淡水养殖系统温室气体CH4和N2O排放量研究进展

2016年全球鱼类产量达到1.71亿t,对动物蛋白消费量的贡献率为17%。淡水养殖是鱼类产品的重要来源,贡献率为30%,大量投喂饲料强烈影响着水体CH4和N2O排放。本文综合分析了淡水养殖系统CH4和N2O排放的特征,稻田转变为具有曝气增氧系统的养殖塘降低了CH4排放,而转变为普通(粗放型)养殖塘则显著提高了CH4排放。稻鱼共作改变了稻田系统CH4和N2O排放,促进了深水层(>11.5 cm)稻田CH4和N2O排放,相反却降低了浅水层(<11.5 cm)稻田CH4和N2O排放;整合全球数据,稻鱼共作稻田在不同类型淡水养殖系统中具有较高的CH4和N2O排放系数,降低水层深度是减缓稻鱼共作稻田温室气体排放的重要途径。与粗放型养殖相比,集约化淡水养殖系统虽然N2O排放系数较高,但是CH4排放量和综合温室效应很低,是淡水养殖发展的方向。全球淡水养殖系统CH4排放量初步估计为6.04 Tg,N2O排放量为36.7 Gg。提升淡水养殖系统集约化水平是提高饲料转化系数、减缓温室气体排放和削减对水体环境负荷的重要途径,是实现可持续发展的关键。

CH4 and N2O emissions from freshwater aquaculture

The global fish production in 2016 has reached 171 million tons, which contributed 17% of the global consumption of animal protein. Freshwater aquaculture is an important contributor of fish, and is also a key source of atmospheric CH₄ and N₂O. In this paper, the fluxes of CH₄ and N₂O in the different type of freshwater aquaculture were summarized. The conversion of paddy field to extensively managed freshwater aquaculture(pond)increased CH₄ emissions, and in contrast, conversion of paddy field to intensively managed aquaculture reduced CH₄ emissions. Rice-fish paddy field is found to be a hotspot of atmospheric CH₄ and N₂O, with the highest emission factors of CH₄ and N₂O in freshwater aquaculture system. It is necessary to develop necessary field management practices such as decreasing water layer depth to reduce greenhouse gas emissions from paddy fields. Although N₂O emission factor of the applied N in the intensively managed freshwater aquaculture was high, however CH₄ emission factor was close to zero, resulting in the low global warming potential. Thus, the intensively managed freshwater aquaculture is the direction of freshwater aquaculture development. The global budget of CH 4 and N₂O emissions in freshwater aquaculture system was 6.04 Tg and 36.7 Gg, respectively, of which China was the larger contribution country. Thus, it is urgent for China to improve the equipment level and intensively management level in freshwater aquaculture in order to improve feed conversion coefficient and reduce the potential pollution on neighboring water body.