11 March 2006 / NewScientist Magazine issue 2542
MANGROVE forests play a major role in pumping carbon from the atmosphere into the ocean, and may help regulate greenhouse gas concentrations. The trouble is, they are disappearing.
Mangroves are the intertidal forests that fringe many tropical coastlines. Like all plants, mangroves fix carbon dioxide from the air through photosynthesis and return organic material to the soil when they decompose. But because their roots and soil are regularly washed by tides, much of this organic carbon leaches into the ocean.
Researchers led by Thorsten Dittmar of Florida State University in Tallahassee measured how much mangroves contribute to the organic carbon dissolved in ocean waters off the coast of Brazil. They estimated that, worldwide, mangroves contribute a hefty 10 per cent to the ocean's dissolved organic carbon (Global Biogeochemical Cycles, DOI: 10.1029/2005GB002570).
This is roughly equal to the amount entering the ocean from the Amazon river, the largest single source of dissolved organic carbon. Much of the carbon produced by mangroves is in the form of molecules that are highly resistant to decomposition, so it is likely to remain in the ocean for decades instead of being returned to the atmosphere as carbon dioxide.