and academic institutions. This is essential for India so that demonstrated potentials of isotopeapplications in hydrologycan be effectively used to mitigate water resource scenario in the country. This paper aims to provide a snapshot review of evolution of groundwater isotope hydrologyin India over the past five decades.