关键词: 三江平原, 典型湿地, CH⁴、N²O通量

Abstract:

Methane and nitrous oxide are the very important greenhouse gases.Although CH₄ and N₂O concentrations are considerably lower than that of CO₂ in the atmosphere,however they are more effective on a molar basis than CO₂ in resulting in radiative heating.Increasing CH₄ and N₂O concentrations in the atmosphere have stimulated studies on CH₄ and N₂O emissions from terrestrial and aquatic environments.Wetlands are regarded as one of the major sources of CH₄,about 21% of global methane emission come from natural wetlands. The Sanjiang plain,the largest and most concentrated marsh-wetland region in China,is located in the northeast of Heilongjiang province.Its total marsh-wetland area is about 83.5×10⁴ hm²with rich carbon resources. There are many rivers and lakes in this region and wide flood plain were formed along the river.The study was carried out at the Ecological Experimental Station of Mire-Wetland in the Sanjiang Plain,Chinese Academy of Sciences（47°35′ N,133°31′ E;56 m above sea level）,center of the Sanjiang plain.The mean annual precipitation is 550-600 mm and the mean annual temperature 1.9 ℃.The vegetation types are marshes and wet meadows.The main soil types are marsh soil,meadow soil and lessive soil.Three typical types of wetlands of perennial waterlogged Carex lasiocarpa marsh,seasonal waterlogged Deyeuxia angustifolia wet meadow and perennial non waterlogged brushy wetland are selected as samples of study.The methane and nitrous oxide fluxes were measured by sealed stainless steel chamber and gas chromatography（Agilentilent 4890） system. The experiment lasted from June 2002 to August 2004,measurement was done twice a week in growth season,once a month in winter,and daily change observation was performed several times at the clear day during growth season and three repeats were practised at each sample site.Meanwhile,the inside and outside chamber air temperature,surface and 5 cm deep soil temperature were measured at the same time. The two year's experiments resulted in the following conclusion: There are obvious interannual and seasonal variations in methane and nitrous oxide emissions from the three typical wetlands in the Sanjiang plain,the greenhouse gases fluxes were mostly controlled by water regimes and temperature conditions.There are two methane fluxes peaks in the seasonal drought year,one is in June and the other is in August during growth season（from May to October）,but there is only one peak in the waterlogging year.We found there are still methane emissions from Carex lasiocarpa marsh and Deyeuxia angustifolia wet meadow during frozen season（from November to April）,and the brushy,wetland is a weak sink in winter.The three typical wetlands are all the source of atmospheric nitrous oxide and there are two nitrous oxide fluxes peaks during the plant growth season,the first peak appears in May and the second in July or August.The three typical wetlands are weak sink in snow covered time.The methane and nitrous oxide emissions are notably negative correlated.

Key words: Sanjiang Plain, typical wetland, CH⁴,N²O fluxes