Don’t Drain the Swamps: Tidal Wetlands Store Huge Amounts of Carbon

Research just published by the American Geophysical Union digs deeper into the carbon-storing power of wetlands along North America’s Pacific coast.

A new paper featuring Hakai Institute researchers and led by Oregon State University reveals that the forested tidal swamps of the Pacific Northwest, alongside mangroves in Mexico, stash away the largest amounts of carbon on the Pacific coast of North America.

Analyzing transboundary datasets from Canada, the United States, and Mexico, the study contributes vital regional estimates for the carbon-storing potential of different coastal ecosystems, including seagrass meadows, unvegetated mudflats, marshes, mangroves, and tidal swamps—which are all threatened by development.

While mangroves have become known for their carbon-rich soils—due to the trees and plants that deposit carbon locally in their soils, and the low-oxygen conditions that lock it away—the new research shines a light on forested tidal swamps. These wetlands are defined by large tide swings and woody shrubs and trees, including northern species such as willows and Sitka spruce. The study finds that forested tidal swamps in the Pacific Northwest can bury around three million tonnes of organic carbon (or around 10 million tonnes of carbon dioxide) in the top meter of sediment alone. That’s equivalent to around what two million gas cars burn every year, and is more carbon storage per area than all the terrestrial ecosystems the authors analyzed save for Canadian peatlands.

“Our northwest tidal swamps are some of the best tidal swamps in the world in terms of carbon storage,” says Margot Hessing-Lewis, one of the Hakai Institute researchers involved in the study. “It’s a unique but very understudied ecosystem that’s quite threatened. They’re like the temperate version of mangroves.”