【作者】 程芳晋；

【导师】 俞志明； 宋秀贤；

【作者基本信息】 中国科学院研究生院（海洋研究所） ， 海洋生态学， 2012， 博士

【摘要】 沿海经济的快速发展极大地改变了海岸带的生态环境甚至生态系统,导致近海海域严重富营养化。富营养化的加剧为赤潮的发生提供了物质条件，在受人类活动强烈干扰的地区,赤潮发生的频率和强度都在快速增加。其中长江口及其邻近海域已成为我国富营养化最严重的地区，极大影响着该海域的生态环境。因此，研究该海域富营养化和赤潮历史的演变有助于了解其形成机制和发展态势，有助于了解人类活动在赤潮和富营养化关系中的作用。本文选取长江口邻近海域赤潮高发区典型站位的两根柱状沉积物为研究对象，在年代测定的基础上，综合地质动力参数、地球化学参数以及沉积硅藻参数，研究了生源要素（C、N、Si）、沉积硅藻群落组成及其随年代的变化趋势，结合长江口及其邻近海域水体环境的历史调查资料，推测了富营养化在上个世纪以来的发展趋势，讨论了人类活动对长江口及其邻近海域的影响以及与富营养化演变的关系。本文研究的主要结论如下：两根柱状沉积物²¹⁰Pb测年结果表明，位于东海泥质区的ZC13和ZA3柱状沉积物的沉积年代分别为54年（1955²009）和139年（1871²010），ZC13柱状沉积物的平均沉积速率为0.89cm/yr；ZA3柱状沉积物的沉积速率为：0²5cm为0.71cm/yr，26¹15cm为1.78cm/yr。两柱状沉积物高分辨率粒度分析结果显示：ZC13柱状沉积物以砂质粉砂为主，粒径相对较粗，粘土含量相对较少，粒度组成和粒度参数在前10cm变化较频繁；ZA3柱状沉积物由顶部至100cm粒度组分及相关参数变化稳定，粘土含量高，岩性上表现为较细的粘土质粉砂，100cm以后粘土含量明显降低，砂质组分增高，岩性总体上表现为粉砂质砂，粒度参数变化较为频繁，故选择该柱状沉积物0¹00cm进行生源要素以及沉积硅藻分析。两根柱状沉积物的岩性均表明其适合生源要素和沉积硅藻的埋藏，有助于从中提取信息。分析测定了两根柱状沉积物生源要素：总有机碳（TOC）、总氮（TN）以及生物硅（BSi）的含量及其变化趋势。结果表明：1970年以前：TOC、TN以及BSi含量在整个柱状沉积物剖面属于较低的水平且变化稳定，说明在这一时期，我国工业化尚未兴起，人类活动对东海影响较少，此海域初级生产力水平处于较低的水平。20世纪70年代初至90年代中期：TOC、TN、BSi含量呈显著上升趋势，显示了上层水体中初级生产力的增高，说明在这一时期，人类活动的干扰增加了陆源物质和营养元素的输入，从而导致长江口及其邻近海域富营养化趋势的增强，造成赤潮爆发的频率和规模越来越大。20世纪90年代中期至今：TOC、TN以及BSi含量呈波动上升趋势。N、P的增加会导致营养盐结构的转变，有利于除硅藻之外的其他藻类的生长，最终导致三个参数均在此时期呈现波动状态。而甲藻赤潮在此时期于东海的大规模爆发恰好证明了这一结论。分析研究了两柱状沉积物中沉积硅藻群落结构的演替特征、方向及其对环境的指示意义。结果表明:两柱状沉积物中硅藻的细胞丰度、生态特征参数（多样性指数、物种丰富度）、以及优势种组成发生了明显演替。硅藻群落的组合特征不同时期之间存在明显差异，硅藻细胞丰度自20世纪70年代开始增加，90年代中期后开始加速增加，这种数量的变动主要是由上层水体沉积的浮游硅藻引起的，浮游硅藻的细胞丰度在20世纪70年代中期以后呈现出明显的上升趋势，90年代中期后上升速度加快，而底栖硅藻的细胞丰度波动不明显。与此同时，赤潮藻的细胞丰度也开始增加。相关时期文献资料表明，该时期水体中由于营养盐的持续输入，导致富营养水平加剧。2000年以后，硅藻的细胞丰度及生态特征参数呈现波动上升状态，与此时期生源要素的波动吻合，赤潮藻的含量亦随硅藻丰度的变化而变化。硅藻丰度总体的增高揭示了水体中营养盐水平的增高，这与相关文献中该海区进行调查所获得营养盐输入的增高的事实相一致。而这种数据随年代的波动也从侧面为一定时期的硅限制提供了依据，反映了水体中富营养水平的进一步增高导致浮游植物群落结构的改变。上述研究表明：生源要素（C、N、Si）的含量变化以及沉积硅藻群落对上世纪以来长江口邻近海域富营养化演变具有指示意义，且得出一致的结论：即长江口邻近海域20世纪70年代富营养化开始出现，90年代中期开始加剧，从而导致越来越多大规模赤潮的爆发。更多还原

【Abstract】 The rapid development of economy in coastal cities in China has greatly changedthe environment and ecological system and led to serious eutrophication in theestuaries and coasts. As a result, the occurrence and intensity of algae blooms haveincreased due to the high loadings of nutrients brought by eutrophication especially inthe areas by more anthropogenic effects. The Changjiang （Yangtze） River and itsadjacent East China Sea （ECS） is the most serious eutrophied space in China. Thehistorical records which embedded in the sediments can be used to provide keyinformation on the timing and magnitude of ecological changes in estuaries andcoastal and help us to understand the mechanism and develop trends in eutrophicationand red tide. Hence, in this study, two sediment cores were selected from sitesaffected by eutrophication and being the high frequency of red tides in the Changjiang（Yangtze） River estuary and its adjacent ECS. On the basis of core chronologies, weused multiproxy approach both in biological and geochemical analyses revealedchanges in diatom assemblages, total organic carbon （TOC）, total nitrogen （TN） andbiogenic silica （BSi）, as well as historical monitoring data. We gave an indication ofnutrient in status and trends in Changjiang River estuary and its adjacent East ChinaSea and we also discussed the relationship between the anthropogenic activities anddevelop trends in eutrophication. The main study results are follows:The²¹⁰Pb dating of the core ZC13showed that the mean sedimentation rate was0.89cm/yr, in corresponding to the sedimentation duration of54years （1955–2009）. The mean sedimentation rate of core ZA3was0.71cm/yr in the upper25cm and1.78cm/yr in the rest of the core, in corresponding to the sedimentation duration of139years （1871–2010）.The main part of the sediments of core ZC13belong to the sandy silt. Inlithology, the core is of coarse grain and have fluctuations in the upper10cm. Themain part of the sediments of core ZA3belong to the clayey silt and the trends ofcomponent and gain size parameters stay stable in the upper100cm. The core is ofcoarse sand during the100cm to the bottom in lithology and we selected the upper100cm for geochemistry and diatom analyses. The sandy silt and clayey silt aresuitable for geochemical and diatom information preservation.The total organic carbon （TOC）, total nitrogen （TN） and biogenic silica （BSi）were determined in the two cores. The results showed the trends in profiles of TOC,TN and BSi were relative low and stable before the1970s, suggesting a low andstable primary production in the water column compared to recent years. The profiesof the three proxies were in increasing trends during the1970to the mid-1990s,indicating increasing nutrient loads and more anthropogenic influence on the ECSduring this period. There were fluctuations of the three proxies from the mid-1990s tothe present, but with a rising trend overall, indicating the surplus nutrients loadings inthe ECS and there were remarkable changes in structure of nutrients which was slightsilica limitation and led to more dinoflagellates blooms.The succession of sediment diatom in the two cores and significance onenvironmental change were analysed. The results indicated that the diatom cellabundance, diversity, species richness and dominant species occurred an markedsuccession in the last century. The profiles of diatom cell abundance showed increasetendency since1970s and accelerated since min-1990s and this change was driven byincrease of the planktonic diatoms. Simultaneously, the content of red tide specieswere in the increase trend since1970s, indicating the serious eutrophication occurred.The profiles of diatom cell abundance, diversity and species richness were influctuations since2000, coincides with the trends of geochemical indexes in thisperiod and support the interpretation of these indexes. Using the multiproxy approach both in geochemical and diatom, we have shownthe history of eutrophication of two sites in the Changjiang River estuary and itsadjacent ECS. Both sites were not eutrophic in the past and have been under eutrophicconditions since the1970s and the eutrophication has accelerated since the1990s,linked with anthropogenic activities.更多还原