Ecological consequences of hydropower development in Central America: impacts of small dams and water diversion on neotropical stream fish assemblages

Small dams for hydropower have caused widespread alteration of Central American rivers, yet much of recent development has gone undocumented by scientists and conservationists. We examined the ecological effects of a small hydropower plant (Doña Julia Hydroelectric Center) on two low‐order streams (the Puerto Viejo River and Quebradon stream) draining a mountainous area of Costa Rica. Operation of the Doña Julia plant has dewatered these streams, reducing discharge to ～10% of average annual flow. This study compared fish assemblage composition and aquatic habitat upstream and downstream of diversion dams on two streams and along a ～4 km dewatered reach of the Puerto Viejo River in an attempt to evaluate current instream flow recommendations for regulated Costa Rican streams. Our results indicated that fish assemblages directly upstream and downstream of the dam on the third order Puerto Viejo River were dissimilar, suggesting that the small dam (< 15 m high) hindered movement of fishes. Along the ～4 km dewatered reach of the Puerto Viejo River, species count increased with downstream distance from the dam. However, estimated species richness and overall fish abundance were not significantly correlated with downstream distance from the dam. Our results suggested that effects of stream dewatering may be most pronounced for a subset of species with more complex reproductive requirements, classified as equilibrium‐type species based on their life‐history. In the absence of changes to current operations, we expect that fish assemblages in the Puerto Viejo River will be increasingly dominated by opportunistic‐type, colonizing fish species. Operations of many other small hydropower plants in Costa Rica and other parts of Central America mirror those of Doña Julia; the methods and results of this study may be applicable to some of those projects. Copyright © 2006 John Wiley & Sons, Ltd.     

Effects of dam removal on brook trout in a Wisconsin stream

Dams create barriers to fish migration and dispersal in drainage basins, and the removal of dams is often viewed as a means of increasing habitat availability and restoring migratory routes of several fish species. However, these barriers can also isolate and protect native taxa from aggressive downstream invaders. We examined fish community composition two years prior to and two years after the removal of a pair of low‐head dams from Boulder Creek, Wisconsin, U.S.A. in 2003 to determine if removal of these potential barriers affected the resident population of native brook trout (Salvelinus fontinalis). Despite the presence of other taxa in the downstream reaches, and in other similar streams adjacent to the Boulder Creek (including the brown trout, Salmo trutta), no new species had colonized the Boulder Creek in the two years following dam removal. The adults catch per unit effort (CPUE) was lower and the young‐of‐the‐year catch per unit effort (YOY CPUE) was higher in 2005 than in 2001 in all reaches, but the magnitude of these changes was substantially larger in the two dam‐affected sample reaches relative to an upstream reference reach, indicating a localized effect of the removal. Total length of the adults and the YOY and the adult body condition did not vary between years or among reaches. Thus, despite changes in numbers of adults and the YOYs in some sections of the stream, the lack of new fish species invading Boulder Creek and the limited extent of population change in brook trout indicate that dam removal had a minor effect on these native salmonids in the first two years of the post‐removal. Copyright © 2007 John Wiley & Sons, Ltd.     

Impact of weirs on fish communities in a piedmont stream

The impact of large dams on fish communities is much better documented than that of weirs. This paper investigates the influence of weirs on fish community patterns along a piedmont river (the River Viaur). Presence/absence of species was obtained distant from a weir (NW), and immediately downstream (DW) and immediately upstream (UW) of the weir. More than half of the species captured were non‐native, probably introduced when upstream reservoirs were built. Most of these species were eurytopic or limnophilic. Species richness at UW sites and the number of introduced species found at each site did not depend on the distance from the source (DFS). UW sites had more introduced and limnophilic species than NW sites. Conversely, NW had more rheophilic species than UW. Furthermore, total species richness (SRT) was higher at DW than NW suggesting a direct influence of the weir on the downstream community. UW sites were characterized by the presence of tench, roach and bleak which were scarce in NW sites where brown trout predominated. Weirs appear to modify habitat to favour the colonization of introduced species, and therefore have influenced the structure of fish communities. The study underlines the importance of local conditions in artificially‐influenced rivers. Copyright © 2007 John Wiley & Sons, Ltd.     

Spatial patterns of fish communities in the Upper Mississippi River System: assessing fragmentation by low‐head dams

We assessed the similarity of fish communities among river reaches to assess community‐level fragmentation by low‐head dams in the Upper Mississippi River System (UMRS). The spatial coverage of standardized electrofishing sampling used in the Long Term Resource Monitoring Program (LTRMP) was extended for three of the six regional trend areas (RTA; pools 4, 13, and the Open River Reach) to include river reaches (outpools) immediately upstream and downstream from the standard RTA from 15 June to 31 October 2000. Additionally, pools 19 and 20 were sampled in September 2000. Cluster analysis and non‐metric multidimensional scaling of community composition and structure data revealed two major groups, upper and lower reaches, and four (for composition) or five (for structure) sub‐groupings of river reaches. In general, all outpools grouped with the nearest RTA for both community composition (no exception) and community structure (one exception). This suggests that fragmentation of fish communities from low‐head dams is minimal. Mantel correlations demonstrated strong inverse association between the similarity of fish communities with the distance between reaches. Habitat variables measured during electrofishing collections were significantly correlated with spatial variation of fish composition and community structure, but provided only marginal improvements to correlations with distance between reaches alone. Furthermore, habitat variability among river reaches also was related to distance between reaches. Determining the extent to which variation of fish communities is related to habitat or demographic processes (e.g. migration, larval drift, source‐sink dynamics) will be challenging for this system. Although low‐head dams on the UMRS may restrict movements for individuals and populations of certain fish species, we found little evidence that these effects have led to substantial, community‐level fragmentation. Copyright © 2006 John Wiley & Sons, Ltd.     

北江大型底栖无脊椎动物群落结构及水质的生物评价

对北江25个采样点的大型底栖无脊椎动物进行采样调查,并根据大型底栖无脊椎动物的群落结构特征对水质进行生物评价。研究中共采集到大型底栖无脊椎动物46属,分别隶属于15目31科,其中水生昆虫30属,占65.22%;软体动物8属,占17.39%;环节动物6属,占13.04%;甲壳动物2属,占4.35%。出现频率最高的3个种属分别为多足摇蚊属(Polypedilum)、巴蛭属(Barbronia)以及苏氏尾鳃蚓(Branchiurasowerbyi)。应用Shannon-Wiener多样性指数、Margalef多样性指数、Pielou均匀度指数、生物学污染指数BPI(biotic pollution index)、BI(biotic index)、FBI(family biotic index)、Goodnight-Whitley修正指数(GBI)7种生物指数对北江水质进行综合评价。结果表明:与20世纪80年代的评价结果相比,北江的大型底栖无脊椎动物在种类和数量等多方面均发生了较大的变化,生物多样性减少,耐污种所占比例增加,水质理化参数恶化;7种生物指数的评价结果存在一定的差异,部分指数之间存在较高的相关性,FBI指数和BPI指数的准确性和科学性更强,适用于北江水质的生物评价。在25个采样点中,6个采样点水质综合评价等级为较差或极差,16个采样点水质评价等级为一般,3个采样点水质等级为良好,整体水质属于一般的水平。人类活动对河流的水质状况造成了一定的影响。从水质生物学的角度衡量,北江水质整体呈现下降趋势。     

水利水电工程对鱼类的影响及保护措施

主要介绍水利水电工程建设对鱼类产卵、鱼类栖息地、鱼类洄游、鱼类区系等的影响,及水利水电工程导致的下泄水温、气体过饱和对鱼类的影响,同时介绍过鱼设施、人工增殖放流等保护措施;阐述水电工程对鱼类产卵的影响,提出根据不同鱼类的洄游时间、产卵和孵化条件要求,因时因地选取不同的引水方式组合,如底层取水、表层取水、中下层组合取水、...     

Effects of human activities on benthic macroinvertebrate community composition and water quality in the upper catchment of the Mara River Basin,Kenya

Land‐use changes in the upper reaches of the Mara River Basin have modified their biophysical and hydrological processes, resulting in water quality degradation in streams. This study was conducted to investigate the effects of human activities on water quality and macroinvertebrates along the Nyangores River, one of the main tributaries of the Mara River, Kenya. Seven sampling sites were chosen to correspond to the loss of riparian cover, livestock watering and human activities (e.g. laundry washing, bathing, cultivation, wastewater inputs, dumping of solid wastes from urban areas and settlements along the river). Physical–chemical variables and water samples for nutrient analyses were collected monthly from February to July 2012. Benthic macroinvertebrates also were collected at the same sites as for the water quality samples. Two‐way analysis of variance tested the significant differences for each variable among the sites. Similarity percentages (SIMPER) analysis was used to identify the key taxa contributing to differences between minimally disturbed and most disturbed conditions in the study area. The results indicated increased nutrient concentrations in agricultural and settlement areas. Significant (P < 0.05) spatial–temporal variations in water quality variables were observed. A total of 42 macroinvertebrate genera were encountered, with Ephemeroptera, Plecoptera and Trichoptera orders dominating the minimally disturbed areas, and Diptera dominating the disturbed areas receiving point and no‐point solid and liquid wastes, including nutrients, from urban areas and settlements. Canonical correspondence analysis (CCA) revealed significant relationships between macroinvertebrate communities and measured physicochemical variables. The results of this study indicate the need for protection of riparian zones and treatment of sewerage wastes before their release into waterways. The dumping of solid wastes near streams and rivers also is discouraged, to maintain the quality of surface waters and aquatic organisms.     

The influence of riparian shade on lowland stream water temperatures in southern England and their viability for brown trout

Suitable thermal conditions in streams are necessary for fish and predictions of future climate changes infer that water temperatures may regularly exceed tolerable ranges for key species. Riparian woodland is considered as a possible management tool for moderating future thermal conditions in streams for the benefit of fish communities. The spatial and temporal variation of stream water temperature was therefore investigated over 3 years in lowland rivers in the New Forest (southern England) to establish the suitability of the thermal regime for fish in relation to riparian shade in a warm water system. Riparian shade was found to have a marked influence on stream water temperature, particularly in terms of moderating diel temperature variation and limiting the number of days per year that maximum temperatures exceeded published thermal thresholds for brown trout. Expansion of riparian woodland offers potential to prevent water temperature exceeding incipient lethal limits for brown trout and other fish species. A relatively low level of shade (20–40%) was found to be effective in keeping summer temperatures below the incipient lethal limit for brown trout, but ca. 80% shade generally prevented water temperatures exceeding the range reported for optimum growth of brown trout. Higher levels of shade are likely to be necessary to protect temperature‐sensitive species from climate warming. © Crown copyright 2010.     

Response of epiphytic diatom communities from the tailwaters of glen Canyon Dam,Arizona, to elevated water temperature

The composition of epiphytic diatom communities from the cold tailwaters (12°C) of Glen Canyon Dam, Arizona, was analysed after a 2 wk incubation period at 12°C, 18°C and 21°C. There was a significant change in diatom composition between 12°C and 18°C, while no significant changes occurred between 18°C and 21°C. This suggests that a temperature threshold exists between 12°C and 18°C for the diatom flora in the tailwaters of Glen Canyon Dam. At the two higher water temperatures, smaller and closely adnate taxa became more important numerically than larger, upright, cold water stenotherms. The potential importance of this compositional shift in epiphytic diatoms on macroinvertebrate grazers has management implications regarding different release programs from reservoirs.     

Effects of draining and desilting a small weir on downstream fish and macroinvertebrates

Draining a small off-take weir in February 1991 before desilting introduced large amounts of sediment (at least 100m³) into the downstream creek. Increased suspended solids concentrations up to 4610 mg/l were recorded downstream during the release. Large volumes of sand were deposited close to the weir, with finer fractions (silt) deposited up to 2 km further downstream. Very fine silt was washed through the system to a major river 4.5 km below the weir. Over the first day of the release, at a site 2.1 km below the weir, there was a reduction of 19.4% in the total number of benthic macroinvertebrate taxa, and average reductions of 63.9% in the abundance of and 39.7% in the number of taxa per sample. Over the following 45 days the fauna recovered towards pre-release diversity and density. This recovery was not sustained and further reductions in diversity and abundance were recorded over the following five months, probably due to fresh disturbance from desilting works and further mobilization of sediment during high flows. A major storm and flood in September 1991 apparently flushed all additional silt from the creek and the macroinvertebrate fauna subsequently recovered to higher diversity and density levels than before the release. Compared with densities recorded in 1985 and 1988, the population of river blackfish (Gadopsis marmoratus) was reduced by 93% after the release at a site 250m downstream of the weir, with reductions of 81 and 59% at distances from the weir of 2.1 and 2.7 km, respectively. An additional reduction in this fish population occurred at the lower site in late 1991, probably due to further flushing of sediments during the September flood. Although reductions in fish numbers occurred across the whole population, greater reductions were recorded for the younger age classes. Small subsequent increases in fish numbers at upper sites during 1992-1993 indicated that a recovery of the blackfish population may be occurring through recruitment, but such a recovery will only be confirmed over the long term.     

高海拔地区混凝土坝温控防裂及工程应用研究

我国大型水电资源开发的重心已向云南、四川、青海和西藏等高海拔、高寒地区转移。此类地区气候环境条件恶劣,对混凝土大坝的筑坝技术、温控设计和施工方法提出了新的要求和挑战。本文重点分析介绍了高海拔地区的气候特征、筑坝材料特点、混凝土温度控制的特点以及混凝土温控防裂的关键技术和研究成果,并结合目前在建的西藏地区藏木水电站混凝土重力坝工程,介绍了高海拔、高寒地区混凝土温控技术的应用情况及存在问题。     

Influence of navigational lock and dam structures on adjacent fish communities in a major river system

We assessed the effects of a series of navigational lock and dam (L/D) structures on the composition of their adjacent fish communities. The Allegheny and Monongahela Rivers of southwestern Pennsylvania contain 14 lock and dam installations, eight and six respectively, which transform their river corridors into a series of contiguous pools. We selected two targeted fish assemblages, large‐bodied fishes (>250 mm TL) susceptible to gill‐netting and small‐bodied benthic species captured by trawling, for assessment upstream and downstream of each L/D installation. Gill nets were fished for approximately 16 h/net, while trawls were performed across three parallel 2‐min hauls. A total of 56 samples were collected over the spring/summers, 2004–2008. Species richness, abundance and the Jaccard Coefficient of Community Similarity (JCS) were calculated for each targeted fish community. Small‐bodied species, particularly darters, were depauperate upstream L/D while abundant and diverse downstream L/D on the Allegheny River. However, Monongahela River upstream and downstream L/D communities were similar. Jaccard Coefficient of Similarity values were comparable for both targeted fish assemblages on the Monongahela River, but differed markedly among Allegheny sites. While JCS values of large‐bodied fish assemblages of both rivers were strongly correlated with lockage frequency, this pattern was not replicated among small‐bodied assemblages. The near doubling of yearly lockages on the Monongahela River compared with the Allegheny may account for the similarity of its upstream and downstream ichthyofauna. Serial L/D navigational facilities on a large river may alter biotic connectivity patterns through physical isolation of adjacent fish communities. Copyright © 2010 John Wiley & Sons, Ltd.     

Characterizing physical habitat preferences and thermal refuge occupancy of brook trout (Salvelinus fontinalis) and Atlantic salmon (Salmo salar) at high river temperatures

Anthropogenic influences, including climate change, are increasing river temperatures in northern and temperate regions and threatening the thermal habitats of native salmonids. When river temperatures exceed the tolerance levels of brook trout and Atlantic salmon, individuals exhibit behavioural thermoregulation by seeking out cold‐water refugia – often created by tributaries and groundwater discharge. Thermal infrared (TIR) imagery was used to map cold‐water anomalies along a 53 km reach of the Cains River, New Brunswick. Trout and salmon parr did not use all identified thermal anomalies as refugia during higher river temperature periods (>21°C). Most small‐bodied trout (8–30 cm) were observed in 80% of the thermal anomalies sampled. Large‐bodied trout (>35 cm) required a more specific set of physical habitat conditions for suitable refugia, that is, 100% of observed large trout used 30% of the anomalies sampled and required water depths >65 cm within or adjacent to the anomaly. Densities of trout were significantly higher within anomalies compared with areas of ambient river temperature. Salmon parr were less aligned with thermal anomalies at the observed temperatures, that is, 59% were found in 65% of the sampled anomalies; and densities were not significantly different within/ outside anomalies. Salmon parr appeared to aggregate at 27°C, and after several events over 27°C variability in aggregation behaviour was observed – some fish aggregated at 25°C, others did not. We stipulate this is due to variances of thermal fatigue. Habitat suitability curves were developed for velocity, temperature, depth, substrate, and deep water availability to characterize conditions preferred by fish during high‐temperature events. These findings are useful for managers as our climate warms, and can potentially be used as a tool to help conserve and enhance thermal refugia for brook trout and Atlantic salmon in similar systems.     

灌溉水温对高寒地区水稻的影响及增温措施

水温是高寒地区制约水稻生产的主要因素之一。通过对水稻生长与水温的关系 ,灌溉水温对水稻生长和产量的影响以及各种提高灌溉水温的措施进行试验研究 ,取得了明显的增温、节水、增产效果     

隔水幕布改善深水水库下泄低温水效果研究

深水水库的低温水效应明显,以往常采用叠梁门、多层取水口等结构解决下泄低温水问题,但此类方案需在水库投入运行前完成且会造成一定的发电损失。针对已投入运行但未设计建设分层取水设施的水库水温问题,本文提出了在电站进水口前设置隔水幕布的新型水库低温水治理方案,建立三维水动力水温数值模拟模型,模拟分析了隔水幕布改善水库下泄低温水的效果及其主要影响因素。模拟结果表明,隔水幕布可使春夏季水库下泄水温提高2~8℃,幕布型式、淹没水深和坝前水温分布是影响改善效果的主要因素;并基于上述结论提出了隔水幕布方案的下泄水温预测公式。隔水幕布改善水库低温水的效果良好,具有广泛的推广应用前景。     

太阳辐射和地温对冰盖下水温的影响

太阳辐射可以透射穿过雪盖和冰盖与地温一起影响冰下水温的变化,加剧冰盖底部的融解和冲蚀,使得冰盖更易于崩溃开河。基于现有理论和原型观测研究成果,建立了描述太阳辐射在雪盖、冰盖和水体中的透射和吸收规律的数学模型;利用观测数据回归分析的方法,提出了太阳辐射可见光在水体中消光系数的参数化模型;然后研究了冰下水温的变化与太阳辐射和地温的函数关系。研究证实,冰下水温随太阳净辐射和地温的增加而升高,随雪厚和冰厚的增加而下降,并且与水体与冰盖的热交换系数成反比。此外,太阳辐射的透射可能使得开河期冰盖糙率不是减小,而是增大。     

A review of the effects of pollution and water scarcity on the stream biota of an intermittent Mediterranean basin

This review presents the main results of a 10‐year research study conducted in a Mediterranean intermittent basin (Evrotas River). By assembling the main outcomes of past and ongoing research projects, this study provides an overview of multiple stressor effects, with emphasis on water scarcity, focusing on hydro‐biogeochemical processes, as well as on spatial and temporal variations in benthic macroinvertebrates and fish fauna. The major impact in the basin has been the over‐exploitation of surface and groundwater resources, which, in combination with droughts, has resulted in the recurrent artificial desiccation of large parts of the hydrological network. The response to intermittency of the macroinvertebrate fauna is characterized by high resilience through various drought‐resistant evolutionary mechanisms, with assemblages recovering successfully after recurrent droughts. However, when pollution is evident in combination with drought, effects on benthic species richness, abundance, and assemblage structure can be severe. Similarly, pollution and water stress may result in massive fish mortalities due to hypoxic conditions, with fish populations requiring long periods to recover. However, the fish fauna appears to be relatively resilient to drought‐driven reach‐scale desiccation, and ultimately recovers, provided that aquatic refugia are available to supply colonists and that there are no physical barriers impeding recolonisation. Appropriate conservation measures are urgently required to address the effects of recurrent bouts of water stress, as well as of other stressors on the freshwater communities of the Evrotas River, both at the level of water management and of water policy and at the local and the national level.     

淮河流域问坝特征及其对水质 改善作用分析

以淮河部分干流、沙颖河水系、涡河水系、淮河干流南岸诸水系为研究范围,在详细介绍闸 坝基本资料的基拙上,阐述淮河流域闸坝分布特征,定性分析了闸坝对水质的改善作用,提出了闸坝 改善河流水质作用的量化指标。本研究对进一步了解淮河流域的闸坝情况和闸坝作用有借鉴意义,也 为闸坝改善河流水质的进一步研究提供了思路。