Wetlands – marshes, swamps, mangroves, coastal lagoons, estuaries and the like – perform a wide variety of essential ecosystems services essential to supporting all forms of life. Yet they have been, and continue to be, dug up, filled in, plowed over and built on at alarming rates over the past 50-plus years.
Wetlands provide organic waste and wastewater treatment, among other important ecosystem services. Invariably, this natural process results in production and emission of methane (CH4). Essentially the same molecule we burn in natural gas furnaces and boilers, methane is a greenhouse gas that doesn't last nearly as long in the atmosphere as carbon dioxide. It is, however, 28-36 times more potent a greenhouse gas as CO2 over a 100-year time frame.
For many years, scientists have puzzled over the rate of methane emissions originating in the wetland forests of the Amazon, which are partially submerged during annual wet seasons. The amount of methane emissions from Amazon wetlands measured via satellite-based remote sensing devices and theoretical climate models has been much greater than that they could reasonably account for.
Scientists from the U.K.'s Open University, working in collaboration with colleagues from the University Federal of Rio de Janeiro, the Universities of Leeds, Linkoping, British Columbia and others believe they have found the explanation. Measuring the gas emissions from the trunks of more than 2,300 Amazonian floodplain trees, they found that they act as chimneys, funneling methane soaked up from soils. In sum, Amazonian floodplain trees count as the largest diffusive source of methane emissions ever recorded in wetlands.
Methane emissions and the Amazon floodplain
Ranging from 15.1 million to 21.2 million metric tons annually, the scientists determined that the methane emissions from Amazonian floodplain trees exceed that of the world's oceans or Arctic tundra, which come in at an estimated 18 million and 16-27 million metric tons per year, the study authors highlight.
"Methane is around 34 times more powerful than carbon dioxide at trapping heat in the atmosphere so it is really important to understand where this gas comes from in both natural ecosystems and from human activity,” report co-author and Open University Professor of Global Change Ecology Vincent Gauti said.
Large portions of the Amazon rainforest are flooded for a large part of the year. That makes for an ideal environment for methane production. The quantity of methane emissions scientists have measured from the water surface falls far short of the quantity measured by satellites and theoretical models, however.
“We have discovered that large emissions from trees, sometimes flooded by up to 10 meters, fill this gap," Gauti said.
A fuller picture
Report co-author and Research Fellow at Lancaster University Sunitha Pangala carried out the research while a post-doctoral researcher at the Open University. She warned that as large as they are, Amazonian floodplain trees provide vital ecosystems services and have been a natural, balanced and functioning part of the Amazon for a long, long time.
Pangala also pointed out that there are much larger sources of methane emissions to be concerned about. "We are not, in any way, saying that trees are bad for the environment -- this is how natural forests function,” she was quoted.
“We now have a fuller picture of the sources of greenhouse gas emissions and this could help to inform how environmental change can have a knock on effect on the tropical wetland methane source.”
Pangala highlighted that the methane emissions originating from Amazonian floodplain trees are only half as great as those created by humans via landfills and waste. “So we should be targeting reductions in human emissions. This also includes the dairy and meat industries, and fossil fuel emissions, such as from fracking.”
*Images credit: WWF; Wikimedia; UNEP