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World Water Day 2018: 'Nature for Water'

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This year’s theme for World Water Day is ‘Nature for Water’ — exploring nature-based solutions to the water challenges we face in the 21st century. By helping scientists across the world apply isotopic techniques to study groundwater, the IAEA contributes to protecting this valuable resource. This article explains the science behind isotope hydrology — a discipline that, according to Douglas Kip Solomon, professor of Geology and Geophysics at the University of Utah, “is one of the most powerful, trustworthy tools available to assess groundwater thoroughly.”

With the help of isotope hydrology, scientists can determine the quantity and quality of water supplies. They use naturally occurring isotopes as tracers to find out where groundwater comes from, if it is recent or old, if it is being recharged or polluted and how it travels.

How does it work? Every water molecule has hydrogen and oxygen atoms, but these are not all the same: some atoms are lighter and some are heavier.

“All natural waters have a different hydrogen and oxygen isotopic composition,” said IAEA isotope hydrologist Lucía Ortega. “We use this isotopic composition as the fingerprints of water.”

As water evaporates from the sea, molecules with lighter isotopes tend to preferentially rise. As rain falls, molecules with heavier isotopes fall sooner. The further the cloud moves inland, the higher the proportion of molecules with light isotopes in rain.

When water falls to the earth, it fills lakes, rivers and aquifers, Ortega said. “By measuring the difference in the proportions between the light and heavy isotopes, we can estimate the origin of different waters.”

In addition, naturally occurring radioactive isotopes present in water such as tritium, carbon 14 and noble gases can be used to estimate groundwater age — from a few days to one millennia. When groundwater is found to be tens of thousands of years old, this means that the water flow is very slow and that, if inappropriately extracted, can take tens of thousands of years to replenish again.

(Infographics: F. Nassif/IAEA)

“And this is key to help us assess the quality, quantity and sustainability of water,” she said.

The value of finding out all this data is that policy makers can then use it to design improved water management models. For example, knowing that groundwater is not being regularly recharged can lead to stricter water extraction rules, or finding the potential source of pollution in one aquifer can lead authorities to protect that area and promote sustainable practices.

Examples of recent initiatives in this area include a 2017 IAEA project which demonstrated that significant reserves of good quality water are available in Africa’s drought-prone Sahel region. The findings were the result of a four-year effort to help 13 African countries use isotopic techniques to assess groundwater origin and quality in five shared aquifers and basins. This was the first ever regionwide assessment of groundwater in the Sahel.

In Argentina, isotope hydrologists have been gathering and interpreting data from two strategic regions with the help of the IAEA since 2016. Authorities want to find out if the water of various aquifers is being sustainably extracted, if the aquifers have enough capacity to support more water use, and if the water is of good quality.

Today’s World Water Day theme, ‘The Answer Is in Nature’, highlights the collective commitment to Sustainable Development Goal 6: ensuring that everyone has access to safe water by 2030, which includes targets on protecting the natural environment and reducing pollution. Through training workshops, laboratory services and expert visits, the IAEA is supporting this goal by helping scientists and policy makers better understand and protect their water.

For more information on this year’s World Water Day, visit www.worldwaterday.org.

For more information on our work in this field, visit www.iaea.org/topics/water.

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