Pre-existing greenhouse gas emissions from Brazilian hydropower reservoirs

Abstract

This paper presents results of greenhouse gas (GHG) measurements in the pre-filling phase of three hydroelectric reservoirs in Brazil: Belo Monte Hydroelectric Complex, Batalha Hydroelectric Plant and Santo Ant“nio Hydroelectric Plant. 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.Carbon dioxide and methane flux measurements were carried out in terrestrial (in different types of soil and vegetation) and aquatic (rivers, lakes and marshes) ecosystems 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 CH4 emissions were 9.97±3.55mgCH4m−2day−1 and 11.34±1.62mgCH4m−2day−1 for pasture and forest, landuse types, respectively. For CO2 emission was 10,448.41±3036.48mgCO2m−2day−1 and 8004.50±1314.98mgCO2m−2day−1 for pasture and forest lands, respectively. The median fluxes for N2O were near zero, and 0.78±0.56mgN2Om−2day−1 for pasture and 0.67±0.29mgN2Om−2day−1 for forest. The study showed that the terrestrial areas prior reservoir creation act as potential emitters of greenhouse gases. Hydropower sites under construction, where hydroelectric reservoirs have not been installed yet create a great opportunity to carry out gas flux measurements in the pre-filling phase. The results can be further compared with the same measurements after the dam closure in order to more precisely estimate the net reservoir emissions. In the case of reservoirs already built, off course the possibility of taking pre-filling phase measurements no longer exists. However, the results of the present study allow for reassessment of the available flux estimates for such reservoirs.