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Blue Carbon: The Ecosystem Service Hidden Beneath Your Feet

Though their geographic extent may not rival that of their terrestrial counterparts, coastal ecosystems such as mangroves, seagrass beds and wetlands store carbon at the highest rates per unit area of natural ecosystems. Blue Carbon refers to the carbon stored in biomass – such as leaves and roots – and deep sediments of coastal and marine ecosystems. Increasingly referred to as “blue” due to proximity of the ocean, the carbon stored in these ecosystems has both internal and external sources, allowing the system to act as a carbon sink for an extensive area.

Blue carbon is found in marshes, seagrasses and tidal wetlands around the world.

Wetlands influenced by daily tides – known as tidal wetlands – are particularly important ecosystems when considering drawdown and storage of atmospheric and oceanic carbon. At low tide wetland vegetation utilizes and stores carbon from the atmosphere (CO2) during photosynthesis. When winter comes and this dense vegetation dies back, the carbon held within can be stored in the sediment. At high tide the vegetation slows oncoming waves allowing the sediment and carbon they carry to settle on the wetland surface. 

Wetlands can vertically increase gaining height often in pace with sea level rise. Over time and under the right conditions, these wetlands have the ability to vertically increase, gaining height often in pace with sea level rise in a way man-made structures (such as bulkheads or sea walls) cannot.

Wetlands can vertically increase gaining height often in pace with sea level rise.

This vertical growth provides the potential for un-saturated blue carbon burial and storage as sediment is deposited.

 

 

Potential for un-saturated blue carbon burial and storage as sediment is deposited.

Existing carbon stores, and the ability of tidal wetlands to continue to store carbon over time are increasingly at risk from natural and human-caused stressors including urban development and sea level rise. These stressors can degrade wetlands over time resulting in a transition from carbon sink, to source. With global annual loss between 0.7-7%, coastal ecosystems are disappearing at an alarming rate and releasing an estimated 0.15-1.02 billion tons of once stored carbon back into the atmosphere each year.

As a graduate student in North Carolina, I wanted to quantify what degradation and loss of wetlands would mean for the carbon stored within the soils of my state’s wetlands. My graduate research focuses on how effects from sea level rise including increased saltwater intrusion and erosion will affect existing carbon stores and future storage capacity of tidal wetlands within the Cape Fear River Estuary (CFRE).

Dark soil core rich in carbon from the Cape Fear River wetland.

By determining where carbon stores are located within the estuary and how fast they are growing I can determine – along with the current rate of sea level rise in the region – which carbon stores are at risk of being degraded and transformed from a carbon sink to a carbon source. Carbon storage is increasingly becoming one of the most important ecosystem services our coastal ecosystems can perform. As sea level rise continues to pose problems for our nation’s coastal communities, the ability of wetlands to evolve over time – unlike man-made structures which stay stagnant – is an incredibly powerful tool. My hope is by understanding how carbon stores within wetlands of the CFRE function and are impacted by effects of sea level rise, results from my research can inform local governments, land managers and environmental policy makers, and ensure future protection of these wetlands as valued ecosystems for the carbon they store.

Learn more about Blue Carbon

References

Fry, Brian. Stable Isotope Ecology. Springer, 2008.

Giese, G.L., Wilder, H.B. & Parker, G.G. Hydrology of Major Estuary & Sounds of North Carolina. U.S. Geological Survey- Water    Supply Paper 2221. 19-37.

McLeod, E., Chmura, G.L., Bouillon, S., et al. (2011). A blueprint for blue carbon: toward an improved understanding of the role of vegetated coastal habitats in sequestering CO2. Frontiers in Ecology. 9:10:552-560.

McTigue, N., Davis, J., Rodriguez, A. B.,McKee, B., Atencio, A., & Currin, C. (2019). Sea level rise explains changing carbon            accumulation rates in a salt marsh over the past two millennia. Journal of Geophysical Research: Biogeosciences, 124.

Nittrouer, C.A., Sternberg, R.W., Carpenter, R. & Bennett, J.T. (1979). The use of Pb-210 geochronology as a sedimentological     tool: application to the Washington continental shelf. Marine Geology. 31: 297-316.

About the Author

A graduate student at UNC-Wilmington, Mackenzie Taggart [she, her] studies coastal wetland dynamics as a part of the Coastal & Estuarine Studies Lab under the advisement of Dr. Devon Eulie. After graduating in 2022 with a Masters in Marine Science, she hopes to continue her work by developing science-based policies to protect these valuable coastal ecosystems and the carbon they store.