CO₂emissions from a tropical hydroelectric reservoir (Balbina, Brazil)

Abstract

[1] Hydroelectric reservoirs can release significant quantities of CO 2 , but very few results are available from the tropics. The objective of the present study was to estimate the emission of CO 2 from the Balbina hydroelectric reservoir in the central Brazilian Amazon. Diffusive and ebullitive emissions were estimated at regular intervals, both above and below the dam, using a combination of static chambers and submerged funnels. Gas releases immediately below the dam were calculated as the difference between gas flux at the entrance and the outflow of the hydroelectric turbines. An inundation model derived from a bathymetric map and daily stage readings was used for spatial and temporal interpolation of reservoir emissions. Annual emissions of CO 2 , upstream and downstream of Balbina dam for 2005, were estimated as 2450 and 81 Gg C, respectively, for a total annual flux of 2531 Gg C. Upstream emissions were predominantly diffusive with only 0.02 Gg C yr −1 resulting from ebullition. On average, 51% of the downstream emission was released by degassing at the turbine outflow, and the remainder was lost by diffusion from the downstream river. The total annual greenhouse gas emission from Balbina dam, including the CO 2 equivalent of previously estimated CH 4 emissions, was 3 Tg C yr −1 , equivalent to approximately 50% of the CO 2 emissions derived from the burning of fossil fuels in the Brazilian metropolis of São Paulo.

Spatial and seasonal variability of CO2 flux at the air-water interface of the Three Gorges Reservoir

“…A wide variation in the intensity of the emissions was noted, indicating the influence of many other different factors: flooded organic carbon, allochthonous carbon, primary productivity, and dissolved oxygen (St Louis et al, 2000;Barros et al, 2011;Wang et al, 2011;Kemenes et al, 2011). However, the relationships between CO 2 flux and these factors were not found in our study because every reservoir had its specific characteristics.…”

“…If adding in the diffusive CH 4 emission from the surface of the TGR (2.46 Gg CH 4 /yr; Chen et al, 2011), the total diffusive emissions of C-CO 2 and C-CH 4 were 0.36-0.38 Tg C/yr from the reservoir surface (CO 2 equivalent) ( Table 3). The diffusive CO 2 flux at the surface was the dominant fraction in a hydroelectric system, which accounted for 99% of the total CO 2 emission from the reservoir surface (Rosa et al, 2003;Abril et al, 2005;Kemenes et al, 2011). The frequency of bubble occurrence was 5% in our experiment.…”

“…turbines accounted for about 1.6%-7% of the total CO 2 emission and 1.5%-70% of the total CH 4 emission in a hydroelectric system (Soumis et al, 2004;Abril et al, 2005;Fearnside, 2005;Chanudet et al, 2011;Kemenes et al, 2011). Referring to these two proportions, the degassing emission at the turbine outflow of the TGR was estimated to be 0.006-0.135 Tg C/yr.…”

“…Besides the difference in water velocity between the two places, the dissolved CO 2 in the hypolimnion at Zigui probably contributed significantly to the high CO 2 flux at Sandouping because of the disturbance by turbines. Rivers downstream of dams have been considered as contributing a significant fraction of the CO 2 emission from hydroelectric systems (Guérin et al, 2006;Kemenes et al, 2011). CO 2 emissions downstream from hydroelectric dams were often reported to be significantly larger than that upstream from hydroelectric dams (Roland et al, 2010;Wang et al, 2011).…”

“…1.2 Measurement of CO 2 flux CO 2 flux was measured at the air-water interface of the TGR using floating static chambers (Kemenes et al, 2011). The chamber (65 cm in length × 45 cm in width × 40 cm in height) consisted of a plastic box without a cover that was wrapped in light-reflecting and heatproof films to prevent temperature variation inside the chamber.…”