CO₂ fluxes contrast between aquaculture ponds and mangrove forests and its implications for coastal wetland rehabilitation in Leizhou Peninsula, China

Coastal wetlands have great potential to mitigate climate change. However, in recent decades, the construction of aquaculture ponds has degraded coastal habitats, especially mangroves. Meanwhile, the lack of synchronized monitoring of carbon dioxide (CO₂) fluxes in coastal ponds and mangroves hinders the promotion of carbon neutrality target through the implementation of coastal wetland rehabilitation. To address this issue, we deployed two eddy-covariance systems in the ponds and nearby mangroves to measure the net ecosystem CO₂ exchange between atmosphere and ecosystems for two years. The results indicated that both the ponds and mangroves were CO₂ sinks at the annual scale, with mean net ecosystem production (NEP) of 123 ± 39 and 1296 ± 32 g C m⁻² year⁻¹, respectively. During the 2-year period, the ponds acted as CO₂ sources in certain seasons, while the mangroves displayed consistently high seasonal NEP. The construction of ponds by clearing mangroves would reduce NEP along the coasts of the Leizhou Peninsula by about 91% (96% for China), while abandoning all ponds for mangrove rehabilitation could have a significant CO₂ mitigation benefit (i.e., 214.7 Gg year⁻¹). Moreover, we compared how CO₂ fluxes responded to global solar radiation and temperature by analyzing relevant parameters in the two ecosystems. Overall, the ponds showed lower light-saturated net CO₂ exchange and Q₁₀ values compared to the mangroves. Finally, we applied an advanced machine learning local interpretation algorithm to investigate the crucial drivers and their main effects on NEP. This analysis highlighted global solar radiation as the predominant driver for NEP in both ecosystems. High temperature and vapor pressure deficit inhibited mangrove NEP, particularly during summer, whereas pond NEP exhibited greater volatility in response to meteorological conditions such as temperature. Our findings provide insights for further proceeding with mangrove restoration and management to enhance the carbon sequestration capacity of coastal wetlands.