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长江口邻近海域有害藻华演替过程模拟与演变趋势分析
周正熙
学位类型博士
导师于仁成 ; 周名江
2017
学位授予单位中国科学院大学
学位授予地点北京
学位专业环境科学
关键词有害藻华 东海 演替 演变 多元统计 数值模拟
其他摘要    长江口邻近海域是我国近海有害藻华高发区之一,有害藻华(有害赤潮)的发生频率、规模及持续时间均呈现不断升高的态势。自21世纪初期开始,东海原甲藻(Prorocentrum donghaiense)和米氏凯伦藻(Karenia mikimotoi)在该海域形成大规模藻华,引起广泛关注。以往调查研究发现,长江口邻近海域有害藻华优势类群具有明显的季节性演替现象:硅藻藻华通常在初春暴发,在硅藻藻华后期,甲藻逐渐取代硅藻成为新的藻华优势类群,这一硅藻藻华向甲藻藻华的演替现象通常在春末夏初出现。我们认为,有害藻华的季节性演替过程反映了两类微藻之间的竞争策略及其对海域环境适应性的差别,而环境因素的长期变化,改变了硅藻藻华和甲藻藻华的相对竞争优势,导致了近期甲藻藻华的大规模暴发。因此,解析两类有害藻华优势类群的演替过程及机制,对于阐明该海域大规模甲藻藻华的成因、提出针对性的防控对策具有重要意义。
    藻华的形成与海域温度、光照、盐度以及营养盐等环境因素密切相关。长江口邻近海域受长江冲淡水和台湾暖流(特别是台湾东北部黑潮次表层水的入侵)影响,环境条件复杂多变。为查清长江口邻近海域不同类型藻华形成和演替的关键控制因素,分析有害藻华的长期演变趋势,本论文计划利用历史调查资料,通过统计分析方法揭示两类藻华与环境因子的关系,在此基础上构建反映藻华演替过程的数值模型,分析各种环境因素对藻华演替过程的影响,预测有害藻华的长期演变趋势。
    基于 2005 年长江口邻近海域春季现场调查资料,本论文通过主成分分析、多元回归分析和通径分析等多元统计方法,对目标海域藻华发生过程中各项环境因子的作用进行了比较。结果表明,硅藻藻华主要受长江冲淡水影响,磷酸盐和硅酸盐是影响硅藻藻华的主要环境因素,而甲藻藻华主要受台湾暖流影响,硝酸盐、磷酸盐、温度和浊度是影响甲藻藻华的主要环境因素。同时,通过非线性拟合方法,构建了春季硅藻藻华和甲藻藻华期间浮游植物生物量与无机营养盐、温度和盐度之间的定量关系方程,获得了硅、甲藻藻华形成的最适环境条件,为开展长江口邻近海域藻华形成和演替过程的数值模拟和参数化提供了参考依据。此外,本论文基于观测资料对比分析了硅藻藻华和甲藻藻华期间水体层化情况,探讨了硅、甲藻藻华的分布状况及其与温、盐跃层之间的关系。发现藻华主要分布在温、盐跃层上方,硅藻藻华的分布主要与长江冲淡水导致的层化有关,而甲藻藻华多呈斑块状分布,可能与底层外海水入侵及上升流有关。
    在上述研究基础上,本论文针对长江口邻近海域的硅、甲藻藻华演替过程构建了零维数值模式,并基于该模式对各项环境因子在藻华演替过程中的作用进行了诊断分析。结果表明,磷酸盐限制是决定硅藻藻华规模及其向甲藻藻华演替的主要因子,而硝酸盐决定了甲藻藻华的规模。考虑到长江冲淡水对目标海域营养盐状况的长期影响,本研究在综合分析历史资料的基础上,对目标海域藻华的演变历程进行了反演。模拟结果表明,长江径流输入营养盐的年代际变化,对研究海域有害藻华的演变具有重要控制作用。通过设定多组情景分析发现,如果保持现有营养盐污染态势,甲藻藻华的规模将会进一步扩大;而通过对长江径流输入硝酸盐、磷酸盐和硅酸盐的调控,甲藻藻华的规模将会得到有效控制。
    总之,本论文采用多元统计分析方法,对影响长江口邻近海域硅藻藻华和甲藻藻华的主要环境因子进行了分析,明确了各项环境因子在藻华形成和演替过程中的作用;应用数值模拟方法,对研究海域藻华优势类群的长期演变趋势进行了反演和预测。所得到的实验结果和科学认识为进一步分析东海大规模甲藻藻华成因提供了理论依据,也为有害藻华防控提供了可量化的对策建议。;     The sea area adjacent to the Changjiang River estuary is the most notable region for harmful algal blooms (HABs) in China, the frequency, scale and duration of HABs increased dramatically. Since the beginning of the 21st century, large-scale blooms of dinoflagellates (ig. Prorocentrum donghaiense and Karenia mikimotoi) started to appear in this region, and the mechanisms for the occurrence of dinoflagellate blooms kept an intriguing issue. According to the previous studies, succession of different algal blooms was observed in this area. Diatom blooms usually occur in early spring, and dinoflagellates take the place of diatoms to form blooms in late spring and early summer. The seasonal succession processes reflect the differences of the bloom causative species in competitive and adaptive strategies. With the long-term changes of environment, the relative intensity of diatom bloom and dinoflagellate bloom changes accordingly, and finally leads to the large-scale dinoflagellate blooms. Therefore, a better understanding on the succession mechanism of different microalgal blooms would give help to elucidate the mechanisms for the occurrence of large-scale dinoflagellate blooms in this region.
    The formation of HABs is closely related to the environmental factors including temperature, light intensity, salinity and nutrients. Affected by the Changjiang diluted water (CDW) and Taiwan warm current (TWC, particularly the branches of Kuroshio), the environmental conditions in the coastal waters adjacent to the Changjiang River estuary are quite complex. In order to obtain a better understanding of the mechanisms of HABs in this region, statistical analysis on the basis of survey data were performed to reveal the relationships between two types of blooms and environmental factors, and numerical models were developed to evaluate the effects of environmental factors on the seasonal succession and long-term changes of HABs.
    Based on the field observations conducted in the coastal waters adjacent to the Changjiang River estuary in 2005, statistical analysis were performed using principle component analysis (PCA), multiple regression analysis (MRA) and path analysis (PA). The results suggested that phosphate and silicate are major factors directly affecting diatom blooms, while dissolved inorganic nitrogen (DIN), temperature and turbidity are factors influencing dinoflagellate blooms. CDW and the TWC have different roles in affecting the two types of algal blooms. CDW, which has a high concentration of nitrate and silicate, is essential for diatom blooms, while the intrusion of the offshore waters is critical for the maintenance of dinoflagellate blooms. Based on above viewpoints, nonlinear fitting methods were used to establish equations representing the quantitative relationships between phytoplankton biomass and inorganic nutrients, temperature and salinity during the diatom and dinoflagellate blooms. The optimum values for different algal blooms could provide references for further studies on numerical simulation and parameter optimization of harmful algal blooms. Besides, the relationships between water stratification and two types of blooms were examined. The results indicated that the blooms were mainly distributed above the thermocline and halocline. The CDW played an important role in affecting the distribution of diatom bloom in this region, while the dinoflagellate bloom was partially affected by the upwelling and intrusion of seawater from the open ocean.
    Based on the studies above, a simple zero-dimensional numerical model was established to simulate the succession of microalgal blooms. The model could well reproduce the succession from diatom blooms to dinoflagellate blooms. Using this model, analyses were performed under different scenarios to analyze the effects of temperature, light and nutrients on the succession of different microalgal blooms. It was found that phosphorous stress was the most critical factor controlling the succession from diatom blooms to dinoflagellate blooms, and nitrate played an important role in affecting the scale of dinoflagellate blooms. Considering the effects of nutrients transported by the Changjiang River and their long-term changes, the historical patterns of HABs were retrieved using the numerical model. It can be seen that inter-decadal changes in nutrient supply from the Changjiang River play notable roles on the changes of HABs. Besides, a set of scenario analyses indicate that dinoflagellate blooms would be getting worse if the nutrient pollution were not controlled, but the intensity of dinoflagellate blooms could be reduced based on the regulation of nutrients discharged from the Changjiang River.
    In summary, a set of statistical models were applied to find the factors controlling diatom blooms and dinoflagellate blooms, and evaluate the effects of each environmental factor. Moreover, a numerical model was developed to simulate the seasonal succession from diatom blooms to dinoflagellate blooms, and to predict the trend of HABs in this region. The findings could further improve the current understandings on the mechanisms of large-scale dinoflagellate blooms in the East China Sea, and help to develop prevention strategies against HABs in this region.
学科领域地球科学 ; 海洋科学 ; 环境科学技术 ; 环境学 ; 统计学 ; 环境与生态统计学
语种中文
文献类型学位论文
条目标识符http://ir.qdio.ac.cn/handle/337002/136629
专题海洋生态与环境科学重点实验室
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周正熙. 长江口邻近海域有害藻华演替过程模拟与演变趋势分析[D]. 北京. 中国科学院大学,2017.
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