Emissão de CO2 e CH4 nas savanas úmidas de Roraima

Abstract

Amazon wetlands are significant sources of carbon dioxide (CO2) and methane (CH4), important greenhouse gases. However, limited data are for moist savannas of Roraima. This study contributed to describe the dynamics on the emission of CO2 and CH4 in these areas in order to improve regional emission estimates. Flows were measured with floating chambers and inverted funnels in 80 lakes of humid savannas of Roraima. Wind speed, temperature, depth, variation of the water height White River and dissolved oxygen on the surface and the bottom of lakes were related to diffusive gas emissions. The dimension of the lakes varied seasonally throughout the year following the quota White River. The flooded area varied between months, totaling 13269.85 km2, equivalent to 33.34 % of the total area of the humid savanna of Roraima. There were no emissions by boiling, CO2 and CH4. The coordinate of the White River ranged from 1.6 to 6.6 m, with peak in August 2012. The dissolved oxygen ranged from 4.6 to 1.4 mg.l-1 on the surface of water and 2.1 to 0.0 mg.l-1 in the bottom of the lake, decreasing with depth, rarely forming anoxic hypolimnion. Water temperature ranged from 21.5 to 35.2°C. CO2 concentrations (from 220.616 to 404.271��M ) and CH4 (1.09 to 1.39 ��M ) in water varied significantly over the months. The total emissions of CO2 and CH4 differed significantly between months, throughout the year, with their annual totals obtained from the sum of the average monthly emissions multiplied by the flooded area were Lavrado 13.14 TgC-CO2.ano-1 and 0.0125 TgC-CH4.ano-1, which corresponds to 2.80 % and 0.06 % of carbon equivalent emissions regional CO2 and CH4. The significant differences between monthly emissions were related to wind speed and water temperature and depth of the lakes directly, inversely. These results demonstrate the need to revise the emissions of CO2 and CH4 made throughout the Amazon, especially in humid savannas of Roraima.