摘要:

Abstract1The distribution and diet of two groups of captive‐bred, re‐introduced ottersLutra lutra(L.) was assessed through the collection and analysis of spraints (faeces), collected between July 1992 and March 1994 from the Rivers Stort, Lee and Rib in Hertfordshire (UK).2Almost immediately after release in 1991, both groups of otters moved upstream of their release sites. In February 1992, one male was found dead on a road near the River Stort, and both groups appeared to have moved downstream, their total range eventually extending to about 40 km, from 8 km downstream of the confluence of the Rivers Stort and Lee to about 16 km up the Stort and 16 km up the Lee.3Fish, principally cyprinids, formed the major dietary element, with spatial differences in prey availability influencing the range of secondary items taken. Eels were the only prey category to show significant seasonal variation in spraints, occurring more often than expected in spring and summer spraints. Mammals/amphibia and birds were taken as prey only occasionally. Where environmental quality and/or prey species diversity were low, small‐bodied fish species, such as three‐spined sticklebackGasterosteus aculeatus, bullheadCottus gobioand stone loachBarbatula barbatula, occurred more frequently in the diet.4Only two of the seven IUCN criteria for re‐introductions appear to have been met before the otters' release, and subsequent assessments suggest that most other criteria were not. As there has been only one possible, but unconfirmed, sighting of a female with cubs, it remains unclear whether the released otters have reproduced and thus the success of the re‐introduction

ISSN:1052-7613    

DOI:10.1002/aqc.3270050202

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract1Regions of reduced velocity adjacent to spur dikes along the Lower Mississippi River are valuable aquatic habitats. Similar zones along other large rivers have been converted to terrestrial habitats by sediment deposition.2Repetitive hydrographic surveys of 26 representative groups of dikes are examined to determine the direction and rates of change.3Since the dikes were constructed, the aquatic volume and area of associated low‐velocity habitats have been reduced by 38% and 17%, respectively. Examination of time series shows that most changes occur shortly after construction, and after initial adjustment, habitat area and volume fluctuate about a condition of dynamic equilibrium.4Sedimentation rates were most rapid for dike fields constructed on the inside of bends to prevent chute development. Dike fields built to force or maintain thalweg crossings exhibited erosion rather than depositio

ISSN:1052-7613    

DOI:10.1002/aqc.3270050203

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract1The planning, design and evaluation of a restoration project should be guided largely by an understanding of past channel changes.2A historical analysis can sometimes reveal underlying causes of channel change and document prior habitat conditions, both useful in setting appropriate objectives for restoration.3Restoration planning should address the historical causes and patterns of channel degradation that cannot be detected by examining current conditions alone. Moreover, ongoing adjustments in the channel and changes in the catchment must be understood when interpreting channel changes following construction of restoration projects.4Changes in channel form (and the independent geomorphological variables of run‐off and sediment load from the catchment) can be documented from a variety of sources, including historical maps, boundary lines, aerial photography, bridge and pipeline surveys, gauging records, field evidence and archival sources. Historical riparian vegetation, and use by fish and wildlife, may also be documented from early survey records, photographs and written accounts.5Historical analysis should cover an area large enough to capture all events potentially influencing the project reach. The entire catchment upstream should be examined to identify events affecting the flow regime and sediment load, such as deforestation or dam construction. For channels in erodible alluvium, the study should include the channel downstream to the first stable grade control to capture events whose effects may propagate upstream, such as channelization or base lowering.6Application of historical channel analysis to the San Luis Rey River in California served as a basis for evaluating the potential for (and hydrological constraints upon) riparian restoratio

ISSN:1052-7613    

DOI:10.1002/aqc.3270050204

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract1Land managers in western North America have embraced classification of stream channels based on geomorphological characteristics as the importance of channel stability in successful restoration of aquatic and riparian habitat has become widely recognized.2Classification can permit rapid inventory of large regions, provide a stratified geomorphological framework within which more detailed observations can be organized, and provide an initial basis for selecting restoration strategies.3Existing classifications are arbitrary, developed by creating classes out of a continuum of channel form. Moreover, stream channels are dynamic, and the existing condition does not necessarily reflect former, long‐term, or future conditions.4The user should not confuse the classification exercise with a complete understanding of the channel. Before any channel works are actually undertaken, site‐specific studies are essential, including historical studies to determine former channel conditions and to shed light on underlying causes for degradation of aquatic or riparian resources.5When applying a classification system, the raw data collected should be reported, not simply the resultant channel classes. Channels that do not fit neatly within pre‐existing classes should be reported as such and not lumped in classes where they ‚shou

ISSN:1052-7613    

DOI:10.1002/aqc.3270050205

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

摘要:

Abstract1Throughout the Temperate Forest biogeographical zone, river valleys were once heavily wooded. Fallen trees had a major impact upon river systems by ponding water and storing sediments, and valley floors were characterized by extensive wetlands with networks of minor channels linking to the main channel. Concern for environmental conservation and for the rehabilitation of damaged aquatic ecosystems has led to research on the links between river channel dynamics and vegetation, and an interest in the use of dead wood for environmentally sensitive engineering approaches to river management.2Accumulations of coarse woody debris (CWD) have an impact on the hydrological, hydraulic, sedimentological, morphological and biological characteristics of river channels. These impacts are very significant for the stability and biological productivity of river channels in forested catchments.3As a result of the geomorphological and ecological importance of CWD in river channels in forested catchments, such debris requires careful management. In particular indiscriminate removal of CWD should be avoided.4In the context of commercial forestry, a sequence of linked management options can be employed to control sediment and organic matter transport within river systems and to enhance channel stability and physical habitat diversity. These management options include selective removal of less stable debris, addition of debris to the river where the natural supply is inadequate, the maintenance of buffer strips of riparian trees which can act as a source of CWD, and the active management of woodland buffer strips to provide a wide range of physical habitat characteristics including light, temperature, flow, sediment transport and substrate conditions, thereby promoting high biological diversity within the river environment.

ISSN:1052-7613    

DOI:10.1002/aqc.3270050206

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:1052-7613    

DOI:10.1002/aqc.3270050207

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:1052-7613    

DOI:10.1002/aqc.3270050208

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:1052-7613    

DOI:10.1002/aqc.3270050209

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:1052-7613    

DOI:10.1002/aqc.3270050210

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY

ISSN:1052-7613    

DOI:10.1002/aqc.3270050211

出版商:John Wiley&Sons, Ltd    

年代:1995

数据来源: WILEY