三峡库区支流中水体的垂向掺混对于藻类生长的影响

三峡水库蓄水之后库区支流水华问题给当地生态环境造成了较大影响,也引起了广泛的关注和重视,然而针对这一问题尚未取得很好的解释和解决方案。本文采用EFDC模型对于2008年坝前库区干支流的三维水动力和水质进行了数值模拟,并从水体垂向掺混的角度分析支流的水华现象。模拟结果成功再现了香溪河库湾中的温度分层和异重流现象,流场、温度场的计算值和实测值吻合较好。统计结果表明:长江干支流水动力特性的差异显著,干支流垂向紊动黏性系数、垂向紊动扩散系数沿垂线分布呈现出不同的形态,且长江干流的垂向掺混强度明显高于香溪河。同时,叶绿素浓度与垂向紊动扩散系数呈显著的负相关关系,随着水体垂向紊动扩散系数的增加,叶绿素浓度逐渐降低,这一规律的发现可为采用物理方法防治三峡库区支流水华打下基础。

Effects of vertical mixing on algal growth in the tributary of Three Gorges Reservoir

Algal blooms that occurred frequently in the tributaries following the impoundment of the Three Gorges Reservoir has become a great challenge for ecology and environment, and aroused wide concern. However, this problem still remains unresolved. In this paper a numerical simulation using the EFDC model was conducted to simulate the three-dimensional hydrodynamics and water quality of the mainstream and Xiangxi Bay in front of the dam in 2008, and the algal blooms was investigated in terms of vertical mixing. The simulation succeeded in reproducing the thermal stratification and density currents in the Xiangxi Bay. The computed results of velocity and temperature coincide well with the field data. The results show that there are significant differences between the hydrodynamic characteristics in the Yangtze River and Xiangxi Bay, the vertical mixing intensity in main stream is much higher than that in the Xiangxi River. Besides, chlorophyll concentration shows a negative correlation with vertical turbulent diffusivity. These results could provide a foundation for the control of algal blooms with physical methods.