【作者】 李一平；

【导师】 逄勇；

【作者基本信息】 河海大学 ， 环境工程， 2006， 博士

【摘要】 湖水透明度是描述湖泊光学的一个重要参数,能够直观反映湖泊水下光场的分布情况,而水下光场是湖泊水生态系统的重要影响因子,直接影响到水生植物的生长和繁殖,探求影响透明度的主导因子和有效改善措施是进行水生植被恢复的基础和前提。太湖透明度主要受悬浮物、藻类和可溶性有机物浓度的影响,而这三者又均与湖泊水动力过程密切相关。本文通过室内外实验,研究了水动力条件下透明度各影响因子的特征和变化规律,并建立了相应的数学模型,最后将各影响因子的数学模型耦合,建立了水动力作用下的太湖透明度模型,为太湖水生植被恢复和健康生态系统重建提供了科学依据。 太湖透明度的各影响因子均受水动力过程的影响,所以研究太湖水动力特征是透明度研究的基础和前提。本文基于实测资料,分析了太湖湖流和波浪的基本特征,分别建立了数学模型。并将湖流模型和波浪模型耦合,分析了湖流对波浪的影响。波浪模型采用的是基于动谱平衡方程的SWAN波浪模型,在考虑实际水底地形、波浪折射、浅化、反射、破碎、湖流等条件下,对太湖在盛行风作用下的波高、波周期、波长、波陡、近底水质点的运动速度等波浪参数进行模拟并研究了太湖波浪的影响因子。 悬浮物是太湖透明度的主要影响因子,通过室内外实验,研究了太湖底泥在水动力作用下的再悬浮、沉降规律,并建立了水动力条件下太湖悬浮物模型。在室内环形水槽中,模拟了太湖底泥的起动规律,得出了太湖底泥在不同起动标准下的起动流速,建立了底泥中TN、TP的释放通量与水体流速的定量化关系;在野外实验中,着重研究了水动力作用下,太湖底泥的再悬浮和沉降规律、以及底泥再悬浮沉降中引起的营养盐的变化规律。探讨了再悬浮通量的计算方法,并建立了太湖底泥再悬浮通量、悬浮物沉降通量与水动力条件的关系。通过室内静沉降实验,计算了悬浮物在不同浓度下的沉降速度。根据实验结果和悬浮物特征,建立了水动力作用下太湖悬浮物模型。在模型中综合考虑波浪和湖流对底泥的扰动,并将床面层附近底泥的起悬量和沉降量分开处理,引入了底泥起悬条件,动态模拟了水动力作用下悬浮物的变化规律。 另外,太湖藻类和可溶性有机物对光也具有吸收和散射作用,是影响水体透明度的次要因子。藻类和有机物对透明度的影响不确定性较大,藻类对透明度的影响受季节影响,夏季较冬季要大;可溶性有机物对透明度影响一直不是很大,但也不能忽视更多还原

【Abstract】 Water transparency is an important parameter characterizing lake optics, which can directly reflect light field distribution below water surface of lakes. Light field below water surface is a significant factor of lake ecosystem, which has direct effects on the growth and propagation of aquatic plants. Therefore, the basis and prerequisite for aquatic plant restoration is to understand the main factors affecting water transparency and study on efficient control measures. Water transparency of Lake Taihu is mainly affected by suspended solids (SS), concentrations of algae and dissoluble organic matter, all of which are closely related to hydrodynamic processes of the lake. In this paper, the characteristics and changes of the effecting factors of water transparency under different hydrodynamic conditions were studied by lab and field experiments. The data from these experiments were presented in models for respective effecting factor. The water transparency model of Lake Taihu under hydrodynamic conditions was developed by coupling the models of each effecting factor. This coupling model provides scientific basis for restoration of aquatic plants and rehabilitation of healthy ecosystem of Lake Taihu.The effecting factors of water transparency of Lake Taihu are related to hydrodynamic conditions. Thus, study on hydrodynamic characteristics of Lake Taihu is the basis and prerequisite for water transparency study. In this paper, we analyzed the basic characteristics of lake current and wave of Lake Taihu based on measured data. Respective numerical models were developed. Lake current model and wave model (SWAN model) were coupled to analyze the effects of wave on lake current. In swan the evolution of the wave spectrum is described by the spectral action balance equation. Considering conditions such as wind input, bottom friction, bottom topography, whitecapping, depth-induced wave breaking, wave refraction, nonlinear wave-wave interaction, lake current etc., wave parameters (wave height, wave period, wave length, wave steepness and the orbital velocity near the bottom, etc.) under the condition of dominant wind at Lake Taihu area were simulated using this model. The effecting factors of wave of Lake Taihu were also studied.SS is the main factor affecting water transparency of Lake Taihu. Lab and field experiments were conducted to study on the resuspension and sedimentation characteristics of Lake Taihu sediments under different hydrodynamic conditions, and then develop SS model of Lake Taihu. By using bench-scale circular water tank, the starting pattern of Lake Taihu sediment was simulated. From this experiment, the incipient velocities under different starting standards were tested and then the quantitative correlations betweennutrient (nitrogen and phosphorus) release flux and flow velocity were developed. By field experiments, resuspension and sedimentation patterns of sediment, changes of nutrients induced by the process of sediment resuspension and sedimentation under different hydrodynamic conditions were mainly studied. The calculation method of resuspension flux was discussed, and then the correlations of resuspension flux of Lake Taihu sediments, SS sedimentation flux and hydrodynamic conditions were established. Additionally, settling experiment under static condition was conducted to calculate the settling velocity of SS under different concentrations. The hydrodynamic SS model of Lake Taihu was developed based on these experimental results and SS characteristics. In the model, the disturbance of wave and lake current to sediments was considered. The suspension amount and sedimentation amount of sediments close to bed surface were treated separately, and starting conditions of sediment suspension were introduced in the model. Dynamic simulation of SS changes under different hydrodynamic conditions was conducted.Additionally, algae and dissoluble organic matter are the minor factors affecting water transparency, because they can absorb and disperse light. However, the effects of algae and organic matter on water transparency are relatively uncertain. Effects of algae are different by seasons. The effects are more significant in summer. Effects of organic matter are not distinct, but cannot be overlooked. In this paper, eutrophication model and water quality model of Lake Taihu were developed according to measured data, to simulate the transportation and diffusion patterns of algae and dissoluble organic matter under hydrodynamic conditions.Temporal and spatial distribution of water transparency of Lake Taihu was analyzed based on measured data. And the multiple regression equations for Lake Taihu water transparency and three effecting factors (SS, algae, CODmr) for different seasons and lake parts were deduced. Numerical models for lake current, wave, SS, water quality and algae were coupled to simulate water transparency of Lake Taihu based on the multiple regression equations.更多还原