【作者】 林军；

【导师】 朱建荣；

【作者基本信息】 华东师范大学 ， 自然地理学， 2011， 博士

【摘要】 河口海域是海洋中的高生产力区,往往又是人类活动的重要区域和重要渔场所在。长江是我国第一大河,长江巨大径流带来的丰富营养盐使长江口附近海域成为高生产力海区,口外海域历史上是著名的渔场。长江流域是经济的迅猛发展和城市化进程的加快使工农业废水和生活污水排放量不断增加,长江口外海域富营养化加剧,导致赤潮频发。环境的破坏加之过度捕捞等因素,长江口外海区的生态严重失衡,海洋经济生物个体小型化、低值化现象严重。长江口外海区受复杂底形(如水下河谷)、巨量径流、季风、陆架环流的影响,动力过程十分复杂。研究长江口外海域的浮游植物生态动力学,对于长江口外海域的生态修复、环境保护和赤潮防治,渔业资源的可持续利用等具有重要的科学和现实意义。本文主要通过现场观测、资料分析和数值模型试验相结合的方法研究了长江口外海域浮游植物的时空分布特征,着重分析了浮游植物生长的主要限制因子和关键物理过程对浮游植物生长的作用。利用细胞体积转换生物量法,对2006年7月大面调查的浮游植物种类鉴定和细胞丰度计数结果进行了叶绿素a浓度的计算,并分别给出了硅藻和甲藻类的生物量。通过浮游植物细胞体积估算生物量是研究浮游植物现存量的一个可行的方法,能较客观地反映浮游植物的生物量,有助于在物种水平上开展海洋浮游生态系统模型的数值模拟研究。调查结果显示,长江口外海域夏季的浮游植物转换生物量在冲淡水区最高,江苏外海居中,而近河口区和台湾暖流区最低。温盐、水体稳定度和营养盐是影响长江口外海域浮游植物分布的主要环境因子。2009年8月底至9月初的长江口外海区多学科综合观测结果也显示,长江口外海的叶绿素a分布可分为四个特征区：高度层化的长江冲淡水扩展区,浊度锋向海侧为表层叶绿素a浓度高值区,叶绿素a高值区下层存在DO浓度小于2.00mg/L的低氧区；高度层化的台湾暖流区,表层叶绿素a浓度低,相对高值区位于次表层；表底层混合良好的江苏外海,叶绿素a浓度居中；近岸层化、低叶绿素a的高浊度区。123.0°E以西海域的叶绿素a高值区位于表层水中,即盐度跃层上方,而123.0°E以东海域的叶绿素a高值区位于次表层水,即温度跃层上方。海水表层DO的分布取决于叶绿素a浓度的分布,表层以下水体的含氧量则与水体层化程度密切相关。数据分析显示水体层化程度(PEAP)与水体缺氧程度存在较强的线性相关性。根据调查资料构建了一个夏末长江口外海域叶绿素a分布态势形成机制图。在分析观测资料和历史资料的基础上,基于海洋数值模式ECOM-si,耦合太阳辐射强度、海表热通量和泥沙计算模块,考虑硅藻和甲藻两个浮游植物类群,建立了一个N2P2ZD型的海洋浮游植物生态动力学数值模型。模型经参数敏感性测试,稳定性良好,通过长时间序列站点和大面调查资料验证,模式具有一定的精度,可应用于长江口外海域浮游植物生态动力学的研究。以2006年和2009年的现场调查范围为参考,设定29.5°N-32.5°N,122.25°E-124.0°E范围内的海域为浮游植物生态动力学数值模拟研究的目标海域。目标海域浮游植物的生长主要受控于营养盐、周年变化的水温和光照条件,同时受处在食物链上游的浮游动物摄食压力的控制。硅藻有春季和夏末两次较明显的水华,甲藻仅有春季水华。水温控制水华年内首次发生的时间。7月后,受水温过高的影响,甲藻生物量处于较低水平,生物基础浓度无法达到发生赤潮的量值。硅藻在5月至9月均保持较高的生物量,说明这段时间都是长江口外海域硅藻赤潮可能发生的时间窗口。硅藻的生长更多地受光照和营养盐的限制,而甲藻生物量更多受水温的限制。目标海域的DIN浓度受长江径流高浓度DIN入海的影响较大,而来自长江径流的P04-P浓度相对较低,因此长江径流的P04-P输入相对不是目标海域最主要的P04-P来源。目标海域的P04-P平均浓度更多受外海开边界的影响。开边界的营养盐输入对目标海域的浮游植物年均生物量有较大影响,特别是来自台湾海峡边界的P04-P输入。台湾海峡边界营养盐的输入较台湾以东边界重要,且对硅藻的影响大于甲藻。更多还原

【Abstract】 Estuary is always the high productivity of the ocean area, they often are an important area of human activity and an important fishing ground lies. The Changjiang (Yangtze River) is China’s longest, and its huge runoff with rich nurients make the Changjiang Estuary to be productive waters. There are famous fishing grounds lies in the Changjiang Estuary in history. The rapid economic development and urbanization process of Changjiang Valley accelerated industrial and agricultural waste water and domestic sewage discharge rising waters of the Changjiang Estuary eutrophication, leading to frequent red tide. Damage to the environment coupled with overfishing and other factors, situation of ecological imbalance and individual smaller and lower value of marine economic organisms is serious off the Changjiang Estuary. Affected by the complex bottom topography (such as submarine valley), huge runoff, monsoon and shelf circulation, dynamic process off the Changjiang River is very complicated. Though, phytoplankton dynamics Study off the Changjiang Estuary has important scientific and practical significance to ecological restoration, environmental protection, red tide prevention, sustainable use of fishery resources.Mainly through field observations, data analysis and numerical model simulation, this paper studied the phytoplankton ecosystem characteristics off the Changjiang Estuary, focusing on the analysis of the major limiting factor and the key physical processes on phytoplankton growth.Using data of phytoplankton species identification and cell abundance during the large area survey in July 2006, the cell volume based conversion biomass (chlorophyll-a concentration) was calculated, and were given diatoms and dinoflagellates biomass respectively. Estimation of phytoplankton cell volume based conversion biomass is a feasible method to objectively reflect the phytoplankton biomass, contributing to the species level in the conduct of marine phytoplankton dynamic numerical model study. Phytoplankton biomass off the Changjiang Estuary waters in summer was the highest in the Changjiang Dilute Water (CDW) area, medium off Jiangsu Coast (JSC), and in areas near the river mouth and the Taiwan Warm Current (TWC) were the lowest. Temperature, salinity, water stability and nutrients that affect the distribution of phytoplankton off the Changjiang Estuary were the most important environmental factors.A multidisciplinary observations in the end of August 2009 to early September off the Changjiang Estuary also showed that chlorophyll-a distribution can be divided into four zones:the CDW expansion area, featuring high chlorophyll-a in the surface water on the offshore side of turbidity front, and a hypoxic zone where DO was 1.02-2.00 mg/L underneath the high chlorophyll-a zone; the TWC zone which had strong stratification,with low chlorophyll-a in the surface water and relatively high value in the subsurface water; off the well mixed JSC (Jiangsu Coast) zone, featuring medium chlorophyll-a of 2-6 mg/m3 in the areas of shallower than 20 m; and the stratified strongly Near-shore Diluted Water(NDW) zone, with relatively low chlorophyll-a. The high chlorophyll-a zone west of 123.0°E located in the surface water above the halocline, the relatively high chlorophyll-a zone east to 123.0°E located in the subsurface water above the thermocline. Data analysis show that there is a strong linear relationship between the degree of water stratification (PEAP) and the oxygen level of water. According to the survey data, the dynamics pattern of chlorophyll-a distribution in later summer was obtained.Based on the analysis of observational and historical data, a N2P2ZD style numerical phytoplankton dynamics model coupled the ocean marine model ECOM-si with additional modules of solar radiation, sea surface heat flux and sediment was established. In the model, phytoplankton was divided into two groups, diatoms and dinoflagellatesc. Through sensitivity test, a long sequence sites and large area survey data validation, the model was validated stability and has a certain precision, can be applied to ecological dynamics study of phytoplankton off the Changjiang Estuary.We take the 2006 and 2009 field survey area as a reference and set area 29.5°N-32.5°N,122.25°E-124.0°E as the target area for the phytoplankton dynamics model study. Phytoplankton growth in the target area is mainly controlled by nutrients, annual changes in water temperature and light conditions, and endured the grazing pressure of zooplankton which is on the upper food chain. Diatoms have two obvious algal blooms in spring and late summer, dinoflagellates have bloom only in spring. Water temperature was the key factor of the first bloom occurred time. After July, by the impact of the high water temperature dinoflagellate biomass was at a low level, the basis biomass before the red tide occurrence can not be achieved. In May to September, diatoms maintained a high biomass, which means these months are the time window that red tide of diatoms may occur off the Changjiang Estuary. Growth of diatoms affected more by light and nutrient limitation, and biomass of dinoflagellates affected more by water temperature.DIN concentration in target area affected significantly by the high concentration of DIN during the Changjiang runoff discharged into the estuary while the PO4-P concentration in the Changjiang runoff is relatively low, so PO4-P input by the Changjiang runoff is not the most important source of PO4-P in the target area. The annual average concentration of PO4-P in the target area is more affected by the open boundaries. Nutrient supply from the open boundaries has a great impact on annual average biomass of phytoplankton in the target area, especially the PO4-P input from the Taiwan Strait boundary. Nutrients input of Taiwan Strait boundary is more important than the boundary east of Taiwan, and the effect on diatoms is more than dinoflagellates.更多还原