Freshwater aquaculture ponds collectively cover a large area in southeast China. They are an important anthropogenic source of CH4 emissions, however current knowledge of CH4 emissions from aquaculture ponds is limited. During September 2017 and August 2018, two independent sampling campaigns of CH4 flux measurements over annual cycles were carried out in a fish-aquaculture pond in southeast China using a floating chamber and diffusion model methods for comparison. The purpose of this study is to investigate the variation of CH4 fluxes obtained from the fish-aquaculture pond, analyze the emission mechanisms, and amplify the CH4 emissions inventory. The diffusion model method can further quantify the contribution of diffusion transmission to CH4 emissions. The seasonal variations of CH4 fluxes measured by the two methods were similar, with higher CH4 fluxes appearing in summer and fall and lower CH4 fluxes appearing in spring and winter. CH4 fluxes measured by the floating chamber method and diffusion model method ranged from 0.14-3.13 mg·(m2·h)-1 and 0.04-1.41 mg·(m2·h)-1, respectively, and the respective average values were (0.86±0.30) mg·(m2·h)-1and (0.45±0.08) mg·(m2·h)-1. The CH4 fluxes were positively related to water temperature, dissolved organic carbon (DOC) and chemical oxygen demand (COD), but negatively related to the water dissolved oxygen (DO) concentration in the fish-aquaculture pond. CH4 fluxes calculated by diffusion model methods were 45% lower than those determined by the floating chamber methods over annual cycles. The result suggested that the floating chamber method is more suitable than the diffusion model method for measurements of CH4 fluxes in freshwater aquaculture ecosystems.
Keywords: diffusion model; emissions; fish-aquaculture pond; floating chamber; methane.