Downstream emissions of CH₄ and CO₂ from hydroelectric reservoirs (Tucuruí, Samuel, and Curuá-Una) in the Amazon basin

Abstract

Carbon dioxide (CO 2) and methane (CH 4) generated in reservoirs are released downstream of dams, and few studies have considered these downstream emissions. Fluxes downstream of 3 Amazon hydroelectric reservoirs (Tucuruí, Samuel, and Curuá-Una) are reported here. Degassing through turbines was calculated as the difference between intake and outflow concentrations. Additional releases along the Tocantins, Jamari, and Curuá rivers were measured at downstream sites over a distance of 30 km. About 50% of the CH 4 and 30% of the CO 2 emitted downstream of the dam were liberated at the turbine outflow. The total downstream emissions are sufficiently large to require consideration in assessments of greenhouse gas emissions from hydroelectric reservoirs.

The carbon footprint of a Malaysian tropical reservoir: measured versus modeled estimates highlight the underestimated key role of downstream processes

“…Once GHGs have exited the reservoir, a large fraction (40 and 65 % for CO 2 and CH 4 respectively) is immediately lost to the atmosphere as degassing emissions (Table 1), which is in line with previous literature reports ( Kemenes et al, 2016). Along the outflow river, CO 2 and CH 4 concentrations gradually decreased, δ 13 CO 2 remained stable, whereas δ 13 CH 4 steadily increased indicating riverine CH 4 oxidation (Figure 3).…”

The carbon footprint of a Malaysian tropical reservoir: measured versus modelled estimates highlight the underestimated key role of downstream processes

“…Equation (7) is based on a non-steady-state isotopic model developed considering evasion (emission to the atmosphere) and oxidation as the two loss processes for CH 4 in the outflow river, assuming negligible isotopic fractionation for evasion (Knox et al, 1992) and a fractionation of α = 1.02 for oxidation (Coleman et al, 1981) (Myhre et al, 2013). For each flux pathway, annual flux was estimated as the average of the sampling campaigns.…”

“…3). Given the very small isotopic fractionation (0.9992) of CH 4 during gas evasion (Knox et al, 1992), the only process that can explain the observed δ 13 CH 4 increase is CH 4 oxidation (Bastviken et al, 2002;Thottathil et al, 2018). We estimated that riverine CH 4 oxidation ranged from 0.38 to 1.80 mmol m −2 d −1 (expressed per squared metre of reservoir area for comparison), transforming 18 % to 32 % (depending on the sampling campaign) of the CH 4 to CO 2 within the first 19 km of the outflow.…”

Represas hidroeléctricas en la Amazonia brasileña: impactos ambientales y sociales

“…Las presas amazónicas son importantes fuentes de gases de efecto invernadero, especialmente metano (CH4). Esto se ha demostrado mediante mediciones directas de las emisiones de presas, como Petit Saut (Abril et al, 2005;Delmas et al, 2001) y Balbina (Kemenes et al, 2007(Kemenes et al, , 2011(Kemenes et al, , 2016, y mediante cálculos para represas como Tucuruí, Samuel, Curuá-Una y Belo Monte con Babaquara/Altamira (Fearnside, 2002(Fearnside, , 2005a(Fearnside, , b, 2009. Las represas en los trópicos húmedos emiten más CH4 que las de otras zonas climáticas (Barros et al, 2011).…”