Effects Of Enrichement Of Nitrogen And Sulfate Load On CH₄ And CO₂ Fluxes From The Cyperus Malaccensis Marsh In The Min River Estuary

Coastal estuarine marsh,located along the intersection between sea and land,is an important ecosystem type,which is sensitive to the global change and human activities.Unique susceptibility to outside stress response makes it become an important area of the carbon cycle research.In recent years,rising intensity of human activities,such as fossil-fuel combustion and nitrogen fertilizer application,have resulted in much higher nitrogen?N?and sulfate(SO₄^2-)loads in near-shore waters,becoming a key factor in changing the biogeochemical cycle of these environments.Although estuarine tidal marshes are important contributors to GHG emissions,the relationships between GHG emissions,N and SO₄^2-enrichment have not been thoroughly investigated in these environments.Using field simulation and laboratory incubation techniques,we determine and reveal the effect and mechanism of N and SO₄^2-load on CH₄ and CO₂ fluxes from cyperus malaccensis marsh in the Min River estuary.The main results were as follows:?1?The effects of N and SO₄^2-addition on CH₄ and CO₂ fluxes from cyperus malaccensis marsh are not consistent in the Min River estuary during the experiment.Compared to the control,CH₄ fluxes in the ammonium nitrogen?NH₄⁺-N?,nitrate nitrogen?NO₃^--N?,sulfate?SO4--S?and N plus SO₄^2-addition treatments were increased by 164.10%,23.08%,-28.21%and 112.82%,respectively;CO₂ fluxes were increased by 158.32%,54.66%,71.20%and 100.52%,respectively.CH₄ fluxes increased significantly from the addition of NH₄⁺-N,and N plus SO₄^2-?P<0.05?;CO₂ fluxes increased significantly from the addition of NH₄⁺-N?P<0.05?.CH₄ and CO₂ fluxes in different treatments were significantly higher in summer and lowest in winter.?2?Stepwise regression analysis showed that the impact factors of CH₄ and CO₂ fluxes from varying treatments were different.Overall,temperature,pore water SO₄^2-,Cl^-,inorganic N and DOC,soil EC are the main environmental factors affecting CH₄ and CO₂ emission fluxes in the Min River estuary marsh.Temperature,salinity,sulfate reduction,N availability and soil enzyme activities are key factors affecting CH₄ and CO₂ emissions in the Min River estuary due to the N and SO₄^2-treatment.?3?CH₄ and CO₂ emissions from the high tidal flat marsh in the Min River estuary exhibited typical temporal dynamics,with the effects of exogenous N and SO₄^2-broadly following changes over time.Different sampling times in different seasons have an impact to GHG fluxes after adding exogenous substances.In different seasons,CH₄ fluxes increased significantly in the NH₄⁺-N and N plus SO₄^2-treatments?P<0.05?,and has obvious fluctuation variation characteristics over times.CO₂ fluxes have a similar time dynamics following the N and SO42" treatment.?4?The effects of N and SO₄^2-addition on the fractions of organic carbon?DOC,MBC and EOC?from cyperus malaccensis marsh are not consistent in the Min River estuary.Overall,the contents of DOC,MBC and EOC were promoted by N and SO42"addition,while the contents of DOC,MBC and EOC were not significantly changed?P>0.05?,except NH₄⁺-N treatment significantly increased the soil DOC?P<0.05?.?5?In different seasons,soil organic carbon mineralization rate significantly increased by N and SO₄^2-addition?P<0.05?,except for NO₃^--N treatment.And soil CO₂ production rate under different N and SO₄^2-addition showed increasing with the incubation time.CH₄ production rate in the estuarine marsh was significantly promoted by the addition of NH₄⁺-N;while the CH₄ production rates were not significantly changed by the additions of NO₃^--N and SO₄^2--S.CH₄ oxidation rate was significantly promoted by the addition of NO₃^--N;and was inhibited by the addition of NO₃^--N;while was not significantly changed by the addition of SO₂'-S.?6?Estuarine marsh soil CH₄ production/oxidation rate,organic carbon mineralization rate were mainly affected by the contents of soil DOC,NO₃^--N and Cl^-.The promotion or inhibition of the N and SO₄^2-addition on CH₄ production/oxidation rate,and organic carbon mineralization rate,are the main driving force of CH₄ and CO₂ emission.