Tracing water flows with tritium will rapidly become impossible, research shows

Water scientists around the world are facing a challenge: concentrations of tritium, a type of hydrogen that is used to study underground flows of water, are declining. The conventional way of research is at risk of becoming useless, with implications for the development of sustainable water management around the world. A group of researchers including scientists from Utrecht University worked out just how long the old tritium method will still be useful across the world: “In some locations the tritium method will remain useful for a few decades, but for 80% of the world, other methods will be necessary.”

Understanding the way in which water infiltrates through soil is important for managing the quality and quantity of water resources. It helps to understand contaminant transport, hazardous waste disposal and storage, and water resources management. Although the scientific understanding of underground water movement has improved, it is difficult to directly “trace” water as it moves through the soil. You can’t just follow a single water molecule as it moves underground!

One way of solving this problem is by studying tritium, explains co-author Jaivime Evaristo, Assistant Professor at the Copernicus Institute for Sustainable Development. “Tritium is heaviest variant of hydrogen, which is part of the water molecule. Water molecules containing tritium are distinct from other water molecules, because tritium decays over time. This makes tritium an ideal ‘tracer’ to study the way water moves underground.”

Method may still be applicable for the next few decades

Tritium is naturally present in water, but significant amounts of tritium were newly created as a result of nuclear bomb testing in the 1950s and 1960s. Since atmospheric nuclear tests were banned in 1963, the amount of tritium in soil water has been declining. As a result, the usefulness of the tritium method for studying groundwater recharge is now up for debate. If tritium runs out, a new method is necessary. Jaivime Evaristo and his  colleagues Edwin Sutanudjaja and Mark Bierkens from the Department of Physical Geography co-authored the recently published research which explores the current-day usefulness of the tritium method worldwide.

We obtained samples from 17 locations across the world and, using advanced models of water transport, estimated how long the tritium method may still be useable

“We obtained samples from 17 locations across the world and, using advanced models of water transport, estimated how long the tritium method may still be useable”, says Evaristo.  The results indicate that the method may still be applicable for the next few decades, in specific locations such as China, Australia, the United States and Senegal. In those places, roughly 20 percent of the global land surface, Evaristo affirms, scientists can take full advantage of the environmental tritium method. In the remaining 80 percent, other tracing methods need to be applied to map underground water movement. But no need to worry, according to Evaristo. Other tracing methods are available to trace water flows and aid the shift to sustainable water management worldwide.