Effects Of Simulated Constant And Fluctuating Salinity On CH₄ Fluxes,Methanogens And Sulfate-Reducing Bacteria In Estuarine Wetland

As an important type of natural wetlands,estuarine tidal wetland is a natural atmospheric methane(CH4)source that can not be ignored Global climate change,sea level rise,and seawater intrusion,combined with the effects of river runoff and ocean tides,have caused significant salinity changes in the estuarine wetlands and have profoundly affected the production and release of CH4 in the estuarine wetlands.This paper collected the soil core and plant from the Cyperus malaccensis marsh and non-vegetated wetland(bare mudflat)of the Tiaojiaozhou in the Min River estuary,and further constructed the mesocosm.A simulation experiment was conducted to study the effects of constant and fluctuating salinity on the CH4 flux,the community structure and abandunce of methanogens and sulfate reducing bacteria(SRB)in estuarine freshwater tidal wetlands,and the main environmental factors affecting the CH4 flux.At the end of the experiment,the soil methane production potential under different treatments was measured using the anaerobic culture method,and the impact of different treatments on the methane production potential of the soil was analyzed.The results show:(1)Compared with the estuarine freshwater tidal wetland,the constant salt water treatment has a significant inhibitory effect on the CH4 emission,while the inhibitory effect of fluctuating salinity treatment was relatively weak.Under different treatments,the CH4 fluxes in the C.malaccensis wetlands were all higher than those in the non-vegetation-covered wetlands in different degrees.(2)There is a negative correlation between the CH4 fluxes and porewater salinity,NH4+-N concentration,TN concentration,Cl-concentration,SO42-concentration,and soil conductivity,and there was a positive correlation between dissolved CH4 concentration and porewater pH.The temperature,humidity,and dissolved CH4 concentration in porewater had significant contributed to the CH4 flux in the C.malaccensis wetland;the air pressure,dissolved CH4 concentration and porewater pH had significant contribution to the CH4 flux in non-vegetated cover wetland.(3)The methanogens detected in the C.malaccensis marsh and non-vegetated wetland included:Methanosarcinales,Methanomicrobiales,Methanobacteriales.Constant salt water treatment significantly reduced the distribution of Methanosarcinales in wetland soils compared to constant fresh water treatment,but increased the Methanomicrobiale and Methanobacteriales,especially Methanobacteriales.(4)The SRB detected in the C.malaccensis marsh and non-vegetated wetland included:Desulfovibrionales,Desulfobacterales,Syntrophobacterales,Clostridiales.Constant salt water treatment significantly increased Desulfobacterales compared to constant freshwater treatment;both of constant salinity and fluctuating salinity treatments increased Syntrophobacterales in C.malaccensis wetland soils but are slightly reduced in non-vegetated wetlands.(5)In the C.malaccensis wetland,compared to constant fresh water treatment,both constant salinity and fluctuating salinity treatment reduced the methanogenic bacteria in the C.malaccensis wetland,but the reduction in constant salinity treatment was bigger than the fluctuating salinity treatment.In the non-vegetated wetlands,fluctuating salinity treatment increased the abandunce of methanogens and SRB,and constant salinity treatment reduced the abandunce of methanogens and SRB.(6)Comparing to the fresh water treatment,both constant saline water treatment and fluctuating salinity treatment reduced the rate of CH4 production in estuarine wetland.The rates of CH4 production in the C.malaccensis wetland under different treatments were all greater than those in non-vegetated wetlands.