【作者】 赵秀侠；

【导师】 周忠泽；

【作者基本信息】 安徽大学 ， 生态学， 2013， 博士

【摘要】 水华蓝藻早在上个世纪已经出现在富营养化的内陆、河口和海岸等水域。浮游植物是水生生态系统生物资源的重要组成部分,是水域食物链的基础环节,作为水环境中的主要自养生物,浮游植物的种类组成特点和数量分布等生态特征,在一定程度上反映了水域生态环境的基本特征。多年来,针对太湖浮游植物群落结构的野外观测、数值模拟等方面进行了大量研究工作。但目前已有的研究中,多集中在水华蓝藻发生的机制研究和水华暴发过程中的浮游植物优势类群与环境因子二者的相关性分析方面,对浮游植物的群落结构,特别是水华爆发期的浮游植物的群落结构的时空变化特征的研究明显不足；此外,研究区域多数局限于蓝藻水华暴发水域以及与湖心区的对比等。本文通过对2009至2010年对太湖浮游植物时空分布特征、营养盐分布进行了全湖性的阶段性监测。分析了浮游植物群落结构的分布特点,包括浮游植物种类组成、优势种组成、细胞数量、时空分布、季节动态等,利用多元统计分析(CCA和RDA)进一步主要环境因子对浮游植物群落组成的影响；为了进一步验证营养盐对水华蓝藻暴发的作用,对蓝藻优势种Microcystis aeruginosa进行精确的室内控制培养,结果发现在室内培养中,该优势种只表现出生长快的特征,而没有发生相应的藻类聚集的特点。主要研究结论如下：(1)本次调查研究的结果中,浮游植物种类数量共计为8门、79属、207种,分别属于8个门,其中蓝藻门26种,占总种数的11.1%；硅藻门73种,占总种数的31.1%；绿藻门种类最多,108种,占总种数的46.00%；裸藻门20种,占8.50%：甲藻门3种,占1.3%；隐藻门2种,占0.9%；金藻门4种,占1.7%。结合太湖40多年的研究资料分析,得出总趋势为藻类的物种数量减少而细胞密度急剧增加。浮游植物优势类群和常见属种的变化相对较小。(2)通过水华暴发期和非水华暴发期间的浮游植物优势类群空间分布的对比研究,发现水华暴发期的浮游植物的群落结构具有非常明显的特征,铜绿微囊藻M. aeruginosa生物量最大为2.987mg/L,其次为阿氏拟鱼腥藻0.306mg/L；它们的细胞丰度分别为192.98×105cell/L和7.47×105cell/L。因此微囊藻属Microcystis不仅是蓝藻门中的优势类群,且是整个浮游植物群落的优势类群,特别是微囊藻属Microcystis生物量和细胞丰度可作为监测太湖水质和富营养化进程的指示物种和指标。(3)通过浮游植物群落结构在蓝藻水华暴发前期、爆发期和蓝藻越冬期的动态研究分析得出,1月由于水温较低,处于4℃以下,虽然水体中的营养盐浓度高,铜绿微囊藻M. aeruginosa在沉积物表层中以活体形式存在,但不能形成蓝藻水华。推断低水温(<4℃)是驱动太湖浮游植物群落季节演替的主要因子,是蓝藻水华发生的最重要限制因子。(4)利用多元统计分析方法(CCA和RDA)分析了营养盐、透明度等主要环境因子对浮游植物群落组成和优势类群的影响,结果表明：总磷、总氮、氨态氮和透明度是影响浮游植物群落结构的主要因子。梅梁湾、西太湖湾水体中氮磷含量均很高且总氮含量高于总磷含量,均值分别达到2.0mg/L和0.14mg/L,N/P为12时,形成明显的蓝藻水华；而在太湖东太湖湾,水体中氮磷含量相对较低,分别为1.52mg/L和0.09mg/L,其N/P为16时,不形成蓝藻水华,因此推测高氮磷含量和较低的N/P是蓝藻水华发生的营养盐限制因子。(5)通过不同氮磷浓度对铜绿微囊藻M. aeruginosa生长实验,结果为：铜绿微囊藻M. aeruginosa最大现存量出现在氮磷比为10时,随着所设定的磷浓度的增加而增大。盘星藻Scenedesmus. sp随着培养基中磷浓度增大,细胞最大现存量的数值逐渐减小。混合培养条件下,3种藻类中铜绿微囊藻M. aeruginosa的藻类细胞现存量最大,当氮磷比为20和30,蛋白核小球藻C. pyrenoidosa和盘星藻Scenedesmus.sp的藻类细胞现存量数值差别不大。(6)通过3种磷源对藻类的生长实验得出三聚磷酸钠Na5P3O10对M. aeruginosa现存量的影响最大,与该盐能够分解为HPO42-和P043-两种离子有关。焦磷酸钠Na4P2O7为磷源的水体中藻类现存量是3种氮源中最低的,降幅为40%～59%之间。(7)通过3种氮源对藻类的生长实验,分析不同的氮源对藻类的生长促进作用不同,硝态氮和氨态氮是藻类的主要无机氮源,氨氮是藻类能够优先利用的氮源。尿素小分子有机氮也促进了水体铜绿微囊藻M. aeruginosa生长。更多还原

【Abstract】 Rapidly growing anthropogenic inputs, associating with agriculture, aquaculture, urbanization and industrial expansion is a primary cause of the water quality declining. Within the past several decades, many of our freshwater lakes have changed from productive ecosystems to ones experiencing sudden trophic changes, biogeochemical alterations, and a deterioration in habitat quality. Nuisance and harmful phytoplankton blooms are becoming more common generally. These blooms are increasing worldwide and representing a serious threat to drinking water supplies, and the economic sustainability. Nutrients over richment of waters by urban, agricultural, and industrial development have promoted the growth of cyanobacteria. Phytoplankton utilizes light, carbon dioxide, a range of inorganic and organic nutrients to generate compounds by photosynthesis, which provides fundamental energy and matter for food webs. The ecological characteristics of phytoplankton species composition and abundance may be in response to aquatic environment gradients to a certain extent. Taihu Lake has experienced accelerating eutrophication over the past several decades. It has changed from a mesotrophic, diatom-dominated lake to hyper-eutrophic, cyanobavteria-dominated system, with Microcystis blooms now occurring regularly. In the last few years, already a large literature referring to field observation and numerical modeling of cyanobacterial blooms, and the phosphorus controlling of phytoplankton biomass seems more valuable than the nitrogen and phosphorus controlling. However, more researches have focused on the mechanism of algal bloom and relationships analysis between phytoplankton community structure and the possible controlling factors. There is apparently deficient about the spatial and temporal characteristics of phytoplankton community structure. In addition, studied area mostly confined to the comparative between cyanobacteria bloom zone and central lake zone. This paper studied the processes of spatial-temporal variability in the phytoplankton community structure, biomass, dominance species, and the nutrients concentrations characteristics in Taihu Lake during2009-2010year. We analyzed biological responses to these nutrient alterations including shifts in probable nutrient limitations for phytoplankton growth, shifts in phytoplankton production, and indicators of eutrophication. Considering the occurrence of cyanobacterial bloom, the aims of the present study were also to analyze the linkage between nutrient-eutrophication and dominance species Microcystis, to try exploring the competitive mechanism of dominance species. This paper aimed to provide the information about phytoplankton community composition and succession changes, and to aid understanding of lake ecosystems as well as for effective management of lake.(1) A total of207phytoplankton species were identified from the May2009to August2010, belonged to8phyla,79genera. Over the whole water column the Chlorophyceae dominated total species richness, followed by Bacillariophyceae, and then the Cyanophyceae. However, Cyanophyceae dominated during the study period, with peak abundance occurring in summer and autumn. Based on the studies of the past40years about Taihu Lake, result showed that phytoplankton species composition and cell abundance had changed significantly. The general trend was the species number reduced while cell abundance accelerated sharply, and with relatively little changes about dominant species and common genera. These reflected that the seriousness of water pollution and eutrophication status.(2) Through the comparative study of phytoplankton community spatial distribution in bloom and non bloom period, we found that phytoplankton community structure was with obvious characteristics during bloom period. In May, there was visible bloom strips distribution in lake, the cyanobacterial biomass was about1.01～21.56%of total phytoplankton biomass. While in the bloom period, the block and patchy distribution of cyanobacteria could be observed, the proportion of cyanobacteria biomass was increased significantly, and the ratio often comprised of an excess of90%at some water zone. Microcystis not only was the dominant species of cyanobacteria, also was the dominant species of total phytoplankton. The phytoplankton biomass values and cell abundance could be as indicators of water quality and eutrophication progress of Taihu Lake. (3) In January, due to water temperature was4℃, Microcystis couldn’t find or rarely exist in surface layer, while hibernated in surface layer or mid layer of sediments. Taihu Lake is a larger shallow lake with the temperature difference between surface layer and bottom water in general is between0～1℃. Microcystis could withstand lower water temperatures and would be expected to survive at sediment during winter in Taihu Lake. Although with higher nutrients concentrations and Microcystis species, the algal bloom was not forming due to the lower water temperature. Thus, the lower water temperature is the most significant factor in blooming occurrence.(4) The nitrogen content and phosphorus content in Taihu Lake were high and the nitrogen concentration was higher than phosphorus’s. Nutrients contents, especially increasing nitrogen values could not influence on phytoplankton biomass, but may have impact on phytoplankton community structure and succession needed to be studied further future. Phosphorus could be a key factor to determine the distribution of cyanobacterial bloom in Taihu Lake.(5) The experiment results showed that Microcystis aeruginosa growth had different sensitivity to nitrogen sources; ammonium and nitrate were the major inorganic nitrogen. M. aeruginosa growth preferred ammonium to nitrate, and organic nitrogen (CO(NH2)2) could promote Microcystis aeruginosa growth. Therefore, recent frequent cyanobacterial bloom may relate to urea concentrations and be worth to study further.(6) Among three phosphorus sources, M. aeruginosa standing crop was highest by phosphorus sources of Na5P3O10, while by the Na4P2O7with the lowest values, and the M. aeruginosa standing crop decreased about40%-59%.There was relative importance of picophytoplankton to total phytoplankton biomass. A comprehensive observation of that picophytoplankton, including phytoplankton biomass, growth rates and so on, has contributed to explainations of water bloom in Taihu Lake. Then, the water body turbulence from other factors, such as wind force, wind direction, bottom terrain and light, and the influence from interaction between those factors on phytoplankton community should be studied further.更多还原