Methane (CH4) oxidation in flooded forests of the amazon basin

Abstract

Methane oxidation has been observed in a wide range of aquatic environments worldwide, and measurements are rare in tropical floodplains. The Amazon floodplain is one of the largest tropical wetlands with seasonally flooded forests representing up to 80% of the area of aquatic habitats in the lowland Amazon. Hence, we measured methane oxidation rates (Mox) in two different flooded forests (várzea, in white waters; igapó, in black waters) and evaluated effects of dissolved oxygen and CH₄ concentrations, and water temperature on methane oxidation. We found high Mox in near-bottom waters associated with high CH₄ concentrations (1.0–2.4 µM) and hypoxia, with volumetric rates ranging from 9.8 to 73 mg C m⁻³ d⁻¹ in the igapó, and from 2.3 to 101.4 mg C m⁻³ d⁻¹ in the várzea. Depth integrated Mox rates ranged from 177 to 213 mg C m⁻² d⁻¹ for the igapó, and 159 mg C m⁻² d⁻¹ in the várzea, and were one to two orders of magnitude higher than CH₄ fluxes from water to the atmosphere, emphasizing the important role of Mox in attenuating CH₄ emissions from tropical flooded forests. The present study contributes to understanding of the complex processes involved in carbon dynamics on tropical floodplains.