Pre-existing GHG emissions from Brazilian hydropower reservoirs

Abstract This paper presents results of greenhouse gas measurements in the pre-filling phase of hydroelectric reservoirs in Brazil. In contrast to most of the estimates available in the literature on hydroelectric reservoirs, which take into consideration only gross emissions, these data will enable the calculation of the net emissions of the hydroelectric reservoirs studied. 1 Hydropower sites under construction, where hydroelectric reservoirs have not been installed, are a great opportunity to carry out gas flux measurements in the pre-filling phase and then return to the same reservoirs after the dam closure. In the case of reservoirs already built, the possibility of taking measurements before closing no longer exists. Thus, in addition to providing the opportunity for net measurement estimates, based entirely on specific measurements, the campaigns before the dam closure promote the expansion of the available database to subsidize flux estimates. Three hydroelectric reservoirs were surveyed in Brazil: Belo Monte Hydroelectric Complex, Batalha Hydroelectric Plant and Santo Antonio Hydroelectric Plant. Gas measurements were carried out in land areas (in different types of soil and vegetation use) and in the aquatic areas (rivers, lakes and marshes) before the reservoir flooding. In each reservoir, four measurement campaigns were carried out in order to represent different rainfall regimes and river water levels. The median values of CH 4 emissions were 9.97 ± 3.55 mg CH 4  m −2  day −1 and 11.34 ± 1.62 mg CH 4  m −2  day −1 for pasture and forest, respectively. For CO 2 in the pasture was 10,448.41 ± 3036.48 mg CO 2  m −2  day −1 and 8004.50 ± 1314.98 mg CO 2  m −2  day −1 for forest. The median fluxes for N 2 O were near zero, and 0.78 ± 0.56 mg N 2 O m −2  day −1 for pasture and 0.67 ± 0.29 mg N 2 O m −2  day −1 for forest. The study showed that the terrestrial areas previous reservoir creation act as potential emitter of greenhouse gases.