Predicting River Flow Dynamics Using Stable Isotopes for Improved Ecosystems

IAEA's Groundbreaking Study

The International Atomic Energy Agency (IAEA), using isotope hydrology techniques, has pioneered a method to assess the contributions of different water sources to river flow in a new publication set to be released on July 17 in Nature Water. By analysing the stable isotopes of oxygen and hydrogen in water molecules from 136 perennial rivers and 45 large catchments globally, the IAEA was able to determine the fraction of river water that was less than two to three months old, also known as "young water fraction." Additionally, the study introduced a dynamic water retention indicator to depict river flow dynamics.

A high dynamic water retention suggests that water moves through the catchment slowly, indicating a slower response to hydroclimate events. Conversely, low dynamic water retention indicates rapid water movement and a faster response to such events. The study identified key factors influencing dynamic water retention, including land-use changes (such as crop and forest cover) and climate changes (such as air temperature and precipitation).

Why does a river flow when it's not raining?

Rivers are the lifelines of our planet, supporting a vast array of ecosystem services. They nurture riverine animal and plant communities, deliver essential nutrients to the marine environment, provide transport routes for trade, generate hydroelectric power, and offer recreational opportunities for tourism and sports. Essentially, they are the arteries of the Earth, transporting life-sustaining water from one region to another.

Rivers continue to flow even when it's not raining due to contributions from various sources such as direct precipitation, surface runoff, interflow through soil and baseflow from groundwater. The relative proportions of these sources can vary greatly depending on the river's catchment area (the area where water collects when it rains). The transport time for these water components ranges from immediate (direct precipitation) to significantly older (groundwater that has resided in the catchment for more than a year).