Study Finds That Half of All Methane Emissions Come from Aquatic Ecosystems

By Amy Lupica, ODP Staff Writer

A new paper published Monday in the journal Nature Geoscience found that up to half of the global methane emissions come from aquatic ecosystems and man-made water sources like flooded agricultural land, ponds, wetlands, reservoirs, and salt marshes. Experts say that these emissions have gone uncounted for too long and that they threaten to derail the world’s climate action goals. They are still investigating how and when these emissions began to skyrocket – but we need to know so that we can make the right land use and management choices to reduce emissions and thus mitigate climate change.

Why This Matters: Methane is one of the most devastating greenhouse gasses and has a warming potential that is 25 times that of CO2 over the next century.  Sixty percent of all methane emissions are due to human activity, and drastically reducing that contribution could mean the difference between meeting the Paris agreement targets — or failing miserably. In addition to aquatic ecosystems, the world is currently plagued by a variety of methane sources like millions of leaking methane wells, livestock and agriculture, and even melting permafrost in the Arctic. While countries work to tackle all of these methane sources, this new paper shows that there are still bigger fish to fry, so to speak.

Rivers, Lakes, and Oceans

Methane from aquatic ecosystems is produced by microscopic organisms in deep, oxygen-free sediments by consuming organic matter like dead algae. That methane then gets consumed by other micro-organisms, but sometimes, it ends up in the atmosphere. 

  • Freshwater ecosystems, which are the type humans often artificially construct, tend to produce more methane than coastal or oceanic systems. 
  • Fertilizer runoff and other pollution that adds excess nutrients to water systems can lead to increased methane production.
  • Global rice cultivation, which often uses flood irrigation, produces more methane per year than “all coastal wetlands, the continental shelf and open ocean together,” according to the paper.

Additionally, particularly damaged or threatened aquatic ecosystems produce more methane than their healthier, undisturbed counterparts. Now, researchers say that the combined methane from natural, impacted, and man-made aquatic ecosystems may contribute 41% to 53% of the world’s total methane emissions. 

Methane Mystery

Methane concentrations in the atmosphere have risen by 150% since the beginning of the industrial revolution, but they mysteriously stabilized between 2000 and 2006. Experts are still debating what caused the dip, and why methane has begun rising rapidly again. Some posit that there has been an increase in methane sources since 2006. Just last year, the Trump administration rolled back regulations on methane emissions. But others argue that the rising emissions are caused by the loss of many “methane sinks,” land and sediment that sequester methane like those now exploding into massive craters in the Russian Arctic. 

Experts say that no matter what the cause of the spike, we can fight off accelerating methane emissions by smart land management practices. The paper suggests rotating wet and dry conditions in aquaculture and rice paddies, restoring damaged salt marshes and mangrove habitats (which Louisiana is now doing on a scale never seen before), and reducing nutrient and fertilizer runoff into freshwater habitats. Protecting and restoring our freshwater habitats, both natural and manmade, is a tall order for every country, but experts say if we succeed, we can not only curtail climate change, but also prevent mass biodiversity loss.

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