A two‐dimensional self‐adaptive hydrodynamic scheme for the assessment of the effects of structures on flooding phenomena in river basins

In order to assess the effects of river and floodplain engineering projects on flooding, a new self‐adaptive hydrodynamic scheme for the simulation of two‐dimensional river flows is proposed. The depth‐averaged motion equations are solved numerically using a fractional step method, in which the convective terms are calculated using the inverse characteristics method and the remaining terms with an explicit method based on a finite difference method. The integration is performed on a dynamically self‐adaptive calculus grid, which allows representation of the movable boundary between wetting and drying regions of the basins to follow the effective development, in time and space, of the expansion phenomenon of flood. The proposed procedure allows the grid's dynamic refinement to avoid coordinate transformation or the use of unstructured grids. The proposed method is simple and allows the thickening of the grid to accommodate the flooding phenomena on the floodplain and to calculate the velocity in the domain regions in which a higher space resolution is required. Therefore, flows running through structures such as weirs, gates, bridges or culverts can be simulated. In the paper two different case studies, approached with the proposed self‐adaptive calculation scheme, are discussed. The studies concern the analysis of the effects of structures, such as roads or embankments, on flooding phenomena in the Tiber and Tanaro basins respectively. Copyright © 2003 John Wiley & Sons, Ltd.     

Spatial modelling of freshwater fish in semi‐arid river systems: a tool for conservation

This paper examines the feasibility of using multivariate statistics to model fish species distribution and habitat requirements for intermittent streams in semi‐arid regions, many of which are coming under increasing pressure from water resource development schemes. The assessment was based on the geographical distribution of six endemic fish species in the Guadiana river, a semi‐arid river system in southern Iberia. Their presence was related to 20 environmental variables linked to climate, geomorphology, riparian vegetation and location in the drainage basin. These variables were collected in the field or from topographical maps to evaluate habitat suitability and to predict the presence of the species according to season. Multivariate logistic regression in a geographic information system (GIS) environment was performed to identify regions with high probability of occurrence for each species. The variables that best explained the occurrence of the species were the sample location in the drainage basin, the geomorphology and the riparian vegetation. The models presented have a high predictive power and can be used in monitoring and predicting temporal changes caused by human activities. This modelling approach can be used to predict the areas that need to be conserved to protect or rehabilitate the endangered species. Armed with this information, managers can formulate conservation measures to prevent further degradation of the stocks and possibly enhance the populations. Copyright © 2002 John Wiley & Sons, Ltd.     

Field evaluation of a two‐dimensional hydrodynamic model near boulders for habitat calculation

Two‐dimensional hydrodynamic models are now widely used in aquatic habitat studies. To test the sensitivity of calculated habitat outcomes to limitations of such a model and of typical field data, bathymetry, depth and velocity data were collected for three discharges in the vicinity of two large boulders in the South Platte River (Colorado) and used in the River2D model. Simulated depth and velocity were compared with observed values at 204 locations and the differences in habitat numbers produced by observed and simulated conditions were calculated. The bulk of the differences between simulated and observed depth and velocity values were found to lie within the likely error of measurement. However, the effect of flow simulation outliers on potential habitat outcomes must be considered when using 2D models for habitat simulation. Furthermore, the shape of the habitat suitability relation can influence the effects of simulation errors. Habitat relations with steep slopes in the velocity ranges found in similar study areas are expected to be sensitive to the magnitude of error found here. Comparison of habitat values derived from simulated and observed depth and velocity revealed a small tendency to under‐predict habitat values. Published in 2009 by John Wiley & Sons, Ltd.     

A simple method for sampling invertebrate drift in large rivers and boulder‐bed streams

Sampling invertebrate drift in high‐gradient boulder‐bed channels or large turbulent rivers is challenging, because the traditional approach of driving stakes into the stream bed to secure drift nets may not work. We describe a simple method using a split wading rod to collect drift samples from the wadeable river margin or bank as an alternative method for rapid assessment of invertebrate drift when boat access is not possible. Pilot sampling in a large river shows that near‐shore drift samples collected with this approach are broadly similar to samples collected from the centre of the channel using more conventional methods, although our results suggest that depth and velocity effects may cause drift concentrations to be elevated closer to the bank.     

Leaf‐Nets (LN): A New Quantitative Method for Sampling Macroinvertebrates in Non‐Wadeable Streams and Rivers

The ecological knowledge of large rivers is still scarce or highly fragmented mainly because of complex, laborious and expensive procedures to collect informative samples from the benthic biota. Standard sampling protocols for macroinvertebrates were mainly developed and calibrated for wadeable streams, while a number of heterogeneous non‐standard sampling procedures are available for large rivers. We propose the new, easy‐to‐build and cost‐effective leaf‐nets (LN) method to quantitatively sample benthic invertebrates in non‐wadeable waterways. The LN method uses Phragmites australis leaves as substrate and combines the characteristics of the leaf‐bags and the Hester–Dendy (HD) multiplates methods. We compared the effectiveness of the LN and HD methods in a near‐pristine and in an impacted stream‐reach (downstream an aquaculture plant) of a non‐wadeable second‐order stream of Central Apennines (Italy). Twenty‐five of the 34 cumulatively collected macroinvertebrate taxa were common to both methods, while seven taxa were found only on LN and two only on HD. Taxonomic richness and total macroinvertebrate abundance were higher for LN assemblages. Number of Ephemeroptera, Plecoptera and Trichoptera taxa (EPT) also tended to be higher on LN. Assemblage composition was different on LN and HD. Both methods documented a significant decrease in EPT taxa and a concomitant increase in the total abundance of more pollution‐tolerant taxa in the impacted stream‐reach, but the LN method was more sensitive to impact‐associated changes in macroinvertebrate assemblage structure. In contrast to the hardboard plates of HD, the assembled leaves of the LN may act as a direct or indirect food source and may better mimic the texture and composition of more heterogeneous natural substrates thus favouring the migration–colonization process from both bottom and littoral benthic invertebrates. The sampling efficiency, cost effectiveness and simplicity warrant the routine use of the new LN method in large‐river ecological assessment. Copyright © 2015 John Wiley & Sons, Ltd.     

Long‐term fish assemblages of inner bends in a large river

We sampled fishes at 17 inner bend sites on the Wabash River in 2008 to compare with collections from 1977 to 1997. We used the same seine collection methods as previous years and collected a total of 37 species. Mean site Shannon‐Wiener diversity, species richness, evenness and abundance for all years were similar. We used multivariate analyses to test for patterns in fish assemblage structure among all sites and all years. The multivariate analyses resulted in distinct assemblages for each collection‐year, suggesting shifts in assemblage composition among years. We used separate multivariate analyses to examine fish assemblage variation within individual years. Variation that corresponded to an upstream–downstream pattern was present in 1977 and 2008, but not in 1997. A hydrologic analysis based on daily discharge revealed that eight large flood events occurred from 1928 to 2007, with four of these events during the recent 20 years. We quantified substrate variation at the 17 sites in 2008 and identified a longitudinal gradient in dominant substrate categories with gravel upstream and sand downstream that was correlated with the first axis of the 2008 fish assemblage ordination. We suggest that observed changes in fish assemblages in decadal periods were from hydrologic impacts of large floods on local habitats. Copyright © 2010 John Wiley & Sons, Ltd.     

Effect of sampling method on diatom composition for use in monitoring and assessing large river condition

Multiple diatom sampling methods exist for the assessment of lotic systems but few comparisons of their application efficacies in monitoring have been conducted. In this study 60 sites were sampled on four large, non‐wadeable rivers in Ohio and Kentucky, USA, which varied in depth, flow rate, surrounding land use and hydrologic modification. Four algae sampling methods were tested: three methods U.S. Environmental Protection Agency (U.S. EPA) Environmental Monitoring and Assessment Program (EMAP), U.S. Geological Survey (USGS QUAL and USGS QUAN) collected algae from rocks, debris and sediment in the littoral zone along a 1–2 km reach, while one method (USGS PHYTO) consisted of three cross‐river phytoplankton grab samples collected from a boat. Physical and chemical data were also collected. Little difference in diatom assemblage composition was found among the EMAP, QUAL and QUAN methods. Although compositionally similar, the PHYTO method collected a substantial proportion of relatively unique diatoms compared to the littoral zone methods. Two disturbance gradients were calculated, one based on 1 km upstream land use within a 500 m buffer, and the other based on principal component analysis dimension reduction of measured water parameters (PCAWQ). Metrics, generally indicators of eutrophication, were calculated for each sampling method and correlated with the disturbance gradients. After Bonferroni corrections, the EMAP method had six metrics correlated with the PCAWQ, while the PHYTO and QUAL methods each had four correlated metrics. Two QUAN metrics were correlated with the PCAWQ. Few metrics were correlated with the land use measure of disturbance. While the EMAP method had the most correlated metrics, this method, along with QUAL and QUAN methods are time and labour intensive (>1 h), relative to the phytoplankton method (<20 min). Resource managers may desire to weigh the benefits of two additional metrics with the EMAP method versus the costs associated with increased sampling time and effort. Published in 2007 by John Wiley & Sons, Ltd.     

Sample size determination for soft‐bottom sampling in large rivers and comparison with the chironomid pupal exuvial technique (CPET)

Our objective in this study was to determine the adequate sample size for the use of grab sampling in the biomonitoring of large soft‐bottom rivers. We also compared two sampling methods, grab sampling and the Chironomid Pupal Exuvial Technique (CPET), in detecting anthropogenic impacts in a large boreal river and assessed the degree of concordance between the two data sets. Sample size determination showed that, at the lowest possible taxonomic level, a minimum of eight benthic samples was required to obtain a reliable picture of benthic communities. When using the CPET, the number of chironomid species was nearly twice that of all benthic macroinvertebrates in the grab samples. In addition, a majority of the chironomid species found in the grab samples was also detected using the CPET. Although both data sets indicated significant differences in benthic communities between the sampling sites in the river Kymi, a Mantel test showed that patterns in community composition were not concordant. This was mainly because benthic samples from the deep depositional areas of the river indicated poorer ecological status than did the CPET data, which integrate species from various depths and habitats. Thus, samples from a single macrohabitat may not adequately represent environmental conditions of large rivers. Overall, our results suggest that the CPET provides a reliable and cost‐effective alternative, or a supplementary assessment tool, to more traditional sampling methods when assessing anthropogenic stresses in large boreal rivers. Copyright © 2008 John Wiley & Sons, Ltd.     

Comparison of littoral and deep water sampling methods for assessing macroinvertebrate assemblages along the longitudinal profile of a very large river (the Danube River,Europe)

We comparatively examined the role of littoral and deep water sampling methods in assessing macroinvertebrate assemblages and in characterizing longitudinal changes in assemblage structure along >2,500‐km–long course of the Danube River, Europe. The effectiveness of detecting taxa corresponded well with an inshore–offshore gradient in sampling (i.e., distance from shore). Nevertheless, each method (i.e., littoral multihabitat sampling, kick and sweep sampling, and deep water dredging) contributed to some degree to overall taxa richness and species composition. Sampling in different depth zones characterized different assemblages, and consequently, inshore–offshore position was at least as important determinant of assemblage structure as longitudinal position of sampling sites in the river. Although we found significant congruency in the spatial variability of assemblages among the sampling methods, the relationships were only moderate. Our study on the large Danube River confirms studies from smaller rivers in other geographic regions that littoral monitoring provides higher taxa richness and more responsive changes to longitudinal gradients than deep water samples. Nevertheless, it also shows that sampling in different depth zones provides supplementary information on assemblage structure. Understanding changes in macroinvertebrate assemblages related to differences in sampling method is crucial to improve the bioassessment and environmental management of large rivers.     

Development of a standardized large river bioassessment protocol (LR‐BP) for macroinvertebrate assemblages

Efforts to develop benthic macroinvertebrate sampling protocols for the bioassessment of lotic ecosystems have been focused largely on wadeable systems. As these methods became increasingly refined and accepted, a growing number of monitoring agencies expanded their work and are now developing sampling protocols for non‐wadeable large rivers. Large rivers can differ from wadeable streams in many ways that preclude the use of some wadeable stream sampling protocols. Hence, resource managers need clear and consistent large river bioassessment protocols for measuring ecological integrity that are cost effective, logistically feasible, and meet or are adaptable to the multi‐purpose sampling needs of researchers and managers. We conducted a study using an experimental macroinvertebrate sampling method that was designed to overcome limitations of several methods currently in use. Our objectives were to: (1) determine the appropriate number of sampling points needed; (2) determine an appropriate laboratory subsample size to use and (3) examine how varying reach length affects assemblage characteristics. For six reaches in each of two large rivers, we sampled the macroinvertebrates of both banks at 12 transects separated by increasingly larger distances using a multi‐habitat, semi‐quantitative technique. Interpretation of results relied on the values attained for nine benthic macroinvertebrate assemblage metrics. Results from Monte Carlo methods indicated that, using the sampling methods described herein, a representative sample of the assemblage was collected by sampling both banks on 6 transects. Across all sites, we did not observe a consistent relationship between transect spacing (i.e. total reach length) and metric values, indicating that our sampling protocol was relatively robust with respect to variation in reach length. Therefore, flexibility exists that permits the study reach length to be dictated by the spatial scale (e.g. repeating geomorphic units) in question. For those preferring to use a fixed reach length, we recommend that transects be spaced at a minimum of 100 m intervals over a 500 m distance. We recommend that the field method be coupled with a fixed laboratory subsample size of 300 organisms for bioassessment purposes, with the recognition that a subsample size of 500 organisms may be needed to meet the objectives of more rigorous studies. It is likely this approach will over‐sample sites of uniform composition, but the goal was to develop a robust sampling protocol that would perform well across sites of differing habitat composition. Possible modifications to the method to streamline its future application in the field are provided. Published in 2006 by John Wiley & Sons, Ltd.     

Impoverishment of YOY‐fish assemblages by intense commercial navigation in a large Lowland river

Navigation‐induced physical forces have been suggested to modify the structure of riverine fish assemblages by impeding especially the recruitment of littoral bound species. To investigate the effect of vessel frequency on fish, we compared the composition and seasonal succession of young‐of‐the‐year (YOY) fish assemblages in three similarly degraded river reaches differing in average vessel passages (2, 6 and 41 per day). Fish were caught by electrofishing biweekly between May and September. Multivariate tests were used to analyse differences between YOY‐fish assemblages and hurdle regression models applied to determine abiotic factors predicting fish occurrence and abundance. Roach (Rutilus rutilus) and perch (Perca fluviatilis) densities were compared. Roach larvae remain in the littoral zone while perch larvae shift to the pelagic zone immediately after hatch. YOY‐fish assemblage structure substantially changed along the traffic intensity gradient. In the high traffic intensity reach, species number and total fish density were markedly reduced compared to the other reaches. Roach densities were lowest in the high traffic intensity reach whereas perch densities did not decline along the gradient. Hurdle regressions confirmed a stronger effect of commercial navigation traffic intensity on roach than on perch. The total zooplankton biomass was highest in the high traffic intensity reach. Our results provide empirical evidence that intensive commercial navigation impoverishes fish assemblages in width‐restricted waterways. They underlined that in particular those species that have their first nursery habitats in shoreline areas were more affected by intensive commercial navigation than species whose larvae live predominantly pelagic. The results indicate that the negative effect of intensive navigation on riverine fish results primarily from the navigation‐induced hydraulic disturbances along the banks. Therefore, mitigation of navigation‐induced hydraulic forces is required to prevent degradation of fish communities in waterways. Copyright © 2010 John Wiley & Sons, Ltd.     

Modelling the effects of climate and flow regulation on ice‐affected backwater staging in a large northern river

In cold region environments, ice‐jam floods (IJFs) pose a severe risk to local communities, economies, and ecosystems. Previous studies have shown that both climate and regulation affect IJF probabilities, but their relative impacts are poorly understood. This study presents a probabilistic modelling framework that couples hydrologic and hydraulic models to assess the relative role of regulated and naturalized flows on ice‐affected backwater staging. The framework is evaluated at an IJF‐prone town on the Peace River in western Canada, which has been regulated since 1972. Naturalized flows were generated for the comparison, and ice‐affected backwater profiles were calculated along jams of varying length and location and for different combinations of model parameters and boundary conditions. Results show significant differences in backwater staging (~2 m for a return period of T = 1:10 year) between two study time periods (1973–1992 vs 1993–2012) as compared with two different hydraulic flow conditions (regulated vs naturalized), suggesting a larger role of climate than regulation in backwater staging. However, regulation was found to offset flood risk during the 1973–1992 period and exacerbate flood risk during the 1993–2012 period.     

An assessment of the effectiveness of a vertical‐slot fishway for non‐salmonid fish at a tidal barrier on a large tropical/subtropical river

Fishways for salmon in temperate rivers have often been successful, but salmonid‐type fishways for non‐salmonid species in tropical and subtropical rivers have frequently failed. This study assessed the effectiveness of modifying a salmonid‐type pool‐and‐weir fishway into a vertical‐slot design on a tidal barrage on the subtropical Fitzroy River, in Queensland, north‐eastern Australia. In 38 paired samples of the top and bottom of the fishway, over 16 months, 29 fish species and over 23 000 fish were collected at a maximum rate of 3400 per day. This study shows much greater potential for success with a vertical‐slot fishway as relatively few fish negotiated the original pool‐and‐weir design. Common species using the vertical‐slot fishway included blue‐catfish (Arius graeffei [Ariidae]), bony herring (Nematalosa erebi [Clupeidae]), striped mullet (Mugil cephalus [Mugilidae]), barramundi (Lates calcarifer [Centropomidae]), and long‐finned eels (Anguilla reinhardtii [Anguillidae]). Freshwater shrimp (Macrobrachium australiense [Palaemonidae]), juvenile crabs (Varuna litterata [Grapsidae]) and long‐finned elvers did not ascend the full length of the fishway and specific fishways for these species are recommended. Fish between 25 and 640 mm in length ascended the fishway, although the passage of smaller size classes of immature fish was restricted and this may be important for the sustainability of these migratory populations. The barramundi (200–640 mm) which ascended the fishway were all immature fish. However, during a period of low river flows enlarging the width of the vertical‐slot from 0.15 to 0.45 m only encouraged a small number of larger fish (890 mm maximum length) to enter. The strong diel movement patterns of many species will need to be considered in future fishway design. Blue‐catfish could ascend the fishway in 2 h, but many fish remained in the fishway and this behaviour may cause crowding and a reduction in fishway capacity. Further work is needed to assess the proportion of fish finding the fishway entrance. However, the findings suggest that vertical‐slot fishways with lower water velocities and turbulence than salmonid fishways have great potential to pass the diverse migratory fish fauna of subtropical and tropical rivers. Copyright © 1999 John Wiley & Sons, Ltd.     

Long‐term changes in macroinvertebrate communities of a heavy metal polluted stream: the river Nent (Cumbria,UK) after 28 years

The macroinvertebrate fauna of the river Nent, a heavy metal polluted upland stream in northern England, first surveyed in 1976, was re‐examined in 2004 to assess long‐term changes in relation to activities in the catchment which have included, a river restoration project, works associated with the development of a mine heritage site and the removal of a chicken farm and more effective organic pollution control measures. The degree of change between years in total abundance, numbers of taxa and community composition varied considerably between sites. Two tributary sites showed marked changes between years due to a reduction in acidity in one and changed substratum in the other but in the main river no significant difference in total taxa and total abundance was observed between years, although seasonal differences were significant. Multivariate community analyses grouped 1976 samples with those taken in 2004 but revealed a clear separation between upper and lower Nent sites. This observed difference may be related to increased algal cover in the lower sites in conjunction with geomorphological features of the lower Nent. Environmental assessment methodology River Invertebrate Prediction and Classification System (RIVPACS) identified ‘sensitive’ faunal groups and indicated that the extensive impact of zinc pollution in the main river has remained practically the same between 1976 and 2004. This persistence of community structure despite the heavily disturbed nature of the river is attributed to relative constancy in instream habitat conditions. The recent activities in the catchment have had little effect on the overall controllers of faunal communities in this system, zinc concentrations and geomorphological characteristics of the stream. However, further disturbances involving movement of spoil heaps and channel alterations in the upper catchment may increase both sediment and heavy metal loadings to the river. Copyright © 2007 John Wiley & Sons, Ltd.     

The influence of hydro‐climatic and anthropogenic effects on the long‐term variation of commercial fisheries in a large floodplain river

This study deals with the effects of climate fluctuations and anthropogenic impacts on fisheries of Paraná River over the last 100 years. It is the first attempt to appraise the influence of hydro‐climatic and anthropogenic variables on the population changes of the most important inland fisheries of Argentina. Datasets covering more than eight decades (1935–2016) of a number of frequent and abundant commercial species inhabiting the main channel as well as the large floodplain of Paraná River were used. Our results suggest that fish catches and structure changed over time. Long and short‐term changes and reductions were closely related to fluctuations of 18 hydro‐climatic variables. Positive effects on the ichthyofauna were recorded during humid periods (1930–1940 and 1970–2000), when the frequency of large spring–summer floods increased. An increase in anthropic impacts (accounted for with nine variables) were recorded during the last two decades. We highlight the usefulness of the approach to support the management of the resources, ensuring sustainability of commercial fish assemblages and the long‐term conservation of biodiversity in big rivers.     

Regime shifts observed in Lake Kasumigaura,a large shallow lake in Japan: Analysis of a 40‐year limnological record

Lake Kasumigaura, which is composed of the two basins (Nishiura and Kitaura), is a large, shallow, hypereutrophic lake. Phytoplankton and water quality records from the past forty years were analysed to elucidate whether or not, when, and what type of certain regime shifts may have occurred, based on using inferential regime shift detectors. Characteristics of the phytoplankton and water quality changes were similar at 6 sampling sites in the two basins, with 20 water quality parameters being classified into four groups, based on cluster analysis. Shifts in dominant plankton groups (DPGs) and water quality occurring almost concomitantly, concentration on the period from 1987 to 1992 (Shift A) and from 1997 to 2001 (Shift B), with those observed for the two basins usually being similar with small differences. Two types of inferential regime shift detectors (sequential t‐test type; Rodionov's RSD and sequential F‐test type: package strucchange in R) yielded similar timings and significances of the shifts. Furthermore, changes in skewness and conditional heteroskedasticity (package early warnings in R) usually represented early warning signals before the shifts. Correlation analysis and ratios of dissolved inorganic nitrogen (DIN) vs. total phosphorus (TP) supported the hypothesis that phosphorus was the phytoplankton biomass limiting nutrient, except for one period for the Nishiura basin. Neither the nitrogen:phosphorus (N/P) ratio hypothesis and ammonia–nitrate (NH₄‐N/NO₃‐N) hypothesis satisfactorily explain the DPGs before and after Shift A (Microcystis spp. and Planktothrix spp., respectively), although it may be possible that these ratios triggered the DPG change in this shift. A considerable increase in silicon was observed for Shift B when the DPGs changed from cyanobacteria to diatoms. Further studies on the accurate types and triggers of the regime shifts are necessary to better understand the interactions between ecosystem and water quality for this and similar lakes elsewhere.     

Monitoring of environmental flow outcomes in a large river basin: The Commonwealth Environmental Water Holder's long‐term intervention in the Murray–Darling Basin,Australia

The Murray–Darling Basin in south‐eastern Australia contains over 70,000 km² of wetlands and floodplains, many of which are in poor condition. In response, Australian governments have committed to a major restoration program, the Murray–Darling Basin Plan that includes management of 2,750 Gl of environmental water to protect and restore aquatic ecosystems. The restoration is being undertaken within an adaptive management framework that includes monitoring the outcomes of environmental flows in seven river valleys. This paper provides an overview of the 5‐year monitoring project and some preliminary results. Monitoring design considered the Basin Plan's environmental objectives, conceptual models of ecosystem responses to flow, and an outcomes framework linking flow responses to the environmental objectives. Monitoring indicators includes ecosystem type, vegetation, river metabolism, and fish. Responses are evaluated to identify the contribution of environmental flows to Basin Plan environmental objectives and continual improvements in management. The program is unique in that it seeks to monitor long‐term outcomes of environmental flows at the river basin scale. Despite many challenges, the monitoring has become a key part of the adaptive management of environmental flows in the Murray–Darling Basin.     

The performance and efficacy of a two‐person operated portable PIT‐antenna for monitoring spatial distribution of stream fish populations

Passive Integrated Transponder (PIT) technology has enabled the tracking of individual fish by using data‐logging stations and one‐person operated portable tracking units. Whereas data‐logging stations are fixed at a certain location, the portable units have traditionally been used in studies that require tracking operations at small spatial scales (<1000 m²) due to the time investment necessary to fully scan the stream channel. We developed a two‐person operated portable antenna that is stretched between the operators and the area in between is scanned for PIT‐tags. The antenna was five metres wide but can be customized to fit stream‐specific needs. The antenna can be used with existing Texas Instruments Series 2000 tracking units, and the detection distance ranged between 46 and 61 cm when using 23‐ or 32‐mm PIT‐tags, respectively (tag held parallel to the plane of the open coil inductor loop). To assess antenna performance in field trial, we compared the efficacy (% tags found) and time‐efficiency (time used to track a study site) between one‐ and two‐person antennae in three separate stream sites. The new antenna type proved to be very efficient (95.2–100%) for locating tags in all trials. However, the new antenna type might not perform adequately in areas with high structural complexity (e.g. logjams, overhanging vegetation) and a follow‐up with one‐person operated antenna is recommended in such complex habitats. The time consumption was always lower (10–53%) with the new antenna and significant time savings can be assumed especially in areas with a low density of PIT‐tagged individuals. Further, we have successfully used the new antenna type to track juvenile Atlantic salmon both in winter conditions (ice‐free) and warmer water (14°C) without causing fright responses. The new antenna type makes the use of PIT‐technology feasible not only at the micro/mesohabitat scale but also at the segment/reach scale and can thus be used to monitor behavioural responses of fish at the population level in wadable streams. Copyright © 2007 John Wiley & Sons, Ltd.     

Process‐based assessment of success and failure in a constructed riffle‐pool river restoration project

Although there is increasing consensus that river restoration should focus on restoring processes rather than form, proven techniques to design and monitor projects for sediment transport processes are lacking. This study monitors bedload transport and channel morphology in a rural, an urban unrestored, and an urban restored reach. Objectives are to compare bedload transport regimes, assess the stability and self‐maintenance of constructed riffle‐pool sequences, and evaluate the impact of the project on coarse sediment continuity in the creek. Sediment tracking is done using radio frequency identification tracers and morphologic change is assessed from repeated cross‐section surveys. Mean annual velocity is used to quantify the average downstream velocity of tracers, defined as the mean overall tracer travel length divided by the total study duration. The channel reconstruction slows down the downstream velocity of particles in the D₇₅ and D₉₀ size classes, but does not significantly change the velocity of particles in the D₅₀ size class or smaller. Surveys show that riffle features remain stable and that pool depths are maintained or deepened, while tracer paths match with what has been observed in natural riffle‐pools. However, the slowdown of coarse sediment and increase in channel slope may lead to future failures related to over‐steepening of the banks and a disruption in the continuity of sediment transport in the creek. This study demonstrates how bedload tracking and morphological surveys can be used to assess river restoration projects, and highlights the importance of incorporating coarse sediment connectivity into restoration design and monitoring.     

Effects of river discharge on abundance and instantaneous growth of age‐0 carpsuckers in the Oconee River,Georgia, USA

The Oconee River in middle Georgia, U.S.A., has been regulated by the Sinclair Dam since 1953. Since then, the habitat of the lower Oconee River has been altered and the river has become more incised. The altered environmental conditions of the Oconee River may limit the success of various fish populations. Some obligate riverine fishes may be good indicator species for assessing river system integrity because they are intolerant to unfavourable conditions. For example, many sucker species require clean gravel for feeding and reproduction. Further, age‐0 fishes are more vulnerable than adults to flow alterations because of their limited ability to react to such conditions. In this study, we investigated the relationship between abundance and growth of age‐0 carpsuckers to river discharge in the Oconee River. A beach seine was used to collect age‐0 carpsuckers (Carpiodes spp.) from littoral zones of the lower Oconee River from May through July of 1995 to 2001. Regression models were used to assess whether 12 river discharge categories (e.g. peak, low, seasonal flows) influenced age‐0 carpsucker abundance or instantaneous growth. Our analysis indicated that abundance of age‐0 carpsuckers was significantly negatively related to number of days river discharge was >85 m³ s^?1(r² = 0.61, p = 0.04). Estimates of instantaneous growth ranged from 0.10 to 0.90. Instantaneous growth rates were significantly positively related to summer river discharge (r² = 0.95, p <0.01). These results suggest that (1) moderate flows during spawning and rearing are important for producing strong‐year classes of carpsuckers, and (2) river discharge is variable among years, with suitable flows for strong year‐classes of carpsuckers occurring every few years. River management should attempt to regulate river discharge to simulate historic flows typical for the region when possible. Such an approach is best achieved when regional climatic conditions are considered. Published in 2007 by John Wiley & Sons, Ltd.