Bosnia and Herzegovina and Montenegro are part of the Dinaric karst, a region of impressive limestone mountains and countless caves, sinkholes, springs and underground streams that stretches along the Adriatic coast.

Karst is a complex geological environment shaped by water, which corrodes and dissolves the soft stone. Because limestone is porous, surface water does not collect in karst landscapes — instead, it seeps down through the rock to form aquifers.

Bosnia and Herzegovina and Montenegro share the Oko-Bijela Gora karst aquifer, which spans the border between the two countries and covers some 1800 square kilometres. Karst aquifers are key to sustaining the natural environment and are an important source of drinking water and water for agriculture, industry and electricity generation. More than a quarter of the world’s population depends on water from karst aquifers. However, their porosity makes them vulnerable to contamination and the impacts of climate change.

Using isotopes to decode karst aquifers

Until recently, neither country had a good understanding of their aquifer’s hydrological conditions. In 2020, both countries joined 25 others across Europe and Central Asia in participating in an IAEA regional technical cooperation project to study how climate change influences groundwater resources. The project aimed to train water specialists in the latest techniques for water sampling and analysis, calculating recharge rates and developing models for regional water cycles. Through fellowships, scientific visits and a regional meeting, participants deepened their knowledge of climate change scenarios and formed a regional network of experts with the skills and equipment to monitor and evaluate water resources using isotope hydrology.

Hydrologists from Bosnia and Herzegovina and Montenegro worked together to develop the first conceptual model of the Oko-Bijela Gora karst aquifer. The IAEA provided equipment and supplies for fieldwork and laboratory analysis and training in isotope analysis. The scientists collected precipitation, groundwater and surface water samples and used their newly acquired skills in isotopic analysis to study factors affecting the aquifer’s sustainability, including as a source of drinking water and for hydropower generation.

Combining these findings with historical hydrological and meteorological data, the researchers determined the conditions for the aquifer’s recharge. With this new knowledge, they developed models and maps to identify groundwater recharge areas and explored how surface water affects the aquifer’s hydrogeological cycle. This information provides a blueprint for a water resource management policy that could help both countries protect their shared aquifer.

“The implementation of this project has set a clear direction for guiding the design of future research in the field of water research management and climate change,” said Uro? Juro?evi?, Head of the Department for Geographic Information Systems at the Geological Survey of the Republic of Srpska in Bosnia and Herzegovina.

The project was the first to use isotopic techniques to investigate transboundary groundwater and surface water management in the region. It demonstrated that isotope hydrology is an important tool for studying karst aquifers.

“Working together with colleagues from the region strengthens mutual understanding and supports the sustainable management of this vulnerable karst system,” said Dragan Radojevi?, Head of the Department for Hydrogeology and Geotechnical Investigations at the Geological Survey of Montenegro.

Cooperating across borders

Over 150 countries share transboundary water resources, which account for 60% of global freshwater flows.

The experience of Bosnia and Herzegovina and Montenegro, as well as other participants in the IAEA project, showed that regional cooperation is fundamental to the resilience and sustainability of transboundary water systems in a changing climate.

“Cooperation on shared water resources can improve water management. It can also pave the way for cooperation in other sectors,” said Najat Mokhtar, IAEA Deputy Director General and Head of the Department of Nuclear Sciences and Applications.

Bosnia and Herzegovina and Montenegro are continuing their joint work on the Oko-Bijela Gora karst aquifer through a new IAEA regional technical cooperation project to enhance national isotope hydrology capacities and support evidence based water management.

“The aim is to translate scientific knowledge into practical policy that strengthens water management, which is especially important for shared water resources and in light of climate change,” said Sibel Unlu, an IAEA technical cooperation programme management officer. “Improved transboundary water management, in turn, strengthens water resource management.”

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