Using radioactive markers to assess the scope and condition of groundwater resources
By Freeman Ngulu.
The Ministry of Agriculture, Water and Land Reform is working with the International Atomic Energy Agency (IAEA) and the German Institute of Geosciences and Resources on a national project to determine the scope and reliability of local groundwater resources.
The intended result is to protect groundwater resources by managing and limiting extraction, ensuring that they provide water year-round and that they last indefinitely.
The study will start by taking samples from the Kuiseb aquifer, a source under extreme stress from supplying water to the growing towns of Walvis Bay and Swakopmund.
Results from these samples will be used to predict the future impact of climate change on national groundwater resources and guide protection and governance activities.
Anna Grigoryan, The IAEA’s Programme Management Officer is coordinating the activities. “The use of isotopes is an area of great importance in adapting to climate change. Through technical assistance and targeted capacity building, the IAEA is continuously building partnerships to coordinate responses to drought emergencies and ensure countries are able to manage water resources in a sustainable way,” she said.
Earlier this year, Namibia and the IAEA penned an agreement setting the framework for the aquifer project. This cooperation builds on previous successful projects with the country in using nuclear techniques to create new crop varieties, and ensure the safe transport of radioactive material.
The project will use isotope hydrology techniques to monitor groundwater resources and to assess the impact of climate change and variability in water from major aquifers.
Ioannis Matiatos, an isotope hydrologist at the IAEA said that isotope hydrology techniques are a well-established tool for the assessment of groundwater resources and could be the problem solver for Namibia’s droughts. “At the IAEA, we’ve been closely collaborating with experts from all around the world on the use of environmental isotopes to improve the availability and sustainability of freshwater resources,’’ he said.
Using environmental isotopes to trace groundwater origin and flow. Bodies of water are naturally labelled with unique isotopic signatures. By using these signatures, water origin and movement can be tracked through its entire cycle of existence. A laser spectroscopic analyser is used to examine groundwater samples and interpret them based on the stable isotopes present in the water molecule.
Groundwater provides half of all drinking water worldwide. The impact of climate change on groundwater sources is severely impacting availability and quality in many countries, including Namibia. With a drought emergency declared in 2019 and increasingly extreme weather conditions, annual rainfall may not be sufficient to replenish groundwater resources, according to experts. The growing influx of people living in and moving to the capital Windhoek and to coastal cities is adding to Namibia’s struggle to maintain water supplies.
Aquifers are sensitive to both human activities and natural changes, and the IAEA has used isotope hydrology tools to assess availability and the impact of contamination, in Bolivia and South Africa.
Understanding the evolution of the country’s rain distribution during the rainy summer season and the dry winter season through isotopes will indicate how the availability of groundwater can be altered in cases of drought due to climate change. Through the improved knowledge of groundwater dynamics, experts in Namibia will be able to manage water resources better and avoid water emergencies like in 2019, Matiatos said.
Though virtual capacity building due to the COVID-19 pandemic the cooperation continued uninterrupted. An online training course launched at the end of May 2021 helped participants understand how isotope hydrology can be used to accurately assess and manage groundwater.
Kaupuko David, a hydrogeologist at Namibia’s Ministry of Agriculture, Water and Land Reform said that, when faced with the potential of devastating drought, the use of the isotopic techniques helps to assess if the country’s current plans are sufficient.
“If we suffer from a drought, the Windhoek aquifer becomes our emergency water supply for the city and can last at least three years. However, it’s unclear how using the aquifer in this way would impact its future and we’ve been trying to use surface water from our dams to recharge it for times of drought. But with a growing population, it’s never enough,” David said.
The training session taught her and her team how to plan their field trips and collect samples of stable isotopes, as well as considerations and equipment needed to collect good quality samples for analysis. “We are looking forward to an upcoming fellowship in Germany where we hope to learn more about analysing samples and deriving actionable information from the data,” she said.
Other naturally occurring isotopes can be found in aquifers, such as carbon-14 (14C) — a radioactive isotope commonly used to date fossils and archaeological specimens. By measuring the 14C content in water samples, scientists can estimate the age of the groundwater which can be as old as 40,000 years. Other isotopes, such as tritium (hydrogen-3) and those found as dissolved noble gases, — helium-3, helium-4, argon-39 and krypton-81, are powerful tools that allow scientists to date from young to very old groundwater systems.
This information informs water specialists on the nature, history and flow of sampled groundwater and helps them calibrate and improve groundwater numerical models that predict the aquifer’s response to climate change.