崇明东滩湿地CO2 、CH4和N2O 排放的时空差异

通过静态暗箱—气相色谱法研究了长江口崇明东滩四类典型湿地(围垦湿地、高潮滩、中潮滩和低潮滩)CO₂、CH₄和N₂O排放特征及影响因素。结果表明,在生长季尺度下,CO₂、CH₄和N₂O均以排放为主;在昼夜尺度下,CO₂和CH₄在夜间排放量大于白昼排放量,而N₂O的排放高峰出现在下午;在潮水退去、潮滩暴露初期,CH₄和N₂O有大量排放,CO₂正好相反。崇明东滩温室气体排放通量自岸向海有明显的梯度变化,总体趋势是越近岸通量值越大。观测与实验表明,温度、潮汐、土壤理化性质、植物和土地利用变化都对温室气体排放通量有明显的影响,其中滨海潮滩湿地特有环境因子潮汐以"淹没—暴露"光滩沉积物的方式控制温室气体的排放。

Characteristics and influencing factors of CO2, CH4 and N2O emissions from Chongming eastern tidal flat wetland

The temporal and spatial variations and effect factors of greenhouse gases (CO₂, CH₄ and N₂O) emission from Chongming eastern tidal flat, the typical and most important wetland of the Yangtze estuary, have been studied on three time scales, i.e. seasonally, diurnally and tidally, and at four sampling areas, i.e. reclaimed wetland, high tidal flat, middle tidal flat and low tidal flat. On the scale of growing season, all of the gases emitted significantly from wetland. Diurnal fluxes of CO₂ and CH₄ were less than nocturnal ones, and N₂O flux peak was found in the afternoon. In the early stage of the exposure after tide ebbed, CH₄ and N₂O emitted from sediments, while CO₂ was absorbed by sediments. The spatial variation of greenhouse gases was related to water gradient along the direction from land to sea. CH₄ emission from high tidal flat was significantly higher than that from reclaimed wetland and from middle tidal flat, and a slight consumption was observed at low tidal flat. N₂O emitted only at reclaimed wetland and consumed at other sampling sites. CO₂ showed a significant emission from the planted sites and a slight consumption at low tidal flat. Both air temperature and soil temperature exerted influence on gases emission, with plants as intermediary. Tide-caused "immergence-exposure" change in sediment proved to be indispensable to gases emission from tidal wetlands. Physic-chemical characteristics of soil, such as organic carbon, ammonium, sulfate and redox potential, had profound effects on gases emission. Cutting of plants led to consequent additional emission. Land use change caused change of gases emission: as high tidal flat was converted into reclaimed wetland, flux of CH₄ decreased and fluxes of N₂O and CO₂ increased. The estimated emissions in growing season from the Chongming eastern tidal flat wetland were 5.1×10⁷ g CH₄, 1.0×10⁵ g N₂O and 1.7×10¹¹ g CO₂, respectively.