Methane Production Linked to Organic Matter Molecule and Methanogenic Community in Estuarine Benthic Sediments

The importance of dissolved organic matter (DOM) and methanogenic community to methane (CH4) production in estuarine benthic sediments remains poorly understood. Here, we determined CH4 production rate, DOM molecule, and methanogenic community in benthic sediments of Min River Estuary. CH4 production rates in freshwater and saline sediments varied between 0.28 and 0.56 μg CH4 m−2 h−1, and between 0.17 and 0.27 μg CH4 m−2 h−1, respectively. CH4 production rates in freshwater sediments were increased by 36%–66% under saline incubation, compared to freshwater incubation, indicating that elevated salinity can stimulate CH4 production. The δ13C‐CH4 decreased and fractionation factor between δ13C‐CO2 and δ13C‐CH4 increased from high‐ to low‐OM sediments, suggesting a shift of CH4 production from acetoclastic to hydrogenotrophic pathways. A decrease in labile fractions and an increase in recalcitrance fractions of DOM were accompanied by the decrease in CH4 production. The Methanoregula, Methanocellales, Methanosarcina, and Methanosaeta were the predominant methanogenic communities in mediating CH4 production. The differences in DOM molecules and methanogenic archaea taxa could drive the distinct CH4 production rates in estuarine benthic sediments. These results suggest that DOM quantity and molecules and methanogenic archaea can substantially affect CH4 production, which have broader implications for global CH4 estimates under the ongoing eutrophication in estuarine and coastal ecosystems.