Ebullitive CH4 flux and its mitigation potential by aeration in freshwater aquaculture: Measurements and global data synthesis
2022
Fang, Xiantao | Wang, Chao | Zhang, Tianrui | Zheng, Fengwei | Zhao, Jianting | Wu, Shuang | Barthel, Matti | Six, Johan | Zou, Jianwen | Liu, Shuwei
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%.
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