Engineering aspects of tidal power barrages: Their influence on the environment

Summary A tidal power barrage will locally reduce the rise and fall of water level in the reservoir it creates when it produces electricity from the energy of the tides. This Paper sets out the character and principal effects of such a physical change, and indicates the possible influence of these changes on a range of environmental issues. The presentation is made in the context of information compiled for the Severn Estuary, UK.The decision to proceed with a tidal barrage would mean a reduced need for other types of power station. When measuring the advantages and disadvantages of possible barrages, this wider situation must also be considered.     

Tidal Barrages and Birds

This paper reviews the main effects that building tidal power barrages would have on the bird populations using Britain's estuaries. The changes in the tidal prism that would occur after a tidal power barrage is built are discussed in the context of their effect on the ecology of the estuary. Three main issues are discussed; the effect of changes in size and nature of the intertidal areas of the estuary, effects on saltmarshes, and the displacement of birds at closure. Recently, tidal stream technologies have been developed which are individually likely to have small effects on birds. However the cumulative effects of large scale tidal stream arrays need to be investigated. Finally, the effects of tidal barrages are put in the context of Britain's energy policy and the need to reduce greenhouse gas emissions. Should tidal power barrages be considered in the future, there will be a need for strategic assessments to be used to select sites that maximize the energy produced while minimizing the impacts on bird populations.     

Vegetation development on salt-marsh flats after disappearance of the tidal factor

Summary Vegetation succession on the tidal flats of the Middelplaten, isolated from tidal action after the construction of a barrage in 1961, has been studied with cluster analysis. Data of yearly cover-abundance estimates of species over 1963–73 produced from the Big Island have been partitioned at two levels yielding 7 and 17 clusters respectively. Mapping the 17 clusters for the successive years showed pathways in cluster distribution related with the desalinization rate and water relations in the soil. From the cluster transitions three successional lines could be recognized. They represent developments under different environmental conditions in which differences in desalinization rate, water relations and availability of nutrients are deciding.In the whole area of investigation two invasions could be recognized in the period of colonization, one of halophytes, and the other of glycophytes. In the early years the vegetational pattern is mainly temporal, probably related with unidirectional environmental processes and strategies of species. In later years the pattern is mainly spatial, partly due to fossilization of earlier stages of succession for which reduction in availability of mineral nutrients may be responsible.Vegetational diversity expressed in numbers of clusters reaches a maximum about 10 years after the barrage had been constructed. It is suggested that a second period of succession will be initiated by long-term ecological processes, such as humification, decalcification and acidification, in which the vegetation will participate.Nomenclature of vascular plants follows Heukels-van Ooststroom, Flora van Nederland, 19th Ed. Wolters-Noordhoff, Groningen, 1977.Contribution to the Symposium of the Working Group for Succession Research on Permanent Plots, held at Yerseke, The Netherlands, October 1975.The authors would like to thank Dr. K. F. Vaas and Dr. A.H.L. Huiskes (Yerseke) for reviewing the English text, and Mr. M.C. Daane and Mr. W. de Munck (Yerseke) for their help in producing the data.Communication Nr. 172.     

Changes of fish assemblages after construction of an estuary barrage in the lower Nakdong River,South Korea

In the Nakdong River, an estuary barrage was constructed in 1987, and it divided the freshwater and the seawater, resulting in a change in the ecosystem. To estimate the impact of barrage construction on fish assemblages, we evaluated 20 years of monitoring data before and after the construction of the estuary barrage, and evaluated the role of fishways. The barrage construction generated entire changes of fish assemblages. After construction, the number of fish species dropped sharply, and 36 species disappeared. Conversely, 18 species appeared at this site, including eight freshwater species, seven of which were exotic or translocated species. Barrage construction affected freshwater fish more severely than it did estuarine and marine species because of the existence of an estuarine environment below the barrage. We did not detect any evidence of recovery of fish assemblages. A total of 31 species were collected at fishways, and the number of individuals collected at each fishway was positively correlated with the amount of discharge from the estuary barrage, mean daily tide level, and water temperature. Migratory fish using a fishway had obvious occurrence periods. Therefore, the efficiency of fishway use can be increased if an appropriate management plan is prepared and implemented.     

Rocky shore zonation in the Ranee tidal power basin

Data from a series of rocky shore transects, within the enclosed basin of the Ranee estuary and immediately outside the barrage, describe the distribution and zonation patterns of the intertidal biota, after more than a decade of its regular operation as a tidal power station. In the absence of quantitative pre-barrage information, the distribution of species has been compared with published information on their former extent of penetration into the estuary.     

中国栽培糙皮侧耳品种体细胞不亲和性实验与RAPD分析结果的比较

对收集的糙皮侧耳Pleurotus ostreatus19个栽培菌株在贫营养的半PDA培养基中配对进行拮抗线实验,考察其相互间体细胞不亲和性。结果表明,此19个菌株间出现拮抗线的比率是100%,形成的拮抗线类型可分为菌丝集结型(A型)、隔离带型(B型)和暗线型(D型)三类,出现的比例分别是24.9%、23.7%和51.4%。显微观察暗线型拮抗线区域有菌丝自融形成的溶菌沟,另2种拮抗线中没有菌丝自溶。以拮抗线类型分别作为变量进行NTSYS-PC聚类分析,从相似性系数0.48处截断可将其分为3大类,第一类包括802和黑平王等9个菌株;第二类包括苏引6号和江都71等6个菌株;第三类包括夏王40和早秋高丰等4个菌株。应用13条随机引物扩增此19株糙皮侧耳菌株总DNA,共扩增出917条不同分子量的DNA条带。RAPD聚类分析表明,这些菌株的遗传相似性高达85%以上。从相似性系数0.86处截断,也可将这些菌株分为3大类,第一类包括了802和黑平王等17个菌株;第二类仅包括推广一号和夏王40两个菌株;第三类只有831一个菌株。两种方法的聚类分析结果没有相关性。因此,拮抗反应可以作为评价糙皮侧耳栽培菌株之间遗传多样性的方法之一,但与基因组DNA指纹多样性分析结果并不完全吻合,更不能代替分子指纹分析。     

Climate change and the green energy paradox: the consequences for twaite shad Alosa fallax from the River Severn, U.K

A stock-recruitment model with a temperature component was used to estimate the effect of an increase in temperature predicted by climate change projections on population persistence and distribution of twaite shad Alosa fallax. An increase of 1 and 2° C above the current mean summer (June to August) water temperature of 17·8° C was estimated to result in a three and six-fold increase in the population, respectively. Climate change is also predicted to result in an earlier commencement to their spawning migration into fresh water. The model was expanded to investigate the effect of any additional mortality that might arise from a tidal power barrage across the Severn Estuary. Turbine mortality was separated into two components: (1) juvenile (pre-maturation) on their out migration during their first year and on their first return to the river to spawn and (2) post-maturation mortality on adults on the repeat spawning component of the population. Under current conditions, decreasing pre-maturation and post-maturation survival by 8% is estimated to result in the stock becoming extinct. It is estimated that an increase in mean summer water temperature of 1° C would mean that survival pre and post-maturation would need to be reduced by c. 10% before the stock becomes extinct. Therefore, climate change is likely to be beneficial to populations of A. fallax within U.K. rivers, increasing survival and thus, population persistence.     

Low tide distribution of wintering waders and shelduck on the Severn Estuary in relation to the proposed tidal barrage

Waders and shelduck were counted at low tide on 162 sectors comprising 85% of the intertidal area (21 467 ha) of the Severn Estuary on 12 occasions during winter 1987/88. On average, 50% of birds present at low tide utilized just 13 sectors (12% of the area); 90% of birds occurred on only 56 sectors, leaving large expanses of intertidal sand virtually devoid of birdlife. Dunlin, the numerically dominant species, occurred widely on the middle and outer estuary, whereas shelduck predominantly occurred on the outer estuary and redshank around many tributary river mouths. Curlew, the most ubiquitous species, was the only one concentrated on the inner estuary. Severe gales in both late December and mid-January concentrated all main species within fewer sectors, probably by the short-term removal of surface sediment from substantial areas. It is estimated that the proposed tidal barrage would eliminate intertidal areas accounting for between c. 40% (for shelduck and curlew) and 80% (for redshank) of current total low tide usage by the internationally important populations present.     

Availability of and access to critical habitats in regulated rivers: effects of low-head barriers on threatened lampreys

1.  Conservation of freshwater animal populations requires their access to, as well as sufficient availability of, critical habitats, such as those for reproduction. Abundant small-scale barriers may cause extensive fragmentation of freshwater habitat but, by comparison to larger structures their effects are rarely considered by catchment managers. The relationship between the distribution of, and access to, spawning habitat in a regulated river, characterized by abundant small barriers, was examined for river lamprey Lampetra fluviatilis , a threatened migratory fish.
2.  Telemetry of adult lamprey in the River Derwent, North East England was used to quantify upriver migration and access to spawning habitat, together with surveys of spawning habitat availability and spawning activity between 2002 and 2007.
3.  Access in to the Derwent appeared severely restricted by a tidal barrage, beyond which lamprey migrated rapidly in unobstructed reaches. Of all lamprey tagged in the lower 4 km of river, or ascending the barrage, 64% and 17% passed the first and second weirs respectively, with high flows crucial for this. Although over 98% of lamprey spawning habitat occurred more than 51 km upstream, on average just 1.8% of river lamprey spawners were recorded there.
4.  In order to protect or rehabilitate species or species assemblages, greater attention needs to be paid to the relative spatial distribution of low-head barriers and the resultant availability of key habitats within individual catchments. This is particularly important given the renewed emphasis internationally on low-head hydropower solutions as a source of renewable energy, and the rapid growth in numbers of low-head barriers in many catchments.     

Absence of a tidal component in the diel pattern of locomotory activity of sea catfish,Arius felis

Synopsis Sea catfish, tested individually for 3-day periods in an automated data acquisition system, displayed a nocturnal pattern of locomotor activity with 62% of the activity occurring during scotophase. In addition, there were two relative maxima of activity at 0700–0900 and 1300–1500 C.S.T. This diel pattern of activity could not be correlated with tidal phenomena in the fish's natural environment and is virtually identical to that exhibited by several freshwater catfish species. Thus, even though sea catfish are a primarily estuarine fish and subject to daily tidal fluctuations, tidal rhythmicity is apparently not used as a cue for diel activity patterns.     

The biology of the twaite shad, Alosa fallax fallax (Lacépède), in the Severn Estuary

The estuarine biology of the twaite shad was studied in the Severn Estuary. Adults enter the estuary at the start of the freshwater phase of their spawning migration between April and June. Peak immigration generally occurs in May and is associated with temperatures in the range 10.6–12.3°C. The mean (± s.d. ) instantaneous mortality rate for the mature population was 0.53±0.18. The effect of additional mortality on the spawning population was modelled assuming constant recruitment and no density-dependent effects.
Juvenile twaite shad are present in the estuary from July until they emigrate seaward during the autumn. A portion of these fish re-enter the estuary the following April–May and remain until late summer/early autumn before once more migrating seaward.
The 0 + age group feed mainly on harpacticoid and calanoid copepods and mysids, the relative preponderance of these in the diet being apparently related to tidal conditions. The possible implications of the proposed tidal power barrage in the Severn Estuary on the twaite shad population are discussed in relation to movement, diet and additional mortality of the mature population.     

Intertidal ecology and potential power impacts, Bay of Fundy, Canada

A large-scale tidal power project in the upper reaches of the Bay of Fundy would cause major changes in the tidal elevations of the headpond which would have a pronounced effect on intertidal ecology. The new mean low water level would be, on average, slightly above the present mean sea level whilst the new mean high water level would drop about 0.7 m. This would result in a much compressed intertidal zone. Mud and sand flats, below the present mean sea level, would be converted to sub-tidal habitat, whilst the high saltmarsh, flooded at present only on the highest spring tides, would become colonized by terrestrial vegetation. There would be major shifts in the relative importance of primary production by saltmarshes, intertidal microalgae and phytopiankton, but overall, it is likely that production would increase. Changes in both primary food sources and habitat area would affect the abundance of intertidal invertebrate organisms and the fish and migratory shorebirds that feed upon them.     

Ecological engineering analysis and eco-hydrodynamic simulation of tidal rivers in Shenzhen City of China

A comprehensive approach using ecological engineering analysis and eco-hydrodynamic simulation was conducted on the tidal rivers in Shenzhen City of China in this study. A tidal river along a near-shore city should be evaluated and regulated from a multidisciplinary point of view, focused especially on ecology, in order to maintain and enhance the ecological structure and function of the river. Firstly, eco-hydrodynamic control can be used, based on simulated modeling of tidal water circulation, to trace the distribution of pollutants and to predict circulation of tidal water. Using findings from this modeling effort, some water control facilities, such as additional channel connection and water gates, can be established. Appropriate operation strategy is to use tidal energy to promote effective water exchange in the water bodies and thereby improve water quality in the tidal river. Secondly, ecological engineering methods should be integrated with hydraulic measures to further improve the environment. Appropriate plant communities for this ecological engineering can be selected. Based on the simulated results of eco-hydrodynamic model, the optimum locations for adding reclaimed land can be determined. These ecological engineering methods are as follows: (1) it is necessary to calculate the ecological water requirements for the tidal river. The water effluent from the sewage treatment plant can be considered as reclaimed water and pumped to upstream of the tidal reach for reuse; (2) well planned aquatic plant systems composed of emergent, floating, and submergent plants can be used to promote water treatment; (3) the configuration of the engineered landscape should give preference to indigenous plants and appropriate non-indigenous plant species; (4) constructed wetlands, especially mangroves at coastal city sites, can also improve the tidal river aquatic environment.     

Involvement of phospholipase A2 in Pseudomonas aeruginosa-mediated PMN transepithelial migration

Oxidative damage to surfactant can decrease lung function in vivo. In the current study, our two objectives were: 1) to examine whether the adverse effects of oxidized surfactant would be accentuated in animals exposed to high tidal volume ventilation, and 2) to test whether supplementation with surfactant protein A (SP-A) could improve the function of oxidized surfactant in vivo. The first objective was addressed by evaluating the response of surfactant-deficient rats administered normal or oxidized surfactant and then subjected to low tidal volume (6 ml/kg) or high tidal volume (12 ml/kg) mechanical ventilation. Under low tidal volume conditions, rats administered oxidized surfactant had impaired lung function, as determined by lung compliance and arterial blood gas analysis, compared with nonoxidized controls. Animals subjected to high tidal volume ventilation had impaired lung function compared with low tidal volume groups, regardless of the oxidative status of the surfactant. The second experiment demonstrated a significantly superior physiological response in surfactant-deficient rats receiving SP-A containing oxidized surfactant compared with oxidized surfactant. Lavage analysis at the end of the in vivo experimentation showed no differences in the recovery of oxidized surfactant compared with nonoxidized surfactant. We conclude that minimizing excessive lung stretch during mechanical ventilation is important in the context of exogenous surfactant supplementation and that SP-A has an important biophysical role in surfactant function in conditions of oxidative stress. Furthermore, the oxidative status of the surfactant does not appear to affect the alveolar metabolism of this material.     

Tracking variations in airway caliber by using total respiratory vs. airway resistance in healthy and asthmatic subjects.

An index of airway caliber can be tracked in near-real time by measuring airway resistance (Raw) as indicated by lung resistance at 8 Hz. These measurements require the placing of an esophageal balloon. The objective of this study was to establish whether total respiratory system resistance (Rrs) could be used rather than Raw to track airway caliber, thereby not requiring an esophageal balloon. Rrs includes the resistance of the chest wall (Rcw). We used a recursive least squares approach to track Raw and Rrs at 8 Hz in seven healthy and seven asthmatic subjects during tidal breathing and a deep inspiration (DI). In both subject groups, Rrs was significantly higher than Raw during tidal breathing at baseline and postchallenge. However, at total lung capacity, Raw and Rrs became equivalent. Measured with this approach, Rcw appears volume dependent, having a magnitude of 0.5-1.0 cmH2O. l-1. s during tidal breathing and decreasing to zero at total lung capacity. When resistances are converted to an effective diameter, Rrs data overestimate the increase in diameter during a DI. Simulation studies suggest that the decrease in apparent Rcw during a DI is a consequence of airway opening flow underestimating chest wall flow at increased lung volume. We conclude that the volume dependence of Rcw can bias the presumed net change in airway caliber during tidal breathing and a DI but would not distort assessment of maximum airway dilation.     

江苏沿海滩涂围垦与社会经济发展的耦合关系

沿海滩涂湿地是脆弱的生态敏感区,滩涂围垦是沿海国家和地区拓展土地资源的重要方式之一。近年,沿海地区快速城市化下的滩涂围垦导致了沿海湿地生态系统退化等一系列环境问题。基于环境库兹涅茨曲线（Environmental Kuznets Curve,EKC）模型,以江苏北部沿海湿地为研究区,结合遥感影像和社会经济数据,刻画滩涂围垦过程、强度及社会经济发展过程,揭示近40年江苏沿海滩涂围垦主要类型、阶段性变化特征,阐述滩涂围垦与社会经济发展的耦合关系。研究结果显示,养殖水体扩张是近40年江苏滩涂围垦利用的主要方式;相比养殖水体聚集发展的盐城市,以启东为典型代表的南通市经历了相对较完整的养殖水体的滩涂围垦过程,其养殖水体面积与区域渔业产值存在指数关系,即当人均地区产值达到约9.55万元时,区域渔业产值的增长不再以通过围垦增加养殖水体面积为主要途径;从江苏沿海滩涂围垦来看,滩涂围垦与社会经济发展之间存在典型倒U型曲线关系。苏北滩涂围垦可分为3个阶段,初期阶段（1980-2005年）,滩涂围垦随着经济发展而急剧增加;中期（2005-2014年）,当人均GDP约为3.64×10⁴元时滩涂围垦速度达最大;后期（2014-2018年）,滩涂围垦随着经济发展呈现下降趋势。3个阶段中,单位滩涂围垦面积与人均GDP增长关系由4.11元/km²,17.08元/km²增加至60.77元/km²,呈显著增加的趋势。经济发展,农业和农村经济改革以及国家和地方各级政策均对滩涂围垦具有重要影响。严格的国家环境保护政策将是有效控制滩涂围垦、保护生态环境的重要手段。     

On the independence of barrage formation and heterokaryon incompatibility in Neurospora crassa

A barrage is a line or zone of demarcation that may develop at the interface where genetically different fungi meet. Barrage formation represents a type of nonself recognition that has often been attributed to the heterokaryon incompatibility system, which limits the co-occurrence of genetically different nuclei in the same cytoplasm during the asexual phase of the life cycle. While the genetic basis of the heterokaryon incompatibility system is well characterized in Neurospora crassa, barrage formation has not been thoroughly investigated. In addition to the previously described Standard Mating Reaction barrage, we identified at least three types of barrage in N. crassa; dark line, clear zone, and raised aggregate of hyphae. Barrage formation in N. crassa was evident only when paired mycelia were genetically different and only when confrontations were carried out on low nutrient growth media. Barrages were observed to occur in some cases between strains that were identical at all major heterokaryon incompatibility (het) loci and the mating-type locus, mat, which acts as a heterokaryon incompatibility locus during the vegetative phase of N. crassa. We also found examples where barrages did not form between strains that had genetic differences at het-6, het-c, and/or mat. Taken together, these results suggest that the genetic control of barrage formation in N. crassa can operate independently from that of heterokaryon incompatibility and mating type. Surprisingly, barrages were not observed to form when wild-collected strains of N. crassa were paired. However, an increase in the frequency of pairings that produced barrages was observed among strains obtained by back-crossing wild strains to laboratory strains, or through successive rounds of inbreeding of wild-derived strains, suggesting the presence in wild strains of genes that suppress barrage.     

Prediction of macrozoobenthic species distribution in the Korean Saemangeum tidal flat based on a logistic regression model of environmental parameters

This study aims to contribute to the development of heuristic statistical models, which are able to predict benthic macrofaunal responses to environmental gradients in coastal areas, such as tidal flats. Ecological response surfaces were derived for 15 intertidal macrobenthic species, using logistic regression based on three separate environmental parameters (shore level, mud content, and organic content) measured on the tidal flats of the Saemangeum estuary, Korea. The presence/absence of the 15 intertidal macrofauna was accurately predicted from each separate environmental factor in the environmental models, with a prediction accuracy of ~65–92%. Subsequently, geographical comparison was made between the mapped probability surfaces and maps of observed species occurrence. The results indicated that the models developed for different species exhibited a wide variety of functional forms, highlighting potential variability in species response to changes in habitat conditions, even for closely associated species with a similar trophic type. Our modeling approach was capable of predicting macrobenthic species distributions with a relatively high degree of accuracy, although the ecological processes controlling intertidal macrobenthic distribution could not be fully determined. Overall, good agreement between modeling results and field observations, with relatively high concordance regardless of target species, emphasized that such an approach would be of practical use in terms of ecosystem approach to tidal flat management.     

Differences in the activity rhythms of juvenile gobiid fish,Chasmichthys gulosus,from different tidal localities

Activity patterns of intertidal gobiid fish,Chasmichthys gulosus, collected from different tidal localities, were recorded in a constant environment. Gobies collected from a rocky shore with a large tidal range and a regular tidal regime displayed a ca. 12 hour rhythm in their activity pattern. Gobies from a rocky shore with a small tidal range and an irregular tidal regime, however, did not clearly display any such rhythm. The ecological implications of such activity rhythms are discussed from the viewpoints of feeding and avoidance of predators.     

Larval release rhythms and tidal exchange in the estuarine mudprawn, Upogebia africana

The mudprawn, Upogebia africana is common in intertidal regions of many South African estuaries. The life cycle is complex, incorporating a marine phase of development during the larval stages. Breeding peaks are in summer and first-stage larvae are released into the plankton at night. Maximum release activity and export to the marine environment follow a semi-lunar cycle synchronized to the time when high water in the estuary is crepuscular. This occurs after peak spring tidal amplitude. Estuarine reinvasion by postlarvae is also nocturnal, and maximum return occurs after neap's when low water at sea occurs around sunset. Rhythmic cycles of larval export and postlarval estuarine reinvasion are therefore asynchronous during the lunar cycle and are best explained by the timing of the change in light intensity relative to high and low water respectively. If maximum activity rhythms of Stage 1 and postlarvae are independent of tidal amplitude, then timing of maximum release and reinvasion during the lunar cycle would alter as the time of sunset shifts between solstices. Much of southern Africa experiences a semi-arid type climate and most estuaries close off from the sea for varying periods owing to sandbar development across tidal inlets. Larvae do not metamorphose if trapped in estuaries and recruitment ceases. Thus, mudprawn populations are directly affected by tidal inlet dynamics. In extreme cases populations become locally extinct if inlets remain closed for extended periods.