【作者】 刘雅淑；

【导师】 孙松； 朱仁斌；

【作者基本信息】 中国科学技术大学 ， 环境科学， 2011， 博士

【摘要】 目前,全球变暖导致南极冰川融化退缩,南极沿海无冰区苔原面积日益扩大;同时,南极海岸也是重要的海洋动物聚居地,每年夏季大量海洋动物排泄物为苔原土壤提供了丰富的养分,从而为土壤中CO₂、CH₄、N₂O等温室气体的产生与排放创造了有利条件。在中国第15次南极科学考察期间,孙立广教授首次开拓了西南极法尔兹半岛苔原N₂O、CH₄通量的观测,之后美国、韩国、意大利和巴西等国的学者也在南极苔原区开展了相关观测研究。但前期的研究在区域上比较单一,难以准确获得南极苔原温室气体通量的时空变化规律及其影响因素;另一方面,已有的研究多侧重于宏观温室气体排放通量的观测,而在南极苔原土壤温室气体产生的微观机理层次上的研究严重欠缺。鉴于以上两点考虑,本文以西南极法尔兹半岛和东南极米洛半岛地区为研究区域,采用静态箱法对南极苔原不同生态区（包括:普通苔原、海洋动物聚居地以及湖泊湿地等）温室气体通量进行了较为系统的现场观测,结合大量模拟实验研究了南极苔原土壤温室气体产生与排放的过程;并首次应用稳定同位素手段来研究南极苔原土壤源温室气体的产生机理,获得大量科学数据,在微观与宏观层次上拓展和深化了南极苔原温室气体的研究领域。主要研究内容及研究结果如下:（1）西南极法尔兹半岛苔原不同生态区温室气体通量时空变化规律对西南极法尔兹半岛苔原不同生态区温室气体排放通量进行了对比观测研究,发现海洋动物聚居地是南极大气N₂O的强排放点源,是全球N₂O的新来源,同时也是南极大气CH₄的重要排放源;而普通苔原土壤是弱的N₂O和CH₄排放源。相关分析表明:土壤中海洋动物粪来源的TOC、TN含量和土壤水位控制着南极苔原N₂O和CH₄排放通量的空间变化,冻融过程影响N₂O和CH₄通量的季节变化。另外,对阿德雷岛和生物湾的苔原植被区进行了连续两年夏季的现场观测,发现靠近企鹅、海豹聚居地的苔原植被区是大气CO₂较强的吸收汇和N₂O的排放源。（2）东南极米洛半岛湿地湖泊系统温室气体通量时空变化规律对东南极米洛半岛苔原湿地和富藻湖泊近岸水体的温室气体通量进行了观测,结果表明:苔原湿地是较强的N₂O排放源和弱的CH₄排放源。苔原湿地N₂O通量随地下水位的增长而降低,水位是控制N₂O通量空间变化的主要因素;CH₄通量则受到水位和地温的共同影响。此外,观测结果表明米洛半岛富藻湖泊是南极夏季强烈的CO₂吸收汇和重要的N₂O、CH₄排放源,且温室气体通量受到多种因素的影响:湖泊近岸水体N₂O通量和气温、NO₃^--N浓度显著正相关,与水位呈负相关关系;CO₂通量和日辐射量（DTR）、水温呈负相关关系;CH₄通量受到湖泊温度、水位和总溶解性固体（TDS）含量的综合影响。（3）南极苔原土壤温室气体产生与排放过程实验模拟研究恒温条件下,企鹅粪、鸟成土和海豹粪土在有氧条件下的CO₂、CH₄排放通量高于厌氧培育,通量与TOC含量显著相关;企鹅粪在有氧条件下的N₂O通量较高,但粪土样品则是在厌氧条件下排放出更多的N₂O,表明反硝化是粪土N₂O的主要产生过程。同时,冻融交替过程能促进土壤温室气体的迸发排放,其中企鹅粪是强的CH₄和CO₂排放源而粪土是强的N₂O排放源。此外,土壤水分变化对温室气体通量影响显著:CH₄排放通量在77%Mc含水率时达到最大;N₂O通量在29%⁴9%Mc范围内随土壤水分含量的增加而增加;CO₂排放通量与土壤水分含量呈对数相关关系。不同培育条件的室内模拟实验结果表明:在南极夏季,海洋动物新鲜粪、鸟成土和海豹粪土有较强的温室气体排放潜力。（4）南极地区和海洋大气温室气体稳定同位素时空变化特征在野外获得了海洋动物聚居地土壤N₂O同位素自然丰度,与当地背景大气相比,海洋动物聚居地排放的N₂O显著富集轻同位素。野外同位素数据与室内厌氧培育条件下得到粪土N₂O同位素值相近,表明反硝化是粪土N₂O的主要产生过程。对近地面大气的研究发现,南极近地面大气N₂O浓度低于全球大气N₂O平均值,但其同位素值偏高,且N₂O的δ¹⁵N和δ¹⁸O与气温、大气N₂O浓度负相关,表明南极大气N₂O可能受到了平流层低浓度、富¹⁵N与¹⁸O的N₂O向对流层反向注入的影响。同时,南极近地面大气CH₄浓度略高于全球大气CH₄平均浓度,且δ¹³C值较大气背景值略高,可能受到了南极地区富13C的人为源的影响。此外,采集了上海至南极航线上（30°N⁶9°S）的洋面大气样品,发现洋面大气N₂O浓度由北向南逐渐降低,N₂O的¹⁵N与¹⁸O的空间变化规律不一致,可能受到局部洋区复杂因素的影响。而航线上北半球海洋边界层大气的CH₄浓度明显高于南半球,δ¹³C平均值也高于大气背景值,表明海洋边界层大气CH₄受到富¹³C的人为源的影响。更多还原

【Abstract】 Antarctic glacier is melting because of global warming and the area of ice-free tundra in coastal Antarctica is expanding. Coastal Antarctica is important habitat for marine animals. Due to the deposition of marine animal excreta every summer, the fertile tundra soil in coastal Antarctica is favorable to the production and emission of greenhouse gases （CO₂, CH₄ and N₂O）. During CHINARE-15, for the first time, Prof. Sun Liguang observed N₂O and CH₄ fluxes from tundra soils on Fildes Peninsula, western Antarctica. Later, scholars from America, Korea, Italy and Brazil also observed greenhouse gas fluxes in Antarctica tundra zones. However, former study regions in Antarctica are limited and it is difficult to obtain exact temporal and spatial variations of greenhouse gas fluxes and influence factors. On the other hand, many studies focused on the macro-observation of fluxes and researches on production mechanism of greenhouse gases are scare. Therefore, we observed greenhouse gas fluxes from different ecological zones （normal tundra, sea animal colonies, tundra wetland and littoral zones of lake） on Antarctica using static chamber method. Main study areas are located on Fildes Peninsula, western Antarctica and Millor Peninsula, eastern Antarctica. Field observations combined with simulation experiments, the processes of greenhouse gas production and emission were studied. And for the first time, stable isotope technique was used to study the production mechanism of greenhouse gases emission from Antarctic tundra soil. A lot of data was obtained and the studies of greenhouse gases in Antarctic tundra were expanded and deepen at micro and macro levels. Main contents and results are as follows:（1） Temporal and spatial variations of greenhouse gas fluxes from different tundra ecosystems on Fildes Peninsula, western AntarcticaGreenhouse gas fluxes from different ecological zones were observed on Fildes Peninsula. Results implied that marine animal colonies were strong source of N₂O in coastal Antarctica and new source of global N₂O. The colonies also were important source of Antarctic atmospheric CH₄. However, normal tundra soil was weak source of N₂O and CH₄. Correlation analysis results implied that, the content of soil TOC and TN from marine animal excreta and water table controlled spatial variation of N₂O and CH₄ fluxes while freezing-thawing process controlled temporal variaton of the fluxes. In addition, greenhouse gas fluxes from two moss tundra zones of Ardley Island and Shengwu Cove were observed for two continuous summers, indicating that moss tundra zones were the sink of atmospheric CO₂ and weak source of N₂O in Antarctica.（2） Temporal and spatial variations of greenhouse gas fluxes from tundra wetlands and littoral zones of lakes on Millor Peninsula, eastern AntarcticaGreenhouse gas fluxes from tundra wetlands and littoral zones of lakes on Millor Peninsula were observed, indicating that tundra wetlands were strong source of N₂O and weak source of CH₄. N₂O fluxes from tundra wetlands decreased with increasing water table, so water table affected N₂O spatial variation; CH₄ fluxes were controlled with water table and ground temperature together. In addition, the observations showed that alga-rich lakes were strong sink of atmospheric CO₂ and important source of N₂O and CH₄ in Antarctica. Greenhouse gas fluxes from lakes were influenced with various environmental factors. N₂O flux was significantly correlated with air temperature and NO₃^--N concentration, but negatively correlated with water table. Daily total radiation （DTR） and water temperature affected CO₂ emission while water temperature, water table and total dissolved solids （TDS） content affected CH₄ emission together.（3） Simulation experiments about greenhouse gas fluxes from Antarctic soilsUnder constant temperature conditions, CO₂ and CH₄ fluxes from all soil samples under aerobic conditions were higher than under anaerobic conditions and the fluxes were correlated with soil TOC contents. N₂O fluxes from penguin guano under aerobic conditions were higher than under anaerobic conditions while N₂O fluxes from ornithogenic soil and seal colony soil under anaerobic conditions were higher, indicating that denitrification was the main production process of N₂O emission from ornithogenic soil and seal colony soil. Furthermore, freezing-thawing cycles could induce high greenhouse gas fluxes. Penguin guano was stronger emitter for CH₄ and CO₂ while seal colony soil was stronger emitter for N₂O. Water content also had an impact on greenhouse gas fluxes. CH₄ flux at 77%Mc was the largest; N₂O flux increased with increasing water content in the range of 29%Mc⁴9%Mc; CO₂ flux had a logarithmic correlation with water content. Simulation experiment results showed that penguin guano, ornithogenic soil and seal colony soil had strong potential for greenhouse gas emissions.（4） Temporal and spatial variations of isotope values of atmospheric greenhouse gases in Antarctica and above oceanic surfaceThe natural stable isotope abundance of N₂O emitted from Antarctic sea animal colonies was analyzed. The soil-emitted N₂O was ¹⁵N- and ¹⁸O-depleted compared with N₂O in local ambient air. The data from in situ field observations and laboratory experiments pointed to denitrification as the predominant N₂O source from Antarctic sea animal colonies. In addition, the concentrations and isotopes of atmospheric N₂O and CH₄ near the surface in Antarctica were investigated. Results showed that average atmospheric N₂O concentration in Antarctica was lower than global average while the averageδ¹⁵N andδ¹⁸O-N₂O value in Antarctica was higher than global average. Theδ¹⁵N andδ¹⁸O showed significantly negative correlation with N₂O concentration, indicating that theδvalues of N₂O were significantly affected by the return flux into the troposphere of stratospheric N₂O with low levels and the enriched ¹⁵N and ¹⁸O. The average concentrations of atmospheric CH₄ in Antarctica was slightly higher than global average and averageδ13C-CH₄ value was also higher than global average, indicating that theδvalues of CH₄ may be affected with ¹³C-riched CH₄ with from anthropogenic source in Antarctica. The temporal and spatial variations ofδ¹⁵N andδ¹⁸O of atmospheric N₂O andδ13C of atmospheric CH₄ on the course from Shanghai to Antarctica（30°N⁶9°S）were analyzed. Atmospheric N₂O concentration above the oceanic surface decreased from Shanghai to Antarctica. Theδ¹⁵N linearly increased with latitude and negatively correlated with air temperature. The differences between spatial variations ofδ¹⁵N andδ¹⁸O indicated the isotopic compostions of atmospheric N₂O above the oceanic surface were affected by complicated factors such as the currents in the regional ocean areas. Meanwhile, atmospheric CH₄ concentration of Northern Hemisphere was higher than the concentration of Southern Hemisphere and the averageδ¹³C of CH₄ was higher than global average, suggesting the major proportion of CH₄ may be affected with ¹³C-riched CH₄ from fossil fuel and biomass burning.更多还原