Discharge pulses of hydroelectric dams and their effects in the downstream limnological conditions: a case study in a large tropical river (SE Brazil)

To address daily fluctuations in electricity demands, the quantities of water passing through the turbines of hydropower plants can vary significantly (up to fourfold) during a 24‐h cycle. This study evaluates the effects of hourly variations in water discharges on the limnological conditions observed in two below‐dam river stretches. The study reservoirs, Capivara and Taquaruçu, are the 9th and 10th reservoirs in a cascade of dams in the Paranapanema River in south‐east Brazil. The reservoirs exhibit different trophic conditions, water retention times, thermal regimes and spillway positions. Capivara Reservoir is deeper, meso‐eutrophic, with a high water retention time and hypolimnetic discharges (32 m) varying between 500 and 1400 m³ s^?1. In contrast, Taquaruçu Reservoir is relatively shallow, oligo‐mesotrophic, and has a low retention time, with water discharges varying between 500 and 2000 m³ s^?1. Its turbine water intake zone also is more superficial (7 m). For two periods of the year, winter and summer, profiles of limnological measurements were developed in the lacustrine (above‐dam site) zones of the reservoirs, as well as in the downstream river stretches (below‐dam site). In both cases, the sampling was carried out at 4‐h intervals over a complete nictemeral cycle. The results demonstrated that the reservoir operating regime (water discharge variations) promoted significant differences in the conditions of the river below the dams, especially for water velocity, turbidity, and nutrient and suspended solids concentrations. The reservoir physical characteristics, including depth, thermal stratification and outlet structure, are also key factors influencing the limnology and water quality at the below‐dam sampling sites. In the case of Capivara Reservoir, for example, the low dissolved oxygen concentration (<5.0 mg L^?1) in its bottom water layer was transferred to the downstream river stretches during the summer. These study results demonstrated that it is important to continue such investigations as a means of verifying whether or not these high‐amplitude/low‐frequency variations could negatively affect the downstream river biota.     

Spatial effects of reservoirs on fish assemblages in Great Plains streams in Kansas,USA

Reservoirs are important components of modern aquatic ecosystems that have negative impacts on native aquatic biota both up‐ and downstream. We used a landscape‐scale geographic information system (GIS) approach to quantify the spatial effects of 19 large reservoirs on upstream prairie fish assemblages at 219 sites in Kansas, USA. We hypothesized that fish assemblage structure would vary with increasing distance from a reservoir and that the abundance of reservoir fishes in upstream reaches would decline with distance from a reservoir. Ordination of sample sites showed variation in fish assemblage structure occurred primarily across river basins and with stream size. Variance partitioning of a canonical ordination revealed that the pure effect of reservoir distance explained a small but significant (6%; F = 4.90, P = 0.002) amount of variability in fish assemblage structure in upstream reaches. Moreover, reservoir species catch per unit of effort (CPUE) significantly declined with distance from a reservoir, but only in fourth‐ and fifth‐ order streams (r² = 0.32, P < 0.001 and r² = 0.49, P < 0.001, respectively). Finally, a multivariate regression model including measures of stream size, catchment area, river basin, and reservoir distance successfully predicted CPUE of reservoir species at sites upstream of Kansas reservoirs (R² = 0.45, P < 0.001). Overall, we found significant upstream effects of reservoirs on Kansas stream fish assemblages, which over time has led to a general homogenization of fish assemblages because of species introductions and extirpations. However, characteristic reservoir species are present throughout these systems and the importance of spatial proximity to reservoirs is probably dependent on the availability of suitable habitat (e.g. deep pools) in these tributary streams. Copyright © 2005 John Wiley & Sons, Ltd.     

Small hydropower dam alters the taxonomic composition of benthic macroinvertebrate assemblages in a neotropical river

Hydropower dams substantially modify lotic ecosystems. Most studies regarding their ecological impacts are based on large dams and provide little information about the far more abundant effects of small hydropower dams. Our aim was to characterize the ecological effects of a small hydropower dam and run‐of‐the‐river reservoir on the structure of benthic macroinvertebrate assemblages in the Pandeiros River located in the neotropical savanna of Brazil. We tested the hypothesis that benthic macroinvertebrate assemblages in sites directly affected by the dam and reservoir would show a different taxonomic structure compared with those in free‐flowing sites. We expected to find sensitive native species associated with the free‐flowing sites, whereas resistant and non‐native invasive taxa were expected in impounded sites. We also explored associations between the presence of native and non‐native invasive taxa to each habitat type. We found that the structure of benthic macroinvertebrate assemblages was significantly different between free‐flowing and impounded sites. Also, we found that the dam and reservoir facilitated colonization of non‐native invasive species (Corbicula fluminea and Melanoides tuberculata) because only in those sites they were found in high abundance, in contrast to the free‐flowing sites. Although the environmental conditions imposed by the impoundment altered the structure of benthic macroinvertebrate assemblages, the effects were limited to sites closest to the dam. Our results highlight the necessity of understanding physical habitat changes caused by the presence and management of run‐of‐the‐river dams and reservoirs.     

Gradients in Catostomid Assemblages along a Reservoir Cascade

Serial impoundment of major rivers leads to alterations of natural flow dynamics and disrupts longitudinal connectivity. Catostomid fishes (suckers, family Catostomidae) are typically found in riverine or backwater habitats yet are able to persist in impounded river systems. To the detriment of conservation, there is limited information about distribution of catostomid fishes in impounded rivers. We examined the longitudinal distribution of catostomid fishes over 23 reservoirs of the Tennessee River reservoir cascade, encompassing approximately 1600 km. Our goal was to develop a basin‐scale perspective to guide conservation efforts. Catostomid species composition and assemblage structure changed longitudinally along the reservoir cascade. Catostomid species biodiversity was greatest in reservoirs lower in the cascade. Assemblage composition shifted from dominance by spotted sucker Minytrema melanops and buffalos Ictiobus spp. in the lower reservoirs to carpsuckers Carpiodes spp. midway through the cascade and redhorses Moxostoma spp. in the upper reservoirs. Most species did not extend the length of the cascade, and some species were rare, found in low numbers and in few reservoirs. The observed gradients in catostomid assemblages suggest the need for basin‐scale conservation measures focusing on three broad areas: (1) conservation and management of the up‐lake riverine reaches of the lower reservoirs, (2) maintenance of the access to quality habitat in tributaries to the upper reservoirs and (3) reintroductions into currently unoccupied habitat within species' historic distributions. Copyright © 2017 John Wiley & Sons, Ltd.     

Short‐term effects in a reduced flow stretch: The case of the Antas River in South Brazil

The building of adduction channels (penstocks) that conduct water from reservoirs to turbines, which are located kilometres from the dam, is becoming common, optimizing the electricity generation in small dams. This design creates a river stretch with reduced discharge between the dam and the powerhouse. This study evaluates the short‐term impacts of the below‐dam decrease in river flow on fish assemblages. Samples were collected in the reduced flow stretch of the Castro Alves Hydropower Plant (Antas River, Rio Grande do Sul, Brazil) before the reservoir started operating (January 2008; mean discharge of 103.7 m³/s) and immediately after operation began (March 2008; mean discharge of 12.4 m³/s). Sampling was conducted in distinct habitats of the reduced flow stretch (slow waters—gillnets, sand beaches—seining nets, structured littoral—electrofishing, and fast waters—cast nets) with a strongly standardized effort. The attributes of the fish assemblages were not negatively affected by the flow reduction in any habitat sampled. However, distinct changes in the spatial structure were observed considering the different types of habitat predominantly used by the species, which represents an entire reorganization of the fish assemblages in the short term. It is fundamental that these short‐term aspects be considered in the licensing of hydropower plants in addition to the long‐term changes.     

The effects of water retention time and watershed features on the limnology of two tropical reservoirs in Brazil

Although reservoirs are similar to natural lakes in many respects, such driving forces as water retention time and watershed features can play important roles in the limnology of manmade lakes. With the goal of investigating how these factors influence the limnology of tropical reservoirs, physical and chemical variables were measured at four sampling sites in two reservoirs in southern Brazil, from June 2002 to June 2003. Funil Reservoir is located in one of the most-populated areas in the country, in the Paraíba do Sul river basin, which drains and drastically influences the water quality of the reservoir. In contrast, Lajes Reservoir is located in a well-preserved area, with its water retention time varying from six to 30 times longer than for Funil Reservoir. Funil Reservoir is a turbid (median euphotic zone = 4.3 m), eutrophic reservoir (median total phosphorus (TP) = 3.1 µm ), with a high phytoplankton biomass (median chlorophyll-a concentration = 10.0 µg L⁻¹). In contrast, Lajes Reservoir is a transparent (median euphotic zone = 9.2 m), mesotrophic water system (median TP = 1.0 µm ), with a low phytoplankton biomass (median chlorophyll-a = 1.9 µg L⁻¹). Both reservoirs were stratified during the summer months, but isothermy was only observed in Funil Reservoir. Because of its short water retention time, Funil Reservoir is a much more dynamic system than Lajes Reservoir, with a pronounced temporal pattern related to changes in its water column and its phytoplankton biomass. Spatial heterogeneity is more evident in Lajes Reservoir, mainly as a consequence of its location in a preserved area, long water retention time and the presence of net cages for fish culture in the waterbody. The typical spatial zonation found in reservoirs, related to nutrient sedimentation and light availability, however, is more evident in Funil Reservoir than in Lajes Reservoir. Despite the similarities between these two water systems, which are in the same geographical region with similar climate, and are comparable in size, the distinct watershed features and water retention time are responsible for marked differences between these reservoirs.     

The effects of impoundment and non‐native species on a river food web in Mexico's central plateau

Habitat modifications, non‐native species and other anthropogenic impacts have restructured fish communities in lotic ecosystems of central Mexico. Conservation of native fishes requires understanding of food web changes resulting from the introduction of non‐native species, flow alteration and other human impacts. Using δ¹³C and δ¹⁵N analysis of fishes and invertebrates we investigated the effects of non‐native species, and reservoirs on food webs of the Laja river ecosystem (Guanajuato, central Mexico). We estimated trophic position (TP), relative trophic niche and food web dispersion at 11 reservoir, river and tailwater sites. Reservoirs and non‐native fishes modified food webs in the Laja. Food web dispersion was greater in reservoir than in tailwater and river sites. Reservoir food webs had the greatest range of δ¹³C values, indicating a more diverse resource base compared to rivers. δ¹³C values increased with distance downstream from reservoirs, suggesting declining subsidies of river food webs by reservoir productivity. Stable isotopes revealed potential effects of non‐native fishes on native fishes via predation or competition. Non‐native Micropterus salmoides were top predators in the system. Non‐natives Cyprinus carpio, Oreochromis mossambicus and Carassius auratus exhibited lowest TP in the Laja but overlapped significantly with most native species, indicating potential for resource competition. Native Chirostoma jordani was the only species with a significantly different trophic niche from all other fish. Many rivers in central Mexico share similar anthropogenic impacts and similar biotas, such that food web patterns described here are likely indicative of other river systems in central Mexico. Copyright © 2008 John Wiley & Sons, Ltd.     

金沙江梯级与三峡水库联合防洪调度研究

金沙江下游溪洛渡、向家坝梯级水库具有对川江沿岸重要城市和配合三峡水库对长江中下游进行防洪的双重防洪功能,如何科学划分金沙江梯级水库有限防洪库容、协调各防洪对象的调度方式,是溪洛渡、向家坝配合三峡防洪调度这一面向多区域防洪问题的关键科学问题。首先在金沙江溪洛渡、向家坝梯级规划设计防洪库容的基础上,按照所在河段防洪目标及配合三峡水库对中下游防洪的次序,探讨了川渝河段及长江中下游重点区域防洪对溪洛渡、向家坝梯级水库防洪库容的预留要求;进而分析了上、下游洪水遭遇类型及相关性,寻求针对不同区域防洪的库容共用空间,确定防洪库容分配方案;最后,分析了上游水库拦蓄方式对三峡入库洪水的影响,提出科学、合理、可行的金沙江溪洛渡、向家坝梯级配合三峡水库联合防洪的调度方式。分析认为,联合调度可有效减轻长江中游的防洪压力,经济效益显著。     

Ecological Assessment of a Sediment By‐pass Tunnel on a Receiving Stream in Switzerland

Reservoir siltation is a major problem worldwide, decreasing reservoir storage capacity, trapping entrained sediment, and altering the natural sediment regime. Sediment By‐pass Tunnels (SBTs) are used to connect reservoirs with downstream receiving waters during high flows to reduce sediment accumulation in the reservoir. When operating, large volumes of sediment‐laden waters are released into the receiving river for short periods of time (h). The aim of this study was to assess the impact of SBT events on the downstream riverine ecosystem. We measured physico‐chemical properties, sediment respiration, periphyton biomass and chlorophyll‐a, and macroinvertebrate assemblages along a 5‐km stretch of river during the first two years of SBT operation. During the study, five major SBT events occurred. Few changes were found in physico‐chemical properties, mainly due to the input of tributaries entering the system. Results showed a clear reduction in sediment respiration, an indicator of ecosystem metabolism, especially after large SBT events. Periphyton levels and macroinvertebrate density/richness also decreased after SBT events. A non‐metric multidimensional scaling distinguished both temporal and spatial shifts in macroinvertebrate assemblages after SBT events, being related to downstream distance and SBT event magnitude. In summary, SBT events acted as a pulse disturbance, similarly to natural floods, followed by recovery of measured ecosystem indicators. Sediment By‐pass Tunnel events can enhance sediment and flow connectivity, although the magnitude and frequency of operations should be controlled to prevent catastrophic disturbances. Copyright © 2017 John Wiley & Sons, Ltd.     

Impact of damming the Mogi-Guaçu River (São Paulo State, Brazil) on reservoir limnological variables

This study examined the effects of the damming of the Mogi‐Guaçu River (São Paulo State, Brazil) on the surface current velocity, water temperature, Secchi disc transparency, turbidity, colour, conductivity, pH and concentrations of nutrients and pigments. Surface‐water samples were taken before, during and after the reservoir was filled. Three sampling sites were established, one in the upper reach of the reservoir, one in the central area of the reservoir and one downstream from the dam. An additional sampling site was established on the Peixe River, the major tributary of the Mogi‐Guaçu in the study area. After filling of the reservoir, the surface current velocity tended to decrease, excepting downstream of the dam. The pH, and the Kjeldahl nitrogen, ammonia and chlorophyll‐a concentrations, tended to increase. The nitrite concentrations increased mainly in the upper reach and central area of the reservoir. The Secchi disc transparency and colour tended to decrease. A decreasing trend in dissolved oxygen concentration was observed mainly at the central area of reservoir. The conductivity tended to decrease, later returning to levels observed prior to reservoir filling. The nitrate, total phosphorus and orthophosphate concentrations exhibited an increasing trend after reservoir filling, followed by a decreasing concentration, reaching lower levels than those found prior to reservoir filling. High phaeophytin concentrations were measured for the filling phase. The observed water quality changes for Mogi‐Guaçu Reservoir generally were not as extreme as those observed for other tropical reservoirs. This trend was related to the operation of the reservoir. As Mogi‐Guaçu Reservoir is a run‐of‐the‐river reservoir with a short water retention time, the flooded area is not extensive and the retention of material and sedimentation upstream from the dam is not remarkable. These facts explain the small water quality changes observed for most of the variables after reservoir filling. The water quality decreased at the in‐lake site in the central part of the reservoir, attaining a hypereutrophic condition. This fact was related to the ageing of the reservoir and to cultural eutrophication.     

黄柏河流域水库底泥内源磷释放对水质影响分析

为分析宜昌市黄柏河流域饮用水水库内源磷释放对水质的影响,于2016年对流域内3座梯级水库的水体进行了逐月采样,在10月进行一次沉积物柱状样品的采集。根据样品分析数据,估算了沉积物-水界面磷释放通量,以及内源磷占磷总量的比例。结果发现:流域内玄庙观水库磷释放通量为0.492 mg/(m~2·d);天福庙水库为0.37 mg/(m~2·d),西北口水库为0.175 mg/(m~2·d);玄庙观水库年内内源磷释放最大月份占比为28.4%,天福庙水库为18.5%,西北口水库为19.5%;水库底泥内源磷释放已对水库水质产生了影响。研究结果为黄柏河流域饮用水水库的水质治理、保护提供了科学依据。     

梯级水库群超标洪水的协同应急调度研究

受全球气候变暖影响,极端天气事件发生频次增加,超标准洪水灾害的突发性、危害性和不可预见性更加突出,使得梯级水库面临的应急处置问题日益凸显,其中大坝溃决或连溃是梯级水库面临的最大威胁。针对超标洪水,实施水库群协同应急调度,是发挥水库综合利用效益的有效手段之一。本文选取最高水位最低化准则作为超标洪水协同应急调度模型的目标函数,采用逐步优化算法求解梯级水库群超标洪水协同应急调度模型,对梯级水库群超标洪水应急调度方案进行了有益的探索,并以大渡河流域瀑布沟水库、深溪沟水库和枕头坝一级水库为例,对其超标洪水过程进行调度计算,验证了上述模型的合理性和可靠性。结果表明:通过梯级水库群的协同应急调度,各水库在洪水前期预泄水库水量,尽可能腾出更多的水库库容,便于迎接后期可能发生的洪水,尽可能地降低各水库的水位,有效确保梯级水库群的防洪安全。研究成果对各大流域梯级水库群超标洪水的应急调度机制的建立具有重要的理论意义和工程实践价值。     

Spatial and seasonal variations in δ13C AND δ15N of particulate organic matter in a dam‐controlled subtropical river

Alteration of stream flow by artificial dams has been observed to be a significant factor for river water environmental changes. Therefore, understanding the biogeochemical processes occurring in the dam‐controlled rivers is important for water resource management. In this paper, δ¹³C and δ¹⁵N signatures of particulate organic matter (POM) in a dam‐controlled subtropical river, Beijiang River, in south China are reported for their spatial and seasonal distributions. POM affected by reservoirs is lighter in δ¹³C and heavier in δ¹⁵N relative to unaffected POM. In April, POM δ¹³C and δ¹⁵N values show less spatial variation in the mainstem, and suggest relatively greater contributions of terrestrial organic matter (OM) to POM. This could be related to the onset of summer monsoon that caused an abrupt increase in terrestrial input to the river by the monsoon‐induced enhancement of rainfall and runoff. In August and December, however, POM isotopic values for the sites affected by the Feilaixia dam reservoir in the middle of the river show marked changes, suggesting aquatic plankton proliferation in the reservoir during the times. Upstream from the reservoirs, POM isotopes are seasonally less varied and suggest mainly terrestrial origin. However, the isotopic signals of aquatic plankton proliferation in the reservoir in August and December is imprinted on the POM isotopic compositions downstream the reservoir, indicating far‐reaching influences of the reservoir on the downstream water environment. Copyright © 2008 John Wiley & Sons, Ltd.     

Typology of a Great River Using Fish Assemblages: Implications for the Bioassessment of the Danube River

Matching habitat typology and ecological assemblages can be useful in environmental management. We examined whether a priori defined riverine sections correspond with distinct fish assemblage types along the >2000 km long course of the Danube River, Europe. We also tested whether different sampling methods (i.e. day and night inshore electric fishing and offshore benthic trawling) provide consistent typological results. Analysis of assemblage similarities, indicator species analysis, non‐metric multidimensional scaling (NMDS) and k‐means analyses indicated that fish assemblages of the a priori defined Upper‐, Middle and Lower‐Danubian sections differed slightly, but within class variability was high. Although indicator species analysis showed that the Upper‐Danube belongs to the barbel (Barbus barbus) zone and the Middle‐ and Lower Danube belong to the bream (Abramis spp) zone, indicator values of the character species were generally low. The NMDS analyses suggested a weak gradient in assemblage structure along the course of the river with relatively high variability between neighbouring sites. K‐means analyses revealed that many sampling sites were in a different class than the a priori defined sections, and classifications at other group numbers did not lead to better classification outcome. Overall, the results do not suggest clearly distinguishable assemblage types with distinct boundaries in the potamal section of a great river. Nevertheless, the division of the potamon to smaller sections may explain some variability in fish assemblage structure, and could be used for bioassessment purposes. The study also shows the importance of multihabitat and multigear surveys in the typological assessment of great rivers. Copyright © 2016 John Wiley & Sons, Ltd.     

INTRA‐ANNUAL VARIATION IN RIVER–RESERVOIR INTERFACE FISH ASSEMBLAGES: IMPLICATIONS FOR FISH CONSERVATION AND MANAGEMENT IN REGULATED RIVERS

While much is known about the fish assemblages, habitats, and ecology of rivers and reservoirs, there has been limited study of the fish assemblages in transitional habitats between these lotic and lentic habitats. Data about these river–reservoir interface (RRI) fish assemblages are needed to guide integrated management efforts of river–reservoir ecosystems. The aim of these efforts is to recommend flows for natural river function, conserve native riverine fish assemblages, and maintain reservoir sport fisheries. We used a multigear approach to assess the fish assemblages of four RRIs in the Colorado River Basin, Texas. In addition to characterizing RRI fish assemblages using species richness and evenness metrics, and habitat‐use guilds, we used a multivariate approach to evaluate intra‐annual shifts in species composition and abundance. All RRIs had high species richness and evenness values and included both macrohabitat generalist and fluvial species. RRIs also contained high proportions of the fish species available within each river–reservoir ecosystem, ranging from 55% to 80%. Observed intra‐annual shifts in RRI fish assemblages resulted from changes in abundance of dominant species rather than changes in species composition, with abundance of most species increasing from early spring to summer. Fish species responsible for intra‐annual shifts included mostly floodplain and migratory species, suggesting that species both used littoral habitats within RRIs and migrated through RRIs to river and reservoir habitats. The diversity of fishes found within RRIs highlights the importance of including these areas in future conservation and management efforts of river–reservoir ecosystems. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of light and mixing regime on bloom‐forming phytoplankton in a subtropical reservoir

The joint influence of local climatic and hydrological conditions on the vertical distribution of bloom‐forming phytoplankton was analysed for the Salto Grande Reservoir, a large and enriched subtropical system on the Uruguay River (South America). Threshold of physical factors hindering or impeding blooms was obtained and then contrasted with worldwide observations in reservoirs at similar latitudes. Inflowing discharge, water level, and wind velocity intensity interacted with temperature, producing mixing and light regimes with overriding influence on the vertical distribution of Microcystis spp., Dolichospermum spp., and Ceratium furcoides , hence affecting their maximum abundance and biomass. Cyanobacteria (Microcystis  > Dolichospermum ) showed the most heterogeneous distribution in the depth profile during strong thermal stratification, showing surface scums prone to horizontal displacements. C. furcoides was evenly distributed in the water column in correspondence to windy periods. Blooms of both Cyanobacteria and dinoflagellates did not occur when inflowing discharge exceeded 10,000 m³ s^?1. Nutrient influence on phytoplankton vertical distribution appeared strongly subordinate to the effect of light. Highest microcystin concentrations (>WHO alert Level 2) occurred especially after blooms collapsed during highly turbulent situations.     

Ecology of an estuarine mysid shrimp in the Columbia River (USA)

The estuarine mysid, Neomysis mercedis, has colonized John Day and other run‐of‐the‐river Reservoirs of the Columbia River, over 400 km from the estuary. In John Day Reservoir N. mercedis numbers peaked (2 m^?3) in August in areas near the dam in association with lower water velocity and softer bottom than at the upstream sampling sites. Neomysis broods were primarily released in late spring and early fall. Gut content analysis showed that Neomysis feeds mostly on cladoceran zooplankton and rotifers in John Day Reservoir. Diel vertical migration was documented, with daytime distribution restricted to the bottom and preferentially to the soft‐textured sediments in the deepest areas. Common pelagic fishes in the reservoir, especially juvenile American shad (Alosa sapidissima) and chinook salmon (Oncorhynchus tshawytscha), are daytime zooplankton feeders that cannot prey on Neomysis owing to mysid diel vertical migration. Thus, Neomysis has become an important food web component in John Day Reservoir. We also collected N. mercedis further upstream in Lower Granite Reservoir, where another estuarine crustacean, Corophium salmonis, also is reported, underscoring the need to better understand the role of these estuarine invertebrates in the trophic ecology of the Columbia River. Copyright © 2006 John Wiley & Sons, Ltd.     

Characterization of water quality in a small hydropower plant reservoir in southern Brazil

The construction of large reservoirs can cause profound environmental changes. Reduced water flow, increased water residence time, thermal stratification, increased sedimentation rates and decreased dissolved oxygen concentrations are examples of such changes. These changes can affect water quality and the biota in the environments adapted to the natural conditions of a river. Small reservoirs developed in conjunction with hydropower plants, however, could reduce the degraded water quality. This study focuses on characterizing water quality in a small hydroelectric reservoir. The study reservoir has an area of 1.4 km² and a short water retention time. The Monte Claro Hydroelectric Power Plant is part of a complex consisting of three plants on the Antas River in the north‐west of Rio Grande do Sul state, Brazil. The reservoirs associated with these plants are operated as run‐of‐the‐river facilities. Monitoring results obtained by CERAN, the Energetic Company of Antas River (Companhia Energética Rio das Antas), were used to evaluate the reservoir water quality. Three samples were collected seasonally (spring, summer, autumn and winter) in the area of influence of this plant following the filling of the reservoir (2005–2008). The examined water quality parameters were electrical conductivity, colour, turbidity, alkalinity, pH, biological oxygen demand (BOD), chemical oxygen demand (COD), total phosphorus, dissolved oxygen, sulphate, nitrate, nitrite, ammonia, suspended and dissolved solids, chlorophyll‐a, total and faecal coliforms, water temperature and Secchi depth transparency. The results were interpreted using an index of water quality, Trophic State Index, reservoir water quality and CONAMA Regulation 357/05 (Brazilian legislation). Based on these analyses, no significant changes were exhibited in the water quality of the reservoir from the hydroelectric plant operation.     

乌江梯级开发对东风水库水温分布影响分析

为探讨梯级电站联合运行对下游水库水温影响,以乌江梯级开发电站中的东风水库为研究对象,根据东风水库2002年及2006年实测水温数据,分析了东风上游水库建成前后东风水库水温的变化过程,同时运用EFDC模型计算了东风水库上游引子渡和洪家渡水电站下泄低温水对东风库区表层水温及坝前垂向水温的影响。结果表明:梯级水库运行对天然河道水温的累积性影响程度跟主要支流水体温度及流量均有关,入库流量越大,东风库区相同位置库表水温越低,与天然水温的温差越大;下泄低温水温度越低,相同位置库表水温越低,与天然水温的温差越大;入库流量越大、入流温度与天然水温温差越大,低温水影响越大,上游下泄低温水对库区累积性作用越明显。     

Environmental variables and diversity index as a tool for management in tropical man‐made lakes

Fish and water samples were collected from various randomly situated sampling sites in two tropical man‐made lakes, Peechi and Pothundi reservoirs, in South India. The fish samples collected during 2014 to 2015 were taxonomically identified and the fish diversity indices of these reservoirs evaluated. The water samples collected were analysed for such environmental variables as pH, electrical conductivity, dissolved oxygen concentration, alkalinity, hardness, chlorophyll and nutrient concentrations. T‐tests indicated significant difference in both the fish diversity and environmental variables between these two reservoirs. The Pearson correlation test identified electrical conductivity as a highly correlated environmental variable to the ichthyodiversity index in Peechi and Pothundi reservoirs, with coefficients of 0.939 and 0.7012, respectively. Principal co‐ordinate analysis also was conducted on the variables to identify the best combination of variables subjective to the particular sampling site influencing the fish diversity. The analyses explained 72.8% of the total variations for Peechi reservoir, which was represented with eigenvalues of 7.53 and 3.393, respectively, for the first two dimensions. A similar analysis of Pothundi reservoir produced eigenvalues 7.05 and 3.01, respectively, for the first two dimensions, explaining 67.1% of the total inertia. The individual factor maps (IFM‐I and IFM‐II) for Peechi and Pothundi reservoirs identified a high diversity at sampling site 3 in Peechi reservoir, and a similar finding for sites 3 and 7 in Pothundi reservoir, being related to the interactions with other environmental variables, which were greatly influenced by the predominance of macrophytes. The latter is a characteristic of rainfed tropical reservoirs, with special reference to the native fish diversity and environmental variables. The findings of this study suggest management decisions for any aquatic system may be considered after prior assessment of environmental variables and the ichthyodiversity index of the indicated waterbody.