Coastal wetland restoration
Coastal wetlands–mangroves, marshes, and seagrass beds–store huge amounts of carbon despite their relatively small total area. For example, while only occupying approximately 14.5 million hectares of tropical coastlines, mangroves are among the most carbon rich forests in the world on a per-hectare basis.
The true potential for mangrove climate mitigation rests in the soil, where, left undisturbed, the carbon can remain for centuries or more. Yet around the world, many coastal wetlands are being damaged by human activity. Drainage and pollution are degrading mangroves, salt marshes and seagrass beds at an alarming rate, releasing carbon that has been stored for millennia into the atmosphere.
Fortunately, coastal wetlands can often be restored by reducing pollution, replanting lost vegetation and/or repairing the natural flow of water.
According to the latest research, some 30 million hectares of degraded coastal wetlands could be restored–an area roughly the size of Italy. Of that total, 59 percent is seagrass beds, 34 percent is mangroves and 7 percent is salt marsh.
Restoring those damaged wetlands could sequester up to 200 million tonnes of carbon dioxide equivalent per year (MtCO2e/year). That’s comparable to the emissions from 43 million passenger vehicles per year.
Restoring wetlands can be straightforward from a technical point of view. Mangroves, for instance, are easily planted, but in many cases restoring the hydrology alone is all that is needed to allow natural recolonization. But the opportunity cost for such restoration is sometimes high where former wetlands are now developed, or used in productive aquaculture.
Another common challenge comes from obscure land tenure, which has greatly hindered some efforts to ascertain ownership or to undertake restoration in appropriate locations relative to the tidal cycle.
In addition, seagrass restoration is largely dependent on improving on-shore watershed and nutrient management practices. Such management policies can be expensive and often take many years to implement fully.
Due to the technical costs of restoration, re-establishing coastal wetlands can be a relatively high-cost pathway although it varies according to ecosystem and geography. For example, mangrove restoration in developing countries is low cost compared to tidal marsh restoration in the US. Nevertheless, it’s a pathway that is available to implement right now. Indeed, efforts to restore mangroves, salt marshes and seagrasses are already underway in many parts of the world, and there are large areas, particularly of abandoned or unproductive aquaculture where restoration would yield rapid returns in both carbon and co-benefits.
In future, mangrove restoration is likely to be most important in areas that have experienced high rates of loss, including South Central America, Indonesia, Papua New Guinea and the Philippines. Seagrass restoration will be important in the Eastern U.S. and the South Pacific. For salt marshes, the restoration benefit will be greatest in the U.S., which contains more than 80 percent of the world’s salt marshes.
Spotlight: The Virginia Coast Reserve, United States
The 65-mile long barrier islands of the Virginia Coast Reserve (VCR) help buffer Eastern Shore communities from storms, as well as thousands of acres of pristine salt marshes, vast tidal mudflats, shallow bays, and productive forest uplands. It is the longest expanse of coastal wilderness remaining on the eastern seaboard of the United States, known globally as an important concentration area for migratory and breeding coastal birds.
The Nature Conservancy is working with the Virginia Institute of Marine Science on the largest seagrass restoration project in the world. Eelgrass is a simple seagrass that once thrived in the coastal bays of Virginia. In 1933, an outbreak of disease and a major hurricane virtually wiped it out. However, since 1999, the Seaside Seagrass Community Restoration Program has been conducting successful efforts to restore eelgrass in the nearby coastal bays–disseminating more than 30 million seeds so that the species is now thriving across many of the VCR bays .
These findings could be critical because, in almost every coastal region around the world, the area of seagrass beds is shrinking due to seafloor disturbance and impaired water quality, especially nitrogen from coastal lawns and septic systems.