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.