Wetlands Responsible For Recent Increase In Atmospheric Methane
Methane is a potent greenhouse gas and recent observations have shown an exponential rise in the levels of atmospheric methane. According to a news release Monday, wetland emissions are hugely responsible for this rise, which may continue, as northern wetlands continue to thaw and tropical ones to warm.
The study conducted by an international team of scientists and led by a University of Guelph researcher, seeks to create an increased awareness towards conservation of these fragile ecosystems that have long been target to unchecked human activities. According to Prof. Merritt Turetsky, lead author from the Department of Integrative Biology, this is the right time for such a study since the Intergovernmental Panel on Climate Change is preparing to examine land use impacts on greenhouse gas emissions.
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The study is one of the largest-ever analyses of global methane emissions. The team looked at almost 20,000 field data measurements collected from 70 sites across arctic, temperate, and tropical regions. A paper on the study has been published today in Global Change Biology. The paper was coauthored by researchers from Canada, the United States, the United Kingdom, Finland, Germany, and Sweden.
Methane though more potent is often overshadowed by carbon dioxide as a greenhouse gas. Although human activities such as raising livestock and burning fossil fuels contribute greatly, natural sources such as microbes in saturated wetland soils are a major source of atmospheric methane.
Due to several reasons, atmospheric methane levels slowed in 1991 and remained so for around a decade. But since 2007, it has started rising again. Scientists think it's likely due to increased methane emissions from thawing northern wetlands, which is considered to be largest in the tropics.
"But our analyses show that northern fens, such as those created when permafrost thaws, can have emissions comparable to warm sites in the tropics, despite their cold temperatures. That's very important when it comes to scaling methane release at a global scale," says Turetsky.
The study emphasizes the need for better understanding of different types of wetlands and methane release rates between flooded and drained areas.
According to Turetsky, fens, which are the most common type of wetland in Canada need to be studied more "Not only are fens one of the strongest sources of wetland greenhouse gases, but we also know that Canadian forests and tundra underlain by permafrost are thawing and creating these kinds of high methane-producing ecosystems," she said.
Most methane studies focus on measurements at a single site, said co-author Narasinha Shurpali, University of Eastern Finland. "Our synthesis of data from a large number of observation points across the globe is unique and serves an important need."
The research showed that even small temperature variations can increase the levels of methane released. But the effect of climate change on methane emissions will depend on soil moisture, said Turetsky.
Under warmer and wetter conditions, much more of the gas will be emitted. If wetland soils dry out from evaporation or human drainage, emissions will fall but there will be other associated problems. For example, drying peatlands can spark more wildfires.
According to coauthor, Kim Wickland, from United States Geological Survey, methane emissions vary between natural and disturbed or managed wetlands, and "this study provides important data for better accounting of how methane emissions change after wetland drainage and flooding."
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