Knowledge Resource Center for Ecological Environment in Arid Area
| 干旱-半干旱区大型浅水湖泊碳埋藏研究——以呼伦湖为例 | |
| 其他题名 | The carbon burial in lake sediments of the arid/semi-arid region: a case study in Hulun Lake |
| 张风菊 | |
| 出版年 | 2017 |
| 学位类型 | 博士 |
| 导师 | 薛滨 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 碳循环不仅是生态系统对全球变化响应的综合表现，同时还直接和大气温室气体浓度的变化密切相关，从而对全球气候的稳定产生重要影响，因而成为全球变化研究的重要内容之一。湖泊由于面积较小，先前研究往往忽视了其在碳循环中的作用，近来越来越多的研究表明，湖泊既是重要的CO2排放源，也是重要的碳汇，在区域乃至全球碳循环中发挥着重要作用。研究湖泊碳埋藏的时空变化及其影响机制、揭示湖泊的碳源/汇功能不仅可为评估未来气候变化和人类活动影响下湖泊碳源/汇潜力变化提供基础数据和理论支撑，同时还可为制定应对气候变化的湖泊管理政策提供科学参考。论文以我国北方干旱-半干旱区大型浅水湖泊呼伦湖为例，开展了不同时间尺度下（现代、近百年来及中全新世以来）呼伦湖沉积物有机碳及无机碳含量及其埋藏量的时间和（或）空间变化，探讨了不同时间尺度下呼伦湖沉积物碳埋藏的可能影响因素。同时，采用清单研究法，研究了2015年呼伦湖水-气、水-陆及水-沉积物三个界面的碳收支，初步评估了呼伦湖的碳源/汇功能，并结合内蒙古地区陆地植被碳储量简要评估了呼伦湖在区域碳循环中的作用。主要研究结果如下： （1）呼伦湖表层沉积物TOC变化范围为2.08-3.55%，且主要由湖泊内源产生；受湖泊水深、水动力及营养水平等影响，TOC总体上表现为湖泊东北部高于南部及西南部的变化特征。表层沉积物TIC的变化范围为1.72-3.67%，且主要是湖泊自生的碳酸盐；TIC含量总体上表现为北部明显高于南部，这种空间分布可能与湖泊温度、水动力条件等因素有关。（2）近百年来呼伦湖有机碳埋藏速率（7.65-83.24 g m-2 yr-1）及无机碳埋藏速率（7.10-74.29 g m-2 yr-1）空间变化差异显著，且均表现为湖泊西北部高于东南部的分布格局。从时间变化来说，有机碳埋藏速率和无机碳埋藏速率均随时间变化呈现增加的趋势。1950年之后的有机碳埋藏速率分别是1900年之前及1900-1950年间的3.67和1.59倍，1950年之后的无机碳埋藏速率分别是1900年之前及1900-1950年间的3.94和1.56倍。近百年来呼伦湖的有机碳储量和无机碳储量分别约为9.99 Tg C和11.05 Tg C。呼伦湖无机碳埋藏速率及其储量均比有机碳埋藏速率及其储量要高，表明无机碳在区域乃至全球碳循环中的也发挥着重要作用，在必要在今后的研究中应予以重视。（3）尽管呼伦湖沉积物有机碳矿化随温度升高而增加，但近百年来呼伦湖有机碳埋藏速率与湖区温度及降雨量表现为显著正相关的关系，而与人类活动（人口数量、耕地面积、渔获量等）的相关性不是很明显。无机碳埋藏速率与温度呈现正相关性，与降雨量及人类活动的相关性不是十分显著。表明气候变化可能是驱动近百年来呼伦湖有机碳及无机碳埋藏的最主要因子，而人类活动在近百年呼伦湖碳埋藏中可能发挥着次要作用。（4）中全新世以来呼伦湖有机碳埋藏速率和无机碳埋藏速率平均值分别约为2.06 g m-2 yr-1和3.84 g m-2 yr-1，相应的有机碳和无机碳储量分别约为35.25 Tg C和65.70 Tg C。同时，利用呼伦湖沉积物TOC/TN值、有机质δ13Corg变化以及二元模型确定了呼伦湖沉积物有机质主要以外源输入为主，同时内源有机质所占比例在近千年来逐渐增加并最终占据主导地位。（5）中全新世以来呼伦湖有机碳埋藏速率与湖区温度及降水均表现为反相关的关系，而无机碳埋藏速率与湖区温度呈现一定的正相关关系，与降水的相关性不显著，表明在不同时间尺度上气候条件变化对湖泊有机碳埋藏的影响可能不同，但具体机制仍有待以后进一步的深入研究。（6）利用质量平衡法和气体释放-碳埋藏两种方法对呼伦湖2015年的碳源/汇功能进行了评估。结果表明，从碳质量平衡的角度来说，呼伦湖2015年总的碳收入约为2.66×105 t，总的碳支出为4.43×105 t，净碳收支为-1.77×105 t，因此呼伦湖为碳汇。从气体释放-碳埋藏的角度来说，呼伦湖水-气界面CO2的释放量约为4.42×105 t，碳埋藏量约为1.57×105 t，由呼伦湖向大气释放的CO2约是碳埋藏量的2.82倍，呼伦湖对于大气也是个碳源。综合来看，呼伦湖在2015年期间可能为碳源，而非碳汇。此外，不同时间尺度下呼伦湖沉积物碳库与内蒙古地区陆地生态系统碳储量的比较表明，虽然呼伦湖总的碳储量小于土壤和草地碳库，但单位面积的碳储量却远远高于草地生态系统，甚至可能还高于土壤碳库。加之湖泊沉积物较生物量和土壤能够保存更长的时间，因此，湖泊在维系区域碳平衡中同样起着重要的作用，湖泊及其流域生态系统在区域碳循环中的作用不容忽视。 |
| 英文摘要 | Carbon cycle is not only an important indicator of how ecosystems respond to globle change, but also directly influences the concentrations of the greenhouse gases (GHG) in the atmosphere. Therefore, the carbon cycle plays a substantial role in the stability of global climate, and has become a hotspot in the global change research. The role of lakes, particularly that of lake sediments, has been of great interest in the global and regional carbon cycle, although been ignored in the past due to its small size in the earth land surface. Lake sediments potentially store substantial quantities of carbon and can be regarded as an important carbon sink or source. The study of the temporal and spatial changes of carbon burial in lake sediments and its driving mechanisms, as well as the carbon source/sink function of lake ecosystems can not only provide basic data and theoretical support for assessing the carbon source/sink potential in the future, but also provide a scientific reference for the lake management under the influence of climate change and human activities.Hulun Lake, a large shallow lake in the arid and semi-arid region in China, was selected as the study area in this thesis. This study was designed to investigate the spatio-temporal variability and influencing factors of carbon burial in response to the interactive effects of climate change and human activities at different time scales. In addition, the carbon budget of Hulun Lake during 2015 was estimated from water-air, water-land and water-sedimet interfaces to assess the net carbon source/sink function of Hulun Lake. Moreover, the role of Hulun Lake in the regional carbon cycle was also assessed by comparing with the carbon burial in terrestrial ecosystems in Inner Mongolia.The main conclusions were as follows:(1) The TOC content in the surface sediment varied from 2.08% to 3.55% among the fifteen sediment cores, and the TOC was mainly from autochthonous sources. The TOC content was higher in the northwestern part of the lake than in the south and southwest lake region, and this spatial distribution characteristic was likely linked to the warer depth, lake hydrodynamic and the eutrophication level. The TIC cotent in the surface sediment ranged from 1.72% to 3.67%, and TIC was mainly authigenic carbonate. The TIC content was higher in the northern part of the lake than the southern part, and the spatial distribution of TIC was mainly under the influence of temperature and lake hydrodynamic and so on. (2) Both organic carbon burial rates (OCBR) (7.65-83.24 g m-2 yr-1) and inorganic carbon burial rates (ICBR) (7.10-74.29 g m-2 yr-1) varied greatly among the studied sediment cores over the past 150 years, and exhibited an overall northwest?southeast gradient, with the higher rates in the northwest part of the lake. The OCBR increased on average by a factor of 3.53 (all cores) when the post-1950 period was compared with the pre-1900 period, and the OCBR increased during the 20th century (i.e., the ratio of post-1950 to 1900-1950 OCBR) by a factor of 1.68 on average, indicating that OCBR showed an increasing trend over the past 150 years. For the ICBR, the ratios of the post-1950 period to the pre-1900 and 1900-1950 periods were 3.94 and 1.56, respectively, suggesting that an increasing trend of the IC burial rate over the past 150 years. The OC storage and the IC storage during the past 150 years were about 9.99 Tg C and 11.05 Tg C, respectively. The ICBR and the IC sequestration were higher than the OCBR and the OC sequestration, suggesting that inorganic carbon also played an important role in the carbon cycle and more attention should be paid to inorganic carbon burial in lake sediments.(3) Although the mineralization of organic carbon in lake sediments exhibited a positive relationship with temperature, the OCBR was positively correlated with precipitation and temperature while showed weak correlation with human influence (such as population, arable area and fish harvest) over the past 150 years. The ICBR was positively correlated with temperature, and no significant correlations were found between ICBR and human activities and precipitation. These observations implied that climate change was the most important factor in regulating the carbon burial in Hulun Lake while human activities played a relatively minor role. (4) The average OCBR and ICBR were about 2.06 g m-2 yr-1 and 3.84 g m-2 yr-1 since the mid-Holocene, with total OC and IC pools of 35.25 Tg C and 65.70 Tg C, respectivly. Relative contributions of allochthonous and autochthonous OC input since the mid-Holocene were estimated by the TOC/TN ratio, the changes of δ13Corg and the binary model. The results revealed that OC being buried in Hulun Lake was mainly generated from terrigenous vegetation. The binary model also revealed that autochthonous OC demonstrated an increasing trend in the last 1000 years.(5) The OCBR was negatively linked to temperature and precipitation while the ICBR was positively correlated with temperature and not related to precipitation since the mid-Holocene, implying that the increase of temperature and precipitation might lead to the decrease of OC burial and the increase of IC burial in Hulun Lake in the long term scale. It also showed that the impacts of climate change on OC burial might be different at different time scales, but the detail mechanism was still not clear.(6) Using two methods, overall mass balance and gas exchange and carbon burial balance, the carbon source/sink function of Hulun Lake was assessed during the year of 2015. With the overall mass balance calculations, total carbon input was 2.66×105 t, total carbon output was 4.43×105 t, and net carbon budget was -1.77×105 t, suggesting that Hulun Lake was a great carbon source. For the gas exchange and carbon burial balance, gaseous carbon (CO2) emission across the water-air interface totaled 4.42×105 t while carbon burial in the lake sediment was 1.57×105 t. The ratio of carbon emission into the atmosphere to carbon burial into the sediment was about 2.82. This ratio also indicated that Hulun Lake was a great carbon source. Moreover, the carbon storage and carbon density in Hulun Lake at different time scales were compared with that of in terrestrial ecosystem in Inner Mongolia. The results demonstrated that the total C sequestration in Hulun Lake was trivial compared with the C storage by terrestrial vegetation and soils because lake area was relatively small compared to that of land. However, the C density in Hulun Lake was comparable to or even higher than that of grasslands and soils. In particular, lake sediments can be preserved for quite longer times than forest biomass or soil, thus it is reasonable to conclude that lakes play a much larger part in the regional carbon cycle and should be taken into consideration in the regional and global carbon budget. |
| 中文关键词 | 碳埋藏速率 ; 碳储量 ; 影响因素 ; 碳源/汇 ; 呼伦湖 |
| 英文关键词 | carbon burial rate carbon storage influence factors carbon source/sink Hulun Lake |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 自然地理学 |
| 来源机构 | 中国科学院南京地理与湖泊研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287834 |
| 推荐引用方式 GB/T 7714 | 张风菊. 干旱-半干旱区大型浅水湖泊碳埋藏研究——以呼伦湖为例[D]. 中国科学院大学,2017. |
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