CH₄ Analysis Of Methane Emission Characteristics And Its Influencing Factors Over Aquaculture Ponds

Aquaculture ponds are important sources of atmospheric methane?CH₄?.The emission pathes of CH₄from aquaculture ponds are mainly ebullition and diffusion,which are influenced by natural factors including air pressure,water temperature,and dissolved oxygen concentration and p H value of water,as well as human management including drainage,tanning and manure application.With the rapid development of aquaculture industry,the area of aquaculture ponds increases year by year,so it is important to identify the spatial pattern and temporal variability of CH₄emissions and its influencing factors for the investigations on the inland water and global carbon cycle.In order to investigate the CH₄emission characteristics of aquaculture ponds and the influencing factors,we conducted intensive campaigns in each season from 2017 to 2018 over two typical ponds in Yangtze River Delta.The ebullition and diffusion flux of CH₄were measured with inverted-funnels and calculated based on bulk diffusion model,respectively.The main conclusions are as follows:?1?The ebullition,diffusion and total flux?ebullition+diffusion?of CH₄in the aquaculture pond showed significant temporal variabilities.On daily scale,CH₄ebullition showed significant diurnal variation,with larger values from 0:00 to 6:00,and lower value from 18:00 to midnight.On seasonal scale,the variabilities of CH₄ebullition flux and total flux showed a pattern of summer>spring>autumn>winter.While the seasonal variabilities of CH₄diffusion flux were different,with seasonal mean value of summer>winter>spring>autumn.On annual scale,the interannual variability was obvious,with the annual mean values of the CH₄ebullition flux,diffusion flux and total flux were 120.281?1.889 and122.170 mg??m²?d?^-1in 2017,and reduced by half in 2018.?2?The spatial variabilities of the CH₄ebullition flux and CH₄total flux were more internsive than thoes of the CH₄diffusion flux.The range of spatial variability for CH₄diffusion flux was 10^-2–10¹mg??m²?d?^-1,which was much smaller than that of CH₄ebullition flux[10^-2–10³mg??m²?d?^-1].The CH₄emission was dominated by ebullition,which accounted for 60%of the total CH₄emission.Therefore,the spatial variability of the CH₄total flux was mainly caused by that of the CH₄ebullition flux.?3?The temporal variability of CH₄emission from aquaculture ponds was influenced by natural factors.The control factors of CH₄ebullition flux and total flux were air pressure,water temperature,p H value and dissolved oxygen concentration of water.The CH₄ebullition flux and total flux were positively correlated with water temperature at 20 cm significantly,and negatively correlated with air pressure,p H value and dissolved oxygen concentration.The CH₄diffusion flux had no significant correlation with meteorological factors.?4?Regarding anthropogenic factors,the temporal variability of CH₄emissions in winter was affected by drainage,while the spatial pattern in spring was controlled by manure treatment.Winter drainage enhanced both of the CH₄ebullition flux and the total flux of the aquaculture ponds in winter significantly.During the drainage period in winter,the water depth was negatively correlated with the CH₄ebullition flux and total flux,and with the decrease of water depth,the CH₄ebullition flux and total flux increased exponentially.In spring,the magnitude of the CH₄ebullition flux and total flux at the launch points of chicken manure were two to three orders higher than other sampling points.In 2018,the CH₄ebullition flux at the chicken manure launch points reached 1002.336 mg??m²?d?^-1,and accounted for more than 99.9%of the CH₄total flux.Anthropogenic factors had no obvious influence on CH₄diffusion flux.This study can provide fundamental data support and theoretical reference for assessing the contribution of CH₄emissions from small aquaculture ponds to the global greenhouse gas cycle.