Competitive CH4 bubble growth in aquatic muds

Methane (CH₄) bubbles residing in shallow aquatic muds pose a significant threat to the environment. Impeded by the muddy sediment opacity and insufficient resolution for their characterization, past studies overlooked bubble interactions during their growth. The competitive growth of CH₄ bubble pairs with different initial sizes is simulated, using a mechanical/reaction-transport numerical model. Mechanical and solute transport interactions were found to dominate at the different stages of the bubble growth, both retarding the smaller competitive bubble growth. Stress from the large competitive bubble affects the inner pressure and diffusive flux to the smaller bubble, producing its slower initial growth. The large competitive bubble diverts CH₄ from the smaller one at the later stages, thus inhibiting its growth even more. Bubble stress interactions may produce more laterally oriented smaller bubbles and significant deformations of the larger ones. Competitive bubble growth may shape a bubble size distribution pattern, promote muddy sediment CH₄ gas retention, and produce gas domes. The latter acts as pockmark precursors whose formation induces a violent gas release to the water column and potentially to the atmosphere. Our study presents a basis for proper upscaling to various effective gassy muddy sediment characteristics and gas retention models. It contributes to the evaluation and even reduction of a long-persisting uncertainty related to the CH₄ fluxes from the shallow aquatic sediments.