| Ozone Depletion has been one of the biggest environmental problems at present.Although CH3 Cl and CH3 Br in the atmosphere are the simplest compounds of the volatile halogenated hydrocarbon,they are the main substances which destroy the atmospheric ozone layer.Because of its high photochemical stability and low water solubility properties,their atmospheric life are about 1.0 years and 0.7 years respectively,and thus they have enough time to be transported to the stratosphere and further destroy the atmospheric ozone layer.The 17% of chlorine free radicals and 34% of bromine free radicals which destroy the ozone layer are courtesy of CH3 Cl and CH3 Br respectively.In addition,the methyl halide in the atmosphere also participate in photochemical reaction,and also has a certain greenhouse effect and toxic pollution function,and thus constantly get the attention of people.Coastal salt marshes,located in the transition zone between the ocean and land ecosystem and submerged by regular or irregular sea tide,are one type of the wetland ecosystem which are surrounded by the higher herbs or low shrubs vegetation.That is to say,the release of the halogen methane in the salt marshes is not only influenced by the sea and rivers through the tidal action?moisture fluctuation process,flooded length,water depth?,but also affected by the salt marsh vegetation,fungi,algae,and anaerobic-aerobic soil microbial community.As a result,that choose the coastal salt marshes and study the emission flux of the CH3 Cl and CH3 Br have a significant meaning on estimating the emission flux of the global ecosystem CH3 Cl and CH3 Br and clearing its global “source” and “sink” functions.The international dates of emission of methyl halide of salt marshes in the time and space are very lack,especially the domestic research is very limited.The emission of the methyl halides in salt marshes is lack of continuous,systematic,long-term and obdifferent regions of the observation data.The research on emission mechanism is lack and research on the emissions of salt methyl halides need to be strengthened.Choosing the Spartina alterniflora wetland and bare beach offshore as the research object and using static box-gas chromatography method,by field situ observation and indoor experiment analysis,CH3 Cl and CH3 Br emission laws and environmental factors have been analyzed,daily changes,monthly and seasonal changes of CH3 Cl and CH3 Br emission fluxes and influences of environmental factors have been discussed.Main conclusions are as follows:1)The dalily emission fluxes of CH3 Cl and CH3 Br in S.alterniflora wetland and bare flat are 0.109 0.427 ?mol·m-2·d-1,3.159 33.993 nmol·m-2·d-1,-0.328 -0.127 ?mol·m-2·d-1,-5.897 -2.698 nmol·m-2·d-1 respectively,the average value are 0.250 ?mol·m-2·d-1,20.825 nmol·m-2·d-1,-0.214 ?mol·m-2·d-1,-4.081 nmol·m-2·d-1 respectively.The maximum of the emission flux of the CH3 Cl in S.alterniflora wetland is at 13:00 and the minimum of that is at 23:00,however,that in bare flat is at 23:00 and 13:00 respectively.The maximum of the emission flux of the CH3 Br in S.alterniflora wetland is at 10:00 and the minimum of that is at 3:00 while that in bare flat is at 3:00 and 10:00 respectively.2)Except November,the monthly variations of the emission flux of CH3 Cl and CH3 Br in S.alterniflora wetland decreased gradually with the increase of the month?from September to December?.From September to October,the emission flux of CH3 Cl and CH3 Br increased gradually with the increase of the month,but decreased significantly in November,the emission flux of CH3 Cl and CH3 Br in Decemebr was positive.3)The seasonal changes of the emission flux of the CH3 Cl and CH3 Br in S.alterniflora wetland is bigger in autumn than that in winter.The emission flux of the CH3 Cl and CH3 Br in bare flat is nagetive in autumn,while the emission flux of the CH3 Cl and CH3 Br in bare flat is positive in winter.4)The experiment of plant aboveground biomass removal showed that the aboveground biomass of the plant is the source of CH3 Cl and CH3 Br,which indicated that the aboveground biomass of the plant releases CH3 Cl and CH3 Br.5)The main effects that influence the emission fluxes of CH3 Cl and CH3 Br in S.alterniflora wetland are pH,water contents,salinity and ground tempertuare.6)Compare with the other wetland in the world,the emission flux of CH3 Cl and CH3 Br in S.alterniflora wetland is lower than theirs.7)The emission fluxes of CH3 Cl and CH3 Br is significantly related,and the average CH3 Cl : CH3 Br molar flux ratio is 16.64. |
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