Nonpoint source pollution entering rivers will pollute water quality, degrading the health of aquatic ecosystems. However, owing to the lack of quantitative research on the effects of nonpoint source pollution on the structure of aquatic food webs, there is a lack of quantitative basis for river management. Nonpoint source pollution is not only difficult to control effectively, but also the success rate of water ecological restoration projects is low. With the increasing proportion of nonpoint source pollution in water environmental problems, it is urgent to quantitatively assess and predict the impact of nonpoint source pollution on the structure of food webs. Therefore, this thesis presents a method for quantitatively assessing and predicting the impact of nonpoint source pollution on the structure of food webs through using fuzzy clustering to screen the typical points of the impact of nonpoint source pollution, then using canonical correspondence analysis (CCA) and partial least squares regression analysis to comprehensively filtrate the driving factors affect food web that results in nonpoint source pollution, and then determining the impact of each driving factor on the structure of food webs. Finally, the change trend of food web structure is predicted. The results show that (1) the driving factors that the nonpoint source pollution that affects the food web structure is NH₃‐N and chemical oxygen demand (COD). The increase in NH₃‐N and COD promotes the growth of phytoplankton, causing the change of the primary productivity of the ecosystem, and ultimately changes the entire food web structure; (2) NH₃‐N and COD affect the stability, maturity, connectivity and complexity of the aquatic food web structure. The increase of NH₃‐N increases the connectivity and maturity of the food web structure but reduces complexity and stability; the increase of COD increases the connection of the food web structure, while reducing the other three indicators; (3) in some areas with good water quality, aquatic species diversity is high, the relationship of interspecies dietary is complex, food web structure level index is high and the structure of food web is stable. The food web structure in the rainy season will be better than that in the dry season. In some areas with severe water pollution and poor food web structure, the ability of the food web to resist external interference is weak. The food web structure in the rainy season will be worse than that in the dry season owing to rainfall into the river. The methods and conclusions in this treatise can provide a reliable and quantitative scientific basis for river ecosystem management and ecosystem restoration and can improve the success rate of ecological restoration projects.

中文翻译：

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面源污染对水生食物网结构的影响和预测

进入河流的非点源污染将污染水质，降低水生生态系统的健康。然而，由于缺乏关于面源污染对水生食物网结构影响的定量研究，因此缺乏用于河流管理的定量基础。面源污染不仅难以有效控制，而且水生态修复工程的成功率很低。随着非点源污染在水环境问题中所占比例的增加，迫切需要定量评估和预测非点源污染对食物网结构的影响。因此，本文提出了一种方法，通过使用模糊聚类筛选非点源污染影响的典型点，然后使用规范对应分析（CCA）和偏最小二乘，定量评估和预测非点源污染对食物网结构的影响。平方回归分析可全面过滤影响食物网的驱动因素，从而导致面源污染，然后确定每个驱动因素对食物网结构的影响。最后，预测了食物网结构的变化趋势。结果表明：（1）影响食物网结构的面源污染是NH的驱动因素。然后使用规范对应分析（CCA）和偏最小二乘回归分析全面过滤影响食物网的驱动因素，从而导致面源污染，然后确定每个驱动因素对食物网结构的影响。最后，预测了食物网结构的变化趋势。结果表明：（1）影响食物网结构的面源污染是NH的驱动因素。然后使用规范对应分析（CCA）和偏最小二乘回归分析全面过滤影响食物网的驱动因素，从而导致面源污染，然后确定每个驱动因素对食物网结构的影响。最后，预测了食物网结构的变化趋势。结果表明：（1）影响食物网结构的面源污染是NH的驱动因素。₃ N和化学需氧量（COD）。NH ₃ -N和COD的增加促进了浮游植物的生长，引起了生态系统初级生产力的变化，并最终改变了整个食物网的结构。（2）NH ₃ -N和COD影响水生食物网结构的稳定性，成熟度，连通性和复杂性。NH ₃的增加‐N增加了食物网结构的连通性和成熟度，但降低了复杂性和稳定性；化学需氧量的增加增加了食物网结构的联系，同时减少了其他三个指标；（3）在一些水质较好的地区，水生生物多样性高，种间饮食关系复杂，食物网结构水平指数高，食物网结构稳定。雨季的食物网结构要好于旱季的食物网结构。在一些水污染严重且食物网结构不良的地区，食物网抵抗外部干扰的能力较弱。由于雨水进入河流，雨季的食物网结构将比旱季的食物网结构差。