水体分层-掺混-混合状态判定及其对藻类垂向分布的影响

The eutrophication and algal blooms in the tributaries of the Three Gorges Reservoir (TGR) have become the main water environmental problem and got worldwide attention. The vertical movement of water has a significantly effect on the formation and disappearance of algae bloom. The present sign to distinguish weather the water mixes or not is that there is no or little deference(0.5℃) in vertical water temperature. However, in that way, the water can only be divided into two states-"stratified" and "un-stratified". The state "un-stratified "has not been subdivided into "mixing" and "mixed". These two states have distinct influences on passive vertical migration of microalgae. It caused that the formation and disappearance of algae bloom were difficult to be explained and numerical-simulated. This study is proposed to give a detailed analysis of the algal blooms in the tributaries of the TGR. Combined with previous data of our group, we try to determine the three states (Stratified-mixing-mixed) of water column and to study its effects on vertical distribution of algae in the tributaries of the TGR through several methods including in-situ enclosure experiments and theoretical analysis. The expected results of this research also can be used to provide a theoretical support for further modeling and predicting the process of river-type reservoir algal blooms and eutrophication control.

三峡水库支流水华问题一直是国内外学者关注的热点，水体垂向运动强弱对水华生消影响作用极为显著，而目前仅用水温均匀分布作为水体混合与否的表征，尚未区分正在掺混（Mixing）与已经混合（Mixed）二种状态，而这二种状态对藻类垂向被动迁移作用截然不同，前者有作用而后者没有作用，致使目前关于水华突然暴发或消亡的现象难以解释和模拟。本项目拟以三峡水库支流水华为研究对象，结合课题组已有野外观测数据，通过野外围隔实验和理论分析等手段，探究水体三种状态（稳定分层（Stratified）、垂向掺混（Mixing）、混合均匀（Mixed））的判定参数及阈值，揭示外力作用（风力、降雨）对水体分层-掺混状态的影响规律，最终确定不同混合状态对水华藻类迁移、聚集及垂向分布的作用机制。本研究对深入认识水库水华生消机制、精准开展水华预测预报具有重要的指导作用，同时也能为后期通过水动力控制藻类水华提供理论支撑。

项目针对三峡水库支流水华问题，结合课题组已有野外观测数据，系统开展了野外围隔实验和室内实验，探究了水体三种状态（稳定分层（Stratified）、垂向掺混（Mixing）、混合均匀（Mixed））的判定参数及阈值。通过数值模拟手段，根据不同掺混状态下的室内控制实验，基于CE-QUAL-W2模型，构建了不同掺混状态下的室内小尺度水动力模型。针对香溪河库湾水华生消的判定指标及不同藻类水华暴发所对应的混光比临界值进行了系统研究，并评估了不同生态调度工况对藻类水华生消的影响，为三峡水库采用生态调度方式防控支流水华的暴发提供了参考。