KU News Release

KU researcher finds exploitation of aquifers may add to global warming dilemma

LAWRENCE — The next time you open a soda can or bottle of champagne, you’ll release a tiny amount of carbon dioxide into the air. The bubbles that give such beverages their fizz are transferring C0₂ from the liquid into the atmosphere.

Today, a researcher at the University of Kansas is studying this phenomenon on an exponentially larger scale.

Gwen (G.L.) Macpherson, associate professor of geology, said substantial amounts of carbon dioxide are set free as more communities and industries around the world tap underground aquifers. She has found that this growing dependence on groundwater adds significantly to the concentration of gasses responsible for climate change.

“Virtually all groundwater contains carbon dioxide,” Macpherson said. “C0₂ in groundwater is 10 to 100 times higher than it is in the Earth’s atmosphere. Most of the C0₂ in groundwater comes from the soil zone. As water passes through the soil on its way to recharging an aquifer, it picks up C0₂.”

Worldwide, groundwater accounts for approximately one-fifth of total freshwater used for domestic, industrial and agricultural purposes. That number is on the rise because there is roughly 30 times more fresh water underground than on the Earth’s surface.

“As we contaminate more surface water sources and withdraw more water from rivers and lakes, less of it is available,” said Macpherson. “As population grows, we need more water. There’s a lot more groundwater available, which makes it a good resource.”

But like the opening of a carbonated drink, the tapping of aquifers results in degassing, or discharge of carbon dioxide into the air. According to the KU researcher, dissolved carbon dioxide in unconfined groundwater is “typically one to two orders of magnitude higher” than in surface waters. As a groundwater chemist, Macpherson now is focused on gauging the extent of C0₂ released by all the world’s aquifers tapped by humans.

“We’re talking about one more piece of the carbon dioxide puzzle,” Macpherson said. “My initial calculations show that it could be a fairly significant amount of carbon dioxide that goes into the atmosphere. It’s nothing like fossil-fuel-generated C0₂ — maybe up to 1 percent of that. Nevertheless, every little bit that we put in there adds carbon dioxide to the atmosphere.”

By way of comparison, Macpherson calculates that degassing of aquifers through groundwater extraction represents as much as seven to eight times more than the average yearly C0₂ output from the Earth’s volcanoes.

Macpherson’s research may be unique among hydrogeologists, who collectively have not yet considered the total impact of groundwater usage on the planet’s climate. “It might contribute to the greenhouse effect,” she said. “This is a new area of inquiry. I don’t know of anybody who has tried to see how big of an effect it is.”

With 35 wells and 100 soil lysimeters, Macpherson studies C0₂ levels within a pristine watershed located at the Konza Prairie Biological Station near Manhattan. She has discovered that underground aquifers act as beneficial “carbon sinks” for mounting levels of carbon dioxide generated by human activity.

“There is an increasing amount of carbon dioxide being stored in groundwater,” Macpherson said. “This is a very good thing. It may mean that just like the oceans are soaking up C0₂ from the atmosphere, groundwater is doing is the same thing. The mechanism is a little harder to understand — we don’t really know what it is. Somehow the soil is shunting this C0₂ down into the groundwater system, and it’s storing it there for us.”

Macpherson recently presented her findings in Denver at the annual meeting of the Geological Society of America.

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