Methane and carbon dioxide evasion from a mosaic of Amazon lakes, river channels, and inundated forests

Seasonally inundated forests are the largest type of wetland in the Amazon basin. Here we provide new data from inundated forests, a lake, and river channels during high water in the forested Anavilhanas archipelago (Negro River, Brazil). Evasion pathways of methane (CH₄) in flooded forests include tree trunks, diffusion from the water, and ebullition. Within flooded forest sites, diffusive CH₄ fluxes were lowest (mean, 6.2 µmol m⁻² h⁻¹), ebullitive fluxes averaged 50 µmol m⁻² h⁻¹, and fluxes from the trees had the highest fluxes when expressed per inundated surface area (83 µmol m⁻² h⁻¹). The lake and river channels usually had higher CH₄ and CO₂ fluxes than inundated forests. Overall, mean CH₄ fluxes from inundated forests in our study were lower than fluxes measured in nutrient-rich inundated forests. Our results contribute to understanding the heterogeneity of C fluxes from inundated forests. Water levels, currents, and extent of inundated habitats contribute to variability in gas fluxes. Outgassing rates are expected to become more variable with projected periods of especially high and low water levels as the climate changes.