What is blue carbon and why should we care about coastal mud?


 |  Science & The Environment

It’s a beautiful day, and you’re strolling along the coast. You suddenly find yourself knee deep in mud! Why is all this mud here? Well, my friend, it seems you’ve stumbled into one of the ocean’s most prolific carbon sinks: the salt marsh. 

Salt marshes, as well as seagrass meadows and mangroves, are important coastal ecosystems that sequester blue carbon, which is the carbon stored in the plants and sediments of these habitats. That mud you’re stuck in holds vast amounts of carbon that’s been accumulating for thousands of years. Altogether, these habitats cover less than 2% of the ocean floor, but contain over half of all carbon stored in ocean sediments. A 2009 report suggested that by preserving and restoring these ecosystems, humanity could offset between 3-7% of global fossil fuel emissions over the course of twenty years.

On the other hand, destroying these ecosystems for development purposes can release ancient carbon dioxide into the atmosphere, turning them into carbon sources that put our climate at risk. In Canada, the Bay of Fundy salt marshes contain more than 14.2 million tonnes of carbon. Over 85% of these marshes have been destroyed for development, including the construction of dikes to create agricultural land. The Blue Carbon Initiative estimates 340,000 to 980,000 hectares of blue carbon ecosystems are destroyed each year

So what’s to be done? How do we protect these ecosystems and keep this carbon in the mud? 

We can start by making sure existing coastal developments work harmoniously with salt marsh dynamics, to allow natural sedimentation processes to occur. The Clean Foundation, an environmental organization based in Nova Scotia, recently restored a salt marsh in the Northumberland Strait in Nova Scotia, that had been cut in half by a road. They removed small culverts that failed to allow the tide to flow sufficiently between the isolated marsh, and replaced them with a bridge, restoring seven hectares of habitat that allowed natural tidal flow to resume. The project was recognized by Clean50 as one of the top sustainable projects of 2020.

Scientists are also attempting to restore salt marshes across Nova Scotia, by strategically reflooding diked agricultural areas. These areas are already at risk of overflooding from sea level rise, so controlled reflooding can restore the natural salt marsh habitat, and help bring back the natural salt marsh plants and shore birds. Projects like these are happening across the country. In British Columbia, the Comox Valley Project Watershed Society will receive $700,000 from the provincial government to take apart an abandoned sawmill and restore a salt marsh on the Courtenay River on Vancouver Island. 

These coastal restoration efforts in Canada may eventually be eligible to receive carbon credits, which is already occurring in other countries around the world. The Virginia Nature Conservancy and University of Virginia restored 3,600 hectares of destroyed seagrass meadows, allowing the habitat to sequester close to 1800 metric tonnes of carbon dioxide a year. In April 2021, they applied for carbon credit certification from Verra, a non-profit organization based in Washington, D.C. that issues carbon credits. Verra has issued just under 970,000 credits (970,000 metric tonnes of CO2 equivalents) to blue carbon projects since 2015, when they opened their certification process to blue carbon projects. In addition to the many ecological benefits of restoring coastal ecosystems, such as protecting land against sea level rise and providing habitat for marine creatures, blue carbon credits may help provide a monetary incentive to preserve and restore these important environments.

Interested in getting involved with blue carbon restoration efforts?

Check out The Blue Carbon Initiative’s resources page to find out what work is being done in blue carbon restoration around the world. You can also check out Verra’s website to learn more about carbon credit certification. And the next time you get stuck in a salt marsh, rest easy in the knowledge that this mud has been working around the clock to absorb carbon dioxide and help us fight climate change.