大型调水工程影响硅藻生长的多因子耦合机制及阈值

The operation of a large water transfer project can change the hydrological conditions and affect transport and transformation of nutrients and algal community structure, which may threaten aquatic ecological health. Diatom growth in a river is complexly affected by multi-environmental factors and shows spatial-temporal variability. This research plans to conduct monthly and daily monitoring of water quality, hydrological and meteorological conditions, and zooplankton and diatom community structures in the heavily polluted reaches in the middle and down streams of Han River under the operation of the Middle Route of South-to-North Water Transfer Project. The experiments of the constant-temperature flow circulation instrument will be designed to expand the limitation of field observations. Dynamic Factor Analysis and Structural Equation Modeling will be used to identify the key factors triggering diatom bloom and qualify the effect of hydrological conditions on diatom community structure in different monthly and daily scales. Then, Copulas function will be used to establish the joint probability distribution of the diatom community structure indicators and the key factors which will be used to determine the warning thresholds variation of key factors triggering diatom bloom in various flow states. The results will propose how to reduce the occurrence probability of diatom bloom through control of flow or water quality condition and provide scientific basis for the prevention and control of diatom bloom and water quality management in watershed under the operation of a large water transfer project.

大型调水工程改变河流水文条件，影响河流营养盐迁移转化及藻类群落结构变化，并有可能威胁水域生态健康。河流硅藻生长受多个环境因子的复杂影响且存在时空差异性。本研究基于南水北调中线工程实施下，在汉江中下游重污染河段，通过长期逐月（月尺度）及硅藻水华易发期间（日尺度）密集观测水质、水文、气象、浮游动物群落结构及硅藻群落结构等数据，并结合恒温循环水槽控制实验以补充实地采样数据可能的局限。以动态因子分析及结构方程模型为关键技术，在不同的月及日尺度下，探明影响硅藻水华的关键因子及水文条件对硅藻群落结构的影响过程与定量关系；并以Copulas函数为关键技术建立硅藻群落结构指标与关键因子的联合概率分布，提出不同流量条件下，引发硅藻水华的关键因子警戒阈值的改变规律。成果可应用于提出控制关键的水文或水质等条件以降低硅藻水华发生概率的建议，为流域硅藻水华防控及水质管理提供科学理论依据。

水利工程的实施改变河流水文条件，影响河流营养盐迁移转化及藻类群落结构，并有可能威胁水域生态健康。本研究基于中线工程实施下，在汉江中下游重要河段，通过长期逐月及硅藻水华易发期间密集野外观测，并结合微宇宙控制实验，研究水文、水质、气象、及浮游动物生物量等条件对硅藻群落结构与生物量及引发硅藻水华关键因子阈值的影响。主要结果如下：（1）揭示了复杂条件下流域水文、水质时空变异性，建议于低流量条件下，汉江中游和汉江下游流量应分别控制在700 m3/s 和800 m3/s以上，以防止水质恶化。(2)构建可衡量区域特性的水质指数评价方法，该评价方法成功识别汉江中下游农业及城市所排放的水质污染特性。（3）分析了汉江中下游浮游植物群落结构与气候环境变化之时空分布格局，并揭示不同流量情境下浮游植物群落构建过程之差异。（4）探明了多因子协同影响汉江武汉段水华生消机制与水华爆发风险及环境因子警戒阈值。发现汉江武汉段，當水温于8.5-15.5 ℃区间，而总磷> 0.11 mg/L、总氮> 1.90 mg/L、水位差< 2.1 m为水华爆发警戒阈值。（5）建置植生滤带探讨其特性对削减面源氮、磷污染物之效益，揭示河岸带地下水位变化明显影响地表径流量传输，及相对应的削減植生濾帶的效益。最后并透过微宇宙实验探讨藻分解条件下沉积物-水界面氮、磷迁移转化过程，分析此过程对水质的影响。研究结果可用于中线工程实施后汉江中下游硅藻水华防控及流域水质管理提供科学理论依据。