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Greenhouse gas emissions from a semi-arid tropical reservoir in northeastern Brazil

Rodriguez, Maricela, Casper, Peter
Regional environmental change 2018 v.18 no.7 pp. 1901-1912
carbon, carbon dioxide, coal, deaeration, electricity generation, greenhouse gas emissions, greenhouse gases, littoral zone, metabolism, methane, mixing, natural gas, power plants, semiarid zones, turbines, water flow, water power, Brazil
We estimated carbon dioxide (CO₂) and methane (CH₄) emissions by diffusion, ebullition, and degassing in turbines from a semi-arid hydropower reservoir in northeastern Brazil. Sampling sites were allocated within the littoral and deeper waters of one embayment, the main-stream, and at turbines. Annual carbon emissions were estimated at 2.3 × 10⁵ ± 7.45 × 10⁴ t C year⁻¹, or in CO₂-equivalents (CO₂-eq) at 1.33 × 10⁶ ± 4.5 × 10⁵ t CO₂-eq year⁻¹. Diffusion across the water surface was the main pathway accounting for 96% of total carbon emissions. Ebullition was limited to littoral areas. A slight accumulation of CO₂, but not of CH₄, in bottom waters close to the turbines inlet led to degassing emissions about 8 × 10³ t C year⁻¹. Emissions in littoral areas were higher than in main-stream and contribute to 40% of the total carbon. Carbon (C) emissions per electricity generated, at 60% of installed capacity, is 0.05 t C-CO₂-eq MWh⁻¹. The ratio increases to 0.09 t C-CO₂ MWh⁻¹, equating 80% of the emissions from natural gas and 40% of diesel or coal power plants. Retention time and benthic metabolism were identified as main drivers for carbon emissions in littoral areas, while water column mixing and rapid water flow are important factors preventing CH₄ accumulation and loss by degassing. Our results indicate that Itaparica Reservoir, located in the semi-arid region of Northeastern Brazil, acts as a source of GHGs. Management measurements are needed to prevent emissions to raise in the future.