本文選題：長江口海域 + 環(huán)境因子��； 參考：《中國海洋大學(xué)》2014年博士論文

【摘要】：近半個多世紀(jì)以來長江入海徑流量、泥沙通量和營養(yǎng)鹽通量的變異對長江口海域生態(tài)系統(tǒng)造成一系列影響，主要表現(xiàn)為長江口及其鄰近海域的富營養(yǎng)化程度逐漸加重，超四類海水水質(zhì)標(biāo)準(zhǔn)的海域面積明顯擴大，，底層缺氧現(xiàn)象不斷加重；并由此導(dǎo)致長江口及其鄰近海域赤潮頻發(fā)且發(fā)生面積逐漸增大、赤潮類型由單一的硅藻赤潮演變?yōu)楣柙?甲藻赤潮的交替發(fā)生。然而，目前對長江入海物質(zhì)通量變異引起的長江口海域生態(tài)環(huán)境長期變化缺少定量化分析，尤其是對近年來長江入海泥沙通量的降低對長江口及其鄰近海域生態(tài)系統(tǒng)影響的研究還是空白，對于長江口海域生物群落對生態(tài)環(huán)境變化的響應(yīng)缺乏系統(tǒng)化描述，對近30年來浮游植物生物量快速增加的主要影響因素缺少深入探討。因此，有必要對長江口近岸海域生態(tài)環(huán)境的長期變化進(jìn)行研究，以期獲得其動態(tài)變化規(guī)律，甄別長江口海域生態(tài)環(huán)境變化的主要影響因素或控制因子。 本文搜集并統(tǒng)計了近半個多世紀(jì)以來長江入海徑流、泥沙通量和營養(yǎng)鹽通量相關(guān)資料，結(jié)合長江口及其鄰近海域表層海水鹽度、懸浮物、營養(yǎng)鹽（DIN、PO4-P和SiO3-Si）的歷史文獻(xiàn)資料和現(xiàn)場調(diào)查數(shù)據(jù)，定量化描述了入海物質(zhì)通量變異對長江口生態(tài)環(huán)境的影響，并從浮游植物生物量及其群落結(jié)構(gòu)、底棲生物種類數(shù)及其生物量等方面的長期變化來闡釋長江口海域生態(tài)環(huán)境變化導(dǎo)致的生態(tài)效應(yīng)，最后初步得出長江口海域生態(tài)系統(tǒng)變化及其演變過程的控制因素。主要結(jié)論如下： 1.長江入海物質(zhì)通量的變異 半個多世紀(jì)以來，長江入海徑流量變化不大。與徑流量變化不同，長江入海泥沙量總體上呈降低趨勢，這歸因于長江入海水中泥沙含量的逐年降低，導(dǎo)致長江入海泥沙通量相應(yīng)程度地降低，近30年來下降趨勢尤為顯著，尤其是進(jìn)入21世紀(jì)后，泥沙入海通量降低速度明顯加快。長江水中三類營養(yǎng)鹽含量表現(xiàn)出不同的變化趨勢。1980s之前，長江水中DIN和DIP濃度分別在20μmol/L和0.5μmol/L上下波動，80年代之后，DIN快速上升，進(jìn)入21世紀(jì)后，DIN增加速度放緩，濃度維持在120～140μmol/L上下；而DIP自80年代中期開始，濃度略有升高，進(jìn)入21世紀(jì)之后，DIP增加趨勢依然顯著，但兩者在21世紀(jì)初期均達(dá)到歷史最高值；而長江水中SiO3-Si濃度呈現(xiàn)出明顯的降低趨勢，尤其是20世紀(jì)80年代后，其下降速度明顯加快，進(jìn)入21世紀(jì)之后，SiO3-Si達(dá)到歷史最低值，其濃度維持在100μmol/L上下，變化不再明顯。 2.長江入海物質(zhì)通量的變異引起長江口海域關(guān)鍵環(huán)境因子的變化 近30年來，長江入海物質(zhì)通量的變異引起長江口海域環(huán)境因子相同的變化態(tài)勢。在長江入海徑流量變化不大的前提下，長江口海域表層海水鹽度變化不大，沖淡水東部邊界基本出現(xiàn)在123.5°E附近海域。29個航次的懸浮物數(shù)據(jù)顯示，由于入海泥沙通量的降低，研究海域表層海水懸浮物含量明顯降低，下降幅度約為51%，年均下降率約為1.7%。且20mg/L的TSS濃度等值線（長江沖淡水主體）明顯向河口方向位移。與此同時，61個航次的營養(yǎng)鹽結(jié)果表明，入海水中DIN、DIP濃度的增大和SiO3-Si濃度的降低造成長江口海域表層海水DIN、PO4-P濃度增加和SiO3-Si濃度降低，三者的變化幅度分別約為103%、102%和-33%，對應(yīng)的年均變化率約為3.32%、3.19%和-1.03%。營養(yǎng)鹽濃度的變化導(dǎo)致Si/N比值/P發(fā)生變化，其中N/P比值始終維持在45左右，變化不大；Si/P比值越來越接近16（Redfield比值）；而Si/N比值由原來大于1至2005年后小于1，導(dǎo)致硅酸鹽含量小于無機氮含量，這將有利于非硅藻類浮游植物的競爭。 3.長江口海域關(guān)鍵環(huán)境因子變化引發(fā)的生態(tài)效應(yīng) 自1981-2011年50個航次的葉綠素a數(shù)據(jù)顯示，以葉綠素a表征的浮游植物生物量呈現(xiàn)出指數(shù)增加的趨勢。由網(wǎng)采和水采得出的長江口及其鄰近海域70個航次的浮游植物細(xì)胞密度變化趨勢與葉綠素a一致。2003年之后的調(diào)查數(shù)據(jù)顯示，小尺寸、小細(xì)胞的浮游植物（主要是甲藻）增加更為明顯。與此同時，浮游植物群落結(jié)構(gòu)的變化表現(xiàn)為以硅酸鹽為主要營養(yǎng)的硅藻相對豐度逐漸降低，而甲藻相對豐度表現(xiàn)出逐漸升高的趨勢。尤其是進(jìn)入21世紀(jì)后，甲藻占優(yōu)勢的調(diào)查航次比例增大。長江口及其鄰近海域32個航次的底棲生物結(jié)果表明，其總生物量和種類數(shù)均有所降低，其中種類數(shù)降低更為明顯。近年來個體較小、生活周期短的且對環(huán)境污染承受能力強的多毛類所占比例增大，逐漸代替?zhèn)�體較大、生活周期相對長的棘皮動物和軟體動物成為優(yōu)勢種。 4.長江口海域的懸浮物和營養(yǎng)鹽條件愈來愈有利于浮游植物的生長繁殖，最終導(dǎo)致赤潮頻發(fā)且分布范圍更廣，并逐漸出現(xiàn)在低鹽的河口海域 利用22個夏季航次數(shù)據(jù)探討近30年來長江口海域表層海水各生態(tài)環(huán)境因子之間的關(guān)系，結(jié)果表明：葉綠素a高值對應(yīng)的鹽度不僅有向河口方向位移的趨勢，而且其對應(yīng)的鹽度范圍明顯擴大。低鹽度（S=10）和中鹽度（S=20、S=25）對應(yīng)的DIN和PO4-P濃度有所升高、TSS濃度有所下降，而相對高鹽度（S≥30）對應(yīng)DIN和PO4-P濃度的升高、TSS濃度的下降均更為顯著。雖然SiO3-Si濃度有所下降，但近30年來，SiO3-Si沒有形成對浮游植物生長的限制。最終導(dǎo)致長江口海域環(huán)境更適宜于浮游植物的生長，這也是近年來赤潮頻發(fā)、發(fā)生面積增大、發(fā)生區(qū)域逐漸向低鹽的河口方向位移的主要原因。 5.長江口海域浮游植物生物量增加的主要影響因素存在季節(jié)及區(qū)域差異 在年際尺度上，浮游植物生物量的增加主要受入海營養(yǎng)鹽通量增加以及入海泥沙通量降低的影響。在季節(jié)尺度上，春季，長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響；夏季，長江徑流通常達(dá)到一年中的最大值，入海營養(yǎng)鹽通量、泥沙通量與浮游植物生物量增加的關(guān)系均不顯著。在不同的鹽度區(qū)域，低鹽的近河口海域，入海泥沙通量減少對浮游植物生物量的增加效應(yīng)最顯著；在中鹽度的羽狀鋒區(qū)，浮游植物生物量的增加可能是由于入海營養(yǎng)鹽通量增加以及泥沙通量降低共同作用的結(jié)果；在相對高鹽的外海域，入海營養(yǎng)鹽通量的增加對浮游植物生物量的增加效應(yīng)最顯著，入海泥沙通量的降低對浮游植物生物量增加的貢獻(xiàn)相對較弱。
[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.

【學(xué)位授予單位】：中國海洋大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：X145;X55

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