Conversion of coastal marsh to aquaculture ponds decreased the potential of methane production by altering soil chemical properties and methanogenic archaea community structure

Coastal wetlands are among the most productive and dynamic ecosystems globally, contributing significantly to atmospheric methane (CH₄) emissions. The widespread conversion of these wetlands into aquaculture ponds degrades these ecosystems, yet its effects on CH₄ production and associated microbial mechanisms are not well understood. This study aimed to assess the impact of land conversion on CH₄ production potential, total and active soil organic C (SOC) content, and microbial communities. We conducted a comparative study on three brackish marshes and adjacent aquaculture ponds in southeastern China. Compared to costal marshes, aquaculture ponds exhibited significantly (P < 0.05) lower CH₄ production potential (0.05 vs. 0.02 μg kg⁻¹ h⁻¹), SOC (17.64 vs. 6.97 g kg⁻¹), total nitrogen (TN) content (1.62 vs. 1.24 g kg⁻¹) and carbon/nitrogen (C/N) ratio (10.85 vs. 5.66). CH₄ production potential in aquaculture ponds was influenced by both microbial and abiotic factors. Specifically, the relative abundance of Methanosarcina slightly decreased in aquaculture ponds, while the potential for CH₄ production declined with lower SOC contents and C/N ratio. Overall, our findings demonstrate that converting natural coastal marshes into aquaculture ponds reduces CH₄ production by altering key soil properties and the structure and diversity of methanogenic archaea communities. These results provide empirical evidence to enhance global carbon models, improving predictions of carbon feedback from wetland land conversion in the context of climate change.