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1.
Two lead-210 (210Pb) dated sediment cores from Chapala Lake were studied to identify the mineral composition of the sediments and to discuss its relation with trace metals. Minerals and trace metals reflected the domain of volcanic rocks (i.e. basalts, rhyolite and andesite) that characterize Chapala Lake and the Lerma River watershed. Redundancy analyses (RDA) were used to identify the sedimentary variables (magnetic susceptibility, organic matter, sand content, and mineral composition) that could be related to elemental composition. Despite the distance between the two cores (7.3 km) and hydrodynamic circulation the RDA showed that the main mechanism that controls the input of mineral species, and, therefore, element distributions in the lacustrine sediment of Chapala Lake, is related to the weathering of volcanic rocks in the Lerma-Chapala watershed, the consequent runoff and transport of fine grained catchment materials, and later in-lake processes. These findings highlight the importance of controlling watershed erosion to contribute to the improvement of the environmental quality of the lake.  相似文献   

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4.
Terrigenous (Sc, Fe, K, Mg, Al, Ti) and anthropogenic (Pb and Cu) element fluxes were measured in a new sediment core from Lake Biel (Switzerland) and in previously well-documented cores from two upstream lakes (Lake Brienz and Lake Thun). These three large peri-alpine lakes are connected by the Aare River, which is the main tributary to the High Rhine River. Major and trace element analysis of the sediment cores by inductively coupled plasma mass spectrometry (ICP-MS) shows that the site of Lake Brienz receives three times more terrigenous elements than the two other studied sites, given by the role of Lake Brienz as the first major sediment sink located in the foothills of the Alps. Overall, the terrigenous fluxes reconstructed at the three studied sites suggest that the construction of sediment-trapping reservoirs during the twentieth century noticeably decreased the riverine suspended sediment load at a regional scale. In fact, the extensive river damming that occurred in the upstream watershed catchment (between ca. 1930 and 1950 and up to 2,300 m a.s.l.) and that significantly modified seasonal suspended sediment loads and riverine water discharge patterns to downstream lakes noticeably diminished the long-range transport of (fine) terrigenous particles by the Aare River. Concerning the transport of anthropogenic pollutants, the lowest lead enrichment factors (EFs Pb) were measured in the upstream course of the Aare River at the site of Lake Brienz, whereas the metal pollution was highest in downstream Lake Biel, with the maximum values measured between 1940 and 1970 (EF Pb > 3). The following recorded regional reduction in aquatic Pb pollution started about 15 years before the actual introduction of unleaded gasoline in 1985. Furthermore, the radiometric dating of the sediment core from Lake Biel identifies three events of hydrological transport of artificial radionuclides released by the nuclear reactor of Mühleberg located at more than 15 km upstream of Lake Biel for the time period 1970–2000.  相似文献   

5.
Field data are essential in evaluating the adequacy of predictive equations for sediment transport. Each dataset based on the sediment transport rates and other relevant information gives an increased understanding and improved quantification of different factors influencing the sediment transport regime in the specific environment. Data collected for 33 sites on 31 mountain streams and rivers in Central Idaho have enabled the analysis of sediment transport characteristics in streams and rivers with different geological, topographic, morphological, hydrological, hydraulic, and sedimentological characteristics. All of these streams and rivers have armored, poorly sorted bed material with the median particle size of surface layer coarser than the subsurface layer. The fact that the largest particles in the bedload samples did not exceed the median particle size of the bed surface material indicates that the armor layer is stable for the observed flow discharges (generally bankfull or less, and in some cases two times higher than bankfull discharge). The bedload transport is size‐selective. The transport rates are generally low, since sediment supply is less than the ability of flow to move the sediment for one range of flow discharges, or, the hydraulic ability of the stream is insufficient for entrainment of the coarse bed material. Detailed analyses of bedload transport rates, bedload and bed material characteristics were performed for each site. The obtained results and conclusions are used to identify different influences on bedload transport rates in analyzed gravel‐bed rivers. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

6.
To investigate the role of coastal canyons in the transfer of organic matter from the shelf to the slope and basin, we deployed sediment trap/current meter pairs at the head of five canyons in the Gulf of Lions (GoL) between November 2003 and May 2004. Analysis of organic carbon, biogenic silica, Corg isotopic composition, Corg/total nitrogen, chloropigments, and amino acids clearly shows the seasonal influence and effect of extreme meteorological events on the composition of collected particles. The sampling period was divided into three “scenarios”. The first corresponded to a large easterly storm and flood of the Rhone river during stratified water column conditions; the composition of material collected during this event was influenced by increased transfer of riverine and coastal particulate matter, with a lower Corg content. During the second “fall-winter” scenario, northern and northwestern winds blowing over the shelf caused cooling and homogenization of the shelf water column; particles collected at this time reflected the homogeneous source of particulate matter transported through canyons; particles sitting in the vicinity of canyon heads are most likely swept downslope by the general south-westward circulation. Organic tracers indicate a degraded origin for organic matter transported during this period. A third “spring” scenario corresponded to northern winds alternating with eastward windstorms that triggered and/or enhanced the cascading of dense waters accumulated on the bottom of the shelf due to previous cooling. These conditions occurred in conjunction with increased phytoplankton productivity in shelf surface waters. Organic matter advected mainly by dense shelf water cascading was fresher due to the transport of newly produced particles and a variable terrestrial fraction; this fraction depended on the proportion of resuspended material accumulated during previous high discharge periods that was involved in each transport pulse. The tight link shown between meteorological conditions and organic matter transport is important for continental margin geochemical studies as future changes in climatic conditions may lead to dramatic changes in carbon sequestration capability and in the ecosystems of deep margin environments.  相似文献   

7.
We exploit a natural experiment caused by an extreme flood (~500 year recurrence interval) and sediment pulse derived from more than 2500 concurrent landslides to explore the influence of valley‐scale geomorphic controls on sediment slug evolution and the impact of sediment pulse passage and slug deposition and dispersion on channel stability and channel form. Sediment slug movement is a crucial process that shapes gravel‐bed rivers and alluvial valleys and is an important mechanism of downstream bed material transport. Further, increased bed material transport rates during slug deposition can trigger channel responses including increases in lateral mobility, channel width, and alluvial bar dominance. Pre‐ and post‐flood LiDAR and aerial photographs bracketing the 2007 flood on the Chehalis River in south‐western Washington State, USA, document the channel response with high spatial and temporal definition. The sediment slug behaved as a Gilbert Wave, with both channel aggradation and sequestration of large volumes of material in floodplains of headwaters' reaches and reaches where confined valleys enter into broad alluvial valleys. Differences between the valley form of two separate sub‐basins impacted by the pulse highlight the important role channel and channel‐floodplain connectivity play in governing downstream movement of sediment slug material. Finally, channel response to the extreme flood and sediment pulse illustrate the connection between bed material transport and channel form. Specifically, the channel widened, lateral channel mobility increased, and the proportion of the active channel covered by bars increased in all reaches in the study area. The response scaled tightly with the relative amount of bed material sediment transport through individual reaches, indicating that the amount of morphological change caused by the flood was conditioned by the simultaneous introduction of a sediment pulse to the channel network. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

8.
A fluorescent labelling method is presented as a new tool for the investigation of organic particle transport and biogenic carbon cycling processes in sandy littoral interstices at Lake Tegel, Berlin, Germany. Passive particle transport through the pore system was studied by in situ exposition of 2.4 μm monodisperse polymeric resin microparticles stained with 7-amino-4-methylcoumarin (AMC). Uptake of fluorescein-5-isothiocyanate (FITC)-labelled Chlorella vulgaris and fine particulate organic matter (FPOM) by the interstitial fauna was investigated in laboratory and field experiments. The major portion (>85%) of the FITC-labelled particles added to sediment cores was recovered from the topmost centimetre of sediment during the study period of 14 days. Uptake of FITC-labelled FPOM was observed in several benthic groups, e.g. chironomids, microcrustaceans, oligochaetes and tardigrads, whereas C. vulgaris was ingested by oligochaetes only. There is evidence to suggest that both are suitable materials for investigating the fragmentation and ingestion of organic material by herbivorous and detritivorous fauna. Field experiments with inert microparticles and FITC-labelled FPOM (<1 mm) prepared from dried alder leaves were carried out in plexiglass tubes as in situ whole core technique. Within the investigation period of two weeks, the transport of FPOM was restricted to the topmost 2–3 cm of sediment in conjunction with a distinct fragmentation to finer size classes with respect to increasing sediment depth. Vertical FPOM transport was hindered by a high interstitial concentration of natural POM and an intensive settlement of the interstices by algae (mainly epispammic algae, 65–96% of algae cell number) and extra-cellular polymeric substances (EPS), which formed a dense three-dimensional structure.  相似文献   

9.
Deposition and storage of fine‐grained (<62·5 μm) sediment in the hyporheic zone of gravel bed rivers frequently represents an important cause of aquatic habitat degradation. The particle size characteristics of such fine‐grained bed sediment (FGBS) exert an important control on its hydrodynamic properties and environmental impact. Traditionally, particle size analysis of FGBS in gravel bed rivers has focused on the absolute size distribution of the chemically dispersed mineral fraction. However, recent work has indicated that in common with fluvial suspended sediment, significant differences may exist between the absolute and the in situ, or effective, particle size composition of FGBS, as a result of the existence of aggregates, or composite particles. In the investigation reported in this paper, sealable bed traps that could be remotely opened to sample sediment deposited during specific storm runoff events and a laser back‐scatter probe were used to quantify the temporal and spatial variability of both the absolute and effective particle size composition of FGBS, and the associated suspended sediment from four gravel bed rivers in the Exe Basin, Devon, UK. The absolute particle size distributions of both the FGBS and suspended sediment evidenced c. >95%<62·5 μm sized primary particles and displayed a seasonal winter–summer fining, while the opposite trend was displayed by the effective particle size distribution of the FGBS and suspended sediment. The effective particle size distributions of both were typically highly aggregated, comprising up to 68%>62·5 μm sized particles. Spatial variation in the effective particle size and aggregation parameters was of secondary importance relative to temporal variation. The effective particle size distribution of the FGBS was consistently coarser and more aggregated than the associated suspended sediment and there was evidence of aggregate break‐up in samples of resuspended bed sediment. The implications of these findings for sediment transport modelling are considered. Copyright © 1999 John Wiley & Sons, Ltd.  相似文献   

10.
P. I. A. Kinnell 《水文研究》2012,26(10):1449-1456
Sheet and interrill erosion areas are sources of soil material rich in nutrients and pollutants. The loss of soil, nutrients and other chemicals from these areas is a matter of concern both in terms of maintaining soil productivity and the health of offsite environments. Many experiments on rainfall erosion have shown enrichment of fine material, nutrients and other chemicals in the sediment discharged for sheet and interrill erosion areas, but often these results were obtained over short periods of time. A qualitative mechanistic model of raindrop‐induced saltation is used to illustrate how this transport mechanism influences the composition of sediment discharged by rain‐impacted flow. Initially, fast moving particles are enriched in the sediment discharge but, over time, during a rainfall event, slower moving particles become more represented. Raindrop‐induced saltation promotes the storage of material on the soil surface with a coarser composition than the original soil. Winnowing of material from this storage by the development of flow‐driven saltation during high‐intensity events can modify the composition of the sediment discharged later by raindrop‐induced saltation. Given stable soil particles, the composition of the sediment discharged at the steady state is the same as the original soil. Enrichment is a non‐steady‐state phenomenon and failure to recognize the transient nature of enrichment may lead to inappropriate interpretation of the implications of the results from short‐term experiments. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

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12.
Fine‐grained (<62·5 µm) suspended sediment transport is a key component of the geochemical flux in most fluvial systems. The highly episodic nature of suspended sediment transport imposes a significant constraint on the design of sampling strategies aimed at characterizing the biogeochemical properties of such sediment. A simple sediment sampler, utilizing ambient flow to induce sedimentation by settling, is described. The sampler can be deployed unattended in small streams to collect time‐integrated suspended sediment samples. In laboratory tests involving chemically dispersed sediment, the sampler collected a maximum of 71% of the input sample mass. However, under natural conditions, the existence of composite particles or flocs can be expected to increase significantly the trapping efficiency. Field trials confirmed that the particle size composition and total carbon content of the sediment collected by the sampler were representative statistically of the ambient suspended sediment. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

13.
Particle selectivity plays an important role in clarifying sediment transport processes in vegetative filter strips (VFS). 10-m long grass strips at slopes of 5° and 15° were subjected to a series of sediment-laden inflows experiments with different particle sizes to investigate the sediment transport and its response to overland flow hydraulics. The inflow sediments came from local soil, river-bed sand, and mixed, with median particle size d50 of 39.9, 207.9 and 77.4 μm, respectively. Three independent repeated experiments were carried for each treatment. The results show that when the sediment trapping lasted for a certain length of time, the re-entrainment of some small-sized particles was greater than the deposition; that is, net loss occurred, which was not erosion of the original soil. Net loss of particles is mainly determined by the particle diameter. The coarser the inflow sediment particles and/or the steeper the slope, the coarser the particles can be net lost. Deposited sediment causes the VFS bed surface to become smooth and hydraulic resistance decrease exponentially. Unit stream power P is more suitable than shear stress τ of overland flow to be used to describe the process of sediment particle transport in VFS. The relationship between P and d50 of outflow sediment is very consistent with the form of power function with a constant term. These results are helpful to understand the physical process of sediment transport on vegetation hillslopes.  相似文献   

14.
No consistent functional grouping of organisms as stabilizers vs destabilizers, respectively decreasing or enhancing erodibility, is possible. Benthic organisms can affect erodibility in particular—and sediment transport in general—via alternation (1) of fluid momentum impinging on the bed, (2) of particle exposure to the flow, (3) of adhesion between particles, and (4) of particle momentum. The net effects of a species or individual on erosion and deposition thresholds or on transport rates are not in general predictable from extant data. Furthermore, they depend upon the context of flow conditions, bed configuration, and community composition into which the organism is set. Separation of organism effects into these four categories does, however, allow their explicit incorporation into DuBoys-type and stochastic sediment dynamic models already in use and thus permits the specification of parameters whose measurement will enhance predictability of sediment transport modes and rates in natural, organism-influenced, marine settings.If the variable of prime concern is the total amount of sediment transported, rather than the frequency of transport events or the spatial pattern of erosion and eposition, and if most transport occurs in rare but intense bouts (e.g., winter storms on boreal continental shelves), then it may be possible to ignore organism effects without major sacrifices in accuracy or precision. Under high transport rates, suspended load effects override organism-produced bottom roughness, abrasion removes adhesives from transporting grains, and transport rates (normalized per unit width of the channel or bed) exceed feeding and pelletization rates. Moreover, at high rates most material transports as suspended load, effectively out of reach of the benthos. The transport rates at which organism effects are overridden, however, remain to be determined. For lower transport rates, foraging theory promises to provide insights into organism effects.  相似文献   

15.
As a part of the ANR-Forclim experiment, particle mass fluxes and sedimentation processes were investigated on the slope of Aquitanian margin of the Bay of Biscay, between the canyons of Cap-Breton and Cap-Ferret. Interface sediments were collected along a depth transect from 145 to 2000 m; simultaneously a mooring line was deployed at the deepest station (WH, 2000 m) with two traps (800 and 1700 m) for a 16-month period (June 2006–November 2007). 210Pb activities of settling particles and of interface sediments were determined to study transport processes of particles. Sediment and mass accumulation rates, calculated from excess 210Pb profiles in the sediment column, show the expected decreasing trend with depth, as usually observed on margins. Mean particulate mass fluxes at 800 and 1700-m depth at site WH are, respectively, 27 and 70 g m?2 a?1.The 210Pb budget points out events of temporary high lateral input of particles. The comparison of mass and 210Pb fluxes between the water column and the seabed indicates that lateral transport plays an important role in particle accumulation on the Aquitanian margin. Regarding the objectives of the ANR-Forclim program, which aims to improve significantly the interpretation of fossil foraminifera signals, as a proxy for hydrological changes in the North Atlantic ocean, these results highlight advection processes must be considered when interpreting fluxes of foraminifers on the Aquitanian margin.  相似文献   

16.
To achieve the sustainable use of dams, the development of methods for sediment management in reservoirs is required. One such method includes the use of Sediment Bypass Tunnels (SBTs) to divert sediment around a dam, thereby preventing sedimentation in the reservoir. However, SBTs are prone to severe invert abrasion caused by the high sediment flux. Therefore, it is necessary to establish a measurement system of the sediment transport rate in these tunnels. One system to measure sediment transport in rivers is the Swiss plate geophone, which can register plate vibrations caused by particle impact. In Japan, the Japanese pipe microphone is used, and sediment transport is measured based on the sound emitted by the particle impact. In this study an attempt was made to optimize the advantages of both systems by fixing a microphone and an acceleration sensor to a steel plate. The results of calibration experiments with this new system are presented and compared with the existing methods. It was found that the acceleration sensor can detect sediment particles larger than 2 mm in diameter. Moreover, a new parameter, referred to as the detection rate, was introduced to describe the correlation between the actual amount of sediment and the registered output. Finally, two parameters - the saturation rate and hit rate - are introduced and exhibit strong correlation with the detection rate.  相似文献   

17.
Research on suspended sediment transport in the catchments of the Old Mill reservoir and Slapton Lower Ley, South Devon, has attempted to discriminate changing catchment sources on the basis of downcore variations in the mineral magnetic properties of lake, reservoir and floodplain sediments. Here, we examine these downcore variations and also explore the variability in catchment sources and the influence of topographic controls on mineral magnetic signatures of topsoils and subsoils. Particle size controls on the mineral magnetic signatures are explored by an analysis of a fractionated sediment sample, whilst the possible impact of diagenesis is assessed by an examination of the Mn profiles in the lake and reservoir sediments. From this analysis it is evident that the mineral magnetic signatures of well sorted floodplain deposits are more likely to reflect the particle size composition of the transported material. By contrast, the mineral magnetic record in the sediment of Slapton Ley appears to be most strongly influenced by dissolution of magnetic minerals. The sediment of the Old Mill reservoir provides the only suitable record for the application of a simple mixing model which is developed in order to quantify changes in the relative contribution of topsoil and subsoil through time. The research has important implications for attempting to reconstruct sediment sources in highly eutrophic lakes and emphasizes the uncertainty in the application of simple mixing models. © 1998 John Wiley & Sons, Ltd.  相似文献   

18.
The operational time distribution (OTD) defines the time for bed‐load sediment spent in motion, which is needed to characterize the random nature of sediment transport. This study explores the influence of bed clusters and size gradation on OTD for non‐uniform bed‐loads. First, both static and mobile bed armouring experiments were conducted in laboratorial flumes to monitor the transport of mixed sand/gravel sediments. Only in the mobile armouring experiment did apparent bed clusters develop, because of stable feeding and a longer transport period. Second, a generalized subordinated advection (GSA) model was applied to quantify the observed dynamics of tracer particles. Results show that for the static armour layer (without sediment feed), the best‐fit OTD assigns more weight to the large displacement of small particles, likely because of the size‐selective entrainment process. The capacity coefficient in the GSA model, which affects the width of the OTD, is space dependent only for small particles whose dynamics can be significantly affected by larger particles and whose distribution is more likely to be space dependent in a mixed sand and gravel system. However, the OTD for the mobile armour layer (with sediment recirculation) exhibited longer tails for larger particles. This is because the trailing edge of larger particles is more resistant to erosion, and their leading front may not be easily trapped by self‐organized bed clusters. The strong interaction between particle–bed may cause the capacity coefficient to be space‐dependent for bed‐load transport along mobile armour layers. Therefore, the combined laboratory experiments and stochastic model analysis show that the OTD may be affected more by particle–bed interactions (such as clusters) than by particle–particle interactions (e.g. hiding and exposing), and that the GSA model can quantify mixed‐size sand/gravel transport along river beds within either static or mobile armour layers. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

19.
Sediment transport has been extensively studied. There is still a need to learn more about the mechanisms that make bed particles move, which is caused by turbulent flow in the low transport stages(above the motion threshold and below continuous transport). This work is focused on the use of an advanced tool to obtain a better perception of sediment transport dynamical methods: an instrumented particle equipped with a micro-electromechanical systems(MEMS) sensor. Particle transport experiments w...  相似文献   

20.
《国际泥沙研究》2022,37(5):619-638
The large confluence between the Yangtze River and the outflow channel of Poyang Lake is receiving attention due to its importance in flood control and ecological protection in the Yangtze River basin. There is a large floodplain along the outflow channel of Poyang Lake, which is submerged during high flow and dry during low flow. The effects of the submergence of this floodplain on sediment and morphological characteristics at this large confluence have not been known. Hence, a field investigation was done in March 2019 (relatively high flow, Survey 3) to complement the previous field studies done in August (high flow, Survey 1) and December 2018 (low flow, Survey 2) to identify the temporal variations of sediment and morphological characteristics considering the submergence of this large floodplain. The predominant sediment transport modes were wash load for Poyang Lake and confluence particles and mixed bedload/suspended load for the Yangtze River particles. The sediment transport processes were largely affected by both the secondary flows and the water density contrast between the tributaries with a lock-exchange sediment rich, denser flow moving across the inclined mixing interface in Surveys 1 and 2. The sediment flux across the mixing interface was weakened in Survey 3 when the density contrast was very small. The stagnation zone near the confluence apex had a low sediment concentration and played a role in preventing the sediment flux exchange between the two flows, and its size, and, thus, its importance as a barrier to sediment mixing were related to the submergence of the floodplain. The bed morphology with the local scour holes at the confluence was largely affected by the large-size helical cells, and this kind of effect was weakened as the secondary flows got restricted in Survey 3. The current results expand the database and knowledge on the sediment transport and morphological features of large river confluences.  相似文献   

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