海洋生态与环境科学重点实验室知识库

摘  要

海洋作为地球系统的巨大碳库，在全球碳循环过程和气候变化调节中扮演着重要角色。边缘海以不足10%的面积承载了全球海洋有机碳80%的埋藏总量，是陆源有机质和海源有机质埋藏的热点区域。中国东部边缘海存在较为复杂的碳循环机制。在水动力学过程、气候变化与人类活动等多重因素的影响下，有机碳经历广泛的细菌改造过程，埋藏命运难以确定。因此，通过对边缘海有机质来源、迁移转化和微生物降解等生物地球化学过程的研究可以了解中国边缘海碳埋藏途径与潜力，为我国海洋碳汇研究提供参考。

本研究综合分析了南黄海和长江口及其邻近海域表层沉积物中有机质含量与同位素特征，讨论了有机物的来源；以氨基糖为生物标志物，对比分析了两个海域沉积物中氨基糖的含量与组成特征，评估了沉积物中有机质的降解状态和细菌有机碳对总有机碳的贡献率，得到了以下结果和认识：

1. 南黄海与长江口及其邻近海域表层沉积物中总有机碳、总氮的相对含量及同位素特征表明，海洋自生来源是表层沉积物中有机质的主要组成部分，约占总有机质的70%，呈现由近岸向远岸逐渐增加的分布特征。

有机质来源是影响有机质埋藏的一项关键因素，在复杂的沉积环境中空间分布差异显著。在调查的34个站位中，总有机碳（TOC）与总氮（TN）存在显著的正相关关系（R²=0.94，p<0.01），表明TN主要以有机氮的形式存在。基于碳氮比（C/N）、碳氮同位素（δ¹³C和δ¹⁵N）对海陆有机质的相对贡献进行估算，发现浮游植物为代表的海源有机质是研究区域表层沉积物有机质的主要贡献者。随着距陆地距离的增加，陆源有机质的相对贡献逐渐减少。

南黄海和长江口及其邻近海域沉积物中有机质δ¹³C的平均值分别为-21.96±0.62‰和-22.57±1.61‰，随着陆地距离的增加而逐渐富集，估算海洋有机质的贡献为72.75±8.66%和64.33±22.29%。陆源有机质输入影响较大的区域为南黄海西部的江苏近岸海域、南黄海东北部海域与长江口内区域。虽然利用C/N估计沉积物中有机质的主要来源也为海洋有机质，但是受细菌活动与无机氮组分的干扰导致低估了陆源有机质贡献。δ¹⁵N的范围为-2.02‰ ~ 5.34‰，在南黄海西部近岸区域和长江口近岸区域较为贫化，表明近岸水体中化肥与陆生植物对表层沉积物中有机氮的贡献较高。

2. 南黄海与长江口及其邻近海域表层沉积物氨基糖中葡萄糖胺与半乳糖胺之比（GlcN/GalN）普遍小于3，表明有机质经历了较深程度的降解。在泥质区中GlcN/GalN相对较高，有机质降解程度相对较低且活性较高。基于细菌特异性氨基糖胞壁酸估算的细菌有机质贡献结果显示，细菌有机质是研究海域沉积物中有机质的重要来源，平均约占总有机碳的20.92%。长江口内表层沉积物接收了大量来自土壤的细菌残体而呈现较高的细菌有机质贡献。南黄海表层沉积物中有机质的细菌贡献（20.24±7.45%）略高于长江口及其邻近海域（14.95±5.22%），表明南黄海在中国东部边缘海细菌有机碳长期封存中可能发挥更重要的作用。相较于长江口及其邻近海域，南黄海泥质区等远端泥质区受人类活动干扰程度更小，将成为有机碳长期埋藏的热点区域。

本研究中，南黄海表层沉积物中氨基糖总量为0.68 ~ 2.08 nmol mg^-1；长江口及其邻近海域表层沉积物中氨基糖总量为0.40 ~ 1.91 nmol mg^-1，受到泥沙输入影响相对含量略低。沉积物主要检测出三种氨基糖组分，分别为葡萄糖胺、半乳糖胺、胞壁酸，平均占氨基糖总量的59.39%、35.87%和4.63%。沉积物中氨基糖的主要来源为细菌来源，几乎所有站位的GlcN/GalN都在3以下，在长江口及其邻近海域与南黄海的平均值分别为1.76±0.72和1.83±0.66，表明长江口及其邻近海域沉积有机碳较南黄海发生更深层次降解。南黄海上层水体中颗粒物沉降相对缓慢，导致有机质经历了长时间的降解，但在冷水团的保护作用有利于有机质长时间保存。南黄海122°E水柱中10 ~ 30米深度存在叶绿素高值，藻类产生的活性有机质能较快到达沉积物中，呈现GlcN/GalN值较高，表明沉积物中有机质活性相对较高。长江口邻近海域颗粒物的沉降较快，但在长江冲淡水、台湾暖流、潮汐作用等更强水动力条件下发生再悬浮，导致其返回上层好氧水体中被细菌进一步降解。

长江口内区域、长江口邻近海域、南黄海沉积物中细菌有机质的贡献分别为39.28±20.37%、14.95±5.22%和20.24±7.45%，表明长江口内区域内存在更活跃的细菌有机质合成。但南黄海的细菌有机质贡献高于长江口邻近海域，表明南黄海代表的远端泥质区具有更稳定的长期碳汇能力。随着人类活动的影响，河流径流量和泥沙量呈下降的总体趋势，长江口邻近海域沉积物中陆源有机碳来源将会减少，沉积物再悬浮加剧，使得有机质经历进一步降解的可能性增大；而南黄海泥质区等远端泥质区具有相对稳定的沉积环境和细粒径沉积物，具有更稳定的有机质长期埋藏能力。

Abstract

As a huge carbon reservoir of the Earth system, the oceans play an important role in the global carbon cycle process and climate change regulation. With less than 10 percent of its area, the marginal sea carries 80 percent of the total amount of global marine organic carbon, making it a hotspot for the burial of organic matter of land and sea origin. A complex carbon cycle mechanism exists in the marginal sea of eastern China. Under the influence of multiple factors, such as hydrodynamic processes, climate change and human activities, organic carbon undergoes extensive bacterial modification, and the fate of burial is difficult to determine. Therefore, by studying the biogeochemical processes of organic matter sources, transport and microbial degradation in the marginal sea, we can understand the carbon burial pathways and potentials in the marginal sea of China, which can provide a reference for the study of Chinese marginal sea carbon sinks.

In this study, we analyzed the organic matter content and isotopic characteristics of surface sediments in the South Yellow Sea and the Yangtze River estuary and its adjacent seas, and discussed the sources of organic matter; we compared the content and compositional characteristics of amino sugars in the sediments of the two seas using amino sugars as a biomarker, and evaluated the degradation status of organic matter in the sediments and the contribution rate of bacterial organic carbon to the total organic carbon, and got the following results and understandings:

1. The relative content and isotopic characteristics of total organic carbon and total nitrogen in the surface sediments of the South Yellow Sea and the estuary of the Yangtze River and its adjacent seas show that marine autochthonous sources are the main components of organic matter in the surface sediments, accounting for about 70% of the total organic matter, and presenting a gradual increase in the distribution of the characteristics from the near shore to the far shore.

The source of organic matter is a key factor affecting the burial of organic matter, and there are significant spatial distribution differences in complex sedimentary environments. Among the 34 investigated sites, total organic carbon (TOC) is significantly positively correlated with total nitrogen (TN) (R²=0.94, p<0.01), indicating that TN mainly exists in the form of organic nitrogen. Based on C/N and δ¹³C, the relative contributions of marine and terrestrial organic matter were estimated, revealing that marine-derived organic matter represented by phytoplankton is the main contributor to surface sediment organic matter in the study area. As distance from land increases, the relative contribution of terrestrial-derived organic matter gradually decreases.

The average values of organic matter δ¹³C in the sediments of the South Yellow Sea, Yangtze River Estuary and adjacent sea areas are -21.96±0.62‰ and -22.57±1.61‰ respectively, gradually enriching with increasing distance from land. The estimated contribution of marine organic matter to the ocean is 72.75±8.66% and 64.33±22.29% respectively. The regions most affected by terrestrial organic matter input are the nearshore areas of Jiangsu in the western South Yellow Sea, the northeastern South Yellow Sea, and the upstream area of the Yangtze River Estuary. Although using C/N to estimate the main source of organic matter in sediments also indicates marine organic matter, interference from bacterial activity and inorganic nitrogen components leads to an underestimation of contributions from terrestrial organic matter. The range of δ¹⁵N is -2.02‰ ~ 5.34‰, showing depletion in nearshore areas in western South Yellow Sea and near the mouth of Yangtze River Estuary, indicating a higher contribution of fertilizer and terrestrial plants to surface sediment organic nitrogen content in coastal waters.

2. The ratio of glucosamine to galactosamine (GlcN/GalN) in the amino sugars in the surface sediments of the South Yellow Sea and the Yangtze River estuary and its neighbouring seas is generally less than 3, indicating that the organic matter has undergone a deeper degree of degradation. Relatively high GlcN/GalN in the mud region was associated with relatively low organic matter degradation and high activity. The results of bacterial organic matter contribution based on the estimation of bacterial-specific aminoglycan cytosolic acid showed that bacterial organic matter was an important source of organic matter in the sediments of the study area, which accounted for an average of about 20.92% of the total organic carbon. The surface sediments in the Yangtze River estuary received a large amount of bacterial residues from the soil and showed a high contribution of bacterial organic matter. The bacterial contribution of organic matter in the surface sediments of the South Yellow Sea (20.24 ± 7.45%) was slightly higher than that of the Yangtze River estuary and its adjacent waters (14.95 ± 5.22%), suggesting that the South Yellow Sea may play a more important role in the long-term sequestration of bacterial organic carbon in the marginal seas of eastern China. Compared with the Yangtze River estuary and its adjacent seas, the South Yellow Sea mud areas and other distal mud areas are less disturbed by human activities, and will become a hotspot for long-term organic carbon sequestration.

In this study, the total amount of amino sugars in the surface sediment of the South Yellow Sea ranged from 0.68 to 2.08 nmol mg ^-1; while in the surface sediment of the Yangtze River Estuary and its adjacent sea area, it ranged from 0.40 to 1.91 nmol mg ^-1, with a slightly lower relative content influenced by sediment input. Three main components of amino sugars were detected in the sediments, namely glucosamine (GlcN), galactosamine (GalN), and muramic acid (MurA), accounting for an average of 59.39%, 35.87%, and 4.63% of the total amino sugar content respectively. The major source of amino sugars in the sediment was found to be bacteria-derived, with GlcN/GalN ratios at nearly all sites being below 3. The average values in the Yangtze River Estuary and its adjacent sea area as well as the southern Yellow Sea were 1.76±0.72 and 1.83±0.66, indicating a slightly higher overall degradation degree of organic carbon in the sediments of the Yangtze River Estuary and its adjacent sea area compared to that in the southern Yellow Sea. The deep degradation of organic matter in sediments in the southern Yellow Sea is attributed to relatively low settling rates of overlying water column particles leading to longer degradation times during settling but easier long-term burial under protection from cold water masses. Additionally, high chlorophyll values were observed at depths between 10-30 meters along the water column at 122°E in the southern Yellow Sea due to shallow depth allowing faster arrival into sediments shortening degradation time within water columns resulting in higher GlcN/GalN values indicative of relatively active organic matter within sediments. In contrast, stronger hydrodynamic conditions such as those caused by dilution from freshwater discharge from the Yangtze River or Taiwan Warm Currents and tidal action promote resuspension of surface sediments returning them for additional aerobic degradation within upper water bodies offshore areas near the mouth of Yangtze River.

The contributions of bacteria organic matter in the sediment of the mouth of the Yangtze River, the adjacent sea area, and the South Yellow Sea were 39.28±20.37%, 14.95±5.22%, and 20.24±7.45% respectively, indicating a more active bacterial organic matter synthesis in the nearshore mouth area of the Yangtze River estuary. However, the bacterial organic matter content in the South Yellow Sea is higher than that in the adjacent sea area of the Yangtze River estuary, indicating that the distant muddy area represented by the South Yellow Sea has a more stable long-term carbon sink capacity. With human activities affecting a general downward trend in river runoff and sediment load, there will be a reduction in organic carbon sources in Yangtze River estuarine sediments; however, there remains a high proportion of resuspended sediments which increases the possibility of further degradation of organic matter. In contrast, relatively stable sediment environments and fine-grained sediment in the South Yellow Sea may have a more stable long-term burial capacity for organic matter.

第1章 绪论

1.1 选题背景与研究意义

1.1.1 边缘海及其有机质埋藏特征

1.1.2 细菌对有机碳埋藏的作用

1.2 海洋有机碳来源与降解程度鉴别方法

1.2.1 有机质来源判别方法

1.2.2 有机质降解程度判别方法

1.3 海洋中氨基糖的分布与指示作用

1.3.1 氨基糖的组成与指示作用

1.3.2 氨基糖在环境中的分布

1.4 论文研究内容与研究意义

第2章 研究区域与研究方法

2.1 研究区域

2.1.1 南黄海

2.1.2 长江口及其邻近海域

2.2 样品采集与保存

2.3 样品处理与分析

2.3.1 总有机碳、总氮及其同位素、Chl-a

2.3.2 氨基糖的提取与测试方法

2.4 数据处理

2.4.1 细菌有机碳贡献计算

2.4.2 数据分析

第3章 中国东部边缘海表层沉积物有机碳的来源判别

3.1 沉积物生物地球化学参数分布特征

3.1.1 TOC、TN、δ¹³C与δ¹⁵N

3.1.2 Chl-a

3.2 表层沉积物有机质来源判别

3.2.1 TOC/TN

3.2.2 δ¹³C与δ¹⁵N

3.3 本章小结

第4章 中国东部边缘海表层沉积物中氨基糖的分布特征及其对有机质降解的指示作用

4.1 氨基糖的分布与组成特征

4.2 氨基糖有机质指标及其指示作用

4.2.1 有机质活性与降解程度

4.2.2 细菌有机碳贡献的估算

4.2.3 对边缘海碳埋藏的启示

4.3 本章小结

第5章 结论与展望

5.1 主要结论

5.2 不足与展望

参考文献

致 谢

作者简历及攻读学位期间发表的学术论文与其他相关学术成果