In Maine, we have tens of thousands of acres of salt marshes and eelgrass meadows. Beyond being photogenic and great for bird watching, they’re also serving a vital function in mitigating climate change. If you’ve heard about natural carbon sinks, you probably think of lush, tall forests and the ways they remove carbon dioxide from the atmosphere and store it over long periods with incredible natural efficiency.
The Sprague River winds through a salt marsh in this view from the top of Morse Mountain at Phippsburg’s Bates-Morse Mountain Conservation Area in 2007. Salt marshes and eelgrass beds account for at least 6 percent of the total carbon removed from the atmosphere every year in Maine while occupying less than 0.1 percent of the land area. Robert F. Bukaty/Associated Press, File
But salt marshes, seagrass meadows, mangroves and seaweed beds also serve this function. Known as “blue carbon,” these systems are absolute powerhouses of carbon absorption and storage. On a per-acre basis, healthy blue carbon coastal ecosystems are up to 10 times more efficient at capturing and storing carbon than forests. But they rarely get the recognition they deserve.
A major and welcome exception is the four-year Climate Action Plan recently released by the Maine Climate Council. Titled “Maine Won’t Wait,” the plan recognizes the value of blue carbon in our state by recommending the protection and restoration of blue carbon ecosystems as one of many strategies for enhancing our natural carbon sinks.
In Maine, salt marshes and eelgrass beds account for at least 6 percent of the total carbon sequestered every year while occupying less than 0.1 percent of the land area. They convert carbon dioxide into plant tissue, much of which gets buried in soils for hundreds, maybe even thousands of years. Recent studies of seaweeds indicate up to 70 percent of the plant biomass is buried in adjacent sediment.
As a member of the International Blue Carbon Scientific Working Group and an earth and climate sciences professor at Bates College, I spend a lot of time in salt marshes, sampling and studying them, so I’ve seen those efficiencies up close. In healthy systems, marsh grasses grow thickly on the surface, and the underlying soils are black and rich with carbon derived from the long-term burial of plant matter.
The marshes where I do much of my research endured some degradation (in the 19th and middle 20th centuries, the grasses were regularly cut to feed livestock, and ditches were dug to reduce mosquito habitat) but fortunately are now conserved. Other Maine marshes and eelgrass beds have not been as well stewarded. When plants are absent or in poor health, carbon buried in their soils can be released back to the atmosphere, contributing to climate change instead of combating it. Salt marshes cut off from the tides by antiquated or poorly designed road crossings or dams can release methane, a greenhouse gas 30 times more potent than carbon dioxide.
Degraded eelgrass beds resulting from excess nutrients, dragging for shellfish and invasive species can also release previously stored carbon into the atmosphere. For this reason, restoring and preserving coastal blue carbon ecosystems is an important step towards mitigating climate change. Healthy coastal blue carbon ecosystems also create more secure coastal communities by maintaining biodiversity while reducing the impacts of pollution, erosion, flooding and storms, and by providing nutrients and habitat for marine wildlife and fisheries.
The blue carbon component of the “Maine Won’t Wait” plan is just one of a variety of strategies for reducing greenhouse-gas emissions while creating jobs as we transition to a clean-energy economy.
Beyond the Maine plan, on a federal level, the Ocean-Based Climate Solutions Act of 2020 was released last October. This bill, sponsored by House Natural Resources Committee Chair Rep. Raúl Grijalva and co-sponsored by Maine Rep. Chellie Pingree, implements a suite of ocean-based climate solutions, including setting the goal of protecting and restoring 1.5 million acres of blue carbon ecosystems nationwide over the next 10 years.
Maine is poised to benefit from all these plans and policies. The removal of tidal restrictions, reduction of nutrients in coastal waters and active restoration of salt marshes and eelgrass beds where conditions are suitable provide quantifiable climate mitigation benefits. Implementing these actions will reduce our carbon footprint and enhance the health and biodiversity of our coast. I’m grateful to the Maine Climate Council and Rep. Pingree for recognizing the importance of coastal blue carbon to our state. I urge everyone to join me in supporting Maine’s Climate Action Plan and the Ocean-Based Climate Solutions Act.
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