الأرجنتين تطبّق التكنولوجيا النووية على المياه

“We look to find out exactly how water moves inside aquifers, how it interacts with rivers, and how much of it is left,” said Sandra Ibáñez, Isotope Hydrologist at the University of Cuyo in Mendoza, who is participating in an IAEA technical cooperation project in the country. The IAEA supports scientists around the world on isotope hydrology, sending experts to the field and training local hydrologists in the use of these isotopic techniques.

Since early 2016, Argentinian isotope hydrologists have been gathering and interpreting data from two strategic regions with the help of the IAEA. The idea is for policy makers to use this information and design improved water management models —hydrological models— for these regions.

“Argentina is lucky to have a very good amount of water per inhabitant, but this water is distributed very unevenly across the country,” said Daniel Cicerone, Environmental Manager at Argentina’s National Atomic Energy Commission (CNEA). “In some regions, finding out if the water we are using on a daily basis is regularly recharged, running out, or at risk of contamination can make the difference between poverty and prosperity.”

Hidden reserves

The two regions were selected for different reasons. The first region is the arid valley of Mendoza, western Argentina, where people rely on the fresh underground water of the Uspallata and Yaguaráz aquifers, along with other, smaller ones. Authorities are keen to find out whether this water is being sustainably extracted, and if the aquifers have enough capacity to support increased water use.

“We need water for everything. Water is our daily bread,” said Sergio Cirauqui, who works in a kayaking and rafting adventure shop off the top of a mountain in Uspallata. “But we are very conscious of the fact that water is a finite resource and that we have to take care of it. And as a finite resource, we should make almost sacred use of it.”

Argentinian isotope hydrologists have been hiking the mountains and plains of Mendoza for more than a year, collecting water from wells, lakes and rivers accompanied by international and IAEA experts. Back in their labs, they are interpreting the results to paint a clearer picture of what is available.

Based on data such as the recharge rate of water in aquifers, policymakers are in a better position to establish rules for the use of water for drinking, agriculture and industry. Knowing that surface water is infiltrating groundwater, for example, can lead to stricter regulations on acceptable pollution levels.

“Once we have the results, we can decide what business activities to develop in Mendoza,” said Juan Andrés Pina, Deputy Director of the Groundwater Division at Mendoza’s General Department of Irrigation.  

The second region under study is a streambed in Los Gigantes, Córdoba, an old mining complex about 700 km west of Buenos Aires. Here, Argentinian authorities are implementing an environmental remediation project, working side by side with isotope hydrologists to find out more about the quality of the groundwater and its potential vulnerability to contamination.

After the two uranium mines closed, scientists and authorities were vigilant about groundwater in the area. Through the IAEA project, scientists are now monitoring whether water recharging the San Roque lake reservoir, a source for human consumption in the city of Córdoba, is clean and safe.

And while they have found that uranium levels in the groundwater are safe, they are working to find the exact origin and movement of groundwater, including recharge areas, age, volume, behaviour and vulnerability to future contamination. 

“This interdisciplinary and interinstitutional study will help authorities improve the conceptual model and hydrological understanding of the area and strengthen the remediation of the site,” said Daniel Martínez, geologist and researcher at the National Council forScientific and Technological Research (CONICET).   

The regional technical cooperation projects have been essential in transferring knowledge and technology to national and local institutions, said Raúl Ramírez García, Section Head at the IAEA’s Department of Technical Cooperation.

“The new information provided by isotopic techniques will help monitor the water resources and support the kind of decision making that will lead to social and economic benefits for the population of these regions,” Ramírez García said.

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, the abundance of naturally occurring radioactive isotopes present in water, such as tritium and carbon 14, and that of noble gas isotopes dissolved in the water, 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.

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