Loss of habitat complexity through river channelization can have adverse affects on riverine fauna and flora through reductions in abundance and diversity of species. Habitat enhancement schemes are used to improve the physical and biological heterogeneity of riverine habitats. Between 1996 and 1997 the Environment Agency undertook a habitat enhancement scheme on the Huntspill River, Somerset, England to improve conditions for coarse (non-salmonid) fishes. The scheme involved reducing bank gradients and the construction of off-channel bays in parts of the channel, all of which were planted with willow (Salix sp.) and common reed (Plaragmites australis). The effectiveness of the enhancement scheme was investigated by comparing 0-group fish assemblages in manipulated and unmanipulated sites. Abundance and diversity of 0-group fishes was significantly higher in manipulated habitats. There was no significant difference detected in the effects of the different types of enhancement measure used. The significance of microhabitats produced by habitat enhancement schemes is discussed with respect to spawning, nursery and refuge sites for 0-group coarse fish assemblages. Copyright (C) 2001 John Wiley & Sons, Ltd.
A reservoir sediment release along the North Fork Cache la Poudre River (North Fork) in northern Colorado resulted in a massive fish kill and channel sedimentation that filled pools critical to fish as overwinter habitat. Recognition of the hazards associated with a large influx of sediment into a riverine ecosystem is critical for a greater understanding of the effects of sediment releases, and hence, future management of sediment within reservoirs. Two one-dimensional sediment transport models, HEC-6 and GSTARS 2.0, were evaluated for applicability to predict sediment removal along the steep gradient, bedrock-controlled pool-riffle North Fork. The ability of both models to identify flushing discharges that assist channel recovery was also evaluated. Two modeling scenarios representing a low and high flushing discharge were modeled. Within each scenario, two levels of simulations were conducted to represent conditions of data availability, a default simulation for limited data input, and a robust simulation that utilized the entire set of field data, collected over a 1-year period. The models were calibrated against quantitative measurements of pool bed elevation obtained during field resurveys. Preliminary analyses were conducted to identify the appropriate sediment transport equations. HEC-6 results indicate that long-term, robust simulations yield the closest agreement between predicted and measured pool bed elevation change. More than 50% of the actual scour and deposition within three pools was modeled using HEC-6. Modeling accuracy using GSTARS 2.0 was considerably lower, and it appears that the present construct of the model does not reflect the physical processes operating along the North Fork. Computer models are useful tools in the sediment management decision process, provided adequate data collection and calibration are conducted. In situations where restrictions exist on available flushing discharges, sediment transport modeling can assist management decisions, and modeling is always preferable to uncalibrated estimates. Copyright © 2001 John Wiley & Sons, Ltd.
River management has affected the ability of colonially-nesting waterbirds to reproduce in the Barmah-Millewa forest, south-eastern Australia. Relationships between reproductive performance and flow variability were quantified in order to establish the significance of the impact. The method of investigation involved: developing a conceptual framework describing four breeding-flow relationships (excellent, poor, abandoned and nil); obtaining measures for each relationship using annual breeding records (19 years; 1979-1997), habitat data (two traditional nest sites, one foraging area) and flow data (Murray River at Yarrawonga); and testing their predictive power at a landscape level. The effect of river management on the reproductive performance of colonially-nesting waterbirds was then assessed. Annual pulse dimensions in two runs produced by the monthly simulation model (natural and current flow; 1891-1992) were compared with the breeding-flow measures to obtain computer generated breeding level predictions. A major impact of river management was an 80% reduction in the frequency of successful breeding episodes compared to the natural precedent. The interval between breeding episodes during extended drought periods was identified as the most critical factor likely to affect the long-term stability or persistence of waterbird breeding in the forest. A literature review provided evidence of declining abundance and diversity of colonially-nesting waterbirds, and gave insight to the timing and factors contributing to the decline of many species. The principal conclusion is that three river flow objectives need to be addressed to ensure the long-term stability or persistence of breeding populations in the forest. Copyright (C) 2001 John Wiley & Sons, Ltd.
Habitat use and habitat selection by young Atlantic salmon and brown trout were investigated by direct underwater observation. We sampled during winter and summer water temperatures (low: 3-7 degreesC; high: 9-12 degreesC) coinciding with low and high waterflows (12-20 and 60-80 m(3) s(-1)), and during day and night in winter, and on six selected stations in the river. Observations of 396 salmon and 120 trout indicated a distinct seasonal pattern in behaviours and habitat selection. Feeding was the dominant behaviour at high water temperatures during summer. In winter, there was a diurnal pattern in behaviour; both species sheltered in interstitial spaces in the substrate during daylight, but during night held positions on or close to the substrate in slower flowing stream areas. Coarse substrate providing cover was therefore an important habitat factor during daylight at low water temperatures, while slow-flowing water was important during night. Although spatial niche overlap was considerable both in summer and winter, salmon and trout segregated with respect to meso- and microhabitat selection, and relatively more at low temperatures. Both species changed their use of mesohabitats towards more slow-flowing glide/flat habitats in winter. Irrespective of season, trout preferred in general more slow-flowing water than salmon did, but the difference was more pronounced in winter. Salmon used a wider range of water depths and in particular water velocities, than did trout. Both species were less tolerant of high water velocities at low water temperatures. The seasonal and diurnal pattern in habitat selection reported have important implications for habitat research and habitat-hydraulic modelling. Copyright (C) 2001 John Wiley & Sons, Ltd.
Lowland reaches of 40 rivers in New South Wales, Australia, were designated as ‘regulated’ or ‘unregulated’, depending upon the degree to which flows were modified by the operation of a dam upstream. Five replicate rivers of each type were selected from the North Coast, South Coast, Darling and Murray regions in the State. Fish communities in each river were sampled in summer and winter in two consecutive years. Regulated and unregulated rivers contained significantly different fish communities, although communities in each region retained characteristic features. The proportion of native species in the total catch was greater in unregulated rivers in all regions, ranging from 27% in the Murray region to 100% in South Coast rivers. In regulated rivers, native species made up 20% of the catch in the Murray region compared with a maximum of 99% in the North Coast. Carp, Cyprinus carpio , were the main alien species contributing to changes in the proportional abundance of native fish. Native species most affected by river regulation were western carp gudgeons, Hypseleotris spp., bony herring, Nematalosa erebi , and striped gudgeons, Gobiomorphus australis. Fifteen native species showed some effect of river regulation on their population structures. Individual species showed positive, negative or mixed positive and negative, effects of regulation, at population, species or community levels. Three abundant alien species and seven native species showed only positive or mixed responses, whereas 13 native species exhibited only negative effects. Flow regulation has reduced the resilience of New South Wales rivers and native fish communities to invasion by alien species. New research has commenced to investigate whether recently introduced environmental flow rules are effective in reducing the effects of river flow alteration on fish communities in New South Wales rivers. Copyright © 2001 John Wiley & Sons, Ltd.
This paper aims to show how hydrological, ecological and climatological data may be analysed to assess the temporal and spatial scales at which hydroclimatological variables influence instream ecology. A groundwater-dominated chalk stream (Little Stour River, Kent, UK), for which ecological data are available over 6 years (1992-1997), provides the focus for the testing and application of these techniques. Correlation and regression analyses are undertaken to highlight the dominant hydroclimatological factors influencing community abundance at a range of spatial scales encompassing: the entire river, upstream and downstream sectors, habitat type (riffle) and individual riffle sites. To set these results in a longer-term context, temporal sequencing of annual air temperature and discharge regimes is undertaken (based upon 30 years of data, 1969-1999). A classification of annual discharge hydrograph 'shape' and 'magnitude' identifies years with early, intermediate or late peaks, which may be assigned into three magnitude groups. Four annual air temperature 'magnitude' classes are apparent. The regime analysis clearly reveals inter-annual variability in both these key physical habitat parameters. Analysis of variance indicates a significant difference in macroinvertebrate community abundance for the hydrograph 'shape', 'magnitude' and combined classes identified at all scales of analysis, although the influence of air temperature only varied significantly between riffle sites. The techniques used may be easily adapted to water resource management. Copyright (C) 2001 John Wiley & Sons, Ltd.
Between June 1998 and May 2000 an adult fish sampling was carried out in the lowland River Oder using bottom otter trawls in the mid channel and electric fishing at the shorelines. This study focused on the lateral connectivity between mid channel and river margins with the aim to characterize the importance of mid-channel sections as fish habitat.Altogether 15 660 fish of 30 species were sampled, 8169 fish of 20 species in the mid-channel section and 7491 fish of 27 species at the shoreline. At the shoreline we observed significantly higher fish densities (345.4 +/- 51.8 fish per 1000 m(3) compared to 5.2 +/- 1.0, mean +/- standard error) and numbers of species (11.1 +/- 0.5, respectively, 5.2 +/- 0.3). However, three species were exclusively in the mid channel and a further six more frequent there. The mid channel was dominated by silver bream (Abramis bjoerkna) representing 75.6% of the total catch. It was generally colonized by bigger fish (22.1 +/- 0.12 cm. total length compared to 13.0 +/- 0.08 cm).According to the observed significant habitat preferences, we classified a guild of potamal species, which shift during their first year of life to mid-channel habitats and exhibited the highest relative abundance there. To this guild belong the following species: silver bream, common bream (Abramis brama), blue bream. (Abramis ballerus), whitefin gudgeon (Gobio albipinnatus), zander (Sander lucioperea) and wels (Silurus glanis). Copyright (C) 2001 John Wiley & Sons, Ltd.
The Mississippi and Missouri Rivers experienced flooding in 1993 that fell outside the annual predictable flood period of spring and early summer. Flooding began in late June, peaked in late July (25732 m(3)/s on the upper Mississippi and 21240 m(3)/s on the Missouri) and remained at or near flood stage into October 1993. This study was performed to determine if disturbance by an unpredicted flood event would alter trophic dynamics of river-floodplain systems by creating shifts in the composition of organic matter available to consumers. The Ohio River, which did not flood during the same period, was examined for comparison. Stable isotopic ratios of carbon and nitrogen from samples collected in 1993 and 1994 were used to characterize potential food sources and determine linkages between food sources and invertebrate and fish consumers. Pairwise contrasts, performed separately For each river, indicated there were few interannual differences in delta C-13 and delta N-15 of organic matter sources and consumers. Between sample period (flood year versus normal water year) trends in both flooded rivers were similar to between-year trends observed for the Ohio River. Trophic structure of the Mississippi and Ohio Rivers was similar in both years. with fine and ultra-fine transported organic matter and dissolved organic matter representing the major sources of organic matter. Overlapping isotopic signatures in the Missouri River made tracking of sources through the consumers difficult, but similarities in delta C-13 and delta N-15 between years indicated trophic structure did not change in response to the flood. The results suggest that consumers continued to rely on sources of organic matter that would be used in the absence of the unpredicted 1993 flood. It is proposed that trophic structure did not change in response to flooding in the Mississippi and Missouri Rivers because both rivers exhibited the same trends observed in the Ohio River. Copyright (C) 2001 John Wiley & Sons, Ltd.
Terrestrial arthropod communities remain poorly described for riparian ecosystems of the arid southwestern United States, and the effects of extensive river regulation and habitat alteration on these potentially important invertebrates are largely unknown. Beginning in 1991, surface-active arthropods were trapped at two riparian sites along the Rio Grande, in central New Mexico, for 2 years. One site was then experimentally flooded from mid-May to mid-June for each of the next 3 years to simulate historic, low intensity flooding, after which arthropod collections were continued. These primary sites, located outside the riverside levee, and isolated from flooding for about 50 years prior to the experiment, were compared with a naturally flooded site and a second non-flooded reference. Experimental flooding and observations of the naturally flooded site indicated that flooding did not affect total taxonomic richness, nor richness of spiders, beetles or ants. However, flooding may have slightly increased the number of carabid beetle taxa present. Flooding altered the overall composition for all taxa, insects, beetles and carabid beetles. Spider taxa composition may be insensitive to flooding, while ant responses were not clear. Abundance of terrestrial isopods and spiders decreased after flooding, while overall beetle abundance did not change. Abundance of crickets and carabid beetles increased, but the response was delayed until after the second flood. Changes in taxa composition and abundance after experimental flooding were generally consistent with arthropod community structure observed at a nearby naturally flooded site. This similarity suggests that reorganization of the terrestrial arthropod community may follow restoration of flooding to this riparian ecosystem. Copyright © 2001 John Wiley & Sons, Ltd.
Hydrochemical changes were monitored in a simulated, sea run salmon redd in a small agricultural stream in northeast Scotland following the 1998-1999 spawning season. Immediately after redd construction, the hydrochemical characteristics of hyporheic water, at depths of 0.1 m and 0.3 m, were very similar to stream water. These apparently well-mixed waters were alkaline, well-oxygenated and enriched in nutrients. In the weeks and months following redd construction, clear and statistically significant differences in the chemistry of stream and hyporheic waters were observed. Typically, hyporheic water had lower concentrations of dissolved oxygen (mean 7.35 mg L-1 at 0.3 m depth) than stream waters (mean = 11.26 mg L-1). Alkalinity, calcium, sulphate and conductivity levels tended to be higher in hyporheic waters, with concentrations increasing with depth. These data implied an increasing influence of groundwater with depth in the hyporheic zone following redd construction; an inference supported by subsequent hydraulic head measurements, which revealed an upwards groundwater flux in the stream bed. However, groundwater-surface water interactions were dynamic and complex: road salts eluted into the stream during periods of snowmelt simulated tracer experiments that implied that a reversed hydraulic gradient may occur at high flows with deeper streamwater penetration and mixing in the hyporheic zone. High flows also result in the mobilization of fine sediments from the stream bed which subsequently infiltrated into spawning gravels. These appear to cause `capping' of redds and probably reduce the hydraulic conductivity of the redd matrix. Infiltrating sediments also contain a small, but probably important organic component, the decomposition of which may contribute to oxygen consumption and nutrient mineralization in the hyporheic zone. Copyright (C) 2001 John Wiley & Sons, Ltd.
The River Rhine has suffered severely from pollution and stream regulation over the last two centuries, Industrial effluents and municipal wastewater have imposed pollutant loads, and major engineering works for drainage and navigation have changed the ecological condition of the river. Only during the last three decades has the rehabilitation of the river system been a topic of concern.The present Fish fauna is dominated by eurytopic cyprinids. Rheophilous species have declined in numbers, and anadromous fish have become scarce or extinct.Various forms of ecological rehabilitation in the Dutch Rhine are identified: floodplain development; optimization of migration routes with emphasis on the entrance of migrating species from the sea into the river; and restoration of spawning and nursery areas. Ecological restoration of the Rhine is an international effort. The present socio-economic functions of the river pose serious constraints on the feasibility of ecological targets. Copyright (C) 2001 John Wiley & Sons, Ltd.
Indicators of ecological health are problematic for wetlands in dry regions because distinctive communities are associated with dry and wet phases of indefinite duration. The propagule bank. including the resting stages of aquatic animals and plants, maintains the community's capacity to recover from drought or disturbance. This paper records observations of invertebrates, protists and algae emerging in laboratory microcosms following the inundation of dry sediments from two temporary lakes on the River Murray floodplain in South Australia. A simple experiment carried out on the sediment from one lake showed that increased salinity was associated with lower diversity (richness) but higher abundance of emergent organisms. The effect on diversity was evident at salinities above 11-17 mS cm(-1), and the effect on abundances was evident above 6-11 mS cm(-1) (salinity here is indicated by electrical conductivity at 25 degreesC), These data suggest that propagule banks may be useful as complementary indicators of wetland health. Copyright (C) 2001 John Wiley & Sons, Ltd.
The restoration of floodplain woodlands demands an understanding of the linkages between process, form and past management history at both a local and catchment scale. Site and reach scale processes that influence the species composition of floodplain woodland species are described with a particular focus on the relationships between hydrological and sediment inputs to floodplains and the regeneration response by tree species. The importance of integrating natural science knowledge gained at the site reach scale with decisions taken at the catchment scale on water allocation priorities is then discussed.Research was carried out on the River Ore in Sweden, The River Ouse in the United Kingdom and the River Is re and River Garonne in France. Research results at the site and reach scale allow broad definition of ideal conditions for the regeneration and growth of floodplain tree species and the flows that provide them: (1) channel movement has to occur for the creation of sedimentation sites required for the regeneration of early successional species and the flows that provide them; (2) flooding events should occur periodically to cause both channel movement and recharge floodplain water tables; (3) water table decline rates following a flood event must be slow enough that seedling roots can maintain contact with the retreating water front; (4) unseasonal flood events can cause high mortality of seedlings and prevent successful regeneration in any season. Some of the requirements for the restoration of floodplain woodlands can be delivered through site and reach scale restoration projects with reasonably predictable ecological outcomes. A more holistic approach to the provision of regeneration sites for floodplain woodlands would also include water allocation decisions targeted at providing flow conditions which could restore geomorphological processes. However, it is difficult to predict ecosystem responses to catchment scale flow allocation measures and, therefore, in the intensively managed river corridors of Western Europe, river restoration initiatives tend to be restricted to the site and reach scale. Copyright (C) 2001 John Wiley & Sons, Ltd.
Research on tropical fish ecology in South America is focused mainly on the effect of environmental variables on aquatic organisms. Physical, chemical and biological characteristics of water measured at a local scale (local variables) are used, although geomorphological and hydrological factors measured at a regional scale (regional variables), as well as temporal and spatial heterogeneity, can also be considered. However, the use of this multi-scale approach increases the perceived complexity, heterogeneity and variability of rivers. Thus, it is important to determine the magnitude of habitat variability and those parameters having the greatest influence on it. In this study, 28 stations distributed on 16 different rivers in French Guiana were sampled during high water at a meso spatial scale. Physical features of the rivers were sampled along an 800-m stretch, where nine transversal transects were established on the main channel. At each river, 17 local and six regional variables were measured. Local variables relating to the physical characteristics of the channel bank and main channel and regional variables characterizing the whole basin and the position of the station in the basin were qualitatively and quantitatively described. All variables were submitted to multivariate analysis in order to determine their relative contribution to total variance. Two quantitative regional variables (drainage area upstream from station and river drainage basin), five quantitative local variables (channel width, water temperature, channel depth, Secchi transparency and conductivity) and one qualitative local variable (channel substrate) were shown to differentiate the 16 rivers sampled. This result shows the poor contribution of qualitative variables compared with quantitative ones. Gradual change in qualitative variables is probably responsible for this poor contribution to the total variance; thus. the use of such variables is not possible for spatial habitat differentiation in this study. Copyright (C) 2001 John Wiley & Sons, Ltd.
We revisit the serial discontinuity concept (SDC), which predicts river ecosystem responses to stream regulation in the context of recovery with distance downstream from the dam (discontinuity distance). Many studies have described pervasive interruptions of natural biophysical gradients of dams by comparing conditions in tailwaters to reference or pre-impoundment conditions. But only a few studies provide data or interpretations that explicitly test the SDC within entire stream corridors or along specifically defined reaches where recovery was expected in view of the predictions of the SDC. We present discontinuity distance measures for nine rivers around the world where the predictions of the SDC were substantiated. In two cases, recovery trajectories were overwhelmed by other human sources of disturbance. In one case, the SDC did not hold up, but only biotic measures were made. We conclude that, in general, the SDC is a sound construct that in most cases can be used to predict, or at least clearly articulate, the consequences of new regulation. The next step is to develop better empirical models of the SDC and to validate them experimentally through re-regulation of entire river corridors.
Running water ecology is a young science, the conceptual foundations of which were derived largely from research conducted in Europe and North America. However, virtually all European river corridors were substantially regulated well before the science of river ecology developed. While regulation of North American river systems occurred later than in European systems, river ecology also developed later. Therefore, there is a general impression of rivers as being much less heterogeneous and much more stable than they actually are in the natural state. The thesis of this paper is that established research and management concepts may fail to fully recognize the crucial roles of habitat heterogeneity and fluvial dynamics owing to a lack of fundamental knowledge of the structural and functional features of morphologically intact river corridors. Until quite recently, most concepts in river ecology were based on the implicit assumption that rivers are stable, single-thread channels isolated from adjacent floodplains. Unfortunately, many rivers are in just such a state, but it should be recognized that this is not the natural condition. This incomplete understanding constrains scientific advances in river ecology and renders management and restoration initiatives less effective. Examples are given of the high level of spatio-temporal heterogeneity that may be attained in rivers where natural processes still operate on a large scale. The objective of this paper is to promulgate a broader and more integrative understanding of natural processes in river corridors as a necessary prelude to effective river conservation and management. Copyright (C) 2001 John Wiley & Sons, Ltd.
Habitat suitability of brown trout (Salmo trutta fario) was studied in the upper portion of the Adda River, Northern Italy. Measurements were made for 528 individuals distributed in two life-stage classes, adult and juvenile, based on body length. In order to provide basic biological information for the physical habitat simulation (PHABSIM) system of the instream flow incremental methodology (IFIM) in the Italian regulated rivers, habitat suitability curves (HSCs) have been developed with respect to several microhabitat riverine parameters. Initially, current velocity, water depth, substrate class size and cover were analysed with an univariate approach, then bivariate habitat suitability models were developed from depth and velocity data. The comparison of experimental univariate HSCs with those from the literature outlined some differences that can essentially be explained by characteristics of the investigated river, confirming the necessity of using site-specific curves in relation to each experimental study area. To compare the univariate and bivariate approaches, the weighted usable area (WUA)–discharge relationships were calculated using both types of HSCs. Response curves obtained from the two approaches turned out to be quite different. In PHABSIM habitat modelling, HSCs univariate functions need to be aggregated to produce the WUA–discharge relationship. A multiplicative criterion is generally used for the combined suitability factor; by means of this aggregation criterion all variables have equal weight. According to bivariate models, depth is much more important than velocity in defining habitat suitability requirements. Copyright © 2001 John Wiley & Sons, Ltd.
Although lake-dwelling trout frequently eat smaller conspecifics in the absence of other fish prey, there are fewer reports of cannibalism in stream populations. However, a coarse riverbed structure and low discharge may facilitate cannibalism by providing pools for large fish whilst limiting refuges for small ones.We estimated the autumn size structure and density of the seatrout population in a regulated stream in western Norway over a period of 12 years. Bioenergetics models were used to relate energy intake in large trout ( greater than or equal to 17 cm) to the biomass of small fish present.The number of 0 + trout in autumn decreased with increasing abundance of large trout (log-log regression, nonlinear R-2 = 0.80, n = 10, p = 0.0005). The size distribution of 0 + trout in autumn had a lower mean, but more positive skewness, when many small fish were present. Twenty percent of the large trout sampled had parr of trout or salmon Salmo salar in their stomach. The total food consumption estimated for large trout exceeded the total energy content of small fish in years with few small per large trout.We conclude that cannibalism appears to be an important cause of small-fish mortality in this stream, regulating the abundance and size distribution of small trout. In streams with low discharge, weir building can improve conditions for large trout, presumably reducing the density of small fish. However, it is difficult to predict the net effect on smolt production of improved growth but increased mortality. Copyright (C) 2001 John Wiley & Sons, Ltd.
Over the past two decades of refinement and application of instream flow evaluations, we have examined the hydraulic habitat of aquatic macroinvertebrates in a variety of conditions, along with the role of these macroinvertebrates in sustaining ecosystem integrity. Instream flow analyses assume that predictable changes in channel flow characteristics can, in turn, be used to predict the change in the density or distribution of lotic species or, more appropriately, the availability of useable habitat for those species. Five major hydraulic conditions most affect the distribution and ecological success of lotic biota: suspended load, bedload movement, and water column effects, such as turbulence, velocity profile, and substratum interactions (near-bed hydraulics). The interactions of these hydraulic conditions upon the morphology and behavior of the individual organisms govern the distribution of aquatic biota. Historically, management decisions employing the Physical Habitat Simulation (PHABSIM) have focused upon prediction of available habitat for life stages of target fish species. Regulatory agencies have rarely included evaluation of benthos for flow reservations. Although 'taxonomic discomfort' may be cited for the reluctant use or creation of benthic criteria, we suggest that a basic misunderstanding of the links between benthic macroinvertebrate and the fish communities is still a problem. This is derived from the lack of a perceived 'value' that can be assigned to macroinvertebrate species. With the exception of endangered mussel species (for which PHABSIM analysis is probably inappropriate), this is understandable. However, it appears that there is a greater ability to predict macroinvertebrate distribution (that is, a response to the change in habitat quality or location) and diversity without complex population models. Also, habitat suitability criteria for water quality indicator taxa (Ephemeroptera, Plecoptera, and Trichoptera; the so-called 'EPTs') may also provide additional management options to stream regulators. The greatest application for macroinvertebrate criteria will be in low-order streams where a more immediate link to fish communities can be established. We present an example from Queens Creek, in North Carolina, USA, in which monthly allocations required to preserve the integrity of the benthic macroinvertebrate community were significantly higher than for the target benthic fish species, Cottus bairdi. In the months when both Cottus and community diversity of macroinvertebrates were the 'bottleneck' life stages, preservation of only fish species could result in an additional 5-25% loss in macroinvertebrate habitat. We suggest that, as there becomes an increased emphasis on maintaining macroinvertebrates as monitors of stream health, there will be a concurrent emphasis on incorporating hydraulic habitat conditions as a part of bioassessment. Copyright (C) 2001 John Wiley & Sons, Ltd.
Owing to river regulations in the past and intensive farming, the ecological value of the floodplains of the River Rhine in The Netherlands has decreased dramatically. One way to restore riverine biotopes is to create permanently flowing channels in the floodplain. Along the River Waal, the main branch of the Lower River Rhine, two such secondary channels have been created since 1994. A post-project monitoring programme of 5 years was set up, which included hydrological, morphological and ecological parameters. This article focuses on the monitoring of aquatic macrophytes, aquatic macroinvertebrates, fish and wading-birds.The results show that man-made, excavated secondary channels function as a biotope for riverine species including the more demanding rheophilic species. The demands for shipping and protection against flooding on the River Waal cause constraints on secondary channels. Despite these constraints there is still enough space for hydromorphological processes to create new habitats in secondary channel 1, near Opijnen. The space for hydromorphological processes is less in secondary channel 2, near Beneden-Leeuwen. The density and the number of (rheophilic) species are for a large part influenced by the water level and frequent inundation caused by the high hydrological connectivity. Man-made secondary channels seem to provide suitable habitat that is currently lacking for a broad range of rheophilic macroinvertebrate and fish species in the Lower River Rhine in The Netherlands. Owing to the lack of suitable habitats for rheophilic macroinvertebrate and fish species before the creation of the secondary channels, the importance of longitudinal and transversal migration could be illustrated by the drift of macroinvertebrates during floods and the seasonal migration of Age-0 and Age-1 + fish species. Copyright (C) 2001 John Wiley & Sons, Ltd.
