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.     

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.     

Massive Growth of the Invasive Algae Didymosphenia Geminata Associated with Discharges from a Mountain Reservoir Alters the Taxonomic and Functional Structure of Macroinvertebrate Community

The objective of this paper is to determine the alteration of the taxonomic composition and functional structure of macroinvertebrate community associated with a massive growth of the invasive algae Didymosphenia geminata downstream of a mountain reservoir (Pajares Reservoir, La Rioja, Northern Spain). As the massive growth of the alga disappears a few kilometres downstream of the reservoir associated with the input of nutrients from a nearby village sewage, we may compare the community composition between nine stations in three different conditions: three stations heavily affected by the presence of D. geminata, three further downstream stations without the algal massive growth but affected by river regulation and three control stations (unregulated and without the algae). Results show a significant disturbance of the composition and structure of macroinvertebrate community in sites affected by the stream flow regulation downstream of the dam compared with unregulated streams, but the alterations are more dramatic in the area where the growth of D. geminata is massive because of the total substrate occupation by the algal filaments. Scrapers and others invertebrates living on the coarse substrate are especially affected at such sites. Moreover, an important increase in the relative abundance of chironomids is associated with the algal massive growth, especially in case of Eukiefferiella devonica and Cricotopus spp., reducing the assemblage diversity and leading to the taxonomic and functional homogenization of the community. Changes in the reservoir management (such as releasing the water from surface rather than from the hypolimnion) may be useful to control the massive growth of D. geminata and thus reducing the effects of river regulation on macroinvertebrate assemblage composition. Copyright © 2014 John Wiley & Sons, Ltd.     

Discontinuity of trichopteran (caddisfly) communities in regulated waters of the clearwater river,Idaho, U.S.A.

Riverine trichopteran (caddisfly) communities were sampled seasonally at eight locations over a two-year period to determine if a multiple-level release hydroelectric dam created a faunal discontinuity along the longitudinal profile of the Clearwater River in northern Idaho. The confluence of a non-regulated river with a regulated reach provided an unusual opportunity to examine the recovery of community parameters in a semi-regulated river. A marked discontinuity in the caddisfly community occurred in the regulated reach immediately below the dam, reflected by greatly reduced diversity and abundance values, and by shifts in functional relationships. These faunal changes are primarily attributable to the modified temperature, discharge, and food resources induced by river regulation. The non-regulated river exerted a major mitigative effect on the trichopteran fauna below its confluence with the regulated reach, despite maintenance of semi-regulated conditions. Trichopteran community parameters approached near normal levels concomitant with partial reductions in flow fluctuations, and partial recovery of temperature and food resources. In addition, the non-regulated river provided an important colonization pathway for riverine species to enter the semi-regulated lower reaches.     

Ecological monitoring of fish assemblages downstream of a hydroelectric dam in French Guiana (South America)

Dam impacts on the downstream section of dammed rivers are known to be important for fish because of changes in the physical and chemical river characteristics. However, the available data seem to be insufficient to draw general conclusions regarding the transformation of fish communities. A hydroelectric dam was built on the Sinnamary River in French Guiana and closed in January 1994. From December 1991 to December 1996 fish collections were made from the downstream section. The results show a rapid decrease in fish abundance in the middle downstream course immediately after dam closure. This low abundance was observed until the end of the filling phase, when the flow was maintained at a minimum level. Afterwards, abundance returned to a level comparable with that prior to dam closure. Fish collection in different zones showed that the decrease in abundance was probably due to the escape of fish to shelter areas. Another marked effect was the reduction of sample diversity due to a decrease in species richness, as well as in the regularity of the distribution of species’ relative abundance. Examination of biological traits of species suggests that under these conditions feeding strategies could have been the most important factor affecting the abundance of populations. Copyright © 1999 John Wiley & Sons, Ltd.     

Assessing the recovery of fish assemblages downstream of hydrological barriers in India's Western Ghats

River flow regulation by dams and barrages threatens freshwater fish diversity globally. However, factors contributing to the recovery of fish communities downstream of barriers to river flow are not well understood. It is crucial to identify processes that might enable river restoration despite the presence of river barriers. In this study, we assess recovery of fish species, including endemics, downstream of large and small barriers in the Malaprabha basin in the Western Ghats of India. We define “fish species recovery” as the proportion of fish species occurring in river reaches downstream of barriers, of the species pool occurring in upstream unregulated segments with similar elevation, stream order, and habitat characteristics. As per the serial discontinuity concept, we predicted that recovery will reduce immediately after, but gradually increase with, increasing distance downstream of barriers, due to contributions from unregulated streams joining the river. As expected, fish recovery decreased immediately downstream of barriers and increased at greater distances and declined when the number of upstream barriers increased, indicating cumulative impacts. Dissolved oxygen and total alkalinity were positively and negatively correlated with both recovery and distance from barrier. Water temperature and rocky instream habitat influenced recovery positively, but independent of distance from barriers. Recovery of fish species, including Western Ghats endemics, was promising even under the current level of river regulation in the area, mainly due to connectivity with undammed tributaries. Strict limits on future stream regulation within already regulated basins will be critical for conservation of freshwater fish biodiversity in this region.     

Determining the effects of dams on subdaily variation in river flows at a whole‐basin scale

River regulation can alter the frequency and magnitude of subdaily flow variations causing major impacts on ecological structure and function. We developed an approach to quantify subdaily flow variation for multiple sites across a large watershed to assess the potential impacts of different dam operations (flood control, run‐of‐river hydropower and peaking hydropower) on natural communities. We used hourly flow data over a 9‐year period from 30 stream gages throughout the Connecticut River basin to calculate four metrics of subdaily flow variation and to compare sites downstream of dams with unregulated sites. Our objectives were to (1) determine the temporal scale of data needed to characterize subdaily variability; (2) compare the frequency of days with high subdaily flow variation downstream of dams and unregulated sites; (3) analyse the magnitude of subdaily variation at all sites and (4) identify individual sites that had subdaily variation significantly higher than unregulated locations. We found that estimates of flow variability based on daily mean flow data were not sufficient to characterize subdaily flow patterns. Alteration of subdaily flows was evident in the number of days natural ranges of variability were exceeded, rather than in the magnitude of subdaily variation, suggesting that all rivers may exhibit highly variable subdaily flows, but altered rivers exhibit this variability more frequently. Peaking hydropower facilities had the most highly altered subdaily flows; however, we observed significantly altered ranges of subdaily variability downstream of some flood‐control and run‐of‐river hydropower dams. Our analysis can be used to identify situations where dam operating procedures could be modified to reduce the level of hydrologic alteration. Copyright © 2009 John Wiley & Sons, Ltd.     

The downstream impacts of the burgomillodo reservoir,Spain

The Burgomillodo Dam, located in the middle Rio Duraton (north Spain, Duero Basin), has created a small eutrophic reservoir with a capacity of 15 × 10⁶ m ³ and a maximum depth of 40m. Burgomillodo Reservoir is solely used for producing hydroelectric power. The regulated flow pattern of hypolimnial waters is characterized by higher daytime flows than those by night, with low flows at weekends all the year round. The environmental impact generated by this hydropower scheme on the river downstream was assessed by comparing physiochemical characteristics and aquatic communities of an upstream site (reference station) with those of three downstream stations, which were located 0–2, 2–5, and 7–6 km below the dam. Water temperature, pH and dissolved oxygen were significantly lower downstream from the reservoir. Hardness, alkalinity, suspended inorganic matter, and conductivity had reduced annual variability below the dam. Photosynthetic activity was directly involved in the recovery of dissolved oxygen and pH values. Species richness and abundance of macrophytes increased just below the dam. Macrobenthic and fish communities were composed of higher numbers of potamic species. Number of taxa, density, biomass, and diversity were higher at the reference site, recovering their values as the distance below the reservoir increased. Macrobenthic trophic structure was changed by an increase in predators and filter feeders and a decrease in shredders. Environmental impact values for the macrobenthic community living just below the dam were higher than those for the fish community. It is concluded that the main physiochemical factors involved in environmental impacts were dissolved oxygen deficit and short-term flow fluctuations for the macrobenthic community, and oxygen deficit for the fish fauna. Benthic macroinvertebrates appear to be the best aquatic organisms for detecting changes and for reflecting the spatial recovery of environmental conditions.     

Long‐term faunal changes in a regulated and an unregulated stream—Cow Green thirty years on

Cow Green dam is situated in Northern England on the River Tees in a region with high average wind speeds (24 km h^?1), low average annual temperatures (circa 5°C) and average rainfall of 1800 mm. The River Tees was impounded by the Cow Green dam in 1970 and early studies revealed significant changes arising from flow regulation. This study compares macroinvertebrate communities in 2004 with those recorded in the first 5 years after impoundment in the Tees and in the unregulated Maize Beck. Nineteen of the 31 common taxa in the regulated sites declined in abundance by a factor of 5 or more. These included Hydra sp., Ancylus fluviatilis, Naididae, Heptageniidae, Leuctridae and Brachycentrus subnubilus. Some taxa, Lymnaea peregra, Ephemerella ignita, Hydroptila sp. increased in numbers, and others Hydropsychidae and Gammarus pulex declined at sites nearest the dam but increased downstream. In Maize Beck there were fewer changes. The changes in faunal communities in the Tees were evident from multivariate analyses where the Tees sites sampled in 2004 were separated from those sampled in the period 1972–1975, as a result of abundance changes in common taxa and the appearance of taxa not previously recorded. Maize Beck in contrast was characterized by few changes in abundance and no new taxa and samples from all years grouped together. The results suggest that the Tees communities have changed since 1975 and are still possibly undergoing change, although without evidence from intervening years this cannot be proved. A narrower range of environmental conditions and increased flow stability have led to a dynamically fragile community (indicated by observed changes in community diversity and abundance) which is very susceptible to perturbations because it has developed in their absence. Periphyton and reservoir plankton play an important role in structuring the faunal composition by creating an environment where biotic interactions are more likely. Increased interaction between components of the faunal community may account for the observed changes since 1975 in the regulated sites in contrast to the situation in the unregulated Maize Beck where there has been little change in faunal community between the original study and the 2004 survey. An unregulated natural flow regime continues to dominate the Maize Beck environment and the variable and unpredictable conditions have resulted in a dynamically robust faunal community. Copyright © 2006 John Wiley & Sons, Ltd.     

Biotic and abiotic gradients in a regulated high elevation Rocky mountain river

Samples were collected year-round over a one-year period at sites 250m, 500m, 1000m, 2300m, 5200m, and 11000m downstream from a hypolimnetic-release reservoir on the Blue River, Colorado, to examine biotic and abiotic gradients induced by river regulation. The impoundment had only minimal effects on river chemistry and chemical variables failed to exhibit discernible downstream patterns. The temperature regime was markedly altered by regulation and exhibited a distinct downstream recovery gradient. The progressive downstream increase in zoobenthos species diversity is attributed, in part, to the thermal recovery. The average size of mineral substratum particles was greater at sites nearest the dam, although cobble and pebble predominated at all sites. A downstream decrease in bed stability was accompanied by decreased water clarity and increases in scour and ice action. These factors may have accounted for the higher standing crops of periphyton near the dam and a shift from filamentous chlorophytes to a predominance of diatoms with increasing distance downstream. The amount of leaf detritus in the substratum increased downstream. The abundance of shredders, zoobenthic species that feed on leaf detritus, tracked the downstream increase in coarse sedimentary detritus. Spatial patterns of organic seston within the study reach, influenced partly by sloughing of periphyton, are thought to account for the downstream species replacement patterns exhibited within the filter-feeder guild.     

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.     

Patterns of channel adjustment to impoundment of the upper River Spey,Scotland (1942–2000)

Over the last 30 years, understanding of how river channel morphology adjusts to upstream impoundment has been improved considerably with clearwater erosion close to the dam and aggradation downstream of unregulated tributary confluences being identified. In a UK context our understanding of channel response to impoundment has been based principally on analysis of a number of regulated rivers using a time–space substitution approach but the temporal pattern of channel change was not fully observed. This paper details channel change over almost six decades following impoundment of the River Spey, Scotland, primarily via the use of cartographic and aerial photographic evidence. Channel change initially involved the formation of tributary confluence bars followed by bench development and vegetation colonization and development on the benches and gravel bars. Sixty years after impoundment, the channel is still adjusting its form at distance from the dam to be in quasi‐ equilibrium with its regulated flow regime; indeed adjustment was most rapid between 1989 to 1995. This accelerated adjustment is due to the occurrence of a greater number of large and geomorphologically significant flood events in this period. Sediment supply limitation from unregulated tributaries will have stemmed the rate of narrowing and bench development prior to 1989. This spatial and temporal pattern of adjustment supports, for the most part, the model advocated by Petts (Progress in Physical Geography, 1979, Vol. 3, pp. 329–362). The wider implications of the channel change for river conservation and management are addressed. Copyright © 2003 John Wiley & Sons, Ltd.     

THE MANAGEMENT MODES OF SEASONAL FLOODS AND THEIR IMPACT ON THE RELATIONSHIP BETWEEN CLIMATE AND STREAMFLOW DOWNSTREAM FROM DAMS IN QUEBEC (CANADA)

The goal of the study was to compare the modes of management of seasonal floods for different dams and to constrain their impact on the relationship between climate variables and streamflow downstream from the dams. At the Rawdon dam, downstream from which the Ouareau River is characterized by a natural‐type regulated flow regime, a ‘type A’ flood management mode prevails, in which the same rainfall and/or snowmelt events account for seasonal floods both in the unregulated (natural) stretch of river upstream from the dam and in the river downstream from the dam. As a result, seasonal floods in the natural setting and downstream from the dam are nearly synchronous. In contrast, downstream from the Matawin dam (Matawin River), which produces an inversion‐type regulated flow regime, the prevalent flood management modes are of types B and D, whereby seasonal floods observed upstream and downstream from the dam are not caused by the same rainfall and/or snowmelt events and, as a result, are not synchronous. This difference in seasonal flood management modes affects the interannual variability of the magnitude of seasonal daily maximum flows related to the seasonal floods. Thus, the interannual variability of these flows downstream from the Matawin dam differs significantly from that of flows upstream. No correlation is observed between climate variables and streamflow downstream from the Matawin dam. This absence of correlation disappears gradually at the annual scale, at which streamflow is correlated with rainfall, as is observed upstream from the dam. Copyright © 2013 John Wiley & Sons, Ltd.     

GEOMORPHOLOGICAL CONTROLS ON VEGETATION RESPONSES TO FLOW ALTERATIONS IN A MEDITERRANEAN STREAM (CENTRAL‐WESTERN SPAIN)

The expected recovery of the natural conditions of large regulated rivers over the distance downstream from a dam is limited by relative tributary size according to the Serial Discontinuity Concept; however, geomorphology may also influence the recovery process. We examined the woody vegetation of the riparian zone in seven river segments distributed along the regulated reach of the Tiétar River in central‐western Spain, which flows through two distinct geomorphic templates. Whereas the annual runoff has decreased by 30% on average along the entire studied reach following the construction of the Rosarito Dam and the initiation of field irrigation in the region, the magnitude and frequency of the peak flows decreased by 30% immediately downstream from the dam but recovered the natural values with the distance downstream. We evaluated the recovery patterns toward the natural riparian conditions by comparing woody species composition, diversity and distribution of vegetation patches established prior to and after dam completion. Our results did not indicate a recovery gradient of any of the analysed vegetation attributes downstream from the dam. Instead, we found that the difference in the slope of the stream channel and banks, the width of the valley and the size of substratum particles among the surveyed patches were factors that significantly mediated dam and tributary effects on vegetation and influenced the degree of vegetation recovery. Hence, the maintenance of the intensity of the flow alteration scheme by the numerous water withdrawals and the low tributary contributions, coupled with differential geomorphological characteristics along the reach, overwhelmed the natural tendency for the river to restore its natural conditions with distance downstream. Improving water management and, particularly, restoring endangered riparian ecosystems require a detailed understanding of existing and potential woody species behaviour across the geomorphological settings of rivers. Copyright © 2012 John Wiley & Sons, Ltd.     

Relationship between river surface level and fish assemblage in the Ocklawaha River,Florida

Understanding the relationship between river flows and levels and fish communities is important to setting minimum flow and level regulations designed to prevent ecological harm. We reviewed a long‐term Florida Fish and Wildlife Conservation Commission data set from the Ocklawaha River, Florida, to evaluate trends in fish abundance and fish communities relative to historical river levels. Fish data were collected using electrofishing at the Ocklawaha River, Florida, during 1983–1994. Electrofishing data were used to estimate catch per minute and biomass per minute of selected species, fish diversity, richness and evenness. Catch rate variables were compared among years and significant differences in abundance and community indices were related to historical water levels using multiple regression models. Results indicated that differences in abundance and community indices among years were more common at the site with increased river level variability. Regression models indicated that fish abundance and species richness were positively related to river levels, and species diversity was negatively related to variability in river level during the two years prior to sampling. Spotted sunfish Lepomis punctatus exhibited the most variability in species‐specific catch per effort and spotted sunfish abundance was positively related to river levels. Low river levels negatively influenced fish abundance and fish communities, and minimum flows in Florida should manage for the periodicity of low flow events to prevent sequential years of adverse effects on fish populations. Copyright © 2005 John Wiley & Sons, Ltd.     

Changes to herbaceous plant communities on a regulated desert river

Riparian plant communities are shaped by gradients of disturbance intensity and frequency and resource availability. Reservoir operation can alter the composition and abundance of riparian vegetation by changing the flood regime and by trapping fine sediments and associated nutrients within the reservoir system. We examined differences in herbaceous species richness, abundance and composition in Populus‐Salix stands along an unregulated and regulated reach of a river in semi‐arid Arizona, contrasted flood inundation frequency and edaphic conditions (soil moisture, nutrients and texture) between the reaches, and interpreted the vegetation differences in light of observed differences in environmental conditions. Flooding frequency was similar between reaches, but the proportion of fine textured soils in the unregulated reach was nearly double that of the regulated reach and soil nutrient levels were up to three times higher in the unregulated reach. Herbaceous cover and richness were consistently lower in the regulated reach, with between‐reach differences greatest during dry seasons. These patterns suggest that an edaphic‐based change in resource availability is the principal pathway by which river damming is altering herbaceous vegetation in this system. Our results demonstrate that sediment transport within riparian corridors is important for maintenance of herbaceous communities and that restoration of flow regimes alone may be insufficient to restore herbaceous flora on some regulated reaches. Copyright © 2008 John Wiley & Sons, Ltd.     

Importance of Reservoir Tributaries to Spawning of Migratory Fish in the Upper Paraná River

Regulation of rivers by dams transforms previously lotic reaches above the dam into lentic ones and limits or prevents longitudinal connectivity, which impairs access to suitable habitats for the reproduction of many migratory fish species. Frequently, unregulated tributaries can provide important habitat heterogeneity to a regulated river and may mitigate the influence of impoundments on the mainstem river. We evaluated the importance of tributaries to spawning of migratory fish species over three spawning seasons, by comparing several abiotic conditions and larval fish distributions in four rivers that are tributaries to an impounded reach of the Upper Paraná River, Brazil. Our study confirmed reproduction of at least 8 long‐distance migrators, likely nine, out of a total of 19 occurring in the Upper Paraná River. Total larval densities and percentage species composition differed among tributaries, but the differences were not consistent among spawning seasons and unexpectedly were not strongly related to annual differences in temperature and hydrology. We hypothesize that under present conditions, densities of larvae of migratory species may be better related to efficiency of fish passage facilities than to temperature and hydrology. Our study indicates that adult fish are finding suitable habitat for spawning in tributaries, fish eggs are developing into larvae, and larvae are finding suitable rearing space in lagoons adjacent to the tributaries. Our findings also suggest the need for establishment of protected areas in unregulated and lightly regulated tributaries to preserve essential spawning and nursery habitats. Copyright © 2014 John Wiley & Sons, Ltd.     

Effects of hydropeaking operations on the growth of Alabama bass Micropterus henshalli and redeye bass Micropterus coosae in the Tallapoosa River,Alabama, USA

Anthropogenic factors such as dam construction and hydropower generation can dramatically alter the flow regime of rivers and may impact growth of aquatic organisms. Using incremental growth techniques, annual growth of Alabama bass Micropterus henshalli and redeye bass M. coosae in the Tallapoosa River, Alabama, USA, was evaluated in response to variation in flow regime. Fish were collected from the Tallapoosa River above Harris Dam (unregulated site) and at two sites downstream of the dam (regulated sites), as well as Hillabee Creek (unregulated tributary). Flow variables were calculated for each growth year, and the best model that described growth for each species at each location was determined using Akaike's Information Criterion. Additionally, growth increments of each species at ages 1, 2, and 3 were compared between years characterized by low and high flow variability. Age was the best explanatory variable that described growth in all models, although flow variables were included in more than half the models. In all cases, annual and seasonal flow variables had low predictive power and explained <2% of the variation in growth. Growth was higher for age‐1 fish in years with less flow variation but was similar among years for age‐2 and age‐3 fish. Overall, this study provided little evidence that annual growth of either species was heavily influenced by flow in this regulated river.     

Low‐Head Dam Impacts on Habitat and the Functional Composition of Fish Communities

The natural flow regime of many rivers in the USA has been impacted by anthropogenic structures. This loss of connectivity plays a role in shaping river ecosystems by altering physical habitat characteristics and shaping fish assemblages. Although the impacts of large dams on river systems are well documented, studies on the effects of low‐head dams using a functional guild approach have been fewer. We assessed river habitat quality and fish community structure at 12 sites on two rivers; the study sites included two sites below each dam, two sites in the pool above each dam and two sites upstream of the pool extent. Fish communities were sampled from 2012 to 2015 using a multi‐gear approach in spring and fall seasons. We aggregated fishes into habitat and reproductive guilds in order to ascertain dams' effects on groups of fishes that respond similarly to environmental variation. We found that habitat quality was significantly poorer in the artificial pools created above the dams than all other sampling sites. Fast riffle specialist taxa were most abundant in high‐quality riffle habitats farthest from the dams, while fast generalists and pelagophils were largely restricted to areas below the downstream‐most impoundment. Overall, these dams play a substantial role in shaping habitat, which impacts fish community composition on a functional level. Utilizing this functional approach enables us to mechanistically link the effects of impoundments to the structure of fish communities and form generalizations that can be applied to other systems. Copyright © 2017 John Wiley & Sons, Ltd.     

Benthic macroinvertebrate communities in nonregulated and regulated waters of the clearwater river,Idaho, U.S.A.

Benthic macroinvertebrates were examined over a two-year period in nonregulated, regulated, and semiregulated reaches of the Clearwater River in northern Idaho. Macroinvertebrate communities in the nonregulated reach above Dworshak Reservoir were taxonomically diverse at all stations. In contrast, the macroinvertebrate community in the regulated reach of the North Fork of the Clearwater River (NFCR) was severely altered with high macroinvertebrate abundance and low taxa richness (2 to 8 taxa). Orthoclad chironomids dominated this reach composing between 68 and 99 per cent of total benthic invertebrate numbers. The mayfly Ephemerella infrequens was the only other macroinvertebrate to be abundant in the regulated reach. The major factors contributing to the simplified macroinvertebrate community are reduced habitat diversity, fluctuating water levels, altered thermal regime, and possibly an altered food supply. The effects of the dam were mitigated in the semiregulated Mainstem of the Clearwater River (MSCR) due to the merger of a nonregulated fork entering 2.5 km downstream from the dam. The macroinvertebrate community in the semiregulated MSCR was more complex than the regulated reach with a community structure resembling that found above the reservoir.