Rivers comprise less than one per cent of all available freshwater, yet are central to humankind for water supply, energy and transportation. Stable isotopes are powerful tracers to study river-groundwater interactions, assess aquatic nutrient sources and dynamics, quantify the water balance of watersheds and address sedimentation dynamics.

The importance of rivers for humanity cannot be overstated. They have been a strategic asset to civilizations since antiquity and resources for humans across borders and boundaries.

In the global hydrologic cycle, rivers act as conduits returning rain, snow, ice and groundwater back to the world’s oceans. However, pollution, the building of dams and reservoirs and intensive agriculture irrigation practices have dramatically altered most of the world’s large rivers and watersheds. They have affected discharge rates and the seasonality of the water flow, degraded water quality and affected sensitive aquatic habitats.

There is tremendous international interest in scientific information that assists cooperative river water stewardship. Using oxygen and hydrogen isotopes, the sources of river water can be traced, whereas nitrogen, carbon and sulphur isotopes and other geochemical parameters constrain and help model nutrient and sediment dynamics in river basins. To improve our global understanding of rivers, the IAEA has set up an online resource tool with such information, the Global Network of Isotopes in Rivers.

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