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blue carbon

New evidence on coastal wetlands as carbon sinks

Marea E. Hatziolos's picture

In the corridors of COP 16 in Cancun last December, `blue carbon’ was being discussed in the context of Reduced Emissions from Deforestation and Forest Degradation (REDD+). The notion that wetlands and near-shore marine habitats constitute significant but largely unaccounted for natural sinks of atmospheric CO2 was just beginning to surface. Since then, there has been a surge in interest in Coastal Carbon Sinks, as evidence begins to mount on their ability to suck up CO2 and store it in their biomass and in deep sub-surface soil layers. A recently published study in Nature GeoScience cites evidence from field measurements that mangroves in Indonesia can actually store carbon at four times the rate of their terrestrial forest counterparts.

In contrast to terrestrial forests, mangroves and other wetlands store most of the carbon below ground, in a rich organic soil layer, which can run several meters deep. When this soil layer is disturbed—as happens when wetlands are drained or converted for other land use—huge amounts of carbon are released into the atmosphere in the form of CO2, and centuries or millennia of accumulated carbon can be emitted over the course of a few decades.

The extent of these emissions in estuaries and deltas, is highlighted in a detailed World Bank technical report. The preliminary findings of the report were summarized for decision-makers in a brief issued last December at the COP 16. The technical report, Mitigating Climate Change through Restoration and Management of Coastal Wetlands and Near-shore Marine Ecosystems: Challenges and Opportunities, is available on line and is being launched today in Indonesia at a Workshop on Tropical Wetland Ecosystems of Indonesia,in Bali.

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.