摘要:

AbstractAlthough river channel management now generally uses soft rather than hard engineering techniques the considerable research achieved for woodland river channels has not been completely collated with reference to management implications. Research results from 22 research papers show how debris dams have a significant influence upon the morphological, the process and the ecological aspects of channels; vary in their permanence, and differ in stability according to the overall organic matter budget. A summary diagram contrasts the impact of dams on river channel morphology, process and ecology before and after dam removal. Four major types of specific recommendation about the management of channels in woodland areas are identified from 29 research papers are that (1) management should be undertaken against a background knowledge of the behaviour of coarse, woody debris under natural conditions and that the organic matter budget should be disturbed as little as possible; (2) logging operations should minimize the amount of disturbance to, and disruption of, channel processes; (3) management should optimize the maintenance of habitat diversity and minimize the ecological disturbance to the channel; (4) in some areas specific management practices may require the introduction of new material into the channel. These recommendations are applied to the New Forest, southern U.K., which has a long history of clearance and management of coarse woody debris and where the requirements for clearance in relation to fish, drainage, and aesthetic impact can be achieved by minimizing the amount of removal of material from the river channel. In managing channels with debris dams in woodland areas, it is desirable to work with the river in a holistic basin context.

ISSN:0886-9375    

DOI:10.1002/rrr.3450070202

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractRegulation of lowland rivers often alienates large areas of the floodplain, altering the natural regime of flooding frequency, duration, and magnitude. The extent to which such changes alter the productivity of river‐floodplain ecosystems and the contribution of aquatic invertebrates emerging from dry floodplain sediments is unknown. To examine this in a section of the River Murray in South Australia, fourteen replicate sods of dry sediment collected from four areas of the floodplain that had experienced different average flood recurrence frequencies (annually, 1 in 7, 1 in 11, and 1 in 22 years) were inundated in the laboratory, simulating flooding. Invertebrates emerging from the dry sediments were sampled with replacement 1, 2, 3, 7, 10, 14, 21, and 28 days after inundation, enabling comparisons of temporal changes in faunal composition and biomass. The greatest biomass and numbers of invertebrates emerged from annually‐flooded sods whereas sediments usually flooded once in 22 years yielded only protozoans. Large numbers of cladocerans and rotifers were recorded within two days of inundation whereas ostracods were not numerous until two weeks later. Heterogeneity in faunal composition and biomass among replicates probably reflected patchiness in microtopography and resting stage settlement, and variable hatching ‘strategies’. Although experimental conditions rapidly diverged from the natural situation over time because of the unrealistic constraints of enclosure, results suggest a potentially significant contribution by emergent invertebrates to the newly‐inundated floodplain foodweb. Reducing floodplain inundation frequency through regulation and flood mitigation probably severely reduces this reserve, removing a food resource for young fish and other

ISSN:0886-9375    

DOI:10.1002/rrr.3450070203

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe interstitial fauna of an alluvial pond on the floodplain of the Adour River, South‐west France was sampled over a period of 13 months. The pond was connected to the adjacent river through phreatic flow and its water level varied in an annual cycle related to the level of the river. Monthly samples were taken from fixed points along five transects across the pond. The littoral zone was sampled between +20 and −80 cm from the substrate surface. From the seasonal variations in the distribution and abundance of invertebrates, the dynamics of their colonization and decolonization cycles could be elucidated and related to the variations in the groundwater level. Eight different colonization/decolonization cycles were determined, each one being characterized by a ‘typical’ common species. These included both passive and active movements in response to the changes in water level. Many taxa were shown to have behavioural strategies which altered according to the stages of their life cycles. Most aquatic invertebrates were adapted to move into the most stable conditions at a given time of the year. Certain terrestial species were also shown to tolerate short periods of im

ISSN:0886-9375    

DOI:10.1002/rrr.3450070204

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractA list of 196 Coleoptera taxa, larvae and adults, covering 113 species, was obtained from several surveys of a flood plain of the Rhô river. From published reports and personal experience, each taxon is linked with the modalities of nine environmental and three biological variables. The resulting 12 ecological profiles for 196 taxa are analysed by correspondence analysis. The simultaneous ordination of the taxa and variables allows presentation of the more synthetic correspondence between the Coleoptera and their ecological and biological characteristics. The niche dimensions of the 12 variables tested here are organized along a current‐substrate gradient, from stones in rapid flow to mud in still water, which is associated with the other ecological conditions. This ordination reflects environmental conditions in a transverse direction, particularly from the central channel to the furthest annexes of the river. The Coleoptera are shown to be describers of the connectivity with the main channel. The 196 studied taxa are positioned along the gradient. They are subdivided into seven faunal groups based on their habitat range or niche width. The larger species are confined to the stagnant side of the gradient. Other variables, such as feeding and vertical distribution, clearly separate carnivores from herbivores and also larvae from adults. The next step of this study will be to extend these investigations to other functional variables and to all the species of Coleoptera in France. The information given by the Coleoptera will then be compared with actual field measuremen

ISSN:0886-9375    

DOI:10.1002/rrr.3450070205

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe natural hydrobiological conditions of southern Moravian floodplains have been drastically altered by regulation of the lower Dyje river and its tributaries. Natural floodplains were characterized by temporary pools and swamps, each inhabited by a typical community of aquatic invertebrates, and permanent water bodies (rivers and abandoned channels). Some aquatic taxa migrated onto ‘terrestrial’ localities during flood periods. Following regulation, floods were eliminated and most of the wet floodplain habitats disappeared, together with their typical species. The results of faunistic studies carried out in different permanent and temporary water bodies of the floodplains are reviewed. Altogether 188 taxa of planktonic and 206 taxa of benthic and semiplanktonic animals have been recorded. Of the planktonic community, rotifers (96 taxa) and copepods (41 taxa) have very favourable conditions for their development, especially in the spring. The main season for cladocera (53 taxa) development (summer) is less favourable due to the short duration of flooding (in flooded meadows) or poor oxygen conditions (in temporary pools with a high content of decaying organic matter). Among the zoobenthos, mainly facultative aquatic macroinvertebrates (larvae of insects) appear in these localit

ISSN:0886-9375    

DOI:10.1002/rrr.3450070206

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractWater End, Hertfordshire, has been designated as a Site of Special Scientific Interest due to the presence of some of the most important swallow holes in southern England. However, the swallow holes are being infilled by sediment and rubbish, resulting in severe environmental deterioration. Sedimentation appears to have been accelerated by human disruption of the Mimmshall Brook catchment, within which the swallow holes are located. A study of the sediment dynamics within the Mimmshall catchment was undertaken to identify instabilities and sediment transfer dynamics in the fluvial system. Channelization is shown to be the primary cause of the sedimentation problem. It was found that channelization triggers sediment flux divergences which in turn necessitate channel changes to restore equilibrium. As nickpoints migrate upstream of channelized reaches, bed degradation increases bank height. This decreases the stability of the bank with respect to mass failure. Bank failures occur under ‘worst case’ conditions once the threshold of bank instability is crossed. Bank erosion and mass failures were found to be the major sources of sediment to Water End and it was concluded that bank retreat must be controlled if environmental deterioration at Water End is to be slowed or rever

ISSN:0886-9375    

DOI:10.1002/rrr.3450070207

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

摘要:

AbstractThe effects of trout stock, discharge and predation risk on habitat use by brown trout, Salmo trutta, were studied in four artificial streams. Trout stock had no effect on habitat use as both wild and hatchery fish used similar habitats. The presence of pike (Esox lucius) caused trout to decrease their use of pools, the habitat in which pike occurred, and increase their use of other habitats. Decreasing discharge reduced available area of the stream and resulted in fewer fish in the shallow margins. Both decreased flow and increased predation risk caused more overlap in habitat use, and thus increased the potential for intraspecific competition, predation and the use of poorer habitats. The results illustrate the danger of applying habitat use relationships obtained from one stream to all other streams where habitat availability and biotic interactions may differ.

ISSN:0886-9375    

DOI:10.1002/rrr.3450070208

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070209

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070211

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY

ISSN:0886-9375    

DOI:10.1002/rrr.3450070212

出版商:John Wiley&Sons, Ltd    

年代:1992

数据来源: WILEY