海洋生态与环境科学重点实验室知识库

边缘海作为海洋有机碳埋藏的重要储库，其复杂的生物地球化学过程及海洋生态环境变化对全球碳氮循环和海洋服务功能具有重要影响。东海内陆架作为我国重要的陆架边缘海，其有机质归趋、季节性低氧等海洋生态环境问题一直是备受关注的焦点。细菌藿多醇BHPs是一种同时集合生物来源专属性和环境特异性的较新型微生物标志物，其对海洋环境变化响应敏感且易保存，受成岩作用的影响较小，在追踪有机质来源，指示海洋低氧环境以及反演环境演变过程方面具有较大潜力。但是，目前对于BHPs在中国近海环境指示作用的关注很少，环境指示功能尚未明确。本学位论文聚焦细菌藿多醇对东海内陆架生态环境长期变化的指示与潜在应用这一关键科学问题，系统分析了东海内陆架沉积物中BHPs的组成、分布及来源等生物地球化学行为特征，重点探讨了BHPs对东海内陆架有机质来源的判别及对低氧环境的响应，初步揭示了特征BHPs对厌氧氨氧化活动和甲烷氧化活动的指示作用，并以此为理论反演了百年来东海内陆架生态环境的演变过程。获得的主要成果和结论如下：

1.系统研究了东海内陆架沉积物中BHPs的地球化学特征。发现长江口邻近海域和东海沉积物中BHPs具有显著的空间分布和来源特征。海源自生来源的细菌藿四醇BHT和陆源贡献的腺苷藿烷分别呈现明显的离岸增加和降低趋势。

长江口邻近海域和东海两个调查航次的表层沉积物中共检测出包括细菌藿四醇（BHT）、BHT同分异构体（BHT-II）、2-甲基BHT、腺苷藿烷和氨基BHPs等在内的12种BHPs。长江口邻近海域和东海表层沉积物中总BHPs含量范围（以TOC计，下同）分别为3.79~269 μg·g^-1和3.79~361 μg·g^-1，整体表现出由近岸向外海显著升高的空间分布趋势。两个航次调查中BHPs均以BHT、BHT-II、2-甲基BHT、氨基藿三醇及腺苷藿烷为主要组分，在长江口邻近海域表层沉积物中分别占总BHPs的比例为39.69%、8.46%、21.85%、9.28%和4.39%，在东海表层沉积物中分别占总BHPs的比例为41.41%、6.24%、27.65%、7.91%和2.49%。

长江口邻近海域和东海表层沉积物中BHPs组分均表现出明显的空间分布和来源特征。其中，BHT呈现出显著的“离岸增加”特征，其主要为海洋自生来源，由海洋中蓝细菌、变形杆菌和紫色非硫细菌等多种微生物产生；而腺苷藿烷等土壤标志物BHPs呈现出显著的“离岸降低”趋势，由陆源土壤中固氮细菌和氨氧化细菌等微生物产生；2-甲基BHT主要为海洋水体中蓝细菌的原位贡献；氨基藿多醇主要来源于陆源甲烷氧化菌的输入；藿四醇酐则主要为BHT在酸催化条件下的早期成岩降解产物。

2. 深入探讨了东海内陆架沉积物中BHPs对海洋生态环境变化的指示作用。发现新型陆源有机质判别指标R_soil指示了沉积有机质的混合来源；细菌藿四醇同分异构体BHT-II可用于指示海洋低缺氧环境；氨基藿四醇和氨基藿五醇可用于指示好氧甲烷氧化活动的强度。

基于土壤细菌来源BHPs（土壤标志物BHPs）和海洋细菌来源BHPs（BHT）比值的R_soil指数，是一种指示陆源有机质输入的新型指标。基于R_soil的二端元混合模型估算结果显示，长江口邻近海域沉积有机质中河流输入的陆源有机质贡献比例为1.7%~61.5%，东海沉积有机质中陆源有机质的贡献为0.8%~63.2%，二者均呈现出显著的“离岸降低”特征。与基于δ¹³C的模型计算结果基本一致，表明东海内陆架沉积有机质的混合来源，陆源有机质输入在近岸海域占主要地位，而外海海域中以海源沉积有机质为主。

东海内陆架沉积物中的BHT-II主要来自于底层低氧水体中的厌氧氨氧化菌。研究发现，表层沉积物中BHT-II相对含量与底层水体溶解氧浓度之间具有显著负相关关系（r为0.556~0.820，p<0.01），且BHT-II相对含量的高值区与近20年来长江口低氧区（DO<3 mg·L^-1）分布对应一致，尤其是长江口门北部的最高值区域与近年来低氧区的北向扩展趋势相吻合。因此该海域沉积物中BHT-II相对含量可用于指示水体厌氧氨氧化活动的强度及底层海水的低缺氧状况。对全球海域已有研究的BHT-II相对含量进行综合分析，发现在缺氧环境（O₂<0.2 mg·L^-1）中，BHT-II相对含量>0.45；在低氧环境（0.22<3 mg·L^-1），BHT-II相对含量为0.20~0.45；在富氧环境（O₂>3 mg·L^-1），BHT-II相对含量<0.20；这些阈值具有作为海洋环境氧化还原状况判别指标的潜能。

氨基藿四醇和氨基藿五醇及其相关结构对I型和II型甲烷氧化菌具有高度来源特异性，被作为甲烷氧化标志物。长江口和近岸海域高浓度的甲烷为好氧甲烷菌提供了充足的碳源和能源，使得甲烷氧化菌活性和好氧甲烷氧化强度增强，有利于氨基藿四醇和氨基藿五醇的生成。而向外海方向，微生物介导的好氧甲烷氧化过程显著减弱，甲烷浓度和氨基藿四醇、氨基藿五醇含量也均迅速降低。这些证据均表明氨基藿四醇和氨基藿五醇具有指示长江口邻近海域好氧甲烷氧化活动强度的潜能。

3. 利用BHPs特征指示指标重建了东海内陆架百年来的有机质来源、低氧和厌氧氨氧化等演变历程。发现近百年来东海内陆架中海陆有机质贡献比例逐渐增加，低氧整体呈现持续增加趋势；厌氧氨氧化活动与低氧的演变历程相似，但存在一定的时间滞后性，整体也表现为增强趋势。

东海内陆架近百年来沉积有机质表现出陆源有机质贡献比例明显降低，海源有机质贡献比例升高的变化趋势。柱状沉积物在第I、II阶段（1961~2000年），陆源有机质贡献比例波动幅度较大。该时期陆源有机质输入的不稳定性较大。在第III阶段（2000年以后），伴随着陆源有机质贡献比例的逐渐降低，海源有机质贡献波动增加。该时期内由于人类活动增加，大量生源要素和营养物质输入海洋，促进了海洋初级生产力的提高和海洋来源有机质贡献的增加。

近百年来长江口海域低氧核心区沉积物记录中BHT-II相对含量高峰值对应的时期与20世纪中期以来的三个严重低氧时期相一致，进一步表明BHT-II相对含量指标可用于记录和反演过去海水低氧的演变过程。柱状沉积物第I阶段（1961~1975年），BHT-II相对含量有所增加，表明该阶段低氧程度有所增强。第II阶段（1975~2000年），BHT-II相对含量呈现先加速增加后降低的变化趋势。该阶段内低氧程度持续增强，20世纪90年代左右低氧状况加剧并达到峰值，而后由于水体生产力有所降低，使得有机质分解消耗的氧气减少，低氧环境趋于缓解。第III阶段（2000年以后），BHT-II相对含量波动增加，低氧状况加剧。

近百年来东海内陆架厌氧氨氧化活动与低氧的演变历程相似，但存在一定的时间滞后性。1980年以前柱状沉积物中的BHT-II含量较低，表明厌氧氨氧化活动强度较弱；1980年后厌氧氨氧化活动的强度快速增加，特别是在低氧时期呈现出较高强度，这是由于富营养化和低缺氧有利于厌氧氨氧化菌的生长和厌氧氨氧化活动的增强；2010年以后柱状沉积物中的BHT-II含量呈现波动增加的趋势，表明该海域厌氧氨氧化活动进一步加强。此外，20世纪90年代和21世纪初期，低氧状况加剧、氮损失增加的同时，海洋中固氮作用也有所增强。

The marginal sea is an important reservoir for marine burial organic carbon, and its complex biogeochemical processes and ecological environmental changes have important impacts on the global carbon and nitrogen cycles and marine service functions. The inner shelf of the East China Sea is an important shelf marginal sea. Its marine ecological environments such as the fate of organic matter and seasonal hypoxia have always been the focus of attention. Bacteriohopanepolyols (BHPs) are microbial markers that have specificity in bacterial origin and environmental response They are sensitive to marine environmental changes, are easy to preserve and less affected by diagenesis. BHPs have shown great application potential in tracking organic matter source, indicating marine hypoxia and reconstructing environmental evolution processes. However, the researches on BHPs in the coastal waters of China have seldom carried out, and the environmental indication functions of BHPs have not been clarified yet. This study focused on the key scientific issue of “The indications and potential application of Bacteriohopanepolyols on the long-term changes of the ecological environment in inner shelf of the East China Sea (ECS)”. The biogeochemical characteristics of the compositions, distributions and sources of BHPs in inner shelf of the ECS were systematically analyzed, the indications of BHPs in organic matter sources and marine hypoxia were discussed, and the indications of BHPs in anaerobic ammonia oxidation and aerobic methane oxidation were revealed. Furtherly, the ecological environmental evolution processes over the last century in inner shelf of the ECS were reconstructed based on BHPs. The main conclusions obtained from this study are as follows:

1. The geochemical characteristics of BHPs in the sediments of the ECS inner shelf were systematically analyzed. It is found that BHPs in the sediments of the Yangtze estuary and its adjacent areas and the ECS have significant spatial distribution and source characteristics. Bacteriohopanetetrol (BHT) from marine sources and adenosylhopane from terrestrial sources showed significant offshore increase and offshore decrease trends, respectively.

A total of 12 BHPs were detected and identified in surface sediments of the Yangtze estuary and its adjacent areas and the ECS, including bacteriohopanetetrol (BHT), BHT isomers (BHT-II), 2-methyl BHT, adenosylhopane and amino-BHPs. Total BHPs contents (normalized to TOC, same as below) in surface sediments of the Yangtze estuary and its adjacent areas and the ECS ranged from 3.79 to 269 μg·g^-1 and 3.79 to 361 μg·g^-1, respectively. Total BHPs contents showed an obvious increase seaward. In the two voyage surveys, BHPs were mainly composed of BHT, BHT-II, 2-methyl BHT, aminotriol and adenosylhopane. The averaged proportions relative to total BHPs in the surface sediments of the Yangtze estuary and its adjacent areas were 39.69%, 8.46%, 21.85%, 9.28% and 4.39%; the averaged proportions relative to total BHPs in the surface sediments of the ECS were 41.41%, 6.24%, 27.65%, 7.91% and 2.49%.

The BHPs components in the surface sediments of the Yangtze estuary and its adjacent areas and the ECS both showed obvious spatial distribution and source characteristics. BHT presented a significant "offshore increase" trend, produced by various microorganisms such as cyanobacteria, proteobacteria and purple non-sulfur bacteria in the ocean. Soil marker BHPs showed a significant "offshore decrease" trend, which was mainly from terrestrial organic matter inputs, produced by microorganisms such as nitrogen-fixing bacteria and ammonia oxidizing bacteria in the soil. 2-methyl BHT mainly contributed from the in-situ production of cyanobacteria in seawater; amino-BHPs were mainly derived from the inputs of terrestrial methanotrophs. AnhydroBHT was mainly the product of BHT early diagenesis under acid-catalyzed conditions.

2. The indications of BHPs on the marine ecological environmental changes of the ECS inner shelf have been discussed emphatically. It was found that the new terrestrial organic matter identification index R_soil indicated the mixed sources of sedimentary organic matter. The BHT isomer BHT-II could indicate the hypoxic marine environment. Aminotetrol and aminopentol can be used to indicate the intensity of aerobic methane oxidation activity.

The R_soil index based on the ratio of terrestrial BHPs (soil markers BHPs) and marine BHPs (BHT) is a new index indicating the inputs of terrestrial organic matter. Based on the two end-member model of R_soil, it was quantitatively calculated that the contribution of terrestrial organic matter carried by the Changjiang River to the Yangtze estuary and its adjacent areas was 1.7%~61.5%; and the contribution of terrestrial organic matter to the ECS was 0.8%~63.2%. Both of them showed obvious "offshore decrease" trends. It was basically consistent with the calculation results of the model based on δ¹³C, indicating the mixed source of sedimentary organic matter in the inner shelf of the ECS. The input of terrestrial organic matter was dominant in the coastal waters, and the marine sedimentary organic matter was the main source in the outer waters.

The BHT-II in sediments of the inner shelf of the ECS is mainly derived from anammox bacteria in the bottom hypoxic seawater. The results showed that the DO concentrations in bottom waters also showed a significant negative correlation with the BHT-II ratios in surface sediments (r=0.556~0.820, p<0.01). And high-value zones of BHT-II ratio in the surface sediments were basically located in the hypoxic zones (DO<3 mg·L^-1) of the Yangtze estuary and its adjacent areas in the past 20 years. In particular, the highest BHT-II ratios in the northern Changjiang Estuary were consistent with the northward migration of hypoxic zones. Therefore, the BHT-II ratios in sediments of this sea area can indicate the intensity of the anaerobic ammonia oxidation activity in the seawater and the hypoxic condition of the bottom seawater. A comprehensive analysis of the BHT-II ratios in existing studies of the global seas suggested that the BHT-II ratios were >0.45 in anoxic environment (DO < 0.2 mg·L^-1), the BHT-II ratios were ranged from 0.20 to 0.45 in hypoxic environment (0.2 mg·L^-1 < DO < mg·L^-1), and the BHT-II ratios were < 0.20 in oxic environment (DO > 3 mg·L^-1). These thresholds would have the potential to identify the marine redox conditions.

Aminotetrol, aminopentol and their related structures have high specificity to type I and type II methanotrophs, and are used as CH₄ oxidation markers.The high methane concentrations in the Yangtze estuary and coastal areas provided more carbon and energy sources for methanotrophs, increasing the abundance of methanotrophs and enhancing the intensity of aerobic methane oxidation activity near the estuary, which was conducive to the production of aminotetrol and aminopentol. Whereas, both of the microbial-mediated methanogenesis and aerobic methane oxidation were significantly weakened in the outer seas, resulting in the rapid decrease of methane concentration and aminotetrol, aminopentol contents. These evidences all indicate that aminotetrol and aminopentol have the potential to indicate the intensity of aerobic methane oxidation activity in the Yangtze estuary and its adjacent areas.

3. The ecological environmental evolutionary history of organic matter sources, hypoxia and anaerobic ammonia oxidation activity over the last century in inner shelf of the ECS were reconstructed through characteristic BHPs indicators. It was found that the proportion of marine and terrestrial organic matter contribution has gradually increased in the past 100 years, and the hypoxia showed a continuous increase trend. The evolutionary history of anammox activity was similar to that of hypoxia, but there was a certain time lag for anammox activity. The anammox activity over the last century also showed a gradual increase trend.

Sedimentary organic matter on the continental shelf of the ECS over the past 100 years showed obvious trends that the contribution of terrestrial organic matter decreased, and the contribution of marine organic matter increased significantly. In the I and II stages (1961~2000 AD) of core sediments, the contribution ratio of terrestrial organic matter fluctuated greatly. The input of terrestrial organic matter was unstable during this period. In the III stage (after 2000 AD), along with the gradual decrease in terrestrial organic matter contribution, the fluctuation of marine organic matter contribution increased. During this period, due to the increase of human activities, a large number of biogenic elements and nutrients were imported into the ocean, which promoted the increase of marine primary productivity and the contribution of marine autochthonous organic matter.

The high values of BHT-II ratios recorded in hypoxic zone sediments of the Yangtze estuary over the past 100 years were consistent with the three severe hypoxic periods since the middle of the 20th century, further indicating that the records of BHT-II ratios in core sediments have the potential to reflect the hypoxic evolution history. The BHT-II ratios increased in the I stage of core sediments (1961~1975 AD), indicating that the hypoxic condition in this stage increased. In the II stage (1975~2000 AD), the BHT-II ratios increased first and then decreased. During this period, the hypoxic situation continued to increase and reached the peak in the 1990s. Then, due to the marine productivity decrease, the oxygen consumed by the decomposition of organic matter was reduced, so that the hypoxic environment tended to alleviate. In the III stage (after 2000 AD), the BHT-II ratios showed a fluctuating increase trend and the hypoxic condition worsened.

In the past 100 years, the evolutionary history of anaerobic ammonia oxidation activity on the continental shelf of the ECS was similar to that of hypoxia, but there was a certain time lag for anaerobic ammonia oxidation activities. Before 1980 AD, the BHT-II ratios in core sediments were maintained at a low level, indicating that the intensity of anammox activity was weak. The intensity of anammox activity increased rapidly after 1980 AD. Especially, it showed higher intensity in the hypoxic period. This is because eutrophication and hypoxia are conducive to the growth of anammox bacteria and the enhancement of anammox activity. After 2010 AD, the BHT-II ratios in core sediments showed a fluctuating increase trend, indicating that the anaerobic ammonia oxidation activity was further strengthened during this period. In addition, as hypoxia and nitrogen loss increased in the 1990s and early 2000s, the nitrogen fixation in the ocean also increased.

第1章 绪论... 1

1.1 海洋环境中的生物标志物... 1

1.2 生物标志物细菌藿多醇概述... 2

1.2.1 细菌藿多醇的组成... 2

1.2.2 细菌藿多醇的环境分布特征... 6

1.3 细菌藿多醇对海洋生态环境的指示与反演... 9

1.3.1 BHPs追踪海洋有机质来源... 9

1.3.2 BHPs示踪海洋低缺氧和厌氧氨氧化活动... 10

1.3.3 BHPs指示好氧甲烷氧化活动... 10

1.3.4 细菌藿多醇对海洋古环境的反演... 11

1.4 本论文的研究意义与研究内容... 11

第2章 材料与方法... 13

2.1 研究区域... 13

2.2.1 东海内陆架的环境特征... 13

2.2.2 长江口海域的低氧特征... 13

2.2 样品采集与研究方法... 15

2.2.1 沉积物样品采集... 15

2.2.2 海水溶解氧和溶解甲烷测定... 16

2.2.3 沉积物元素分析... 16

2.2.4 沉积物²¹⁰Pb年代分析... 17

2.3 细菌藿多醇的分析... 17

2.3.1 分离提取方法... 17

2.3.2 检测分析... 18

2.3.3 BHPs指数计算... 18

第3章 东海内陆架细菌藿多醇的环境指示作用... 21

3.1表层沉积物中BHPs及指标的环境地球化学特征... 21

3.1.1 BHPs的分布特征... 21

3.1.2 BHPs相关指数的分布特征... 25

3.1.3 C、N及其同位素的分布特征... 25

3.2 BHPs的来源判别... 28

3.2.1 BHPs的陆源来源... 28

3.2.2 BHPs的海源自生来源... 32

3.3 海洋中沉积有机质来源判别... 35

3.3.1 碳氮同位素指示海洋沉积有机质来源... 35

3.3.2 BHPs追踪海洋沉积有机质来源... 38

3.4 BHPs响应海洋低氧环境... 42

3.5 BHPs指示好氧甲烷氧化活动... 45

第4章 BHPs对东海内陆架生态环境演变历程的反演... 47

4.1 柱状沉积物中BHPs及指标的环境地球化学特征... 47

4.1.1 柱状沉积物定年结果及沉积速率... 47

4.1.2 BHPs及其指标的垂向分布特征... 47

4.1.3 碳氮同位素和有机质贡献的垂向分布特征... 49

4.2 东海内陆架百年来沉积有机质来源和相对贡献变化... 50

4.2.1 东海内陆架百年来BHPs的来源... 50

4.2.2 东海内陆架百年来沉积有机质相对贡献的变化... 52

4.3 东海内陆架百年来低氧演变历史... 53

4.4 东海内陆架百年来厌氧氨氧化和氮循环演变过程... 56

4.5 BHPs对东海内陆架生态环境的潜在应用... 57

第5章 结论与展望... 59

5.1 主要结论... 59

5.2 不足与展望... 63

参考文献... 65

致谢... 77

作者简历及攻读学位期间发表的学术论文... 79