Guest Op-Ed: Blue Carbon and Belle Isle Marsh

By Ana Tavares Leary and Julie Conroy 

Climate change is currently the most pressing environmental crisis of our time. However, there is a largely overlooked solution to this problem; carbon sequestration (storage) that is provided by wetlands.

Carbon sequestration is the process of capturing carbon dioxide from the atmosphere, measured as a rate of carbon uptake per year. Carbon storage is the long-term confinement of carbon in plant materials and sediment, measured as a total weight of carbon stored.

Fresh and saltwater wetlands hold a disproportionate amount of the earth’s total carbon emissions within their soil; approximately 20 to 30% of the estimated 1,500 petagrams of global soil carbon (one “pg” is equal to one billion tons), despite occupying only 5% to 8% of the Earth’s land surfaces. Wetlands in the conterminous United States store a total of 11.52pg.

Salt marshes are coastal ecosystems that are flooded and drained by salt water brought in by the tides and are dominated by salt-tolerant plants. Belle Isle Marsh is one of the last remaining salt marshes within Boston Harbor. It provides a myriad of benefits  including reducing the impact of storms to developed areas, filtering pollutants from water and air, supporting healthy fisheries, providing habitat for over 271 species of birds, improving public health and well-being, and mitigating climate change impacts by storing significant amounts of carbon emissions. Salt marshes also play a critical role in protecting development investments and the regional economies. According to a study conducted by the University of California, San Diego in 2020, salt marshes provide storm protection services averaging $36 million per km2 over a 30-year period. 

Salt marshes have been found to be one of the most effective carbon sinks on the planet, able to sequester carbon up to 10 times faster than tropical rainforests. This carbon storage is known as “blue carbon.” Globally, it is estimated that coastal ecosystems—salt marshes, mangroves, and seagrass meadows—are responsible for sequestering up to 1.4 billion tons of carbon per year. This is equivalent to the annual emissions of 553 million cars. Salt marshes can sequester about 1,940 pounds of carbon per acre per year. Belle Isle Marsh, therefore, sequesters approximately 350 tons of carbon per year, or the equivalent of emissions from 319,000 miles of air travel.

Despite the many benefits that salt marshes provide, they face many threats including their elimination and degradation by development and polluted waterways from stormwater runoff and industrial waste. The destruction of salt marshes also releases stored carbon back into the atmosphere, contributing to climate change (instead of fighting it).

The most important way to protect these critical ecosystems, and all the benefits they offer, is to implement policies that protect these ecosystems from destruction by adjacent development. Additionally, if wetlands are degraded, it is important to restore them by whatever method is needed. There are also several market-based approaches that can be used to incentivize the protection and preservation of salt marsh ecosystems, such as carbon credits and payments for wetland protection and restoration. 

The protection and restoration of all wetlands should be an essential part of any comprehensive climate change mitigation strategy. By recognizing the value of wetlands and promoting their protection and restoration, we can work towards a healthier and more sustainable future for ourselves and future generations. For further information, please visit our website:

Ana Tavares Leary and Julie Conroy are with the Friends of Belle Isle Marsh

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