城市河湖系统是由河流、湖泊、沼泽、漫滩、地下含水层、不同等级的支流和干流、人工修建的水库、闸坝、泵站、渠道等水利工程，及它们之间的水文和生态联系构成的具有一定的边界并与流域环境发生关系的复杂的“自然-人工”地理综合体。城市河湖系统在人类社会的发展过程中具有非常重要的生态意义和保护价值，为人类社会提供了丰富的生态系统服务功能，如维持生物多样性，养护渔业资源；截留和吸收营养物质，净化水体；蓄水调洪，补充地下水；调节区域气候；为人类提供审美、休闲的场所等。在气候变化和人类活动的双重影响下，城市河湖系统空间格局发生了显著变化。城市河湖水文连通性受损，河湖系统面积萎缩、生境破碎化加剧，河湖系统的自然生态、水文、地球化学过程受到干扰，诸多服务功能逐渐被削弱。因此，在这种背景下，急需定量研究城市河湖系统水文连通强度变化特征，揭示城市河湖系统水文连通变化的驱动机制及其生态环境效应，并通过完善调控措施优化河湖系统水文连通性。

本研究基于系统论理论基础，以长江流域安徽省铜陵市河湖系统为例，瞄准城市河湖水文连通的量化和作用机制的关键科学问题，对城市河湖水文连通机制及模型优化展开研究。从城市河湖系统的结构、过程、功能三方面考虑，将地形地貌、气候因素、水利工程建设、土地利用等属性引入城市河湖水文连通性评价中，建立城市河湖水文连通性评价指标体系，揭示城市河湖系统结构连通性以及基于水文过程、水质过程、水热过程的河湖连通性在时间尺度和空间尺度上的变化特征，阐明基于生态需水保障、水环境改善的城市河湖连通机制，基于最低成本路径的方法对河湖连通性进行优化，确定最佳连通模式和路径。本研究对于城市河湖系统生态需水保障以及水环境改善具有重要意义，为城市河湖系统的保护和修复实践提供理论支撑和技术指导。论文主要研究结论如下：

城市河湖水文连通性评价

本研究充分考虑城市河湖系统的结构特征和功能特性，基于自然环境和人类活动对河湖通量的影响因素，构建城市河湖水文连通性评价指标体系，分别定义了基于水文过程、水质过程、水热过程的河湖连通性指标。首先基于流域的产流与汇流，考虑影响自然条件下各个过程中通量产生和运输的因素，包括降雨径流、植被覆盖、地形梯度、土地利用、岸堤渗透系数、气温、地表温度，评估城市河湖系统的自然通量；其次，将水闸的调度规则纳入连通性评估，超过警戒水位或降雨为暴雨级别时水闸关闭，采用概率密度函数计算水闸的开启概率。因此提出一种新的基于通量的水文连通指标URLC，用来识别城市河湖水文连通性的变化特征。将该方法在铜陵市河湖系统进行了应用，主要通过ArcGIS的水文工具箱分别对结构连通性和基于水文过程、水质过程、水热过程的水文连通性进行计算，探讨了铜陵市河湖水文连通性的时空变化特征。

结果显示，从1950年到2018年，铜陵市河湖系统的结构连通性平均值总体呈下降趋势，在受水利工程影响较小的1950年，非汛期和汛期结构连通性基本一致；随着水利工程的修建，非汛期结构连通性平均值下降了73.6%，汛期结构连通性下降了78.3%。江北片区的汛期结构连通性在1950-1980年之间下降最严重，非汛期结构连通性下降58.9%，汛期结构连通性下降59.8%，1980年之后，成缓慢下降趋势。江南片区河湖系统结构连通性呈阶梯状下降趋势，1950-2018年非汛期结构连通性下降了73.9%，汛期结构连通性下降了78.2%。基于水文过程、水质过程、水热过程的连通性自1950年至2018年均呈下降趋势，且非汛期连通性小于汛期连通性。通过城市河湖系统长时间尺度水文连通性的分析，确定不同区域连通性空间部分状况，为城市河湖系统的调控、保护、恢复工作提供科学依据和理论支撑。

基于生态需水保障的城市河湖连通机制

生态需水的保障与流量变化关系密切，而河湖水文连通往往是导致水文情势变化的直接原因。本研究首先分析了铜陵市的径流特征以及生态需水现状。近几十年来，在气候变化和人类活动双重影响下，铜陵市径流量波动较大，但未发生显著变化。根据Mann-Kendall趋势变化及突变点检验显示，整体上铜陵市水文过程未见显著突变特征，年径流量没有明显变化趋势但年际波动较大，汛期径流量随时间变化有轻微下降趋势，非汛期径流量虽然有增长趋势，但不存在显著的趋势变化。通过对各河流干流及支流的野外调查，基于各河段的生态目标，考虑生态基流、蒸发渗漏需水、植被需水、鱼类产卵繁殖期需水以及底栖动物需水，计算了主要河流的现状生态需水量并进行了水量盈缺分析。结果显示，从各月份生态需水总量来看，各月生态需水总短缺量均小于生态需水总富余量；部分河段水量处于盈余状态，部分河段水量处于短缺状态。说明铜陵市总水量尽管充足，但时空分布不均匀。除了在7月份能够保证河道都满足适宜生态需水外，其他月份均存在不同程度的短缺。从季节上，秋冬缺水较为严重，秋季缺水的数量达到最大；春季，降水量逐渐增大，河流的生态需水基本能够得到满足；夏季降水充沛，生态用水能够满足大多数河流的需求。铜陵市河流在3、6、7、8、9月份部分河段超过了最大生态需水，主要集中在7月份，这与铜陵市径流变化规律一致，7月份是洪水频发的时段。本研究进一步探究了铜陵市河湖水文连通性与生态需水满足率的相关关系，结果显示河湖水文连通性与生态需水满足率有显著的中度正相关关系（p<0.001），随着水文连通性的增高，生态需水满足率也会增强。

（3）基于水环境改善的城市河湖连通机制

良好的河湖水文连通性可以改善河湖系统的水动力条件，增强水体富氧能力，强化对污染物的稀释、扩散和降解作用，进而达到改善水环境的目的。因此本研究在分析铜陵市河湖水环境现状的基础上，进一步探究了水文连通性对水环境的影响机制。首先对铜陵市不同区域、不同时期的河湖水质进行了分析，探讨了铜陵河湖水质的时空变异特征及主要影响因子和可能的污染源。铜陵市河湖水质表现出显著的空间差异，白荡湖流域水质变异主要与 COD、TP有关，水质的变异受到了来自化工厂、化学药品工厂的工业废水影响；枫沙-陈瑶湖流域主要与COD和TN有关，水质变异受到来自生活污水、工业废水和废水处理厂排放的废水等的影响；顺安黄浒河流域主要与TN和COD 有关，水质变异受到了来自农田和养殖场的污水、生活污水和排放自纺织厂、食品厂、化工厂和皮革制造厂的废水的影响，同时水质变异受到水温的影响。进而分析水质与不同缓冲区内不同土地利用面积比例的响应关系，并探讨了土地利用变化对河流水质变化的影响。研究发现不同区域的水质对土地利用类型面积比例有不同的最佳响应缓冲区半径，且不同土地利用类型面积比例对水质参数的影响不同。铜陵市水文站显示水温1959-2019年呈线性上升趋势，根据Mann-Kendall趋势变化及突变点检验显示，在2004年水温发生突变。近几十年来，铜陵市水温发生显著变化，水温的上升导致了溶解氧含量的下降，不利于河湖生态功能的发挥。

通过野外调查及数据收集，计算了各河流的水环境容量，确定需要水环境改善的水功能区有枞阳长河、罗昌河、钱桥河、杨市河、横埠河、横埠后河、横埠前河、环圩干渠、钟仓河、黄浒河上游河段和钟鸣河；依据溶解氧与水温的响应关系，以及底栖动物的适宜水温，发现水温高于30℃之后，溶解氧含量不足5mg/L，不利于底栖动物的生存，因此确定需要调节水温的河段有钱桥河、横埠后河、钟仓河、劳改河和环圩干渠。探讨水环境容量对基于水质过程的城市河湖水文连通性变化的响应表明， 中等程度连通性时河流水环境容量最高，水文连通的中断或受阻，水文条件发生改变，水环境容量也会随之变化；通过建立水温变化率与基于水热过程的城市河湖连通性的关系，发现随着河段平均连通性的升高，升温率逐渐下降，河流调节水温能力增强。

（4）城市河湖水文连通性优化

本研究综合考虑了生态需水量、水环境容量、水温，以识别河湖系统需要连通和优化的河流。基于铜陵市河湖水量盈缺现状，以及独立湿地斑块的纳污能力，采用最低成本路径（LCP）方法优化铜陵市河湖水文连通性。为了找到最低成本连通路径，本研究基于水质保护、段首控制的原则，考虑了不同土地利用类型、地形坡度、起伏度对新建路径的难易程度的影响及空间距离等因素，计算最低成本，以搜索河流调水路径以及用于连接独立斑块湿地的路径，生成新的河湖系统。在不宜构建新路径的河流处，本研究采用构建梯级河滨湿地的方式以减少面源污染。优化后的河湖系统，每个月生态需水短缺的河流数量减少，其中12月份生态需水得到满足的河流湿地数量增长最多，是优化前的1.24倍；每个月河流缺水量减少，其中6月份和4月份河流湿地的生态需水短缺量分别仅占优化前的1%和3%。TN和COD污染得到了进一步的改善，春季和秋季河湖水系削减COD的比例达到了100%，说明优化后的水系可以完全削减优化前水系中存在的COD污染物；尽管TN污染物有一定程度的削减，但削减比例低于COD；铜陵市江南片区基于水质过程的水文连通性优化后略微增加，水环境容量变化不大，新增的河流可以进一步缓解面源污染；铜陵市江北片区河流四季的URLCTN 值优化后均呈增加状态，春季连通性是优化前的1.17倍，夏季连通性是优化前的1.18倍，秋季连通性是优化前的1.09倍，冬季连通性是优化前的1.09倍。随着连通性的增强，水环境容量呈现增长的趋势，因此江北片区优化后的水系污染物削减能力增强。优化后铜陵市基于水热过程的连通性，江南是优化前的1.08倍，江北连通性是优化前的1.09倍，均有所增强，河流水温调节能力得到提升，水温增长速率下降。

The urban river and lake system is a complex "natural artificial" geographical complex with a certain boundary and relationship with the flow environment, which is composed of rivers, lakes, swamps, floodplains, underground aquifers, different grades of tributaries and main streams, artificial reservoirs, dams, pumping stations, channels and other water conservancy projects, and the hydrological and ecological links between them. Urban river and lake system has very important ecological significance and protection value in the development of human society, and provides rich ecosystem services for human society, such as maintaining biodiversity and conserving fishery resources; Intercept and absorb nutrients to purify water; Water storage and flood regulation to supplement groundwater; Regulate regional climate; Provide aesthetic and leisure places for human beings. Under the dual influence of climate change and human activities, the spatial pattern of urban river and lake system has changed significantly. The connectivity of the urban river and lake system is damaged, the area of the river and lake system is shrinking, the habitat fragmentation is intensified, the natural ecological, hydrological and geochemical processes of the river and lake system are disturbed, and many service functions are gradually weakened. Therefore, in this context, it is urgent to quantitatively study the changes in the hydrological connectivity of urban river and lake systems, explore the influencing factors and ecological impacts of the changes in hydrological connectivity of urban river and lake systems, and optimize the hydrological connectivity of river and lake systems through regulatory measures.

Based on the system theory, this study takes the river and lake system of Tongling City, Anhui Province, in the Yangtze River basin as the research object, focuses on the quantification of urban river and lake connectivity mechanism and connectivity, and studies the hydrological connectivity mechanism and model optimization of urban rivers and lakes. Considering the structure, process and function of urban river and lake system, the attributes of topography, climate, water conservancy project construction and land use are introduced into the evaluation of urban river and lake system connectivity, the evaluation index system of urban river and lake system connectivity is established, and the structural connectivity of urban river and lake system is analyzed based on hydrological process, water quality process The change characteristics of river and lake connectivity in the time and space scales of the hydrothermal process, and the urban river and lake connectivity mechanism based on the ecological water demand guarantee, as well as the impact of urban river and lake system connectivity on water quality improvement and water temperature regulation. This study is of great significance for the protection of ecological water demand of urban river and lake system and the improvement of water environment, and provides theoretical and practical guidance for the protection and restoration of urban river and lake system. The main research conclusions are as follows:

(1) Hydrological Connectivity evaluation of urban river and lake system

Based on the factors affecting the connectivity of urban rivers and lakes, from the perspective of urban rivers and lakes system, this study defines the connectivity indicators of rivers and lakes based on hydrological process, water quality process and hydrothermal process, and quantifies them on a large scale by using the existing public data. The method considers the factors that affect the water production and transportation process in the urban river and lake system, including vegetation coverage, terrain gradient, underlying surface, rainfall runoff, and water conservancy facilities; Several factors affecting the adsorption, sedimentation, retention and transportation of nutrients in the river and lake system are considered, including land use, vegetation cover, terrain gradient, rainfall erosion and terrain characteristics; The factors affecting the heat generation and transportation process in the urban river and lake system are considered, including air temperature, surface temperature, vegetation cover, terrain gradient, underlying surface, rainfall runoff, and water conservancy facilities. The method is applied to the river and lake system in Tongling City, and the structural connectivity and connectivity based on hydrological process, water quality process and hydrothermal process are analyzed respectively, and the spatiotemporal change characteristics of the river and lake connectivity in Tongling City are discussed. The results show that from 1950 to 2018, the structural connectivity of the river and lake system in Tongling City showed a general downward trend. In 1950, which was less affected by water conservancy projects, the structural connectivity in non-flood season and flood season was basically the same; With the construction of water conservancy projects, the structural connectivity in non-flood season is significantly higher than that in flood season. The connectivity based on hydrological process, water quality process and hydrothermal process showed a downward trend from 1950 to 2018, and the connectivity in non-flood season was less than that in flood season. Through the analysis of the long-term structural connectivity of urban river and lake system, the spatial part of connectivity in different regions is determined, which provides scientific basis and theoretical support for the regulation, protection and restoration of urban river and lake system.

(2) Urban river and lake connectivity mechanism based on environmental flow

In recent decades, under the dual influence of climate change and human activities, the runoff of Tongling has changed significantly. According to the Mann-Kendall trend change and mutation point test, the hydrological process in Tongling City has no significant mutation characteristics on the whole. The annual runoff has no obvious change trend but the interannual fluctuation is large. The runoff in flood season has a slight decline trend with time change, while the runoff in non-flood season has a growth trend, but there is no significant trend change. Through the field survey of each river, based on the ecological objectives of each river, considering the ecological base flow, water demand for evaporation and leakage, water demand for vegetation, water demand for fish spawning and breeding period, and water demand for benthic animals, the current ecological water demand of the main rivers is calculated and analyzed. The results show that from the total ecological water demand in each month, the total shortage of ecological water demand in each month is less than the total surplus of ecological water demand, indicating that although the total water demand in Tongling City is sufficient, the spatial and temporal distribution is uneven. In addition to ensuring that the rivers can meet the appropriate ecological water demand in July, there are different degrees of shortages in other months. Seasonally, the water shortage in autumn and winter is relatively serious, and the amount of water shortage in autumn reaches the maximum; In spring, the precipitation gradually increases, and the ecological water demand of the river can be basically met; Summer rainfall is abundant, and ecological water can meet the needs of most rivers. The rivers in Tongling City exceeded the maximum ecological water demand in some sections in March, June, July, August and September, mainly in July, which is consistent with the rule of runoff change in Tongling City. July is the period of frequent floods. It provides a scientific basis for the optimization of urban river and lake connectivity and water allocation.

(3) Urban river and lake connectivity mechanism based on water environment improvement

Firstly, the water quality of rivers and lakes in different regions and different periods in Tongling City is analyzed, and the space-time variation characteristics, main influencing factors and possible pollution sources of the water quality of Tongling rivers and lakes are discussed. The water quality of rivers and lakes in Tongling City shows significant spatial differences. The variation of water quality in Baidang Lake basin is mainly related to COD and TP, and the variation of water quality is affected by industrial wastewater from chemical plants and chemical plants; The Fengsha-Chenyao Lake basin is mainly related to COD and TN, and the water quality variation is affected by domestic sewage, industrial wastewater and wastewater discharged from wastewater treatment plants; The Huanghu River Basin in Shun'an is mainly related to TN and COD. The water quality variation is affected by the sewage from farmland and aquaculture farms, domestic sewage and wastewater discharged from textile factories, food factories, chemical factories and leather manufacturing factories. At the same time, the water quality variation is affected by water temperature. Then the response relationship between water quality and different land use area ratio in different buffer zones is analyzed, and the impact of land use change on river water quality change is discussed. The study found that the water quality of different regions has different optimal response buffer radius to the proportion of land use type area, and the impact of different land use type area proportion on water quality parameters is different. The hydrological station of Tongling City showed that the water temperature showed a linear rising trend from 1959 to 2019. According to the Mann-Kendall trend change and the mutation point test, the water temperature changed suddenly in 2004. In recent decades, the water temperature in Tongling has changed significantly. The rise of water temperature has led to the decrease of dissolved oxygen content, which is not conducive to the exertion of the ecological functions of rivers and lakes.

Through field investigation and data collection, this study calculated the water environment capacity of each river, and determined that the water function areas that need to improve the water environment include Zongyang River, Luochang River, Qianqiao River, Yangshi River, Hengbu River, Hengbuhou River, Hengbuqian River, Huanwei Main Canal, Zhongcang River, the upper reaches of Huanghu River and Zhongming River; According to the response relationship between dissolved oxygen and water temperature, as well as the suitable water temperature of benthic animals, it is found that after the water temperature is higher than 30 ℃, the dissolved oxygen content is less than 5mg/L, which is not conducive to the survival of benthic animals. Therefore, it is determined that the water temperature needs to be adjusted in the reach of Qianqiaoqiao River, Hengbuhou River, Zhongcang River, Laogai River and Huanwei Main Canal. By establishing the relationship between the water environmental capacity and the connectivity of urban rivers and lakes based on the water quality process, it is found that the river water environmental capacity is the highest when the connectivity is medium; By establishing the relationship between the water temperature change rate and the connectivity of urban rivers and lakes based on the hydrothermal process, it is found that with the increase of the average connectivity of the river section, the heating rate gradually decreases, and the ability of the river to regulate the water temperature increases. It provides scientific basis for the restoration and improvement of water environment.

(4) Optimization of urban river and lake system

In this study, the ecological water demand, water environment capacity and water temperature change rate are comprehensively considered to identify the rivers that need to be connected and optimized in the river-lake system. Our method provides a more comprehensive basis for the river and lake connection project. In order to find the best connection path, this study is based on the principle of water quality protection, taking into account the impact of different land use types, terrain slope, undulation on the difficulty of the new path and the spatial distance and other factors, and calculates the lowest cost path to search the river water transfer path and the path used to connect the independent patch wetland, and generate a new river and lake system. In this study, the way of constructing cascade riverside wetlands is adopted to reduce non-point source pollution in rivers where new paths are not suitable. After the optimization of the river and lake system, the number of rivers with ecological water shortage decreases every month, and the water shortage also decreases to a certain extent; TN and COD pollution has been further improved; The connectivity of the river and lake systems in the Jiangnan and Jiangbei areas of Tongling City has been enhanced, the water temperature regulation ability of the river has been improved, and the water temperature growth rate has decreased.