| As one of the most significant features of global change, global warming has become an indisputable fact in recent centuries. The latest research suggests that global warming is still on the way, and it has been one of the world’s most important environmental problems. Greenhouse gas emissions got the widespread international concern after the conference of Copenhagen, carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O), are the three most important greenhouse gases. The study of greenhouse gas emissions in estuarine wetlands is very significant, because the estuaries are important sources of greenhouse gas emissions. In addition, the estuarine greenhouse gas emissions always have great spatial and temporal variability due to its complexity and the strong interference of human activities. As one of the China’s eastern coastal estuarine wetlands.and the important part in the natural wetland in our country, the Chongming Dongtan wetland has large representative and research value., the study of greenhouse gas emissions and absorption of Yangtze estuary wetland should be an important component of greenhouse gas emission inventory. The reed is the dominant species in Yangtze estuary, so the study of the reed wetland greenhouse gas emissions is very important.This paper is supported by the project of National Natural Science Foundation (Grant No.40903049) and the project of Shanghai Science and technology commission (Grant No.10JC1404300). The reed community in Chongming Dongtan wetland park was selected as the research object. By means of the field monitoring and laboratory experiments, we studied the characteristics of greenhouse gas emission flux and also the influencing factors of flux variation in different seasons. The N2O emission mechanisms in the reed wetland was also discussed. The main conclusions are summed up as follows:(1) The N2O, CH4and CO2emission fluxes of reed wetland ranged-11.67-16.43μgN2O·m-2·h-1,-194.34-722.63μgCH4·m-2·h-1and-250.15-16.49mgCO2·m-2·h-1, respectively. The annual average emission fluxes were respectively (2)2.14μgN2O·m-2·h-1,151.51μgCH4·m-2·h-1and-101.93mgCO2·m-2·h-1. The emission fluxes of N2O, CH4and CO2showed significant seasonal variations. The emission fluxes of N2O and CH4were significantly higher in summer than that in other seasons, and the absorption flux of CO2was also higher than that in other seasons.(3) The maximum emission flux of N2O in a day generally appeared at13:00in the afternoon, while the minimum flux generally appeared at1:00or19:00. The daily variation in May and September of N2O flux was far greater than any other months.(4) Temperature is one of the main factors that affect the reed wetland N2O, CH4and CO2emission fluxes. It reveals that temperature was significant positively correlated with the fluxes of N2O and CH4, while the temperature was negatively correlated with the flux of CO2. The organic carbon content is not a link factor of denitrification process, the emission fluxes of N2O and CH4did not show a certain positive correlation with organic carbon content. Through the analysis of the relationship between the fluxes of CH4, CO2and the soil moisture content, we found that the flux of CH4is larger when the soil moisture content was35%-40%, at the same time, the absorption rate of CO2was higher. When the soil moisture content was more than40%or less than35%, the flux of CH4was small, and the absorption rate of CO2was low.(5) Vegetation factor also plays an important role on the emission fluxes of CH4and CO2. Reed plants have a significant influence on the efficiency of gas transmission in the gas exchange process. The emission flux of CH4greatly reduced, but the CO2emission increased when the aboveground reeds were clipped.(6) The denitrification rate of reed wetland sediment at the depth of0-12cm varies from0.91ngN2O-N·g-1·h-1to7.32ngN2O-N·g-1·h-1, and it shows significant seasonal differences. The denitrification rate of surface0-2cm depth sediment is significantly higher than that in the deeper sediment.(7) The study of reed wetland denitrification potential showed that the denitrification rate increased until the incubation last24h. Then the denitrificdation decreased and the denitrification potential of reed wetland is31.69ngN2O-N·g-1·h-1. (8) Through the indoor simulation experiment, it was found that the optimum temperature for reed wetland sediment denitrification ranged from25℃to32℃. Nitrate concentration is a direct factor that affecting denitrification rate, while ammonia concentration plays an indirect effect on denitrification rate through the coupled nitrification and denitrification processes. |
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