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1.
The turbulent kinetic energy dissipation rate, ε, in tidal seas is maximum at the bottom during full flood and during full ebb, i.e. when tidal currents are strongest. In coastal regions with tides similar to a Kelvin wave, this coincides with high water and low water. If there is a freshwater source at the coast, stratification in such a region will be most stable at high water and least at low water. Measurements of ε in the Rhine region of freshwater influence performed by previous studies have revealed bottom maxima at both high and low water. In addition, a maximum in the upper half of the water column was found around high water, which cannot be explained by tidal shear at the bottom, convective instabilities or wind mixing. This study investigates the dissipation rate and relevant physical properties in the Rhine region of freshwater influence by means of three-dimensional numerical simulations using the General Estuarine Transport Model and idealised conditions. The measurements are well reproduced; two distinct peaks of ε are evident in the upper layer shortly before and after high water. These maxima turn out to be due to strong peaks in the alongshore shear occurring when the fore- and the back-front of the plume transit the water column.  相似文献   

2.
《Continental Shelf Research》2007,27(10-11):1568-1583
A study is presented where satellite images (SeaWiFS), in situ measurements (tidal cycle and snapshot) and a 2D hydrodynamic numerical model have been combined to calculate the long term SPM (Suspended Particulate Matter) transport through the Dover Strait and in the southern North Sea. The total amount of SPM supplied to the North Sea through the Dover Strait is estimated to be 31.74×106 t. The satellite images provide synoptic views of SPM concentration distribution but do not take away the uncertainty of SPM transport calculation. This is due to the fact that SPM concentration varies as a function of tide, wind, spring-neap tidal cycles and seasons. The short term variations (tidal, spring-neap tidal cycle) have not been found in the satellite images, however seasonal variations are clearly visible. Furthermore the SPM concentration in the satellite images is generally lower than in the in situ measurements. The representativness of SPM concentration maps derived from satellites for calculating long term transports has therefore been investigated by comparing the SPM concentration variability from the in situ measurements with those of the remote sensing data. The most important constraints of satellite images are related to the fact that satellite data is evidence of clear sky conditions, whereas in situ measurements from a vessel can be carried out also during rougher meteorological conditions and that due to the too low time resolution of the satellite images the SPM concentration peaks are often missed. It is underlined that SPM concentration measurements should be carried out during at least one tidal cycle in high turbidity areas to obtain representative values of SPM concentration.  相似文献   

3.
《Continental Shelf Research》2006,26(17-18):2019-2028
Measurements of turbulence and suspended particulate matter (SPM) were measured over a 50 h period at a site in high tidal energy, mixed waters of the Irish Sea, NW European shelf. Turbulence parameters included both production (variance method from seabed ADCP) and dissipation (FLY profiler); SPM parameters included mass and volume concentrations and particle size (LISST 100 C). It is shown that the resultant SPM time series was due to a combination of time-varying turbulence at the measurement site and space-varying turbulence advecting through the site. Time asymmetry in turbulence at the site produced an asymmetric M4 signal in SPM volume concentration due to resuspension and disaggregation of flocs at times of peak turbulent energy. In terms of mass, the disaggregation contribution was 43% as much as the resuspension contribution near the bed, and 20% as much integrated throughout the water column. There was aggregation of flocs at high and low slack waters but the largest flocs occurred at low slack waters. Space-varying ambient turbulence was responsible for a horizontal gradient in floc size with small and large flocs at the high and low ends of the gradient, respectively; this generated a M2 signal in SPM properties. SPM concentrations and properties at any time resulted from combination of M2 and M4 variations which are responsible for the well-known twin peaks signature seen in transmissometer time series in tidal waters.  相似文献   

4.
A two-part study conducted in Elimbah Creek, a shallow estuarine waterway in south-east Queensland, Australia, examined the variations in physico-chemical parameters of water quality, chlorophyll a, and faecal indicator bacteria abundances of total coliform, Escherichia coli and enterococci, spatially at high and low tide and also over a 12h tidal cycle. Gradients of increasing faecal indicator bacteria from the mouth to the upper, tidal freshwater reaches were observed, despite isolated peaks during either tidal phase. Phytoplankton biomass (measured as chlorophyll a) did not noticeably increase during the study. Variations in the abundances of all three faecal indicator bacteria and their correlations with physico-chemical parameters indicated that although the creek was likely subject to some level of faecal contamination, tidal movement serves to limit faecal indicator and phytoplankton levels in the creek through physico-chemical stress and dilution. However, each faecal indicator bacteria investigated provided different estimations of faecal contamination, which challenges the effectiveness of employing a single type of faecal indicator bacteria when investigating the level of faecal contamination in waterways.  相似文献   

5.
Tidal channels are ubiquitous in muddy coastlines and play a critical role in the redistribution of sediments, thus dictating the general evolution of intertidal landforms. In muddy coastlines, the morphology of tidal channels and adjacent marshes strongly depends on the supply of fine sediments from the shelf and on the resuspension of sediments by wind waves. To investigate the processes that regulate sediment fluxes in muddy coastlines, we measured tidal velocity and sediment concentration in Little Constance Bayou, a tidal channel in the Rockefeller State Wildlife Refuge, Louisiana, USA. The tidal measurements were integrated with measurements of wave activity in the bay at the mouth of the channel, thus allowing the quantification of feedbacks between waves and sediment fluxes. Results indicate that the sediment concentration in the channel is directly related to the wave height in the adjacent bay during flood and high slack water, whereas the concentration during ebb depends on local channel velocity. Moreover, the sediment flux during ebb is of the same order of magnitude as the sediment flux during the previous flood, indicating that only a small fraction of transported sediments are stored in the marsh during a tidal cycle. Finally, very low tides, characterized by high ebb velocities, export large volumes of sediment to the ocean. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

6.
Mainstem–floodplain material exchange in the tidal freshwater reach of major rivers may lead to significant sequestration of riverine sediment, but this zone remains understudied compared to adjacent fluvial and marine environments. This knowledge gap prompts investigation of floodplain-incising tidal channels found along the banks of tidal rivers and their role in facilitating water and suspended-sediment fluxes between mainstem and floodplain. To evaluate this role, and how it evolves along the tidal river and with time, we measured water level, flow velocity, temperature, and suspended-sediment concentration (SSC) in four tidal channels along the tidal Amazon River, Brazil. Eleven deployments were made during low, rising, high, and falling seasonal Amazon discharge. Generally, channels export high-SSC water from the mainstem to the tidal floodplain on flood tides and transfer low-SSC water back to the mainstem on ebbs. Along the length of the tidal river, the interaction between tidal and seasonal water-level variations and channel–floodplain morphology is a primary control on tidal-channel sediment dynamics. Close to the river mouth, where tides are large, this interaction produces transient flow features and current-induced sediment resuspension, but the importance of these processes decreases with distance upstream. Although the magnitude of the exchange of water and sediment between mainstem and floodplain via tidal channels is a small percentage of the total mainstem discharge in this large tidal-river system, tidal channels are important conduits for material flux between these two environments. This flux is critical to resisting floodplain submergence during times of rising sea level. © 2019 John Wiley & Sons, Ltd.  相似文献   

7.
Microbial activity in permeable tidal flat margin sediments is enhanced by two main processes. First, organic matter is supplied by rapid sedimentation at prograding tidal flat margins. Second, surface and deep pore water advection lead to a replenishment of the dissolved organic matter and sulfate pools. Increasing microbial activity towards the low water line is reflected in sulfate and methane profiles as well as in total cell numbers, sulfate reduction rates, and remineralization products. The impact of high sedimentation rates on pore water biogeochemistry is confirmed by inverse modeling reproducing the depth profiles obtained by measurements. In central parts of the tidal flats, low sedimentation rates and pore water flow velocities limit microbial activity despite the high availability of electron acceptors for microbial respiration such as sulfate. Therefore, tidal flat margins with high microbial activity are of special importance for budgeting biogeochemical cycling in tidal flat areas.  相似文献   

8.
In this paper, we analyzed the high/low water levels of eight stations along the Pearl River estuary and the high/low tidal levels of Sanzao station, and streamflow series of Sanshui and Makou stations using wavelet transform technique and correlation analysis method. The behaviors of high/low water levels of the Pearl River estuary, possible impacts of hydrological processes of the upper Pearl River Delta and astronomical tidal fluctuations were investigated. The results indicate that: (1) the streamflow variability of Sanshui and Makou stations is characterized by 1-year period; 1-, 0.5- and 0.25-year periods can be detected in the high tidal level series of Sanzao station, which reflect the fluctuations of astronomical tidal levels. The low tidal level series of Sanzao station has two periodicity elements, i.e. 0.5- and 0.25-year periods; (2) different periodicity properties have been revealed: the periods of high water levels of the Pearl River estuary are characterized by 1-, 0.5- and 0.25-year periods; and 1-year period is the major period in the low water levels of the Pearl River estuary; (3) periodicity properties indicate that behaviors of low water levels are mainly influenced by hydrological processes of the upper Pearl River Delta. High water levels of the Pearl River estuary seem to be affected by both hydrological processes and fluctuations of astronomical tidal levels represented by tidal level changes of Sanzao station. Correlation analysis results further corroborate this conclusion; (4) slight differences can be observed in wavelet transform patterns and properties of relationships between high/low water levels and streamflow changes. This can be formulated by altered hydrodynamic and morphodynamic processes due to intensifying human activities such as construction of engineering infrastructures and land reclamation.  相似文献   

9.
The hydrodynamics of a small tributary channel and its adjacent mudflat is studied in Willapa Bay, Washington State, USA. Velocity profiles and water levels are simultaneously measured at different locations in the channel and on the mudflat for two weeks. The above tidal flat and channel hydrodynamics differ remarkably during the tidal cycle. When the water surface level is above the tidal flat elevation, the channel is inactive. At this stage, the above tidal flat flow is predominantly aligned along the Bay axis, oscillating with the tide as a standing wave with peak velocities up to 0.3 m/s. When the mudflat becomes emergent, the flow concentrates in the channel. During this stage, current velocities up to 1 m/s are measured during ebb; and up to 0.6 m/s during flood. Standard equations for open-channel flow are utilized to study the channel hydrodynamics. From the continuity equation, a lateral inflow is predicted during ebb, which likely originates from the drainage of the mudflat through the lateral runnels. Both advective acceleration and lateral discharge terms, estimated directly from the velocity profiles, play a significant role in the momentum equation. The computed drag coefficient for bottom friction is small, due to an absence of vegetation and bottom bedforms in the channel. Sediment fluxes are calculated by combining flow and suspended sediment concentration estimated using the acoustic backscatter signal of the instruments. A net export of the sediment from the channel is found during ebb, which is not balanced by the sediment import during flood. When the mudflat is submerged, ebb-flood asymmetries in suspended sediment concentration are present, leading to a net sediment flux toward the inner part of the Willapa Bay. Finally, a residual flow is detected inside the channel at high slack water, probably associated with the thermohaline circulation.  相似文献   

10.
From 1989 to 1992, the concentration of formaldehyde was measured along the Elbe estuary as well as at anchor stations. In mesocosm experiments, the turnover of formaldehyde could be investigated avoiding the variability caused by tidal advection of different water bodies. Formaldehyde concentrations in the Elbe estuary ranged from 0.5… 180 μg/L. As sources, a release by algae and microbial processes were identified. Three areas with different dominance of formaldehyde turnover processes were found in the estuary. In the limnic part of the estuary, a release of formaldehyde by algae was dominant. In the mixohaline zone and the turbidity maximum, bacterial degradation of organic matter increased the formaldehyde concentration. In the mouth of the estuary, the adjacent Wadden sea areas influenced the concentration due to formaldehyde-rich runoff from the tidal mud flats. In the other parts of the estuary, a fast degradation of formaldehyde kept the formaldehyde concentration at a low level. In sediment cores from the Elbe and a mesocosm, the formaldehyde concentrations were in the same range as in the water column. Mesocosms with and without sediment showed no significant differences in concentration levels which were similar to those measured in the Elbe at the same time. During the investigated period, no anthropogenic impacts of formaldehyde into the Elbe estuary could be detected.  相似文献   

11.
Salut-Mengabong Lagoon is located at the west coast of Sabah facing the South China Sea. At the bay side of the main inlet the lagoon splits into Salut and Mengabong Channels. Sediment dynamics at the inlets of the lagoon have recently received considerable attention. But any direct measurement of hydrodynamics and sediment flux are yet to be well documented. This study covers the field measurements of current velocity, water flux, suspended sediment concentration and sediment flux across the three transects (main inlet, Salut entrance and Mengkabong entrance) during typical spring and neap tidal cycles in southwest monsoon and northeast monsoon. Temporal variations and time-averaged values of measured parameters are discussed. The inlets of Salut-Mengkabong Lagoon are found to be ebb-dominated. The time-averaged velocities during spring tidal measurements are found to be higher in the main inlet followed by Mengkabong entrance and Salut entrance. Suspended sediment concentration and sediment fluxes are substantially higher in spring tidal cycles compared to the same in neap tidal cycles. During spring tidal cycles, ebb tidal sediment fluxes are higher than the flood tidal fluxes. The ebb dominated flux across the main inlet led to the large ebb shoal.  相似文献   

12.
The research presented in this paper involves the application of the joint probability method to the estimation of extreme water levels resulting from astronomical tides and surge residuals and the investigation of the effects of tide–surge interactions on extreme water levels. The distribution of tide peaks was analysed from field records (<20 years) and a 46-year dataset of monthly maximum tidal amplitudes. Large surges were extracted from both field records and a numerical model hindcast covering the 48 largest storm events in the Irish Sea over the period 1959–2005. Extreme storm surges and tides were independently modelled using the generalised extreme value statistical model, and derived probability distributions were used to compute extreme water levels. An important, and novel, aspect of this research is an analysis of tide–surge interactions and their effects on total water level; where interactions exist, they lead to lower total water levels than in the case of independency. The degree of decrease varies with interaction strength, magnitude of surge peak at a particular phase of tide and the distribution of peaks over a tidal cycle. Therefore, including interactions in the computation of extreme levels may provide very useful information at the design stage of coastal protection systems.  相似文献   

13.
Large sets of suspended particulate matter (SPM) concentration data from in situ and remote sensing (moderate resolution imaging spectroradiometer, MODIS) samplings in the Belgian nearshore area (southern North Sea) are combined in order to evaluate their heterogeneity and the sampling techniques. In situ SPM concentration measurements are from a vessel (tidal cycle) and from a tripod. During the tidal cycle measurements, vertical profiles of SPM concentration have been collected; these profiles have been used as a link between satellite surface and near-bed tripod SPM concentrations. In situ time series at fixed locations using a tripod are excellent witnesses of SPM concentrations under all weather conditions and may catch SPM concentration variability with a much finer scale. The heterogeneity has been statistically assessed by comparing the SPM concentration frequency distributions. Tidal cycle, tripod and MODIS datasets have different distributions and represent a different subpopulation of the whole SPM concentrations population. The differences between the datasets are related to meteorological conditions during the measurements; to near-bed SPM concentration dynamics, which are partially uncoupled from processes higher up in the water column; to the sampling methods or schemes and to measurement uncertainties. In order to explain the differences between the datasets, the tripod data have been subsampled using wave height conditions and satellite and tidal cycle sampling schemes. It was found that satellites and low-frequent tidal cycle measurements are biased towards good weather condition or spring–summer seasons (satellite). The data show that the mean surface SPM concentration derived from satellite data is slightly lower than from in situ tidal cycle measurements, whereas it is significantly lower than the mean SPM concentration interpolated to the water surface from the tripod measurements. This is explained by the errors arising from the interpolation along the vertical profiles, but also by the fact that satellite-measured signal saturates in the visible band used to retrieve SPM concentration in very turbid waters.  相似文献   

14.
We use a hydrodynamic model applied to an idealized fan-shaped basin to explore the morphology and dynamics of radial sand ridges in a convergent coastal system. A positive morphological feedback between channel incision and flow redistribution is responsible for the formation of the channel-ridge pattern. The selection mechanism of bottom wavelength is associated with flow concentration in the deeper part of the channels. Our results are compared to sediment and hydraulic dynamics in the radial sand ridges (RSRs) in China. In a convergent, sloping basin the tangentially averaged tidal velocity peaks at 47 km from the apex. This distance is similar to the arc distance, 62 km, where the RSRs are most incised. An offshore shift in tidal phase results in stronger flows near the north coastline, explaining the presence of asymmetric channel patterns. A numerical stability analysis indicates that small radial oscillations with a wavelength of 10° to 15° maximize the velocity in the troughs. This oscillation wavelength also emerges in the RSRs, which display a peak in spectral energy at a radial wavelength between 25° to 37.5°. High-resolution numerical simulations in the RSRs confirm that flow concentration occurs in the deeper part of the channels, keeping them flushed. We therefore conclude that the RSRs display morphometric characteristics similar to other tidal incisions, like tidal inlets and intertidal channels. This result further supports the dominant role of tidal prism and related peak velocities in incising coastal landscapes. © 2020 John Wiley & Sons, Ltd.  相似文献   

15.
Sediment flux in marsh tidal creeks is commonly used to gauge sediment supply to marshes. We conducted a field investigation of temporal variability in sediment flux in tidal creeks in the accreting tidal marsh at China Camp State Park adjacent to northern San Francisco Bay. Suspended‐sediment concentration (SSC), velocity and depth were measured near the mouths of two tidal creeks during three 6‐ to 10‐week deployments: two in winter and one in summer. Currents, wave properties and SSC were measured in the adjacent shallows. All deployments spanned the largest spring tides of the season. Results show that tidally averaged suspended‐sediment flux (SSF) in the tidal creeks varied from slightly landward to strongly bayward with increasing tidal energy. SSF was negative (bayward) for tidal cycles with maximum water surface elevation above the marsh plain. Export during the largest spring tides dominated the cumulative SSF for each deployment. During ebb tides following the highest tides, velocities exceeded 1 m s?1 in the narrow tidal creeks, resulting in negative tidally averaged water flux, and mobilizing sediment from the creek banks or bed. Storm surge also produced negative SSF. Tidally averaged SSF was positive in wavy conditions with moderate tides. Spring tide sediment export at the creek mouth was about twice that at a station 130 m further up the tidal creek. The negative tidally averaged water flux near the creek mouth during spring tides indicates that in the lower marsh some of the water flooding directly across the bay–marsh interface drains through the tidal creeks, and suggests that this interface may be a pathway for sediment supply to the lower marsh as well. Copyright © 2018 John Wiley & Sons, Ltd.  相似文献   

16.
Studies on distribution and habitats of mangrove molluscs of the Bonny and New Calabar rivers (Niger Delta) were made at ten shore stations from the river mouth to the tidal fresh water zone. Forty-three species were collected and thirty-nine were identified. Investigations into tidal zonation patterns showed that molluscs inhabited the high, mid and low intertidal stretches of the shore. In the tidal fresh water and low-salinity brackish water zone, the low intertidal is poor in molluscs. Many species have restricted salinity ranges occuring either in the high or low salinity limits. The collected data on occurence of species were analyzed by different methods from multivariate data analysis, namely cluster analysis, principal component analysis and partial least squares. These allowed to visualize structures among mollusc species and stations according to distribution patterns and to estimate the degree of relation between these patterns and salinity.  相似文献   

17.
Back-barrier tidal flat systems are characterized by basins and inlets through which water is exchanged with the coastal sea by tidal water movements. The hydrographic and morphometric properties at the inlets and in the basins vary considerably, but there is little information available how biogeochemical properties in the water column at these different sites respond to these differences. Therefore, we investigated tidal dynamics of suspended particulate matter (SPM), particulate and dissolved organic carbon (DOC), chlorophyll a, phaeopigments, numbers of particle-associated (PA) and free-living bacteria (FL), bacterial biomass production, and concentrations of dissolved manganese (Mn). Samples were taken at the surface, a mid-depth and 1 m above the bottom at a fixed station at the inlet and in the basin of the Spiekeroog back-barrier tidal flat system in the German Wadden Sea. Five tidal cycles representative for typical seasonal situations, January (winter), April and May (late spring bloom), July (summer), and November (late fall) were studied in 2005 and 2006. In July, processes related to phytoplankton dynamics and bacterial decomposition were much more enhanced in the basin, whereas in April, these processes were enhanced at the inlet but were particularly low within the basin itself. The low values within the basin were a result of the settled phytoplankton spring bloom and represent a rather short period at the decline of this bloom. In November and January, differences were much less pronounced than during the growing season and restricted mainly to SPM and PA bacteria, exhibiting higher values in the basin. FL bacteria, DOC, and dissolved Mn exhibited different patterns and much less differences between the two stations, indicating that biogeochemical processes in the dissolved phase were controlled by different factors than PA biogeochemical processes. These differences reflect the retentive properties of the basin for particles and PA biogeochemical processes, particularly during the growing season, and in general emphasize the high productivity of back-barrier tidal flat systems.  相似文献   

18.
The formation and evolution of tidal platforms are controlled by the feedbacks between hydrodynamics, geomorphology, vegetation, and sediment transport. Previous work mainly addresses dynamics at the scale of individual marsh platforms. Here, we develop a process-based model to investigate salt marsh depositional/erosional dynamics and resilience to environmental change at the scale of tidal basins. We evaluate how inputs of water and sediment from river and ocean sources interact, how losses of sediment to the ocean depend on this interaction, and how erosional/depositional dynamics are coupled to these exchanges. Model experiments consider a wide range of watershed, basin, and oceanic characteristics, represented by river discharge and suspended sediment concentration, basin dimensions, tidal range, and ocean sediment concentration. In some scenarios, the vertical accretion of a tidal flat can be greater than the rate of sea level rise. Under these conditions, vertical depositional dynamics can lead to transitions between tidal flat and salt marsh equilibrium states. This type of transition occurs much more rapidly than transitions occurring through horizontal marsh expansion or retreat. In addition, our analyses reveal that river inputs can affect the existence and extent of marsh/tidal flat equilibria by both directly providing suspended sediment (favoring marshes) and by modulating water exchanges with the ocean, thereby indirectly affecting the ocean sediment input to the system (favoring either marshes or tidal flats depending on the ratio of the river and ocean water inputs and their sediment concentrations). The model proposed has the goal of clarifying the roles of the main dynamic processes at play, rather than of predicting the evolution of a particular tidal system. Our model results most directly reflect micro- and meso-tidal environments but also have implications for macro-tidal settings. The model-based analyses presented extend our theoretical understanding of marsh dynamics to a greater range of intertidal environments. © 2020 John Wiley & Sons, Ltd.  相似文献   

19.
Submarine ground water discharge (SGD) is now recognized as an important water pathway between land and sea. It is difficult to quantitatively predict SGD owing to its significant spatial and temporal variability. This study focuses on quantitative estimation of SGD caused by tidally induced sea water recirculation and a terrestrial hydraulic gradient. A two-dimensional hydrogeological model was developed to simulate SGD from a coastal unconfined aquifer in the northeastern Gulf of Mexico, where previous SGD studies were performed. A density-variable numerical code, SEAWAT2000, was applied to simulate SGD. To accurately predict discharge, various influencing factors such as heterogeneity in conductivity, uncertain boundary conditions, and tidal pumping were systematically assessed. The tidally influenced sea water recirculation zone and the fresh water–salt water mixing zone under various tidal patterns, tidal ranges, and water table heights were also investigated. The model was calibrated and validated from long-term, intensive measurements at the study site. The percentage of fresh SGD relative to total SGD ranged from 4% to 50% under normal conditions. Based on simulations of two field measurements in summer and spring, respectively, the fresh water ratios were 9% and 15%, respectively. These results support the hypothesis that the SGD induced by tidally driven sea water recirculation is much larger than terrestrial fresh ground water discharge at this site. The estimates of total and fresh SGD are at the low and high ends, respectively, of the estimation ranges obtained from geochemical tracers (e.g., 222Rn).  相似文献   

20.
Matching signals have previously been identified from about eighty repeating deep moonquake sources. These moonquakes clearly display tidal periodicities in their histories of origin times and signal amplitudes; they are presumably triggered by the solid-body tide in the moon, raised primarily by the earth. The A1 hypocentre has been the most active and has also produced seismograms with signals of reversed polarity. In an attempt to deduce focal mechanisms for these events, we calculated various tidal stress functions at the Al hypocentre using a homogeneous moon model, and correlated them with the origin times of events. No good correlation was found, either for tidal stress peaks of consistent polarity, or for tidal stress peaks of opposite polarity at the times of “inverted” events. This could be due to an inaccurate moon model, but it has also been noted that the relative amplitudes of signals recorded at different seismic stations vary between events from the same hypocentre. Earthquake swarms often contain events with fault-plane solutions in very different orientations. A similar variation between events from each deep moonquake hypocentre would explain the different amplitude ratios and also the “inverted” events.  相似文献   

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