Greenhouse gases fluxes at Chongming Dongtan Phragmites australis wetland and the influencing factors

Methane(CH₄), nitrous oxide(N₂O)and carbon dioxide(CO₂)are primary greenhouse gases, many recent studies indicate that wetland is one of the major atmospheric greenhouse gases sources in the world. In order to understand the mechanisms and factors that influence greenhouse gases production in and emission from reed(Phragmites australis)wetland during its growth cycle, static closed chamber combined with a gas chromatograph technique was used to investigate the flues of three greenhouse gases(CH₄, N₂O and CO₂)at a Phragmites australis wetland in Chongming Dongtan. The results showed that the flux of CH₄ was greatly influenced by temperature, which the fluxes were significantly higher in summer than in other seasons. Annual average flux of CH₄ is 74.46 μg/(m²·h). The maximum flux of N₂O is in winter and the annual average flux of N₂O is 2.22 μg/(m²·h). There is obviously seasonal change in CO₂ absorption with the annual average flux as -101.93 mg/(m²·h). The production and emission of CH₄ were also affected by the photosynthesis and respiration of Phragmites australis, while the Phragmites australis communities showed consumption of N₂O because of the shortage and limitation of nitrogen in sediment. The emission and consumption of CO₂ were mainly controlled by the photosynthesis of Phragmites australis and the soil respiration which was influenced by temperature seasonal change. The developed aerenchyma of Phragmites australis provides a channel which makes CH₄ and N₂O diffuse from atmosphere to sediments, meanwhile molecular diffusion process is also a way and methods that makes CH₄, N₂O and CO₂ diffuse form sediments to atmosphere.