CO₂ and CH₄ emissions from subtropical aquaculture ponds under different management practices

Aquaculture ponds, among the fastest-growing inland water bodies, are hotspots of carbon emissions. However, carbon emissions from aquaculture ponds exhibit significant variability under different management practices, complicating carbon flux quantification. By conducting year-round monthly observations in a fishpond (P1) and a shrimp pond (P2) in subtropical Hong Kong, this study examined their carbon emissions and influencing factors under different management practices. Our results showed that under different management practices, the main drivers of carbon emissions were different. For P1 with low artificial disturbance and increased ecosystem stability, increasing temperature indirectly reduced CO₂ emissions by enhancing photosynthetic intensity while directly promoting CH₄ emissions. In comparison, adjustment of water depth and fertilizer application largely regulated carbon emissions from P2. Consequently, P1 exhibited high primary productivity and functioned as a net CO₂ sink (−42.33 ± 18.91 mmol m⁻² d⁻¹). However, the absence of draining-drying and the presence of a thicker sediment layer in P1 led to stronger CH₄ emissions (29.41 ± 27.53 mmol m⁻² d⁻¹). Conversely, intensive artificial management practices in P2, including draining, drying, and refilling, significantly disrupted its primary productivity and shifted it to a CO₂ source (62.89 ± 106.61 mmol m⁻² d⁻¹) while substantially reducing its CH₄ emissions, especially CH₄ ebullition. The total CO₂-eq emission flux for P2 was approximately 62 % lower than that for P1. This study underscores the substantial impact of human disturbance, especially the draining-drying-refilling practice, on carbon cycling in aquaculture ponds, which should be fully incorporated into future carbon flux estimations.