Methane Dynamics in Large Amazonian Rivers

Abstract:

The emission of methane (CH₄) from rivers is not always included in the greehouse gas budget for inland waters, mainly due to a lack of information available for these systems. Unraveling the dynamics that control fluvial CH₄ sources and sinks is critical for understanding the contribution of CH₄ to riverine and global carbon budgets. Here, we present estimates of CH₄ sources and sinks in numerous large Amazonian rivers during periods of high and low discharge. Calculations based on CH₄ flux measurements and isotopic data (δ¹³CH₄) of dissolved CH₄ and bubbles in riverbed sediments were performed to assess the sources and sinks of river water CH₄. Molecular analysis (qPCR) in river water samples was used to determine methanotrophic bacterial density. Methane-oxidizing bacterial counts were compared to oxidation estimates in order to assess the relationship between methane sinks and in situ bacterial communities. In general, rivers that had an enriched δ¹³CH₄ in the water also had a higher density of methanotrophic bacteria in the water column, illustrating an important control on CH₄ availability and flux related to physicochemical factors that control the abundance and activity of methanotrophic bacteria. Further, we observed a distinct relationship between the type of river (e.g. clear, white, or black water) and the flux of methane from the water column.