海洋生态与环境科学重点实验室知识库

  长江口水域是一个受到人类活动影响剧烈的河口水域。近几十年来，长江径流输送大量的营养盐入海，为周边海域提供大量营养物质的同时，也造成了日益加重水域的富营养化现象，赤潮等生态灾害频发。长江口水域营养要素迁移和转化，直接关联河口生态系统健康。针对长江口水域营养盐的时空分布这一问题，本文通过长江口4个季节航次（2014年2、5、8和11月）和5个年度航次（2014、2015、2016、2017和2018年春季）调查数据，探究了长江口水域营养盐的年内和年际变异，并结合盐度（S）、溶解氧（DO）、温度（T）、悬浮体（SPM）和叶绿素a等环境和初级生产要素，深入探究营养盐迁移过程的影响机制。研究结果可为长江口水域生源要素物质循环提供数据支撑，为长江口生态系统健康管理提供科学依据。

(1)长江口水域营养盐的季节变化

  通过研究2014年4个季节航次的营养盐和水环境数据得到以下结论：NO₃-N、SiO₃-Si和PO₄-P在长江口水域的时空分布主要受长江陆源输入的影响，随长江冲淡水扩展范围的季节变化而出现时空分布的差异。除冬季外，在122°20′E以东的水域，营养盐的时空分布主要受到温盐跃层的影响，在31°N断面出现明显的分层现象，而在冬季水体垂直混合均匀，其垂直分布较为均匀。春季长江陆源输入较高浓度的NO₃-N，高浓度NO₃-N在长江口水域又较大范围的扩展，40 µmol/L的NO₃-N随长江冲淡水向东北方向最远扩展到123°E,垂直方向上扩展至水深10 m，而秋季长江陆源输入较高浓度的SiO₃-Si和PO₄-P，其浓度分别为40 µmol/L和0.6 µmol/L的等值线分别向东最远扩展到123°E、123°20′E和水深20 m、50 m。由于受到生物吸收，硝化作用等因素的影响，NO₂-N和NH₄-N的时空分布比较复杂，季节分布规律不明显，而在冬季NO₂-N和NH₄-N自口门处向外海浓度逐渐降低，垂直分布也相较均匀。本章节通过盐度这一保守性指标引入理论稀释线研究营养盐的迁移过程的影响因素，结合叶绿素a和SPM的数据表明：春、夏季营养盐浓度低于理论稀释浓度可能与生物作用密切相关，而PO₄-P在春、夏和秋季均有散点高于理论稀释浓度可能与悬浮颗粒物释放有关。

(2)春季长江口水域营养盐的年际变化及对浮游植物的限制

  利用近五年春季（2014~2018年，5月）长江口水域的营养盐、叶绿素a和水文数据，得出以下结论：近五年长江径流输送的DIN,DIP和DSi自2014年显著降低至2016年，再显著升高至2018，这与径流呈负相关；在径流较小的2014和2018年，陆源输送较高浓度的DSi、DIN和DIP，对应高浓度营养盐在长江口水域有较大的扩展。长江口水域营养盐对浮游植物的限制主要是P限制，P限制与径流输送DIP的浓度密切相关，在径流输送DIP的浓度较低时，更容易产生P限制，限制站位更集中在31.5°N以北，和123°E以东的水域。叶绿素a高值水域对应氮磷比和硅磷比的高值区域，这种吻合程度在叶绿素a较高的年份（2015、2017和2018年）更加明显，这表明生物吸收作用消耗水中DIP，会导致并加剧P限制程度。通过研究叶绿素a与log（DIN/DIP）的关系得出以下结论：log（DIN/DIP）大于2.5的站位叶绿素a的浓度也较高（Chl a>10μg/L），且叶绿素a的浓度越高，比值可能越大。叶绿素a高值站位表层DIP的浓度较低，随着水深增加，有机质分解消耗DO，在20m层DIP出现高值，相应的出现DO及其饱和度的最低值。

可以看出，长江陆源输入、稀释和生物吸收共同驱动了长江口营养盐时间和空间分布，各营养要素响应机制存在一定差异。

  The Yangtze River Estuary severely affected by human activities. In recent decades, the Yangtze River runoff has transported a large number of nutrients into the China east sea, which has caused the eutrophication of the water area to increase, and ecological disasters such as red tides have occurred frequently. Aiming at the problem of the spatial and temporal distribution of nutrients in the waters of the Yangtze River Estuary, this master's thesis has studied the four-season voyages of February, May, August, and November 2014, and the five springs investigations of 2014, 2015, 2016, 2017, and 2018. The survey data of the voyage explored the seasonal and interannual changes of nutrients in the Yangtze River Estuary waters, combined with the environment of salinity (S), dissolved oxygen (DO), temperature (T), suspension (SPM), and chlorophyll-a parameters to further explore the influencing factors of nutrient migration process. This provides basic data for long-term observation of nutrients in the Yangtze River estuary and provides a reference for the study of the mechanism of harmful red tides and other disasters.

（1) Seasonal changes of nutrients in the Yangtze River estuary

  Based on four investigations conducted in February, May, August and November 2014, results show that NO₃-N, PO₄-P and SiO₃-Si were mainly affected by the Changjiang terrigenous input, consisting with the variation of Changjiang Diluted Water (CDW). In the east of 122°20′E, water stratification caused by the thermocline and halocline besides winter, and the vertical distribution of nutrients was stratified obviously. In contrast, the water in vertical direction mixed well in winter, as well as nutrients. In spring, the Changjiang terrigenous input supplying high-concentration NO₃-N, the 40µmol/L isoline extended northeastward as far as 123°E, and reaching the water depth of 10m. In autumn, the Changjiang terrigenous input supplying high-concentration SiO₃-Si and PO₄-P, 40µmol/L and 0.6µmol/L isolines extended eastward to 123°E and 123°20′E, and reaching the water depth of 20m and 50m, respectively. The distribution of NO₂-N and NH₄-N were complicated, affected by many factors such as bioabsorbable and nitrification, and the seasonal variations were not obvious. The theoretical dilution line was introduced to study the mixing behaviors of NO₃-N, SiO₃-Si and PO₄-P in the Changjiang River Estuary. The results show that nutrients consumed in spring and summer might be related to the primary production, and PO₄-P showed positive deviation with respect to conservative mixing could be connected with the process of SPM releasing.

(2) Interannual changes of nutrients and its limitation for phytoplankton in the Yangtze River estuary

  Using the nutrients, chlorophyll-a and hydrological data of the Yangtze River estuary in the past five years in the spring (2014-2018), the following conclusions have been drawn: Changjiang terrigenous input higher concentrations of DIN, DIP, and DSi in the past five years have been significantly reduced from 2014 to 2016, then it increased significantly to 2018, which was negatively related to runoff. In 2014 and 2018, where the runoff was smaller, Changjiang terrigenous input higher concentrations of DSi, DIN, and DIP, corresponding to higher concentrations of nutrients in the Yangtze River estuary. The limitation of phytoplankton by nutrients in the Yangtze River estuary is mainly the P limitation. The P limitation is closely related to Changjiang terrigenous input concentration of DIP. When Changjiang terrigenous input higher concentrations of DIP is low, the P limitation is more likely to occur, and the P limitation station is more concentrated at north of 31.5°N, and east of 123° E. The areas of high concentration of chlorophyll-a correspond to the areas of high N/P ratio and  Si/P ratio. This agreement is more obvious in the years with higher chlorophyll-a (2015, 2017, and 2018), which indicates that biological absorption consumes DIP in water. This process will cause and exacerbate the degree of P limitation. By studying the relationship between chlorophyll-a and log (DIN / DIP), the following conclusions are obtained: the concentration of chlorophyll-a at a site with log (DIN / DIP) greater than 2.5 is also higher (Chl a> 10 μg/L), and the chlorophyll-a The higher the concentration, the larger the ratio may be. The concentration of DIP in the surface layer of high-value chlorophyll-a sites is low. With the increase of water depth, organic matter is depleted by DO, and the high value of DIP appears in the 20m layer, and the lowest value of DO and its saturation appears accordingly.

  It can be seen that Yangtze terrigenous input, water dilution and biological absorption jointly drive the nutrients spatial and temporal distribution, and also, nutrients have different spatiotemporal mechanisms.

第一章  绪论   1

1.1  研究意义  1

1.2  研究现状  2

1.2  本论文的研究内容       4

第二章  长江口水域营养盐的季节变化特征       6

2.1  前言   6

2.2  样品采集及分析方法   6

2.3  结果   7

2.3.1  溶解无机氮的平面分布   9

2.3.2  溶解硅的平面分布    11

2.3.3  溶解无机磷的平面分布   12

2.3.4  31°N断面的水文特征   16

2.3.5  溶解无机氮的断面分布   18

2.3.6  溶解硅的断面分布    19

2.3.7  溶解无机磷的断面分布   20

2.4 讨论     23

2.4.1 营养盐时空分布的季节变化特征   23

2.4.2 二端元模型研究营养盐的受控因素      24

2.5 小结     27

第三章  春季营养盐的时空分布和浮游植物的营养盐限制    29

3.1  前言   29

3.2  样品采集及分析方法   29

3.3  结果   30

3.3.1  近五年春季营养盐浓度及其比值 30

3.3.2  近五年春季表层营养盐及其比值平面分布      32

3.3.3  叶绿素a的平面分布 35

3.3.4  春季浮游植物的营养盐限制  36

3.4  讨论   38

3.4.1  春季长江径流输入与河口营养盐浓度的关系  38

3.4.2   N/P与Chl a的耦合关系      40

3.4.3  春季叶绿素a高值区营养盐的垂直变化   42

3.5  小结   43

第四章  结论与展望     45

4.1 结论和创新点   45

4.1.1 结论  45

4.1.2 创新点     46

4.2 不足与展望       46

参考文献    47

作者简历及攻读学位期间发表学术论文 57

作者简历：       57

已发表的学术论文：     57