| Methane（CH4）and nitrous oxide（N2O）are important trace greenhouse gases,which have a significant impact on global climate change.Coastal estuaries,lagoons and other waters with frequent human activities are important sources of CH4 and N2O in the atmosphere.The research on the biogeochemistry cycle of CH4 and N2O in typical water bodies such as lagoons has enriched the list of sources and sinks of CH4 and N2O in the global atmosphere,which is of great significance to the research on global climate change and carbon sources and sinks.In this study,two surveys were carried out in November 2021 and May 2022 in Xincun Bay.The concentration of CH4,N2O and hydroxylamine（NH2OH）and hydrological parameters in seawater were measured,and the air-sea exchange fluxes of CH4 and N2O were estimated.From June to July 2022,surveys were conducted in the tidal flat area of Xincun Bay Seagrass Bed Wetland,the concentrations of CH4 and N2O in sediment interstitial water at different depths and their influencing factors were investigate.The release fluxes of CH4 and N2O at the sediment atmosphere interface were measured.The sediments were cultured in the laboratory to explore the impact of different electron acceptor and substrates on CH4 production potential.The main conclusions are as follows:The average concentrations of CH4 in spring and autumn in Xincun Bay were 49.44±18.87 nmol/L and 52.28±11.62 nmol/L,respectively,and the average concentrations of CH4 in bottom water were 55.07±16.92 nmol/L and 51.30±9.19 nmol/L,respectively.The difference between the table and the bottom of each season is small,and the seasonal change is not significant.In situ production is the main source of CH4 in water.The average concentration of N2O in surface water in spring and autumn was 6.47±0.62 nmol/L and 6.39±0.62 nmol/L,and that in bottom water was 6.71±0.49 nmol/L and 6.23±0.60 nmol/L,respectively.There is little difference in the average concentration of N2O in different seasonal tables and bottom layers.N2O comes from partial nitrification,which is the main source of N2O in water.The CH4 saturation range（average）in spring and autumn was 656%to 4525%（2532±970%）,1483%to 4467%（2478±552%）,and N2O saturation range（average）was 93%to 130%（110±10%）and 84%to 118%（97±9%）,respectively.CH4 is supersaturated in spring and autumn and is the source in the atmosphere.N2O is in a state of low saturation in spring and autumn,and it is a weak source or even sink of the atmosphere.Using W2014 and N2000 formulas,the exchange flux ranges of CH4 at the sea-air interface in spring and autumn were estimated to be 0 to 57.99 μmol·m-2·d-1（0.01 to 72.91μmol·m-2·d-1）and 2.92 to 228.51 μmol·m-2·d-1（6.55 to 252.40 μmol·m-2·d-1）,respectively.The exchange fluxes of N2O at the air-sea interface were-0.12 to 1.62μmol·m-2·d-1（-0.19 to 2.01 μmol·m-2·d-1）and-0.39 to 1.26 μmol·m-2·d-1（-0.55 to 1.51μmol·m-2·d-1）,respectively.The fluxes of CH4 and N2O were higher in autumn.The average concentration of CH4 in the sediment interstitial water of the high,medium,and low tidal flats in Xincun Bay is significantly higher at the middle tidal level than at the low and high tidal flats,while the average concentration of N2O did not change significantly.CH4 concentration in interstitial water of sediment at middle tide is mainly affected by oxidation reduction potential,organic matter and nutrient content in shallow sediment.The CH4 emission fluxes of sediment-atmosphere interface at the high,middle and low tidal flat were 0.024 μg·m-2·h-1,0.031 μg·m-2·hland 0.018 μg·m-2·h-1,respectively.The N2O emission fluxes were-0.004 μg·m-2·h-1,0.036 μg·m-2·h-1 and-0.003 μg·m-2·h-1,respectively,which shows middle tidal flat>high tidal flat>low tide flat,and the sediment of high and low tide flat is the weak sink of N2O.Laboratory incubation of different electron receptors were added,the potential production of CH4 was inhibited in different degrees,and the inhibition degree of different electron receptors was different in each tide level culture process,which was affected by the background environmental factors.Through the culture experiment with different substrates,it was found that methanol was the main substrate for the production of CH4 in Xincun Bay. |
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