Biogeochemical and microbial controls on methane emissions from (sub)tropical aquaculture ponds

Aquaculture ponds are significant hotspots of methane (CH₄) emissions, yet the mechanisms regulating CH₄ production and emissions across diverse pond types remain poorly understood. By investigating 20 aquaculture ponds with diverse culture systems in (sub)tropical southern China, we examined CH₄ emissions (FCH₄) and their underlying drivers. Our preliminary results reveal substantial CH₄ emissions from (sub)tropical aquaculture ponds, with significant variations among pond types. Fish ponds exhibited the highest FCH₄ (226 ± 441 mg m^–2 d^–1), followed by shrimp ponds (68 ± 159 mg m^–2 d^–1) and crab ponds (49 ± 112 mg m^–2 d^–1). Ebullition was the dominant pathway of CH₄ emissions, accounting for over 70% of the total CH₄ flux. CH₄ emissions were collectively regulated by management practices, environmental variables, and methane-cycling microbial communities. Salinity suppressed FCH₄ by inhibiting methanogen metabolism and restructuring methanogenic community, while elevated organic substrates could offset the salinity-driven inhibitory effect. Furthermore, rising temperature could substantially stimulate CH₄ emissions, especially ebullition, with an 11% increase in FCH₄ per 1 °C rise in water temperature. This thermal sensitivity of FCH₄ was further amplified in ponds with higher organic substrates, revealing a synergistic effect between temperature and substrate availability in promoting CH₄ production. Notably, low-latitude aquaculture ponds exhibited greater temperature sensitivity. Our study highlights the considerable CH₄ emission potential of (sub)tropical aquaculture ponds and identifies salinity, organic matter, and temperature as key regulators of FCH₄. These findings provide a framework for scaling the contribution of aquaculture ponds to the global CH₄ budgets.