Diffusive emission of methane and carbon dioxide from two hydropower reservoirs in Brazil

Emissões difusivas de metano e de dióxido de carbono oriundas de dois reservatórios hidrelétricos

The role of greenhouse gas emissions from freshwater reservoirs and their contribution to increase greenhouse gas concentrations in the atmosphere is currently under discussion in many parts of the world. We studied CO₂ and CH₄ diffusive fluxes from two large neotropical hydropower reservoirs with different climate conditions. We used floating closed-chambers to estimate diffusive fluxes of these gaseous species. Sampling campaigns showed that the reservoirs studied were sources of greenhouse gases to the atmosphere. In the Serra da Mesa Reservoir, the CH₄ emissions ranged from 0.530 to 396.96 mg.m^–2.d^–1 and CO₂ emissions ranged from –1,738.33 to 11,166.61 mg.m^–2.d^–1 and in Três Marias Reservoir the CH₄ fluxes ranged 0.720 to 2,578.03 mg.m^–2.d^–1 and CO₂ emission ranged from -3,037.80 to 11,516.64 to mg.m^–2.d^–1. There were no statistically significant differences of CH₄ fluxes between the reservoirs, but CO₂ fluxes from the two reservoirs studied were significantly different. The CO₂ emissions measured over the periods studied in Serra da Mesa showed some seasonality with distinctions between the wet and dry transition season. In Três Marias Reservoir the CO₂ fluxes showed no seasonal variability. In both reservoirs, CH₄ emissions showed a tendency to increase during the study periods but this was not statistically significant. These results contributed to increase knowledge about the magnitude of CO₂ and CH₄ emission in hydroelectric reservoirs, however due to natural variability of the data future sampling campaigns will be needed to better elucidate the seasonal influences on the fluxes of greenhouse gases.

hydropower; dissolved organic carbon; greenhouse gas effect; lakes; reservoirs; CO₂ emissions