悬移质泥沙和底泥对河道型水华过程的影响机理研究

The river style algal blooms were influenced by several factors including boundary conditions, sediment, nutrients, etc., and their mechanism of occurrence and the evolution process involved much complexity. Field observation, numerical modeling and laboratory experiments will be conducted to study the roles of different factors that induce the river-style algal blooms, especially the effect of sediment. The numerical modeling is based on an unstructured-mesh ecological model which incorporates the adsorption-desorption process between suspended sediment(SS) and nutrients, the impact of light attenuation on algae photosynthesis due to the presence of SS, the release of nutrients from the bed sediment, and the influence of flow speed on algae growth. The new model is capable to simulate river-style algal blooms with complex geometric boundary forms, such as the tributaries in the upper Yangtze River or the river-lake system. The ecological model has been applied for studying the Xiangxi River (XXR) in TGP reservoir, the field observed data and experimental data were both used to calibrate and verify the model, showing that the calculated results could reproduce the XXR algal bloom evolution processes.Based on sensitivity calculation with different boundary conditions, the mechanism of the XXR algal bloom is expected to be understood, and countermeasures for preventing the water quality problem in TGP reservoir are then proposed. The research method supplies a new tool for studying river-style algal bloom problems and promotes interdisciplinary investigation and engineering practice. The research results provide insights for better management of the TGP reservoir water quality.

河道型水华受河道边界、泥沙、营养物质等诸多因素影响，发生机理及演变较为复杂。项目拟采用原型观测数据分析、数值模拟及室内实验的方法，定量研究不同因素对河道型水华的触发机制，重点研究泥沙对水华过程的影响。在传统水华数学模型的基础上，考虑悬移质泥沙吸附营养物质、泥沙增大遮光效应影响水藻的光合作用、底泥释放营养物质、增大流速限制水藻生长等模块，建立适合模拟河道型水华的数学模型，开发适用于具有复杂边界的河流或河湖水系的水质模拟研究的非结构网格模型。以三峡库区一级支流香溪河为研究背景，采用实验数据和现场观测数据对生态动力学模型进行参数率定和验证计算，复演和预测香溪河水华的发展过程，通过敏感度分析探讨三峡库区支流水华的发生机制和工程防治措施。研究成果可为三峡库区水质治理提供参考，为河道型水华研究提供新手段并促进学科交叉，对生态水利学科发展和工程应用具有重要价值。

河道型水华受河道几何边界、悬移质泥沙和底泥、营养物质和浮游藻类等状态变量初始浓度等诸多因素影响，发生机理及演变过程复杂。本项目经过3年的试验和数值模拟系统研究，分别开展了以下几方面的工作并获得了相关认识：.（1）基于实验室内几组不同工况的水质观测试验（在不锈钢桶内进行试验），控制光照条件和初始营养物质及叶绿素浓度，通过观测水样的溶解氧、总磷、总氮和叶绿素等浓度变化，探明了光照条件和水质状态变量的初始浓度对水华过程的影响机理，表明通过控制光照和增加水动力循环可明显抑制浮游藻类细胞增殖。.（2）在传统水质模型基础上，考虑悬移质泥沙吸附营养物质、泥沙增大遮光效应影响水藻的光合作用、底泥释放营养物质、增大流速限制水藻生长、底泥生化反应等模块，参考WASP模型原理和框架，开发了耦合水动力模型SELFE和扩展的WASP模型以及底泥模型CANDI。同时，采用分离涡模型（DES）研究了三峡库区2个典型弯道的湍流结构，揭示中小尺度涡旋对底泥运动、水沙界面的物质交换过程的影响，研究表明：河床附近的营养物质浓度受底泥生化反应过程影响明显，可形成低浓度含氧层。.（3）以三峡湖北省境内库区（包括若干支流）的水质演变为研究背景，采用试验数据和现场观测数据对水质模型进行参数率定和验证计算，复演和预测香溪河水华的发展过程，通过敏感度分析探讨三峡库区支流水华的发生机制、泥沙的干扰过程及气候变化对浮游藻类增殖的影响。应用数学模型研究了长江干支流的水体及营养物质交换以及汇流口附近的3维螺旋流结构。