【作者】 李云；

【导师】 李道季；

【作者基本信息】 华东师范大学 ， 自然地理学， 2008， 博士

【摘要】 河口生物群落具有适应不同时间尺度上各种化学、生物和物理影响的能力。近二十年来,生物评价方法和评估标准开始被应用于研究生物群落对全球气候变化、人类活动的响应,其中,浮游生物作为指示类生物较多的应用于监测河口环境状况。浮游生物处于河口生态系统食物链始端,其群落结构和功能的变化与水环境因子的变化存在较高相关性,可为水质变化提供早期预警信息,是河口监测的主要指示类群之一。自上世纪五十年代以来,许多学者对长江口浮游生物进行了广泛研究,多涉及不同季节浮游生物空间分布的变化,很少涉及微微型浮游生物和病毒的周日变化过程。另外,随着长江三峡工程截流蓄水和投入运行,长江口水域营养盐和悬浮物输入量等将显著变化,可能导致浮游生物的空间分布和季节变化模式发生改变。同时,全球气候变化和人类活动对河口生态环境的影响往往在较长的时间尺度上才能显现,因此有必要对浮游生物群落结构的年际变化过程进行研究。本文基于2005年7月和11月的走航观测数据,2006年6月的走航观测和定点观测数据,以及近十年（1996-2005年）的历史观测数据,从不同时间尺度研究了长江口及毗邻海域浮游生物群落变化过程。结果如下:（1）周日变化定点观测的叶绿素α浓度、微微型浮游生物（Picoplankton）和病毒（Viruses）丰度的时间序列数据,通过非线性矩形方程进行曲线拟合,结果表明了潮汐动力过程是影响河口区叶绿素α浓度、微微型浮游生物和病毒丰度周日变化过程的主要因子。表层叶绿素α浓度、微微型浮游生物和病毒丰度的周日波动呈现典型的半日周期（11-13小时）变化,而中层和底层由于沉积物再悬浮作用和水体层化现象的影响,波动周期与表层明显不同。叶绿素口浓度、微微型浮游生物和病毒丰度的周日变化与各环境因子（温度、盐度、浊度和无机营养盐）之间没有显著的相关关系。（2）夏、秋季变化夏、秋季分别鉴定浮游植物203种和298种,其中,赤潮种中肋骨条藻（Skeletonema costatum）是该海域绝对的优势种。浮游植物细胞平均丰度夏季(5.48×10⁴cells L^-1)低于秋季(2.70×10⁵ cells L^-1),而叶绿素α平均浓度夏季(2.34mg m^-3)高于秋季(1.32 mg m^-3)。多样性指数（H′）均值夏季（1.51）高于秋季（0.86）,均匀度（J）均值夏季（0.59）也高于秋季（0.34）。浮游植物的空间分布具有明显的块状区域特征,其季节变化主要受海区的流系特征、营养盐、悬浮物等因素的制约。虽然,浮游植物的空间分布和季节变化模式与三峡工程蓄水前后无明显差异,但所鉴定的浮游植物种类数量与三峡工程蓄水前同期相比明显增多,这可能与三峡工程蓄水后泥沙输入量显著减少、海流入侵等有关。应用流式细胞仪同步分析了夏季水样中微微型浮游生物和病毒丰度。聚球藻（Synechococcus）、微微型真核浮游植物（Picoeukaryotes）、异养细菌（Heterotrophic bacteria）和病毒平均丰度分别达数量级10⁷、10⁶、10⁹、10⁹ cellsL^-1。回归分析结果表明,病毒丰度与盐度呈正相关关系,与浊度、硝酸盐、磷酸盐、硅酸盐呈负相关关系,可见,病毒对河口环境变化具有高度的敏感性。聚球藻、微微型真核浮游植物、异养细菌和病毒丰度与三峡工程蓄水前后研究结果相比有所变化,特别是病毒,丰度减少达一个数量级,这可能与三峡工程蓄水后径流量减少、海流入侵等密切相关。因此,病毒可作为河口环境变化的高敏感性指示因子。（3）年际变化近十年来,长江口及毗邻海域浮游生物群落结构己发生明显变化。由于长江三峡工程截流蓄水的影响,自2000年以来,该水域悬浮物、COD、无机氮和硅酸盐浓度呈显著下降趋势,富营养化程度有所缓解,但氮磷比值始终高于40,远大于Redfield比值16,硅氮比值也从1996年的1.35下降到2005年的0.94。长期氮磷硅比值的失衡导致了具有光合性和非光合性营养方式的甲藻类在浮游植物群落中所占比例大幅攀升,硅藻的组成比例下降,甲藻类赤潮频繁发生。硅藻群落的减少,致使饵料生物主要组成者桡足类的组成比例正逐渐下降,非饵料生物水母的比例正逐渐增高。近几年来,为改善海域环境现状,控制西部陆源污染物输入量的措施已取得一定效果,但河口水质并无明显改善。浮游生物群落结构年际变化表明了维持其群落结构的稳定性控制输入营养盐比例相对于控制西部陆源污染物输入量可能更为重要。更多还原

【Abstract】 Estuarine plankton communities can respond to global climate change and human activities at different timescales,and there are obvious relationships between the changes in plankton communities and water environmental factors.Hence plankton may serve as a bioindicator to monitor estuarine environmental conditions. Since the 1950s,many scientists have conducted an extensive number of studies on plankton seasonal changes in spatial distribution in the Changjiang Estuary and adjacent sea,but rare of them has focused on diel changes of picoplankton and viruses. In addition,nutrient and suspended matter discharges from the Changjiang River will tremendously decrease due to the water storage of the Three Gorges Dam,thus may lead to some changes in spatial distribution and seasonal variation patterns of plankton.Further more,the impacts of global climate change and human activities on estuarine eco-environment exhibit on a long time scale,and then interannual study on plankton community is necessary.Based on the data from cruise monitoring in July and November 2005 and in June 2006,anchor monitoring in June 2006,and historical observations from 1996 to 2005,we studied the changes in plankton community in Changjiang Estuary and adjacent sea at different timescales.The results are as follows:（1）Diel changesTime-series data sets on the fluctuations of the Chlorophyllα,the picoplankton and viruses with tide were obtained and treated by a tidal model based on a rectangle equation.The results reveal that tidal action is a major factor in affecting diel variations of chlorophyllα,picoplankton and viruses in the Changjiang Estuary.The chlorophyll a concentration varied with a semidiurnal period of～11 hr in surface waters,and the cell abundances of picoplankton and viruses～13 hr,coinciding with the tidal period.However,different periods were found in middle and bottom waters, due to the influences of tidal induced physical forcings such as resuspension and stratification.The diel variations of chlorophyllα,picoplankton and viruses are no significant correlation with the environmental factors（temperature,salinity,turbidity, inorganic nutrients）.（2）Changes in summer and autumnTwo hundred and three phytoplankton species in summer and 298 in autumn were identified.Skeletonema costatum was the dominant species identified.The average cell abundance was lower in summer(5.48×10⁴ cells L^-1)than in autumn (2.70×10⁵ cells L^-1),however,the average chlorophyllαconcentration was higher in summer(2.34 mg m^-3)than in autumn(1.32 mg m^-3).The average diversity index（H’） was higher in summer（1.51）than in autumn（0.86）,as was the average evenness（J） （0.59 and 0.34,respectively）.Spatial distribution of phytoplankton featured distinct regionality,and the seasonal variation was controlled by factors such as water source, nutrient,suspended matter,and so on.Although the spatial distribution and seasonal variation patterns were found no difference between before and after the water storage of the Three Gorges Dam,identified species number was higher than that before the dam,which may be related to the consequent changes such as reduced sediment discharge and intensified seawater intrusion after the dam.Cell abundances of picoplankton and viruses were simultaneously determined by flow cytometry.The average abundances of Synechococcus,picoeukaryotes, heterotrophic bacteria and viruses were at the order of 10⁷,10⁶,10⁹ and 10⁹ cells L^-1, respectively.Regression analysis results reveal that viral abundance was positively correlated with salinity,and negatively correlated with turbidity and inorganic nutrient concentrations,indicating that viruses can be the most sensitive to environmental changes compared with the picoplankton groups.Cell abundances of picoplankton and viruses were found changes after the water storage of the Three Gorges Dam.Particularly,viral abundance decreased to one order of magnitude. Therefore,viruses may serve as a high sensitive indicator to monitor estuarine environmental changes.（3）Interannual changesPlankton community structure has changed in the Changjiang Estuary in the last ten years.The annual average concentrations of suspended matter,COD,TIN and silicate have clearly decreased since 2000,which is attributed mainly to the Three Gorges Project.Although eutrophication has declined to a certain extent since 2000, N/P ratio was always much higher than 40 and Si/N ratio reduced from 1.35 in 1996 to 0.94 in 2005.As an ecological consequence to such nutrient balance changes,the dominance of diatoms decreased,dinoflagellates increasingly dominated the phytoplankton population,and the frequency of harmful algal blooms caused by dinoflagellates increased.Furthermore,due to the reduced diatom availability,the dominance of copepods decreased,and medusas increasingly dominated the zooplankton population.Nutrient ratios,therefore,are more important in controlling the stability of plankton community structure than are the amounts of contamination loadings from land.更多还原