跨流域调水工程引起的水文变化对水生生物的影响机制是保护湖泊水生态的重要研究内容。南四湖和东平湖具有丰富的淡水资源及水生生物资源，是我国山东省重要的物资保障，作为南水北调工程中重要的输水通道，保证其水生态系统的健康具有重要战略意义。调水工程的实施打破并重构了南四湖和东平湖的水文格局，从原本主要受降雨径流影响转变为受降雨径流和调水入流的多重影响，这种改变使南四湖和东平湖水文条件复杂化，这种变化是否对湖泊水生态系统造成扰动以及如何对水生态系统进行扰动是本研究重点关注的问题。因此，本研究基于调水引起的复杂水文条件对湖泊水生态系统作用机制的揭示尚有不足的现状，从南水北调东线工程反向调水和脉冲式调水的特点出发，解析了南四湖和东平湖在南水北调东线工程实施之后水文条件的复杂性，通过水文水动力外部耦合模拟和数理统计分析等方法，从不同时间尺度厘清了调水工程前后南四湖中下级湖、上级湖和东平湖水位、水质及水体交换能力的变化特征及其影响因素。结合野外实地调研和历史数据，分析了下级湖和上级湖以及东平湖中大型底栖动物群落的时空变化特征，并在此基础上定性分析并定量描述了水文条件的改变对湖泊内大型底栖动物群落的扰动作用，以期能够为未来评估水利工程建设对湖泊水生态系统的影响提供理论依据。论文主要结论如下：

（1）基于调水影响下水文学条件复杂性解析的水位水质变化特征的分析：调水工程实施之后，南四湖上级湖和东平湖通过柳长河建立水力联系，各湖区从主要受径流引起的季节脉冲的影响转变为受调水脉冲与径流脉冲的叠加影响，调水期的水位波动整体小于非调水期。下级湖、上级湖和东平湖的年际水位主要受调水的明显影响，下级湖和上级湖年际水位还主要受入湖径流的影响，各湖区月尺度水位主要受降雨、径流以及调水的重要影响，因此调水作为重要角色参与了径流对受水湖泊年尺度和月尺度水位的扰动。下级湖、上级湖和东平湖的水质综合污染指数在近十几年呈下降趋势，且在2013年之后达到一个低值并保持稳定，调水水质整体优于径流水质，且与湖水水质相当，调水在整体上对水质的提升有积极作用。水质综合污染指数在调水工程实施后的偶尔上升，主要是由入湖径流和调水中总氮（TN）浓度高于湖泊TN浓度造成的。

（2）基于区域化方法优化和水文水动力联合模拟的水体交换能力变化特征解析：优化后的区域化方法在总径流偏差（PBIS）和纳什系数（E_NS）及决定系数（R²）上的表现均优于单独使用参数转移法或排水面积比法，解决了南四湖水动力模拟输入数据不足的问题。通过实测径流数据的检验，以HSPF水文模型输出结果为边界条件而构建的EFDC二维水动力模型，能够较准确地反映南四湖和东平湖的水位变化。基于EFDC模型获取的湖泊水龄值显示，在调水工程实施之后东平湖和南四湖的水体交换能力有了明显提升，这主要受调水和入湖径流的共同影响，但非调水期的平均水体交换能力仍然强于调水期。调水对水体交换能力的影响在小面积湖泊中表现的更明显，而在湖面面积较大的南四湖中，这种影响更多的是体现在局部水域。

（3）调水工程实施前后及不同时期中大型底栖动物群落的时空变化特征辨析：东平湖、上级湖和上级湖在野外调研中共鉴定出大型底栖动物3类，按密度占比依次为软体动物、寡毛类和水生昆虫类。调水工程实施之后，东平湖中大型底栖动物群落从由水生昆虫类主导转变为由软体动物主导，上级湖和下级湖中软体动物的优势在调水工程实施之后更加凸显。随着时间的变化，大体型软体动物的占比在年尺度上增大，小体型寡毛类和水生昆虫类占比减小，多样性也下降。在季节尺度上软体动物占比通常在调水期减小，在非调水期增大。沿下级湖到上级湖再到东平湖方向，即沿调水方向大型底栖动物群落呈现出大体型软体动物占比下降，小体型水生昆虫和寡毛类占比上升的空间变化特征。

（4）水文条件变化引起的生境要素改变对大型底栖动物群落作用机制的揭示：大体型软体动物密度在非调水期与重金属有强相关性，在调水期与水质有强相关性。生境要素之间的交互作用使其对软体动物占比及Shannon指数的影响变大：随着水深的减小Shannon指数降低，当Cr大于80 mg/kg时，Shannon指数整体上相对更低；随着Pb含量的减小软体动物占比降低，当TN大于0.5 mg/L时，软体动物占比整体上相对更低。调水和径流在调水期和非调水期交替扰动湖泊水位，从而引发水位波动上升，导致对环境变化适应性强的大体型软体动物占比增大；调水在年尺度和季节尺度上均有改善南四湖和东平湖水质的潜力，这有利于软体动物在环境适宜的栖居环境中发挥其生长优势；同时调水脉冲与径流脉冲的叠加使湖泊水体处于高流速的时间变长，延长了不利于小体型物种稳定生长的时间，进而导致小体型寡毛类和水生昆虫类占比减小大体型软体动物占比增大。

The study on the influence mechanism of hydrology change caused by inter-basin water transfer project on lake ecosystem is an important research content for the protection of lake ecological health. Because of rich fresh water resources and aquatic lives, Nansihu lake and Dongpinghu lake are the important material guarantee of Shandong Province, and as the important water transport channel in the South-to-North Water Transfer Project (SNWTP), it is of strategic significance to ensure the health of their water ecosystem. Because of the implementation of water diversion project, the inflow of Nansihu lake and Dongpinghu lake changed from rainfall runoff to alternate inflow of rainfall runoff and transferred water. This change made the hydrological conditions complicated. In this paper, the study focuses on whether and how to disturb the lake ecosystem due to the complicated hydrological conditions caused by SNWTP. The aim of the research is to reveal the mechanism of complex hydrological conditions caused by SNWTP on lake ecosystem. From the perspective of reverse transferred water and transferred water pulse of the eastern route of SNWTP, we analyzed the complex hydrological conditions of Nansihu lake and Dongpinghu lake after the implementation of the eastern route of SNWTP. By means of hydrohydrodynamic external coupling simulation and mathematical statistical analysis, the variation characteristics and influencing factors of water level, water quality and water exchange capacity of Nansihu lake and Dongpinghu lake before and after water transfer project were clarified from different time scales. Based on field investigation and abundant historical data, this reasearch analyzed the temporal and spatial succession characteristics of macrozoobenthic communities in Nansihu lake and Dongpinghu lake. Based on the previous study, the effects of hydrological conditions on macrozoobenthic communities were qualitatively analyzed and quantitatively described. It provides a basis for evaluating the impact of hydraulic engineering construction on lake ecosystem in the future. The main conclusions are as follows:

First, analysis of the characteristics of water level and water quality changes based on the complexity of hydrological conditions under the influence of water transfer: the water level fluctuation in Dongpinghu Lake, the Upper lake and the Lower lake has shown an upward trend in the past two decades. After the implementation of the SNWTP, Nansihu Lake and Dongpinghu Lake established a hydraulic connection through the Liuchang River. The lakes have changed from being mainly affected by seasonal pulses caused by runoff to being affected by the superposition of transferred water pulses and runoff pulses, and the water level fluctuations in the water transfer period are generally smaller than in the non-water transfer period. The interannual water level changes in Dongpinghu Lake and Nansihu Lake are mainly affected by water transfer. The water level of Nansihu Lake is also mainly affected by the runoff into the lake. Precipitation, runoff, and transfer water are all important factors affecting monthly water level changes. Therefore, as an important role, water transfer participates in the perturbation of the annual and monthly water levels of the affected lake by runoff. The comprehensive water pollution index in Dongpinghu Lake and Nansihu Lake has shown a gradual decline in the past ten years, and reached a low value and remained stable after 2013. The water quality of the diversion water is better than the water quality of the runoff as a whole, and the water quality is similar to that of the lake water. So, the SNWTP has a positive effect on the improvement of lake water quality as a whole. The water quality comprehensive pollution index has occasionally increased after the SNWTP, which is mainly caused by the higher TN in runoff and transferred water than that in the lake.

Second, analysis of the change characteristics of water exchange capacity based on the optimization of regionalization methods and the joint simulation of hydrology and hydrodynamics: the optimized regionalization method is based on the screening of information dornors and receivers and the determination of weighting factors. Its performance on PBIS and E_NS/R² is better than using the parameter transfer method and the drainage area ratio method alone, which solves the problem of insufficient hydrodynamic simulation data of Nansihu Lake. Taking the output result of the HSPF model as the boundary condition, the EFDC model is constructed. Through the inspection of the measured runoff data, the model results can more accurately reflect the water level changes of Nansihu Lake and Dongpinghu Lake. The lake water age value obtained based on the EFDC model shows that after the SNWTP, the water exchange capacity of Dongpinghu Lake and Nansihu Lake has been significantly improved, which is mainly affected by the combined effects of water transfer and lake runoff. However, the average water exchange capacity in the non-water transfer period is still stronger than that in the water transfer period. The impact of water transfer on the exchange capacity is more obvious in small lakes, while in the Nansihu Lake with a larger water surface area, it is more reflected in local waters.

Third, discrimination and analysis of the characteristics of temporal and spatial changes in macrozoobenthic communities before and after the water transfer project and in different periods: Dongpinghu Lake, the Upper Lake and the Lower Lake had 3 types of macrozoobenthos, which were mollusks, oligochaetes and aquatic insects in order of the propotion of density in this field survey. After the implementation of SNWTP, the macrozoobenthic community in Dongpinghu lake has changed from being dominated by aquatic insects to mollusks. The advantages of molluscs in the upper and lower lake are more prominent after the water transfer project. As time changes, the proportion of large-sized molluscs has gradually increased on an interannual scale, while the proportions of small-sized species have gradually decreased, and their diversity has also declined. On the seasonal scale, the proportion of molluscs usually decreases during the water transfer period and increases during the non-water transfer period. Along the lower lake to the upper lake to Dongpinghu lake, the macrozoobenthic community showed a gradual decline in the proportion of mollusks, and the proportion of oligochaetes and aquatic insects increased.

Fourth, revealing the mechanism of changes in habitat factors caused by changes in hydrological conditions on macrozoobenthic communities: the density of mollusks has a strong correlation with heavy metals in the non-water transfer period, and has a strong correlation with water quality in the water transfer period. The interaction between habitat elements strengthens the influence of the proportion of molluscs and the Shannon index of the community. As the WD decreases, the Shannon index decreases. When Cr is greater than 80 mg/kg, the Shannon index is relatively lower. As the Pb content decreases, the proportion of molluscs decreases. When TN is greater than 0.5 mg/L, the proportion of molluscs is relatively lower. Water transfer and runoff alternately disturb the water level of the lake during the water transfer period and the non-water transfer period, causing fluctuations in the water level to rise, which leads to an increase in the proportion of large-sized molluscs that are adaptable to environmental changes. Water transfer has the potential to improve the water quality of Nansihu Lake and Dongpinghu Lake on both annual and seasonal scales, which highlights the advantages of big-sized mollusks in a suitable habitat. At the same time, the superposition of water transfer pulse and runoff pulse makes the time for the high flow rate to appear longer, which increases the time that is not conducive to the stable growth of small-sized species. As a result, the proportion of small-sized oligochaetes and aquatic insects decreased, and the proportion of large-sized molluscs increased.