Beyond The Pond

January 9, 2009 06:00 PM

Farm ponds are gaining long-overdue recognition for capturing carbon and helping reduce greenhouse gases.

Henry David Thoreau may have found his muse at Walden Pond some 160 years ago, but the common country puddle is now collecting an entirely new set of environmental admirers. Scientists are discovering that farm ponds bury carbon at a rate that rivals larger bodies of water and even trees. That's a splash of good news in the fight to help rid the air of greenhouse gases that could also yield financial dividends for farmers down the road.

Ponds around the globe may collectively absorb as much carbon as the world's oceans, says Iowa State University lake scientist John Downing. The study of such things is called limnology, and research by Downing, a limnologist, is revealing that the amount of carbon buried by constructed ponds and lakes on farmland in the U.S. has been underrated in the past.

Downing estimates there are 304 mil- lion natural lakes and ponds across the world, covering 1.04 billion acres. He says as many as 90% of these water bodies are two acres or less in size.

"As far as we can tell, farm ponds cover about 19.03 million acres worldwide,” Downing explains. "That's a lot of area for things that are so small. But more importantly, they are extremely active and important locally. This makes them disproportionately important in the global processes.”

Through his research, Downing is finding that constructed ponds and lakes on farmland in the U.S. bury carbon at 20 to 25 times the rate at which trees will trap carbon. He is also finding that ponds will take up carbon at a rate higher than lakes.

"Aquatic ecosystems play a disproportionately large role in the global carbon budget,” he says. "Despite being overlooked in the past, it's small bodies of water that are important because they take up carbon at a high rate and there are more of them than previously thought.

"The combined effect is that farm ponds could be burying as much carbon as the world's oceans each year,” Downing says.

Catching carbon. The science behind capturing carbon in ponds is fairly simple. Algae and plants take carbon dioxide out of the air as they grow, and carbon remains in the pond when the plants die. Soil also enters ponds and adds carbon when there is water run-off from surrounding farmland.

Mark Locke, national design engineer with the Natural Resources Conservation Service, finds the idea of a natural way of trapping carbon to be an exciting new reason for farmers to build more ponds.

"Most ponds and dams we build are multipurpose—from supplying water for livestock to offering recreation opportunities,” Locke says. "If additional benefits are accrued beyond flood prevention and sediment control, we see that as a plus.”

Downing's research is ongoing. He is currently partnering with the U.S. Geological Survey to investigate the role of small Iowa lakes in processing other greenhouse gases, such as carbon dioxide and methane.

Thoreau would've been thrilled.

More than a Puddle

Everyone dreams of a little waterfront property. During the past 50 years, the Natural Resources Conservation Service (NRCS) has built more than 3 million farm ponds, says Mark Locke, NRCS national design engineer.

Locke says landowners should contact their local NRCS field office before undertaking the building of a new pond or lake. You will need permits and approvals before excavating. Field office staff and engineers can also provide on-site advice on pond location, design, construction and cost-share funding.

Sizing the structure to the drainage area is one of the biggest challenges, Locke notes. "It's not as simple as just digging a hole or piling up the soil. You want a pond design that will function properly and protect the watershed downstream.”

You can e-mail Pam Smith at

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