Avoided coastal wetland impacts
Seagrass beds, mangroves and tidal marshes store large amounts of carbon, despite making up a relatively small portion of the planet’s total land area. They trap sediment and draw in carbon as they grow, much of this is later transferred into the rich organic soils held by their roots. The carbon can remain in the soil for thousands of years, making it one of the longest-term climate mitigation solutions. Around the globe, many of these coastal wetlands are converted for agriculture, aquaculture or urban development. The loss of healthy wetlands releases stored carbon into the atmosphere. Polluted runoff can also degrade the health of coastal wetlands, leading to an eventual release of carbon trapped in the soil. Preventing conversion and maintaining the health of coastal wetlands will allow these areas to continue storing and absorbing carbon from the atmosphere.
Coastal wetlands, also known as ‘blue carbon’ ecosystems include mangroves, tidal salt marshes and seagrass meadows. There are approximately 14.5 million hectares of mangroves, but there are still gaps in the data for mapping the extent of salt marshes and seagrasses: the estimated total cover of these three ecosystems is between 30 and 120 million hectares globally–less than 1% of the world’s total land area. However, they are being lost at an alarming rate: scientists estimate that worldwide, a seagrass meadow the size of a soccer pitch may be lost every 30 minutes.
Avoiding the conversion and degradation of coastal wetlands would prevent the release of 273 million tonnes of carbon dioxide equivalent per year. That’s comparable to the emissions from 58 million passenger vehicles per year.
Maintaining the health of coastal wetlands will require strategies specific to each region and each wetland type. In areas such as Southeast Asia, for example, where a portion mangrove forests are converted for aquaculture, new regulations and viable economic alternatives will be necessary to curb wetland loss.
Other challenges are technical. The rate at which salt marshes and seagrass beds are being lost is still uncertain. In particular, much more work is needed to map the locations and size of seagrass beds and salt marshes globally. National level maps do exist in a lot of places but there are gaps such as parts of African and South America.
Avoiding coastal wetland conversion is a low-cost climate mitigation pathway. Many interventions (such as establishing protected areas, improving land tenure and enforcing land-use laws) can be put into place immediately. In the United States, for example, many states have enacted laws to protect tidal marshes, and Florida’s Mangrove Trimming and Preservation Act protects mangroves on uninhabited islands that are publicly owned or on lands set aside for conservation and preservation. Similar laws could be established to protect coastal wetlands around the world.
Spotlight: Kimbe Bay
Papua New Guinea’s Kimbe Bay is rich in marine habitats, including mangroves, seagrasses and coral reefs. For more than 20 years, The Nature Conservancy has worked with local communities and partners to protect these habitats and the thousands of people who rely on them for their food and livelihoods.
The Conservancy helped design the Kimbe Bay Marine Management Area to protect the island’s marine habitats, including its seagrass beds. Yet the region’s coastal wetlands were still threatened by forestry, infrastructure developments and runoff and sedimentation from agriculture. The Conservancy is working with partners and governments to implement land-use practices to maintain the health of the bay’s coastal wetlands and marine environments.
Using a combination of water quality improvements and habitat restoration coastal wetlands in Tampa Bay, Florida has achieved their equivalent area from 1950. Since 2006, coastal restoration efforts in Tampa Bay have sequestered nearly 354,000 tonnes CO2 equivalents and are expected to sequester 74 million tonnes of CO2 equivalents by 2100; the same as removing over 15 million cars from the roads.