Knowledge Resource Center for Ecological Environment in Arid Area
| 多年冻土区温室气体释放的生物地球化学过程 | |
| 其他题名 | Biogeochemical processes of greenhouse gases emission in permafrost regions |
| 牟翠翠 | |
| 出版年 | 2014 |
| 学位类型 | 博士 |
| 导师 | 程国栋 ; 张廷军 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 多年冻土退化对土壤碳氮循环具有重要影响，全球气候变暖背景下多年冻土区土壤有机碳的分解过程是碳循环研究的重要内容，然而目前关于多年冻土区土壤有机碳储量及其潜在释放的研究主要集中在高纬度地区。青藏高原多年冻土区面积约占全球多年冻土面积的6%。青藏高原具有温度高、厚度薄及热状态极不稳定等特征，在全球气候变暖背景下，青藏高原多年冻土退化强烈，其碳释放潜力可能会远大于高纬度多年冻土区。然而，我们目前对青藏高原多年冻土区土壤有机碳的总储量了解很少，而且对多年冻土退化过程是如何影响其有机碳分解及温室气体释放等方面的研究几乎是空白。本论文主要通过野外观测及室内实验，力图估算青藏高原多年冻土区有机碳的总储量及有机碳的分解速率。主要从以下几个方面进行研究：（1）基于已发表的资料及本项目数据，利用706个土壤样点系统估算青藏高原多年冻土区土壤有机碳储量，并与阿拉斯加多年冻土区土壤碳特征进行比较；（2）分析祁连山黑河上游俄博岭多年冻土区土壤碳氮性质及其分布特征，实地监测土壤碳通量，并分析其与环境因子的关系；（3）利用活动层及多年冻土层的土壤样品进行培养，实验模拟温度升高过程中的土壤有机碳分解速率变化规律及微生物产生的热量对土壤温度升高的影响；（4）探讨多年冻土退化形成的热融湖塘水体中溶解性有机碳与温室气体的特征及其碳分解过程。主要结论如下： 青藏高原多年冻土区土壤有机碳（SOC）储量为：0 ~ 1 m范围内15.29 Pg；1 ~ 2 m范围内4.84 Pg；2 ~ 3 m深度内3.89 Pg；3 ~ 25 m深度内43.19 Pg。总结来说，青藏高原多年冻土区SOC总储量约为67.2 Pg，约是北半球多年冻土区碳储量的4%，其中的47.08 Pg（70.1%）存储于多年冻土层中。高寒草甸、高寒草原和高寒荒漠生态系统中SOC储量分别为32.39 Pg、38.79 Pg和0.82 Pg。青藏高原多年冻土区SOC在0 ~ 6 m深度含量变化较大，表明其碳存储深度的变异性要大于北半球多年冻土区（0 ~ 3 m）。因此，青藏高原多年冻土区SOC对全球气候变化具有潜在贡献。 本研究选择多年冻土退化明显、且SOC含量较高的祁连山黑河上游俄博岭多年冻土区为研究区域，探索多年冻土区碳潜在释放及其微生物过程。研究表明，黑河上游俄博岭多年冻土层中SOC、总氮（TN）和土壤无机碳（SIC）含量（依次为71.7 kg m-2、8.0 kg m-2、 34.7 kg m-2）均高于活动层中的含量（依次为44.2 kg m-2、5.3 kg m-2、12.2 kg m-2）。土壤剖面上的稳定碳同位素（δ13C-SOC）分析结果表明，水文条件和成土过程是影响多年冻土区SOC形成的重要因素。多年冻土过渡层及深层土壤的δ13C-SOC和C/N比值表明了土壤剖面上SOC的可降解性方面存在明显差异。多年冻土层中水溶解性有机碳（WSOC）含量比活动层中的含量高，表明多年冻土层土壤中的活性碳含量更高。多年冻土层SIC和冷生结构是影响SOC和TN分布的重要因素，且SIC、pH值和C/N比值间呈显著的负相关关系。全球气候变暖背景下，多年冻土上限附近及深层（414 ~ 448 cm）土壤是主要的潜在甲烷释放区。多年冻土层（280 ~ 350 cm）溶解性有机碳（DOC）和热水提取的碳（HWC）在土壤形成过程中会被微生物分解利用，其微生物过程使δ13C-DOC 和δ13C-HWC均增加了约3‰，而且HWC更容易被微生物利用。 黑河上游俄博岭多年冻土区碳通量监测结果表明该高寒草甸生态系统碳排放具有较大潜力。多年冻土区融化期CO2和CH4通量平均为157.8 μmol CO2 min-1 m-2、0.11 μmol CH4 min-1 m-2；而在冻结期明显降低，平均值为2.39 μmol CO2 min-1 m-2，CH4释放速率低于检出限。活动层厚度越大，土壤温度越高，CO2和CH4释放速率越快。而且多年冻土区微地形也是影响温室气体释放的重要因素。 从负温到正温的升温实验模拟研究过程中，CO2释放速率逐渐增强。相对于多年冻土融化后的土壤，多年冻土温度升高对土壤有机碳分解速率影响较大。从?5℃升温至?0.5℃，土壤碳释放速率增加482.8%（± 60%）；然而从0.5℃升温至5℃，碳释放速率增加102.0%（± 37.5%）。这表明伴随温度升高，冻结的多年冻土有机碳比融化了的有机碳更容易被微生物分解。而且在?5 ~ ?0.5℃时，矿质土的碳释放速率升高幅度比有机土的要大。基于δ13C-SOC和δ13C-CO2分析表明，释放的CO2主要来自10 ~ 20 cm活动层及245 ~ 255 cm和285 ~ 295 cm土层中的有机碳。碳释放过程中微生物产生的热量对土壤温度升高具有一个放大效应：负温、正温时微生物本身产生的热量导致土壤温度升高幅度与培养温度间分别呈一指数、线性相关关系。负温时多年冻土上限附近的有机碳更容易被微生物分解利用，而正温时多年冻土深层土壤对温度升高更敏感。微生物产生的热量最终导致土壤温度升高幅度大于大气环境温度升高幅度。 多年冻土退化会造成大面积的热融湖塘形成，导致溶解性有机碳和温室气体富集在热融湖塘水体中。青藏高原热融湖塘分布广泛，水体中溶解的CO2比CH4浓度高。水体中DOC浓度随着湖体深度（< 1.5 m）和电导率的增加而升高。水中溶解性无机碳（DIC）（δ13C：–15.2 ~ 4.6‰）主要来自碳酸盐（δ13C：–3 ~ 3‰）和DOC的异养呼吸作用（δ13C < 8‰）。湖底沉积物有机质和水中DIC也是影响湖塘水体中溶解CO2的重要因素。CH4稳定碳同位素值（δ13C-CH4：–58.2 ~ –16.5‰）较低，表明CH4主要来自于微生物分解有机质的过程，且夏末时微生物的厌氧呼吸更强烈。青藏高原热融湖塘可能也是多年冻土区温室气体排放的重要来源。 本文初步探索了青藏高原多年冻土区土壤碳储量特征，并通过培养实验研究了碳的分解及微生物产热过程。在自然条件下，多年冻土退化对多年冻土区有机碳的影响十分复杂，例如多年冻土退化还会改变土壤的水分条件，并由此影响温室气体的排放过程。在今后的研究中还要进一步开展不同生态系统多年冻土退化对温室气体释放潜力的机制方面研究，并进而为相关的模型研究提供参数，进而加深多年冻土区对全球气候变化的反馈潜力和过程的认识。 |
| 英文摘要 | Permafrost degradation has a great effect on soil carbon and nitrogen cycle. It is important to study the permafrost organic carbon decomposition with temperature increasing. However, studies on soil organic carbon storage and potential carbon emission mainly focused on the high latitude regions. Permafrost regions on the Qinghai Tibetan Plateau (QTP) account for about 6% of global permafrost area. It has great potential for greenhouse gases emission under global climate warming scenarios since the permafrost has characteristics of high temperature and small thickness. However, presently, SOC storage in the permafrost regions on the QTP has been poorly understood. Moreover, the effects of permafrost degradation on organic carbon decomposition and greenhouse gases emissions are still largely unknown. In the study, we are trying to estimate the storage and decomposition rate of organic carbon in permafrost on the QTP through field observations and laboratory experiments. The detailed contents are as follows: (1) We estimated the permafrost organic carbon stocks using the data from 706 soil pedons on the QTP based on previous reports and this project data. The carbon characteristics were compared with those in permafrost regions in Alaska. (2) We investigated distribution of soil carbon and nitrogen, carbon flux and possible relationships between soil organic carbon and environmental conditions on the Eboling Mountain in the upper reach of the Heihe river basin, northwestern China. (3) We conducted the incubation experiments using the samples from the active layer and permafrost to study decomposition rate of organic carbon with temperature change and effect of microbial heating on soil temperature. (4) We analyzed the characteristics of dissolved organic carbon and greenhouse gases, and carbon decomposition process in thermokarst lakes formed by the permafrost degradation over the QTP. The detailed results and main conclusions are as follows: Soil organic carbon pools on the QTP were estimated to be 15.29 Pg for the 0 ~ 1 m depth, 4.84 Pg in the 1 ~ 2 m, 3.89 Pg in the 2 ~ 3 m and 43.19 Pg for deeper layer of 3 ~ 25 m. In total, permafrost regions on the QTP contain approximately 67.2 Pg of organic carbon, of which approximately 47.08 Pg (70.1%) occurs in perennially frozen soils and deposits. To summarize, the SOC storage on the QTP was approximately 4% of that in the northern hemisphere permafrost. The SOC storage was 32.39 Pg, 38.79 Pg and 0.82 Pg in alpine meadow, alpine steppe and desert, respectively. SOC contents have wider range within depth of 6 m on the QTP, which implies that the depth variability of carbon storage is greater than that (0 ~ 3 m) in northern hemisphere permafrost. Therefore, organic carbon stored in permafrost regions on the QTP may have great potential for the contribution to global climate warming. The Eboling Mountains in the upper reach of the Heihe River basin on the Qilian Mountains has obvious permafrost degradatipn and high SOC contents, which was seleted as the study area to study the potential carbon emission and microbial activity process in permafrost regions. The average storage of soil organic carbon (SOC), total nitrogen (TN) and soil inorganic carbon (SIC) in permafrost above soil parent materials (71.7 kg m-2, 8.0 kg m-2, 34.7 kg m-2) were higher than those in the active layer (44.2 kg m-2, 5.3 kg m-2, 12.2 kg m-2) on the Eboling Mountains. The δ13C-SOC patterns in soil profiles indicated that historical drainage conditions and pedogenesis were important factors in the determinant of SOC storage in this permafrost region. The δ13C and C/N values of the intermediate layer and the some layers of permafrost suggested that the degradations of SOC were different. The average water soluble organic carbon (WSOC) content in permafrost was higher than that in the active layer, suggesting that labile carbon in permafrost soils is of higher quality. SIC was an important factor that affected SOC a |
| 中文关键词 | 多年冻土 ; 碳储量 ; 有机碳分解 ; 稳定碳同位素 ; 热融湖塘 |
| 英文关键词 | permafrost carbon stocks organic carbon decomposition stable carbon isotope thermokarst lakes |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院西北生态环境资源研究院 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287393 |
| 推荐引用方式 GB/T 7714 | 牟翠翠. 多年冻土区温室气体释放的生物地球化学过程[D]. 中国科学院大学,2014. |
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