The identification and accurate quantification of sinks or sources of GHG has become a key challenge for scientists and policy makers groups working on climate change or global warming. The creation of a hydro-reservoir while damming a river for power generation converts the terrestrial ecosystems into aquatic ecosystem and subsequently decomposition of flooded terrestrial soil organic matter stimulates GHG productions and thereby emissions to atmosphere. Tropical or subtropical hydroelectric reservoirs are more significant sources of GHG than boreal or temperate one. The number of hydroelectric reservoirs continues to increase at fast pace specially in the tropical or sub-tropical regions which still hold significant amount of hydropower resources to be exploited. In this context, we study the subtropical hydroelectric Nam Theun 2 (NT2) Reservoir, a complex-structuraldesigned, created on the Nam Theun River in Laos PDR. The main aims of our study are to: (1) Study the GHG dynamics (CH4, N2O and CO2) in the reservoir and in the whole area of influence (downstream and drawdown areas), (2) explore the effectiveness of different methodology (eddy covariance, floating chamber, submerged funnel and thin boundary layer) to assess of GHG emission from a hydroelectric reservoir, (3) determine the environmental controls on the different emission terms; (4) attempt to determine the first net GHG budget of a subtropical hydroelectric reservoir.
