International Journal of Marine Science, 2024, Vol.14, No.5, 312-320 http://www.aquapublisher.com/index.php/ijms 314 and subsequent depletion of electron acceptors (Wallenius et al., 2021). The type of organic matter also influences the methanogenic pathways, with more complex organic compounds favoring aceticlastic methanogenesis, while simpler compounds like methanol and methylamine support methylotrophic methanogenesis (Shuai et al., 2021). 3.2 Role of temperature and pressure in methane generation Temperature and pressure significantly impact methane production in marine sediments. Higher temperatures generally enhance methanogenic activity by increasing the metabolic rates of methanogens. For instance, in sub-Antarctic lake sediments, a temperature increase from 5°C to 20°C resulted in a substantial rise in methane production rates, particularly favoring hydrogenotrophic methanogenesis at higher temperatures (Lavergne et al., 2021). Pressure, on the other hand, affects the solubility of gases and the physical properties of sediments, which can influence microbial activity and methane production. In deep-sea environments, high pressure can limit the diffusion of substrates and products, thereby affecting the overall rate of methanogenesis (Martinez-Cruz et al., 2017). 3.3 Methane fluxes in different marine sedimentary environments Methane fluxes vary significantly across different marine sedimentary environments due to variations in microbial communities, substrate availability, and environmental conditions. Coastal sediments, characterized by lower sulfate concentrations (Figure 1), often exhibit higher methane emissions due to reduced sulfate-dependent anaerobic oxidation of methane (AOM) (Wallenius et al., 2021). In contrast, deep-sea cold seeps and hydrate-bearing sediments show complex methane dynamics, with significant contributions from both methanogenesis and AOM processes. In these environments, microbial consortia involving anaerobic methane-oxidizing archaea (ANME) and sulfate-reducing bacteria (SRB) play a crucial role in mitigating methane emissions (Kong et al., 2022). Additionally, the presence of alternative electron acceptors like nitrate and metal oxides can further influence methane fluxes by supporting different AOM pathways (Jing et al., 2020). Figure 1 The effect of eutrophication on the depth of the sulfate-methane transition zone (SMTZ) in coastal sediment and the potential for Fe-AOM (Adopted from Wallenius et al., 2021)
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