Interactive Effects Of Inudantion And Salinity On Carbon Greehouse Gas Emissions From Fresh Water Tidal Wetlands In Minjiang River Estuary,Southeast China

The sea level rise in the coming future will affect the production and emission of carbon greenhouse gases（i.e.CO₂ and CH₄）in the estuary tidal wetlands.This study examined the interactive effect of increasing inundation（0 cm,15 cm and 30 cm）and salinity（0‰,2.2‰and 8‰）on the soils from freshwater tidal wetlands in the estuary of Minjiang River estuary in Fujian Province.The results indicated that:（1）The CH₄ efflux elevated by 53.59%and 65.24%when the water-level increased15 and 30 cm,respectively,while inundation showed no impact on CO₂ efflux.The increased inundation also exerted a significant influence on dissolved CH₄ concentrations,porewater NH₄⁺and NO₃^-concentrations,the rates of methanogenesis,the ratios of C:N,activities ofβ-glucosidase（BG）and cellobiohydrolase（CBH）.（2）The CH₄ efflux decreased by 63.94%and 90.50%,while CO₂ efflux increased by10.37%and 7.64%,as salinity increased by 2.2‰and 8‰,respectively.The increased salinity also exerted a significant influence on above-and below-ground biomass,total mineralization rates,the concentrations of DOC,activities of BG and CBH,and the rates of methanogenesis.（3）The interactive effects of inundation and salinity has significant impact on CH₄and CO₂ effluxes,the concentrations of porewater NH₄⁺,NO₃^-,the rates of methanogenesis,and the activities of CBH.Significant monthly changes of CH₄ and CO₂ effluxes,the concentrations of dissolved CH₄ DIC,DOC,porewater NH₄⁺and NO₃^-were observed across month.The peaks of CH₄ effluxes ocurred in the summer and autumn,with the lowest values appear in winter and spring.The CH₄ and CO₂ effluxes have an exponential function regression relationship with the porewater NH₄⁺concentration,DOC concentration,and soil temperature.（4）The interactive effects of inundation and salinity has significant impact on the structure and abundance of methanogens communities.Methanomicrobiales and Methanosarcinales were the dominannt species（50%-55%）.Methanoculleus are dominant（10%-16%）,the proportion of other methanogenic archaea is lower.The above results indicated that:although sea-level rise in the future will increase the CH₄ efflux,it will also reduce the CO₂ efflux,Compared with the increase in salinity,the effect of the water-level increase on CH₄ efflux is lower.Under the both inundation and salinity treatments,the comprehensive global warming potentials（dominated by CO₂） were mainly reduced.