Switch from source to Sink: Greenhouse gas fluxes in razor clam aquaculture ponds at different statuses of mangrove restoration

Abstract

Aquaculture ponds significantly contribute to greenhouse gas (GHG) emissions. Ecological restoration of these ponds in China's coastal regions involves transitioning through stages of active cultivation, abandonment, and recovery to restore them into vibrant mangrove forests. However, the GHG emissions across different restoration stages remain under-researched. To bridge this gap, this study monitored carbon dioxide (CO₂) and methane (CH₄) emissions at the water-air interface over a year in Zhangjiang Mangroves, focusing on razor clam aquaculture ponds in three distinct stages of restoration.

Our study revealed that ponds were significant CH₄ emitters, with abandoned ponds emitting the least (0.0049 tCH₄ ha⁻¹ yr⁻¹), followed by restored ponds (0.0061 tCH₄ ha⁻² yr⁻¹), while active culturing ponds had the highest emissions (0.0078 tCH₄ ha⁻² yr⁻¹). Both active culturing and abandoned ponds were net carbon sources, emitting 4.81 tCO₂ ha⁻² yr⁻¹ and 1.04 tCO₂ ha⁻² yr⁻¹ respectively, while restored ponds served as a carbon sink, with a net uptake 0.43 tCO₂ ha⁻² yr⁻¹ throughout the year. Temperature emerges as the most influential factors for both CO₂, and CH₄ emissions. Furthermore, the carbon sequestration capacity of mangrove forests offset 282.7 % of the total CO₂-equivalent GHG flux from the restored ponds. As restoration progresses, the cessation of aquaculture and vegetation recovery can effectively mitigate the greenhouse effect from pond cultivation by 73.8 %. This study provides vital data for China's coastal aquaculture carbon emission inventory and insights into GHG changes following the conversion of aquaculture ponds to mangrove forests, highlighting the significance of mangrove restoration in reducing emissions.