Diffusive emission of methane and carbon dioxide from two hydropower reservoirs in Brazil.

The role of greenhouse gas emissions from freshwater reservoirs and their contribution to increase greenhouse gas concentrations in the atmosphere is currently under discussion in many parts of the world. We studied CO2 and CH4 diffusive fluxes from two large neotropical hydropower reservoirs with different climate conditions. We used floating closed-chambers to estimate diffusive fluxes of these gaseous species. Sampling campaigns showed that the reservoirs studied were sources of greenhouse gases to the atmosphere. In the Serra da Mesa Reservoir, the CH4 emissions ranged from 0.530 to 396.96 mg.m(-2).d(-1) and CO2 emissions ranged from -1,738.33 to 11,166.61 mg.m(-2).d(-1) and in Três Marias Reservoir the CH4 fluxes ranged 0.720 to 2,578.03 mg.m(-2).d(-1) and CO2 emission ranged from -3,037.80 to 11,516.64 to mg.m(-2).d(-1). There were no statistically significant differences of CH4 fluxes between the reservoirs, but CO2 fluxes from the two reservoirs studied were significantly different. The CO2 emissions measured over the periods studied in Serra da Mesa showed some seasonality with distinctions between the wet and dry transition season. In Três Marias Reservoir the CO2 fluxes showed no seasonal variability. In both reservoirs, CH4 emissions showed a tendency to increase during the study periods but this was not statistically significant. These results contributed to increase knowledge about the magnitude of CO2 and CH4 emission in hydroelectric reservoirs, however due to natural variability of the data future sampling campaigns will be needed to better elucidate the seasonal influences on the fluxes of greenhouse gases.

Influence of environmental variables on diffusive greenhouse gas fluxes at hydroelectric reservoirs in Brazil / Influência de parâmetros ambientais em fluxos difusivos de gases de efeito estufa em reservatórios hidrelétricos no Brasil

For almost two decades, studies have been under way in Brazil, showing how hydroelectric reservoirs produce biogenic gases, mainly methane (CH4) and carbon dioxide (CO2), through the organic decomposition of flooded biomass. This somewhat complex phenomenon is due to a set of variables with differing levels of interdependence that directly or indirectly affect greenhouse gas (GHG) emissions. The purpose of this paper is to determine, through a statistical data analysis, the relation between CO2, CH4 diffusive fluxes and environmental variables at the Furnas, Itumbiara and Serra da Mesa hydroelectric reservoirs, located in the Cerrado biome on Brazil's high central plateau. The choice of this region was prompted by its importance in the national context, covering an area of some two million square kilometers, encompassing two major river basins (Paraná and Tocantins-Araguaia), with the largest installed power generation capacity in Brazil, together accounting for around 23% of Brazilian territory. This study shows that CH4 presented a moderate negative correlation between CO2 and depth. Additionally, a moderate positive correlation was noted for pH, water temperature and wind. The CO2 presented a moderate negative correlation for pH, wind speed, water temperature and air temperature. Additionally, a moderate positive correlation was noted for CO2 and water temperature. The complexity of the emission phenomenon is unlikely to occur through a simultaneous understanding of all the factors, due to difficulties in accessing and analyzing all the variables that have real, direct effects on GHG production and emission.

Há quase duas décadas, no Brasil, vêm sendo realizados estudos que revelam que os reservatórios hidrelétricos produzem gases biogênicos, principalmente o metano (CH4) e o dióxido de carbono (CO2), provenientes da decomposição orgânica da biomassa alagada. Observa-se que esse fenômeno é bastante complexo devido a uma gama de variáveis que possuem diferentes graus de interdependência e que influenciam diretamente ou indiretamente nas emissões de gases de efeito estufa (GEE). O objetivo deste trabalho é determinar o grau de relacionamento entre os fluxos difusivos de CO2, CH4 e variáveis ambientais dos Reservatórios Hidrelétricos de Furnas, Itumbiara e Serra da Mesa, através da análise estatística dos dados. Os reservatórios hidrelétricos estão situados no Bioma Cerrado, localizado no Planalto Central do Brasil. A escolha da região deu-se devido a sua importância no contexto nacional, já que corresponde a uma área de aproximadamente dois milhões de quilômetros quadrados, e, nela estão inseridas duas bacias (Bacia do Paraná e Bacia do Tocantins-Araguaia), com a maior capacidade instalada de energia elétrica do país. Esta duas bacias juntas abrangem 23% do território nacional. Neste estudo os resultados revelam que o CH4 apresentou correlação negativa, significativa e moderada com o CO2 e com a profundidade. Observou-se ainda correlação positiva e moderada com pH, temperatura da água e velocidade do vento. O CO2 apresentou correlação negativa, significativa e moderada com pH, com a velocidade do vento, temperatura da água e temperatura do ar. Observou-se também correlação positiva e moderada do CO2 com a temperatura da água. A complexidade do fenômeno de emissão dificilmente ocorrerá pelo entendimento simultâneo de todos os fatores, devido às dificuldades de acessar e analisar todas as variáveis que realmente têm implicação direta nesta produção/emissão de GEE.

Influence of environmental variables on diffusive greenhouse gas fluxes at hydroelectric reservoirs in Brazil.

For almost two decades, studies have been under way in Brazil, showing how hydroelectric reservoirs produce biogenic gases, mainly methane (CH4) and carbon dioxide (CO2), through the organic decomposition of flooded biomass. This somewhat complex phenomenon is due to a set of variables with differing levels of interdependence that directly or indirectly affect greenhouse gas (GHG) emissions. The purpose of this paper is to determine, through a statistical data analysis, the relation between CO2, CH4 diffusive fluxes and environmental variables at the Furnas, Itumbiara and Serra da Mesa hydroelectric reservoirs, located in the Cerrado biome on Brazil's high central plateau. The choice of this region was prompted by its importance in the national context, covering an area of some two million square kilometers, encompassing two major river basins (Paraná and Tocantins-Araguaia), with the largest installed power generation capacity in Brazil, together accounting for around 23% of Brazilian territory. This study shows that CH4 presented a moderate negative correlation between CO2 and depth. Additionally, a moderate positive correlation was noted for pH, water temperature and wind. The CO2 presented a moderate negative correlation for pH, wind speed, water temperature and air temperature. Additionally, a moderate positive correlation was noted for CO2 and water temperature. The complexity of the emission phenomenon is unlikely to occur through a simultaneous understanding of all the factors, due to difficulties in accessing and analyzing all the variables that have real, direct effects on GHG production and emission.