Ebullitive CH4 flux and its mitigation potential by aeration in freshwater aquaculture: Measurements and global data synthesis

Abstract

Freshwater aquaculture ponds constitute one of the important anthropogenic sources of atmospheric methane (CH4). Nevertheless, estimates of global CH4 emissions from freshwater aquaculture have large uncertainties due to a lack of data from different aquaculture types. Furthermore, despite that ebullition is a major pathway of CH4 in aquatic systems, the quantification of ebullitive CH4 fluxes from typical freshwater aquaculture ponds has been poorly represented. Here, field measurements of CH4 fluxes over two years were taken to quantify ebullitive CH4 fluxes from inland freshwater fish and crab aquaculture ponds in subtropical China. Ebullitive CH4 fluxes averaged 15.97 ± 1.57 and 11.22 ± 1.26 mg m−2 d−1 in the fish and crab ponds in the first experimental year, respectively, and were 22.86 ± 2.30 and 21.95 ± 2.19 mg m−2 d−1 in the second year. During aquaculture period, ebullition dominated the emission pathways of CH4, accounting for 83% and 98% of the total CH4 emissions in the fish and crab ponds, respectively. Ebullitive CH4 fluxes exhibited considerable spatial variations, with the lowest flux rates captured at the aeration area due to aerator-use in both the fish and crab ponds. Dissolved oxygen and dissolved organic carbon were the two primary factors that drove ebullitive CH4 fluxes in both aquaculture ponds. By incorporating global measurement data, we further assessed the CH4 mitigation potential of aerator use in freshwater aquaculture and revealed the dominant role of ebullition in this mitigation contribution. Together with the rice-based aquaculture, aerator use could reduce CH4 emissions from freshwater aquaculture ponds globally by 71% and in China by 63%.