三江平原湿地CH_4、N_2O的地-气交换特征

Characteristics of CH_4,N_2O exchange between wetland and atmosphere in the Sanjiang Plain

利用暗箱-气相色谱法对三江平原3种具有代表性的湿地类型（常年积水的毛果苔草沼泽、季节性积水的小叶章湿草甸和灌丛湿地）进行了为期两年的CH4和N2O现场同步观测.结果表明,湿地全年CH4和N2O通量有明显的季节和年际变化,与温度和土壤水分条件密切相关.在发生季节性干旱的年份,生长季（5月～10月）CH4排放通量峰值出现在6月和8月,呈双峰型;而在降水充沛的年份,CH4排放通量峰值出现在6、7月份,呈单峰型.冰冻期（11月到次年4月）CH4排放通量十分的微弱,其中灌丛湿地表现为负排放.3种类型湿地N2O通量一般在非冰冻期表现为排放,呈双峰型,5月份融化期为第一个高峰期,7、8月为第二个高峰期,冰雪覆盖期表现为吸收.湿地CH4和N2O通量在春季的融冻期,存在此消彼长的现象.

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× 10^4 hm^2with 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.