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Abstract

In the Amazon floodplain large areas of unvegetated lake sediments are exposed to air during low water. I measured methane fluxes from exposed sediments of an Amazonian floodplain lake and assessed the regulating factors. Methane emission decreased from values between 10 and 40 μmol CH₄m⁻²h⁻¹ to zero when the sediments were exposed to air. Mean fluxes were about 3.7 μmol CH₄m⁻²h⁻¹. Fluxes were low compared to measurements taken from flooded habitats making exposed lake sediments a negligible source of atmospheric CH₄. This was mainly due to the lack of ebullition which governs methane flux in the flooded phase. Methane oxidation at the sediment surface consumed up to 75% of the methane entering the oxidised zone. Compared with CO₂ emission methane turnover was of minor importance for the carbon budget of the sediments.