International Journal of Marine Science, 2024, Vol.14, No.5, 312-320 http://www.aquapublisher.com/index.php/ijms 313 microorganisms utilize substrates such as carbon dioxide, acetate, and methylated compounds to produce methane. In coastal sediments, methanogenic activity is influenced by the availability of organic matter and electron acceptors. For instance, in the Shenhu area of the northern South China Sea, methanogens such as Methanococcoides and Methanosarcina were found to increase slightly in abundance under certain incubation conditions, although their overall presence remained low (Kong et al., 2022). Additionally, in the Yangtze Estuary, the abundance of methanogens was significantly impacted by anthropogenic activities, with elevated levels of methane metabolism-related microbes observed in areas affected by wastewater treatment plant effluents (Guo et al., 2019). 2.2 Methanotrophs in water columns Methanotrophs are bacteria that oxidize methane, thereby mitigating its release into the atmosphere. These microorganisms are particularly active in the water columns above methane seeps and in the upper layers of sediments. In deep oligotrophic Lake Constance, members of the Methylococcaceae family were found to be highly active in oxidizing methane, significantly reducing methane emissions from sediment seeps (Bornemann et al., 2016). Similarly, in shallow marine seeps near Elba, Italy, Methylococcaceae and Methylophilaceae were identified as key players in rapid aerobic methane oxidation, with Methylococcaceae catalyzing the initial step of methane oxidation to methanol, which was then utilized by Methylophilaceae (Taubert et al., 2019). 2.3 Interactions between methanogens and methanotrophs Methanotrophs are bacteria that oxidize methane, thereby mitigating its release into the atmosphere. These microorganisms are particularly active in the water columns above methane seeps and in the upper layers of sediments. In deep oligotrophic Lake Constance, members of the Methylococcaceae family were found to be highly active in oxidizing methane, significantly reducing methane emissions from sediment seeps (Ruff et al., 2016). Similarly, in shallow marine seeps near Elba, Italy, Methylococcaceae and Methylophilaceae were identified as key players in rapid aerobic methane oxidation, with Methylococcaceae catalyzing the initial step of methane oxidation to methanol, which was then utilized by Methylophilaceae (Jing et al., 2020). 2.4 Influence of environmental factors on microbial activity Environmental factors such as the availability of electron acceptors, organic matter inputs, and anthropogenic impacts play a significant role in shaping the activity and composition of methane-cycling microbial communities. In coastal sediments, the availability of sulfate, iron, and nitrate as electron acceptors can influence the pathways of methane oxidation. Pollution and eutrophication can also alter microbial community structures, as observed in small polluted ponds where high pollution levels led to significant shifts in methanogenic and methanotrophic communities (Wang et al., 2021). Additionally, global warming and climate change can enhance water column stratification and primary production, favoring methanogenesis in coastal areas (Wallenius et al., 2021). 3 Methane Production in Marine Sediments 3.1 Anaerobic methane production 3.1.1 Biochemical pathways of methanogenesis Methanogenesis in marine sediments is primarily driven by methanogenic archaea through several biochemical pathways. The two main pathways are hydrogenotrophic methanogenesis, where methane (CH₄) is produced from hydrogen (H₂) and carbon dioxide (CO₂), and aceticlastic methanogenesis, where methane is produced from acetate (Conrad, 2020; Shuai et al., 2021). Additionally, methylotrophic methanogenesis, which involves the conversion of methylated compounds such as methanol and methylamine to methane, also plays a significant role. These pathways are tightly regulated by the availability of substrates and environmental conditions, such as the presence of electron acceptors like sulfate, nitrate, and metal oxides (Wegener et al., 2016). 3.1.2 Role of organic matter in methane production The availability and type of organic matter are crucial in determining the rate and extent of methane production in marine sediments. Organic matter serves as the primary substrate for methanogenesis, undergoing initial fermentation to produce intermediates like acetate and H₂, which are then utilized by methanogens2. In eutrophic coastal areas, high organic matter inputs can lead to increased methanogenesis due to enhanced microbial activity
RkJQdWJsaXNoZXIy MjQ4ODYzNA==