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La Tour du Valat

Institut de recherche pour la conservation des zones humides méditerranéennes

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Titre :	Carbon Dioxide and Methane Emissions from Mangrove-Associated Waters of the Andaman Islands, Bay of Bengal
Auteurs :	Neetha Linto, Auteur ; J. Barnes, Auteur ; Ramesh Ramachandran, Auteur ; Jennifer Divia, Auteur ; Purvaja Ramachandran, Auteur ; R. C. Upstill-Goddard, Auteur
Type de document :	Article
Dans :	Estuaries and Coasts (37(2) MAR 2014)
Article en page(s) :	381-398
Résumé :	We estimated CO2 and CH4 emissions from mangrove-associated waters of the Andaman Islands by sampling hourly over 24 h in two tidal mangrove creeks (Wright Myo; Kalighat) and during transects in contiguous shallow inshore waters, immediately following the northeast monsoons (dry season) and during the peak of the southwest monsoons (wet season) of 2005 and 2006. Tidal height correlated positively with dissolved O-2 and negatively with pCO(2), CH4, total alkalinity (TAlk) and dissolved inorganic carbon (DIC), and pCO(2) and CH4 were always highly supersaturated (330-1,627 % CO2; 339-26,930 % CH4). These data are consistent with a tidal pumping response to hydrostatic pressure change. There were no seasonal trends in dissolved CH4 but pCO(2) was around twice as high during the 2005 wet season than at other times, in both the tidal surveys and the inshore transects. Fourfold higher turbidity during the wet season is consistent with elevated net benthic and/or water column heterotrophy via enhanced organic matter inputs from adjacent mangrove forest and/or the flushing of CO2-enriched soil waters, which may explain these CO2 data. TAlk/DIC relationships in the tidally pumped waters were most consistent with a diagenetic origin of CO2 primarily via sulphate reduction, with additional inputs via aerobic respiration. A decrease with salinity for pCO(2), CH4, TAlk and DIC during the inshore transects reflected offshore transport of tidally pumped waters. Estimated mean tidal creek emissions were similar to 23-173 mmol m(-2) day(-1) CO2 and similar to 0.11-0.47 mmol m(-2) day(-1) CH4. The CO2 emissions are typical of mangrove-associated waters globally, while the CH4 emissions fall at the low end of the published range. Scaling to the creek open water area (2,700 km(2)) gave total annual creek water emissions similar to 3.6-9.2 x 10(10) mol CO2 and 3.7-34 x 10(7) mol CH4. We estimated emissions from contiguous inshore waters at similar to 1.5 x 10(11) mol CO2 year(-1) and 2.6 x 10(8) mol CH4 year(-1), giving total emissions of similar to 1.9 x 10(11) mol CO2 year(-1) and similar to 3.0 x 10(8) mol CH4 year(-1) from a total area of mangrove-influenced water of similar to 3 x 10(4) km(2). Evaluating such emissions in a range of mangrove environments is important to resolving the greenhouse gas balance of mangrove ecosystems globally. Future such studies should be integral to wider quantitative process studies of the mangrove carbon balance.

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