MARINHO, CC.; CAMPOS, EA.; GUIMARAES, JRD. and ESTEVES, FA.. Effect of sediment composition on methane concentration and production in the transition zone of a mangrove (Sepetiba Bay, Rio de Janeiro, Brazil). Braz. J. Biol. [online]. 2012, vol.72, n.3, pp. 429-436. ISSN 1519-6984. http://dx.doi.org/10.1590/S1519-69842012000300003.
Natural sources such as mangrove sediments, also release green-house gases
The debate on climate change has focused attention on man-made green-house gases (GHG) such as CO2, but GHG are also emitted by natural sources such as mangrove sediments. Researchers from UFRJ measured the concentration and production of methane, a GHG that is 20 times more efficient than CO2 in producing green-house effect, in sediments of a mangrove transect in Coroa Grande, on the southern coast of the state of Rio de Janeiro.
The sampling included one area colonized by the seagrass Spartina, one area at the center of the tidal range and one at the limit of tidal amplitude, colonized by Rhizophora mangrove trees. Both in-situ methane concentrations and production rates upon laboratory incubation of sediments were higher in the sediments influenced by Rhizophora. The latter were richer in carbon and their nitrogen and phosphorous proportions suggest that sediment carbon was produced in the mangrove itself.
According to Claudio Cardoso Marinho, from the Laboratório de Limnologia, UFRJ and first author of the study published in Rev. Bras. Biol., "Mangrove are very important in the carbon cycle, particularly in carbon fixation, due to their high biomass and productivity. In their sediments, organic matter decomposition is mediated by microorganisms that respond in complex ways to the availability and quality of organic matter and to the wide variations in oxygen and salinity that are common in mangrove ecosystems. This complex microbiological community includes bacteria that are capable of producing methane as well as bacteria that feed on it. We should not demonize mangroves because they produce some methane, they are already under sufficient pressure worlwide. These ecosystems, as well as coastal lagoons and other wetland systems, have high biodiversity, support fisheries in the adjacent marine waters and deliver different important environmental services."
The author also pinpoints that despite the relative simplicity of methane emission measurements, we are far from a good inventory of the emissions of this and other GHGs by different ecosystems in Brazil or elsewhere, and still have a poor understanding of how these emissions respond to man-made impacts.
Jean R.D. Guimarães