Effects of hydropeaking on benthic invertebrate community composition in two central Norwegian rivers

Hydropower regulations can have dramatic impacts on river ecological communities. The operation of hydropower stations is related to power demands, but their releases in the receiving water body causes sudden changes in flow, which in turn affect the biota. The effects of such flow variations on benthic invertebrates is not fully understood. Here, we studied the effects of duration and intensity of hydropeaking on benthic invertebrates in two rivers over a 3.5‐year period. We used both quantitative (Surber) and semiquantitative (kick samples) sampling methods to compare the ramping zone with the permanently water covered zone downstream of the hydropower plant, and with corresponding unaffected upstream areas. The ramping zone had a different invertebrate community composition and lower benthic density than other areas, especially after hydropeaking. Mayflies and chironomids were most negatively affected by hydropeaking and oligochaetes largely unaffected. Chironomids and the mayfly Baetis rhodani were able to recolonize the ramping zone and almost reach densities similar to deeper areas within 48 days following hydropeaking. The relative abundance of filter feeders tended to increase and gatherers/collectors tended to decrease from the ramping zone towards the deep, permanently water covered areas. In corresponding areas upstream of the power plant, the relative abundance of different functional feeding groups was the same in the mid‐channel and shore sites. Our study shows that hydropeaking has clear impacts on the functional structure of benthic invertebrates below the power plants. The ecological impact of hydropeaking on invertebrate communities should thus be taken into account, for example, by reducing the amplitude and duration of flow fluctuations.     

Fish age and size distributions and species composition in a large,hydropeaking Prairie River

Fluctuations in river flows result from diverse natural and/or anthropogenic causes. Hydropeaking, an important anthropogenic flow alteration, results from the rapid increase or decrease of water releases from reservoirs at hydroelectric power stations to meet variable demand for electrical power, thereby altering the flow regime of the river downstream of the hydroelectric power station. Hydropeaking causes short‐term, artificial fluctuations in flow on an hourly, daily, and/or weekly basis. The frequent and regular occurrences of these high and low flow events are fundamentally different from natural flood and drought events and may affect fish fauna. We compared the fish species composition and fish age and size distributions in the Saskatchewan River (Saskatchewan, Canada) downstream of a hydropeaking facility with results from an unaffected Reference Site situated upstream of the reservoir. Lower fish diversity was observed in the 2 downstream sites (Sites 1 and 2, number of species = 11 and 9, respectively) closest to Generating Station in comparison to Site 3 (n = 15) situated further downstream and the upstream reference site (n = 13). There was no difference in the age–length relationship of any of the fish species above and below the Generating Station suggesting that fish grew at the same rates. However, lower numbers of small‐bodied and juvenile fish were caught downstream of the Generating Station suggesting the possibility of increased mortality, decreased habitat suitability, or altered behaviour of small fish downstream of the dam. These data illustrate potential impacts of hydropeaking power stations and has management implications.     

Effects of cold and warm thermopeaking on drift and stranding of juvenile European grayling (Thymallus thymallus)

Intermittent water releases from hydropower plants, called hydropeaking, negatively affect river biota. The impacts mainly depend on hydrological alterations, but changes in physical habitat conditions are suspected to be co-responsible. For example, hydropeaking accompanied by a sudden change of water temperature in the downstream river—called thermopeaking—is also presumed to impair aquatic ecosystems. Still, knowledge about these thermopeaking impacts on aquatic species and life-stages is limited. We performed flume experiments under semi-natural conditions to fill this knowledge gap, simulating single hydropeaking events with a change in water temperature. As response parameters, we quantified the drift and stranding of early life-stages of European grayling (Thymallus thymallus L.), a key fish species of Alpine hydropeaking rivers. Hydropeaking events with a decrease in water temperature (“cold thermopeaking”) led to significantly higher downstream drift (mean = 51%) than events with increasing water temperature (“warm thermopeaking”, mean = 27%). Moreover, during cold thermopeaking, a comparably high fish drift was recorded up to 45 min after the start of peak flows. In contrast, drift rates quickly decreased after 15 min during warm thermopeaking. Remarkably, the spatial distribution of downstream drift along gravel bars during cold thermopeaking showed the opposite pattern compared to those triggered by warm thermopeaking events indicating different behavioral responses. Furthermore, the stranding rates of the cold thermopeaking trials were twice as high (mean = 31%) as those of the warm thermopeaking experiments (mean = 14%). The outcomes present vital information for improving mitigation measures and adapting environmental guidelines.     

Past hydraulics influence microhabitat selection by invertebrates and fish in hydropeaking rivers

Hydropeaking hydropower plants are the main source of renewable energy, meeting sub-daily peaks in electricity demand. They induce rapid artificial flow variations, highly variable velocities, drift, and stranding risks for aquatic organisms. In hydropeaking reaches, microhabitat selection likely depends on both present and past hydraulics (flow velocity and water depth); this study aims to assess their relative impact. For this purpose, we used observations of fish abundance in 1,180 microhabitats (507 sampled by electrofishing, 673 by snorkeling) and of invertebrate abundance in 36 microhabitats (hyporheic and benthic) in a medium-sized hydropeaking river. We described past hydraulics of microhabitats over the 15 days preceding sampling, using a 2D hydrodynamic model, by identifying microhabitats dewatering (drying during >10 hr) or with high-velocity conditions (>1.3 m s⁻¹ during >10 hr). Invertebrates guilds (defined based on their selection of present hydraulics in rivers without hydropeaking) responded significantly to past hydraulics, with abundances 3.5–15.3 times lower in dewatering habitats. Selection for present hydraulics by invertebrates was different from that observed in rivers without hydropeaking. For more mobile fish, responses were weaker and different, with a “bank” guild selecting dewatering microhabitats and, secondarily, a “midstream” guild avoiding them. Selection of present hydraulics by fish was similar to that observed in rivers without hydropeaking. Overall, past hydraulics influenced microhabitat selection, with stronger effects on invertebrates and stronger effects of dewatering than of high past velocities. However, high past velocities force fish to move and invertebrates to experience a large range of velocity.     

Invertebrate drift patterns in a regulated river: dams,periphyton biomass or longitudinal patterns?

Macroinvertebrate drift was sampled at 15 sites along the Tongariro River, New Zealand above and below two hydroelectric dams. Sixty‐seven invertebrate taxa were collected in the drift. Trichoptera (31) were the most diverse, followed by Diptera (13), Ephemeroptera (8) and Plecoptera (8). However, chironomidae were the numerically dominant taxa in the drift throughout the river and represented over 80% of all animals collected. Of these, Orthocladiinae and Diamesinae were the most abundant. Taxonomic richness declined with distance downstream and peaked at sites with intermediate levels of periphyton biomass. The per cent of Ephemeroptera, Plecoptera and Trichoptera (EPT) was 3–4 times higher in the unregulated section of the river and declined exponentially with both distance downstream and increase in periphyton biomass, but densities were similar along the river. Of the measured environmental variables periphyton biomass was most closely linked with drift community structure. Periphyton biomass was six times higher in the lower section of the river than the upper unregulated section. The autocorrelation between periphyton biomass and distance downstream complicates the interpretation of results. However, because of the distinct differences between above and below dam sections of river in periphyton biomass and the strong link between it and invertebrate drift we suggest that the alteration of flow patterns by the hydroelectric dams and the associated shift in periphyton biomass is the most likely explanation for invertebrate drift patterns in the river. Copyright © 2009 John Wiley & Sons, Ltd.     

Influence of hydropeaking on the distribution and larval development of the Plecoptera from a mountain stream

The downstream distribution and larval development of the Plecoptera from a Pyrenean stream were studied upstream and downstream of a hydroelectric power plant with intermittent hypolimnetic releases. During power generation, flow and temperature were the two main environmental factors modified. The downstream distribution of the various taxa reflected both the impact of hydropeaking and the natural zonation. The lowest densities and biomasses were estimated at 700 m downstream from the plant, underlining the prominent role of hydropeaking. Above the plant, Plecoptera larvae showed a constant drift due to accidental dislodgement, and behavioural drift was mainly nocturnal. Below the plant, the flushing action of peaking flows added to this a catastrophic drift, which was even higher since the amplitude between natural flow and peak flow was elevated. The life cycle patterns and the growth rates of the five dominating species (Siphonoperla torrentium, Isoperla acicularis, Perla grandis, Amphinemura sulcicollis, Protonemura beatensis) were similar at the various sampling sites, and only slight differences in hatching and/or emergence periods were recorded. The Plecoptera of the Oriège complete their larval development during periods where artificial thermal fluctuations are low and have a minor effect on the populations: from autumn to spring—i.e. when the temperatures remain rather low and during snow melt flood (e.g. S. torrentium, I. acicularis, A. sulcicollis)–or in summer when hypolimnetic releases increase the daily thermal fluctuations but reduce the mean diel temperatures (e.g. P. beatensis). Therefore, under this kind of river regulation, the plecopteran population structure and distribution is mainly governed by hydraulic disturbances. © 1998 John Wiley & Sons, Ltd.     

Influence of mild to severe flow alterations on invertebrates in three mountain streams

Invertebrates were compared upstream versus downstream from diversions on three small, headwater streams in the central Rocky Mountains, USA. Flow alteration of these streams varied from mild (some aspect of all natural flow components was transferred downstream) to severe (nearly 100% of the flow was diverted for 10–11 months of the year). The analysis was separated into periods of frequent (diversion gates often opened and closed; April–October) and infrequent flow fluctuations (stable low flows due to constant diversion; November–March). Invertebrates appeared resilient to mild flow alterations as neither the abundance, diversity, nor spatial and temporal variation in abundance and diversity differed upstream versus downstream during either period. In severely diverted streams, however, total invertebrate density downstream from the diversion was only 50% of upstream. Invertebrate diversity was also reduced; ten taxa abundant upstream were absent in downstream sections. Chironomids, ostracods and Ameletus spp. comprised 80% of total invertebrate density during constant, low flow conditions in the severely diverted streams. Although all taxa in the severely diverted streams recovered (drift) during the period of frequent flow fluctuations, spatial and temporal variation (coefficient of variation) in both density and the number of taxa was significantly greater downstream. Depending on the frequency with which free‐flowing conditions were re‐established, many invertebrate populations (especially mayflies and some stoneflies) declined or were even locally extirpated (e.g. Hesperoperla pacifica, Megarcys signata, Neothremma alicia, Polycelis coronata). Downstream communities in severely diverted tributaries appeared to fluctuate between two stable endpoints; a depauperate low‐flow community dominated by chironomids and ostracods and a more abundant and diverse natural‐flow community dominated by mayflies, chironomids, ostracods, stoneflies and caddisflies. Water abstraction (extent and timing of diversion) could be managed to minimize risks to downstream ecological resources.     

Peaking hydropower and fish assemblages: an example from the Tallapoosa River,AL

Dams alter many aspects of riverine environments and can have broad effects on aquatic organisms and habitats both upstream and downstream. While dams and associated reservoirs can provide many services to people (hydropower, recreation, flood control, and navigation), they can also negatively affect riverine ecosystems. In particular, hydropeaking dams affect downstream fish habitats by increasing variability in discharge and temperature. To assess the effects of Harris Dam on the Tallapoosa River, AL, operating under an adaptive management plan implemented in 2005, we sampled fish for community analyses from four sites on the river: three in the regulated reach downstream of the dam, and one unregulated site upstream. Fish were collected every other month using boat/barge electrofishing. We used Shannon's H, nonmetric multidimensional scaling (NMDS), a multiresponse permutation procedure (MRPP), and indicator species analysis to quantify patterns in fish assemblage structure and determine how assemblages varied among sites. NMDS and MRPP indicated significant fish assemblage differences among sites, with the tailrace fish assemblage being distinct from the other downstream sites and sites becoming more similar to the upstream, unregulated site (relative to fish assemblages) with distance downstream of the tailrace. The tailrace fish assemblage included higher proportions of rheophilic species that may be better suited to variable and/or high flows. Altered fish assemblages demonstrated continued effects of Harris Dam on the downstream aquatic systems, particularly close to the dam. These effects may indicate that further mitigation should be considered depending on conservation and management goals.     

Growth,Condition and Survival of Three Forage Fish Species Exposed to Two Different Experimental Hydropeaking Regimes in a Regulated River

Hydroelectric dam operation can alter discharge and temperature patterns, impacting fish populations downstream. Previous investigations into the effects of river regulation on fish have focused on a single species within a river, yet different results among studies suggest the potential for species‐specific impacts. Here, we compare the impacts of two different hydropeaking regimes relative to a naturally flowing river on three ecologically important members of the forage fish community: longnose dace (Rhinichthys cataractae), slimy sculpin (Cottus cognatus) and trout‐perch (Percopsis omiscomaycus). Annual growth, estimated from otolith back‐calculations, was higher for each of the species in the regulated river relative to the naturally flowing river but did not differ between hydropeaking regimes. Condition was assessed using weight–length relationships and differed between rivers for each species, and between hydropeaking regimes for longnose dace and slimy sculpin. Survival of longnose dace and slimy sculpin was lower in the regulated river relative to the naturally flowing river, but comparable between rivers for trout‐perch. Annual growth was significantly related to mean summer discharge in the regulated river and to mean summer water temperature in the naturally flowing river for each species, and significantly different slopes among species indicate species‐specific responses to discharge and temperature alterations. This study demonstrates different biological responses among fish species within rivers to regulation in general, as well as to specific hydropeaking regimes. Future studies should focus on multiple species and multiple indicators of fish health to more fully characterize the impacts of river regulation on downstream fish communities. Copyright © 2016 John Wiley & Sons, Ltd.     

A probability-based model to quantify the impact of hydropeaking on habitat suitability in rivers

A negative effect of hydropower on river environment includes rapid changes in flow and habitat conditions. Any sudden flow change could force fish to move towards a refuge area in a short period of time, causing serious disturbances in the life cycle of the fish. A probability-based model was developed to quantify the impact of hydropeaking on habitat suitability for two fish species, brown trout (Salamo trutta) and Grayling (Thymallus thymallus). The model used habitat preference curves, river velocity and depth to develop the suitability maps. The suitability maps reveal that habitat suitability deteriorates as flow increases in the studied part of the river. The probability model showed that, on average, suitability indices are higher for adult grayling than juvenile trout in hydropeaking events in this part of the river. The method developed shows the potential to be used in river management and the evaluation of hydropeaking impacts in river systems affected by hydropower.     

Energy stores and mercury concentrations in a common minnow (spottail shiner,Notropis hudsonius) associated with a peaking hydroelectric dam

Peaking hydroelectric facilities release water from dams to match energy production with demand, often on a daily cycle. These fluctuating flows downstream can exert several potential stressors on organisms that may inhibit their growth, indirectly causing higher contaminant concentrations through reduced growth dilution. We collected spottail shiner (Notropis hudsonius) at two sites upstream and two sites downstream of a peaking hydroelectric dam in east‐central Saskatchewan, Canada, and compared their body condition, triglyceride concentrations, and mercury concentrations. Condition decline was observed in one of two downstream sites from August to September, and the lowest triglyceride concentrations were consistently found downstream of the dam where hydropeaking had the most perceptible effects on the shoreline. Mercury concentrations were significantly greater at both downstream sites relative to upstream. Despite these results, inconsistencies in response parameters across sites and time limited our ability to isolate the effects of hydropeaking as a causative agent and suggest indirect effects such as shifts in algal and macroinvertebrate communities may be responsible for our observations. These results suggest that hydroelectric power generation may indirectly increase mercury concentrations in downstream fish, but more research will be required to determine the specific mechanisms by which this occurs. The results and data also provide useful insights into the physiology of wild spottail shiner populations, which can help to inform the development of these fish as a North American sentinel species.     

Hydropeaking effects on movement patterns of brown trout (Salmo trutta L.)

Radiotelemetry was used to investigate seasonal movement and home range of brown trout Salmo trutta (size range 188–420 mm fork length, N = 30) in two reaches of the Noguera Pallaresa River (Ebro Basin, north‐east Spain) subjected to different flow regulation schemes. NP‐1 reach is a bypassed section with near natural flow conditions, whereas the downstream reach NP‐2 is subjected to daily pulsed flow discharge (i.e., hydropeaking) from an upstream hydropower station. Significant differences in home range size (95% kernel estimates) and seasonal movement pattern between study reaches were found. Mean home range size was (μ ± SE) 112.1 ± 11.5 m in the bypassed reach NP‐1 and increased significantly in the hydropeaking reach NP‐2 up to 237.9 ± 37.2 m. There was a large individual variability in fish home range size within reaches. Most of the seasonal differences in fish movement among reaches were associated with the spawning season. Pulsed discharge events in NP‐2 during daytime in summer (lasting about 3 hr and increasing water flow from 1 to 20 m³/s) did not cause significant displacements in either upstream or downstream direction during the duration of the event. Our results highlight the importance of habitat connectivity in hydropeaking streams due to the need of brown trout to move large distances among complementary habitats, necessary to complete their life cycle, compared with unregulated or more stable streams.     

Flow amplitude or up-ramping rate? Quantifying single and combined effects on macroinvertebrate drift during hydropeaking simulations,considering sensitive traits

The hydrological regime of many alpine rivers is heavily altered due hydroelectric power generation. Hydropeaking operation produces frequent and irregular discharge fluctuations. Depending on the operational changes of flow amplitude and/or up-ramping rate as well as on river morphology, hydropeaking can lead to quick and strong variations in hydraulic stress affecting stream invertebrates and causing increased drift. In the present flume experimental study, we analyzed trait-specific drift reactions to single and combined effects of increased flow amplitude and up-ramping rate. We analyzed taxa according to their hydraulic habitat preference and flow exposure, as these traits seem to be indicative toward hydropeaking. The results show that the sudden increase in discharge and related flow velocity led to increased macroinvertebrate drift proportions in hydropeaking treatments, which differed significantly to parallel control runs (mean drift proportion in all hydropeaking setups: 13% compared to 5% in controls). Increasing flow amplitudes led to an increase in drift for most taxa and traits. This was particularly significant for taxa associated with lentic areas. The effect of the up-ramping rate on macroinvertebrate drift was nonsignificant but showed strong interactive effects with the flow amplitude, especially for taxa dwelling on the substrate surface. Our results therefore indicate that discharge-related parameters, such as flow velocity, primarily affect macroinvertebrate drift and the importance of the up-ramping rate increases, if certain discharge-related thresholds are exceeded. Vice versa, a reduction of the up-ramping rate at hydropeaking events with high flow amplitudes may reduce the effect on macroinvertebrate drift. Flow-exposed (surface) and flow-sensitive (lentic) taxa showed distinct drift reactions following hydropeaking treatments, which were significantly higher compared to effects on taxa associated to lotic and interstital habitats. Therefore, we conclude that both traits (hydraulic and vertical habitat preference) have proven as promising for analyzing hydropeaking effects. The trait classifications should be extended to a higher number of taxa and to different life stages as these may show different drift patterns.     

Seasonal effects of a hydropeaking dam on a downstream benthic macroinvertebrate community

As more hydroelectric dams regulate rivers to meet growing energy demands, there is ongoing concern about downstream effects, including impacts on downstream benthic macroinvertebrate (BMI) communities. Hydropeaking is a common hydroelectric practice where short‐term variation in power production leads to large and often rapid fluctuations in discharge and water level. There are key knowledge gaps on the ecosystem impacts of hydropeaking in large rivers, the seasonality of these impacts, and whether dams can be managed to lessen impacts. We assessed how patterns of hydropeaking affect abundance, taxonomic richness, and relative tolerance of BMIs in the Saskatchewan River (Saskatchewan, Canada). Reaches immediately (<2 km) downstream of the dam generally had high densities of BMIs and comparable taxonomic diversity relative to upstream locations but were characterized by lower ratios of sensitive (e.g., Ephemeroptera, Plecoptera, and Trichoptera) to tolerant (e.g., Chironomidae) taxa. The magnitude of effect varied with seasonal changes in discharge. Understanding the effects of river regulation on BMI biodiversity and river health has implications for mitigating the impacts of hydropeaking dams on downstream ecosystems. Although we demonstrated that a hydropeaking dam may contribute to a significantly different downstream BMI assemblage, we emphasize that seasonality is a key consideration. The greatest differences between upstream and downstream locations occurred in spring, suggesting standard methods of late summer and fall sampling may underestimate ecosystem‐scale impacts.     

Individual-based modelling of hydropeaking effects on brown trout and Atlantic salmon in a regulated river

We developed an individual-based model (IBM) to understand the effects of hydropeaking on growth, survival and distribution of age 0+ to 1+ juveniles for high-conservation value populations of native brown trout (Salmo trutta) and Atlantic salmon (S. salar) in river Gullspång, Sweden. We parameterized and applied inSTREAM (7.2-SD) and calibrated the model by comparing predicted versus observed growth under the current hydropeaking regime (n=>1,200 model fish for 365 days). Our objective was to model growth, survival and distribution under flow scenarios with and without hydropeaking. We observed that hydropeaking generally resulted in modest (~10%) negative effects on growth and survival of both species. Survival was more affected than was growth, smaller fish more affected than larger fish. On-peak (high) hydropeaking flows resulted in less profitable feeding conditions (less growth) and higher predation (lower survival). Thus, inSTREAM 7.2-SD appears to capture ecologically-relevant behavioral patterns under hydropeaking, for example, habitat selection, in response to rapid flow changes. Understanding such patterns for large rivers via manipulative field studies, even if possible, would be time-consuming and costly. Our study demonstrates the potential of IBMs as powerful tools for testing research questions and assessing and prioritizing alternative management strategies in regulated rivers.     

Hydropeaking impairs upstream salmonid spawning habitats in a restored Danube tributary

Hydropower is considered an important form of renewable energy, often involving hydropeaking. While the effects of hydropeaking on aquatic communities in areas downstream the dam are well understood, there is a lack of studies investigating potential impacts on tributaries located further upstream. In this study, we tested the effects of hydropeaking operations on upstream tributaries in a restored area of the Danube River, with a focus on the periods of backlog and release of water (up-ramping and down-ramping, respectively) during the filling and release of the reservoir. We used brown trout egg and larval mortality, linked to hydraulic, sedimentary and physiochemical changes in spawning grounds as an indicator. We compared hydropeaking-affected versus non-affected sites in upstream tributaries using HydroEcoSedimentary Tools (HESTs) loaded with clean gravels and brown trout eggs. Egg and larval mortalities were significantly higher in the hydropeaking-affected site with more than 80% egg mortality and almost 100% larval mortality compared to values of 55–63% and 80–85%, respectively, in non-affected sites. Spawning ground quality was significantly altered in the hydropeaking-affected site, where the highest mortalities were observed. Overall, duration of time periods with flow velocities close to zero were a key variable, potentially decreasing oxygen supply for eggs and larvae. Such periods of close to zero flow velocities were driven by backlog periods during the filling of the reservoir, revealing that such events can severely impair ecological integrity of spawning sites in tributaries upstream of dams by slowing the flows in upstream tributaries. Such altered processes can reduce fish population recruitment and need to be considered in future restoration projects.     

Assessing the benefit of flow constraints on the drifting invertebrate community of a regulated river

The downstream effects of hydroelectric dam operations on the abundance and diversity of the macroinvertebrate drift community of a regulated river were compared to that of an unregulated river, longitudinally and across three seasons. The regulated river operated under minimum flow and ramping rate (rate of change of flow) restrictions resulting in a ‘modified peaking’ regime, which means the facility could still peak, but at a slower rate and may not reach maximum turbine flows in the short time typically required to respond to market energy demand. The unregulated river had no dams or other water control structures. There was a trend of increasing abundance and diversity with distance from the dam on the regulated river, with no discernable trend along the unregulated river. While feeding guild proportions did not vary along the unregulated river, within the regulated river feeding guild proportions changed longitudinally as scrapers and collector gatherers increased, and filterers and predators decreased with distance downstream. The regulated river had similar or higher abundance across all seasons, with lower diversity in the spring. Seasonal average discharge was found to be lowest in summer on both rivers, with the regulated river benefiting from a minimum flow to help maintain higher abundance and diversity. Overall, our examination of the drifting invertebrate community on a regulated river support that operational constraints associated with modified peaking regimes helped mitigate the typical negative effects associated with river regulation. Copyright © 2010 Crown in the right of Canada and John Wiley & Sons, Ltd.     

Hydraulic classification of hydropeaking stages in a river reach

Hydropower is an important tool in the struggle for low-emission power production. In the Nordic countries, hydropower operating conditions are expected to change and work more in conjunction with intermittent power production. This in turn might increase the amount of hydropeaking events in the reaches downstream of hydropower plants. The current work investigates the influence of highly flexible, high-frequency hydropeaking on the hydrodynamics in the downstream reach. By quantifying four different dynamic stages in the study reach, the influence of the hydropeaking frequencies was investigated in the bypass reach of the Stornorrfors hydropower plant in the river Umeälven in northern Sweden. The hydrodynamics in the study reach were numerically modelled using the open source solver Delft3D. Eight different highly flexible future hydropeaking scenarios, varying from 12 to 60 flow changes per day, were considered. A method for identifying four hydropeaking stages—dewatering, dynamic, alternating and uniform —was introduced. The hydropeaking frequency directly decided the stage in most of the study reach. Furthermore, a Fourier analysis showed a significant difference between the stages and their corresponding power spectra. The classification of stages put forward in this work provides a novel, simple method to investigate the hydrodynamics due to hydropeaking in a river reach.     

PATTERNS OF BENTHIC INVERTEBRATE RICHNESS AND DIVERSITY IN THE REGULATED MAGPIE RIVER AND NEIGHBOURING NATURAL RIVERS

Fluctuating flows common in hydropeaking operations present biota with contrasting and challenging environments. Taxa that require a narrow range of water velocity or are not adapted to withstand sudden changes in discharge will likely be eliminated or competitively disadvantaged under such circumstances, perhaps leading to reduced biodiversity. I investigated the whole river, longitudinal and lateral patterns of benthic invertebrate abundance, Shannon–Wiener diversity, and rarefied taxa density and richness in the hydropeaking Magpie River and 16 neighbouring natural rivers. The Magpie River had greater abundances of benthic invertebrates than natural rivers, particularly near the dam. General differences in benthic community characteristics were largely based on the near absence of Odonata and Plecoptera and an abundance of snails and worms in the Magpie River. Family density, richness and diversity were greater in the regulated Magpie River and unregulated upper Magpie River than found in natural rivers. Longitudinally, family density, diversity and particularly richness increased downstream in the Magpie River. Laterally, diversity did not show any trends with increasing depth along transects, except at near the dam where it decreased sharply with depth, velocity, and an abundance of filter feeding invertebrates. Taxa density did not show any lateral trends in natural rivers, whereas in the Magpie River, it increased with water velocity and depth. The results of this study are contradictory to the general findings of others implying reduced biodiversity below hydropower facilities. Possible explanations are examined and contrasted with other examinations of benthic invertebrate response below hydropeaking dams. © Her Majesty the Queen in Right of Canada 2012.