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A comparison of methane emissions following rice paddies conversion to crab-fish farming wetlands in southeast China

Hu, Zhiqiang, Wu, Shuang, Ji, Cheng, Zou, Jianwen, Zhou, Quansuo, Liu, Shuwei
Environmental science and pollution research international 2016 v.23 no.2 pp. 1505-1515
aquaculture, aquatic plants, dissolved organic carbon, dissolved oxygen, ecosystems, farming systems, field experimentation, greenhouse gas emissions, methane, paddies, rice, sediments, wetlands, China
Rice paddies and aquaculture wetlands are typical agricultural wetlands that constitute one of the important sources of atmospheric methane (CH₄). Traditional transplanted rice paddies have been experiencing conversion to pond aquaculture wetlands for pursuing higher economic benefits over the past decades in southeast China. A parallel field experiment was carried out to compare CH₄ emissions from a transplanted rice paddy and its converted crab-fish farming wetland in southeast China. Over the rice-growing season, CH₄ fluxes averaged 1.86 mg m⁻² h⁻¹ from rice paddies, and 1.14 and 0.50 mg m⁻² h⁻¹ for the treatments with or without aquatic vegetation present in the crab-fish farming wetlands, respectively. When averaged across the treatments, seasonal CH₄ emissions from crab-fish framing wetlands were 52 % lower than those from rice paddies. The CH₄ fluxes were negatively related to water dissolved oxygen (DO) concentration but positively related to soil/sediment dissolved organic carbon (DOC) content in crab-fish farming wetlands. Dependence of CH₄ fluxes on DO or DOC was intensified by the aquatic vegetation presence. By extrapolating the present CH₄ emission rate with the current rice paddy-converted aquaculture cultivation area, the seasonal CH₄ emissions from inland aquaculture wetlands during the critical farming stage (20 June to 18 October) were estimated to be 33.6 Gg ha⁻¹ in southeast China in 2012. Rice paddies conversion to crab-fish farming wetlands might have reduced CH₄ emissions by 22–54 % in mainland China. Results of this study suggest that the conversion of transplanted rice paddies to crab-fish aquaculture wetlands for higher economic benefits would also lead to a lower ecosystem CH₄ release rate.