ESTIMATES OF BLUE CARBON STORAGE AND SEQUESTRATION IN MAINE SALT MARSHES

Coastal “blue” carbon refers to the carbon captured and stored in coastal marine ecosystems (i.e., salt marshes, mangroves and seagrass beds). These ecosystems are more efficient at capturing and storing carbon than terrestrial forests; therefore, they are important for climate mitigation. The state of Maine has approximately 82 km² of tidal salt marsh, but there is little information on the total amount of carbon stored or sequestered within. In this study, we analyzed plants and multiple (n=25) sediment cores from the Sprague Marsh in Phippsburg, Maine for carbon content, C/N, and stable carbon and nitrogen isotope values. GIS was used to create carbon density maps and isoscapes through 10 cm slices of the marsh, thereby providing a spatial and temporal understanding of carbon deposition and organic sources in Sprague Marsh. At Sprague, the carbon content was initially low everywhere in the marsh and then increased first along the upland borders. The composition of this initial organic matter appears to have been comprised of a mix of C3 and C4 vegetation likely accumulating from deposition on tidal flats. With increasing time, the carbon content increased and the salt marsh platform established in a seaward direction. The total carbon stock at Sprague Marsh is approximately 35 x 10³ (± 10 x 10³) Mg C.

The carbon content was determined more coarsely for several other marshes in southern and central Maine and carbon sequestration data were compiled from the literature. These data were “scaled up” to estimate the total amount of carbon stored and sequestered (±30% error) in salt marshes in the state of Maine. Results from this study will hopefully facilitate further investigation of blue carbon ecosystems in Maine, while providing information to those interested in conserving and restoring salt marshes to mitigate climate change.