Water SecurityNuclear Physics Used to probe Floridan Aquifer Threatened by Climate Change

As rising sea levels threaten coastal areas, scientists are using an emerging nuclear dating technique to track the ins and outs of water flow.

Florida is known for water. Between its beaches, swamps, storms and humidity, the state is soaked. And below its entire surface lies the largest freshwater aquifer in the nation.

The Floridan Aquifer produces 1.2 trillion gallons of water each year — that’s almost 2 million Olympic-sized swimming pools. It serves as a primary source of drinking water for over 10 million people and supports the irrigation of over 2 million acres. It also supplies thousands of lakes, springs and wetlands, and the environments they nurture.

But as glaciers melt due to global warming, rising sea levels threaten this water source — and other coastal aquifers — with the intrusion of saltwater. It’s more crucial than ever to study the history and behavior of water in these aquifers, and Florida’s dynamic water systems make it a prime testbed.

In a study led by the University of Chicago, scientists applied a dating technique developed by nuclear physicists at the U.S. Department of Energy’s (DOE) Argonne National Laboratorythat uses a radioactive version of the element krypton to study the origin and flow of freshwater and saltwater in the Floridan Aquifer. Their findings demonstrate the promise of this novel technique to help understand and forecast the effects of climate change on coastal aquifers, to inform water resource management and to reveal insight into other geological processes.

Counting Krypton
To study the flow of water in the aquifer, the scientists used the TRACER Center at Argonne to perform radiokrypton dating. This technique works by the same principles as carbon dating, where the age of something is determined based on the amount of a certain element remaining in the sample. But instead of carbon, it uses the radioactive isotope krypton-81.

A small amount of krypton-81 is naturally produced in the atmosphere and can dissolve into the water droplets in clouds and bodies of water. Once the water goes underground, it stops absorbing krypton-81 from the atmosphere, and what remains slowly changes into other elements overtime.

If scientists can figure out the ratio between the krypton-81 in the water and in the atmosphere, they can calculate how long it has been underground.

“This is extremely challenging,” said Peter Mueller, a scientist in Argonne’s Physics division. ​“Since krypton-81 is so rare, you need very sensitive measurement tools to detect the tiny amount within a sample.”