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1.
    
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2.
The mean column velocity preference of juvenile Atlantic salmon Salmo salar (LF 30–55 mm) was investigated by observing their spatial pattern of habitat use in a laboratory flume while varying discharge (Q) over a 18‐fold range (Q=2·6–46·8l s‐1). Based on 341 fish observations at three discharges (Q=2·6, 15·0 and 46·8l s‐1), three separate velocity preference curves were developed using standard procedures. The mean column velocities measured at 0·6 depth for the fish positions at the set low, medium and high discharges had medians of 7, 10 and 24 cm s‐1, respectively, and varied significantly between the discharges. Across the range of flows, the fish utilized mean column velocities between 0 and 56 cm s‐1, but the three velocity preference curves differed. Differences between juvenile Atlantic salmon use of habitat, defined according to mean column velocities at different discharges, were greatest at the lower end of the available range of velocities (<20 cm s‐1). Weighted usable area (WUA), the output of the instream flow model PHABSIM that is used to describe the available habitat at a given discharge, was calculated for the flume using the preference curves built at the three set discharges. The model was highly sensitive to differences between the three preference curves and WUA varied by up to a two‐fold difference. Furthermore, habitat‐discharge relationships derived from the three preference curves were very different. Predicted habitat losses across the modelled range of discharges varied by up to 150% depending upon which velocity preference curve was used in the model. Thus, the assumption that a single preference curve can be applied across a range of discharges is not valid and is likely to result in large errors when employing PHABSIM and other models that use similar principles.  相似文献   

3.
Benthic macroinvertebrates were sampled at regular intervals from rural and urban sections of the River Roding, Essex, England, in 1975 and 1976. During the latter year a severe drought led to a marked decline in flows and to desiccation of parts of the river bed. In general, drought conditions resulted in an increase in invertebrate populations and possible reasons for this are presented. A considerable number of individuals of certain groups such as cased caddisfly larvae and prosobranch molluscs were, however, eliminated from the river at this time, mainly as a result of stranding and chemical changes in the environment. The effect of reduced flows on river faunas is briefly discussed.  相似文献   

4.
River discharge has long been recognized as one of the factors that contributes to the high productivity of estuaries. Although there is little evidence that river inputs of terrestrial carbon make a direct contribution to coastal food webs, such exported nutrients may stimulate in situ production in estuaries and thus enhance the survivorship and growth of fish and crustaceans in these systems. Furthermore, fluctuations in salinity and turbidity may influence the extent of available habitat for fish and crustaceans and therefore their distribution and/or catchability. Despite these potential links between flow and the secondary production of estuaries and coastal waters, there is still a common perception that ‘water going to sea is wasted’ and a continuing trend to regulate the flow of rivers. We review the evidence for links between river flow and the productivity of estuarine/coastal fisheries, drawing on a case study of the Logan River in southeast Queensland, and explore the potential mechanisms for these linkages. Our research, and that of others, confirms that high river discharge can have a strong positive effect on the production of commercial and recreational coastal fisheries. It also shows that the seasonal pattern of flow is equally, if not more important, than the magnitude of flow. River regulation is likely to have a dramatic effect on the production of coastal fisheries and, given the current pressures for water resource development, this is an important avenue for future research and evaluation.  相似文献   

5.
Environmental flow releases have been advocated as a useful rehabilitation strategy for improving river condition but assessments of their success have typically focused on surface water quality and biota. In this study, we investigated the impacts of an environmental flow release on water temperature, conductivity, dissolved oxygen, and nitrate concentrations in surface and subsurface (hyporheic) water at upwelling and downwelling zones in three sites along the Hunter River, New South Wales, Australia. We hypothesised that the flow pulse would ‘flush’ the sediments with oxygenated water, stimulating hyporheic microbial activity and nitrification, enhancing nitrate concentrations over time. Surface and subsurface samples were collected before, 7 days after, and 49 days after an environmental flow release of 5000 Ml for a period of 3 days. No lasting effects on dissolved oxygen or conductivity were evident at most sites although dissolved oxygen declined over time at the downwelling site at Bowmans Crossing. At the downwelling zones at all sites, hyporheic nitrate concentrations declined initially following the release, but then rose or leveled off by Day 49. This initial drop in concentration was attributed to flushing of nitrate from the sediments. At two sites, nitrate concentrations had increased by Day 49 in the upwelling zones while at the third site, it fell significantly, associated with very low dissolved oxygen and likely reductive loss of nitrate. Electrical conductivity data indicate that potential inputs of agriculturally enriched groundwater may contribute to the nitrogen dynamics of the Hunter River. This study highlights the spatial heterogeneity that occurs in the hyporheic zone within and among sites of a regulated river, and emphasises the need for multiple-site surveys and an understanding of groundwater dynamics to assess physicochemical responses of the hyporheic zone to environmental flow releases.  相似文献   

6.
In Aberdeen, Scotland, in July 2000, aninternational symposium was held to presentresearch concerning the consequences of growthvariation for the ecology, evolution, andmanagement of salmonid fish. Presentationscovered important topics including linksbetween growth and mortality, interactionsbetween growth and life history, tradeoffsbetween growth and other fitness aspects, andevolutionary implications of growth variation. In addition, the symposium served as a showcaseof new approaches and technologies in salmonidresearch. In this review, I provide anoverview of the presentations, and summarizesome of the major emergent themes of thesymposium.  相似文献   

7.
    
《Ecohydrology》2017,10(3)
Regional classification of streams is an early step in the Ecological Limits of Hydrologic Alteration framework. Many stream classifications are based on an inductive approach using hydrologic data from minimally disturbed basins, but this approach may underrepresent streams from heavily disturbed basins or sparsely gaged arid regions. An alternative is a deductive approach, using watershed climate, land use, and geomorphology to classify streams, but this approach may miss important hydrological characteristics of streams. We classified all stream reaches in California using both approaches. First, we used Bayesian and hierarchical clustering to classify reaches according to watershed characteristics. Streams were clustered into seven classes according to elevation, sedimentary rock, and winter precipitation. Permutation‐based analysis of variance and random forest analyses were used to determine which hydrologic variables best separate streams into their respective classes. Stream typology (i.e., the class that a stream reach is assigned to) is shaped mainly by patterns of high and mean flow behavior within the stream's landscape context. Additionally, random forest was used to determine which hydrologic variables best separate minimally disturbed reference streams from non‐reference streams in each of the seven classes. In contrast to stream typology, deviation from reference conditions is more difficult to detect and is largely defined by changes in low‐flow variables, average daily flow, and duration of flow. Our combined deductive/inductive approach allows us to estimate flow under minimally disturbed conditions based on the deductive analysis and compare to measured flow based on the inductive analysis in order to estimate hydrologic change.  相似文献   

8.
In this study, individual growth patterns of wild‐type and growth‐enhanced coho salmon Oncorhynchus kisutch at 8, 12 and 16° C water temperature were followed. Despite large differences among individuals in growth rates, there was generally little variation in the shape of the growth curves among O. kisutch individuals of both genotypes and at all temperatures. Typically, individuals that were relatively large initially were also relatively large at the end of the growth period. The limitation in variation was more pronounced in the growth‐enhanced O. kisutch than in the wild type, where the relative size of some individuals reared at 12 and 8° C changed by the end of the trial. As a warmer temperature seems to decrease the plasticity of growth trajectories in wild‐type fish, it is possible that global warming will influence the ability of wild fish to adapt their growth to changing conditions.  相似文献   

9.
    
Interactions between birds and fish are often overlooked in aquatic ecosystems. We studied the influence of Atlantic salmon and brown trout on the breeding population size and reproductive output of the white‐throated dipper in a Norwegian river. Acidic precipitation led to the extinction of salmon, but salmon recolonized after liming was initiated in 1991. We compared the dipper population size and reproductive output before (1978–1992) and after (1993–2014) salmon recolonization. Despite a rapid and substantial increase in juvenile salmon, the breeding dipper population size and reproductive output were not influenced by juvenile salmon, trout, or total salmonid density. This might be due to different feeding strategies in salmonids and dippers, where salmonids are mainly feeding on drift, while the dipper is a benthic feeder. The correlation between the size of the dipper population upstream and downstream of a salmonid migratory barrier was similar before and after recolonization, indicating that the downstream territories were not less attractive after the recolonization of salmon. Upstream dipper breeding success rates declined before the recolonization event and increased after, indicating improved water quality due to liming, and increasing invertebrate prey abundances and biodiversity. Surprisingly, upstream the migratory barrier, juvenile trout had a weak positive effect on the dipper population size, indicating that dippers may prey upon small trout. It is possible that wider downstream reaches might have higher abundances of alternative food, rending juvenile trout unimportant as prey. Abiotic factors such as winter temperatures and acidic precipitation with subsequent liming, potentially mediated by prey abundance, seem to play the most important role in the life history of the dipper.  相似文献   

10.
1. A growth model, originally developed for brown trout (Salmo trutta), has now been fitted to data for Atlantic salmon (S. salar) and stone‐loach (Barbatula barbatula) from English populations, and Arctic charr (Salvelinus alpinus) from Sweden. The model relates growth rate to temperature for a fish of standard size and the functional relationship has a triangular shape with a sharp peak at the optimal temperature for growth and zero growth at the base of the triangle. It was unsuitable for growth data for Norwegian salmon, and a curvilinear Ratkowsky model provided a better fit, though the experimental protocol was different in the Norwegian and English experiments. 2. The Norwegian salmon were kept in groups in each tank, had to compete for food, and had to be divided into slow, moderate and fast growers before the Ratkowsky model could be fitted. Each English salmon was kept in its own tank and fed individually. For replicate experiments, fish of similar size were selected. Variation among fish kept under similar conditions was therefore small, and the triangular model was essentially for individual fish, not groups of fish. 3. The present simulation study tests the hypothesis that individual differences in the growth response could account for the curvilinear growth‐temperature relationship for the Norwegian salmon. The triangular model was used to generate the growth response to temperature for a group of salmon, each fish having a slightly different temperature preference and growth rate. The result was a curvilinear response, well approximated by the Ratkowsky model (adjusted R2 = 0.96). When the variability in individual temperature preference was increased, the Ratkowsky model was an even better fit (adjusted R2 = 0.98). Therefore, the apparent discrepancy between the two models was reconciled by allowing for individual differences in temperature preference and growth rate within groups of fish.  相似文献   

11.
1. Our objective was to measure the influence of hydrological connection with anabranch channels on the availability of major carbon sources in a lowland, anabranching floodplain river landscape. 2. Results show that anabranch channels are sinks for large quantities of sediment‐associated carbon, facilitated by high rates of sediment deposition, and are sources for dissolved organic carbon (DOC), partly via inundation‐stimulated release from surface sediments and leaf litter. This dual role influences ecological pattern and process at multiple spatial and temporal scales, including within‐flow pulse phase differences in carbon availability and anticlockwise hysteresis in the DOC–discharge relationship. 3. Hydrological connection with anabranch channels in riverine landscapes appears to increase the retention, concentration and diversity of carbon sources over both space and time, changing the timing of carbon transport downstream and shortening the carbon spiral at a landscape scale. 4. In contrast to floodplains, anabranches exchange carbon sources with the river ecosystem during flow pulses below bankfull. They are relatively easy to target for management because they have definable commence‐to‐flow levels and require relatively small amounts of water for connection. However, the type and amount of carbon exchanged between the anabranches and the river channel will vary depending on the frequency, magnitude and duration of flow pulses. 5. Managed, periodic connection of anabranch channels via environmental flows should be considered as an option between large flood events.  相似文献   

12.
13.
    
Relationships between freshwater flows and growth rates of the opportunistic predatory finfish barramundi Lates calcarifer in a dry tropical estuary were examined using data from a long-term tag-recapture programme. Lagged effects were not investigated. After accounting for length at release, time at liberty and seasonal variation ( e.g. winter, spring, summer and autumn), growth rates were significantly and positively related to fresh water flowing to the estuary. Effects were present at relatively low levels of freshwater flow ( i.e. 2·15 m3 s−1, the 5th percentile of the mean flow rate experienced by fish in the study during time at liberty). The analysis, although correlative, provides quantitative evidence to support the hypothesis that freshwater flows are important in driving the productivity of estuaries and can improve growth of species high in the trophic chain.  相似文献   

14.
1. This study summarises our development and application in developing countries of a process for assessing the ecological, social and economic costs and benefits of water-resource developments, as an aid to basin planning.
2. During 15 years of work in Africa and Asia, the process sequentially included the whole river ecosystem and the whole flow regime in the assessment; used a multidisciplinary team and a scenario-based approach that gave equal weighting to the ecological, social, resource-economic and macro-economic costs and benefits of development; quantified or semi-quantified the costs and benefits in data-poor situations, capturing expert opinion and local wisdom as well as data; recognised that the final allocation of water for ecosystem maintenance should be a societal choice of trade-offs between resource protection and development.
3. Flow assessments were increasingly done at the basin rather than project level and introduced the concept and practicality of Development Space as a tool to aid basin planning.
4. Later assessments included valuation of regulating, cultural and provisioning services provided by rivers as part of the cost-benefit analysis.
5. Implementation of managed flows as outlined above is a complex and long-term process that should include a number of major steps, from development of the appropriate legislation to monitoring of management decisions and adaptive management. Country or region-wide implementation at this scale could well take one to two decades, even where the political will and technical skills exist.
6. We conclude by offering eight principles that we believe would promote genuinely sustainable use of rivers.  相似文献   

15.
Ombredane  Dominique  Haury  J.  Chapon  P. M. 《Hydrobiologia》1995,300(1):259-268
Hydrobiologia - To study the salmonids potential production of a coastal river main stream from simple characterization of the fish habitat, it was necessary to rate the hydrosystem's spatial...  相似文献   

16.
Studies were conducted to determine the effects of experimental manipulations of discharge on invertebrate drift in two regulated rivers in northwestern Montana, USA. During these studies the discharge regime in the Flathead River was characterized by frequent flow fluctuations, while in the Kootenai River high discharge was maintained for much longer periods before flow was reduced to minimum discharge. The magnitude of the response of invertebrates to disturbance was different in the two rivers, in part because of the different frequencies of flow changes. Midstream invertebrate drift increased an order of magnitude during increasing discharges in the Flathead River but was not substantially increased during decreasing discharges. When the prior discharge regime had been sustained at high levels in the Kootenai River, invertebrate drift densities as high as 300 000/100 m3 were measured along the shoreline following reductions in discharge, both immediately after flow began to decrease and after dark on the same day. There was also more recolonization of shoreline areas and more stranding of insects following dewatering of nearshore regions when there had been sustained high discharge levels prior to the flow reduction. More insect stranding occurred during a faster rate of decrease in discharge (50 000 to 100 000 organisms m−2).  相似文献   

17.
  总被引:3,自引:0,他引:3  
The trout (Salmo trutta) has been divided into three forms: sea-run trout, lake-run brown trout, and resident brown trout. They differ in their living environment, migratory behaviour, growth and appearance. As local trout populations are often isolated, and gene flow between them is minimal, differentiation between populations can be expected. The morphology of 1-year-old trout from ten populations representing all three forms was studied in a common-garden experiment. The fish were reared under similar environmental conditions, and 20 morphometric characters were measured from each individual fish. Marked morphological differentiation was found, and differences between populations were greater than differences between forms. The results suggest that the differences have a genetic basis, and they are likely to indicate adaptation to local environmental conditions in the native habitat of the trout.  相似文献   

18.
    
The fourth assessment report of Intergovernmental Panel on Climate Change (IPCC) suggests studies that increase the spatial resolution to solve the scale mismatch between large‐scale climatic models and the catchment scale while addressing climate change impacts on aquatic ecosystems. Impacts occur mostly at the local scale, though potential changes in the hydrological cycle and eco‐hydrological processes are more difficult to model and analyse at this level. The difficulty is even greater for studies on lowland river systems, which require the modelling of hydrological processes in greater detail. In this study, the regional impacts of climate change on river flow and environmental flow requirement, which is a negotiated trade‐off between water uses, are analysed for a lowland catchment in Denmark through MIKE SHE/MIKE 11 coupling. The coupled model possesses an important capacity for simulating stream flows and groundwater head levels in a dynamic system. Although the simulation results from different global circulation models (GCMs) indicate different responses in flows to the climate change, there are obvious deviations of the river flows and environmental flow potentials computed for all the scenario cases from the averages of the base period with current conditions. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

19.
The study explored the combined effects of density, physical habitat and different discharge levels on the growth of juvenile Atlantic salmon Salmo salar in artificial streams, by manipulating flow during both summer and winter conditions. Growth was high during all four summer trials and increased linearly with discharge and mean velocity. Differences in fish densities (fish m?3) due to differences in stream volume explained a similar proportion of the variation in mean growth among discharge treatments. Within streams, the fish aggregated in areas of larger sediment size, where shelters were probably abundant, while growth decreased with increasing densities. Fish appeared to favour the availability of shelter over maximization of growth. Mean growth was negative during all winter trials and did not vary among discharge treatments. These results suggest that increased fish densities are a major cause of reduced summer growth at low discharge, and that habitat‐mediated density differences explain the majority of the growth variation across habitat conditions both during summer and winter.  相似文献   

20.
    
Understanding the links between instream ecology and hydrology has become a critical task in contemporary river research and management. Habitat selection behaviour is a central dimension in applied ecology because it is a primary way that mobile organisms adapt to changing environmental conditions. Here, we analyzed brown trout habitat selection during two consecutive years in rivers presenting contrasting flow conditions to test the following hypotheses: (1) given that adaptation to flow regimes occurs as a response to the interaction between frequency, magnitude and predictability of mortality‐causing events, habitat selection would vary across populations subject to different disturbance regimes; (2) because adaptations are directed towards enduring both intra‐annual and interannual variations in flow, habitat selection would shift across years as a response to changing flow conditions and (3) such responses to yearly flow fluctuations would depend on the historical long‐term hydrologic regime. We found that trout from rivers with highly variable flow and more frequent, longer and stronger extreme flow events were more willing to occupy positions in high‐velocity habitats and showed stronger requirements for velocity refuges, whereas trout inhabiting more stable and benign flow environments selected visually‐covered habitats to minimize biotic interactions. Results also revealed that trout shifted habitat selection patterns across years differing in flow conditions irrespective of river typology, but this shift was markedly stronger in rivers with higher flow variability and extremity. Overall, observed ecological patterns have strong implications for predicting the consequences of flow alteration for species adapted to particular flow regimes. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献   

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