海洋生态与环境科学重点实验室知识库

长江口连接着世界上面积最大的大陆和最宽广的陆架，是有机碳埋藏和转化的主要场所。复杂的水文和水动力条件，源源不断的径流输入和三角洲植被输入使长江口水域的物质循环和能量传递始终处于动态变化之中，加之长江口受流域内各项水利工程、人工采砂、工农业和航运污水排放等人类活动影响明显，入海有机碳的通量和性质发生剧烈变化。溶解态有机碳（DOC，Dissolved Organic Carbon）和颗粒态有机碳（POC，Particulate Organic Carbon）的来源、分布与迁移转化行为同各种水力驱动和生物化学作用关联紧密。本研究基于2013年5月、2014年5月和11月、 2015年5月及2016年5月在长江口水域五个航次的环境综合调查，对长江口水域POC的年际分布变化、通量变化、有机碳的迁移转化及影响因素进行分析。同时，利用碳稳定同位素三端元模型示踪POC的物质来源，估算了长江口有机碳的物源贡献。主要研究结果如下：

（1）2013~2016年春季长江口水域中POC的浓度范围为0.22~16.99 mg/L，均值为1.80 ±2.02 mg/L。调查水域整体年际变化显著，不同区域间存在空间变异及年际差异，但近岸区底层POC常年较高，年际变化不显著。POC呈现近岸高于远岸、底层高于表层的分布趋势，通常在口门外南部水域达到高值，表层POC在123°E附近的远岸区存在次高值，低值区位于远岸区底层。

春季长江口水域POC浓度与盐度（S，Salinity）之间存在显著负相关性，盐淡水混合过程中，沉积物再悬浮是近岸水域不可忽略的重要碳源，海水的稀释作用在远岸水域处于主导地位；POC与总悬浮物（TSM，Total Suspended Matter）浓度之间存在显著正相关，悬浮物在高浊度水域和低浊度水域对POC的影响程度不同，TSM浓度和粒径的变化对长江口水域中POC的浓度以及在悬浮物中的组成比例有极为显著的影响；表层POC与叶绿素a（Chl-a，Chlorophyll-a）没有显著的相关性，但在远岸水域存在极显著正相关性，123°E附近的远岸水域存在Chl-a高值区和POC次高值区；POC主要以有机碎屑形式为主，但在远岸区更倾向于海洋浮游植物贡献。

（2）长江口POC入海通量多年来变化明显，三峡大坝蓄水对泥沙拦截作用显著，POC入海通量也随之下降；春季长江口入海径流量的年际变化趋势与POC浓度截然相反，长江径流的输入作用对河口POC浓度的影响正在减弱。

（3）陆源有机碳由长江径流经河口输送至海洋的过程中，DOC和POC之间存在着形态比例的转化。2014年春季DOC%在18.44~71.50%之间变化，均值为46.78±13.87%；秋季DOC%变化范围为25.46~84.97%，均值为63.35±14.63%，春季POC优势较秋季更为明显。以DOC贡献率等于50%为界，整体呈现远岸水域DOC的优势显著高于近岸水域，且表层DOC比底层更快地占据优势。

多种因素共同作用下，有机碳形态变化主要受盐度和悬浮颗粒物浓度变化的控制；长江口水域耗氧污染物主要是来自悬浮颗粒的有机部分。最大浑浊带（TMZ，Turbidity Maximum Zone）是有机碳浓度和形态转变的重要场所，大量POC在此沉降并矿化，POC解吸和微生物降解促使其向DOC转化。DOC/POC与TSM间存在协同变化，当水体中TSM浓度大于98.41mg/L时，长江口有机碳以颗粒态为主，反之则以溶解态为主。

（4）2014年5月长江口表层POC的海洋来源和三角洲来源贡献率均值分别为17.98%、23.84%，河流端为58.17%；底层POC的海源和三角洲贡献率分别为22.02%、29.19%，河流端为48.79%。POC在口门内主要来源是陆源输入，在门外的近岸水域，陆源贡献由TMZ迅速降低，以海源和三角洲来源的贡献为主，至远岸水域，海洋来源和三角洲来源的贡献率达到最高值。本文认为长江口POC的三角洲来源凸显是由于互花米草入侵显著增加了长江口湿地的土壤有机碳量和微生物碳量，改变了长江口有机碳的δ¹³C值。加之三峡大坝的影响使陆源有机碳输入减少，三角洲冲淤侵蚀，造成盐沼湿地的土壤有机碳和植物有机碳输入到长江口及邻近海域，进而影响长江口湿地生态系统的生物地球化学过程。

Connecting the largest continent and the broadest shelf in the world, the Yangtze River Estuary is the main site of organic carbon burial and transformation. Complicated hydrological and hydrodynamic conditions, continuous runoff and delta vegetation input make the material circulation and energy transfer in the Yangtze River Estuary waters are always in dynamic changes. In addition, the Yangtze River Estuary is obviously affected by human activities such as water conservancy projects, artificial sand mining, industry and agriculture, and the discharge of sewage from ships in the river basin, leading to drastic changes in the flux and properties of organic carbon entering the ocean. The source, distribution and migration and transformation behavior of dissolved organic carbon (DOC) and particulate organic carbon (POC) are closely related to various hydraulic drives and biochemical effects. Based on a comprehensive environmental survey of 5 voyages of the Yangtze River Estuary in May 2013，May and November 2014，May 2015and May 2016，this study analyzed the interannual distribution and flux changes of POC，organic carbon migration and transformation and influencing factors in the waters of Yangtze River Estuary. Meanwhile, the source contribution of organic carbon in the Yangtze River Estuary was estimated by using the three-terminal model of stable carbon isotope to trace the material source of POC. The main research results are as follows:

（1）The concentration of POC in the waters of the Yangtze River Estuary in spring from 2013 to 2016 ranged from 0.22 to 16.99 mg/L，with an average value of 1.80±2.02 mg/L. The overall interannual variation of the surveyed waters is significant，and there are spatial variation and interannual differences among different regions, but the bottom POC in the nearshore region is always at a high value, of which the interannual changes are not significant. POC presents a distribution trend of near shore higher than far shore and bottom layer higher than the surface layer, with a high value in the southern waters outside the entrance. The surface POC has the second highest value in the offshore area near 123°E, while the low value area is located at the bottom of the offshore area.

 There is a significant negative correlation between the concentration of POC and salinity (S) in the Yangtze River Estuary in spring. During the process of salt and fresh water mixing, the resuspension of sediments is an important carbon source that cannot be ignored in the nearshore area, while the dilution effect of seawater is dominant in the offshore area. There is a significant positive correlation between POC and total suspended matter (TSM) concentration. Suspended matter has different effects on POC in high-turbidity and low-turbidity waters. The change of TSM concentration and particle size has a great influence on the concentration of POC and the composition ratio of TSM in the Yangtze River Estuary. There is no significant correlation between surface POC and chlorophyll a (Chl-a) in the total waters，but the positive correlation between surface POC and chlorophyll a is extremely significant in offshore areas where their high-value areas coincide around 123°E. The POC of the Yangtze River Estuary is mainly in the form of organic detritus, but it is more inclined to contribute to marine phytoplankton in the offshore area.

（2）The flux of POC in the Yangtze Estuary has changed significantly over the years. The impoundment of the Three Gorges Dam has a significant effect on sediment interception, resulting in a decline in POC flux. The annual variation trend of runoff in the Yangtze Estuary in spring is completely opposite to the POC concentration. The influence of Yangtze River runoff input on the concentration of POC in the estuary is weakening.

（3）In the process of transporting terrigenous organic carbon from the runoff of the Yangtze River to the ocean through the estuary, there is a transformation between the form ratio of DOC and POC. In spring 2014, DOC% varied from 18.44 to 71.50%, with an average of 46.78±13.87%. DOC% in autumn ranged from 25.46 to 84.97%, with an average of 63.35±14.63%. The POC superiority in spring was more obvious than that in autumn. Taking the contribution rate of DOC equal to 50% as the boundary, the overall advantage of DOC in offshore waters is significantly higher than that in coastal waters, and the surface DOC occupies the advantage faster than that in the bottom.

Under the combined action of many factors, the change of organic carbon form is mainly controlled by salinity and the concentration of suspended particulate matter. The oxygen-consuming pollutants in the Yangtze River Estuary are mainly from the organic parts of suspended particles. The maximum turbidity zone (TMZ) is an important site for the concentration and morphology transformation of organic carbon, where a large amount of POC settles and mineralizes, and POC desorption and microbial degradation promote its conversion to DOC. There is a synergistic change between DOC/POC and TSM. When the concentration of TSM in the water is greater than 98.41mg/L, the organic carbon in the Yangtze River Estuary is mainly in granular form, otherwise, it is mainly in dissolved form.

（4）In May 2014，the average contribution rates of ocean, delta and river sources to POC in the surface layer of the Yangtze River Estuary were 17.98%, 23.84, 58.17%, which in the bottom layer were 22.02%, 29.19%, 48.79%. The terrigenous input is the main source of POC in the entrance, decreasing rapidly from TMZ. In the offshore waters outside the entrance, the contribution of POC is mainly from marine sources and delta sources, and reach the highest value in the offshore area. This paper believes that the invasion of Spartina alterniflora significantly increased the soil organic carbon and microbial carbon of the wetland, which changed the δ¹³C value of organic carbon in the Yangtze River Estuary. Coupled with the impact of the Three Gorges Dam, the input of terrestrial organic carbon has been reduced, and the erosion as well as deposition of the delta caused the organic carbon input from the soil and plants of the salt marsh to the Yangtze River Estuary, thereby affecting the biogeochemical processes of the wetland ecosystem in the Yangtze River Estuary.

摘  要... I

Abstact III

第1章  绪论... 1

1.1  河口有机碳研究背景... 1

1.2  河口有机碳研究进展... 3

1.2.1  组成与迁移转化行为... 3

1.2.2  分布特征与影响因素... 4

1.2.3  POC的物源判别技术... 7

1.3  研究内容与研究意义... 8

第2章  研究区域概况与方法... 10

2.1  长江口及其毗邻海域环境... 10

2.1.1  自然地理环境... 10

2.1.2  社会经济环境... 10

2.1.3  水动力环境... 11

2.2  样品采集及数据分析方法... 11

2.2.1  调查站位设置... 12

2.2.2  样品采集与测定... 13

2.2.3  数据处理与分析... 14

第3章  春季长江口颗粒有机碳的时空分布... 15

3.1  引言... 15

3.2  春季长江口POC浓度分布的年际变化... 15

3.2.1  差异性分析... 15

3.2.2  平面分布变化... 16

3.3  春季长江口POC分布变化的影响因素... 18

3.3.1  盐度对POC的影响... 19

3.3.2  TSM对POC的影响... 21

3.3.3  浮游植物对POC的影响... 23

3.4  小结... 25

第4章  长江口不同形态有机碳的迁移转化... 27

4.1  引言... 27

4.2  长江口陆源有机碳年际迁移变化... 27

4.2.1  长江口POC的年际通量变化... 27

4.2.2  春季有机碳与入海径流的关系... 29

4.3 不同形态有机碳转化行为... 30

4.3.1  长江口DOC与POC的分布特征... 30

4.3.2  长江口有机碳比例的影响因素... 32

4.3.3  TSM浓度梯度下的有机碳行为... 34

4.4  小结... 35

第5章  长江口颗粒有机碳的物源示踪技术... 37

5.1  引言... 37

5.2  长江口颗粒有机碳的物源示踪技术... 37

5.2.1  稳定碳同位素三端元模型... 37

5.2.2  长江口POC的物源贡献率... 38

5.2.3  长江口POC物源变化分析... 40

5.3  小结... 41

第6章  结论... 42

6.1  主要结论... 42

6.2  研究展望... 43

参考文献... 45

附  录... 54

致  谢... 55

作者简历及攻读学位期间发表学术论文... 57