Methane is an important greenhouse gas and there are many situations in which we still do not know in detail where, when, and how methane is emitted and absorbed. Tropical environments are important, and earlier studies have suggested that the Amazon basin contains a large and unrecognised source of methane. Now, researchers seem to have solved the mystery of the missing methane source in the Amazon rainforest. The current study shows that trees growing in the flooded swathes by the Amazon River act as emission pathways for methane formed in the sediments. The emissions from the tree trunks contribute between 15.1 and 21.2 million tonnes of methane (CH4) to the atmosphere every year, comparable to 18 million tonnes from the oceans, or 16-27 million tonnes from Arctic tundra wetlands.
The findings, which are presented in the scientific journal Nature, are the result of a collaboration between researchers from Linköping University, the Open University, the Federal University of Rio de Janeiro, the University of Leeds, the University of British Columbia, and other partners. The researchers measured the gas emissions from the trunks of over 2,300 Amazonian floodplain trees. They found that the trees are the source of the largest emissions ever recorded in wetlands.
“It was quite surprising to find such an important and big global natural methane source, especially because methane is a powerful greenhouse gas. This result reinforces the importance of understanding greenhouse gas emissions from natural ecosystems and from human activities. Our findings show how important it is to increase research in tropical regions, especially in the Amazon basin. Great swathes of this basin become flooded forest for a large part of the year, giving ideal conditions for the production of methane,” says Alex Enrich-Prast, senior lecturer at the Department of Thematic Studies – Environmental Change.
Whilst the gases emitted through the trees contribute to the global climate, the authors want to clearly state that trees are not in any way bad for the environment – this is how natural wetland forests function. The findings contribute to a fuller picture of the sources of greenhouse gas emissions and the knowledge could help to inform how environmental change can influence future greenhouse gas emissions.
“Actions to reduce greenhouse gas emissions must clearly focus on cutting the use of fossil fuels and other human-induced fluxes, not on the natural fluxes. However, it is important to know about all greenhouse gas sources on the planet, and understand how they are regulated, to better predict our future climate. This study contributes an important piece in this puzzle”, says David Bastviken, professor at the Department of Thematic Studies – Environmental Change and one of the researchers behind the study.
The study has received financial support from many sources, including the Swedish Research Council and the Swedish Foundation for International Cooperation in Research and Higher Education (STINT).
The article: Large emissions from floodplain trees close the Amazon methane budget, Sunitha R. Pangala, Alex Enrich-Prast, Luana S. Basso, Roberta Bittencourt Peixoto, David Bastviken, Edward R. C. Hornibrook, Luciana V. Gatti, Humberto Marotta Ribeiro, Luana Silva Braucks Calazans, Cassia Mônica Sakuragui, Wanderley Rodrigues Bastos, Olaf Malm, Emanuel Gloor, John Bharat Miller and Vincent Gauci, (2017) Nature, publicerad online 4 december 2017, doi: 10.1038/nature24639
