ISSN:0886-9375    

DOI:10.1002/rrr.3450100202

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe life cycle of the net‐spinning caddisfly,Arctopsyche ladogensis(Kolenati), was studied at a site 25 km below a major catchment transfer dam on the large Norwegian river, the Glomma. The site experiences 25–50% of pre‐impoundment flows during winter and at times during summer. The sampling frequency varied between 2 and 3 weeks in mid‐summer to every 2 months during winter. There were five larval instars. In the fifth instar there was a clear size bomodality, the females being larger than the males. Pupae were present during the spring flood. The adult flight period extended from early June until mid‐July. There was a mixture of one‐ and two‐year life cycles, with a semivoltine cycle dominating. Such life cycle flexibility is advantageous in adapting to changed temperature and flow regimes in regulated

ISSN:0886-9375    

DOI:10.1002/rrr.3450100203

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractTaxa and community relationships with flow were investigated using National Rivers Authority macroinvertebrate sampling records from a total of 45 sites in the River Glen catchment and daily flow records, taken over the period 1976–1994. Four sites (two upstream and two downstream of an interbasin transfer outflow) were studied in detail. Community analyses of summer samples (41 records from 1977 to 1994) showed April mean flow and low flows in the same summer as sampling to be the best predictors of macroinvertebrate community type. Comparison of the frequency of individual taxa in summers when flows were above or below the flow sustained by the inter‐basin transfer (0.107 m3s−1) showed a relatively high number of taxa, including Sailidae, Molannidae,Planorbisspp. and Haliplidae, to be more frequent in low‐flow summers, whereas other taxa, including Rhyacophilidae and Leptophlebidae, were more frequent in high‐flow summers, differences apparently related to position in the catchment and variability in the development of marginal macrophytes. The implications of altering flow regime on habitat and macroinvertebrate communities are discussed, and the suitability of National Rivers Authority biological records for developing long‐term flow‐preference relationships for individual taxa a

ISSN:0886-9375    

DOI:10.1002/rrr.3450100204

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractFish abundance and size composition in a 28 km stretch of the Vltava River in the Czech capital of Prague were studied using horizontal dual‐beam scientific sonar. Very low fish densities (0.6–0.7 fish/100m3) were found above Prague where the river is influenced by a cascade of reservoirs. These have a retention time of more than 100 days and release hypolimnetic water. A significant increase in fish density was found in the Berounka River confluence (a tributary with a normal, seasonal temperature pattern) just above the city (about 10 fish/100 m3). The fish stock is fairly low in the city itself because of channelization of the river bed (1.3–3.5 fish/100 m3), but much greater densities (14.9–16.9 fish/100 m3) were found below the city where the river receives a high organic load of partially treated sewage and has a semi‐natural shoreline. The largest average fish size and biomass were also reported from thi

ISSN:0886-9375    

DOI:10.1002/rrr.3450100205

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractA habitat suitability model is derived for juvenile 0+ roach [Rutilus rutilus(L.)] in the river Great Ouse (UK) using data collected by point abundance sampling by electrofishing. A total of 1718 point samples was used in the analysis. Of these, 392 contained juvenile roach. Polynomial equations describing habitat suitability are derived from depth, mean substratum particle diameter and water velocity data, and an index of plant cover suitability is described. Optimum conditions for roach are a depth of 1 m with a coarse (particle diameter 15–20 mm) substratum and negligible velocity, in the presence of floating and submerged broadleaved plant cover. The model is capable of discerning between null (fish absent) and non‐null (fish present) points in the original data set. It is shown that sampling effort may be reduced by approximately 60% without altering the model's predicti

ISSN:0886-9375    

DOI:10.1002/rrr.3450100206

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractHydropower generation induces rapid and frequent fluctuations of hydrodynamic parameters in rivers downstream of hydroelectric impoundments. On the FontauliéGre river (ArdéGche basin, France), water releases come from the Loire basin and the flow varies from 1.3 to 20 m3/s for one reach and from 0.1 to 20 m3/s for another reach. A reference site upstream was chosen to compare the communities with two downstream impacted sites. These two sites enabled two different base flow situations to be studied simultaneously and also the effect of base flow enhancement at one site. Benthic and epilithic samples were collected at the three sites on three dates. Epilithon development was linked to hydraulic regimes, with a major increase in algal biomass, dominated by filamentous algae, linked to the minimum base flow level and to the duration of periods without peaks. The macroinvertebrate communities of impacted reaches were less diversified and more specialized, with predominance of one or two taxa, whereas communities in upstream reaches were more diverse. The different morphological units specificity was attenuated in hydropeaking situations. In the case of a very low base flow, the lentic units with very low velocities (less than 4 cm s−1) had different fauna. The downstream algal development explained part of the change in benthic community structure in trophic groups (i.e. dominance of scrapers) in the site with the higher base flow. When the base flow was too low, a trophic discordance was observed and excess algal biomass represented a limiting factor. Thus, this study indicated that base flow level and duration had important effects on epilithic development and on invertebrate trophic structure in terms of mean velocities and of number of days without pe

ISSN:0886-9375    

DOI:10.1002/rrr.3450100207

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe headwater section of the Thomson River has been nominated for listing as a heritage river, mainly because it supports a population of large blackfish, a species which has high conservation value in Victoria. The upper river was dammed in 1983, creating an impoundment of 1.2 × 106Ml capacity. It is anticipated that the dam will provide a reliable water supply to Melbourne for up to 20 years, but minimization of downstream releases will delay augmentation. For the period during which the dam was filling, an interim environmental flow was applied. However, these flows were lower than what was considered at the time to be ideal for maintaining in‐stream habitat in the long term. Despite profound modification of the river's hydrology, there is no evidence for serious environmental impacts. Macroinvertebrate populations have recovered from disturbance during the construction phase, and the diversity of fish has not changed. However, there is concern that a lack of floods will result in contraction of the channel. This would probably mean a loss of available habitat area in the long term. Abstraction of water from the lowland section of the Thomson River began in 1957. Unfavourably low flows have occurred since regulation, but wetland inundation floods still occur with the same frequency. Although current management practices do allow unfavourable flow conditions to occur occasionally, the regulated flow regime has not reduced the diversity of native fish present in the lower river. This is heartening, but given the likelihood of future increases in the demand for water, long‐term protection of in‐stream fauna requires the application of an appropriate environmental flow regime. Habitat area–discharge curves derived from fish hydraulic preference data were used as the basis for devising a minimum flow recommendation. Five different methods of specifying monthly flow regimes are compared. A method is presented that uses hydraulic geometry relations from a neighbouring, hydrologically similar catchment to specify the magnitude and duration of an artificial annual channel maintenance flood. Implementation of the suggested environmental flow regime will probably result in a flow deficit in the lower Thomson River if current irrigation demands are to be met. To offset the deficit, additional water can be released from the dam. The flow required will not reduce the amount of habitat available in the upper Thomson River below the dam, but this strategy will bring forward the date of augm

ISSN:0886-9375    

DOI:10.1002/rrr.3450100208

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractAs part of a fishery enhancement scheme, 70 000 fingerlings of anadromous brown trout (Salmo truttaL.) were stocked in the regulated River Teigdal, western Norway. To evaluate the stocking programme 10 000 of the hatchery reared fish were marked and released at 10 different localities. The results showed that the hatchery reared fish were inferior to wild brown trout. During the first weeks densities were high in the areas of stocking, varying between 27 and 680 individuals per m2. Stocked fish colonizing adjacent areas were mostly found upstream. Very few fish were found to cross the river from the point of release. One week after stocking food consumption of the hatchery reared fish was low compared with wild trout. Stocked trout had a lower growth rate (0.05 mm d−1) than native fish (0.08 mm d−1). However, fish stocked in deeper, slower flowing areas grew faster than those stocked in shallow riffle areas. The mortality of the stocked trout was 99% from July to April, being highest during the winter. Wild fish survived better, having a mortality of 79% over the same period. The value of the stocking programme is questioned. As an alterative, methods of biotope adjustment are proposed to increase the carrying capacity of wild trout in the ri

ISSN:0886-9375    

DOI:10.1002/rrr.3450100209

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe environmental effects of stream regulation are often assessed with reference to changes in river benthos, and biotic scores and indices have been used to summarize data on faunal community structure and richness. Although they have their use in presenting complicated data in a simplified form, they often do not detect the more subtle effects of regulation. In lowland regions the regulation of rivers is most often due to water abstraction, channelization and the construction of weirs or sluices. The effects of this form of stream regulation may sometimes be particularly difficult to demonstrate with conventional biological assessment techniques. In this study we examine a length of stream regulated with sluice gates using conventional techniques and test the applicability of the mesohabitat method (categorization of reaches on the basis of their substratum types) in describing changes brought about by regulation. Conventional biological assessment techniques were unable to demonstrate the regulation effects. This was because, although changes had occurred along the reach, these were not associated with a significant change in scores and indices based on family richness. The changes were subtle and were most clearly revealed by clustering techniques and analysis of variance. Most of the change was due to altered physical habitat and this was reflected in the proportions of mesohabitats above and below the sluice gates. The association of mesohabitats with particular faunal assemblages allows an assessment of the overall effects of habitat change on the composition of the faunal community.

ISSN:0886-9375    

DOI:10.1002/rrr.3450100210

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

AbstractThe serial discontinuity concept (SDC) was developed as a theoretical construct that views impoundments as major disruptions of longitudinal resource gradients along river courses. According to the SDC, dams result in upstream–downstream shifts in biotic and abiotic patterns and processes; the direction and extent of the displacement depend on the variable of interest and are a function of dam position along the river continuum. As originally formulated, the SDC did not consider interactions between the river and its flood plain. The new perspective presented herein is an initial attempt to encompass the dynamics of alluvial flood plain rivers into the model using a three reach characterization: constrained headwater reach, braided reach and meandering reach. The constrained headwater reach has conditions similar to those described in the original SDC, but the braided and meandering reaches provide a perspective that was not addressed in the model. Lateral interactions between the channel and the flood plain are critical to a holistic understanding of natural river ecosystems and the alterations induced by regulation. The fringing flood plain, with its diverse water bodies and alluvial forest mosaic, is considered an integral part of the river syste

ISSN:0886-9375    

DOI:10.1002/rrr.3450100211

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY