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January 22, 2011 – Original Source: Ames Tribune, By Laura Millsaps

The amount of methane gas naturally released from lakes and rivers has been underestimated in scientists’ predictions about climate change, a recent study finds.

An international team of scientists, which includes John Downing, an Iowa State University professor in the ecology, evolution and organismal biology department, has found greenhouse gas uptake by land environments such as forests is less than previously thought because of methane emissions from freshwater areas. Methane is considered a greenhouse gas.

The study, published in the journal Science, finds methane gas release from freshwater areas changes the net absorption of greenhouse gases by natural land environments by at least 25 percent. Before, estimates of carbon and greenhouse gas exchanges on continents did not account for the methane gas that is produced by lakes and running water.

Downing compared the discovery to finding a large error in a financial budget.

“This is really a pretty big error,” he said. “Imagine being off 25 percent in your accounting. It could sink your budget.”

In the same way, Downing said, the study reveals that an underestimation in the amount of methane gas released by freshwater bodies may have made previous estimates about the rate of climate change inaccurate.

Downing said the study tells scientists two important things.

“One, you can’t get a good explanation of the global carbon budget without considering all the possible contributors,” he said. “Freshwater methane emissions were previously overlooked, and we found that to be a big oversight.”

Secondly, Downing said, the greenhouse gas-absorbing benefits of forests and agriculture may not be as much as previously thought, considering the discovery of this additional greenhouse gas contribution.

“Those (benefits) may not get us as far ahead as we thought,” he said.

Methane emissions from lakes and running water occur naturally, but have been difficult to assess. The researchers studied methane fluxes from 474 freshwater areas and calculated emissions based on new estimates of the global area covered by inland waters. The implications for accurately modeling changes in the earth’s climate due to global warming are far-reaching, Downing said, affecting governmental policy and hydrological and urban planning,

“I’m an aquatic scientist, a limnologist,” Downing said. “Now that we know have a really big influence in freshwater systems, what other pieces of this puzzle are we missing? What are other ecosystems contributing to the global carbon budget? I think that’s something we really need to know.”

The international research team also included David Bastviken, Linköping University in Sweden; Lars Tranvik, Uppsala University; Patrick Crill, Stockholm University; and Alex Enrich-Prast, University Federal of Rio de Janeiro.


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