CHBr3 And CHCl3 Fluxes And Controlling Factors In Tidal Flat Wetland Of Jiaozhou Bay

Volatile halocarbons?VHCs?are important trace gases in atmospheric.VHCs can produce photochemical reactions in the atmosphere that destruction of the ozone layer and create a greenhouse effect,which have a significant impact on global climate change.Coastal wetland is an excessive area affected by both ocean and land.It has rich substrate and high content of organic matter in soil,and plays an important role in the global carbon cycle.S.alterniflora is one of the most invasive plants in coastal wetlands of China.Its invasion has not only changed the original ecological structure of the wetland,but also affected the global climate change by changing the regional trace greenhouse gas emissions.Therefore,it is of great significance to study the VHCs flux of S.alterniflora wetland to determine its contribution to atmospheric VHCs and to assess its impact on global climate change.The coastal wetland of the Yanghe River estuary of Jiaozhou Bay was selected as the research object in two habitats,S.alterniflora wetland and bare flat.In July,September,October,November,December of 2016 and March and May of 2017,the flux characteristics of 2 common VHCs were observed by static box method.The temporal and spatial variation of gas flux and its influencing factors are analyzed,which provides important basic data for estimating the contribution of wetlands to atmospheric VHCs at the global scale and the related research in the future.The results of this study as follow:?1?On the whole,the fluxes of two VHCs of CHBr₃ and CHCl₃ in spring,summer,autumn and winter were 37.04 nmol·?m²·d?^-1,18.35 nmol·?m²·d?^-1,4.61 nmol·?m²·d?^-1 and18.98 nmol·?m²·d?^-1;-17.66 nmol·?m²·d?^-1,-15.25 nmol·?m²·d?^-1,-16.29 nmol·?m²·d?^-1 and-22.44 nmol·?m²·d?^-1,respectively.The annual mean fluxes were 19.745 nmol·?m²·d?^-1and-17.91 nmol·?m²·d?^-1,respectively,indicating that coastal wetland acted as CHBr₃source and the sink of CHCl₃.?2?CHBr₃ fluxes had significant differences in different seasons.The seasonal variation of CHBr₃ fluxes were influenced by temperature,and the seasonal variation of flux was consistent with the seasonal variation of temperature.The CHBr₃ flux of bare flat was affected by many factors.There is no significant difference in CHBr₃ flux between different seasons,and seasonal changes in CHBr₃ flux were affected by multiple effects of soil moisture content and other factors?such as salinity and temperature?.?3?The CHBr₃ emission flux of S.alterniflora wetland was higher than that of bare flat,this shows that S.alterniflora can promote CHBr₃ emissions.The uptake of CHCl₃ in S.alterniflora wetland was lower than that of bare flat,indicating that S.alterniflora wetland has the potential to weaken the wetland as CHCl₃ sinks function.?4?Through principal component analysis and linear regression analysis,the results show that the flux of CHBr₃ and CHCl₃ from coasatal wetlands in Jiaozhou Bay were affected by many factors.Different environmental factors have different effects on CHBr₃flux changes.In the S.alterniflora wetland,pH had a significant effect on the CHBr₃ flux;however,no significant regression equation was found between CHCl₃ and environmental factors.The reason may be more complex with the environmental factors of S.alterniflora wetland and the emission of CHCl₃ may be controlled by multiple factors.In bare flat,pH,sediments temperature?20 cm,25 cm?,organic matter and water content all have an significant effect on the CHBr₃ flux,of which pH and sediments temperature have the greatest effect.The water content has a significant effect on the flux of CHCl₃,and other environmental factors also have a certain influence on the change of CHCl₃ flux.Although the impact of other factors on CHCl₃ emissions has not reached a significant level,it cannot be ignored.