In Argentina, like in many parts of the world, water is at risk of over-exploitation and contamination. To protect it, scientists are studying its most invisible details with the help of nuclear technology and the support of the IAEA.
“Most of the fresh, usable water in the world is in the ground, but most of the water that’s available to us is surface water,” said Douglas Kip Solomon, professor of Geology and Geophysics at the University of Utah, who is helping Argentinian experts map their water with the help of the IAEA. “It is extremely important that we understand the interactions between surface water and groundwater so we know how to properly manage these resources and protect them.”
With the help of nuclear techniques, scientists can determine the quantity and quality of their 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.
The science behind this is called isotope hydrology — a discipline that, according to expert Solomon, “is one of the most powerful, trustworthy tools available to assess groundwater thoroughly.”
“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, 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.”
The two regions were selected for different reasons. In the first —the arid valley of Mendoza, western Argentina— people rely on the fresh underground water of the aquifers of Uspallata, Yaguaráz and 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 more water use.
“We need water for everything: to wash our tools, to keep them clean. 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 about 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 an 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 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 of Scientific and Technological Research (COCINET).
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 Technical Cooperation Department.
“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 proportion of isotopes 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.
“And this is key to help us assess the quality, quantity and sustainability of water,” she said.