Emissões de gases de efeito estufa por reservatórios de hidrelétricas

GREENHOUSE GAS EMISSIONS OF DIFFERENT BRAZILIAN HYDROELECTRIC DAMS. Over the 90s surged a growing concern about the participation of hydroelectric dams in the global warming through considerable emission of greenhouse gases. Recently, the results of analysis of some hydroelectric dams in the Amazon have become a matter of controversy, since some of them were based and obtained by poorly reliable scientifi c methods. One of the most controversial aspects are the greenhouse gases emission by the downstream face of the dams i.e. just after the turbines especially of methane, which is found in greater concentrations at greater depths. It has been proposed that the gas concentration that should be considered when calculating the ebullition fl ux should be that of the capitation area, instead of the usually employed methane concentration at greater depths. The greenhouse gas emissions of hydroelectric dams is not constant, and proved to vary in an irregular basis that depends on many factors, including temperature, exposure to sunlight, and water physicochemical and biological traits. There are no established models for the spatial and temporal variations of greenhouse gas emissions by hydroelectric dams, which heavily depend on results of additional controlled studies. There is a lack of data on the carbon cycle conditions in different situations (according with water level, water column position, before and after impoundment, etc). For instance, different types of environments naturally generate methane (swamps, fl ooded forests). These emissions ought to be discounted when calculating methane emissions after water impoundment within such regions, thus ensuring the obtained fi gures really refl ect the increase in methane emissions after the dam was constructed. Carbon dioxide emissions could be incorporated into the hydroelectric dam system through natural cycling within a short time span. Keywords: Hydroelectricity, carbon, methane, carbon dioxide, gas emission Durante a década de 90 surgiram intensas especulações a respeito de que reservatórios de hidrelétricas poderiam estar contribuindo para a intensifi cação do efeito estufa através da emissão de Gases de Efeito Estufa (GEE). Muita polêmica tem sido estabelecida recentemente a partir de estudos realizados nos reservatórios amazônicos, especialmente a partir de estudos teóricos e baseados em extrapolações desprovidas de critérios científi cos estabelecidos. Uma das questões mais polêmicas é a estimativa d