Electron shuttling mediated by humic substances fuels anaerobic methane oxidation and carbon burial in wetland sediments


Edgardo I. Valenzuela1, Karen A. Avendaño1, Nagamani Balagurusamy2, Sonia Arriaga1, Cesar Nieto-Delgado1, Frederic Thalasso3, Francisco J. Cervantes1

1División de Ciencias Ambientales, Instituto Potosino de Investigación Científica y Tecnológica, San Luis Potosí, Mexico

2Facultad de Ciencias Biológicas, Universidad Autónoma de Coahuila, Torreón, Coahuila, Mexico

3Departamento de Biotecnología y Bioingeniería, Centro de Investigación y de Estudios Avanzados del Instituto Politécnico Nacional (Cinvestav-IPN), Av. IPN 2508, Mexico City, Mexico

Corresponding author. E-mail address: fjcervantes@ipicyt.edu.mx.

Key pathways for the anaerobic oxidation ofmethane (AOM) have remained elusive, particularly in organic rich ecosystems. In this work, the occurrence of AOM driven by humus-catalyzed dissimilatory iron reduction was investigated in sediments from a coastal mangrove swamp. Anoxic sediment incubations supplied with both goethite (α-FeOOH) and leonardite (humic substances (HS)) displayed an average AOMrate of 10.7±0.8 μmol CH4cm3 day1, which was 7 and 3 times faster than thatmeasured in incubations containing only goethite or HS, respectively. Additional incubations performed with 13C-methane displayed Pahokee Peat HS-mediated carbonate precipitation linked to 13CH4 oxidation and ferrihydrite reduction (~1.3 μmol carbonate cm3 day1). These results highlight the role of HS on mitigating greenhouse gases released from wetlands, not only by mediating the AOM process, but also by enhancing carbon sequestration as inert minerals (calcite, aragonite and siderite).

Humic substances-methane oxidation