Journal cover Journal topic
Biogeosciences An interactive open-access journal of the European Geosciences Union
Journal topic
Volume 13, issue 10
Biogeosciences, 13, 2981–3001, 2016
https://doi.org/10.5194/bg-13-2981-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Biogeosciences, 13, 2981–3001, 2016
https://doi.org/10.5194/bg-13-2981-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 23 May 2016

Research article | 23 May 2016

Methane and sulfate dynamics in sediments from mangrove-dominated tropical coastal lagoons, Yucatán, Mexico

Pei-Chuan Chuang1, Megan B. Young2, Andrew W. Dale3, Laurence G. Miller2, Jorge A. Herrera-Silveira4, and Adina Paytan1,5 Pei-Chuan Chuang et al.
  • 1Department of Earth and Planetary Sciences, University of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA
  • 2US Geological Survey, 345 Middlefield Rd, MS 434, Menlo Park, CA 94025, USA
  • 3GEOMAR Helmholtz Centre for Ocean Research Kiel, Wischhofstr. 1–3, 24148 Kiel, Germany
  • 4CINVESTAV-IPN, Unidad Mérida, A.P. 73 CORDEMEX, Mérida, Yucatán, Mexico
  • 5Institute of Marine Sciences, University of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064, USA

Abstract. Porewater profiles in sediment cores from mangrove-dominated coastal lagoons (Celestún and Chelem) on the Yucatán Peninsula, Mexico, reveal the widespread coexistence of dissolved methane and sulfate. This observation is interesting since dissolved methane in porewaters is typically oxidized anaerobically by sulfate. To explain the observations we used a numerical transport-reaction model that was constrained by the field observations. The model suggests that methane in the upper sediments is produced in the sulfate reduction zone at rates ranging between 0.012 and 31 mmol m−2 d−1, concurrent with sulfate reduction rates between 1.1 and 24 mmol SO42− m−2 d−1. These processes are supported by high organic matter content in the sediment and the use of non-competitive substrates by methanogenic microorganisms. Indeed sediment slurry incubation experiments show that non-competitive substrates such as trimethylamine (TMA) and methanol can be utilized for microbial methanogenesis at the study sites. The model also indicates that a significant fraction of methane is transported to the sulfate reduction zone from deeper zones within the sedimentary column by rising bubbles and gas dissolution. The shallow depths of methane production and the fast rising methane gas bubbles reduce the likelihood for oxidation, thereby allowing a large fraction of the methane formed in the sediments to escape to the overlying water column.

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A transport-reaction model was used to simulate porewater methane and sulfate concentrations. Model results and sediment slurry incubation experiments show high methane production rates supported by non-competitive substrates and ample dissolved and labile organic matter as well as methane from deeper sediment through bubbles dissolution and diffusion. The shallow methane production and accumulation depths in these sediments promote high methane fluxes to the water column and atmosphere.
A transport-reaction model was used to simulate porewater methane and sulfate concentrations....
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