A study by an international team of researchers has found that trees growing in the Amazon river floodplains emit 15.1 ± 1.8 to 21.2 ± 2.5 teragrams (million metric tons) of methane (CH4) per year. This is in addition to the 20.5 ± 5.3 teragrams a year emitted regionally from other sources. Their study is published in the journal Nature.
The “exceptionally large” emissions from Amazon floodplain trees alone are equivalent in size to the entire Arctic CH4 source and account for about 15% of the global wetland CH4 emission.
Wetlands are the single largest global source of atmospheric methane (CH4), emitting an estimated 160–210 Tg of CH4 to the troposphere each year. Wetlands are concentrated globally in two broad latitudinal bands: one rich in peatlands that spans the boreal and subarctic zones and one in the tropics and sub-tropics that contains vast swamps and seasonally inundated floodplains. Low-latitude wetlands are prolific sources of CH4 because of their substantial net primary productivity and high seasonal temperatures. However, relative to northern wetlands, flux measurements from Amazon floodplain ecosystems are sparse and have focused mainly on soil and water surfaces and gas exchange mediated by aquatic macrophytes.
… We measured CH4 fluxes at 13 floodplain locations in the central Amazon River basin and quantified emissions from all known transport pathways, including forested floodplain soil, aquatic surfaces and floating herbaceous macrophytes, as well as stem and leaf surfaces of mature and young trees. … Methane emissions from tree stems and aquatic surfaces were the dominant egress pathways.—Pangala et al.
Sunitha R. Pangala, Alex Enrich-Prast, Luana S. Basso, Roberta Bittencourt Peixoto, David Bastviken, Edward R. C. Hornibrook, Luciana V. Gatti, Humberto Marotta, Luana Silva Braucks Calazans, Cassia Mônica Sakuragui, Wanderley Rodrigues Bastos, Olaf Malm, Emanuel Gloor, John Bharat Miller & Vincent Gauci (2017) “Large emissions from floodplain trees close the Amazon methane budget” Nature 552, 230–234 doi: 10.1038/nature24639