Effects Of Simulated Saltwater Intrusion And Fe³⁺ Increase On N₂O Emission From Tidal Freshwater Marshin The Min River Estuary

Sea level rise aggravated saltwater intrusion and ferric iron increasement profoundly affect the nitrogen biogeochemical cycle in estuarine tidal wetland.N₂O flux and its main environmental factors under the simulated saltwater intrusion and ferric iron increase were measures using the static black chamber-gas chromatography method in the Tajiaozhou freshwater tidal marsh of the Min River estuary.The acetylene inhibition method was applied to determine the sediment denitrification rates,further the effects of denitrification on the N₂O release were analyzed,and the main ways of N₂O production and its main influence factors of tidal wetland sediments under saltwater intrusion and ferric iron increase were revealed.The results showed that:（1）The Tajiaozhou freshwater tidal marsh functioned as a source of N₂O.N₂O flux of control group ranged from-54.44 to 63.53 μg·m^-2·h^-1 and the average value was 18.79±7.40 μg·m^-2·h^-1,N₂O flux of ferric iron group ranged from 4.38 to 157.15μg·m^-2·h^-1 and the average value was 51.89±12.13 pg·m^-2·h^-1.N₂O flux of saltwater intrusion group ranged from 5.92 to 235.74μg·m^-2·h^-1 and the average value was 72.32±16.82 μg ·m^-2·h^-1 N₂O flux of saltwater intrusion and ferric iron group ranged froml4.34 to362.03 μg·m^-2·h^-1 and the average value was 130.84±20.85 μg· m^-2·h^-1.There were obvious seasonal variations of N₂O fluxes in the four group,the maximum（minimum）value of this four group N₂O flux was all appeared in summer（winter）.（2）The main factor affecting the N₂O flux are soil temperature,salinity,moisture content,inorganic nitrogen,pH value,pH value and coupling of ferric iron content changes.Control group N₂O flux is mainly affected by soil temperature,iron group of N₂O flux is mainly affected by soil temperature,electrical conductivity,SO₄^2-content,Fe³⁺ content of comprehensive effect,salt group of N₂O flux is mainly affected by the conductivity and interstitial water of NH₄⁺ content,the influence of salt and iron group of N₂O flux is mainly affected by soil temperature,electrical conductivity,interstitial water NO₃^-content,Fe³⁺ content of comprehensive effect.Cause salt group,iron group,salt and iron groups N₂O flux higher than the control group is applying salinity and exogenous ferric iron.Salt group N₂O mainly produced from denitrification,pore water NH₄⁺concentration inhibited it.SO₄^2-is an important factor promote N₂O emission in iron group,salt and iron group inhibition control group and salt group.soil temperature increase iron group and salt iron group N₂O emission,pH value and coupling of ferric iron content regulate N₂O emission.（3）Four groups of applying sediment control,iron,salt,salt and iron group of denitrification rate maximum value were appeared in the autumn,salt and iron denitrification rate minimum value in the winter,other groups with the lowest in the summer.Comprehensive sediment denitrification rate of four groups,control iron,salt,salt iron groups corresponding average is:the iron salt group(34.50±34.73 mmol·g^-1·h^-1)>iron(9.33 ± 18.64 mmol·g^-1·h^-1)>control(-0.24 ± 18.73 mmol·g^-1·h^-1)>salt(-0.74±18.57 mmol· g^-1·h^-1).control group and salt group present a N₂O absorption,salt in iron and iron group present a N₂O emissions.（4）The denitrification rate experiment showed that temperature is an important factor affecting sediment denitrification rate and denitrification rate is negative,may be associated with the reduction of N₂O.Four groups main factors causing the denitrification rate is different,the control group effected by the sediment of Cl-content and tide NO₃^-content,iron group and solt iron group of denitrification rate is mainly influenced by the pH value,the tide of NH₄⁺ content and SO₄^2-content,salt iron group of denitrification rate is mainly by the tide of NH₄⁺ content and SO₄^2-content.（5）Processing of exogenous ferric iron,SO₄^2-is increases,ferric iron is run out,denitrification rate is downward trend.pH value and coupling of ferric iron content regulate N₂O emission.（6）Tide NH₄⁺content promoting the denitrification rate of iron group,NO₃^-produced by nitrification through NH₄⁺ by denitrification was used by a more direct,is one reason for the denitrification rate higher than that of the control and salt group.