垦殖对沼泽湿地CH_4和N_2O排放的影响

Effects of marsh reclamation on methane and nitrous oxide emissions

三江平原是我国最大的沼泽化低平原,同时也是受人类活动影响最剧烈的区域之一.选取三江平原两类典型湿地-常年积水的毛果苔草（Carex lasiocapa）沼泽和季节性积水的小叶章（Deyeuxia angustifolia）草甸及其垦殖水田和旱田为研究对象,利用静态暗箱-气相色谱法进行CH4和N2O的田间原位观测.研究结果表明,垦殖导致沼泽湿地CH4排放量大幅度降低,而N2O排放量有所升高.三江平原沼泽湿地、水田、旱田的CH4排放量分别为329.56、94.82 kg·hm^-2·a-1和-1.37 kg·hm^-2·a-1,N2O排放量分别为1.93、2.09 kg·hm^-2·a-1和4.90 kg·hm^-2·a-1.沼泽湿地垦殖使CH4和N2O的综合温室效应降低,在20a到500a的时间尺度上,水田综合GWP为沼泽湿地的30.8%～37.9%,旱田综合GWP仅为沼泽湿地的6.0%～28.7%.垦殖同时也改变了沼泽湿地对大气CO2的源汇功能,2004年,小叶章草甸、水田和旱田碳排放量分别为-3.08、1.79 t·hm^-2和3.35 t·hm^-2,沼泽湿地垦殖为旱田后碳源的功能较水田更强.

The Sanjiang Plain is the largest low-altitudinal swampy plain in China where has been strongly affected by human activities particularly the conversion of marsh to cropland. To evaluate the effect of marsh reclamation on methane and nitrous oxide emissions, field observations were made at the Sanjiang Mire Wetland Experimental Station （47°35′N, 133°31′E）, Chinese Academy of Sciences, located in the eastern part of Heilongjiang Province. The mean annual precipitation and temperature in this region is 550 --600 mm and 1.9℃, respectively. Dominant vegetations are marshes and wet meadows. Soil types are typically marsh soil, meadow soil and lessive soil. CH4 and N2O fluxes were measured by using the static opaque chamber and gas chromatography system. Four plots of Carex lasiocarpa marsh, Deyeuxia angustifolia marsh, rice field and upland were selected. During the experiment periods, measurements were made twice a week in growing season and once a month in the winter. Three replicates were conducted for each plot. Results showed that there existed significant spatial difference in CH4 and N2O emissions from the two marsh plots. The Carex lasiocarpa marsh emitted more CH4 while less N2O than the Deyeuxia angustifolia marsh. Water regime and soil character regulated CH4 and N2O fluxes significantly. Gas exchange between the land and atmosphere in the winter season contributed greatly to the annual budget. CH4 emission in the winter season contributed 2.3%--4.6% to the annual total, while N2O uptake accounts for approximately 14% of the total N2O emission in the growing-season. Field observations also indicated that the conversion of marsh to cropland reduced CH4 emission significantly but increased N2O emission slightly. CH4 emissions from marsh, rice field and upland were 329.56, 94.82 kg·hm^-2· a^-1 and - 1.37 kg·hm^-2·a^-1, respectively. N2O emissions from corresponding plots were 1.93, 2.09 kg·hm^-2and 4.90 kg·hm^-2·a^-1respectively. An integrated global warming potential （GWP） of the CH4 and N2O emissions were assessed for the four plots. The results showed that the integrated GWP for rice field and upland were 30.8%--37.9% and 6.0%-- 28.7% lower than those for marsh, respectively. The conversion of marsh to cropland resulted in a transformation of carbon sink to carbon source, namely marsh acted as a carbon sink and cropland acted as a carbon source. In 2004, carbon emissions were - 3.08, 1.79 t · hm^-1 and 3. 35 · hm^-2 in Deyeuxia angustifolia marsh, rice field and upland, respectively. The carbon source of upland was stronger than that of rice field.