Methane Dynamics in Large Amazonian Rivers

Monday, 15 December 2014
Henrique O Sawakuchi1, David Bastviken2, Andre O Sawakuchi3, Clovis D Borges1, Siu Mui Tsai1, Nicholas D Ward4, Jeffrey E Richey5, Maria Victoria Ballester1 and Alex V Krusche1, (1)USP University of Sao Paulo - CENA, Piracicaba, Brazil, (2)Linköping University, Linköping, Sweden, (3)USP University of Sao Paulo - IGc, São Paulo, Brazil, (4)University of Florida, Geological Sciences, Ft Walton Beach, FL, United States, (5)University of Washington Seattle Campus, Seattle, WA, United States
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.