长江口海域关键环境因子的长期变化及其生态效应

发布时间：2018-05-10 21:18

本文选题：长江口海域 + 环境因子　；参考：《中国海洋大学》2014年博士论文

【摘要】：近半个多世纪以来长江入海径流量、泥沙通量和营养盐通量的变异对长江口海域生态系统造成一系列影响，主要表现为长江口及其邻近海域的富营养化程度逐渐加重，超四类海水水质标准的海域面积明显扩大，，底层缺氧现象不断加重；并由此导致长江口及其邻近海域赤潮频发且发生面积逐渐增大、赤潮类型由单一的硅藻赤潮演变为硅藻-甲藻赤潮的交替发生。然而，目前对长江入海物质通量变异引起的长江口海域生态环境长期变化缺少定量化分析，尤其是对近年来长江入海泥沙通量的降低对长江口及其邻近海域生态系统影响的研究还是空白，对于长江口海域生物群落对生态环境变化的响应缺乏系统化描述，对近30年来浮游植物生物量快速增加的主要影响因素缺少深入探讨。因此，有必要对长江口近岸海域生态环境的长期变化进行研究，以期获得其动态变化规律，甄别长江口海域生态环境变化的主要影响因素或控制因子。本文搜集并统计了近半个多世纪以来长江入海径流、泥沙通量和营养盐通量相关资料，结合长江口及其邻近海域表层海水盐度、悬浮物、营养盐（DIN、PO4-P和SiO3-Si）的历史文献资料和现场调查数据，定量化描述了入海物质通量变异对长江口生态环境的影响，并从浮游植物生物量及其群落结构、底栖生物种类数及其生物量等方面的长期变化来阐释长江口海域生态环境变化导致的生态效应，最后初步得出长江口海域生态系统变化及其演变过程的控制因素。主要结论如下： 1.长江入海物质通量的变异半个多世纪以来，长江入海径流量变化不大。与径流量变化不同，长江入海泥沙量总体上呈降低趋势，这归因于长江入海水中泥沙含量的逐年降低，导致长江入海泥沙通量相应程度地降低，近30年来下降趋势尤为显著，尤其是进入21世纪后，泥沙入海通量降低速度明显加快。长江水中三类营养盐含量表现出不同的变化趋势。1980s之前，长江水中DIN和DIP浓度分别在20μmol/L和0.5μmol/L上下波动，80年代之后，DIN快速上升，进入21世纪后，DIN增加速度放缓，浓度维持在120～140μmol/L上下；而DIP自80年代中期开始，浓度略有升高，进入21世纪之后，DIP增加趋势依然显著，但两者在21世纪初期均达到历史最高值；而长江水中SiO3-Si浓度呈现出明显的降低趋势，尤其是20世纪80年代后，其下降速度明显加快，进入21世纪之后，SiO3-Si达到历史最低值，其浓度维持在100μmol/L上下，变化不再明显。 2.长江入海物质通量的变异引起长江口海域关键环境因子的变化近30年来，长江入海物质通量的变异引起长江口海域环境因子相同的变化态势。在长江入海径流量变化不大的前提下，长江口海域表层海水盐度变化不大，冲淡水东部边界基本出现在123.5°E附近海域。29个航次的悬浮物数据显示，由于入海泥沙通量的降低，研究海域表层海水悬浮物含量明显降低，下降幅度约为51%，年均下降率约为1.7%。且20mg/L的TSS浓度等值线（长江冲淡水主体）明显向河口方向位移。与此同时，61个航次的营养盐结果表明，入海水中DIN、DIP浓度的增大和SiO3-Si浓度的降低造成长江口海域表层海水DIN、PO4-P浓度增加和SiO3-Si浓度降低，三者的变化幅度分别约为103%、102%和-33%，对应的年均变化率约为3.32%、3.19%和-1.03%。营养盐浓度的变化导致Si/N比值/P发生变化，其中N/P比值始终维持在45左右，变化不大；Si/P比值越来越接近16（Redfield比值）；而Si/N比值由原来大于1至2005年后小于1，导致硅酸盐含量小于无机氮含量，这将有利于非硅藻类浮游植物的竞争。 3.长江口海域关键环境因子变化引发的生态效应自1981-2011年50个航次的叶绿素a数据显示，以叶绿素a表征的浮游植物生物量呈现出指数增加的趋势。由网采和水采得出的长江口及其邻近海域70个航次的浮游植物细胞密度变化趋势与叶绿素a一致。2003年之后的调查数据显示，小尺寸、小细胞的浮游植物（主要是甲藻）增加更为明显。与此同时，浮游植物群落结构的变化表现为以硅酸盐为主要营养的硅藻相对丰度逐渐降低，而甲藻相对丰度表现出逐渐升高的趋势。尤其是进入21世纪后，甲藻占优势的调查航次比例增大。长江口及其邻近海域32个航次的底栖生物结果表明，其总生物量和种类数均有所降低，其中种类数降低更为明显。近年来个体较小、生活周期短的且对环境污染承受能力强的多毛类所占比例增大，逐渐代替个体较大、生活周期相对长的棘皮动物和软体动物成为优势种。 4.长江口海域的悬浮物和营养盐条件愈来愈有利于浮游植物的生长繁殖，最终导致赤潮频发且分布范围更广，并逐渐出现在低盐的河口海域利用22个夏季航次数据探讨近30年来长江口海域表层海水各生态环境因子之间的关系，结果表明：叶绿素a高值对应的盐度不仅有向河口方向位移的趋势，而且其对应的盐度范围明显扩大。低盐度（S=10）和中盐度（S=20、S=25）对应的DIN和PO4-P浓度有所升高、TSS浓度有所下降，而相对高盐度（S≥30）对应DIN和PO4-P浓度的升高、TSS浓度的下降均更为显著。虽然SiO3-Si浓度有所下降，但近30年来，SiO3-Si没有形成对浮游植物生长的限制。最终导致长江口海域环境更适宜于浮游植物的生长，这也是近年来赤潮频发、发生面积增大、发生区域逐渐向低盐的河口方向位移的主要原因。 5.长江口海域浮游植物生物量增加的主要影响因素存在季节及区域差异在年际尺度上，浮游植物生物量的增加主要受入海营养盐通量增加以及入海泥沙通量降低的影响。在季节尺度上，春季，长江口海域浮游植物生物量的增加主要受入海泥沙通量的降低影响；夏季，长江径流通常达到一年中的最大值，入海营养盐通量、泥沙通量与浮游植物生物量增加的关系均不显著。在不同的盐度区域，低盐的近河口海域，入海泥沙通量减少对浮游植物生物量的增加效应最显著；在中盐度的羽状锋区，浮游植物生物量的增加可能是由于入海营养盐通量增加以及泥沙通量降低共同作用的结果；在相对高盐的外海域，入海营养盐通量的增加对浮游植物生物量的增加效应最显著，入海泥沙通量的降低对浮游植物生物量增加的贡献相对较弱。
[Abstract]:Over the past half century, the variation of the Yangtze River runoff, sediment flux and nutrient flux has caused a series of impacts on the ecosystem of the Yangtze Estuary, which is mainly manifested by the gradual aggravation of eutrophication in the Yangtze Estuary and its adjacent waters. The area of the sea area of the super four types of water quality is obviously enlarged and the phenomenon of the low level anoxia is aggravated. As a result, the red tide in the Yangtze Estuary and its adjacent sea area increased frequently and increased gradually, and the type of red tide evolved from a single diatom red tide to diatom and alga red tide. However, the quantitative analysis of the long period changes in the ecological environment of the Yangtze Estuary caused by the variation of the material flux into the Yangtze River was not quantified, especially in recent years. The study on the impacts of the decrease of sediment flux on the Yangtze River Estuary on the ecosystem of the Yangtze Estuary and its adjacent sea area is still blank. The response to the ecological environment changes in the Yangtze Estuary is lack of a systematic description. The main factors for the rapid increase of phytoplankton biomass in the last 30 years are not discussed. Therefore, it is necessary to The long-term changes in the ecological environment of the coastal waters of the Yangtze River estuary are studied in order to obtain the dynamic changes of the ecological environment and identify the main factors or control factors of the ecological environment changes in the Yangtze Estuary.
In this paper, the data of runoff, sediment flux and nutrient flux in the Yangtze River over the past half a century have been collected and analyzed. The historical documents and field investigations of the surface salinity, suspended matter, nutrient salt (DIN, PO4-P and SiO3-Si) in the Yangtze Estuary and its adjacent waters, and the data of the field investigation are quantified. The ecological effects of the ecological environment are explained by the long-term changes of the phytoplankton biomass and its community structure, the number of benthic species and the biomass of the zoobenthos. The ecological changes in the Yangtze Estuary are explained. Finally, the control factors of the changes in the Yangtze Estuary and the evolution process are preliminarily concluded as follows:
1. variation in material flux from the Yangtze River into the sea
For more than half a century, the flow of the Yangtze River to the sea has changed little. The sediment volume of the Yangtze River to the sea is decreasing, which is due to the decrease of the sediment content in the Yangtze River, which reduces the sediment flux in the Yangtze River to the sea in the corresponding degree, especially in the last 30 years, especially after the year of twenty-first Century. In the Yangtze River water, the concentration of three kinds of nutrients in water showed a different trend of change.1980s, and the concentration of DIN and DIP in the water of the Yangtze River fluctuated at 20 mol/L and 0.5 mu mol/L respectively. After 80s, DIN increased rapidly. After entering twenty-first Century, the increase of DIN rate slowed down, and the concentration was maintained up and down at 120~140 u mol/L. And the concentration of DIP increased slightly since the mid 80s. After twenty-first Century, the increasing trend of DIP was still significant, but both reached the highest value in the early twenty-first Century, and the SiO3-Si concentration in the water of the Yangtze River showed a obvious decreasing trend, especially after 1980s, the decline speed was obviously accelerated, after twenty-first Century, SiO3-Si Reaching the lowest historical value, its concentration is maintained at 100 mol/L up and down, and the change is no longer obvious.
2. the variation of material fluxes into the Yangtze River causes the change of key environmental factors in the Changjiang Estuary.
In the last 30 years, the variation of the material flux in the Yangtze River has caused the same changes in the environmental factors of the Yangtze Estuary. Under the premise of the small change in the flow of the Yangtze River to the sea, the salinity of the surface sea water in the sea area of the Yangtze River Estuary has not changed much, and the eastern boundary of the fresh water is basically in the sea area of the sea area near the 123.5 degree E. With the decrease of mud and sand flow, the content of suspended matter in the sea surface sea water decreased significantly, the decrease was about 51%, the average annual decline rate was about 1.7%. and the TSS concentration line of 20mg/L (the main body of the Changjiang River fresh water) was obviously shifted to the estuary. At the same time, the nutrient salt results of the 61 voyages showed that the concentration of DIN in the sea water, the increase of DIP concentration and SiO3-Si The decrease of concentration caused the DIN, PO4-P concentration and SiO3-Si concentration in the sea surface waters of the Yangtze Estuary. The changes of the three were about 103%, 102% and -33%, respectively, and the annual average change rate was about 3.32%, 3.19% and -1.03%. were changed to the Si/N ratio /P, and the N/P ratio remained around 45, not much change. The Si/P ratio is getting closer to 16 (Redfield ratio), and the Si/N ratio is less than 1 from 1 to 2005, resulting in less silicate content than the inorganic nitrogen content, which will be beneficial to the competition of non diatom phytoplankton.
3. ecological effects caused by changes in key environmental factors in the Yangtze River Estuary
The chlorophyll a data from 50 voyages in 1981-2011 years showed that the phytoplankton biomass characterized by chlorophyll a showed an exponential increase. The variation trend of phytoplankton cell density in the Yangtze Estuary and its adjacent waters from the net and its adjacent waters and the chlorophyll a showed that the small size was small and small after.2003 years. The growth of phytoplankton (mainly dinoflagellate) was more obvious. At the same time, the variation of phytoplankton community structure showed a gradual decrease in the relative abundance of diatom with silicate as the main nutrient, while the relative abundance of methylene algae showed a tendency to increase gradually. The total biomass and species number of 32 voyages in Jiangkou and its adjacent waters showed that the total biomass and species number decreased, and the number of species decreased more obviously. Animals and mollusks are the dominant species.
4. the suspension and nutrient conditions of the Yangtze Estuary are becoming more and more beneficial to the growth and reproduction of phytoplankton, which eventually leads to the frequent occurrence of red tides and a wider range of distribution, and gradually appears in the estuarine sea area with low salt.
The relationship between the ecological environmental factors of the surface seawater of the Yangtze Estuary in the last 30 years was studied by using 22 summer voyage data. The results showed that the salinity of the high value of chlorophyll a not only has the trend of direction displacement to the estuary, but also the corresponding salinity range is obviously enlarged. The DIN and PO4-P corresponding to the low salinity (S=10) and the medium salinity (S=20, S=25) are corresponding. The concentration of TSS decreased, while the relative high salinity (S > 30) corresponded to the increase of DIN and PO4-P concentration, the decrease of TSS concentration was more significant. Although the concentration of SiO3-Si decreased, but in the last 30 years, SiO3-Si had not formed a restriction on the growth of phytoplankton. This is also the main reason for the frequent occurrence of red tides in recent years, the increase of the area and the gradual displacement of the area towards the low salinity estuary.
5. there are seasonal and regional differences in the main factors affecting the increase of phytoplankton biomass in the Changjiang Estuary.
On the annual scale, the increase of phytoplankton biomass is mainly influenced by the increase of sea nutrient flux and the decrease of mud sand flow in the sea. On the seasonal scale, the increase of phytoplankton biomass in the Yangtze Estuary is mainly influenced by the decrease of sediment flux in the Yangtze Estuary. In summer, the runoff of the Yangtze River usually reaches the maximum of one year. The relationship between the sea nutrient flux, the sediment flux and the increase of phytoplankton biomass is not significant. In the different salinity regions, the decrease of sediment flux to the sea is most significant to the increase of phytoplankton biomass in the low salinity area, and the increase in the biomass of floating vegetation in the middle salinity front area may be due to the salt intake through the sea. The increase of sediment flux and the increase of sediment flux in the sea area of relatively high salinity is the most significant effect on the increase of phytoplankton biomass, and the decrease of the sediment flux to the sea is relatively weak.

【学位授予单位】：中国海洋大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：X145;X55

【参考文献】