三江平原生长季沼泽湿地CH_4、N_2O排放及其影响因素

EMISSIONS OF CH_4 AND N_2O FROM A WETLAND IN THE SANJIANG PLAIN

2003年6-9月采用静态箱-气相色谱法，对三江平原生长季不同淹水条件下沼泽湿地CH4、N2O的排放进行了同步对比研究，并探讨了影响气体排放的主要影响因素。结果表明，生长季沼泽湿地CH4和N2O排放具有明显的时空变化特征。长期淹水的毛果苔草（Carex lasiocarpa）和漂筏苔草（Carex pseudocuraica）植物带CH4的平均排放强度分别为259．2和273．6mg·m^-2·d^-1，高于季节性淹水的小叶章（Oeyeuxia angustitblia）植物带的排放强度（38．16mg·m^-2·d^-1）（P〈0．0001）；而生长季N20的平均排放强度分别为0．969、0．932和0．983mg·m^-2·d^-1，植物带间无显著差异（P=0．967）。相关分析表明，气温和5cm深地温对沼泽湿地CH4生长季排放通量的影响较大，而水位则是影响长期淹水沼泽N2O排放通量的主要因素；不同类型湿地间CH4平均排放强度的差异主要受水位的控制，而强烈的还原环境可能是导致不同类型湿地具有近似的N2O排放强度的原因。

In order to understand more about mechanisms of and factors that influence CH4 and N2O production in wetlands, fluxes of CH4 and N2O were measured using static-chamber and gas-chromatography methods in a marsh wetland, located at the Honghe Farm in eastern part of Heilongjiang Province, China （47°35＇ 17.8” N, 133°37＇48.4＂ E）, from June to September, 2003. Three plant communities, Carex pseudocuraica, Carex lasiocarpa and Deyeuxia angustifolia, were selected to measure fluxes of CH4 and N2O to contrast the variance of the emission rates of both greenhouse gases in these different plant zones. Air temperature and soil temperature at 5 cm depth, soil redox potential （0-100 cm）, and standing water depth at each site also were measured to determine the main factors that control CH4 and N2O emissions within and among plant zones. The wetland was a source of both CH4 and N2O during the growing season and emissions showed conspicuous temporal and spatial variations. Similar temporal variations of CH4 and N2O fluxes were observed in the C. pseudocuraica and C. lasiocarpa sites. Emission rates of CH4 were higher in July and August while emissions of N2O were higher in July and September. However, the highest emissions of CH4 and N2O in the C.angustifolia site occurred about one month earlier than in the C. pseudocuraica and C. lasiocarpa sites. The highest CH4 emissions observed in the wetland were in the C. pseudocuraica site on July 19 with a rate of 696.24 mg·m^-2·d^-1, and the highest N2O emissions were in the D. angustifolia site on June 12 with a rate of 2.53 mg·m^-2·d^-1. The average CH4 flux from the C. pseudocuraica site was 273.6 mg·m^-2·d^-1 the highest among the three sites over the growing season but was not significantly different from 259.2mg·m^-2·d^-1 of the C. lasiocarpa site. However, both were significantly higher than the 38.16mg·m^-2·d^-1 measured in the D. angustifolia site （p 〈 0. 0001）. These results showed that average CH4 fluxes in submerged wetlands were higher than in seasonal wetlands. N2O fluxes from the C. pseudocuraica, C. lasiocarpa and D. angustifolia sites were not significantly different （p=0. 967） with an average flux of 0. 969, 0. 932 and 0. 983mg·m^-2·d^-1, respectively, suggesting that submerged and seasonal wetlands had similar rates of N2O emissions. Air temperature, soil temperature, soil redox potential and standing water depth were important factors influencing emission rates of CH4 and N20 from the wetlands. Relationship analysis showed that CH4 fluxes were correlated weakly with air temperature and soil temperature at 5 cm depth within a site （0.201 〈 r 〈 0.550） but not correlated with standing water depth （（0. 100 〈 r 〈 0. 176）. Strong correlations were found between N20 fluxes and standing water depth （rI = -0.701; r2 = -0. 528）, but no correlation between N20 fluxes and air temperature and soil temperature at 5 cm depth in the C. pseudocuraica and C. lasiocarpa sites （ - 0.089〈 r 〈 0.211） was found. However, in the D. angustifolia site, there were no correlations between N20 fluxes and the three factors （r 〈 0.344）. These results indicated that temperature was more important in influencing CH4 emissions in the seasonal and submerged wetlands whereas standing water depth was more im- pertant in influencing N20 emissions in the submerged wetlands. Furthermore, standing water table was the main control of the difference in CH4 emissions among plant zones. However, there appeared to be similar rates of N20 emissions among plant zones in the wetlands with strongly anaerobic conditions.