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1.
C. Mendoza–Lera A. Larrañaga J. Pérez E. Descals A. Martínez O. Moya I. Arostegui J. Pozo 《河流研究与利用》2012,28(1):13-22
Leaf litter breakdown is a key process, providing matter and energy to communities inhabiting many headwater streams that flow through forests. This detrital pathway is affected by many human landscape transformations; but it is little known about the impact of small headwater reservoirs on leaf litter decay in streams. Alder leaf litter breakdown rates and associated fauna were studied upstream and downstream of five small water supply reservoirs (surface‐release in rainy autumn‐winters), in the Nerbioi‐Ibaizabal drainage basin (Basque Country, Spain), to assess the effect of impoundment on headwater streams function. Breakdown rates were significantly lower below the dams, mainly associated with a reduction of the density and the biomass of shredders. Among the shredders, Nemouridae and especially Protonemura were less abundant downstream of the dam. Alterations in the physicochemical characteristics of the water due to the reservoirs were negligible throughout our study, and temperature showed only slight variations that could not explain the reduction of the rates. The effect on shredders is likely to be related to differences in the riparian environment and flow regulation by the dams. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
Breakdown rates and colonisation of leaves from four tree or scrub species differing in quality are studied upstream and downstream of the Canales reservoir, a dam located in the headwater of the River Genil, Sierra Nevada, in southern Spain. This dam, with hypolimnetic release, displays short‐term fluctuations of discharge and nutrient enrichment in the tailwater during the study period. Breakdown rates of the four leaf species studied do not differ between sites, despite the higher dissolved nutrient concentration in the tailwater. This lack of differences is attributed to the potentially high physical breakage of leaves during peak flows that are of higher magnitude at the upstream site. The invertebrate density in leaf bags does not differ between sites, and Chironomidae and Ephemeroptera are the numerically dominant taxa at both sites. With regard to functional feeding groups, the scarcity and lack of significant differences between sites for shredders do not match the trend predicted by the Serial Discontinuity Concept in relation to the effect of a headwater dam. Possibly, the discharge fluctuations at both sites causes excessive instability of the natural substrate (leaf litter) for the shredder guild. However, as expected, the biomass of collectors colonising leaf bags is significantly higher at the tailwater, which might be explained not in terms of quantity, but as a consequence of the higher nutritional quality of the fine particulate organic matter (FPOM) accumulated in leaf bags at this site, owing to the eutrophication caused by the dam. Despite the scarcity of functional shredders at both sites, at the community level, the leaf material is significantly more ingested at the upstream site, suggesting the importance of this source of nutrition for the trophic web at this site in contrast with the tailwater, as predicted by the Serial Discontinuity Concept. This also suggests that caution is needed in using functional feeding groups as trophic guilds to infer system‐level trophic dynamics in streams, given the prevalence of generalist feeders among benthic macroinvertebrates in these environments. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
3.
Jamal Kabir;Giulio Biondi;Kieran J. Gething;Thomas Aspin;Tim Sykes;Rachel Stubbington; 《河流研究与利用》2024,40(5):863-874
Headwater springs and streams often occur in relatively remote areas, reducing their exposure to human influences and thus increasing their collective capacity to support high biodiversity. Their aquatic macroinvertebrate communities can include species of conservation interest, some of which are specialists associated with groundwater inputs, low water temperature or temporary flow. However, the inaccessibility of some spring and stream networks has left their communities poorly characterized, limiting our capacity to implement effective conservation strategies. We characterized the biodiversity and conservation value of macroinvertebrate communities in a network of 51 relatively inaccessible and unimpacted headwater spring and stream sites spanning multiple catchments in a single landscape type: the chalk downland of south England. At each site, we kick sampled macroinvertebrate communities and recorded environmental variables, including flow permanence. To represent each community, we calculated taxa richness, coverage-adjusted Hill-Shannon diversity, the local contribution to beta diversity, and an index of richness and species rarity. We used the latter three metrics to rank sites based on their biodiversity and conservation value and analyzed relationships between metrics and environmental variables. We found specialists of springs, cold waters, groundwaters and temporary flow regimes, including rare species of conservation value. Some metrics responded to environmental variables, but top-ranking sites had highly variable environmental characteristics. We highlight the value of individual headwater streams with contrasting characteristics as contributors to ecologically heterogeneous site networks. Our results can inform landscape-scale management strategies that protect headwaters as refuges that support biodiverse communities, including rare species, as they adapt to global change. 相似文献
4.
The grain sizes of 53 small lateral and mid‐channel deposits were evaluated on the 2.7 km long channel‐reach of a headwater piedmont stream that has been affected by check‐dams and bed sills constructions (ca. 14 constructions per km), riprap bank stabilisations and the removal of instream wood. Such interventions have led to the loss of natural vertically oscillating bedforms, and pool‐riffles have been replaced by plane beds. The evaluated sediment deposits were divided based on their positions relative to grade‐control structures on downstream, intermediate and upstream types. The individual types of deposits produced different downstream trends in the grain sizes that reflected their positions with respect to the grade‐control structures (GCSs). The downstream deposits generally produced slow downstream coarsening, which may point to the increased efficiency of the energy dissipation of the GCSs under a gradual downstream decrease in the channel slopes. However, they were generally not coarser than the other two types. The upstream deposits did not indicate any notable downstream grain‐size trend. Despite the significant downstream decrease in the channel slopes and related bankfull shear stresses at the positions of the intermediate deposits and the lack of a lateral sediment supply in the studied longitudinal profile, the sediment calibre of the deposits did not produce any systematic downstream fining. Thus, the observed grain sizes most likely pointed to the selective scouring of the fine sediments, which was caused by the presence of the GCSs and their effects on the decreasing sediment connectivity. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
5.
The Almbach, a headwater stream in the Upper Austrian foothills of the Alps bordered by mountain pastures was studied to gain insight into the benthic macroinvertebrate community and its habitat. Two springs, one of them fenced in to prevent livestock access, and two more sites of the headwater section were investigated. A discriminant analysis (DA) based on hydrochemistry and phytobenthos revealed three functions with 86% of all samples correctly classified to the four sites. The first function clearly separated the two springs with phosphorus and oxygen as the most important discriminating factors. Spring sites and headwater sites were split up by the second function mainly due to nitrate concentration, but no differences could be detected for the two stream sites. With the exception of the fenced spring, indicator taxa could be assigned to all sites by means of an Indicator Species Analysis (ISA). Polyvalent taxa groups such as Gastropoda and Ostracoda were indicators for the unfenced spring site. This is in accordance to observed low abundances of sensitive plecopteran taxa and suggests a negative impact of livestock trampling on the invertebrate community. Redundancy Analysis explained 99% of the macroinvertebrate‐environment relation. The first axis separated springs from stream sites and was correlated with nitrate, pH, water temperature and phytobenthos eveness. Phosphorus was responsible for splitting the unfenced spring and the downstream station from the fenced spring and the upstream location along the second axis. Ephemeropteran taxa like Habrophlebia sp. were related to elevated pH, increased water temperature and low nitrate concentrations. In accordance to the ISA, nitrate played an important role for tolerant Gastropoda and Ostracoda at the unfenced spring. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
6.
Using geographic information system and topographic maps, 5829 headwater streams in Florida were surveyed for several parameters including elevation, stream length, flow regime and surrounding geology, and vegetation. Each was assigned to one of four headwater types: wetland, seep, lake, and spring. Wetland headwaters were the most common and widespread followed by seeps, many displaying temporary flow, while springs were perennial and least numerous. Four groups of Florida rivers were identified through cluster analysis of drainage densities (number headwaters/km of river length). Group 1 consisted of six rivers with lowest drainage densities (0.30–1.39 streams/km main channel). All were coastal rivers of peninsular Florida and, with one exception, drain to the Gulf of Mexico. Seven of eight rivers (group 2) with intermediate drainage densities (1.77–3.04 streams/km main channel) were located in peninsular Florida. Only three of 12 rivers comprising the two groups (groups 3 and 4) with greatest drainage densities (5.16–9.37 and 15.49–16.96 streams/km main channel) were not located in the Florida panhandle. Stream conservation efforts should focus on both highly complex dendritic river networks of the panhandle and on the 7000 km2 area in central Florida mostly lacking headwaters that may become a significant dispersal bottleneck for aquatic biota seeking refugia farther north from projected climate change. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
7.
《Journal of Contemporary Water Research & Education》2017,160(1):100-118
Anthropogenic inputs of nutrients threaten water quality around the world, causing eutrophication and altering phytoplankton communities. In freshwater systems, certain physiochemical conditions, including high TP, low TN:TP, and warm temperatures, can lead to problematic cyanobacteria blooms. Cyanobacteria can decrease phytoplankton diversity and phytoplankton diversity has been positively linked to zooplankton diversity, suggesting that cyanobacteria may have indirect negative effects on zooplankton diversity. Using monitoring data from Lake Champlain, we tested three hypotheses: (1) cyanobacteria density and phytoplankton diversity are inversely related; (2) phytoplankton diversity and zooplankton diversity are positively related; and by extension (3) cyanobacteria density and zooplankton diversity are inversely related. Relationships were investigated separately at shallow (4–15 m) and deep (25–100 m) sites using several diversity metrics. At deep sites, cyanobacteria density was only related (positively) to zooplankton Shannon diversity. At shallow sites, all three hypotheses were supported by three of four diversity metrics; low phytoplankton richness appears to be the link between high cyanobacteria density and low zooplankton diversity. Our results suggest that cyanobacteria may indirectly reduce zooplankton diversity by decreasing resource heterogeneity, although our results based on observational data were also consistent with well‐known direct pathways. Because low biodiversity can alter ecosystem processes and impair functioning, our results suggest that shallow systems may be more responsive to global change than deeper systems. 相似文献
8.
L. Ponsatí V. Acuña I. Aristi M. Arroita E. García‐Berthou D. von Schiller A. Elosegi S. Sabater 《河流研究与利用》2015,31(8):1003-1016
Dams regulate downstream hydrology and modify water quality, which in turn can impinge on the biota, especially in rivers naturally subject to large hydrological variability, such as those under Mediterranean climate. The effect of dams on biofilms was analysed in three tributaries (Cinca, Siurana and Montsant) of the Ebro River (NE Spain). We hypothesized that flow regulation would lead to lower spatial variability of biofilms on the streambed and to a decrease in their metabolic rate per unit biomass, especially during low flow periods. Biofilm characteristics were studied in five transects evenly spaced along river reaches upstream (control) and downstream (impact) of dams in each river, along with riverbed granulometry, hydraulics and water chemistry. Chlorophyll‐a, respiratory activity, photosynthetic capacity and efficiency, and extracellular enzymatic activities (β‐d ‐glucosidase, alkaline phosphatase and leucine‐amino‐peptidase) of epilithic biofilms were measured in different seasons. Spatial variability of chemical and biological variables was reduced downstream of the dams. Chlorophyll‐a concentration, photosynthetic efficiency and respiration capacity were higher in impact than in control reaches, but generally, low inorganic phosphorus concentrations resulted in comparable phosphatase activities downstream and upstream of dams. On the other hand, β‐d ‐glucosidase and leucine‐amino‐peptidase activities were higher at impact reaches. Biofilms were thicker and metabolically more active at the impact reaches, with higher ability to transform dissolved organic matter. Overall, results from this study provide evidence that dams can largely affect the structure and activity of river biofilms, with foreseeable important consequences for river ecosystem functioning. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
9.
芦苇占优势农田溪流营养盐滞留能力分析与评估 总被引：1，自引：0，他引：1
2014年9月—2015年4月,在合肥地区二十埠河流域的某一典型农田源头溪流段,选择以Na Cl为保守示踪剂,NH4Cl和KH2PO4为添加营养盐,采用恒速连续投加的方式,开展了7次野外现场示踪试验。在此基础上,利用OTIS模型和营养螺旋原理,从机制层面分析和评估芦苇占优势农田源头溪流氮磷营养盐滞留能力和滞留特征。结果表明,该芦苇占优势渠段的比值As/A明显超过一般源头溪流水体,暂态存储对于营养盐滞留有较大影响;NH4+和SRP的暂态存储区营养盐一阶吸收系数都较主流区高一个数量级,且所有吸收系数均为正值,表明芦苇占优势渠段具有氮、磷\"汇\"的功能;NH4+吸收长度明显低于SRP,特别是冬季和初春,意味着溪流对于NH4+的滞留能力超过SRP;NH4+和SRP的总滞留率分别为14.46%和10.73%,生物滞留率平均值分别为9.17%和3.67%;主流区流动水体和暂态存储区对于NH4+滞留的平均贡献率分别为43.12%、56.88%;对于SRP滞留的平均贡献率分别50.13%、49.87%。 相似文献
10.
This Perspective argues for an expansion of conventional concepts of river biomes to better encapsulate the emerging social understanding of ‘biomes’ as living systems with unique macro- and micro-biotic ecological and biological signatures. We approach this by firstly examining recent interpretations of river biomes that have evolved from original zonal conceptions. We then postulate on the social/public understanding on ‘biomes’ through the popularity of two rich debates: human health via gut microbiomes and soil health via the soil microbiome. With these concepts in mind, we define the river biome as ‘A living flowing aquatic ecosystem, indicative of its environmental context, comprising unique biological, ecological, hydrologic and health characteristics that shape and are shaped by macro- and micro-biotic signatures and functions’. With this definition the term river biome is more aligned with ideas of river health and ecosystem functioning, which we believe may evoke greater public understanding of rivers as complex living systems. Enhanced public understanding of complex natural systems should be encouraged as a means by which to propel policy, funding and research as well as to improve specialist to non-specialist communication and relations. 相似文献
11.
T. J. Hoellein J. L. Tank S. A. Entrekin E. J. Rosi‐Marshall M. L. Stephen G. A. Lamberti 《河流研究与利用》2012,28(9):1451-1461
The assemblage of stream habitat types can drive biofilm composition and activity in headwater streams, thereby influencing rates of ecosystem function. However, the influence of human‐induced alterations to the distribution of benthic habitat such as construction, land‐use changes and restoration on biofilm‐mediated processes has not been well studied. We measured nutrient uptake of ammonium, nitrate and phosphate, as well as gross primary production and community respiration in three streams in Michigan, USA, each with an upstream reference and a downstream restored reach. The restoration included a 10‐m sediment trap, paired with 40–60 m of gravel and boulder added downstream and designed to retain sediment, stabilize banks and provide spawning habitat for trout. We sampled four times in the six stream reaches from May 2006 to September 2007. Across streams, restored reaches reflected the structural manipulation with increased predominance of coarse inorganic sediments, higher gas exchange rate and increased transient storage. However, nutrient uptake and community respiration rates were different between reaches at only one site. The ecosystem response by this stream was driven by the large differences in coarse inorganic habitat between reference and restored reaches. We conclude that restorations of benthic habitat which are visually conspicuous, such as creation of settling pools and gravel‐filled reaches, did not universally affect stream ecosystem function. Initial conditions and magnitude of change may be key factors to consider in explaining functional responses, and predicting the influence of habitat restoration on ecosystem function remains a challenge. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
12.
T. Jutagate S. Lek A. Sawusdee U. Sukdiseth T. Thapanand‐Chaidee S. Thongkhoa S. Lek‐Ang P. Chotipuntu 《河流研究与利用》2011,27(1):47-58
Fish assemblage patterns were studied in the lower river reach of the Uthokawiphatprasit anti‐salt dam, 6 km upstream from the Pak Panang River mouth, Southern Thailand, where the dam was opened occasionally depending on the upstream water level. Matrix data of the presence–absence of 71 fish species in 102 surveys was used in the analysis by applying a self‐organizing map (SOM) model. The trained SOM (lattice 8 × 7) showed that after 6 years of operation, five assemblage patterns were distinguished. These patterns described the probability of the occurrence of fish in each fish environmental guild, which according to changes in flow and water geomorphology. Clusters Ia and Ib were mostly the surveys in upstream stations and occupied by fish in potamonic guilds, whereas the fish in the estuarine guild and marine guilds showed a high probability of occurring in clusters IIa, IIb and IIc, which belonged to the surveys in downstream stations. The surveys of the stations near the dam (i.e. stations 5 and 6) during the opening phase were contained in cluster IIb. The Kruskal–Wallis test showed that there was no statistical difference in the probability of occurrence among assemblages of the diadromous, catadromous and semi‐anadromous fishes but not the amphidromous fishes, which had a low probability of occurrence in clusters Ia and Ib. The fish assemblages were arrayed along a longitudinal gradient, where salinity and pH were the most important controlling variables and explained 94.0% of the total inertia. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
13.
Daniel C. Allen Thibault Datry Kate S. Boersma Michael T. Bogan Andrew J. Boulton Daniel Bruno Michelle H. Busch Katie H. Costigan Walter K. Dodds Ken M. Fritz Sarah E. Godsey Jeremy B. Jones Tatiana Kaletova Stephanie K. Kampf Meryl C. Mims Thomas M. Neeson Julian D. Olden Amandine V. Pastor N. LeRoy Poff Benjamin L. Ruddell Albert Ruhi Gabriel Singer Paolo Vezza Adam S. Ward Margaret Zimmer 《Wiley Interdisciplinary Reviews: Water》2020,7(5)
Conceptual models underpin river ecosystem research. However, current models focus on continuously flowing rivers and few explicitly address characteristics such as flow cessation and drying. The applicability of existing conceptual models to nonperennial rivers that cease to flow (intermittent rivers and ephemeral streams, IRES) has not been evaluated. We reviewed 18 models, finding that they collectively describe main drivers of biogeochemical and ecological patterns and processes longitudinally (upstream‐downstream), laterally (channel‐riparian‐floodplain), vertically (surface water‐groundwater), and temporally across local and landscape scales. However, perennial rivers are longitudinally continuous while IRES are longitudinally discontinuous. Whereas perennial rivers have bidirectional lateral connections between aquatic and terrestrial ecosystems, in IRES, this connection is unidirectional for much of the time, from terrestrial‐to‐aquatic only. Vertical connectivity between surface and subsurface water occurs bidirectionally and is temporally consistent in perennial rivers. However, in IRES, this exchange is temporally variable, and can become unidirectional during drying or rewetting phases. Finally, drying adds another dimension of flow variation to be considered across temporal and spatial scales in IRES, much as flooding is considered as a temporally and spatially dynamic process in perennial rivers. Here, we focus on ways in which existing models could be modified to accommodate drying as a fundamental process that can alter these patterns and processes across spatial and temporal dimensions in streams. This perspective is needed to support river science and management in our era of rapid global change, including increasing duration, frequency, and occurrence of drying. This article is categorized under:
- Water and Life > Nature of Freshwater Ecosystems
- Water and Life > Stresses and Pressures on Ecosystems
- Science of Water > Hydrological Processes
14.
Composition and structure of lotic ecosystems can be affected by substrate instability. Consequently stream ecologists have used various methods to determine bed stability characteristics. However, the link between community composition and these measurements varies because benthic biota often responds to combinations of bed stability characteristics. This paper presents a protocol to determine reach‐scale stream bed stability in mountain streams which is relevant for invertebrate communities (Stream Bed Stability for Invertebrates, SBSI). The approach is calibrated on community composition response to bed stability but does not measure any single bed stability characteristic per se. It consists of 13 parameters that are assessed once at each reach with minimal instrumentation and low interference with the substrate. These 13 parameters cover aspects of sediment supply from banks, transport capacity and substrate erodibility as well as effects of particle transport on channel bottom structures, substrate assemblage and single grains. Application of the SBSI protocol improved the relationship between bed stability and community diversity compared to when conventional bed stability measures were employed. The SBSI protocol provides a cost‐effective and time‐effective assessment method for bed stability and its application can facilitate research on invertebrate community response to physical disturbance. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
15.
Different land uses directly affect the characteristics of a river basin and influence the aquatic biota and ecosystem processes. This study aimed to analyse the community structure and composition of aquatic invertebrates and the role of these organisms in the process of leaf litter breakdown in streams with different land uses. The study was conducted from September to December 2013 in five streams in the Neotropical region. At each stream, we placed 18 bags containing litter for colonization by aquatic invertebrates, and the bags were collected at different exposure times (5, 30, 45, 60, 75 and 90 days). We registered spatial differences in the aquatic invertebrate community structure and composition. There were no significant differences in the activity of invertebrates in the leaf litter breakdown process among streams with different land uses. However, the variability in mass decay rate was lower for the reference stream. This result may have been influenced by habitat quality, availability of organic matter and the structure and composition of benthic community present in the reference stream, which differs significantly among locations with different types of land use. The results of this study shows that human activities, particularly agriculture and urbanization, modify the structure and composition of the benthic community and acts on ecosystem processes, especially in the variability of the processing of allochthonous material invertebrates. However, we reject the hypothesis that land use negatively influences the decomposition of litter, measured by weight loss. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
16.
长江流域水系划分与河流分级初步研究 总被引：1，自引：0，他引：1
将推荐的水系划分与河流分级Horton法相结合,通过合理选取最小河流(流域)单元、科学制作河流树状图表,初步研究了长江流域(不含太湖水系)的河流分级。研究结果显示:①推荐将长江水系划分为干流水系与雅砻江、岷江、嘉陵江、乌江、洞庭湖、汉江、鄱阳湖、太湖8个支流水系;② 581条河流基本特性资料的收集、整理与分析表明长江流域河流的河长与流域面积约为0.5次方关系,选取流域面积不小于2 000 km2或河长不小于100 km的河流为最小河流(流域)单元,确定长江流域(不含太湖水系)河流总数为374条;③以岷江水系为例,精心制作了长江流域各水系的河流树状图表,树状图显示了河流隶属关系、分级数、河长、流域面积等特性;④长江流域(不含太湖水系)最高河流分级数为6级。按河流统计:6级1条(0.3%),5级3条(0.8%),4级6条(1.6%),3级14条(3.7%),2级71条(19.0%),1级279条(74.6%);按水系统计:岷江、嘉陵江、鄱阳湖为5级,干流、雅砻江、洞庭湖、汉江为4级,乌江为3级。 相似文献
17.
砂石是河流生态系统的重要组成部分,是河流生物附着生存的物理基底和重要生境要素。为满足修建公路、桥梁、房地产开发等多方面的需求,河道采砂的强度和规模与日俱增。大规模的河道采砂会引起一系列严重的生态环境后果,包括河床下切导致河势失稳,河道水位和漫滩洪水发生频率下降,地表径流和地下水分配格局发生变化,河流生境和生物多样性下降,威胁着河流生态系统结构和功能的完整性,使得系统稳定性和抵抗力下降。在理解生态环境影响机理的基础上制定有针对性的管理对策,有助于将河道采砂造成的干扰控制在河流系统可以承受的范围之内,减轻或避免产生负面的生态环境问题。 相似文献
18.
多级拦水堰坝调控农田溪流营养盐滞留能力的仿真模拟 总被引：3，自引：1，他引：2
为揭示多级拦水堰坝对于低等级小河流营养盐滞留能力的影响,以巢湖流域某一典型的农田源头溪流为对象,在野外示踪实验和计算机模拟的基础上,针对构建的多级简易水坝,采用暂态存储和营养螺旋指标,仿真模拟多级拦水堰坝对于氮磷营养盐滞留能力的调控效果。结果表明:多级拦水堰坝Darcy-Weisbach阻力系数明显超过无堰坝情形,但其弗劳德数Fr和雷诺数Re则较无堰坝情景低些;多级拦水堰坝相应的交换长度Ls值较无堰坝情景低1~2个数量级,水力持留因子Rh则较无堰坝情景明显增大,表明多级拦水堰坝使溪流的暂态存储能力得到很大提升;在多级拦水堰坝情景下,NH4+和PO43-的吸收长度Sw均有大幅度的下降,其中NH4+削减幅度达70.27%~89.47%,PO43-为75.59%~81.92%;不仅如此,在多级堰坝情景下,NH4+和PO43-的物质传输系数Vf、吸收速率U均显著增大,表明多级拦水堰坝可以有效提高农田溪流氮磷营养盐的滞留潜力。 相似文献
19.
Channel‐spanning logjams completely span the active channel and create longitudinal discontinuities of the water surface and stream bed across at least two‐thirds of the channel width. These jams disproportionately affect channel process and form relative to smaller jams that do not span the entire channel width. We analyze a spatially extensive dataset of 859 channel‐spanning jams distributed along 124 km of 16 distinct rivers on the eastern side of Rocky Mountain National Park, Colorado, USA, with drainage areas spanning 2.6 to 258 km2 and diverse valley geometry and forest stand age. We categorized valley geometry in terms of lateral confinement (confined, partly confined, or unconfined), which correlates with gradient. Jams exhibit substantial downstream variability in spacing at channel lengths of 102–103 m. The number of jams within a reach is explained by a statistical model that includes drainage area, valley type (lateral confinement), and channel width. Longitudinal spacing of jams drops substantially at drainage areas greater than ~20 km2, although jam spacing exhibits tremendous variability at smaller drainage areas. We interpret the lack of jams at larger drainage areas to reflect increasing transport capacity for instream wood. We interpret the variability in jam spacing at small drainage areas to reflect local controls of valley geometry and associated wood recruitment and fluvial transport capacity. Our results suggest that management of instream wood designed to facilitate the formation of channel‐spanning jams can be most effectively focused on smaller drainage areas where these jams are most abundant in the absence of management that alters instream wood recruitment or retention. Unmanaged streams in the study region with drainage area <60 km2 have ~1.1 channel‐spanning jams per 100 m length of stream. The cumulative effects of these jams on instream storage of sediment and organic matter, hyporheic exchange, instream habitat, stream metabolism, and channel–floodplain connectivity are likely to be enormous. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献