Climate warming and aquaculture reclamation activate positive feedback mechanisms for greenhouse gases in a temperate mudflat

Abstract

Conversion of natural bare mudflats to aquaculture ponds is a prevalent practice that fundamentally alters sediment biogeochemistry and microbial processes. However, its impact on greenhouse gas (GHG) production dynamics and their temperature sensitivity remains inadequately quantified. This study combined laboratory incubation with metagenomic sequencing to investigate the effects of converting bare mudflats to moderate- and high-intensity aquaculture ponds on sediment GHG production potential and thermal response patterns. Aquaculture reclamation suppressed methane production potential by 89.89% but enhanced nitrous oxide and carbon dioxide (CO₂) by 78.08% and 10.40%, respectively, while simultaneously altering their temperature sensitivity. Mechanistically, these shifts were driven by modified redox conditions, carbon/nitrogen substrate availability, and restructuring of microbial metabolic networks, including functional gene abundance and community composition. Counterintuitively, moderate, rather than heavy, aquaculture reclamation provides the strongest stimulus to GHG production potential, a pattern that can be summarized as a transition from the activation of biogeochemical processes at moderate disturbance to the suppression of system functioning at high intensities of stress, in which toxic byproducts of excessive organic loading inhibit the microbial metabolism they are supposed to promote. Model projections under 2°C and 4°C warming scenarios indicated that aquaculture reclamation may elevate sediment CO₂-equivalent production potential by 32.59–67.45% through stimulated heterotrophic respiration, establishing a positive climate feedback loop, which we conceptualize as an “aquaculture reclamation-induced GHG amplification” mechanism. This study establishes a mechanistic framework for linking reclamation-climate interactions with microbial carbon/nitrogen cycling, providing insights for predicting and mitigating GHG production from bare mudflats in warming ecosystems.