Methane Emission And Salinity Effects In The Liaohe Estuary Wetland

Liaohe estuary coastal wetland is one of the representative estuarine tidal wetlands in temperate zone of China,where periodic transgression-receding process and the convergence of brackish water led to unique natural environmental characteristics.The change of salt will have an important impact on wetland carbon sinks.However,the influence of salinity on methane?CH₄?generation and emission flux in Liaohe estuary wetland and corresponding mechanism are still to be explored.To have a better understanding,this study was conducted by enclosed chamber and gas chromatography technique in three typical natural wetlands of Liaohe estuary named Phragmites Australis wetland,Saline Seepweed wetland and Mudflat,respectively.Based on in situ observation,combined with methods of laboratory simulated soil core culture and anaerobic control culture,the CH₄ emission flux characteristics and influencing factors of different types of wetland were studied.Also,the effect of salinity on CH4 emissions flux,characteristics and mechanism of CH4 generation responding to specific ionic strength and salinity coupling with temperature were discussed.The main conclusions were drawn as follows:i.CH₄ emission flux in Liaohe estuary wetland varies obviously with season and differed among wetland types significantly,in the order of Phragmites Australis wetland>Mudflat?before tide?>Saline Seepweed wetland?before tide?;Phragmites Australis wetland>Mudflat?during tide?>Saline Seepweed?during tide?.Tide and EC are the key factors inhibiting CH4 fluxes between types of wetland.ii.Salinity had a significant effect on soil microbial biomass carbon?MBC?,dissolved organic carbon?DOC?,plant biomass and CH₄ emission flux.MBC,DOC and plant biomass decreased with elevated salinity;CH₄ emission flux was inhibited by24.2%⁴0.6%with enlarged salinity addition.CH₄ emission flux was positively correlated with MBC and DOC at the end of culture,and also for plant biomass without significant difference.Salinity inhibits CH₄ emissions by reducing MBC,DOC and plant biomass.iii.In terms of wetland types,potential soil CH₄ production presents as Phragmites Australis wetland>Saline Seepweed wetland;in terms of soil depth,potential CH₄ production of Phragmites Australis in the order of topsoil?0¹0 cm?>subsoil?10²0 cm?,although there is no significant difference in Saline Seepweed wetland.Chloride ion?Cl^-?and sulfate ion(SO₄^2-)inhibited the potential CH₄production in two types of wetland soils,and the inhibition was enhanced with the elevated ion strength.Under the condition of salinity input,inhibition of Cl^-is higher than that of SO₄^2-,except for the topsoil of Phragmites australis wetland.iv.Raising temperature is beneficial to the generate potential of CH₄ in wetland soil,however,the effect of Cl^-and SO₄^2-on the potential CH₄ production is opposite under salinity coupling temperature.Elevated temperature weakens the inhibitory effect of Cl^-on the potential of CH₄ production and strengthens the inhibition of SO₄^2-conversely.Meanwhile,addition of Cl^-stimulated the sensitivity of potential CH₄generation to temperature,while a contrary result in that of SO₄^2-addition.Above all,the process of soil CH₄ generation and discharge in Liaohe estuary wetland is obviously restricted by salinity.Elevated salinity can inhibit the potential of CH₄ generation,lower the CH₄ emission flux and reduce the loss of CH₄ release in wetland carbon pool.The mechanism of salinity may due to the change of soil matrix and plant biomass under different intensity and type of ions.