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1.
Cristina Calvo-Fernandez;Elisa L. Sorribes;Jesús Garrido-Moreno;Bárbara Martín-Maldonado; 《河流研究与利用》2024,40(8):1617-1620
The Eurasian otter, Lutra lutra, faced adversity in Europe in the 1950s and 1960s due to hunting, declining fish populations and the American mink invasion. Slow recovery since the 1970s led to a ‘Near Threatened’ in the IUCN Red List status, but recent pollution, fishing pressure and habitat loss caused slight population declines. Otters, known for aquatic habits, are mainly piscivorous and exhibit solitaire or social behaviours. Infanticide with parent-offspring cannibalism has been previously reported in otter species, but although cannibalism has been suggested, it has not been documented before. This study presents the first documented case of cannibalism among free-living Eurasian otters observed in northern Norway. Some authors described cannibalism as an opportunistic resource-efficient behaviour in several mammal species, offering benefits like weight gain and reduced competition, challenging the view of adverse health effects. Factors leading to otter cannibalism include ecological changes, resource competition with other species and global warming and overfishing practices contributing to increased otter competition. Further studies will be vital to answering intriguing questions about the implications of cannibalism for otter conservation. 相似文献
2.
Elizabeth Andrews 《河流研究与利用》1989,4(2):199-202
The British otter Lutra lutra L. requires good water quality, an adequate supply of fish and certain types of vegetation or cavities (holts) adjacent to water bodies for resting and breeding sites. In the U.K. otters and their holts are legally protected. Trained surveyors are needed to confirm the presence of otters on a river as the animals are rarely seen, but their tracks and droppings (spraints) may be detected. To evaluate a river for otters, information is required on water quality, fish species and biomass, as well as available habitat. Pioneer evaluation work based on the River Corridor Survey techniques has been done on Welsh rivers with good otter populations. Riparian vegetation, especially trees, is shown to be particularly important. This work is now being extended to areas on the margins of otter distribution such as the lower river Wye in England and Wales. Such surveys provide important management information for water authorities and give opportunities for enhancement work to benefit this animal. 相似文献
3.
Urban gravel‐bed stream channels in southern Ontario, Canada identified to be in a state of quasi‐equilibrium have been studied over the past 15 years and compared against rural gravel bed stream channels of the same hydrophysiographic region. Bankfull width and depth versus bankfull discharge were not found to increase as a function of increasing urbanization as has been found in many other studies. The observed annual frequency of bankfull discharge was typically less than a 1‐year return period with many sites ranging between 2 and 18 bankfull events per year with higher intensity and shorter duration urban flood responses, which further identified significant limitations in using annual peak discharge methods for predicting morphological forming flows in urban watersheds. The cumulative volume of bankfull and larger flood events from the urban stream channels were very similar to the same annual event volumes in the rural comparison study reaches. Bed material supply was found to decrease with increasing urbanization and the reduction in bed material supply appears to be off‐set by the smaller bankfull channel width, depth and access to floodplains during large flood events. Field evidence may also suggest a even greater reduction in channel width trajectory, relative to the rural setting, with expansive floodplains to maintain quasi‐equilibrium conditions as bed material supply continues to decrease with increased anthropogenic activity. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
4.
The Eurasian otter (Lutra lutra) is a known piscivorous predator throughout its distribution range, although in some regions a more generalist behaviour emerged, such as in southern European latitudes. We evaluated otter feeding preference/avoidance towards the elements of the fish guild inhabiting a Mediterranean environment (Côa River, Central Portugal) and assessed the influence of proximity to a surplus of trophic resources (a rainbow trout production farm) on the species diet. Almost two years of collected spraints revealed that otters subsisted by consuming almost exclusively fish (94% of consumed biomass), especially the rainbow trout (87% of consumed biomass), although in summer this consumption is complemented with reptiles and amphibians. Due to the presence of the trout farm, and the consequent constancy in the availability of trout, the observed otter specialization in rainbow trout represents an extreme opportunistic behaviour. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
5.
A comparative study of two adjacent stream channels in the Santa Clara Valley region of California provided an opportunity to study the relative effects of multi‐faceted watershed‐urbanization impacts on channel evolution and stability. Berryessa Creek (15.5 km2) and Upper Penitencia Creek (61.3 km2) have similar intrinsic watershed characteristics; however, urbanization processes have imposed distinctly different evolutionary trends in each watershed. The influences of drainage network manipulation, hydrologic routing and engineering infrastructure has resulted in Upper Penitencia Creek remaining relatively stable throughout the course of urbanization, while Berryessa Creek has experienced system‐wide channel instability problems. This study enumerates the many anthropogenic impacts and provides insight into basin alterations that can have either positive or negative feedbacks in maintaining or degrading channel stability throughout the course of urbanization. Results show that infrastructure that disrupts the bed material sediment continuity (such as large drop structures or sedimentation ponds) generate long‐term downstream channel instabilities leading to channel degradation and continued maintenance. Off‐line flow diversions (in this study percolation ponds) that do not disrupt bed material transport can emulate pre‐urbanization conditions offsetting channel degradation resulting from changes in hydrology. This study also demonstrates the degradational responses of a stream due to losses in riparian vegetation from water table lowering transforming a perennial stream into an ephemeral stream resulting in increased bank instability. The importance of maintaining floodplains for flood access and channel stability has also been identified and compared to conditions of channel encroachment to facilitate maintenance, which have further exacerbated downstream channel degradation, long‐term channel maintenance and dredging. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
6.
Arnau Tolrà;Joan Lluís Riera;Jordi Ruiz-Olmo; 《河流研究与利用》2024,40(8):1469-1483
To identify and mitigate biodiversity decline, it is necessary to develop and implement appropriate ecological assessment methods. This particularly relevant in ecosystems under strong human pressure, such as riverine environments, in which ecological assessment requires several standardized methods useful in a wide range of riverine characteristics and habitats. In this work, we related otter diet composition with a set of environmental variables in representative river reaches of two contiguous river basins with a high diversity of habitats and varying degrees of human alteration. Our goal was to determine to what extent otter prey communities were sensitive to habitat characteristics and human pressures. Our results suggest that otter prey community in heavily anthropized rivers vary significantly across three gradients: habitat productivity, habitat structure and habitat stability. We also compared the results obtained from the otter diet with those obtained from electrofishing. Overall, the otter diet changed spatially in a similar way to the fish community sampled by electrofishing, but both methods showed disagreements that suggest different biases in some habitats and for some species. We conclude that otter diet analysis is a potential supplementary method for assessing river ecological status and that human alterations related to habitat structural simplification and water extraction can prevent freshwater biodiversity recovery in human-dominated landscapes despite improvements in biochemical water quality. 相似文献
7.
In the United States, several thousand stream gages provide what typically is the only source of continuous, long‐term streamflow and channel‐geometry information for the locations being monitored. In this paper, the geomorphic content of stream‐gage information, previous and potential applications of stream‐gage information in fluvial geomorphic research and various possible limitations are described. Documented applications include studies of hydraulic geometry, channel bankfull characteristics, sediment transport and channel geomorphic response to various types of disturbance. Potential applications include studies to determine the geomorphic effectiveness of large floods and in‐stream habitat change in response to disturbance. For certain applications, various spatial, temporal and data limitations may render the stream‐gage information of limited use; however, such information often is of considerable value to enable or enhance geomorphic investigations. Published in 2008 by John Wiley & Sons, Ltd. 相似文献
8.
C. J. Legleiter 《河流研究与利用》2015,31(10):1328-1343
Recent reservoir construction on Savery Creek provided an opportunity to examine the downstream effects of a dam on a small, meandering channel. The new dam, completed in 2005, modified the flow regime by reducing the magnitude of spring peaks and increasing baseflows, including a second period of high discharge in the fall. A time series of remotely sensed data spanning 1980–2011 was used to measure lateral migration rates, quantify areas of erosion and deposition, and map spatial patterns of channel change. Both migration rates, and gross erosion and deposition increased during the post‐dam era, although 2 years of exceptionally large snowmelt runoff also occurred during this time. Net sediment flux inferred from the image time series was negative for both the upper and lower reaches for the first photo pair after the dam's completion but became positive for the most recent photos. Detailed topographic surveys of five individual meander bends were used to produce digital elevation models of difference and infer bed material transport rates. For three sites located in the upper reach, downstream increases in transport rate implied a sediment deficit satisfied through channel incision and/or bank erosion. For two sites in the lower reach where sediment supply was greater, larger values of gross erosion were balanced by enhanced deposition and transport rates stabilized or increased along each bend. Together, these results suggest that Savery Creek has entered a period of adjustment as the channel adapts to altered, dam‐regulated supplies of water and sediment. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
High‐resolution velocity measurements were taken over a series of redds on a gravel‐bed stream using a Pulse Coherent Acoustic Doppler Profiler (PCADP) to quantify the hydrodynamics of brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) redds. On redds studied, over 4500 velocity measurements per redd were acquired per day to quantify the flow velocity, flow depth and related fluid mechanics metrics of Reynolds numbers, Froude numbers and turbulent kinetic energy per unit area. Results showed that velocity and Froude numbers varied widely at the redd scale, but consistently showed higher velocities and Froude numbers over the tailspill regions relative to the surrounding study limits. Results of Reynolds numbers calculations showed no apparent correlations to spawning location preference and redd structure. Turbulent kinetic energy per unit area consistently demonstrated a strong correlation with redd locations. The metric maintained low values (i.e. unidirectional flow with little turbulence) where all redds and attempted redds were observed. The study also demonstrates that a number of hydraulic metrics and several spatial scales will likely be necessary to understand any inherent relationship between river hydraulics and redd placement. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
The fine‐scale structure of the water–sediment boundary in fluvial environments is dynamic and complex, influencing near‐bed flows, sediment transport and instream ecology. However, accurate high‐resolution surveying of marginally or partially inundated areas of river channels is problematic. Previous work has shown that terrestrial laser scanning (TLS) through relatively shallow‐water columns using standard green‐wavelength equipment introduces errors of <5 mm in a static, clear water column. This paper presents seven laboratory and field tests of through‐water TLS under variable flow velocities, depths, suspended sediment concentrations, water colour levels and scan ranges. Flow velocity decreased point accuracy only for supercritical flows, whereas point density decreased as a function of both water depth and suspended sediment concentration. A similar point return threshold was observed for water colour variations with no grains in suspension. Conversely, point precision and accuracy were a function of suspended sediment concentration alone (a threshold of 0.11 g L?1 was observed). Field tests showed larger errors (<10 mm) and lower point precisions. A clear‐water depth‐penetration limit of 0.68 m was identified. Fluvial bathymetry acquired from through‐water TLS is presented for a gravel/boulder bed reach. Despite observed limits, these experiments demonstrate that our approach provides centimetre‐resolution bathymetry and sub‐aerial survey in an integrated dataset without the need for the following: (i) additional financial resources; (ii) concurrent depth measurements; or (iii) extra field effort for bathymetry acquisition, thereby enabling regular surveys to characterize the fine‐scale structure of channel beds and to constrain the geomorphic effect of individual flood events. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
11.
为研究拆坝对生态环境影响的利弊,介绍了拆坝对水文情势、泥沙输运、河道地貌、河道水质、栖息地质量及生物多样性等生态的影响,综述了拆坝后河道物理化学及重要生态特性之间响应关系的研究进展。拆坝对生态环境的影响具有时空复杂性,且各生态因子相互影响;水文情势的变化是所有生态响应的触发条件,泥沙输运是生态响应的关键性因子。为了河道长期连续性的开发与利用,研究泥沙输运及泥沙污染物的释放规律,预测拆坝后河道水质时空变化过程,分析流域尺度上生态系统之间的响应关系等对拆坝的评估决策十分重要。 相似文献
12.
Reservoir releases on large regulated rivers are increasingly being used to rejuvenate riverine habitat downstream of dams. Determining the effective flow level is complicated by the trade‐off between mobilizing bed particles and retaining coarse sediment in rivers with low sediment supply. This study determined mobilization and transport distance of bed particles using motion‐sensing radio transmitting particles that approximated the reach‐average D84 grain size. The distribution of shear stress at initial motion varied substantially between flood events, and suggests that the sequence of flood events and the history of under‐threshold flows may be an important determinant of bed strength and thus particle mobility. In addition, particle activity was greatest on the rising limb of each flood and was maximized at near bankfull flow. Travel distances did not vary between floods when scaled by transport event duration, and a negative exponential distribution was a good fit to the data. Results of this study provide important insight into individual particle movement, which can be used to inform flow releases and understand the effects of flood magnitude on particle mobility and transport. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
13.
Oliver P. Harmar Nicholas J. Clifford Colin R. Thorne David S. Biedenharn 《河流研究与利用》2005,21(10):1107-1131
During the twentieth century, the planform and profile of the Lower Mississippi River from Cairo, Illinois, to New Orleans, Louisiana, have been transformed by a series of engineering modifications. These include steepening of the long profile by removal of the most sinuous bends, extensive bank stabilization, and regulating sediment movement by dyke field construction. Prior to these modifications, the Lower Mississippi River adjusted its morphology in the planform, long profile and cross‐section. Planform adjustment has, however, effectively been negated and other adjustments are now constrained. Nevertheless, analysis of hydrographic surveys between 1949 and 1989 demonstrates that geomorphological response during the post‐cutoff period remained complex. Morphological adjustments involved phased patterns of aggradation and degradation, together with changes in cross‐sectional form, and in the number, size, location and shape of pools and crossings. Greatest changes occurred in the early post‐cutoff period (1949–64) upstream from Vicksburg, Mississippi, but were accompanied by complementary changes elsewhere which propagated downstream. The combined set of responses may be interpreted with respect to a dynamic equilibrium in which the river responded to additional energy created by the cutoffs by increasing and adapting flow resistance over various scales and time periods. This study helps resolve paradoxes from previous analyses, and has significance for interpreting past engineering impacts and for suggesting future management strategies for the Lower Mississippi River. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
14.
Anaysa Elgueta Martin C. Thoms Konrad Grski Gustavo Díaz Evelyn M. Habit 《河流研究与利用》2019,35(10):1702-1711
Fluvial geomorphology provides an initial starting point for characterizing and understanding the ecogeomorphology of river networks. Knowledge of the spatial organization of morphological features and the way they influence processes within river networks is important for identifying potential links between the physical and ecological character of river systems. Here, a top‐down geographic information system‐based approach for determining the physical typology of river networks was used to determine and characterize the functional process zones (FPZs; large tracts of the river network with similar hydrogeomorphological character) of two rivers in central Chile. Seven distinct FPZs emerged from the analysis, and these had a nonuniform distribution along the river networks of the Biobío and Imperial Rivers. Some FPZs were frequent in number, with each FPZ segment being variable in length, whereas others were short and represented in limited number. A strong association between the physical character of FPZs and fish community was shown for the Biobío and Imperial Rivers. Specifically, dominant fish species varied among FPZs, and their habitat preferences were strongly related to the hydrogeomorphic character of the FPZ they dominated. These results are significant, as they can inform design of future ecological research and development of effective monitoring programmes. 相似文献
15.
The foundations of river restoration science rest comfortably in the fields of geology, hydrology, and engineering, and yet, the impetus for many, if not most, stream restoration projects is biological recovery. Although Lane's stream balance equation from the mid‐1950s captured the dynamic equilibrium between the amount of stream flow, the slope of the channel, and the amount and calibre of sediment, it completely ignored biology. Similarly, most of the stream classification systems used in river restoration design today do not explicitly include biology as a primary driver of stream form and process. To address this omission, we cast biology as an equal partner with geology and hydrology, forming a triumvirate that governs stream morphology and evolution. To represent this, we have created the stream evolution triangle, a conceptual model that explicitly accounts for the influences of geology, hydrology, and biology. Recognition of biology as a driver leads to improved understanding of reach‐scale morphology and the dynamic response mechanisms responsible for stream evolution and adjustment following natural or anthropogenic disturbance, including stream restoration. Our aim in creating the stream evolution triangle is not to exclude or supersede existing stream classifications and evolutionary models but to provide a broader “thinking space” within which they can be framed and reconsidered, thus facilitating thought outside of the alluvial box. 相似文献
16.
Removal of two dams 32 m and 64 m high on the Elwha River, Washington, USA, provided the first opportunity to examine river response to a dam removal and controlled sediment influx on such a large scale. Although many recent river‐restoration efforts have included dam removal, large dam removals have been rare enough that their physical and ecological effects remain poorly understood. New sedimentary deposits that formed during this multi‐stage dam removal result from a unique, artificially created imbalance between fluvial sediment supply and transport capacity. River flows during dam removal were essentially natural and included no large floods in the first two years, while draining of the two reservoirs greatly increased the sediment supply available for fluvial transport. The resulting sedimentary deposits exhibited substantial spatial heterogeneity in thickness, stratal‐formation patterns, grain size and organic content. Initial mud deposition in the first year of dam removal filled pore spaces in the pre‐dam‐removal cobble bed, potentially causing ecological disturbance but not aggrading the bed substantially at first. During the second winter of dam removal, thicker and in some cases coarser deposits replaced the early mud deposits. By 18 months into dam removal, channel‐margin and floodplain deposits were commonly >0.5 m thick and, contrary to pre‐dam‐removal predictions that silt and clay would bypass the river system, included average mud content around 20%. Large wood and lenses of smaller organic particles were common in the new deposits, presumably contributing additional carbon and nutrients to the ecosystem downstream of the dam sites. Understanding initial sedimentary response to the Elwha River dam removals will inform subsequent analyses of longer‐term sedimentary, geomorphic and ecosystem changes in this fluvial and coastal system, and will provide important lessons for other river‐restoration efforts where large dam removal is planned or proposed. Published 2013. This article is a U.S. Government work and is in the public domain in the USA. 相似文献
17.
High‐resolution velocity profile measurements were taken over a series of riffles on a gravel‐bed stream using a Pulse Coherent Acoustic Doppler Profiler (PCADP) to quantify the fluid structure of riffles and nests (redds) where brown trout (Salmo trutta) and rainbow trout (Oncorhynchus mykiss) spawned. Velocity profiles were obtained on a highly discretized planometric scale ranging between 20 and 40 cm grid spacings, with vertical observations occurring every 1.6 cm. From the velocity profiles, between 15 000 and 38 000 velocity measurements were obtained over each riffle on any given day of measurement. Velocity profiles were converted to streamwise velocity magnitude, flow depth, Reynolds number, Froude number, shear stress, vertical velocity components and turbulent kinetic energy per unit area to evaluate the spatial structure of the riffles and the spatial structure of redds (pits and tailspills) relative to the surrounding riffle structure. Semi‐variograms were employed to evaluate the persistence of the fluid structure based upon the metrics evaluated. Results showed that discrete velocity observations poorly described the spatial structure of the flow system and poorly correlated with redd locations. Reynolds number analysis identified a relatively consistent fluid property for distances typically 2–3 times the longitudinal length of redds. Turbulent kinetic energy per unit area consistently identified common regions on all riffles studied that corresponded with the location selections for redds where flow was identified as essentially uni‐directional. Froude number was found to be insensitive in predicting the fluid spatial structure in wadeable flow depths and relating it to the fluid structure of redds. Results indicated that a series of metrics at varying spatial scales of turbulence may be necessary to understand the spatial complexity of redd selection. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
18.
J. B. Atha 《河流研究与利用》2014,30(7):857-864
Fluvial wood has long been known to enhance stream complexity by creating aquatic habitat and by increasing complexity in channel hydraulics and morphology. Although the presence and dynamics of large wood in river floodplains have been studied in a multitude of settings due to its importance in monitoring and managing ecohydrologic systems, limitations occur when studying fluvial wood on a basin scale. I postulate that with the employment of Google Earth, satellite images may be used to identify large wood and measure floodplain width across broader spatial scales previously inhibited by expensive and incomplete geospatial data. In this study, large wood was correctly identified within the floodplain of the Queets River, Washington, USA, through Google Earth; however, correct identification within the wetted channel was only possible during low flow if at least 50% was above water level. Within the study area, fluvial channel widths are measured as well. Google Earth proves to be an effective tool to discern large wood across greater spatial scales if the high‐resolution imagery is available for the study area. Results of statistical analyses derived from the downstream hydraulic geometry of the river reveal that this channel is influenced by bankfull width, the orientation of the wood to the channel, and whether it is located on a bar or within the wetted channel. In addition, wood counts analyzed in the context of the geometry of the river indicate that the fluvial wood has an influence on overall channel behavior. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
19.
《Journal of Flood Risk Management》2018,11(Z2):S1100-S1104
The role of geomorphic processes in flood risk is understudied in the management context. In the United States, only nine states have explored this role and only two – Vermont and Washington State – have developed and implemented legally binding geomorphic‐based flood risk management; both rely on the concept of geomorphic assessment, through which fluvial geomorphic processes are documented and river corridors are mapped. Massachusetts, having incurred substantial damages from landslides, bank failures, bed incision, and sedimentation in recent years, has initiated a programme to examine the inclusion of geomorphic processes into flood risk management. At its core, the programme relies on participation of flood risk management stakeholders representing government (local, state, and federal), non‐governmental organisations, consulting agencies, academia, and industry. A series of workshops with these stakeholders over 4 years has culminated in a needs assessment that articulates what must be included in the development of a Massachusetts fluvial geomorphic assessment programme. In this report, we share the results of this needs assessment. We do this in the hope that other jurisdictions incurring flood damages from geomorphic processes may find it to be a useful model as they work to mitigate these damages. 相似文献
20.
河流生态系统研究的理论框架 总被引：16，自引：4，他引：12
讨论了河流生态系统的时空尺度。论述了景观、流域、河流廊道和河段4种空间尺度间的关系。阐述了河流生态系统的4种背景系统,即自然系统、经济系统、社会系统和工程系统。归纳了水文情势、河流地貌、流态和水质等4个主要生境要素。在此基础上进一步讨论了科学范式和模型的概念,介绍了多种重要生态系统结构与功能模型,提出了描述非生命变量和生命变量之间关系的河流生态系统结构与功能整体模型。最后,探讨了科学研究对于制定流域管理战略的意义以及相关技术开发的方向。 相似文献