Methane Emissions from the Amazon Floodplain

Abstract

Methane emissions to the troposphere from the Amazon River floodplain have been determined. In total, 94 individual flux measurements were made along a 1,700-km stretch of the river during the early falling water period of the flood cycle (July-August 1985). The overall average rate of CH 4 emission from wetlands was 390 mg CH4 m -2 d-x. Water surfaces covered by aquatic macrophytes had the highest emissions, 590 mg CH½ m -2 d -•, while emissions from flooded forests were 110 mg CH,• m -2 d -• and open lake areas averaged 120 mg CH½ m-2 d-•. Ebullition was the dominant mechanism of emission, accounting for 85% of the total. Surface water dissolved oxygen was always undersaturated, while dissolved CO2 concentrations were significantly supersaturated with respect to atmospheric equilibrium. Surface water CH½ concentrations were highly supersaturated, averaging 6.4 pM. The g•3C of the CH½ varied from -42%0 to -73%0 with an apparent trend toward heavier values downstream. Extrapolation to the entire Amazon floodplain results in estimated annual emissions in the troposphere of 10 Tg yr- • and indicates the importance of the area in the global atmospheric CH4cycle