Methane Dynamics of Aquaculture Shrimp Ponds in Two Subtropical Estuaries, Southeast China: Dissolved Concentration, Net Sediment Release, and Water Oxidation

摘要

Aquaculture ponds are potentially large sources of atmospheric methane (CH_4) that can exacerbate climate change. A thorough understanding of various CH_4 biogeochemical processes occurring in the ponds is essential for the prediction and management of CH_4 emissions arising from aquaculture. However, the variations in pond CH_4 biogeochemical processes among estuaries and aquaculture stages remain poorly understood. In this study, we assessed the net sediment release, oxidation, and dissolved concentrations of CH_4 in aquaculture ponds in two subtropical estuaries among three shrimp growth stages in Southeast China. Overall, porewater CH_4 concentrations and sediment CH_4 release rates varied greatly among different stages in the order: middle stage > final stage > initial stage. Water column CH_4 concentrations and overlying water CH_4 oxidation rates showed an increasing trend over the study period. Sediment CH_4 release rates and dissolved CH_4 concentrations also varied considerably between the two estuaries. In the more saline Jiulong River Estuary, sediment CH_4 release rate was lower while the shrimp survival rate and yield were higher as compared to the Min River Estuary with a lower water salinity. Our results suggest that both high water salinity and feed utilization efficiency can effectively mitigate CH_4 emissions from the coastal shrimp ponds. Overall, the large magnitude of net CH_4 emissions observed in our shrimp ponds highlights the urgency of formulating appropriate policies and building sustainable institutions that can strike a balance between land-based aquaculture development and greenhouse gas mitigation in the subtropical coastal regions.