首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 15 毫秒
1.
We conducted systematic postproject appraisals (PPAs) of seven compound channel restoration projects, supplementing available data with new field data and analyses to produce comparable datasets for all seven projects. We describe how systematic PPAs can be developed and illustrate a systematic PPA for compound channel projects organized around performance with respect to geomorphic, habitat, and conveyance objectives. We found that preexisting monitoring programs for a group of similar restoration projects can be supplemented with relatively low‐effort data collection and analyses to produce lessons on a “class” of restoration projects. Using this approach to assess a set of seven compound channel projects, we found that two fully achieved geomorphic objectives, three appear likely to achieve geomorphic objectives with additional time and/or minor interventions, and two did not achieve geomorphic objectives. Further, four projects achieved habitat objectives and three projects appeared likely to achieve objectives if given more time to develop and/or a minor intervention to mitigate limitations on critical ecological processes. Finally, four of the projects satisfied conveyance objectives, and the remaining three appeared likely to satisfy objectives with minor interventions to maintain design roughness and geometry conditions. Based on observations from our new systematic PPA approach applied to compound channels in Mediterranean climates, we suggest application of systematic PPAs for other classes of river restoration projects to evaluate scale and geomorphic setting issues in project design, to refine postproject monitoring guidelines, and to predict vegetation recruitment, growth, and succession patterns to avoid potential vegetation problems.  相似文献   

2.
Incised river channels are dynamic components of fluvial systems, represent geomorphic degradation, and are encountered worldwide. Ecological effects of incision can be far‐reaching, affecting habitat availability and channel processes. Although incision can reflect habitat degradation, some studies suggest that important in‐stream habitats do not differ with the degree of incision. Therefore, we tested whether in‐stream habitat variables that are important to imperiled fishes differ in river reaches with varying degrees of incision. Because incision (measured using entrenchment ratio) had no discernable effect on in‐stream habitat characteristics (i.e., proportion fines, gravel, cobble, and macrophyte occurrence and length), we expanded our analysis to assess the effects of 29 additional geomorphic variables on in‐stream habitat. These analyses indicated that bank height, bed mobility, D84, cross‐sectional area, bankfull width, and wetted perimeter accounted for 42% of macrophyte occurrence and 64% of macrophyte length variance. Postflood surveys indicated that macrophyte occurrence on cobble declined as bank height and bed mobility increased, and sediment size decreased, suggesting that sediment size and bed mobility have a stronger influence on in‐stream habitat than incision. Although channel incision often indicates environmental degradation, important aspects of habitat are not described by this measurement. Strategies that depend on incision to identify restoration sites may have limited habitat benefits in Southeastern Piedmont streams and rivers. Instead, landscape or shoal‐scale restoration approaches that increase coarse sediment proportions may increase macrophyte occurrence, length, and persistence. Sediment budgets that identify coarse and fine sediment sources and transport may be useful to prioritize restoration approaches.  相似文献   

3.
Channel reconfiguration is one of the most common and costly stream restoration techniques, though its effectiveness is frequently questioned. Project monitoring often tracks changes in macroinvertebrate communities and other responses for a 5‐year period. However, channel reconfiguration is a documented disturbance to stream ecosystems, suggesting that this form of restoration initiates succession over longer time frames than monitoring typically captures. To address the role of succession in stream ecosystem recovery, we developed the Phased Recovery Framework (PRF) which proposes benchmarks represented by predictable habitat structure and community composition based on project age. The PRF was tested across nine stream restoration projects in western Montana, ranging in age from 1 to 18 years, each paired with an established reference system. We tested for differences in channel form, habitat character, and macroinvertebrate community composition. While restoration established desired channel form, most biotic variables had not recovered to reference condition even for the oldest projects. Across all sites, phases of the PRF were poor predictors of response. However, analyzing responses to reconfiguration independently for sites in watersheds with unimpaired water quality versus those experiencing excessive nutrient enrichment (i.e. impaired sites) indicated that biological variables converged on reference conditions at unimpaired sites, but diverged across impaired reaches. These large‐scale anthropogenic influences may play a stronger role in recovery than do changes to channel form and need to be incorporated into project design and success criteria. Assessment of the PRF suggests that short‐term monitoring is not likely to produce reliable indicators of effectiveness without incorporating locally appropriate change associated with watershed impairment and successional progression.  相似文献   

4.
Geomorphic thresholds in riverine landscapes   总被引:12,自引:1,他引:12  
1. Rivers are subject to thresholds of several types that define significant changes in processes and morphology and delimit distinctive riverine landscapes and habitats. Thresholds are set by the conditions that govern river channel process and form, amongst which the most important are the flow regime, the quantity and calibre of sediment delivered to the channel, and the topographic setting (which determines the gradient of the channel). These factors determine the sediment transport regime and the character of alluvial deposits along the channel.
2. Changes occur systematically along the drainage system as flow, gradient and sediment character change, so a characteristic sequence of morphological and habitat types – hence of riverine landscapes – can be described from uplands to distal channels. The sequence is closely associated with stream competence to move sediment and with bank stability.
3. The paper proposes a first order classification of river channel and landscape types based on these factors. The riverine landscape is affected seasonally by flow thresholds, and further seasonal thresholds in northern rivers are conditioned by the ice regime.
4. It is important to understand geomorphic thresholds in rivers not only for the way they determine morphology and habitat, but because human activity can precipitate threshold crossings which change these features significantly, through either planned or inadvertent actions. Hence, human actions frequently dictate the character of the riverine landscape.  相似文献   

5.
In rivers supporting Pacific salmon in southeast Alaska, USA, regional trends toward a warmer, wetter climate are predicted to increase mid‐ and late‐21st‐century mean annual flood size by 17% and 28%, respectively. Increased flood size could alter stream habitats used by Pacific salmon for reproduction, with negative consequences for the substantial economic, cultural, and ecosystem services these fish provide. We combined field measurements and model simulations to estimate the potential influence of future flood disturbance on geomorphic processes controlling the quality and extent of coho, chum, and pink salmon spawning habitat in over 800 southeast Alaska watersheds. Spawning habitat responses varied widely across watersheds and among salmon species. Little variation among watersheds in potential spawning habitat change was explained by predicted increases in mean annual flood size. Watershed response diversity was mediated primarily by topographic controls on stream channel confinement, reach‐scale geomorphic associations with spawning habitat preferences, and complexity in the pace and mode of geomorphic channel responses to altered flood size. Potential spawning habitat loss was highest for coho salmon, which spawn over a wide range of geomorphic settings, including steeper, confined stream reaches that are more susceptible to streambed scour during high flows. We estimated that 9–10% and 13–16% of the spawning habitat for coho salmon could be lost by the 2040s and 2080s, respectively, with losses occurring primarily in confined, higher‐gradient streams that provide only moderate‐quality habitat. Estimated effects were lower for pink and chum salmon, which primarily spawn in unconfined floodplain streams. Our results illustrate the importance of accounting for valley and reach‐scale geomorphic features in watershed assessments of climate vulnerability, especially in topographically complex regions. Failure to consider the geomorphic context of stream networks will hamper efforts to understand and mitigate the vulnerability of anadromous fish habitat to climate‐induced hydrologic change.  相似文献   

6.
The Upper Mississippi River is characterized by a series of locks and dams, shallow impoundments, and thousands of river channelization structures that facilitate commercial navigation between Minneapolis, Minnesota, and Cairo, Illinois. Agriculture and urban development over the past 200 years have degraded water quality and increased the rate of sediment and nutrient delivery to surface waters. River enhancement has become an important management tool employed to address causes and effects of surface water degradation and river modification in the Upper Mississippi River Basin. We report information on individual river enhancement projects and contrast project densities, goals, activities, monitoring, and cost between commercially non‐navigated and navigated rivers (Non‐navigated and Navigated Rivers, respectively). The total number of river enhancement projects collected during this effort was 62,108. Cost of all projects reporting spending between 1972 and 2006 was about US$1.6 billion. Water quality management was the most cited project goal within the basin. Other important goals in Navigated Rivers included in‐stream habitat improvement and flow modification. Most projects collected for Non‐navigated Rivers and their watersheds originated from the U.S. Department of Agriculture (USDA). The U.S. Army Corps of Engineers and the USDA were important sources for projects in Navigated Rivers. Collaborative efforts between agencies that implement projects in Non‐navigated and Navigated Rivers may be needed to more effectively address river impairment. However, the current state of data sources tracking river enhancement projects deters efficient and broad‐scale integration.  相似文献   

7.
For restoration to be an effective strategy to reverse large‐scale habitat loss and land degradation, funding programs need policies that promote selection of and commitment to projects that can reasonably be expected to succeed. Programmatic project selection practices have received minimal formal evaluation, despite their importance. In this study, we considered the extent to which a program needs to consider both ecological and organizational factors during project selection in order to minimize the incidence of project failure. Our assessment of a long‐term program that funds ecological restoration efforts across Minnesota (U.S.A.), based on project records, manager surveys, and field surveys, yielded several broadly relevant insights. First, factors well understood to confer ecological resilience (level of landscape alteration and starting condition) were clearly associated with restoration outcomes, regardless of time‐since‐initiation of restoration. Second, restoration of low‐resilience ecosystems is typically a labor‐ and skill‐intensive enterprise for organizations that undertake them. Our analysis revealed four organizational limitations, in addition to insufficient funds, that hindered capacity to keep projects on‐track: lack of planning and goal‐setting, inadequate staffing, leadership change, and incomplete records. Third, to reduce risk, programs do not necessarily need to avoid challenging projects, but do need to consider whether organizations proposing restorations have adequate internal capacity to competently plan and to sustain actions for a duration sufficient to restore ecological resilience. If a restoration is degraded enough to require human intervention to recover, the outcome of a project is as likely to reflect its organizational reality as much as its ecological circumstances.  相似文献   

8.
Stream restoration projects have become increasingly common, and the need for systematic post‐project evaluation, particularly for small‐scale projects, is evident. This study describes how a 70‐m restored reach of a small urban stream, Baxter Creek (in Poinsett Park, El Cerrito, California), was quickly and inexpensively evaluated using habitat, biological, and resident‐attitude assessments. The restoration involved opening a previously culverted channel, planting riparian vegetation, and adding in‐stream step‐pool sequences and sinuosity. Replicated benthic macroinvertebrate samples from the restored site and an upstream unrestored site were compared using several metrics, including taxa richness and a biotic index. Both biological and habitat quality improved in the restored compared with the unrestored section. However, when compared with a creek restored 12 years before, habitat condition was of lower quality in the recently restored creek. A survey of the neighborhood residents indicated that, overall, they were pleased with the restored creek site. The approach used in this demonstration project may be applicable to other small‐scale evaluations of urban stream restorations.  相似文献   

9.
Fish habitat rehabilitation using wood in the world   总被引:1,自引:0,他引:1  
To provide river managers and researchers with practical knowledge about fish rehabilitation, various studies of fish habitat rehabilitation that used wood were reviewed. The review focuses on fish responses, wood installation methods, and geomorphic features of the rehabilitation sites. Most studies were conducted in moderately sized (small and medium) streams with relatively high bed gradients and aimed to improve the habitats of salmonid species. In this stream type, structures spanning the full (log dam) and partial (log deflector) width of the river were most common, and wood structures that created pools and covers were successful in improving fish habitat. Some projects were conducted in moderately sized low-gradient streams, in which wooden devices used to create instream cover were effective for fish assemblages. There were few studies in other aquatic ecosystems. However, well-designed large wood structures, known as engineered log jams, were used in rehabilitation projects for large rivers. In slack-water or lentic systems such as side-channels, estuaries, and reservoirs, small and large wood structures that created cover were used to improve habitat for many fish species. For successful fish habitat rehabilitation projects, the hydrogeomorphic conditions of rehabilitation sites should be carefully examined to avoid physical failure of wood structures. Although artificial wood structures can be used to improve fish habitat in various aquatic ecosystems, they should be considered to be a complementary or interim habitat enhancement technique. The recovery of natural dynamic processes at the watershed scale is the ultimate target of restoration programs.  相似文献   

10.
Post‐project appraisals (PPAs) are systematic assessments of built restoration projects, which provide feedback on performance of restoration approaches to improve future restoration efforts. Unfortunately, most restoration projects are not subject to systematic assessment because of lack of institutional arrangements to sustain long‐term evaluation and the orientation of most funding agencies towards project implementation rather than “studies.” As semester‐long courses on river restoration increasingly appear in university curricula at the graduate and advanced undergraduate level, independent student research projects for such courses can provide a mechanism for building a database of PPAs (and components thereof) and providing the students with a powerful learning experience. In two UC Berkeley courses, we require independent student projects involving original field research, peer review of first drafts, instructor (and often outside) review of second drafts, and presentation of results to a public symposium. Since 1995, the revised, final papers have been added to the University of California library, where they constitute one of the largest collections of restoration‐related studies currently available for any region: over 300 restoration‐related studies, of which 80 are PPAs or components thereof. Since 2003, the papers have been posted on‐line, with 40,000 full text downloads through 2010. Some term projects have directly influenced river restoration programs, inducing changes in salmon habitat enhancement project design, documenting failure of projects based on inappropriate restoration approaches, and contributing to systematic assessments of step‐pool and compound channel designs in urban areas. Student evaluations cite the term projects as valuable learning experiences.  相似文献   

11.
Across the Pacific Northwest (PNW), both public and private agents are working to improve riverine habitat for a variety of reasons, including improving conditions for threatened and endangered salmon. These projects are moving forward with little or no knowledge of specific linkages between restoration actions and the responses of target species. Targeted effectiveness monitoring of these actions is required to redress this lack of mechanistic understanding, but such monitoring depends on detailed restoration information—that is, implementation monitoring. This article describes the process of assembling a database of restoration projects intended to improve stream and river habitat throughout the PNW. We designed the database specifically to address the needs of regional monitoring programs that evaluate the effectiveness of restoration actions. The database currently contains spatially referenced, project‐level data on over 23,000 restoration actions initiated at over 35,000 locations in the last 15 years (98% of projects report start or end dates between 1991 and 2005) in the states of Washington, Oregon, Idaho, and Montana. Data sources included federal, state, local, nongovernmental organization, and tribal contributors. The process of database production identified difficulties in the design of regional project tracking systems. The technical design issues range from low‐level information such as what defines a project or a location to high‐level issues that include data validation and legalities of interagency data sharing. The completed database will inform efficient monitoring design, effectiveness assessments, and restoration project planning.  相似文献   

12.
The Upper Mississippi River system has been modified with locks, dams, dikes, bank revetments, channel modifications, and dredging to provide a nine-foot navigation channel. These activities have changed the river's characteristics. The historical changes in the hydrologic, hydraulic, and geomorphic characteristics were assessed and related to navigational development and maintenance activities in the Upper Mississippi River system. The hydrologic, hydraulic, and geomorphic features studied include river discharges, stages, sediment transport, river position, river surface area, island surface area, and river bed elevation. Water and sediment transport effects on dredging were also estimated. It was found that the general position of the Upper Mississippi River system has remained essentially unchanged in the last 150 years except for specific man-made developments in the river basin. The stage, velocity, sediment transport, and river and island areas were altered by development of the 2.75-m navigation system. Dredging requirements are strongly related to mean annual water discharge. Years in which water discharges were great were generally the years during which large volumes of sediment needed to be dredged from the channel. The backwater areas are experiencing some deposition. With implementation of erosion-control measures in major tributaries and upland areas, better confinement of disposed dredged materials, and better maintenance practices, the sedimentation and pertinent problems in the main channel, as well as in the backwater areas, may be reduced with time.  相似文献   

13.
The preponderance of short‐term objectives and lack of systematic monitoring of restoration projects limits opportunities to learn from past experience and improve future restoration efforts. We conducted a retrospective, cross‐sectional survey of 89 riparian revegetation sites and 13 nonrestored sites. We evaluated 36 restoration metrics at each site and used project age (0–39 years) to quantify plant community and aquatic habitat trajectories with a maximum likelihood model selection approach to compare linear and polynomial relationships. We found significant correlations with project age for 16 of 21 riparian vegetation, and 11 of 15 aquatic habitat attributes. Our results indicated improvements in multiple ecosystem services and watershed functions such as diversity, sedimentation, carbon sequestration, and available habitat. Ten riparian vegetation metrics, including native tree and exotic shrub density, increased nonlinearly with project age, while litter and native shrub density increased linearly. Species richness and cover of annual plants declined over time. Improvements in aquatic habitat metrics, such as increasing pool depth and decreasing bankfull width‐to‐depth ratio, indicated potentially improved anadromous fish habitats at restored sites. We hypothesize that certain instream metrics did not improve because of spatial and/or temporal limitations of riparian vegetation to affect aquatic habitat. Restoration managers should be prepared to maintain or enhance understory diversity by controlling exotic shrubs or planting shade‐tolerant native species as much as 10 years after revegetation.  相似文献   

14.
1. Most attempts to describe the distribution of benthic macroinvertebrates in large rivers have used local (grab‐scale) assessments of environmental conditions, and have had limited ability to account for spatial variation in macroinvertebrate populations. 2. We tested the ability of a habitat classification system based on multibeam bathymetry, side‐scan sonar, and chirp sub‐bottom seismics to identify large‐scale habitat units (‘facies’) and account for macroinvertebrate distribution in the Hudson River, a large tidal river in eastern New York. 3. Partial linear regression analysis showed that sediment facies were generally more effective than local or positional variables in explaining various aspects of the macroinvertebrate community (community structure, density of all invertebrates, density of fish forage, density of a pest species –Dreissena polymorpha). 4. Large‐scale habitats may be effective at explaining macroinvertebrate distributions in large rivers because they are integrative and describe habitat at the spatial scales of dominant controlling processes.  相似文献   

15.
Stream restorations that increase geomorphic stability can improve habitat quality, which should benefit selected species and local aquatic ecosystems. This assumption is often used to define primary restoration goals; yet, biological responses to restoration are rarely monitored or evaluated methodically. Macroinvertebrate communities were inventoried at 6 study reaches within 5 Catskill Mountain streams between 2002 and 2006 to characterize their responses to natural‐channel‐design (NCD) restoration. Although bank stability increased significantly at most restored reaches, analyses of variation showed that NCD restorations had no significant effect on 15 of 16 macroinvertebrate community metrics. Multidimensional scaling ordination indicated that communities from all reach types within a stream were much more similar to each other within any given year than they were in the same reaches across years or within any type of reach across streams. These findings indicate that source populations and watershed‐scale factors were more important to macroinvertebrate community characteristics than were changes in channel geomorphology associated with NCD restoration. Furthermore, the response of macroinvertebrates to restoration cannot always be used to infer the response of other stream biota to restoration. Thus, a broad perspective is needed to characterize and evaluate the full range of effects that restoration can have on stream ecosystems.  相似文献   

16.
The social dimensions of river restoration are not well understood especially in the context of large‐scale restoration projects embedded in a complex social‐ecological system. This study used in‐depth interviews with diverse stakeholders to examine perceptions of restoration success on the Clark Fork River Superfund project in Western Montana. Trust emerged as critical to restoration success and was influenced by public engagement, and by spatial and temporal scale. At this large scale, multiple relationships between agencies, NGOs, businesses, landowners, and other stakeholders meant that building trust was a complicated endeavor. The large spatial scale and long time frame made public engagement challenging, and landowners in particular were critical of the project, expressing mistrust in both agencies and the project as a whole. However, projects focused on smaller spatial scales, such as particular stream reaches, appeared to inspire more effective collaboration. Relationships between organizations were important at this large scale, but inter‐organizational conflict affected trust across the project. Further, because trust requires accepting vulnerability, recognizing the differential vulnerability that particular groups and communities experience, based on the risks and benefits they accrue relative to the project, is important.  相似文献   

17.
The effects of river restoration on hydromorphological conditions and variability are often documented immediately following the restoration, but rarely properly monitored in the long term. This study assesses outcomes of 20 restoration projects undertaken across central and northern Europe for a comprehensive set of hydromorphological parameters, quantified at both larger and smaller spatial scales. For each project, we compared a restored river section to an upstream degraded section. Ten pairs of large projects were contrasted to ten similar but less extensive projects, to address the importance of restoration extent for the success of each project. Overall, river restoration increased habitat diversity through changes in channel morphology. Our results indicated that restoration particularly improved macro- and mesohabitat diversity, but had a limited effect on microhabitat conditions, including the diversity of substrates. We found no significant difference in effects between large and small restoration projects. Our results reveal the need to assess hydromorphological parameters which reflect processes occurring at different spatial scales, including indicators of larger-scale hydromorphological processes such as bank erosion, to monitor restoration effects effectively and accurately. Additionally, our results demonstrate the importance of developing terrestrial parameters, to assess the lateral dimension of river restoration.  相似文献   

18.
Application of Landscape Allometry to Restoration of Tidal Channels   总被引:2,自引:0,他引:2  
Oligohaline tidal channels (sloughs) in the Pacific Northwest were shown to have allometric form with respect to outlet width and depth, channel length, perimeter, and surface area. In contrast, an artificial slough, excavated to mitigate port improvements, did not conform to natural slough allometry, resulting in high retention of allochthonous inputs and sediment accumulation. Additionally, intertidal sedge habitat abundance was related to slough size for smaller sloughs, but larger sloughs did not fit this allometric pattern. This suggests that sedge habitat in large sloughs has been destroyed due to extensive log storage and transportation from the 1890s to the 1970s. Finally, the abundance of salmonid prey of terrestrial origin—aphids and adult flies—in slough surface waters was correlated with slough perimeter and, for aphids, with the amount of intertidal sedge habitat. An allometric perspective on landscape form and function has several implications for habitat restoration and mitigation: (1) Size‐related constraints on replication for landscape‐scale studies are loosened (e.g., rather than requiring reference sites that are similar in size to experimental sites, analysis of covariance can be used to control size effects); (2) physical processes, such as sedimentation and erosion, affect landscape form, whereas landscape form can affect ecological processes, so design of restoration or mitigation projects should conform to allometric patterns to maximize physical and ecological predictability; (3) landscape allometry may provide insight into undocumented human disturbances; and (4) allometric patterns suggest design goals and criteria for success.  相似文献   

19.
  • 1 This paper introduces the Lowland Streams Restoration Workshop that was held in Lund, Sweden in August 1991.
  • 2 Attenders at the Workshop participated in working groups which discussed and reported on the state of knowledge of stream restoration and identified critical areas of information need. Currently, most restoration efforts are emission-orientated (i.e. waste-water management), while the imitation of the geomorphology or of the riparian vegetation of a quasi-natural or natural reference channel receives less attention.
  • 3 Successful stream restoration requires a multidisciplinary approach within a holistic system framework. Monitoring the outcome of past, existing and future steam-restoration projects is required for information on the feasibility of alternative techniques and approaches.
  • 4 It was recommended that systems in pristine condition serve as a point of reference and not as a goal for most stream restoration projects. Restoration goals must be carefully defined so that everyone at every level understands the aim of the project. At the very least, all restoration programmes should consider geomorphic, hydrological, biological, aesthetic, and water quality aspects of the system.
  • 5 Restoration programmes should aim to create a system with a stable channel, or a channel in dynamic equilibrium that supports a self-sustaining and functionally diverse community assemblage; it should not concentrate on one species or group, except at the local level. Preserving the terrestrial -aquatic interface by setting aside riparian land corridors is critical to all stages of restoration. Additional information on the temporal and regional variability in important system processes and functions is needed.
  相似文献   

20.
Habitat selection in ungulates should ensure access to abundant forage of sufficiently high quality. Species living in rugged mountain areas have to face nutritional bottlenecks regularly and should show particularly sophisticated habitat selection behaviour. However, patterns and mechanisms of such adaptations remain little studied. We analysed habitat selection and its seasonal variability of 10 GPS‐collared red deer Cervus elaphus living in a topographically challenging landscape of the Swiss Alps. We hypothesised that resource selection by red deer was scale‐dependent and predicted that scale‐dependence would vary among seasons in relation to seasonal changes of available forage biomass and quality, which we sampled across the entire study area of 250 km2. The studied population of Alpine red deer undertook altitudinal migrations and showed scale‐dependent habitat selection that was strongest in winter and declined through spring and summer. Selection occurred mostly at the larger (landscape/home‐range location) scale and less so at the smaller (within home‐range) scale. Topographic parameters were selected mainly at the landscape scale and mostly in winter. About 70% of all instances of preference for habitat parameters were associated with above‐average forage characteristics, represented mostly by higher crude protein content, in a few cases also by higher biomass or both. The overall pattern of space use by red deer characterised by migration and seasonal habitat selection was therefore closely linked to the quality of food resources, although some trade‐offs with avoiding human disturbance may also have been involved.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号