While the Amazon rainforest is widely recognized as a critical carbon sink, an international study in the journal Nature complicates that picture: even as they absorb carbon, trees in the low-lying wetland areas of the Amazon also emit more than 20 million tonnes of methane per year.
That output of a greenhouse gas that is at least 30 times more potent than carbon dioxide is comparable to “emissions from the Arctic tundra, or emissions from all oceans combined, or the total volume of methane emitted from wild animals and termites globally,” SciDevNet reports.
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The research team reached its conclusion by measuring small-scale emissions gathered in small cylinders wrapped around individual tree trunks, alongside large-scale emissions captured in flights around the Amazon basin.
“These trees act as chimneys, funneling the methane produced in the submerged soil into the atmosphere,” Explained co-author Luciana Vanni Gatti, a chemist from Brazil’s National Institute for Space Research’s Laboratory of Greenhouse Gases. That makes them “the source of the largest diffusive emissions  ever recorded in wetlands.”
One of the outstanding questions for the researchers is the impact of intense hydroelectric development throughout the region on the trees’ release of methane. That matters, SciDevNet notes, with “140 hydroelectric dams in operation or under construction along the Amazon basin, and another 288…planned for the coming years.”
“We do not know the consequences for emissions of such [construction] activity”, emphasized lead author Vincent Gauci of the Open University. “However, any changes to the dynamic hydrology of these systems could alter the function of these trees in unpredictable ways.”