No abstract

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 CO 2 and CH 4 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 CH 4 emissions ranged from 0.530 to 396.96 mg.m -2 .d -1 and CO 2 emissions ranged from -1,738.33 to 11,166.61 mg.m -2 .d -1 and in Três Marias Reservoir the CH 4 fluxes ranged 0.720 to 2,578.03 mg.m -2 .d -1 and CO 2 emission ranged from -3,037.80 to 11,516.64 to mg.m -2 .d -1 . There were no statistically significant differences of CH 4 fluxes between the reservoirs, but CO 2 fluxes from the two reservoirs studied were significantly different. The CO 2 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 CO 2 fluxes showed no seasonal variability. In both reservoirs, CH 4 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 CO 2 and CH 4 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.Keywords: hydropower, dissolved organic carbon, greenhouse gas effect, lakes, reservoirs, CO 2 emissions. Emissões difusivas de metano