客水输移对富营养化浅水湖泊浮游藻类生消的影响机制

Cyanobacterial blooms induced by limnic eutrophication harmfully endanger the lake ecosystems. While allochthonus water transportation, as an emergent hydraulic measure coping with the ecological disaster, can quickly alleviate this crisis in eutrophic lakes. Until now, the regulating mechanism of allochthonus water transportation on occurrence and dispersal of limnetic phytoplankton is needed to be explored deeply and systematically. In this project, the engineering of water transportation from Yangtze River to Taihu Lake will be focused on. To provide insight into the pivotal factors influencing the occurrence and dispersal of phytoplankton, the spatio-temporal heterogeneity of the hydrological, physicochemical characters and planktonic communities will be investigated simultaneously based on experiments of outside observation, numerical simulation, in situ modeling and indoor incubation. For uncovering the quantitative relationships between the key elements of water transportation and the variation of phytoplankton communities, the special attention will be concentrated on the coping relationships between the variations in allochthonus water flow, induced lake flow field, velocity, concentrations of different biogenic elements, inputs of allochthonus planktons and limnetic phytoplankton communities. The regulating mechanism of allochthonus water transportation on occurrence and dispersal of limnetic phytoplankton will be revealed, which will provide a benefit guide for the hydraulic ecological restoration on eutrophic shallow lakes.

富营养化所导致的蓝藻水华灾害严重影响湖泊生态系统的健康。作为应对水华灾害的应急措施，调引过境客水可快速缓解湖泊水华危机。目前，对客水输移过程调控湖泊浮游藻类生消的机制还缺乏更为深入和系统的认识。本研究以大型客水引流工程-引江济太工程为研究对象，通过野外观测、模型数值计算、原位模拟以及室内培养实验，同步研究引江济太工程影响下太湖敏感受水湖区水动力特征、水化学环境及浮游生物群落的时空分异格局，探讨客水输移过程调控湖泊浮游藻类生消的关键因子。重点研究客水流量、引起的湖流流场、流速、不同形态生源要素浓度的改变以及不同种类外源浮游生物的输入与浮游藻类群落及生物量变化间的耦联关系，弄清客水引流关键要素与浅水富营养化湖泊浮游藻类生消间的定量关系。项目预期将阐明客水引流对富营养化浅水湖泊浮游藻类生消的影响机制，为浅水富营养化湖泊蓝藻水华灾害的水利修复实践提供理论依据。

调水工程是应对湖泊水华灾害和改善水质的重要措施，但客水输移过程对湖泊浮游藻类生消的影响机制此前缺乏深入和系统认识。项目以引江济太工程为研究对象，通过野外观测、数值计算、原位模拟等综合手段，分析了客水输移影响下太湖受水湖区湖流流场、敏感理化参数、浮游藻类群落结构的时空分异特征，筛选了客水影响湖泊浮游藻类生消的关键因子，解析了关键因子与藻类群落变动间的定量耦联关系与贡献；结合室内实验，揭示了受水湖泊浮游藻类及生境对引水流量和时长的定量响应关系。成果系统阐明了客水输移对富营养化浅水湖泊浮游藻类生消的影响机制，成果已应用于太湖流域引江济太工程河湖水生态调度实践。主要研究结果如下：.（1）工程现状条件下，季节性引水可显著降低太湖受水湖区水体有机污染程度与pH值，增加氮磷含量，该影响具有明显空间效应，仅望虞河入贡湖湖口附近水域影响显著；季节性引水均会增加受水湖区藻类多样性，削减微囊藻种群比例，改善藻类群落组成。.（2）季节性引水造成的湖泊理化生境要素改变对藻类群落变动贡献为23.3%-31.3%，水温等固有差异贡献为17.0%-31.4%；引水期受水湖泊水体pH、SiO3-Si、CODMn、NO3-N以及SRP浓度与藻类密度以及群落结构显著相关，不同季节总藻、蓝藻及硅藻密度与理化参数定量关系多呈多元线性关系。.（3）太湖模拟生态系统中水体理化环境、藻类密度以及优势藻类群落组成对望虞河引水流量与时长响应均敏感。20天的引水模拟过程中，引水流量（100~200m3/s）短期内（10天内）可有效降低模拟系统中蓝藻密度，增加硅藻密度，改变了蓝藻与硅藻优势种属组成。.（4）客水输移引起的湖流流场改变、理化环境变化以及外源藻类输入等是影响湖泊藻类生消的主要机制。引水增加了湖泊水体交换，产生的动力掺混环境，更有利于硅藻等增殖；引水期小环藻等清水型硅藻比例增加，指示受水湖区有机污染生境的改善影响藻类群落；望虞河藻类物种输入对湖泊藻类多样性的贡献率最高仅为15.8%，但对藻类群落组成变化的贡献则更大。