基于软计算方法的天津海域水体富营养化研究

发布时间：2018-07-17 06:18

【摘要】：近岸海域水体富营养化是目前许多沿海区域面临的一个重要问题。对水体富营养化状况进行准确的评价和预测,并对其规律及影响因素做出合理的分析,可为治理和改善海岸带生态环境提供科学的依据。作为环渤海经济圈中的特大型城市之一,天津经济的快速发展致使其毗邻的渤海湾的生态环境面临着日益增大的压力,海域水体富营养化问题突出。本文选择天津海域为背景,开展水体富营养化的研究。本文建立了沿水深积分的水动力模型和水质模型,模拟了天津海域的余流场和天津海域沿岸陆源排放污染物的迁移路径。结果表明:天津海域四季的余流场的总体特性基本一致——在天津海域存在一对南北双向环流,以大沽口为界,南部环流为顺时针,北部环流为逆时针;天津海域沿岸九个排污口释放污染物的迁移路径受南北双向环流的影响显著,并表现出明显的沿岸线输移趋势。用综合污染指数法和富营养化指数法分析了天津海域水体主要污染因子和富营养化程度,结果表明:DIN、PO_~(3-)-P、BOD和Pb为主要污染物,富营养化随季节变化显著。用主成分分析法提取了影响该海域水体富营养化的主要影响因子,并用空间插值法对三个主成分中的主要影响因子DIN、PO_~(3-)-P和COD的空间分布趋势进行了分析。结果表明:富营养化因子的浓度分布基本上呈现近海高远海低,北高南低的特征;DIN、PO_~(3-)-P北高南低的带状分布特性显著,说明陆源污染物的排放是天津海域水体污染的重要原因。基于天津海域的现场监测数据,结合已有的知识,用结构方程模型(SEM)对天津海域水体富营养化因子与叶绿素a之间的因果关系进行了识别和验证。根据SEM提供的因果关系,建立了基于贝叶斯网络(BN)模型的天津海域赤潮监控区海域水体的富营养化模型,并用监测数据对BN模型进行了检验和性能评价。研究结果表明:与物理因子相比,营养物质对天津海域富营养化的影响较大;近年来无机磷一直为天津海域浮游植物生长的限制因子,但是硅酸盐对浮游植物生长的影响程度越来越大。
[Abstract]:Eutrophication in coastal waters is an important problem in many coastal areas. Accurate evaluation and prediction of eutrophication of water body and reasonable analysis of its law and influencing factors can provide scientific basis for controlling and improving the ecological environment of coastal zone. As one of the super large cities in the economic circle of the Bohai Sea, the rapid development of Tianjin's economy makes the ecological environment of its adjacent Bohai Bay face increasing pressure, and the eutrophication problem in the sea area is prominent. In this paper, the study of eutrophication in Tianjin sea area is carried out. In this paper, a hydrodynamic model and a water quality model are established along the integration of water depth. The residual current field in Tianjin sea area and the transport path of pollutants discharged from land-based sources along the coast of Tianjin are simulated. The results show that the overall characteristics of the residual current field in the four seasons of Tianjin sea area are basically the same: there is a pair of two-way circulation in Tianjin sea area, the boundary is Dagu mouth, the southern circulation is clockwise, and the northern circulation is counterclockwise; The migration paths of pollutants released from the nine discharge outlets along the coast of Tianjin are significantly affected by the circulation in the north and south directions, and the trend of transport along the coastal lines is obvious. The main pollution factors and eutrophication degree of Tianjin waters were analyzed by means of comprehensive pollution index method and eutrophication index method. The results showed that: DINPOP _ 3- ~ (3-) -PHOBOD and Pb were the main pollutants, and the eutrophication varied significantly with the seasons. Principal component analysis (PCA) was used to extract the main influencing factors on eutrophication in the sea area, and the spatial distribution trends of DINPPO-P and COD of the three principal components were analyzed by spatial interpolation method. The results show that the concentration distribution of eutrophication factors is basically high and low in the offshore sea and low in the north and south, and the characteristics of the belt distribution of the north high and the south low are obvious, which indicates that the discharge of land-based pollutants is an important reason for the water pollution in Tianjin sea area. Based on the field monitoring data of Tianjin sea area, the causality between eutrophication factors and chlorophyll a in Tianjin sea area was identified and verified by using structural equation model (SEM). According to the causality provided by SEM, the eutrophication model of red tide monitoring area in Tianjin sea area was established based on Bayesian network (BN) model. The BN model was tested and evaluated by monitoring data. The results show that compared with physical factors, nutrients have a greater effect on eutrophication in Tianjin Sea area, and inorganic phosphorus has been the limiting factor for phytoplankton growth in Tianjin Sea area in recent years. But silicate has more and more influence on phytoplankton growth.
【学位授予单位】：天津大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：X55

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