Diel and lateral patterns of zooplankton distribution in the St. Lawrence River

While the four‐dimensional nature of river ecosystems has been recognized for nearly two decades, the role of lateral complexity has rarely been factored into studies of zooplankton ecology. We examined the importance of hydrologic retention areas (slackwaters) near islands and embayments of the St. Lawrence River for densities, fecundity, and diel migration of planktonic microcrustaceans. Densities of cladocera and copepods (nauplii and adult stages of cyclopoids and calanoids) were sampled from surface and deeper layers both at night (2100–0100 h, near the new moon) and during the day (1000–1400 h) for channel (deep‐fast), offshore (shallow‐slower), and inshore (shallow‐stagnant) habitats. Average zooplankton densities increased laterally from the main channel into the slackwaters with the exception of calanoid copepods, which peaked in the intermediate depths and flows of the offshore habitats. Although the ratio of males to females for the calanoid Eurytemora affinis and the cladoceran Bosmina spp. did not differ among habitats, a greater percentage of ovigerous cladoceran females were present in slackwaters than in channel habitats. Densities of microcrustaceans were generally greater during the night than day, suggesting diel vertical migration. By demonstrating both lateral and diel differences in the spatial distribution of riverine zooplankton, we refute the view of large rivers as well‐mixed homogenous systems. To the contrary, the two non‐random patterns that we document imply that there is an abiotic template that at least microcrustacean potamoplankton can exploit. In turn this suggests more research into the ecological significance of the pelagic structure of other large rivers like the St. Lawrence is justified. Copyright © 2007 John Wiley & Sons, Ltd.     

Identification of gas supersaturation sources in the Upper Colorado River,USA

Atmospheric gas saturation levels were monitored throughout a 40‐km reach of the upper Colorado River during the summer and fall of 1995 to identify possible sources of gas supersaturation in the river. Gas saturation data from seven fixed sampling points and 40 random sampling points were analyzed using analysis of variance (ANOVA) and multiple regression methods. The lowest total gas saturations (ΔP=−27) were found at the bottom release of Williams Fork Reservoir. The highest total gas saturations (ΔP=77) were found at the spillway release of Windy Gap Reservoir and the confluence of Willow Creek and the Colorado River. Spacial and temporal effects were determined to be significant contributors to gas saturation levels. Gas supersaturation in the study area originated from both man‐made and natural sources. Water discharged from the spillway of Windy Gap Reservoir was found to be the main source of man‐made supersaturation, while photosynthetic activity of aquatic plants was determined to be the natural source of supersaturation in the study area. Copyright © 1999 John Wiley & Sons, Ltd.     

Fishway passage and post‐passage mortality of up‐river migrating sockeye salmon in the Seton River,British Columbia

Adult sockeye salmon (Oncorhynchus nerka) were studied to assess the consequences of a dam and vertical‐slot fishway on mortality during their spawning migration in the Seton–Anderson watershed, British Columbia, Canada. Since previous research suggests fishway passage may be difficult, our main hypothesis was that the dam and fishway have post‐passage consequences that affect subsequent behaviour and survival. Eighty‐seven sockeye were caught at the top of the fishway, implanted with an acoustic telemetry transmitter, non‐lethally biopsied to obtain a small blood sample and released either upstream or downstream of the dam. Indices of physiological stress (i.e. plasma cortisol, glucose, lactate and ions) indicated that fish were not stressed or exhausted after capture from the fishway, and were not unduly stressed by transportation to release sites or net‐pen holding. Of 59 fish released downstream of the dam, 14% did not reach the dam tailrace. Overall passage efficiency at the fishway was 80%. Mortality in two lakes upstream of the dam was greater in fish released downstream of the dam (27%) compared to fish released upstream of the dam (7%; p = 0.04) suggesting that dam passage has consequences that reduce subsequent survival. Cumulative mortality of fish released downstream of the dam (n = 55) resulted in only 49% survival to spawning areas, compared to 93% of fish released upstream of the dam (n = 28). Survival was significantly lower for females (40%) than for males (71%; p = 0.03), a finding that has implications for conservation because spawning success of sockeye salmon populations is governed primarily by females. Copyright © 2010 John Wiley & Sons, Ltd.     

Zooplankton density and community composition following an experimental flood in the Colorado River,Grand Canyon,Arizona

Zooplankton density and community composition were examined before and after an experimental flood (22 March–7 April 1996) in the Colorado River, Grand Canyon, north‐central Arizona, USA, and comparisons were made across sampling locations and habitat types. The flood primarily affected longitudinal distribution and community composition of zooplankton. Prior to the flood, zooplankton density declined linearly below Lee's Ferry (R²=0.79) but declined with the fourth power of distance downriver following the flood (R²=0.59). Zooplankton community similarity indices between mainchannel and backwater habitats ranged from 0.08 to 0.89 prior to the flood but increased significantly to 0.64–0.98 after the flood, indicating increased homogeneity between habitat types. The flood displaced resident (i.e. benthic, littoral and/or phytophyllic) taxa from backwater habitats and replaced them with limnetic organisms. Total zooplankton density was greater after the flood (4174/m³) than before (2733/m³), but the increase may have been an artifact of normal seasonal cycles in the Colorado River and/or the upstream reservoir (Lake Powell). Copyright © 2000 John Wiley & Sons, Ltd.     

Zooplankton as an indicator of trophic conditions in two large reservoirs in Brazil

The physical and chemical variables of the water, and the composition and structure of the zooplankton communities, in Três Marias and Furnas Reservoirs in Minas Gerais, Brazil, were compared to characterize these environments in relation to their trophic state. Higher values of electrical conductivity and chlorophyll‐a, total solids, suspended organic matter and total nitrogen concentrations were recorded in Três Marias Reservoir. Higher water transparency and nitrite and nitrate concentrations were observed in Furnas (P < 0.000). Higher zooplankton densities were always obtained in Três Marias Reservoir and, during the rainy period (P < 0.000), with mean values in the dry and rainy periods of 23 721 and 90 872 org m^?3, respectively, in Três Marias Reservoir and 9022 and 40 434 org m^?3, respectively, in Furnas Reservoir. Copepoda was the dominant group in both reservoirs, mainly the younger stages (nauplii and copepodids). Based on the absolute and relative values, the contribution of rotifers was higher in Três Marias Reservoir than in Furnas Reservoir. Although the Trophic State Index, based on water transparency and chlorophyll‐a and total phosphorus concentrations, indicated an oligotrophic state for both reservoirs, the higher densities of the zooplankton community in Três Marias Reservoir, as well as the predominance of cyclopoids and smaller‐sized species such as bosminids, characterized this environment as mesotrophic. Larger‐sized species such as calanoids, daphniids and sidids in Furnas Reservoir characterized the better water quality of this reservoir.     

Early observations on an emerging Great Lakes invader Hemimysis anomala in Lake Ontario

Hemimysis anomala, a Ponto-Caspian littoral mysid, is an emerging Great Lakes invader that was discovered in Lakes Michigan and Ontario in 2006. Similar to the native mysid Mysis diluviana, Hemimysis exhibits a diel vertical migration pattern but generally inhabits shallower and warmer waters than M. diluviana. Because basic information on the distribution, habitat use, and biology of Hemimysis in the Great Lakes is scarce, the potential for food web disruption by Hemimysis cannot easily be predicted. Preliminary observations indicate widespread invasion of Hemimysis in Lake Ontario. In this study, we confirm the presence of Hemimysis at sites spanning the northern and southern shores of Lake Ontario and the presence of the individuals during winter months. In one horizontal tow in November 2007, over 26,000 individuals were collected with a length range of 4.4 to 9.0 mm and an average caloric density of 611 cal/g wet weight. The most effective methods for sampling Hemimysis were horizontal tows with either a zooplankton net in the water column or a benthic sled near the lake bottom. Although more quantitative data on the life history and distribution of this species is necessary, our preliminary observations support the prediction that the potential for Hemimysis to impact the nearshore food web in Lake Ontario appears high.     

长江河口北槽近期盐淡水混合与悬沙输运研究

基于2013年枯季大潮期间在长江口北槽河道现场定点观测数据(包括潮流、悬沙浓度、盐度),通过对盐水入侵影响水流结构及泥沙运动过程的分析,对北槽河道盐淡水混合与悬沙输运进行了研究。结果表明:观测期间,北槽河道纵向及垂向受不同程度的盐度梯度影响,涨落潮过程中垂线流速不再保持无潮河流的分布规律,河口水流结构发生改变,促使出现上层水流向海、下层水流向陆的河口环流。在多重因素作用下,特别是环流阻碍了河流泥沙的正常下泄,并有利于底层泥沙上溯,出现上层输沙向海、下层输沙向陆的现象。各段河道中,垂向净环流项均向陆输沙,但向海的平流输沙及潮泵输沙作用更强,所以观测期间悬沙表现均为向海净输移。     

Evaluation of energy expenditure in adult spring Chinook salmon migrating upstream in the Columbia River Basin: an assessment based on sequential proximate analysis

The upstream migration of adult anadromous salmonids in the Columbia River Basin (CRB) has been dramatically altered and fish may be experiencing energetically costly delays at dams. To explore this notion, we estimated the energetic costs of migration and reproduction of Yakima River‐bound spring Chinook salmon Oncorhynchus tshawytscha using a sequential analysis of their proximate composition (i.e., percent water, fat, protein, and ash). Tissues (muscle, viscera, and gonad) were sampled from fish near the start of their migration (Bonneville Dam), at a mid point (Roza Dam, 510 km upstream from Bonneville Dam) and from fresh carcasses on the spawning grounds (about 100 km above Roza Dam). At Bonneville Dam, the energy reserves of these fish were remarkably high, primarily due to the high percentage of fat in the muscle (18–20%; energy content over 11 kJ g^?1). The median travel time for fish from Bonneville to Roza Dam was 27 d and ranged from 18 to 42 d. Fish lost from 6 to 17% of their energy density in muscle, depending on travel time. On average, fish taking a relatively long time for migration between dams used from 5 to 8% more energy from the muscle than faster fish. From the time they passed Bonneville Dam to death, these fish, depending on gender, used 95–99% of their muscle and 73–86% of their visceral lipid stores. Also, both sexes used about 32% of their muscular and very little of their visceral protein stores. However, we were unable to relate energy use and reproductive success to migration history. Our results suggest a possible influence of the CRB hydroelectric system on adult salmonid energetics. Published in 2006 by John Wiley & Sons, Ltd.     

Importance of biotic interactions in large rivers: an experiment with planktivorous fish,dreissenid mussels and zooplankton in the St. Lawrence River

Physical conditions are usually considered pre‐eminent in controlling river plankton, but biotic interactions may be important in slackwater areas. To begin testing this general hypothesis, we conducted a 12‐day, predator–prey experiment in 3500 litre mesh enclosures in a slackwater area of the St. Lawrence River using planktivorous, juvenile yellow perch (Perca flavescens) and Dreissena mussels. Results generally supported our hypotheses that: (1) perch would directly suppress large zooplankton via predation but benefit microzooplankton through indirect interactions; and (2) dreissenids would directly depress rotifer densities via predation and have indirect negative effects on macrozooplankton. Based on gut contents of experimental fish, cladocera were the principal prey of smaller yellow perch (c. 46–50 mm), followed by copepods, ostracods, and rotifers. Larger juvenile perch (c. 67–73 mm) fed almost exclusively on copepods and ostracods. Densities of calanoid copepodids, nauplii, and some cyclopoid copepods (Diacyclops thomasi) were significantly depressed by perch, and adult Eurytemora affinis (99% of adult calanoids) essentially disappeared from fish enclosures. Despite being a favourite prey item of small perch, densities of the small cladoceran Bosmina (Sinobosmina) spp. were significantly higher when fish were present (150% greater than control densities on Day 12). Densities of the very abundant rotifer Polyarthra were >300% greater in fish enclosures than controls by Day 12, and the rotifers Synchaeta and predaceous Ploesoma were significantly more abundant in the presence of perch. Increases in rotifers and cladocera suggest indirect, positive effects of fish related to significantly higher phytoplankton biomass or decreased densities of predaceous copepods. Densities of eight of ten zooplankton groups examined declined significantly when mussels were present, and calanoid copepodids also declined but not significantly. Chlorophyll‐a concentrations were slightly lower in mussel enclosures. This evidence suggests biotic interactions play important roles among potamoplankton in slackwater habitats, but river‐wide implications of these findings require further study. Copyright © 2003 John Wiley & Sons, Ltd.     

Passage and reproductive activity of fishes in the Igarapava fish ladder,Grande River,Southeastern Brazil

We sampled fishes within the vertical‐slot Igarapava fish ladder (IFL), Grande River, southeastern Brazil, and immediately downstream IFL in 12 field trips from February 2000 to December 2002. A total of 1145 fishes belonging to 13 families and 39 species were captured. The most abundant species captured within the IFL, in order of abundance were: Pimelodus maculatus, Metynnis maculatus, Astyanax altiparanae, Hypostomus spp., Leporinus octofasciatus, Salminus hilarii, Leporinus elongatus, Leporinus friderici, Schizodon nasutus and Prochilodus lineatus. Size distribution of the most abundant fishes captured downstream or within the IFL was similar indicating no constraints to adult fish to ascend the IFL. Except P. maculatus, the number of migratory species captured in the IFL and downstream the IFL were very low. Some of the so‐called sedentary species were collected in the IFL indicating that they possess an innate behaviour to migrate. Juveniles of P. lineatus and P. maculatus were captured ascending the IFL implying a dispersal behaviour. Gonadal analyses of the fishes captured in the reproductive season showed that the overall number of reproductive active fishes (which included fish in maturation, mature and spawned/spent) surpassed those non‐active. Thus, the IFL offers upstream passage for juveniles, some of the so‐called sedentary species, as well as fishes in reproductive migration. Copyright © 2009 John Wiley & Sons, Ltd.     

MULTIPLICATIVE LOSS OF LANDLOCKED ATLANTIC SALMON Salmo salar L. SMOLTS DURING DOWNSTREAM MIGRATION TROUGH MULTIPLE DAMS

Relatively little is known about the downstream migration of landlocked stocks of Atlantic salmon Salmo salar L. smolts, as earlier migration studies have generally focused on upstream migration. However, in watersheds with many hydroelectric plants (HEPs), multiplicative loss of downstream‐migrating salmon smolts can be high, contributing to population declines or extirpations. Here we report the results from a study of wild landlocked Atlantic salmon smolts in the River Klarälven. Salmon smolts, tagged with acoustic transmitters, were released at different locations and followed as they passed 37 receivers along a 180‐km‐long river segment, including eight dams as well as free‐flowing control stretches. We found that 16% of the smolts successfully migrated along the entire river segment. Most losses occurred during HEP passages, with 76% of the smolts being lost during these passages, which contrasts with the 8% smolt loss along unregulated control stretches. Migration speed was 83% slower along regulated stretches than along unregulated stretches. The observed lower migration speed at regulated stretches was dependent on fish size, with large fish moving slower than small fish. Discharge affected migration speed but not losses. As previously shown for anadromous populations, our study of landlocked salmon demonstrates similar negative effects of multiple passages of HEPs by downstream‐migrating smolts. On the basis of this and previous migration studies, we advocate using a holistic approach in the management and conservation of migratory fish in regulated rivers, which includes safe passage for both upstream‐ and downstream‐migrating fish. Copyright © 2012 John Wiley & Sons, Ltd.     

Experimental evidence for density‐dependent effects and the importance of algal production in determining population growth rates of riverine zooplankton

Food limitation effects on life history traits of lake zooplankton have been well documented but few studies have examined linkages between population growth rates and food resources in riverine environments. In rivers, allochthonous inputs of particulate organic matter may mitigate food limitation effects allowing density‐independent mechanisms associated with washout (discharge) and feeding interference (turbidity) to assume greater importance. We experimentally manipulated densities of commonly occurring riverine zooplankton (Bosmina longirostris and cyclopoid copepods) within 2000 l mesocosms containing ambient or algal‐enriched food resources. The experiment was repeated through time (July, August, September) to represent the range of zooplankton densities and food resource levels observed in the Ohio River during warm‐water, low‐flow conditions. High growth rates and low sensitivity to density‐dependent effects were observed during July when particulate organic carbon (POC) and chlorophyll concentrations were highest. Lower growth rates and stronger response to density‐dependent effects were observed during August and September experiments when POC and chlorophyll concentrations were lower. Direct manipulations of algal abundance resulted in higher growth rates when gains in chlorophyll were accompanied by increases in the edible size fraction (September experiment). Algal C concentrations were found to be a significant predictor of variation in population growth rates for Bosmina but not cyclopoids. Algal C concentrations in the Ohio River rarely fell below experimentally derived minimum food thresholds but were often below saturation thresholds suggesting that population growth rates were constrained by autochthonous food resources despite the prevalence of allochthonous carbon. Copyright © 2005 John Wiley & Sons, Ltd.     

Performance of a prototype surface collector for juvenile salmonids at Bonneville Dam's first powerhouse on the Columbia River,Oregon

During April–July 2000, we radio‐tagged and released juvenile Chinook salmon (Oncorhynchus tshawytscha) and steelhead (Oncorhynchus mykiss) to evaluate a prototype surface flow bypass at Bonneville Dam on the Columbia River. The mock bypass, called a prototype surface collector (PSC), had six vertical slot entrances that were each 6 m wide and 12 m deep. The PSC was retrofitted to the upstream face of Bonneville Dam's First Powerhouse. Our objectives were to: (1) assess species‐specific differences in movement patterns and behaviour of fish within 6 m of the face of the PSC, (2) estimate the efficiency and effectiveness of the PSC and (3) evaluate factors affecting the performance of the PSC. We found that 60–72% of the fish, depending on species, detected within 6 m of the PSC entered it. Of the fish that passed the First Powerhouse at turbines 1–6, 79–83% entered the PSC. Diel period was a significant contributor to PSC performance for all species, and day of year was a significant contributor to PSC performance for subyearling Chinook salmon. The PSC was twice as effective (%fish/%flow) as the spillway, passing 2.5:1 steelhead and subyearling Chinook salmon and 2.4:1 yearling Chinook salmon per unit of water. If fully implemented, the PSC would increase the percentage of fish that pass the First Powerhouse through non‐turbine routes from 65–77% (without the PSC) to 76–85% (with the PSC), depending on species. Published in 2008 by John Wiley & Sons, Ltd.     

Effects of fluctuating river flow on groundwater/surface water mixing in the hyporheic zone of a regulated,large cobble bed river

Physicochemical relationships in the boundary zone between groundwater and surface water (i.e. the hyporheic zone) are controlled by surface water hydrology and the hydrogeologic properties of the riverbed. We studied how sediment permeability and river discharge altered the vertical hydraulic gradient (VHG) and water quality of the hyporheic zone within the Hanford Reach of the Columbia River. The Columbia River at Hanford is a large, cobble‐bed river where water level fluctuates up to 2 m daily because of hydropower generation. Concomitant with river stage recordings, continuous readings were made of water temperature, specific conductance, dissolved oxygen and water level of the hyporheic zone. The water level data were used to calculate VHG between the river and hyporheic zone. Sediment permeability was estimated using slug tests conducted in piezometers installed into the river bed. The response of water quality measurements and VHG to surface water fluctuations varied widely among study sites, ranging from no apparent response to covariance with river discharge. At some sites, a hysteretic relationship between river discharge and VHG was indicated by a time lag in the response of VHG to changes in river stage. The magnitude, rate of change and hysteresis of the VHG response varied the most at the least permeable location (hydraulic conductivity (K) = 2.9 × 10^?4 cms^?1) and the least at the most permeable location (K = 8.0 × 10^?3 cms^?1). Our study provides empirical evidence that sediment properties and river discharge both control the water quality of the hyporheic zone. Regulated rivers, like the Columbia River at Hanford, that undergo large, frequent discharge fluctuations represent an ideal environment in which to study hydrogeologic processes over relatively short time periods (i.e. days to weeks) that would require much longer periods (i.e. months to years) to evaluate in unregulated systems. Copyright © 2006 John Wiley & Sons Ltd.     

ARE TWO SYSTEMIC FISH ASSEMBLAGE SAMPLING PROGRAMMES ON THE UPPER MISSISSIPPI RIVER TELLING US THE SAME THING?

We applied an Index of Biotic Integrity (IBI) used on Wisconsin/Minnesota waters of the upper Mississippi River (UMR) to compare data from two systemic sampling programmes. Ability to use data from multiple sampling programmes could extend spatial and temporal coverage of river assessment and monitoring efforts. We normalized for effort and tested fish community data collected by the Environmental Monitoring and Assessment Program‐Great Rivers Ecosystems (EMAP‐GRE) 2004–2006 and the Long Term Resource Monitoring Program (LTRMP) 1993–2006. Each programme used daytime electrofishing along main channel borders but with some methodological and design differences. EMAP‐GRE, designed for baseline and, eventually, compliance monitoring, used a probabilistic, continuous design. LTRMP, designed primarily for baseline and trend monitoring, used a stratified random design in five discrete study reaches. Analysis of similarity indicated no significant difference between EMAP‐GRE and LTRMP IBI scores (n = 238; Global R = ?0.052; significance level = 0.972). Both datasets distinguished clear differences only between ‘Fair’ and ‘Poor’ condition categories, potentially supporting a ‘pass–fail’ assessment strategy. Thirteen years of LTRMP data demonstrated stable IBI scores through time in four of five reaches sampled. LTRMP and EMAP‐GRE IBI scores correlated along the UMR's upstream to downstream gradient (df [3, 25]; F = 1.61; p = 0.22). A decline in IBI scores from upstream to downstream was consistent with UMR fish community studies and a previous, empirically modelled human disturbance gradient. Comparability between EMAP‐GRE (best upstream to downstream coverage) and LTRMP data (best coverage over time and across the floodplain) supports a next step of developing and testing a systemic, multi‐metric fish index on the UMR that both approaches could inform. Copyright © 2011 John Wiley & Sons, Ltd.     

Littoral zooplankton diversity in Himayat Sagar Reservoir,Telangana, India

The present study investigated zooplankton composition and diversity, along with physicochemical parameters from the littoral regions of Himayat Sagar Reservoir, Telangana, India. A total of 84 zooplankton species were found, including 60 rotifer species, 16 cladoceran species and eight copepod species. Keratella tropica, Lecane bulla, Coronatella rectangula and Mesocyclops sp. were observed frequently throught the study period. The Shannon Diversity Index ranged between H′ = 1.8 and 2.1, with a high diversity observed during the summer season. Dominance was greater during the monsoon and winter seasons, being represented by Brachionus calyciflorus, B. angularis, B. falcatus, Keratella tropica, Ceriodaphnia cornuta, Diaphanosoma sarsi and Mesocyclops sp. Correlation coefficients and principal component analysis indicated temperature, pH and nutrients had a major influence on zooplankton community changes in this reservoir. The environmental variables and diversity indices indicated seasonally fluctuating trophic conditions. Himayat Sagar Reservoir requires long‐term monitoring for assessment and better management of its faunal diversity and water quality.     

Ascent of neotropical migratory fish in the Itaipu Reservoir fish pass

The Piracema Canal is a complex 10‐km fish pass system that climbs 120 m to connect the Paraná River to the Itaipu Reservoir along the Brazil–Paraguay border. The canal was constructed to allow migratory fishes to reach suitable habitats for reproduction and feeding in tributaries upstream from the reservoir. The Piracema Canal attracted 17 of the 19 long‐distance migratory species that have been recorded in the Paraná River Basin and Paraguay–Paraná Basin. However, the incidence of migratory fish decreased from downstream to upstream, with the pattern of decrease depending on species. Overall, 0.5% of the migratory fish that entered the Piracema Canal and segment 1, eventually were able to reach segment 5 and potentially Itaipu Reservoir. Ascension rate was examined relative to various physical attributes of canal segments; maximum water velocity emerged as the most influential variable affecting fish passage. Water velocity may be manipulated by controlling water discharge, and by re‐engineering critical sections of the canal. Because the Itaipu Reservoir flooded a set of falls that separated two distinct biogeographical regions, facilitating fish movements through the Piracema Canal into the Itaipu Reservoir presents a management dilemma that requires deliberation in the context of the fish assemblages rather than on selected migratory species. Copyright © 2010 John Wiley & Sons, Ltd.     

Benefits to 0+ fishes of connecting man‐made waterbodies to the lower River Trent,England

Floodplain waterbodies are reputed to enhance recruitment of riverine fish populations via provision of spawning and nursery habitat, refuge from floods, and increased availability of planktonic food resources compared with main river channels. Notwithstanding, there have been few parallel studies of fishes and their food resources at both main river and floodplain sites. Thus, this study investigated the 0+ fishes, zooplankton and phytoplankton (chlorophyll a) at four main river and four (man‐made) floodplain sites on the lower River Trent, England, between May 1999 and October 2004 inclusive. All sites shared the same key fish species, and there were no consistent differences in the densities, growth or condition of 0+ fishes from main river and floodplain sites. Similarly, all sites shared the same key zooplankton taxa. However, zooplankton densities, notably of large‐bodied cladocerans, and chlorophyll a concentrations, were significantly higher at floodplain sites than at main river sites. Thus, connection of man‐made waterbodies has the potential to enhance recruitment of riverine fish populations via provision of important spawning and nursery habitat, and superior feeding opportunities for 0+ fishes compared with main river channels. Copyright © 2007 John Wiley & Sons, Ltd.     

Human and climate impacts on Columbia River hydrology and salmonids

The Columbia River had until recently the world's largest Chinook salmon runs. Restoration of the system's severely decimated runs requires understanding changes in the hydrologic variables (e.g. flow and sediment transport) important to salmonids. We describe here methods to distinguish the human and climate‐induced contributions to Columbia River hydrologic processes relevant to the crucial seaward spring migration of juveniles through the tidal river and estuary. Flow regulation has caused most of the decrease in peak flow and sediment transport; it has contributed to changes in spring freshet timing. Climate change has reduced peak and average flows and sediment transport, changing spring‐freshet timing by several weeks. Irrigation diversion has reduced the annual average flow as much as climate change. A better understanding of historical changes in hydrologic processes entailed in this paper tells us how management and climate have changed the Columbia River system over time. The separation of the climate and anthropogenic influences used here may assist in policy analyses and strategies aimed at restoration of the Columbia River endangered salmonids, and in management of other systems. Copyright © 2010 John Wiley & Sons, Ltd.