【作者】 程曦；

【导师】 李小平；

【作者基本信息】 华东师范大学 ， 生态学， 2011， 博士

【摘要】 本论文从五个方面：1)20多年历史数据分析,2)湖泊营养物及其响应指标的实际观测,3)藻类增长的实验室和现场生物学评价,4)淀山湖浮游藻类群落增长过程的数学模拟,5)淀山湖营养物投入及响应统计学关系分析,验证了淀山湖在重度富营养化状态下,浮游藻类群落生长受到水体中氮磷营养物交替限制的科学假设。研究结果表明：(1)经过15年的营养物积累,淀山湖生态系统发生了重大转折,于1999-2000年前后由中度富营养化转变成重度富营养化。虽然淀山湖水力停留时间较短,但水体中营养物已经累积到足以暴发水华的程度；(2)淀山湖浮游藻类群落的季节演替基本符合PEG (Plankton Ecology Group)模式,但浮游藻类群落正迅速向以绿藻+蓝藻为主的群落结构演替,夏秋季则以蓝藻(微囊藻)为主,其水华对水源保护区构成威胁；(3)藻类群落生长的营养物累积生物学评价实验研究表明,淀山湖春夏季浮游硅藻和绿藻的生长受到水体营养物磷的显著限制,而氨氮则可能是夏秋季(7-9月)浮游蓝藻生长的主要限制因子,控制蓝藻的生物量。淀山湖浮游藻类生长的营养物限制符合氮磷交替限制的季节变化模式,即营养物磷是淀山湖的基本限制因子,夏秋季蓝藻群落占优势时则为氮限制；(4)经典的Logistic增长模型能够很好的描述淀山湖藻类群落春季和夏季的早期增长。近年的数据计算表明,淀山湖春季藻类群落的增长速度从2月下旬开始迅速增加,藻类密度的翻倍时间仅为半个月,到3月中旬藻类群落的增长速度达到最大值29.4μg/L.Month,5-6月份可能形成藻类水华。淀山湖夏季蓝藻藻类群落的增长速度在6月中下旬开始迅速增加,藻类密度的翻倍时间仅26天,到7月下旬藻类群落的增长速度达到最大值22.8μg/L.Month,8-9月份可能形成蓝藻水华；(5)淀山湖营养物输入及响应指标的统计学研究表明,淀山湖水体营养物投入响应指标总磷TP、总氮TN和叶绿素Chl a的平均浓度(平均值μ)和离散程度(标准差σ)随着富营养化程度的增加而增加。在重度富营养化的条件下,TN和TP平均浓度及其离散程度即使变化不大,也会引起Chl a平均浓度及其离散程度的较大的变化。淀山湖TP-Chl a回归方程的斜率随湖泊富营养化程度的增加而增加。目前的数据基础很难给出有统计学意义的氨氮和叶绿素α的经验表达式；依据上述的研究成果,我们可以得到以下的推论：(1)淀山湖虽然已进入重度富营养化阶段,浮游藻类生长,包括藻类早期增长的营养物限制仍然符合氮磷交替限制的季节变化模式。淀山湖控制营养物要有更好的策略；(2)淀山湖在重度富营养化的状态下,即便营养物质得到了控制(水体中营养物质的浓度不再增加),水体藻类的增长也不会马上停止,藻类水华事件还会在一个时期内继续发生；(3)淀山湖浮游藻类的早期增长是可以预计的,控制淀山湖蓝藻水华的根本出路在于早期预警和防治。在此基础上,我设计了淀山湖藻类水华早期预警预报的框架：(?)第一级预警(早期预警)：Chl a=15μg/L,此时浮游藻类群落的增长速度开始迅速增加,增长速度增加最快；(?)第二级预警(水华预警)：Chl a=35μg/L,此时浮游藻类群落的增长速度达到最大值区域；无论是春季还是夏季,在一般通常的气象和水文条件下,如果不采取任何控制措施,藻类叶绿素浓度有第一级预警(早期预警)到第二季预警(水华预警)的时间大约为20天。更多还原

【Abstract】 The scientific hypotheses of hypereuthrophication and seasonal shift of nutrient limitation on algal growth in Dianshan Lake were tested from the following five aspects:1) historical data analyses,2) limnological survey on nutrient inputs and responses,3) lab and field Nutrient Enrichment Bioassays (NEBs),4) mathematic stimulation on algal growth, and 5) statistical analyses on the relationships between nutrient inputs and their response. The results showed that:(1) After more than 15 years of nutrient accumulation, the trophic state of Dianshan Lake transitioned from eutrophic to hypereutrophic in 1999-2000. Despite short residence time of the lake, rapid nutrient accumulation is possible to induce algal blooms;(2) Although the seasonal succession has been fitted into the model of Plankton Ecology Group (PEG) basically, the phytoplankton community of the lake is dominated by green algae and cyanobacteria, Microcystis in summertime, which may threaten the safe of drinking water;(3) In situ nutrient enrichment bioassays (NEBs) on algal community level suggested phosphorus (P) additions significantly stimulated phytoplankton growth in spring and autumn when the algal composition was dominated by diatoms and green algae. In contrast, significant phytoplankton responses to nitrogen (N) additions occurred only in the summer (July to September) when cyanobacteria dominated the phytoplankton. The pattern of shift nutrient limitation is that, P is the primary limiting factor for the lake but that nitrogen deficiency in the water column, which always occurred in summer, may cause N limitation.(4) The early algal growth of the lake can be well described by Logistic model. The stimulation with recent data showed that in spring the algae started its exponential growth at late February, doubled it density within 15 days, reached its maximum growth rate,29.4μg/L.Month, in the middle March, and bloom might occur during the period of May-July. In summertime, cyanobacteria started its exponential growth at the late of June, doubled its density within 26 days, reached its maximum growth rate,22.8μg/L.Month, and cyanobacteria bloom might occur during Augest-September.(5) The statistical analyses on the relationships between nutrients and their response Ch1 a showed that means (μ) and deviations (σ) of TP, TN, and Ch1 a increased with the eutrophication process. In the state of hypereutrophication, even a little variations of mean and/or deviation of nutrients might cause significant increment of Ch1 a. The TP-Chl a regression relationship fitted OECD model well, slopes increased with the eutrophication process. The empirical equation of TN-Chl a was not statistically derived from the existing data set.Based on the above results, some extrapolations were concluded:(1) The trophic state of Dianshan Lake has been transitioned to hyper eutrophication, and algal growth, including early growth is limited by TP and TN alternatively. Better understanding of seasonal shifts in nutrient limitation may help with the development of management strategies for successful lake restoration.(2) In the state of hyereutrophication, even the nutrient concentrations in the water column stop increasing, algae may not change its growth rate simultaneously, and the events of algal bloom may continually occur in a certain period.(3) Prediction of algal early growth is expected. The fundamental way out for controlling harmful algal bloom is early warming and prevention of algal growth.According to these results, a framework was designed for warming system of algal early development:The First Alert Level (Early Warming):Ch1 a=15μg/L, algal exponential growth starts;The Second Alert Level (Bloom Warming):Ch1 a= 35μg/L, algal growth reaches its maximum rate.Under the normal meteorological and hydrological conditions, if there is no action taken, it may take about 20 days that the concentration of Ch1 a be raised from the First Alert to the second.更多还原