Carbon dioxide and methane emissions and the carbon budget of a 10-year old tropical reservoir (Petit Saut, French Guiana)

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Read Full Article (file size: 616926 bytes) Cited by GLOBAL BIOGEOCHEMICAL CYCLES, VOL. 19, GB4007, doi:10.1029/2005GB002457, 2005 Carbon dioxide and methane emissions and the carbon budget of a 10-year old tropical reservoir (Petit Saut, French Guiana) Gwenaël Abril UMR 5805, CNRS, Environnements et Paléoenvironnements Océaniques, Département de Géologie et Océanographie, Université Bordeaux 1, Talence, France Frédéric Guérin UMR 5805, CNRS, Environnements et Paléoenvironnements Océaniques, Département de Géologie et Océanographie, Université Bordeaux 1, Talence, France Laboratoire d'Aérologie, UMR 5560, CNRS, Observatoire de Paris, Toulouse, France Sandrine Richard Laboratoire Environnement, Hydreco, Kourou, France Robert Delmas Laboratoire d'Aérologie, UMR 5560, CNRS, Observatoire de Paris, Toulouse, France Corinne Galy-Lacaux Laboratoire d'Aérologie, UMR 5560, CNRS, Observatoire de Paris, Toulouse, France Philippe Gosse Recherche et Développement, Electricité de France, Chatou, France Alain Tremblay Hydro-Québec Production, Direction Barrages et Environnement, Unité Environnement Montréal, Montreal, Quebec, Canada Louis Varfalvy Hydro-Québec Production, Direction Barrages et Environnement, Unité Environnement Montréal, Montreal, Quebec, Canada Marco Aurelio Dos Santos Instituto Alberto Luis Coimbra de Pós Graduação e Pesquisa em Engenharia, Universidade Fluminense Rio de Janeiro, Rio de Janeiro, Brazil Bohdan Matvienko Centro de Recursos Hídricos e Ecologia Aplicada, Universidade São Paulo, Sao Paulo, Brazil Abstract The emissions of carbon dioxide (CO₂) and methane (CH₄) from the Petit Saut hydroelectric reservoir (Sinnamary River, French Guiana) to the atmosphere were quantified for 10 years since impounding in 1994. Diffusive emissions from the reservoir surface were computed from direct flux measurements in 1994, 1995, and 2003 and from surface concentrations monitoring. Bubbling emissions, which occur only at water depths lower than 10 m, were interpolated from funnel measurements in 1994, 1997, and 2003. Degassing at the outlet of the dam downstream of the turbines was calculated from the difference in gas concentrations upstream and downstream of the dam and the turbined discharge. Diffusive emissions from the Sinnamary tidal river and estuary were quantified from direct flux measurements in 2003 and concentrations monitoring. Total carbon emissions were 0.37 ± 0.01 Mt yr⁻¹ C (CO₂ emissions, 0.30 ± 0.02; CH₄ emissions, 0.07 ± 0.01) the first 3 years after impounding (1994–1996) and then decreased to 0.12 ± 0.01 Mt yr⁻¹ C (CO₂, 0.10 ± 0.01; CH₄, 0.016 ± 0.006) since 2000. On average over the 10 years, 61% of the CO₂ emissions occurred by diffusion from the reservoir surface, 31% from the estuary, 7% by degassing at the outlet of the dam, and a negligible fraction by bubbling. CH₄ diffusion and bubbling from the reservoir surface were predominant (40% and 44%, respectively) only the first year after impounding. Since 1995, degassing at an aerating weir downstream of the turbines has become the major pathway for CH₄ emissions, reaching 70% of the total CH₄ flux. In 2003, river carbon inputs were balanced by carbon outputs to the ocean and were about 3 times lower than the atmospheric flux, which suggests that 10 years after impounding, the flooded terrestrial carbon is still the predominant contributor to the gaseous emissions. In 10 years, about 22% of the 10 Mt C flooded was lost to the atmosphere. Our results confirm the significance of greenhouse gas emissions from tropical reservoir but stress the importance of: (1) considering all the gas pathways upstream and downstream of the dams and (2) taking into account the reservoir age when upscaling emissions rates at the global scale. Received 12 January 2005; accepted 15 June 2005; published 13 October 2005. Keywords: greenhouse gases; hydroelectricity; reservoir; tropical forest. Index Terms: 0429 Biogeosciences: Climate dynamics (1620); 0490 Biogeosciences: Trace gases; 1632 Global Change: Land cover change. Read Full Article (file size: 616926 bytes) Cited by Citation: Abril, G., F. Guérin, S. Richard, R. Delmas, C. Galy-Lacaux, P. Gosse, A. Tremblay, L. Varfalvy, M. A. Dos Santos, and B. Matvienko (2005), Carbon dioxide and methane emissions and the carbon budget of a 10-year old tropical reservoir (Petit Saut, French Guiana), Global Biogeochem. Cycles, 19, GB4007, doi:10.1029/2005GB002457. Copyright 2005 by the American Geophysical Union.

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