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The buzz around blue carbon

Marea E. Hatziolos's picture

Photo credit: J. TamelanderThe delegates and observers at the COP16 in Cancun are getting an earful about Blue Carbon—shorthand for atmospheric carbon sequestered in the earth’s coastal and nearshore environments. Oceans Day at Cancun will feature a session on Blue Carbon, and briefs, and blogs by ocean advocates are circulating on the net and at side events. The reason for the buzz is that coastal wetlands, including tidal salt marshes, estuaries and river deltas, mangroves and sea grass beds are highly efficient at taking up CO2 from the atmosphere and converting it into organic material—then storing it in the soil. In fact, the root systems and sediment layers which build up as this organic material is generated, broken down and deposited, are up to ten times more rich in carbon than the biomass above the surface.

 

This makes coastal wetlands even better at sequestering carbon than tropical forests. And, unlike their counterparts on land whose net growth peaks when the forest matures, wetland vegetation continues to grow and sequester carbon in the soil as long as sediments are deposited and the environment remains healthy. This is why Blue Carbon is being brought into the international dialogue on carbon emission offsets and the domain of REDD+ eligible activities. A statement, signed by 55 marine and environmental stakeholders from 19 countries has been presented to the COP for action.

 

Like peat lands, tidal salt marshes and estuaries can turn from natural sinks to net emitters of greenhouse gasses when they are drained, burned or converted for agriculture, and the soil becomes exposed to air. Mangroves wetlands that are starved of sediment and freshwaters flows through damming of rivers, or converted into shrimp ponds or paddy or beachfront property for five star hotels no longer store carbon. Instead they emit methane, a GHG four times as potent as carbon dioxide, and highly explosive. Less than two weeks ago, a luxury hotel built on top of a mangrove wetlands not far from the where the COP 16 is deliberating in Cancun, suffered a massive explosion and loss of life.

 

Across the Ocean and several continents away in the Bay of Bengal, mangroves play another, more vital role. Battered by cyclones and storm surge, Bangladesh invested in shoring up its exposed coastline through a massive mangrove aforestation program. This proved to be providential. When Super Cyclone Sidr stuck in 2007—the strongest named cyclone on record in the Bay of Bengal—the loss of life was around 4-5,000 people. One year later, in Myanmar, Cyclone Nargis whipped across the Ayerwaddy Delta at similar wind speeds, but without the native mangrove forests to act as a shield—these having been cleared over decades to make room for rice paddy—over 140,000 people lost their lives in the storm surge.

 

Seagrass beds, which are often found adjacent to mangroves in sheltered bays along warm water coasts, also store large amounts of carbon in their root systems and in the soil they bind. This is in addition to stabilizing sediment and providing food for sea turtles, manatees and other important herbivores at the base of the food chain. So, besides stripping CO2 from the atmosphere, coastal wetlands provide a myriad of co-benefits to society that need to be recognized, valued and accounted for. While protection of these natural assets should be the first order of business, restoring degraded wetlands can pay huge dividends in terms of recovering natural carbon sinks, reducing emissions and building resilience into vulnerable coastal communities.

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