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World - Aquatic ecosystems source of half of global methane emissions

Direct human alterations to natural aquatic ecosystems can increase methane emissions, a new study has found.

Atmospheric methane has tripled since pre-industrial times. It traps heat far more effectively than carbon dioxide and accounts for 25% of atmospheric warming to date. And much of that methane is coming from aquatic ecosystems, with human activities contributing to the emissions levels, a new paper published in Nature Geoscience has found.

The global contribution and importance of aquatic ecosystems as methane emitters has been underestimated, says Judith Rosentreter, postdoctoral associate at the Yale School of the Environment (YSE) who led the study with a team of 14 researchers worldwide.

The study authors reviewed methane fluxes from 15 major natural, human-made, and human-impacted aquatic ecosystems and wetlands, including inland, coastal, and oceanic systems. They found that when methane emissions are combined from these aquatic ecosystems, they are potentially a larger source of methane than direct anthropogenic methane sources, such as agriculture or fossil fuel combustion. Aquatic ecosystems and wetlands contribute at least as much as half of the total methane emissions budget.

"An accurate accounting of the sources of methane from aquatic ecosystems, and if they are impacted by human activities, is important to understanding atmospheric methane concentrations,'' says Peter Raymond, professor of ecosystem ecology who co-authored the study.

One issue that stood out is how humans have impacted methane emissions from aquatic sources.

"Anything human-driven or human-impacted had much higher fluxes than more natural sites,'' says Rosentreter, a Yale Institute for Biospheric Studies Hutchinson Fellow.

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