The accumulation of greenhouse gasses in the atmosphere is nothing new. But with other symptoms of climate change becoming increasingly forceful, processes we rely on, such as carbon sequestration, are becoming less dependable. Carbon sequestration is responsible for storing carbon in different sinks during the carbon cycle. After a long period of time, that carbon is respired back into the atmosphere, creating a global balance. With excess amounts of greenhouse gasses in the air, the process of sequestering carbon has become much more vital for maintaining a clean atmosphere. To reduce greenhouse gas emissions, countries are increasingly turning to land-based climate solutions, which rely on using and protecting large plots of land that are known to be carbon sinks. Not only have these pledges been deemed difficult due to the lack of greenspace, but now landscapes that were once seen as dependable carbon sinks are becoming carbon producers.
Some of the world’s best carbon sinks are salt marshes which “sequester carbon at a rate ten times greater than mature tropical forests,” according to the National Oceanic and Atmospheric Administration. Carbon that is captured by mangroves, seagrass beds, and marshes is called “coastal blue carbon” because it is “captured by living coastal and marine organisms and stored in coastal ecosystems.” Sequestration typically happens in salt marshes because the plants there grow rapidly, so they capture more carbon dioxide through photosynthesis. Additionally, salt marsh soil is mostly anaerobic, meaning it does not contain much oxygen. This allows carbon to decompose slowly, keeping it trapped for longer. With salt marshes and other coastal ecosystems disappearing due to sea level rise, reliance on these systems as carbon sinks is becoming increasingly uncertain. Studies in New England and Maryland have found that salt marshes are now releasing more carbon as a result of sea level rise. Although salt marshes can be found in large open meadows, they are most commonly small, fringing wetlands which are found between the coast and a body of salt water. These salt marshes make up “half the total area of wetlands in coastal portions of New England” and have been known to play a vital role in the environment. However, according to a new study from the Woods Hole Oceanographic Institution, small coastal salt marshes are “less commonly studied compared to larger open meadow systems.” Many scientists argue that more extensive research needs to be done on salt marshes. Additionally, there is little information about the exchange between carbon and methane as it circulates through the atmosphere and into the ground.
The process of greenhouse gasses being released into the atmosphere is called a flux, and a recent study found that higher global temperatures have led to more carbon fluxes. Michigan State University’s Department of Forestry describes a carbon flux as “the movement of carbon between land, oceans, atmosphere, and living things,” but if this process is disturbed by climate change, more carbon will be released into the atmosphere than is stored.
The study at Woods Hole found that sea-level rise creates an increase in low altitude marshes, which produce more carbon. Essentially, as the ocean rises, so do the marshes, and the high altitude marshes become low marshes. This change is detrimental because low salt marshes were found to respire more carbon than high salt marshes, making them less reliable as carbon sinks. Another study in New England found that “impaired coastal wetlands display diminished ecosystem functions and services, and their effect on global climate may switch, from carbon sinks to carbon dioxide and methane source.” Because carbon sequestration is a vital step in reducing greenhouse gas emissions in the atmosphere, it is necessary to protect these salt marshes and continue to study them. A study at the University of Delaware also found a coastal salt marsh to be a carbon source, challenging the understanding of salt marshes as carbon sinks. “This tidal salt marsh was a net source of carbon to the atmosphere, with higher global warming potentials from CH4 emissions than CO2 emissions,” the study said. Not only did the evidence agree that salt marshes are becoming emitters of greenhouse gasses, but that more studies need to be done year-round.
The next step is simply protecting these coastal ecosystems. Since 1776, “Boston has lost 81% of its salt marsh.” Along with this significant loss, there has been an increase in the release of carbon emissions. Studying how climate change affects ecosystems is necessary to learn how to mitigate impacts. Not only will preserving salt marshes contribute to additional data collection and safeguard biodiversity, but restoration of salt marshes in degraded habitats “can ensure equity and justice through food security and sustainability,” according to a 2022 study. The study outlined the importance of using a comprehensive understanding of the environment and its ecosystems to combat social and environmental issues. It argues that none of that can be done without preserving influential ecosystems such as salt marshes. By increasing scientific research of the respiration of carbon in salt marshes as a result of climate change, scientists will gain a deeper understanding of how to mitigate those effects and how to stop similar issues from happening. This work cannot be done without preserving and restoring salt marshes. Perhaps this new understanding of salt marshes’ release of carbon will push scientists to complete more comprehensive research on the impacts of climate change in different ecosystems around the world.
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