Complex summer water temperature behaviour below a UK regulating reservoir

Detailed monitoring over a 15-year period has revealed considerable complexity in summer water temperature behaviour below Wimbleball Lake, a large regulating reservoir in south-west England. Continuous records of water temperature in the regulated River Haddeo and the neighbouring unregulated River Pulham, coupled with information on flow in the tailbay of the dam and on the thermal structure of the impounded water body, reveal that the nature and extent of the thermal modification below the reservoir varies from day to day, month to month and year to year. This complexity largely reflects changes in the balance between a springflow and a direct reservoir release component of the compensation runoff, which arise in response to variations within and between summers in hydrometeorological conditions and in the way the reservoir is operated to regulate downstream flows. Temperature behaviour in the regulated river is made more complicated by progressive warming of the springflow during the summer months, the thermal inertia of the stored water, the development of thermal stratification within the reservoir and the alteration of release depth, although the detailed effect of some of these factors depends on weather conditions, the use of destratification equipment and the rapidity of reservoir drawdown. © 1997 John Wiley & Sons, Ltd.     

Seasonal water level fluctuations: Implications for reservoir limnology and management

With the purpose of finding out whether seasonal water level fluctuations could affect water quality in a reservoir subjected to those changes, trends in environmental variables and in phytoplankton and zooplankton assemblages were analysed. The reservoir's hydrological cycle was characterized by three regimes. The maximum level phase lasted from January to the beginning of June, the emptying phase existed between mid‐June to the beginning of September and the minimum level phase lasted from mid‐September to the beginning of the first autumn/winter rain events. The highest values of total phosphorus, soluble reactive phosphorus, nitrate, water colour and chlorophyll a were found during the minimum level phase. The phytoplankton assemblage was dominated by taxa typical of meso‐eutrophic environments during the emptying and minimum level phases. However, during the maximum level phase, taxa generally found in more oligotrophic systems were observed here also. Similar to other disturbed systems, the zooplankton assemblage was dominated by Rotifera, except in summer and autumn when the cladoceran Ceriodaphnia quadrangula and/or the copepod Tropocyclops prasinus became dominant. Although those shifts seem to be related to water level variations, further research is needed to evaluate to what extent they might also be induced by other seasonal factors acting independently of water fluctuations. Based upon the obtained data, suggestions for reservoir management are proposed.     

Effects of water level fluctuations on Vallisneria nana in the Burnett River in Southeast Queensland,Australia

Changes in aquatic macrophyte populations in the Burnett River in southeast Queensland, Australia are described with respect to the effects of water level fluctuations and possible impact on the Queensland lungfish (Neoceratodus forsteri). This protected fish relies on macrophyte beds as spawning and nursery areas. Studies were conducted prior to, during and following construction of a new weir on the river. Comparative results of impounded and non‐impounded sites were conducted to investigate seasonal and inter‐annual changes in macrophytes and the effects of both a rapid rise in water level when the impoundment first filled and a decline, on new plants in shallow water. Macrophyte communities in newly inundated areas were studied to determine the time taken for seedlings to emerge and reach a cover sufficient to represent spawning habitats for the lungfish. Vallisneria nana dominated the macrophyte beds, which were scoured from the river by a large flow event in May 1998, the effects of which persisted for at least 1 year. Most newly emerging seedlings of Vallisneria perished following a small decline of 7 cm in water level. Decrease in plant biomass and death of established plants in highly turbid water resulted within 6–9 weeks following larger water level rises of 4.0–5.5 m in the new impoundment. In the period leading up to the lungfish‐spawning season at least 5 months is required for submerged plants to reach the 90% cover preferred for spawning. Implications of the results for water level management and lungfish populations are discussed. Copyright © 2008 John Wiley & Sons, Ltd.     

整治水位与整治线宽度组合初探

本文提出了整治水位与整治线宽度组合的概念并利用数学模型参数调整方便，运行速度快的优点，采用河流泥沙数学模型，对整治水位与整线宽度的各种组合所引起起的航道冲过程进行概化研究。     

水生植物水体修复机理及其影响因素

阐述了水生植物的定义、利用水生植物进行水体修复的研究现状、水生植物在水体修复过程中的净化机理及其影响因素,提出了水生植物水体修复技术今后有待进一步研究的问题。水生植物水体修复效果受到多种影响因素的制约,主要包括植物选型和群落配置、温度、透明度、污染物浓度等。必须根据实际情况,选择合适的水生植物,采取必要措施,提高水生植物水体修复效果。     

Effects of river regulation on aquatic macrophyte growth and floods in the Hadejia‐Nguru Wetlands and flow in the Yobe River,northern Nigeria; implications for future water management

The Hadejia River is a tributary of the Yobe River in semi‐arid northern Nigeria and is regulated by two major dams. The other main tributary is uncontrolled. Comparison of the discharge data for the controlled and uncontrolled rivers shows an average decrease of 33% in annual flow in the upstream part of the Hadejia River. The total annual flow and the peak flow in the Hadejia River further downstream, just above the Hadejia‐Nguru Wetlands (HNW), however, did not show a significant reduction in discharge. This is related to a relatively small river flow reduction at lower flows in the upstream part of the Hadejia River and the fact that the formal large upstream water users are not (yet) working at full capacity. The major impact of the dams on the downstream part of the river is the change in regime from ephemeral to perennial. The introduced dry season flows created favourable circumstances for the development of aquatic macrophyte blockages in the HNW. Owing to these blockages, the Hadejia River stopped contributing to the flow in the Yobe River for much of the year. Furthermore, after the completion of the dams, the timing of the floods in the HNW became less predictable. Suggestions for improvement of water management are made. These comprise engineering structures, including a flow diversion structure to regulate flows in the HNW, implementation of environmentally acceptable river flow strategies and water allocation management. Copyright © 2002 John Wiley & Sons, Ltd.     

Internal loading: A new solution to an old problem in aquatic sciences

Internal loading has long been regarded as an ‘Achilles heel’ in aquatic science and management. Internal loading is of fundamental importance in large and shallow lakes, where even low wind velocities can cause a considerable resuspension of matter deposited on the lake bed. The resuspended matter, and the chemical substances bound to the resuspended matter, will influence almost all processes in the aquatic ecosystem, such as water clarity and depth of the photic zone, and hence, primary and secondary production. If the sediments are contaminated, it will increase the concentrations of harmful substances in water and sediments and the potential ecosystem effects related to such concentrations. This paper presents an overview of the processes regulating bottom dynamic conditions in lakes (erosion, transport, accumulation), provides examples on the role of internal loading within the context of limnology and water management, and presents a new, general approach to quantify internal loading from sediments in lakes. The new approach has been critically tested, being a key factor behind the increase in predictive power of a new generation of lake models meant to be used for practical water management. Internal loading of any water pollutant depends on sedimentation. Sedimentation in this approach is presented as a function of two substance‐specific variables, including the fall velocity of the carrier‐particles and the particulate fraction (which, by definition, is the only fraction of a water pollutant that can settle out on the lake bed), and three generic variables, including mean depth, suspended particulate matter and ET‐areas (areas of erosion and transport). On ET‐areas there is, by definition, a discontinuous sedimentation of materials that settles according to Stokes' law. Basically, internal loading is the sum of advective (resuspension) and diffusive transport from the sediments. Resuspension from ET‐areas is given as a function of the lake form (a new algorithm based on the volume development) and the age of ET‐sediments.     

洪水位变化对岸滩稳定性的影响

为了较全面地了解洪水涨落对岸滩崩塌的影响,本文通过对洪水期岸滩受力分析,结合岸滩土体性质和洪水浸泡岸滩特点,给出洪水期岸滩稳定系数;进而分析了洪水降落期岸滩稳定性变化,指出洪水骤降时,长期洪水浸泡后黏土岸滩稳定系数将会大幅度减小;在洪水缓慢降落时,黏性岸滩稳定性减小,但减小幅度小于骤降的情况。通过分析对比洪水上涨、洪水浸泡和洪水降落等不同过程的稳定性,指出洪水迅速上涨期岸滩稳定性最好,依次为洪水缓慢上涨期、洪水浸泡期和洪水缓慢下降期,洪水骤降期岸滩稳定性最差。     

Factors affecting the distribution and abundance of aquatic plants in a navigable Lowland river; the River Nene,England

Investigations were conducted into the causes of a decline in the abundance of rooted aquatic plants in the River Nene. These were formerly troublesome to navigation and obstructed summer storm flows and were regularly cut by Anglian Water until 1976. After 1977 plant growth caused only localized problems so cutting ceased. An investigation into the causes of the plant decline was initiated in order to provide predictions for management decisions about the future use of machinery and personnel. It was concluded that there was a natural loss of plants by scouring in the abnormally high flows of 1976/7 winter. The regular pattern of maintenance dredging, which had been implemented following water industry reorganization in 1974, was shown to suppress abundance for at least five years after dredging. These two sequential events had lowered abundance over the navigable Nene to levels which no longer warrant weedcutting.     

Effects of pulsed flows on nuisance periphyton growths in rivers: a mesocosm study

Rivers regulated by dams are typically characterized by altered biotic communities and habitat structure in downstream reaches. In the Jackson River (Alleghany Co., VA), a relatively constant flow regime below Gathright Dam and anthropogenic nutrient loading have apparently contributed to nuisance levels of periphyton (>300 mg chlorophyll a m^?2). These nuisance growths cause low dissolved oxygen concentrations in the water column and altered benthic habitats in the Jackson River. The use of periodic pulsed flows has been suggested as a restoration practice that could potentially reduce periphyton biomass. We investigated the effects of increased flow on periphyton chlorophyll a (chl a), ash‐free dry mass (AFDM), % organic matter (%OM) using streamside channels in which periphyton‐colonized tiles were subjected to near‐bed velocities ranging from 20 (control) to 240 cm s^?1. Analysis of variance (ANOVA) and regression were used to examine periphyton responses to velocity treatments. There was a significant decrease in chl a and AFDM, and significant increase in %OM in velocity treatments of 150, 180 and 240 cm s^?1 (p < 0.001), but not in lower velocity channels. Regression analyses showed a significant positive relationship with %OM (r² = 0.88) and significant negative relationship with chl a (r² = 0.77) and AFDM (r² = 0.63). Algal taxa were dominated by Cladophora glomerata, Melosira varians and Pleurosira laevis. There was a significant positive relationship between treatment velocity and % C. glomerata (p = 0.007, r² = 0.87) as diatoms were differentially removed with increasing treatment velocity. Our results demonstrate that pulsed flows can reduce periphyton standing crops in the Jackson River, but the discharge required to achieve this reduction would probably need to produce near‐bed velocities >100 cm s^?1. Further study is needed to establish specific flow targets and evaluate the direct and indirect effects of pulsed flows on ecological conditions in the Jackson River. Copyright © 2009 John Wiley & Sons, Ltd.     

Reach‐scale interactions between aquatic plants and physical habitat: River Frome,Dorset

Substrate and flow velocity are two key physical factors influencing the distribution of aquatic plants. These two controls are closely related and reflect interactions between flow regime, quantity and calibre of sediment supplied to and bounding river channels, and channel dimensions. Seasonal growth of aquatic plants has important impacts upon flow resistance, flow velocities and sediment dynamics. This paper focuses upon the reach scale and the aggregate impact of the seasonal growth of aquatic plants on the meso‐habitat characteristics of chalk rivers. It provides a contribution to the broader literature by illustrating how submerged and emergent macrophytes interact with one another at the reach scale to control flow patterns and the retention of fine sediment. The research was conducted within the River Frome, Dorset, UK. Four sets of observations from 2004 of the seasonal growth of aquatic plants, flow velocity behaviour and the storage of fine sediment are presented. Aggregate velocity behaviour over the four observation periods is classified using agglomerative, hierarchical cluster analysis. The spatial arrangement of patches exhibiting different aggregate velocity behaviour are explored and the degree to which velocity behaviour can be attributed to physical characteristics of patches and the growth of aquatic plants is discussed. Conclusions include: (i) patterns of aggregate velocity behaviour within reaches are strongly influenced by macrophyte growth; (ii) average fine sediment deposition is higher around emergents such as Sparganium erectum than submerged plants such as Ranunculus penicillatus subsp. pseudofluitans; (iii) complementary flow patterns evolve across the river channel as aquatic macrophytes grow and it appears that this allows marginal emergents to scavenge fine sediment from faster flow velocity threads that become diverted towards the channel edges. (iv) These processes are important for mesohabitat evolution and maintenance, and they also contribute to patterns of bank erosion and aggradation. Copyright © 2006 John Wiley & Sons, Ltd.     

Use of Dynamic Occupancy Models to Assess the Response of Darters (Teleostei: Percidae) to Varying Hydrothermal Conditions in a Southeastern United States Tailwater

During the past 100 years, most large rivers in North America have been altered for flood control, hydropower, navigation or water supply development. Although these activities clearly provide important human services, their associated environmental disturbances can profoundly affect stream‐dwelling organisms. We used dynamic multi‐species occupancy models combined with a trait‐based approach to estimate the influence of site‐level and species‐level characteristics on patch dynamic rates for 15 darter species native to the Elk River, a large, flow‐regulated Tennessee River tributary in Tennessee and Alabama. Dynamic occupancy modelling results indicated that for every 2.5 °C increase in stream temperature, darters were 3.94 times more likely to colonize previously unoccupied stream reaches. Additionally, large‐bodied darter species were 3.72 times more likely to colonize stream reaches compared with small‐bodied species, but crevice‐spawning darter species were 5.24 times less likely to colonize previously unoccupied stream reaches. In contrast, darters were 2.21 times less likely to become locally extinct for every 2.5 °C increase in stream temperature, but high stream discharge conditions elevated the risk of local extinction. Lastly, the presence of populations in neighbouring upstream study reaches contributed to a lower risk of extinction, whereas the presence of populations in neighbouring downstream study reaches contributed to higher rates of colonization. Our study demonstrates the application of a trait‐based approach combined with a metapopulation framework to assess the patch dynamics of darters in a regulated river. Results from our study will provide a baseline for evaluating the ecological consequences of alternative dam operations. Copyright © 2014 John Wiley & Sons, Ltd.     

常见水生植物对富营养化和重金属复合污染水体的修复效果研究

选取大沽排污河原位生态修复工程现场的6种修复植物旱生美人蕉、水生美人蕉、旱伞草、鸢尾、马蔺、菖蒲为研究对象,通过温室培养试验研究了这6种植物对水中氮磷和重金属Cd、Pb复合污染的修复效果。试验结果表明,所选6种植物在复合污染水体中对营养物质和重金属Cd、Pb均表现出较好的修复效果。经50 d修复后,各植物对总氮TN的去除率为53.90%～94.75%,对总磷TP的去除率为46.76%～85.10%;对Cd的去除率达到90.39%～99.47%。其中,菖蒲、鸢尾、马蔺对总氮的修复能力较好;鸢尾、美人蕉和马蔺对氨氮的修复效果较好;而旱伞草、美人蕉和马蔺对总磷的修复能力最强。所有修复植物对Cd和Pb的富集系数都远远大于1,对Cd、Pb表现出很强的富集能力,可作为Cd、Pb超富集植物来修复水体中的重金属Cd、Pb污染。     

基于水权分配与交易的水管理机制研究 ——以新疆塔里木河流域为例

结合新疆塔里木河流域的实际情况，首先从对策论的角度对水资源在上、中、下游地区分配使用的冲突进行了剖析，认为计划经济体制下行政命令式的水管理概念和模式越来越难以适应稀缺程度不断加剧的水资源分配和利用形势。现行水管理机制缺乏相应的利益调节和经济激励手段。作者从水资源产权界定、分配和交易的角度对塔里木河流域水管理机制创新进行了分析和探讨。基于水权分配和交易的流域水管理机制模式为其它流域水资源分配利用和全国水资源实现可持续发展和管理提供了有益的思路。     

Atlantic salmon (Salmo salar) in the regulated River Alta: effects of altered water temperature on parr growth

The chief objective of this study was to analyse the effects of altered water temperature, due to the hydropower regulation of the River Alta, on growth of Atlantic salmon parr. The river was developed for hydroelectric purposes in 1987. A 110 m high concrete dam was built in the main river 49 km upstream from the outlet to the sea. The outlet of the power station is located 2.5 km downstream from the dam. The annual regime of water temperature has been altered downstream from the power station because of the regulation. It has decreased 1–2° C during June, July and the first half of August, while it has increased up to 3° C during late summer. During winter, water temperature has increased from 0° C to about 0.3–0.4° C. Atlantic salmon is the predominant fish species in the river. They can penetrate 46 km from the sea, up to the outlet of the power station. In this paper I have studied the relationship between growth of juvenile Atlantic salmon and water temperature in the upper part of the river. At similar temperatures, the growth rate of salmon parr in the River Alta is higher in early summer than later in the growing season. In early summer the salmon grew faster than the maximum rate predicted by a recently published model. Therefore, I adjusted the model to describe growth rates of salmon in early summer (ice break to mid‐August), using data derived prior to the hydropower development (1981–1986). The new model proved effective at describing growth rates of fish in early summer following the hydropower development (1987–1996). After development, growth rates decreased during early summer, but increased correspondingly later in the season. There was close agreement between these growth changes and the altered annual regime of river temperature. Overall, only minor changes in annual growth rates have been observed after the hydropower development. Copyright © 2003 John Wiley & Sons, Ltd.     

Growth of Phragmites japonica on a sandbar of regulated river: morphological adaptation of the plant to low water and nutrient availability in the substrate

The construction of upstream dams regulates flood magnitudes, reduces the inundation frequency of the riparian zones and curtails the discharge of sediments to the downstream. Adaptation of a Phragmites japonica colony growing at a rarely flooded sandbar (1.4 × 0.25 km) was investigated. Above‐ and belowground biomass was sampled, together with litters on the ground surface of a quadrat and soil in the rhizosphere. Five sampling locations were selected with three locations located in sandy and two in stony areas. The results showed the total biomass and the ratio of above‐ to belowground biomasses were larger at the sandy sites than the stony sites. However, the fraction of root biomass (i.e. root to rhizome ratio) in the belowground biomass at the stony sites was higher than that at the sandy sites. Higher aboveground and total plant biomass in the sandy areas was because the plants had better access to water and nutrients than plants growing in stony beds. A higher proportion of root biomass, at the expense of rhizome biomass, in the belowground biomass of plant growing in stony sites was due to the difficulty in accessing water and inorganic nutrients. The ratios of nitrogen (N) to phosphorus (P) in the plant tissues were mostly between 5 and 10, indicating that plant growth was N limited. Low ratios of total N (TN) to total P (TP) were also recorded in soil samples, where TN was 300–700 mg/kg and TP was 300–350 mg/kg. A wide phenotypic plasticity observed in P. japonica was an importance factor to maximize the plant survival and fitness in frequently disturbed habitats, and this plasticity was the result of both true adjustment and ontogenetic drift. A mitigation effort, aimed to prevent coarsening of the riverbed by supplying sand to the downstream, can actually advance the development of P. japonica colonies. Copyright © 2008 John Wiley & Sons, Ltd.     

三峡库区水位变幅对奉节何家坡滑坡稳定性影响分析

为了更好地研究在三峡库区增大库水降幅条件下奉节何家坡滑坡稳定性,预测评判其发展趋势,通过现场地质调查和勘探,分析了何家坡滑坡的变形模式与形成机制,并考虑了库水位骤降作用。利用Geo Studio有限元分析软件对滑坡在增大库水位变幅的极端工况下进行渗流场模拟与稳定性计算。研究表明,何家坡滑坡变形主要集中在坡体前缘与中部,表现为逐级牵引式变形破坏,库水位降幅1.2 m/d条件下整体处于基本稳定状态。随着库水位下降速率增大,滑坡稳定性系数不断降低,属典型的动水压力型滑坡。     

水量调度对改善黄河水质与水生态的作用探讨

黄河水量调度对增加敏感水域水量,维护基本生态的改善水质恶化的局面将具有重要作用。应充分利用水利工程,采取断面最小下泄流量控制、加强水质监测等多种措施发挥水量调度对水质改善和生态保护的作用。同时,要认识到水量调度在改善水质和水生态方面所受到条件的制约,降低人们思想和行动上的不合理期望,减少对水调的依赖,促使社会采用各种手段,加强水污染防治和生态保护,从根本上解决水质和生态问题。     

PC机实时水位、流速检测系统

本文针对三工模型试验中水位和流速测量需要，开发研制了一套基于PC微机的水位和流速检测系统。该系统配套八路跟踪式编码水位仪、六路光电式和六中睡电阻式旋浆流速传感器，经试用表明该检测系统具有很好的适用性和抗干扰能力，并且用户界面友好，是一种具有推广价值的三工模型试验中必备仪器。     

南水北调引江济汉取水口区河工模型试验研究

通过南水北调引江济汉工程取水口河段河演分析和引水渠进口段河工模型试验,重点研究了三峡工程蓄水运用后取水口河段河道演变规律,引水渠流速流态、进水闸消力池消能情况和沉沙池、沉螺池工程效果等。研究表明:三峡运行初期,取水口河段河势变化不大,对取水工程有利,其研究成果可供工程设计单位采用或参考。