Dissolved N₂O Concentrations And N₂O Fluxes At The Water-atmosphere Interface In Coastal Reclaimed Shrimp Ponds In The Min River Estuary

With the increase of human demand for aquatic products,the area of aquaculture ponds is gradually expanding worldwide.Previous studies had confirmed that aquaculture ponds are potential sources of greenhouse gas emissions.Nitrous oxide?N₂O?as an important greenhouse gases,increasing in N₂O concentration have a great impact on global warming,ozone layer destruction and acid deposition.A comprehensive study on N₂O concentration,transport and emission in aquaculture system water body can support reference value for discussing N₂O biogeochemical cycle in reclaimed aquaculture ponds in estuary area,and also provides basic data for relevant departments to carry out scientific management of reclaimed aquaculture ponds and greenhouse gas emission reduction.In this paper,Litopenaeus vannamei aquaculture pond?hereinafter referred to as shrimp pond?in eel beach wetland of Minjiang estuary was taken as the research object.During the aquaculture period?June-November 2017?,field in-situ observation and laboratory experimental analysis methods were used to carry out the research,and headspace equilibrium-gas chromatography was used to determine N₂O concentration and saturation in shrimp pond water.Diffusion of N₂O and bubble flux at the water-air interface were measured by diffusion suspension box method and inverted funnel method respectively,and the main route of N₂O entering the atmospheric reservoir in shrimp pond water was explored.The main research results are as follows:?1?Environmental factors in shrimp ponds have obvious spatio-temporal dynamic characteristics.In terms of time,the average wind speed,air pressure,pH,conductivity and TDN in June to August are significantly lower than those in September to November,and there is no significant difference between DO,NO₃^--N,NH₄⁺-N and PO₄^3--P in each month.Spatially,DO in the surface layer of water body is significantly higher than that in the bottom layer,and there is no significant difference in other water environmental factors in each layer.?2?The dissolved N₂O concentration ranges from 5.08 to 14.12 nmol·L^-11 in the shrimp ponds,with an average value of 8.33±0.07 nmol·L^-1.The N₂O saturation ranges from105.40 to 335.67%,with an average value of 180.33¹.43%.The shrimp pond as a whole shows N₂O emission source.In time,the concentration and saturation of dissolved N₂O in shrimp pond water fluctuated greatly,and the concentration and saturation of dissolved N₂O in September to November were generally higher than those in June to August.Spatially,there is no stratification in the vertical direction of N₂O concentration and saturation in water.?3?The N₂O diffusion flux ranges from 0.85 to 12.06 g·m^-2·h^-11 at the water-air interface of shrimp ponds,and the bubble flux ranges from 0.00004 to 0.00039 g·m^-2·h^-1.The total N₂O flux ranges from 0.85 to 12.06 g·m^-2·h^-1.From September to November,the total flux is in a high value region,while it is lower in other months.The total flux and diffusion flux of N₂O are significantly positively correlated with wind speed.The change of wind speed on water-air contact area and dissolution rate of sediment carbonate increases N₂O emission flux from water surface.?4?The diffusion suspension box method and inverted funnel method were used to measure the fluxes of N₂O into the atmosphere in the shrimp pond culture period respectively.the results showed that the average values of N₂O diffusion flux and bubble flux were 2.74±1.26 g·m^-2·h^-11 and 0.00015±0.00003 g·m^-2·h^-11 respectively.N₂O diffusion flux accounts for 99.99%of the total flux,and N₂O bubble flux accounts for 0.01%of the total flux,showing the characteristics that the diffusion flux was significantly higher than bubble flux?P<0.05?,indicating that N₂O from shrimp pond water body entered the atmospheric reservoir mainly through diffusion routes.