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91.
Hobbs R 《Journal of environmental management》2009,90(9):2857-2865
In the latter half of the 20th century, native pine woodlands in Scotland were restricted to small remnant areas within which there was little regeneration. These woodlands are important from a conservation perspective and are habitat for numerous species of conservation concern. Recent developments have seen a large increase in interest in woodland restoration and a dramatic increase in regeneration and woodland spread. The proximate factor enabling this regeneration is a reduction in grazing pressure from sheep and, particularly, deer. However, this has only been possible as a result of a complex interplay between ecological, political and socio-economic factors. We are currently seeing the decline of land management practices instituted 150-200 years ago, changes in land ownership patterns, cultural revival, and changes in societal perceptions of the Scottish landscape. These all feed into the current move to return large areas of the Scottish Highlands to tree cover. I emphasize the need to consider restoration in a multidisciplinary framework which accounts not just for the ecology involved but also the historical and cultural context. 相似文献
92.
Stream restoration practices are becoming increasingly common, but biological assessments of these improvements are still
limited. Rock weirs, a type of constructed riffle, were implemented in the upper Cache River in southern Illinois, USA, in
2001 and 2003–2004 to control channel incision and protect high quality riparian wetlands as part of an extensive watershed-level
restoration. Construction of the rock weirs provided an opportunity to examine biological responses to a common in-stream
restoration technique. We compared macroinvertebrate assemblages on previously constructed rock weirs and newly constructed
weirs to those on snags and scoured clay streambed, the two dominant substrates in the unrestored reaches of the river. We
quantitatively sampled macroinvertebrates on these substrates on seven occasions during 2003 and 2004. Ephemeroptera, Plecoptera,
and Trichoptera (EPT) biomass and aquatic insect biomass were significantly higher on rock weirs than the streambed for most
sample periods. Snags supported intermediate EPT and aquatic insect biomass compared to rock weirs and the streambed. Nonmetric
multidimensional scaling (NMDS) ordinations for 2003 and 2004 revealed distinct assemblage groups for rock weirs, snags, and
the streambed. Analysis of similarity supported visual interpretation of NMDS plots. All pair-wise substrate comparisons differed
significantly, except recently constructed weirs versus older weirs. Results indicate positive responses by macroinvertebrate
assemblages to in-stream restoration in the Cache River. Moreover, these responses were not evident with more common measures
of total density, biomass, and diversity. 相似文献
93.
Kondolf GM Angermeier PL Cummins K Dunne T Healey M Kimmerer W Moyle PB Murphy D Patten D Railsback S Reed DJ Spies R Twiss R 《Environmental management》2008,42(6):933-945
Despite increasingly large investments, the potential ecological effects of river restoration programs are still small compared
to the degree of human alterations to physical and ecological function. Thus, it is rarely possible to “restore” pre-disturbance
conditions; rather restoration programs (even large, well-funded ones) will nearly always involve multiple small projects,
each of which can make some modest change to selected ecosystem processes and habitats. At present, such projects are typically
selected based on their attributes as individual projects (e.g., consistency with programmatic goals of the funders, scientific
soundness, and acceptance by local communities), and ease of implementation. Projects are rarely prioritized (at least explicitly)
based on how they will cumulatively affect ecosystem function over coming decades. Such projections require an understanding
of the form of the restoration response curve, or at least that we assume some plausible relations and estimate cumulative
effects based thereon. Drawing on our experience with the CALFED Bay-Delta Ecosystem Restoration Program in California, we
consider potential cumulative system-wide benefits of a restoration activity extensively implemented in the region: isolating/filling
abandoned floodplain gravel pits captured by rivers to reduce predation of outmigrating juvenile salmon by exotic warmwater
species inhabiting the pits. We present a simple spreadsheet model to show how different assumptions about gravel pit bathymetry
and predator behavior would affect the cumulative benefits of multiple pit-filling and isolation projects, and how these insights
could help managers prioritize which pits to fill. 相似文献
94.
The measurement of the bed shear stress along vegetated river beds is essential for accurately predicting the water level, velocity and solute and sediment transport fluxes in computational hydroenvironmental models. Details are given herein of an experimental and theoretical study to determine the bed boundary shear stress along vegetated river beds introducing a novel field measuring method, namely the FliessWasserStammtisch (FST)-hemispheres. Although investigations have been conducted previously for sedimentary channels using the FST-hemispheres, this preliminary study is thought to be the first time that such hemispheres have been used to investigate the bed shear stresses in vegetated channels. FST-hemispheres were first developed by Statzner and Müller [1989. Standard hemispheres as indicators of flow characteristics in lotic benthos research. Freshwater Biology 21, 445-459] to act as an integrated indicator of the gross hydrodynamic stresses present near the bed. Test and validation data were found to be at least of the same order of magnitude for the stresses predicted from literature for sedimentary channels, with this study establishing the commencement of a database of calibrated FST-hemisphere laboratory data for vegetated channel beds. In a series of experiments, depths ranging from 0.1 to 0.28m were considered, equating directly to comparable conditions in small rivers or streams. The results of this study provide a basis for enabling the FST-hemispheres to be used to evaluate the boundary shear stress for a wider range of applications in the future, including vegetated river beds. 相似文献
95.
96.
Human impacts on the stream-groundwater exchange zone 总被引:13,自引:0,他引:13
Hancock PJ 《Environmental management》2002,29(6):763-781
Active exchanges of water and dissolved material between the stream and groundwater in many porous sand- and gravel-bed rivers
create a dynamic ecotone called the hyporheic zone. Because it lies between two heavily exploited freshwater resources—rivers
and groundwater—the hyporheic zone is vulnerable to impacts coming to it through both of these habitats. This review focuses
on the direct and indirect effects of human activity on ecosystem functions of the hyporheic zone. River regulation, mining,
agriculture, urban, and industrial activities all have the potential to impair interstitial bacterial and invertebrate biota
and disrupt the hydrological connections between the hyporheic zone and stream, groundwater, riparian, and floodplain ecosystems.
Until recently, our scientific ignorance of hyporheic processes has perhaps excused the inclusion of this ecotone in river
management policy. However, this no longer is the case as we become increasingly aware of the central role that the hyporheic
zone plays in the maintenance of water quality and as a habitat and refuge for fauna. To fully understand the impacts of human
activity on the hyporheic zone, river managers need to work with scientists to conduct long-term studies over large stretches
of river. River rehabilitation and protection strategies need to prevent the degradation of linkages between the hyporheic
zone and surrounding habitats while ensuring that it remains isolated from toxicants. Strategies that prevent anthropogenic
restriction of exchanges may include the periodic release of environmental flows to flush silt and reoxygenate sediments,
maintenance of riparian buffers, effective land use practices, and suitable groundwater and surface water extraction policies. 相似文献
97.
Thompson DM 《Environmental management》2002,29(2):250-265
Habitat-improvement structures on the Blackledge and Salmon rivers date back to the 1930s and 1950s. Forty of these structures
were investigated to determine their long-term impact on channel morphology. These structures include designs that continue
to be used in modern restoration efforts. During the intervening period since these structures were introduced, several major
floods have affected the two channels. The floods include three flows in excess of the 50-year event, including the flood
of record, which has an estimated recurrence interval of almost 300 years. Despite the extreme flooding, many structures were
discovered in varying conditions of operation. Grade-control structures and low-flow deflectors generally create some low-flow
habitat (P = 0.815) but do not produce the depth of water predicted by design manuals (P < 0.0001). Unintended erosion has developed in response to many of the channel modifications especially along the outside of meanders.
In addition, the mode of failure of grade-control structures has created localized channel widening with associated bank erosion.
Meanwhile, cover structures have produced a 30% reduction in streamside vegetation with over 75% less overhead cover than
unaltered reaches. Based on these results, it is important for prospective designers to carefully consider the long-term impacts
of instream structures when developing future channel-restoration projects. 相似文献
98.
Understanding how hydraulic factors control alluvial river meander migration can help resource managers evaluate the long-term
effects of floodplain management and bank stabilization measures. Using a numerical model based on the mechanics of flow and
sediment transport in curved river channels, we predict 50 years of channel migration and suggest the planning and ecological
implications of that migration for a 6.4-km reach (river miles 218–222) of the Sacramento River near the Woodson Bridge State
Recreation Area, California, USA.
Using four different channel management scenarios, our channel migration simulations suggest that: (1) channel stabilization
alters the future channel planform locally and downstream from the stabilization; (2) rock revetment currently on the bank
upstream from the Woodson Bridge recreation area causes more erosion of the channel bank at the recreation area than if the
revetment were not present; (3) relocating the channel to the west and allowing subsequent unconstrained river migration relieves
the erosion pressure in the Woodson Bridge area; (4) the subsequent migration reworks (erodes along one river bank and replaces
new floodplain along the other) 26.5 ha of land; and (5) the river will rework between 8.5 and 48.5 ha of land in the study
reach (over the course of 50 years), depending on the bank stabilization plan used. The reworking of floodplain lands is an
important riparian ecosystem function that maintains habitat heterogeneity, an essential factor for the long-term survival
of several threatened and endangered animal species in the Sacramento River area. 相似文献
99.
对恢复生态学的研究概况、基本概念、内涵与研究内容以及生态恢复的目标、原则、程序与技术进行了分析与探讨,指出恢复生态学应加强基础理论研究和应用技术研究。生态恢复与重建是指根据生态学原理,通过一定的生物、生态和工程技术,人为地切断生态系统退化的主导因子和过程,调整和优化系统内部及其与外界的物质、能量和信息的流动过程及其时空秩序,使生态系统的结构、功能和生态学潜力尽快成功地恢复到原有的乃至更高水平。 相似文献
100.