Freshwater adds to greenhouse equation

IOWA STATE (US) — Methane emissions from inland freshwater has been underestimated, according to a new study, that finds that greenhouse gas uptake by continents is less than previously thought.

The study, published in the journal Science, indicates that methane gas release from freshwater areas changes the net absorption of greenhouse gases by natural continental environments, such as forests, by at least 25 percent.

Past analyses of carbon and greenhouse gas exchanges on continents failed to account for the methane gas that is naturally released from lakes and running water.

“Methane is a greenhouse gas that is more potent than carbon dioxide in the global change scenario,” says John Downing, professor of ecology, evolution, and oranismal biology at Iowa State University.

Downing, a laboratory limnologist, has also conducted research measuring the amount of carbon sequestered in lake and pond sediment. The new study gives scientists a better understanding of the balance between carbon sequestration and greenhouse gas releases from fresh water bodies.

“The bottom line is that we have uncovered an important accounting error in the global carbon budget. Acre for acre, lakes, ponds, rivers and streams are many times more active in carbon processing than seas or land surfaces, so they need to be included in global carbon budgets.”

Methane emissions from lakes and running water occur naturally, but have been difficult to assess. Small methane emissions from the surfaces of water bodies occur continuously.

“Greater emissions occur suddenly and with irregular timing, when methane bubbles from the sediment reach the atmosphere, and such fluxes have been difficult to measure,” says David Bastviken, principal author and professor of water and environmental studies, at Linköping University in Sweden.

The greenhouse effect is caused by human emission of gases that act like a blanket and trap heat inside the Earth’s atmosphere. Some ecosystems, such as forests can absorb and store greenhouse gases. The balance between emissions and uptake determine how climate will change.

The role of freshwater environments has been unclear in previous budgets, Downing says. The researchers studied methane fluxes from 474 freshwater areas and calculated emission based on new estimates of the global area covered by inland waters.

Researchers from Uppsala University; Stockholm University; and University Federal of Rio de Janeiro contributed to the study.

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