Vertical distribution and controlling factors of methane in sediments of Hangzhou Bay

A large amount of methane is trapped in the sediments of estuarine delta. As a factor of greenhouse gas and a marine geological hazard, the occurrence features of methane in marine sediments can provide theoretical support for shallow gas prevention measures and eco-environmental effects. Based on the test results and geochemical parameters of cores YS3, YS4, YS6, and YS7 in Hangzhou Bay, the methane vertical distribution and the controlling factors were studied. We found one layer of methane gas in 1.5～22.5 mbsf in YS3 and 8～42 mbsf in YS6, and two layers of methane gas in 5～11 mbsf in YS4 and 23～47 mbsf in YS7. Methane in each core was buried in silt and clay-dominated sedimentary layers; the highest contents of CH₄ in the YS3, YS4, YS6, and YS7 cores were 5.66 mM, 1.73 mM, 1.96 mM, and 2.12 mM, respectively, and generated through CO₂/H₂ reduction pathway. The diffusion migration and anaerobic oxidation of methane reached a dynamic equilibrium in the in-situ marine sediment layer. Sediment porosity, clay content, and organic carbon content were important influencing factors on the contents, distribution layers, buried depth, and thickness of methane in the Hangzhou Bay marine sediments.