【作者】 卜发平；

【导师】 罗固源；

【作者基本信息】 重庆大学 ， 环境工程， 2011， 博士

【摘要】 三峡水库的建成将产生巨大的经济、防洪等综合效益。但是,水库的建成与运行也对库区的生态环境产生巨大影响,特别是对次级河流的影响。临江河是三峡库区库尾的一条次级河流。成库前,流速较快,河道比降大;但是在三峡水库蓄水以后,由于受到干流回水的顶托作用,临江河部分河段形成回水区(河段),该区域流速大幅减缓、河道变宽、水深加大,水体也由原来的河流型水体转变为湖泊型水体;加之氮磷充足、光照适宜,这些为回水河段的藻类生长提供了适宜条件。为此,论文以临江河回水河段为对象,全面研究了回水河段的富营养化特性、机制及影响因素;在此基础上,采用人工浮床技术对回水河段的富营养化进行防治,并就其机理展开了探讨。研究成果如下:①通过水质分析、实地调研、TSI评价及因子综合得分评价等方法研究了临江河回水河段的富营养化特性。结果发现:1)回水河段始终处于富营养化水平,且有逐年加重的趋势,每年的5月和夏秋之交尤为严重,其中回水腹心区的富营养化程度又相对较重。2)绿藻、硅藻为回水河段的绝对优势藻群,以小球藻、四尾栅藻和颗粒直链藻为常见种。蓝藻为第三优势种群。3)水温、流速、磷和硅为临江河回水河段富营养化的主要控制因子。统计模型中,多元线性逐步回归模型是较为理想的模型。②采用灰关联的分析方法评判了临江河回水河段富营养化影响因素影响程度的大小,发现在春季和冬季,水温的影响最大,SiO3-Si次之,TN的影响较小。③通过物理模拟试验研究了不同条件下藻类的生长与消亡。结果表明:1)培养水体中Chla含量随时间的变化呈二次曲线的变化模式,其中温度、光照、水动力、泥沙含量和初始氮营养盐水平对藻类比生长速率的影响呈向上抛物线型,而初始TP浓度、硅酸盐浓度对比生长速率的影响呈对数关系。2)氮、磷及硅的半饱和浓度分别为0.326 mg/L、0.163 mg/L、0.095mg/L。3)藻类的最适生长条件为:平均水温22℃、硅酸盐浓度1.98mg/L、光照约4000～4200lx、水动力为60 r.p.m。④论文采用人工浮床技术防治临江河回水河段的富营养化,在此基础上就人工浮床净化效果的影响因素与强化措施进行了探寻。结果发现:1)美人蕉浮床、风车草浮床对富营养化的防治效果良好,特别是抑藻效果良好。对COD、TN及TP的平均去除率达20%以上,可削减50%以上的Chla。2)浮床运行的最适水温为25～29℃;植物生长状况与浮床系统的净化能力呈线性关系;较为理想的岛覆盖率可取45%～60%。3)在植物根系悬挂人工介质是最好的强化措施;而通过机械曝气仅可增加去污能力;增大浮床覆盖率仅对提高Chla的削减能力有明显效果。⑤论文还还从水力特性、DO特性及物料平衡等方面研究了人工浮床防治富营养化的机理。结果显示,人工浮床系统的实际流态介于理想推流和完全混合流之间;浮床系统沿程(水流方向)和水深方向均形成了良好的DO浓度梯度分布;底泥沉积是人工浮床系统中氮磷的主要去除途径,占氮磷去除总量的60%以上。人工浮床中的植物可通过吸收污染物、改善DO分布、提高DO含量、遮光及化感作用来控制富营养化。更多还原

【Abstract】 The construction and operation of the three Gorges Reservoir （TGR） will generate tremendous benefits in economy, flood control, hydropower and etc. Meanwhile, the reservoir built also has significant impact on ecological environment, especially on tributaries.The Linjiang River is located in the upper reach of the Yangtze River. Before the construction of the TGR, the flow velocity of the river was considerably quick. When the TGR started impounding, parts of the Linjiang River became a bay, similar to a lentic reservoir due to the backwater from the Yangtze River, and the hydrodynamics in the bay changed substantially. Equally, the average flow velocity dropped sharply, both the river width and water depth increased significantly. Besides the nutrient concentration in the river is great, together with an appropriate illumination, which provided considerable conditions for algal growth.Field observations show that the algal bloom occurred in May and between in the summer and in the autumn but neither in the summer nor in the winter, in the backwater reach of the Linjiang River. Therefore, we took the backwater reach of the Linjiang River as an example to study its eutrophication charactertics,mechanism and influencing factors; in addition, the artificial floating bed technique used for eutrophication control as well as its removal mechanisms were also studied.Firstly, based on one-year monitoring data and field investigation, we studied the eutrophcation charactertics in the backwater reach of the Linjiang River, and then the trophic state of the reach was assessed using trophic state index and principal component analysis. The study indicated that the trophic state of the backwater reach was consitently eutrophic, and exhibited a aggravated trend. And the trophic state was the most serious in the middle reach of the backwaters in terms of the spatial variety.The Chlorophyta and diatiom were the predominat species in the reach, and followed by Cyanophyta.Additionally, we found that the temperature, the flow velocity, phosphorus and silion were the critical factors inducing the eutrophication in the reach, and the multivariate regression model exhibited the best accuracy among statistical models.Secondly, the influencing degree of related factors associated with the eutrophcation in the backwater reach was studied by gray relational analysis, and results revealed that the temperature has the greatest impact on the eutrophication, followed by SiO₃-Si, and TN ranked the last.Through the simulation test, the algal growth and death was studied. The study indicated that: The algal growth exhbibed a quadratic relationship with the water temperature, light intensity, the flow velocity, the TSS, the nitrogen leval, but a logarithm realationship with phosphorus and silicon, respectively. The semi-saturation concentration of nitrogen, phosphorus and silicon was 0.326 mg/L, 0.163 mg/L, 0.095mg/L, respectively. The optimal condition for algal growth was at 22℃in temperature, 1.98mg/L in silicon, 4000～4200lx in light and 60 r.p.m.In addition, the artificial floating bed was taken as an alternative to control the eutrophication in the backwaters, and the study demonstrated that the floating bed vegetated with Acorus calamus s for Canna indica exhibited a great potential to control the eutrophication, especially on the control of the algal growth.Also, we studied the effect of the temperature, the coverage of the floating bed and, the plant growth on the removal effect of artificial floating beds, and found that the optimal temperature and coverage were 25～29℃and 45%～60%, respectively, and the removal effect exhbibed a linear realationship with the plant growth.Some measures such as artificial aeration, the increase in the coverage etc., were carried out to enhance the removal effect and the results revealed susspendion of the fiber filler was the best enchancement for eutrophication.In addition, the control mechanism was studied in the field of the hydraulic characteristics, DO characteristics and mass balance and results indicated that more than 60% of phosphorus and nitrogen were removed by sedimentation, the actual flow pattern of the floating bed systems was intermediate between the ideal plug flow and a perfectly mixed flow and the floating bed exhibited a better DO gradient distribution. The plants played a critical role in eutrophication control through plant absorbition, allelopathic effects, shading and etc.更多还原