The impact mechanism of greenhouse gas emissions in the dissipation zone of intensive farming fish ponds under water level changes in the lower Yangtze River:a case study of the Nanjing area
The sediment in the aquaculture fish ponds with high greenhouse gas emissions,combined with previous field observation data,was studied to determine the impact of water level changes on greenhouse gas(GHGs)emissions from sediment in freshwater aquaculture fish ponds in Nanjing.Through indoor microcosm cultivation experiments,four different water level treatment groups were set up:high,low,high then low,and low then high.Gas chromatography was also used.Influencing mechanisms were explored using UV visible spectroscopy and 3D fluorescence spectroscopy(3D-EEMs).Research has shown that:the CH4 emission capacity of the static high water level group are 3.46 times that of the static low water level group.The cumulative CO2 emissions of the static low water level group are 1.21 times that of the static high water level group.The static low water level group shows continuous absorption of N2O.The data of the dynamic simulation group shows that both rainstorm and sudden drought promote CO2 and CH4 emissions,and the cumulative emissions of these gases in the simulated rainstorm group are 1.15 times and 2.53 times,of the static low water level group respectively.The cumulative CO2,CH4,and N2O emissions in the simulated drought group were 1.25 times,1.08 times,and 2.84 times higher than those in the static high water level group,respectively.Research has shown that the differences and effects of water level changes in soluble organic matter play a crucial role in the production and emission of GHGs.The correlation between CO2 emissions and soluble organic carbon concentration is highest.There is a significant negative correlation between CH4 emissions and C/N,as well as a significant correlation with dissolved organic matter qualitative spectral indices(HIX and SUVA254).N2O emission is mainly affected by nitrification and denitrification caused by changes in water level.
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