The Earth’s beautiful, ecologically-rich coastal wetlands are enormous long-term carbon sinks, a new study reports. By the same token, the estimated 284 million acres of wetlands worldwide, could release untold tons of carbon into the atmosphere for every acre destroyed. The report, published in “Frontiers in Ecology and the Environment,” suggests wetlands could be a key resource for carbon sequestration, because, while they cover less area than terrestrial forests, they store far more carbon per acre. This makes them an critical site in the battle with climate change. But an estimated 3 percent of the Earth’s wetlands are being drained and developed each year, releasing vast quantities of carbon into the atmosphere. For this reason, protecting, reclaiming and improving coastal ecosystems is essential for carbon mitigation.
Wetlands as blue carbon sink
The largest reservoir of blue carbon, carbon stored in aquatic ecosystems, is the Earth’s oceans. An estimated 20-35 percent of carbon released due to human activity is absorbed there. However, compared with oceans, the study says, coastal wetlands are far easier for humans to access, regulate and manage. This makes wetlands an essential target for blue carbon storage.
Composition & blue carbon storage in wetlands
Coastal wetlands have three distinct ecosystems: mangroves, tidal marshes and seagrasses. Mangroves are tropical forests that flood daily as tides move in and out around them. Tidal marshes consist of small shrubs and plants found in estuaries, where rivers and oceans meet. These plants are unique because they thrive in varying degrees of salinity. Seagrasses are dense underwater meadows of flowering plants stretching along the shallow coastline waters.
These ecosystems sequester and store large amounts of blue carbon by trapping carbon-rich sediments and debris in their complex root systems. Because of tidal action, which inhibits microbial activity, there is less decomposition of organic material in the wetlands, which aides in carbon accumulation in the soil.
Carbon is also stored in woody bio-mass which can remain for years or even decades but it accounts for only a small amount of the total sequestration.
Wetland soils, on the other hand, can store carbon undisturbed for millennia. Holding 50-90 percent of the blue carbon in the wetlands, soil is also the largest storage location. It’s estimated that as much as 25 billion metric tons of carbon is currently being held in the top one meter of wetland soils worldwide. Since the depth of soil in wetlands is several meters deep, this figure is thought to be grossly underestimated.
The flip side of the enormous amount of carbon stored, is how much carbon is released when coastal wetlands are destroyed by development.
When mangrove forests and tidal marshes are drained, a massive amounts of carbon is released. Without tidal action, microbes in the soil begin decomposing organic material through oxidation, allowing carbon to escape into the atmosphere.
Dredging and trawling destroys seagrass meadows and disturbs the seabed, allowing stored carbon to be released.
Protecting coastal wetlands
While protection of our vast coastal wetlands is largely the responsibility of local, state and federal governing agencies, the public plays a huge role in conservation efforts. As recent events have demonstrated, government agencies do, indeed, respond to public input and pressure. Finding out more about these agencies can be found in the Knowledge in Action section on How you can protect & restore coastal wetlands.
In addition to participating in the policy-making aspect of conservation, the Knowledge in Action section can give you a jumping off point for other ways you can help protect coastal wetlands. In doing so, you can help curb the impact of climate change for you and for generations to come.