Relationship Between Changes of River-lake Networks and Water Levels in Typical Regions of Taihu Lake Basin,China

The typical regions of the Taihu Lake Basin,China,were selected to analyze the variation characteristics of river-lake networks under intensive human activities.The characteristics of the fractal dimension of river networks and lakes for different periods were investigated and the influences of river system evolution on water level changes were further explored through the comparison of their fractal characters.The results are as follows:1) River network development of the study area is becoming more monotonous and more simple;the number of lakes is reducing significantly,and the water surface ratio has dropped significantly since the 1980s.2) The box dimension of the river networks in all the cities of the study area decreased slowly from the 1960s to the 1980s,while the decrease was significant from the 1980s to the 2000s.The variations of lake correlation dimension are similar to those of the river network box dimensions.This is unfavorable for the storage capacity of the river networks and lakes.3) The Hurst exponents of water levels were all between 0.5 and 1.0 from the 1960s to the 1980s,while decreased in the 2000s,indicating the decline in persistence and increase in the complexity of water level series.The paper draws a conclusion that the relationship between the fractal dimension of river-lake networks and the Hurst exponents of the water level series can reveal the impacts of river system changes on flood disasters to some extent:the disappearance of river networks and lakes will increase the possibility of flood occurrence.

Responses of soil nutrient to driving mechanism in Taihu Lake basin in last 20 years

The objectives of this study is to understand the changing law of soil nutrient quality in Taihu Lake basin, Yangtze Delta in last 20 years, and reveal the relationship between soil nutrient changes and human driving forces in regional level over long period of time. Experiment on long-term collecting samples was conducted to study changes of soil organic matter, total N, available N, available P and available K in Dongting town, Wuxi city during the last 20 years. The paper analyses the co-relationship of the fluctuation of soil nutrient and state policy, cultivating practice, agricultural input, and per hectare agricultural net income. The results showed that at first the content of soil organic matter increased, then decreased, and increased again. The content of total N and available N steadily increased. The content of available K and available P steadily decreased. The authors found that the influence of state policy and cultivating practice on soil nutrient quality index (SNQI) is obvious, agricultural input and SNQI are positively correlated, and per hectare agricultural net income and SNQI are negatively correlated.

Optical Characteristics of Chromophoric Dissolved Organic Matter(CDOM)in Upstream and Downstream Lakes of Taihu Lake Basin:New Insights for Water Environmental Management

Chromophoric dissolved organic matter(CDOM)is a key component of organic matter that contributes to the ecological functioning of lakes.The lakes in Taihu Lake Basin play an important role in maintaining regional ecological stabilities;however,the optical characteristics of the CDOM in the upstream and downstream lakes in this basin have not yet been systematically studied.Here,the optical characteristics of CDOM in ten lakes of upstream and downstream of the Taihu Lake Basin were studied using UV-Visible and excitation-emission matrix spectroscopies.Three different fluorophores consisting of two humic-like components(C1,C2)and one protein-like component(C3)were identified by parallel factor analysis.Soil or surface erosion was responsible for the higher abund-ance of C1 in the upstream lakes,and increased biological activities accounted for the higher abundance of C3 in the downstream lakes.Rainfall erosion in the wet season led to an increase in CDOM.We also found that the photodegradation and flocculation degree,which played a significant role in reducing CDOM,were higher in downstream lakes than in upstream lakes.Optical analysis of CDOM provides a promising method for monitoring water qualities(e.g.,total phosphorus and potassium permanganate index)in each lake.Re-ductions in soil or surface erosion in the upstream are needed to improve water quality.

GRAIN PRODUCTION AND CLIMATIC VARIATION IN TAIHU LAKE BASIN

Before the end of the Ming Dynasty to the early of the Qing Dynasty, climate was warm, and heat energy was plentiful, so double-cropping of rice in Taihu Lake basin could grow without any protection. Later the global climate entered the Little Ice Age, the double-cropping of rice was extirpated nearly, grain output decreased heavily. After the Little Ice Age, although, the global climate got warm, sometimes, the thermal condition was enough for two crops no three crops one year throughout the period. So both the area and output of of double-cropping of rice was fluctuated with variation of cold/ warm. The condition of heat energy, with the movement of climatic zone, becomes a sensitive factor effecting grain production. Recently, as CO2concentra-tion in atmosphere is increasing, climate is getting warm. With the comprehensive effect of such warming and natural cooling trend, the climate in Taihu Lake basin shows the following trend: warm in winter, cooling in summer, decreasing of annual accumulated

Benefit Assessment of Forest Function in Reducing Soil Erosion and Nutrient Loss in Anji County of Taihu Lake Basin

The non-point source pollution arising from soil erosion is one of the main reasons for the deterioration of the water quality of the Taihu Lake Basin. Forest plays an important role in controlling soil erosion and reducing nutrient loss. Based on the survey data on forest resources in Anji County, we estimate the amount of soil erosion and nutrient loss of nitrogen and phosphorus reduced by forest, using soil erosion modulus method and soil nutrient content. In accordance with the degradation coefficient of pollutant and regional compensation standards of environmental resources, we assess the ecological benefits of forest function in reducing nutrient loss of nitrogen and phosphorus in Anji County. The results show that the forest in Anji County can reduce the soil erosion amount at 1.51 million t annually on the average, so as to control the nutrient loss of 1 409 t of total nitrogen and 577 t of total phosphorus in soil, equivalent to annually avoiding the flow of 824 t of total nitrogen and 410 t of total phosphorus into river water; this ecological service function can make forests in Anji County get 92.55 million yuan of ecological compensation funds (about 688 yuan/hm2·a), equivalent to 15 times of the current ecological compensation standard (47 yuan/hm2). The study reveals the importance of forest function in controlling soil erosion and nutrient loss in the upper reaches of Taihu Lake Basin to water environment protection in the basin, conducive to carrying out pollution control and protection work of the water environment in the basin.

Analyzing the spatial patterns and drivers of ecosystem services in rapidly urbanizing Taihu Lake Basin of China

Quantifying and mapping the distribution patterns of ecosystem services can help to ascertain which services should be protected and where investments should be directed to improve synergies and reduce trade- offs. Moreover, the indicators of urbanization that affect the provision of ecosystem services must be identified to determine which approach to adopt in formulating policies related to these services. This paper presents a case study that maps the distribution of mukiple ecosystem services and analyzes the ways in which they interact. The relationship between the supply of ecosystem services and the socio-economic development in the Taihu Lake Basin of eastern China is also revealed. Results show a significant negative relationship between crop production and tourism income （p 〈 0.005） and a positive relationship between crop production, nutrient retention, and carbon sequestration （p 〈 0.005）. The negative effects of the urbanization process on providing and regulating services are also identified through a comparison of the ecosystem services in large and small cities. Regression analysis was used to compare and elucidate the relative significance of the selected urbanization factors to ecosystem services. The results indicate that urbanization level is the most substantial factor inversely correlated with crop production （R2 = 0.414） and nutrient retention services （R2 = 0.572）. Population density is the most important factor that negatively affects carbon sequestration （R2 = 0.447）. The findings of this study suggest the potential relevance of ecosystem service dynamics to urbanization management and decision making.

Losses of Ecosystem Service Values in the Taihu Lake Basin from 1979 to 2010

The Taihu Lake Basin, an east-coastal developed area, is one of the fastest-growing metropolitan areas in China. Ecosystem services in the Taihu Lake Basin have been overexploited and jeopardized. Based on land-use and land-cover change （LUCC） data from 1979, 1984, 2000, and 2010, in conjunction with the adjusted ecosystem service values （ESV）, changes in ESV were analyzed in detail. Results revealed that LUCC resulted in a substantial decrease in total ESV from S3.92 billion in 1979 to S2.98 billion in 2010. The ESV of cropland decreased from $1.64 billion in 1979 to S1.34 billion in 2010, which represented a 20.28% reduction. The ESV of water areas decreased from S1.08 billion in 1979 to $0.36 billion in 2010, which represented a 65.62% reduction mainly because of a decline in water quality. In terms of annual change rate, cropland and water areas showed a sustained downward trend. Spatially, ESV declines were mainly observed in Suzhou, Wuxi, Changzhou, and Shanghai, probably due to a combination of economic progress, population growth, and rapid urbanization. The research results can be a useful reference for policymakers in mitigating ESV decline.

Calculation of instream ecological water requirements under runoff variation conditions:Taking Xitiaoxi River in Taihu Lake Basin as an example

Climate change and human activity can cause remarkable hydrological variation.Traits of hydrological series such as runoff before and after the change points could be significantly different,so the calculation of instream ecological water requirements(EWRs)is confronted with more challenges.Taking the Xitiaoxi River(XTXR)in the upper reach of the Taihu Lake Basin as an example,this paper investigates the calculation of EWRs using the range of variability approach(RVA)under changing environment.The change point diagnosis of the natural and observed runoff series are conducted for XTXR.Then,differences in the hydrological alternation indicators and instream EWRs processes obtained from various daily runoff series are compared.It was found that the natural and observed annual runoff series in XTXR from 1957 to 2018 both show significant variations,and the change points are in 2007 and 1999 respectively.If runoff data before the change points or all runoff data are used,the instream EWRs obtained from natural runoff are significantly lower than those obtained from the observed runoff.At the monthly time step,EWRs differences within a year mainly occurred from May to August.Also,calculation results of the instream EWRs are strongly related to the selected period of runoff series.The EWRs obtained using runoff series after the change points have rather acute fluctuation within a year.Therefore,when the RVA method is used under changing environment,the instream EWRs should be prudently determined by comparing different calculation results on the basis of river runoff restoration and variability analysis.To a certain extent,this paper enriches our understanding about the hydrological method for EWRs estimation,and proposes new ideas for future research on EWRs.

Encounter probability analysis of typhoon and plum rain in the Taihu Lake Basin

It is of great significance to study the encounter possibility of typhoon and plum rain in the Taihu Lake Basin in order to adjust the schemes of design storm and utilize flood resource and make the decision of real-time scheduling for flood control in the Basin. Based upon the existing research findings of description of encounter phenomena of typhoon and plum rain, the initial time of typhoon affecting the Taihu Lake Basin, the start time of plum rain season and the end time of plum rain season were selected as the characteristic indices of typhoon and plum rain, respectively. According to their synchronous data from 1954 to 2009, the distribution functions of the above-mentioned three random variables were identified and a formula expressing the encounter possibility of typhoon and plum rain was derived. In view of the complexity and solution of this formula, joint distribution functions of typhoon and plum rain were constructed by the use of Gumbel Copula function on the basis of the adaptability comparison among three functions (Gumbel Copula, Clayton Copula and Frank Copula) in Archimedean functions. For the characteristics of the formula with the joint distribution functions based on Gumbel Copula function, two methods, i.e., numerical integration and Monte Carlo simulation, were selected to solve the encounter probability, and the validity of the computed results was analyzed finally.

Trade-offs and Synergies of Ecosystem Services in the Taihu Lake Ba- sin of China

Understanding the spatial interactions among multiple ecosystem services is crucial for ecosystem services management. Ecosystem services, including crop production, freshwater supply, aquatic production, net primary production, soil conservation, water conservation, flood regulation, forest recreation, were measured at 1-km grid scale covering the Taihu Lake Basin(TLB) of China. Our objective is to get a comprehensive understanding of the spatial distributions, trade-offs, synergies of multiple ecosystem services across the TLB. Our results found that: 1) majority of ecosystem services were clustered in space and had a similar spatial distribution pattern with the geographical resource endowment. Most of the landscape contributed a high supply of no services, one or two, and a low supply of three to seven services. 2) There were high correlation between forest recreation and freshwater supply and regulating services. Aquatic production had low correlation with other services. 3) The changes of provisioning services led to trade-offs between regulating services and cultural services in the TLB, while synergies mainly occurred among the provisioning service. 4) The spatial relationships of multiple services are consistent at 1-km spatial scale, counties and provinces. This research could help integrate multiple ecosystem services across scales and serve as a reference for decision making.

Impact of Sea-Land Interaction on Evolution of Taihu Lake

Analyzed in this paper are the influencing factors, characteristics, and mechanism of land-sea interaction for the Taihu Lake Basin. The course of mass movement and energy transformation between land and sea in the Taihu Lake Basin has experienced three different stages, namely, ocean predominance, balance between land and sea, and land predominance. In the paper the process of the formation and the evolution of the Taihu Lake is studied considering the land-sea interaction.

Sediment transport following water transfer from Yangtze River to Taihu Basin

To meet the increasing ：need of fresh water and to improve the water quality of Taihu Lake, water transfer from the Yangtze River was initiated in 2002. This study was performed to investigate the sediment distribution along the river course following water transfer. A rainfall-runoff model was first built to calculate the runoff of the Taihu Basin in 2003. Then, the flow patterns of river networks were simulated using a one-dimensional river network hydrodynamic model. Based on the boundary conditions of the flow in tributaries of the Wangyu River and the water level in Taihu Lake, a one-dimensional hydrodynamic and sediment transport numerical model of the Wangyu River was built to analyze the influences of the inflow rate of the water transfer and the suspended sediment concentration （SSC） of inflow on the sediment transport. The results show that the water transfer inflow rate and SSC of inflow have significant effects on the sediment distribution. The higher the inflow rate or SSC of inflow is, the higher the SSC value is at certain cross-sections along the ：river course of water transfer. Higher inflow rate and SSC of inflow contribute to higher sediment deposition per kilometer and sediment thickness. It is also concluded that a sharp decrease of the inflow velocity at the entrance of the Wangyu River on the river course of water transfer induces intense sedimentation at the cross-section near the Changshu hydro-junction. With an increasing distance from the Changshu hydro-junction, the sediment deposition and sedimentation thickness decrease gradually along the river course.

太湖流域洪水与水量调度方案修订的认识与思考

太湖流域经济社会的快速发展对流域调度工作提出新的更高要求。回顾了《太湖流域洪水与水量调度方案》实施以来流域防洪与水量调度的实践,总结分析了方案修订背景、总体考虑以及修订的主要内容,并作出展望与思考。

基于水供需服务流及外溢价值核算的太湖流域横向生态补偿机制

通过生态补偿协调流域内经济发展与生态保护的关系、缓解上下游利益相关者之间的矛盾是保障流域经济社会可持续发展的关键措施,而流域生态补偿核定的关键在于两点:一是如何模拟并量化水供需服务流动的流向、流量、流速及路径以明确供需双方及其空间关系;二是如何实现栅格尺度-地理单元-行政单元的尺度推演以实现不同行政单元之间生态系统服务的盈余、占用、外溢核算。整合卫星遥感、经济社会统计、水文气象观测等多源异构数据,集成水量平衡、水供需服务流动、生态价值核算等方法,构建了基于水供需流动及其外溢价值核算的流域横向生态补偿标准核定框架,利用D8流向法解决了水供需服务流动的流向、流量、流速及路径模拟与量化,实现了“栅格尺度-地形单元-行政单元”空间尺度推演的外溢价值核算,形成了流域内横向水生态补偿资金收取与分配方案。以太湖流域为例,在全面分析水资源外溢、占用及其价值的基础上,解析了县域尺度的水供需时空关系、流动路径及属性特征,辅以水质指标进而明确界定了责任方与补偿对象,形成了补偿资金收取与分配方案。结果表明,太湖流域水供需双方界线清晰、服务流近似于自然汇流过程,供给方以流域西部、西南部、中部县域为主,特别是西部至中部的县域,应受偿资金较多,平均各县应受偿资金比例超过2%/a,应受偿资金最多的嘉善区,比例超过19.66%/a;需求方聚集于流域中部、东部,特别是黄浦江自然汇流沿岸县域,应收取补偿资金较多,平均各县应收取资金比例超过5%/a,应收取最多的浦东新区,比例超过15.48%/a;净补偿资金基本呈现西高东低的分布特征,流域的大部分城市核心区的县域净补偿资金为负值。研究的核定框架、量化核算方法、资金统筹方案可应用到其他流域的横向生态补偿机制构建,实现流域内部与流域之间生态保护和经济发展的整体协调。

太湖流域水环境治理工程土地节约集约利用评价研究

土地节约集约利用评价及其障碍因子诊断对固守耕地红线、保障国家粮食安全具有重要意义,以太湖流域为例,从建设过程和建设结果两方面构建水环境治理工程土地节约集约利用评价体系,选择信息熵改进TOPSIS模型研究太湖治理工程土地节约集约利用现状及变化趋势,并通过障碍度模型进行障碍因子诊断。研究结果表明:太湖治理工程土地节约集约综合利用水平整体随着时间的推移呈平稳上升趋势,太湖治理工程土地集约利用水平排序依次为新孟河工程(0.564 4)、新沟河工程(0.480 5)、走马塘工程(0.431 6),均处于适度利用等级(Ⅲ级),存在较大提升空间;影响太湖治理工程土地节约集约利用的障碍因子存在差异,障碍度变化各不相同,但总体呈现障碍因子集中、重要障碍因子具有较为明显共性的特点。

文化景观视角下湖州太湖溇港的遗产价值识别与管理

位于太湖南岸的湖州太湖溇港世界灌溉工程遗产是水利工程与生态农业实践的杰出案例,孕育了鱼米之乡、丝绸之府的江南水乡文明,是典型的持续演进的乡村景观。在传统文化遗产保护视角下,单一学科的价值解读方法和分类保护制度未能全面认识和可持续管理太湖溇港的多元价值。基于文化景观自然与文化关联互动视角,通过借鉴国际前沿的乡村景观价值认知与管理的理论和实践研究,构建乡村景观遗产价值的识别框架与管理方法,识别太湖溇港的多元遗产价值和载体,并提出整体化、动态化和多方协同的可持续管理策略。

太湖沿岸浅水湖泊生态修复过程中生态系统健康评价

为评估生态修复过程中太湖沿岸浅水湖泊的生态系统健康状况,于2022年对金墅港圩地水体进行了调查.构建了水生态健康综合评估指标体系,由目标层、准则层、指标层构成.其中,准则层由功能性、完整性、稳定性3项组成,指标层由综合水质、营养状态等14个大项参数和pH值、温度、溶解氧等28个小项参数构成,采用层次分析法分别确定了准则层和指标层的权重系数,再使用比值法统一量纲.结果表明,在生态修复过程中,功能评价指数在秋季达到最高,完整性评价指数在秋、冬两季优于春、夏两季,稳定性评价指数在夏季最高,有70%的点位处于“健康”水平,水生态健康综合评价指数持续上升.说明生态修复工程有效地促进了水生态系统的重建与恢复,这不仅对后续的修复和管理有重要意义,而且能为其他湖泊的水生态修复和评价提供借鉴.

基于补偿水头差的沿江口门引排流量计算方法研究

长江支流口门多建有节制闸,利用涨落潮过程自行引排水,而引排水流态的复杂性使得引排流量过程难以精准确定。以太湖流域杨林塘口门为例,通过分析引排水调度方式及流态特征,发现涨潮时开启中孔闸门引水,内河侧流态复杂且附近水位差别大,而落潮时开启全部闸门排水,外江侧流态复杂且附近水位有所差别。为此,提出了一种基于补偿水头差的沿江口门引排流量计算方法。该方法通过设置系列补偿水头差修正堰流公式中的水位,统计了计算流量与实测流量偏差值,进而建立了流量偏差值与补偿水头差的相关关系,最终确定适宜的补偿水头差,从而建立适宜沿江口门引排流量计算公式。结果表明:利用该方法预测的引水流量误差减小40%~50%,排水流量误差减小3%~6%。相关经验可供工程设计人员及闸管单位运行管理人员借鉴。

太湖流域防洪治理实践与思考

太湖流域是典型低洼感潮平原河网地区,一直受洪涝灾害威胁。新中国成立后,经过多年建设,太湖流域初步建立了流域防洪减灾体系,成功应对了多场次洪水。回顾新中国成立以来太湖流域防洪治理历程和方略,可分为“分散治水、一轮治太、二轮治太”3个阶段,总结了3个阶段的人水关系,以及历经实践形成的“蓄泄兼筹、洪涝兼治,高低分开、分层设防,引排结合、综合治理”防洪治理方略。同时,采用水文统计及数学模型模拟等方法,研究了当前流域高度城镇化和气候变化背景下面临的防洪新形势,剖析了流域防洪面临的人水地矛盾突出、防洪焦点由太湖转化为河网、区域短历时降雨影响加剧和周边潮位呈波动上升趋势等新问题,探讨了新时期太湖流域韧性防洪减灾体系的设想,包括深化人水和谐理念、强化“四个转变”治理思路、采用“蓄泄兼筹、洪涝并治,分区扩排、两网统筹,多措协同、智慧管控”治理策略等。研究成果可为新时期太湖流域防洪治理提供参考。

基于PSR模型的太湖流域生态健康评价及主要影响因素

压力—状态—响应(PSR)模型能反映社会经济状况对湖泊水体生态环境带来的影响。基于PSR模型,构建包含人口密度、流域植被指数、换水周期、浮游植物多样性指数等18项指标的评价指标体系,评价太湖流域生态健康状况。选取1999年、2007年作为历史对照年份,将2011—2020年流域健康状况与对照年份进行比较,分析太湖流域生态健康状况变化。结果显示:1)所构建的指标体系状态层、压力层、响应层权重分别为0.418、0.291、0.291,对太湖流域生态健康产生较大影响的指标主要为大型水生植被覆盖度、湖泊总磷达标率、环保投资占GDP比例、湖泊综合营养状态指数(TSI)、水资源利用开发率及浮游植物多样性指数,其总贡献率为51.74%。2)1999年、2007年太湖流域生态健康评价结果为不健康,2011—2020年处于一般健康至健康状态,其中2015年、2017年生态健康评价指数降低,但总体上2011—2020年流域健康状况呈好转趋势。2011年之后太湖流域健康状况好转主要得益于近十几年中央与地方合力进行流域治理、生态修复和综合管理。2015年、2017年流域生态健康指数波动主要归因于不利的气象因素。3)大型水生植被覆盖度、湖泊总磷达标率、湖泊TSI、浮游植物多样性指数这4项指标的变化与太湖流域生态健康评价指数的变化及健康水平相关性较高,近20年来环保投资占GDP比例的提高、水资源开发利用率的优化在一定程度上减缓了这4项指标下降对太湖流域生态健康带来的不利影响。