title: Oxidative mitigation of aquatic methane emissions in large Amazonian rivers.
abstract: The flux of methane (CH4 ) from inland waters to the atmosphere has a profound impact on global atmospheric greenhouse gas (GHG) levels, and yet, strikingly little is known about the dynamics controlling sources and sinks of CH4 in the aquatic setting. Here, we examine the cycling and flux of CH4 in six large rivers in the Amazon basin, including the Amazon River. Based on stable isotopic mass balances of CH4 , inputs and outputs to the water column were estimated. We determined that ecosystem methane oxidation (MOX) reduced the diffusive flux of CH4 by approximately 28-96% and varied depending on hydrologic regime and general geochemical characteristics of tributaries of the Amazon River. For example, the relative amount of MOX was maximal during high water in black and white water rivers and minimal in clear water rivers during low water. The abundance of genetic markers for methane-oxidizing bacteria (pmoA) was positively correlated with enhanced signals of oxidation, providing independent support for the detected MOX patterns. The results indicate that MOX in large Amazonian rivers can consume from 0.45 to 2.07 Tg CH4 yr(-1) , representing up to 7% of the estimated global soil sink. Nevertheless, climate change and changes in hydrology, for example, due to construction of dams, can alter this balance, influencing CH4 emissions to atmosphere.
authors.affiliation: Center of Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, Piracicaba, SP 13400-970, Brazil.
authors.forename: Henrique O
authors.identifier: http://orcid.org/0000-0002-6815-7261
authors.initials: HO
authors.lastname: Sawakuchi
authors.affiliation: Department of Thematic Studies - Environmental Change, Linköping University, Linköping, SE-581 83, Sweden.
authors.forename: David
authors.initials: D
authors.lastname: Bastviken
authors.affiliation: Departament of Sedimentary and Environmental Geology, Institute of Geosciences, University of São Paulo, Rua do Lago, 562, São Paulo, SP 05508-080, Brazil.
authors.forename: André O
authors.initials: AO
authors.lastname: Sawakuchi
authors.affiliation: Department of Geological Sciences, University of Florida, Box 112120, Gainesville, FL, 32611-2120, USA.
authors.forename: Nicholas D
authors.initials: ND
authors.lastname: Ward
authors.affiliation: Center of Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, Piracicaba, SP 13400-970, Brazil.
authors.forename: Clovis D
authors.initials: CD
authors.lastname: Borges
authors.affiliation: Center of Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, Piracicaba, SP 13400-970, Brazil.
authors.forename: Siu M
authors.initials: SM
authors.lastname: Tsai
authors.affiliation: School of Oceanography, University of Washington, Seattle, WA, 98195-7940, USA.
authors.forename: Jeffrey E
authors.initials: JE
authors.lastname: Richey
authors.affiliation: Center of Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, Piracicaba, SP 13400-970, Brazil.
authors.forename: Maria Victoria R
authors.identifier: http://orcid.org/0000-0003-2567-6747
authors.initials: MV
authors.lastname: Ballester
authors.affiliation: Center of Nuclear Energy in Agriculture, University of São Paulo, Av. Centenário, 303, Piracicaba, SP 13400-970, Brazil.
authors.forename: Alex V
authors.initials: AV
authors.lastname: Krusche
mesh_terms: D000393:Air Pollutants / Q000378:metabolism*; D001419:Bacteria / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000032:analysis; D015415:Biomarkers; D001938:Brazil; D017753:Ecosystem; D004784:Environmental Monitoring; D008697:Methane / Q000378:metabolism*; D010084:Oxidation-Reduction; D045483:Rivers / Q000737:chemistry*
chemical_list: D000393:Air Pollutants; D001426:Bacterial Proteins; D015415:Biomarkers; D008697:Methane
keywords: Amazon; CH
  4; greenhouse gas; methane oxidation; methanotrophs; pmoA gene; sink; tropical rivers