三峡水库回水区蓝藻种群交替模式和产毒能力对营养脉冲响应研究

The development of cyanobacterial bloom in Three Gorges Dam has caused widely concern at home and abroad. Although many studies have investigated the occurrence and abundance of cynobacterial blooms and their underlying mechanisms, knowledge regarding succession pattern for cyanobacteria taxa is scare. It is still unclear whether water level fluctuation have directly or indrectly influence on sustainable competitive advantage of toxigenic strains and toxin production. This proposal is based on succession of cyanobacteria with different morphological characters and toxic genotypes. By means of field samplings, the relationship including nutrient pulses induced by fluctuation of water level, community structure of cyanobacteria and microcystin distribution will be built. To reveal the threshold of the external nutrient conditions when specific taxa of cyanobacteria are dominant, and to elucidate the ecological response of toxic cyanobacteria under the interaction between nutrients and physical indicators such as water flow, temperature and light availability. On the other hand, a series of experiments will be conducted to test the growth and competition of cyanobacteria by different frequency and forms of pulsed nutrient supply. The mechanism of coexistence between toxic and non-toxic cyanobacteria taxa in response to nutrient pluses is proposed. To figure out toxicological response of Microcystis when nutrients pulsed with various stoichiometric ratios were input at varying photo-thermal conditions，and to measure relative importance of different environmental factors effect toxin production of cyanobacteria. The result of this research project will provide theoretical and experimental evidences in further forecasting harmful cyanobacteria in large reservoirs and may be implicated in protecting safety of water quality by means of hydrodynamic regulation.

三峡水库爆发的蓝藻水华问题愈发引起关注。目前，关于库区水华生消机制研究多集中在水华爆发频次和生物量与环境因子相互关系上，对蓝藻种群交替模式缺乏系统深入认识，尤其涉及蓝藻产毒株竞争力及细胞毒性对周期水位脉动的响应特征仍不明晰。本项目以小江流域蓝藻形态型和产毒基因型交替模式为研究核心，探索水位脉动诱发的营养脉冲特征及其对蓝藻种群交替及产毒能力的潜在关联机制。原位研究建立营养盐动态、蓝藻种群结构和微囊藻毒素间定量关系，揭示蓝藻不同种占据优势时外部营养条件阈值范围，阐明优势种对营养盐与水流、光照、温度交互作用下的生态响应；室内研究蓝藻优势种群对不同频率和不同形态营养脉冲的生理状态响应，着重分析营养脉冲对产毒和无毒株优势共存的驱动作用；量化不同光热条件下脉冲氮磷计量比对微囊藻细胞毒性的调节机制，权衡环境因子对蓝藻产毒能力影响的相对重要度，为大型水库蓝藻灾害预警及生态调度运行提供相应的科学依据。

富营养化和气候变化加剧了蓝藻种群的生长、持续和产毒。目前，关于蓝藻水华生消机制研究多集中在生物量与环境因子关系建立上，针对蓝藻优势种群演替及产毒能力的响应机制上缺乏系统认识。本项目首先通过实测地物光谱数据，提出蓝藻-绿藻水华分类光谱指数，实现完整水文年蓝藻-绿藻水华的时空信息提取，并利用小波峰度时序分析方法，分析归纳小江流域十年尺度的蓝藻-绿藻水华演替模式；其次，通过野外大尺度现场数据收集，提出隐变量结构方程模型，量化蓝藻种群间竞争与演替（微囊藻-鱼腥藻-束丝藻）对营养盐与光强、温度等交互作用的生态响应，证实非固氮微囊藻生物量变化主要受到水温和总磷浓度调控，固氮丝状蓝藻生物量依赖于分布区域的生境条件；再次，利用统计机器学习的方法，建立了环境因子、产毒蓝藻及毒素浓度的定量关系，证实水温、光强和氮浓度为调节毒素浓度的关键因子，并借助于贝叶斯推断技术，估算氮、磷营养盐的阈值浓度(TP=0.1mg/L, TN=1.8mg/L)，从毒素控制这一视角强调了氮磷双控的重要性；最后，融合XGBoost与LSTM模型提出一种深度学习框架，利用高阳平湖高频在线监测数据来学习与训练模型，通过耦合水位脉冲和营养脉冲数据，实现叶绿素、藻细胞和藻毒素的高精确预测。研究成果可为大型水体蓝藻灾害预警及生态调度运行提供相应的科学依据。