Purpose

Methane, produced and emitted when organic carbon accumulates in reservoir sediments, can be oxidised microbially before being released into the overlying water by a variety of electron acceptors. This research aimed to investigate the microbial drivers responsible for the specific pattern of methane production and oxidation, as well as the role of electron acceptors in regulating anaerobic oxidation of methane (AOM) along the sediment core of a freshwater reservoir.

Materials and methods

A sediment core was obtained from the Hongfeng Reservoir, a eutrophic lake-type reservoir located in Guizhou Province, China. To estimate methane production/oxidation profiles, the core was stratified and the porewater properties of each sediment layer (organic matter, carbon isotopic compositions, and etc.) were analysed and integrated with microbial communities and the methane production activity.

Results

Methanogens were detected throughout the sediment depth profile. Hydrogenotrophic Methanomicrobiales were identified as the primary producer of methane in the surface layer (<20 cm), whereas Methanobacteriales and aceticlastic Methanosarcinales were revealed as the primary producers in the deeper layer. Additionally, methane was oxidised along the sediment profile with various electron acceptors. The coexistence of sulfate- and iron-oxidising bacteria at the surface layer demonstrated the possibility of sulfate and iron-dependent methane oxidation. Both the potential activity of AOM and the nitrite peak indicated the presence of an active nitrite-AOM zone consisted in the intermediate layer (14–24 cm) underneath the sulfate-AOM zone.

Conclusion

Methane production and oxidation co-exist along the sediment core of a freshwater reservoir. Notably, AOMs have a significant potential to reduce in situ methane emissions from freshwater sediment environments. Additionally, there are multiple electrons available for the microbial AOM, and correspondingly, the functional microorganisms participating in AOMs are distributed across the sediment habitat in a niche-specific manner.

Graphical abstract