There is more to freshwater resources than meets the eye. While fresh water is visible in the form of rivers, lakes and glaciers, fresh groundwater resources — hidden beneath the Earth — often go unseen.
Groundwater is found in spaces within soil, sand and rock, and is stored in, and moves slowly through, aquifers. It accounts for 99 per cent of Earth’s fresh water, and, according to the United Nations Educational, Scientific and Cultural Organization (UNESCO), nearly half of the world’s urban population depends on it. This dependency on groundwater is expected to grow in light of the effects of climate change.
The volatility of rainfall patterns and the frequency of extreme weather events, as well as the challenges posed by pollution and intensive agriculture, affect the distribution and availability of water resources, explained Yuliya Vystavna, an isotope hydrologist at the IAEA. This is particularly relevant in arid and semi-arid regions of Africa, which experience high rates of evaporation, little rainfall and are largely dependent on groundwater resources. “In order to cope with these challenges and the scarcity of water, we need to have an understanding of water resources and manage them in a sustainable way,” she added.
Uncovering groundwater characteristics
North Africa, home to the Sahara Desert, is one of the driest regions on the planet. Tunisia, located in the northernmost part of the African continent, suffers from variability in rainfall and ranks among those countries with the least water resources in the Mediterranean, said Rim Trabelsi, Director of the Department of Geological Engineering and member of Tunisia’s Laboratory of Radioanalysis and Environment (LARAE) of the National Engineering School of Sfax (ENIS). “That’s why groundwater is really the most reliable resource for the sustainable development of Tunisia, and the population is depending more and more on groundwater supplies.”
The increased use of groundwater has highlighted the need to better understand the links between groundwater recharge and discharge — the movement of water from surface water to groundwater and vice versa. “Groundwater management is increasingly important because of climate variability causing groundwater levels to decline throughout the year, and because of the quality risks posed by nitrate pollution, or salinization by seawater intrusion,” Trabelsi said.
By studying isotopes of water, scientists can provide guidance on how to protect and manage this resource. The amount of naturally occurring stable isotopes of water, and of other substances, is used to reveal the water’s origin, movement, quality and age, as well as to identify sources of contamination. Water age, measured by the concentration of specific isotopes, for example, can range from months to millions of years. The age of groundwater is key to predicting the presence of contaminants, and to understanding how quickly aquifers are replenished.
‘Young’ groundwater can be replenished by surface water from precipitation but can also be affected by pollution and changing climatic conditions, Trabelsi explained, while ‘old’ groundwater, which takes much longer to replenish, is less likely to be contaminated or affected by changes in climate.
Growing analytical capacity
As in many scientific fields, the application of isotope hydrology tools and analysis requires building capacity.
When Hamid Marah first began working in the field of water resource management in Morocco in the 1990s, water samples had to be sent to countries outside of Africa for analysis. There were no laboratories in Africa that had the capability to analyse stable isotope compositions, said Marah, Scientific Director at Morocco’s National Centre for Nuclear Energy, Sciences and Technology (CNESTEN). “Thanks to IAEA support, over the years the capabilities of the continent have been enhanced, and we now have several laboratories in Africa that can analyse isotopes reliably.”
Through the IAEA’s technical cooperation programme and coordinated research projects, isotope hydrology tools are spreading across Africa, enabling scientists to sustainably tap into groundwater resources. Over the past ten years, almost half of the IAEA’s climate change adaptation projects, including water resource management projects, have taken place in Africa. Countries such as Morocco and Tunisia are playing a leading role in the application of isotope techniques across the continent and the Middle East.
Since 2009, LARAE and CNESTEN have been AFRA regional designated centres, and in 2015 CNESTEN became an IAEA Collaborating Centre focusing on water resources assessment and management. AFRA, which stands for the African Regional Co-operative Agreement for Research, Development and Training related to Nuclear Science and Technology, is an intergovernmental agreement established by African countries to strengthen and enlarge the contribution of nuclear science and technology to socio-economic development on the African continent. LARAE and CNESTEN regularly train scientists from across Africa and the Middle East and have carried out thousands of isotope analyses for national hydrological studies and IAEA-supported projects, which aim to address water availability and quality issues related to aquifers and basins.
In a 2020 study, for example, groundwater samples from an aquifer in central-west Tunisia were analysed by LARAE for chemical and isotopic measurements. In recent decades, the expansion and development of irrigated agriculture has depleted surface water resources. The study helped to determine the groundwater’s suitability for drinking and irrigation, and identified sources of salinity variation. The study, which was supported by the IAEA through a coordinated research project, was published in the journal Agriculture, Ecosystems & Environment in June 2021.
There will be an opportunity to learn more about groundwater resources and their role in climate change adaptation and mitigation at the IAEA’s International Symposium on Isotope Hydrology, to be held from 3 to 7 July 2023 in Vienna, Austria.
Source: International Atomic Energy Agency