Tidal and seasonal effects on sediment methane emissions from three different mangrove species

Abstract

The anaerobic environment of mangrove sediments due to periodic tides is conducive to methane (CH4) production, but processes and mechanisms of CH4 emission from mangrove sediments are not yet well understood. We used in situ field monitoring and laboratory experiments to investigate the effects of tides and seasons on CH4 emissions from the sediments of Sonneratia apetala (SA), Kandelia obovata (KO), and Avicennia marina (AM), respectively. Methane emissions from the sediments of all mangrove species were significantly higher in summer than in winter, with overall CH4 fluxes being 2.14 times higher during the after-ebb tide compared to the pre-flood tide. Among the mangrove species, AM (16.77 ± 13.73 mg m−2 h−1) exhibited the highest emissions, followed by SA (1.45 ± 0.90 mg m−2 h−1) and KO (0.14 ± 0.16 mg m−2 h−1). CH4 emissions in three mangrove species were mainly driven directly by abiotic factors, including sediment organic carbon (SOC) that could provide substrate for methanogens to generate CH4, and dissolved CH4 concentration in porewater likely served as a carbon source or turnover state for CH4 to eventually enter the atmosphere. Also, sediment CH4 emissions were suppressed by the α-diversity of methanogenic communities. In addition, pH, CH4 flux, SOC, and redox potential significantly shaped structure of the methanogenic communities, potentially regulating sediment CH4 emissions. This study result highlights that abiotic factors can greatly influence CH4 emissions from mangrove sediments, as well as emphasizes the important role of the sediment-porewater-atmosphere pathway on CH4 emissions.