A Comparison Of Nitrous Oxide Emissions From Crab And Fish Aquaculture Wetlands

China leads the world in aquaculture production,and pond farming accounts for more than half of the aquaculture area.The farming wetland contributes a lot to N2O emissions,and crab/fish farming wetland is a typical type of freshwater wetland.In this study,N2O emissions from crab/fish farming wetlands were observed in situ by two different methods.The goal of the study was to explore N2O emission intensity,emission characteristics,driving mechanisms in crab/fish farming wetlands.And,this study can provide data support for greenhouse gas emission reduction of freshwater aquaculture wetlands,and help reduce the uncertainty of greenhouse gas emission estimation of current wetland ecosystem.The main research contents include:1.during the one-year observation period from August 2018 to August 2019,the floating chamber method and the diffusion model method were used to measure the N2O emissions from crab/fish farming wetlands;2.to study the N2O emission intensity,characteristics and driving mechanisms in crab/fish aquaculture wetlands,and to analyze its uncertainty.The main results and conclusions are summarized as follows:(1)The N2O emissions in crab/fish farming wetlands have the same seasonal feature:high emission in summer and autumn and low emission in winter and spring.The annual average flux of floating chamber method in crab farming wetland was 22.09 ?g m-2 h-1,and that of diffusion model method was 8.86 ?g m-2 h-1.The annual average flux of floating chamber method in fish farming wetland was 20.90 ?g m-2h-1 and that of diffusion model method was 19.83 ?g m-2 h-1.There is a linear correlation between the two methods.The results of the diffusion model method vary greatly among two models and there are too many influencing factors.The floating chamber method is fit for the measurement of N2O emission flux in crab/fish farming wetlands.(2)Most N2O emission was released in drainage period,and N2O emission intensity is the highest in drainage period.In drainage period,N2O emissions accounted for 78.32%of the whole year breeding cycle,and 21.73%in flooding period.The average seasonal flux of N2O in drainage period is about 3 times that in flooding period.The average N2O emission flux of the crab farming wetland during the drainage period,the flooding period and the whole year breeding cycle was 7.38?g m-2 h-1,8.89 ?g m-2 h-1 and 22.03?g m-2 h-1,respectively.The annual N2O emission flux of the fish farming wetlands varies between 2.44 and 98.69 ?g m-2 h-1 respectively,with an average flux of 20.90 ?g m-2 h-1.The total emission in winter and spring is 23.65%of the total annual emissions,and 76.35%in summer and spring.(3)Agricultural aquaculture wetland is an important source of atmospheric N2O emission.Water/sediment temperature,water/sediment mineral nitrogen(NH4+-N+NO3--N)and sediment DOC all have significant positive correlation with N2O emission flux.There is a negative correlation between DO and N2O emission flux,and these environmental drivers are important affecting factors of N2O emission in crab/fish farming wetlands.(4)Compared with the crab farming wetland,the fish farming wetland has a lower N2O emission level,which is mainly attributed to the higher water depth,the larger water area,the strong fish activity to create an aerobic environment,and the timely dredging activity.Therefore,the N2O emission can be realized by controlling water temperature,dissolved oxygen and other environmental factors,less use of nitrogen fertilizer and feed,regularly cleaning the bottom silt of farming pond and other engineering and breeding management measures.