Transport Of Sediment Particles Research Articles

Gravity current analyzer for lock-release experiments

Analyzing gravity currents and stratified flows thoroughly is a time-consuming task, particularly in engineering and educational contexts. Despite the availability of numerous tools for studying stratified flows, there is currently no software dedicated to analyzing gravity currents, integrating flow characterization with theoretical and empirical analyses. This study introduces an open-source tool (Dyenamic), specifically designed for conducting in-depth analyses of gravity currents using a single recorded video. The software incorporates a particle image velocimetry routine to examine the velocity field of the gravity current and the sediment particle transport, offering essential physical indices and categorization based on existing literature. Data from modeling results and laboratory experiments are used to perform calibration, validation, and sensitivity analyzes. The findings demonstrate strong alignment with the existing gravity current literature, highlighting the effectiveness of the software in characterizing gravity currents. Dyenamic emerges as a robust, user-friendly, and versatile tool suitable for educational and research endeavors.

Behavioral patterns of turbulent kinetic energy budget and quadrant analysis for flows over bedform under the influence of downward seepage

Seepage is one of the important factors involved in natural flow conditions, contributing to changes in flow turbulence patterns and morphological changes due to the transport of sediments. This transport of sediment particles influences the development of fluvial bedforms in any river channel. However, previous research on fluvial dynamics has not considered the influence of seepage on the flow field over the fluvial bedforms. The present experimental research aims to explore the behavioral patterns of turbulent kinetic energy, the turbulent kinetic energy (TKE) budget, and quadrant analysis for flows over two-dimensional dune shaped bedforms in the absence and presence of downward seepage. Results from the study illustrate that at the measurement locations on the initial and lee side sections of a dune, the TKE increases with the introduction of downward seepage, leading to an increase in turbulence production near the bed-surface region. The flow energy under both no seepage and seepage conditions contributes mainly to the turbulent production. Turbulence diffusion and dissipation rates have been found to decline in the near-bed region of the initial and lee side sections of the dune. However, turbulent production has been found to be significantly higher in the presence of downward seepage than under the no seepage condition. Similarly, turbulent kinetic energy flux increases in the streamwise direction, while it reduces in the vertical direction at initial sections and lee side sections of the dune under seepage conditions. However, at the middle sections and crest portion of the dune, opposite behavioral patterns are observed for all the aforementioned turbulent entities. Quadrant analysis reveals that the sweep and ejection event increases while inward and outward interaction reduces in the near bed zone. Although the contribution of both sweep and ejection events increases in the presence of downward seepage, sweep events have clear dominance in the near bed region, suggesting the possibility of a higher rate and amount of sediment transportation than under the no seepage condition.

Headcut erosion characteristics revealed through simulated rainfall and scouring experiments in the gully region of the Loess Plateau

Headcut erosion is the main sediment source that may cause severe damage to the ecological environment and agricultural production. The study of headcut erosion characteristics, such as gully headcut morphological evolution and sediment particle transport processes, is essential for understanding the mechanism of gully erosion. A series of simulated rainfall combined scouring experiments with constant rainfall intensity (0.8 mm min^–1) and variable flow discharge (3.6, 4.8, 6.0, and 7.2 m³ h^–1) were conducted to illustrate the headcut erosion process in the gully region of the Loess Plateau. The results showed that gully width and gully depth increased as time and flow discharge increased. The headcut retreat length increased exponentially with experiment time. The gully head heights decreased by 10, 13, 21, and 26 cm at different flow discharges after 180 min. The contents of clay and silt in eroded sediment particles decreased by 7.97% to 16.59% and 7.98% to 15.34%, respectively, whereas the sand volume fraction increased by 9.33% to 20.04% compared to that of the original soil. The enrichment rates of clay and silt sediment were 0.83 to 0.92 and 0.85 to 0.92, while the enrichment rate of sand sediment was 1.09 under different flow discharges. The critical particle size was 0.0326 mm. The fractal dimension of the eroded sediment particles was 2.61 to 2.67 and showed good agreement with the clay volume fraction, with a coefficient of determination (<i>R</i>²) of 0.93. These results provide a basis for headcut erosion model establishment, ecological management, and soil and water conservation in the gully region of the Loess Plateau.

Sediment particle selectivity and its response to overland flow hydraulics within grass strips

AbstractParticle 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.

Quantification of probabilistic concentrations for mixed-size sediment particles in open channel flow

The Rouse equation is a well-known deterministic model for suspended concentrations. However, the transport of sediment particles is influenced by several random variables, such as non-uniform sediment size and turbulence structure. Experiments have demonstrated that the stochastic characteristics of turbulence structure, such as ejections and sweeps, can cause fluctuations in sediment concentrations. A new method is proposed to quantify the probabilistic sediment concentrations. In this study, the multiple-state discrete-time Markov chain and stochastic particle tracking model were used to simulate sediment transport with spatially and temporally varying probabilistic concentrations under the stochastic turbulence structure. Point estimate methods were adopted to estimate the variability of non-uniform sediment sizes. The proposed model was implemented for three cases. In the first case, the proposed model was validated against the experimental data. In the second case, spatial and temporal concentrations at high and low Rouse numbers with mean and non-uniform sediment sizes were compared. The result demonstrates that in the prediction with mean sediment sizes, the sediment concentration is overestimated near the bed, and the advection of the sediment concentration in the x-direction is underestimated. In the last case, higher-order statistical moments of the fluctuating concentrations were estimated through simulations using the proposed model. Simulation results conducted using the proposed method were compared with experimental data. The results revealed that the prediction results based on the proposed model are in good agreement with experimental data.

Floodplain Land Cover and Flow Hydrodynamic Control of Overbank Sedimentation in Compound Channel Flows

AbstractOverbank sedimentation is predominantly due to fine sediments transported under suspension that become trapped and settle in floodplains when high‐flow conditions occur in rivers. In a compound channel, the processes of exchanging water and fine sediments between the main channel and floodplains regulate the geomorphological evolution and are crucial for the maintenance of the ecosystem functions of the floodplains. These hydrodynamic and morphodynamic processes depend on variables such as the flow‐depth ratio between the water depth in the main channel and the water depth in the floodplain, the width ratio between the width of the main channel and the width of the floodplain, and the floodplain land cover characterized by the type of roughness. This paper examines, by means of laboratory experiments, how these variables are interlinked and how the deposition of sediments in the compound channel is jointly determined by them. The combination of these compound channel characteristics modulates the production of vertically axised large turbulent vortical structures in the mixing interface. Such vortical structures determine the water mass exchange between the main channel and the floodplain, conditioning in turn the transport of sediment particles conveyed in the water, and, therefore, the resulting overbank sedimentation. The existence and pattern of sedimentation are conditioned by both the hydrodynamic variables (the flow‐depth ratio and the width ratio) and the floodplain land cover simulated in terms of smooth walls, meadow‐type roughness, sparse‐wood‐type roughness, and dense‐wood‐type roughness.

Bioturbation rates in the deep Fram Strait: Results from in situ experiments at the arctic LTER observatory HAUSGARTEN

There are numerous studies measuring the rate and extent of bioturbation worldwide, however, information on mixing rates in the deep ocean, especially in the polar regions, are extremely scarce. The present study presents mixing rates and mixed layer depths for the deep seafloor at the LTER (Long-Term Ecological Research) observatory HAUSGARTEN in Fram Strait, Arctic Ocean. Two stations at similar water depths (HG-IV at 2492 m, and S3 at 2391 m) but different distances to the ice edge (approx. 65 km and 115 km, respectively) were chosen to carry out long-term in situ bioturbation experiments (2 and 4 years, respectively), using luminophores as a tracer. Enhanced bioturbation at the northern site, located closer to the high productive Marginal Ice Zone (MIZ) and thus expected to receive higher amounts of settling organic matter thereby supporting a richer benthic community, could not be confirmed. Instead, biodiffusion-like mixing rates (Db) at the experimental sites showed no significant differences (0.26 ± 0.27 SD cm−2 y−1 at station HG-IV; 0.28 ± 0.40 SD cm−2 y−1 at station S3). Moreover, mixed layer depths (L) at the two sites were almost identical; mixing of surface sediments occurred down to approx. 6–7 cm sediment depth. Indications for a non-local transport of sediment particles from the surface to deeper parts of the sediment, resulting in higher values for the Non-Local Index (NLI), could only be found for the central HAUSGARTEN site HG-IV. Differences in macro- and megafauna communities at the two experimental sites might be responsible for subsurface maxima in luminophore distribution and slightly (non-significantly) higher NLI values at this site (5.37 ± 3.35 SD at station HG-IV; 3.26 ± 1.82 SD at station S3). Temporal variations in benthic activities should have been levelled out in the multi-year experiments, thus providing reliable baseline data for the deep Fram Strait.

Remobilization and bioavailability of polycyclic aromatic hydrocarbons from estuarine sediments under the effects of Nereis diversicolor bioturbation

The effects of Nereis diversicolor bioturbation on the remobilization and bioavailability of polycyclic aromatic hydrocarbons from estuarine sediment were determined after 60 d in a laboratory experiment. The release fluxes and mass transfer coefficients showed that bioturbation by N. diversicolor can lead to a significant remobilization of polycyclic aromatic hydrocarbons (PAHs) from estuarine sediments. Bioturbation enhanced the release of PAHs from sediment to water by accelerating the transport of sediment particles to the sediment-water interface followed by PAHs desorption to the water. The bioavailability of PAHs was described by SPMD-sediment accumulation factors (SSAF). The SSAF of low molecular weight PAHs with bioturbation was significantly higher than that of PAHs without bioturbation, and there were no significant variations in high-molecular-weight PAHs. Our results revealed that N. diversicolor bioturbation significantly increased PAHs release from sediment to water but only increased the bioavailability of low-molecular-weight PAHs.

An Experimental Study on Sediment Discharge in River Channel for the Reduction of Sediment Disaster

최근 기후변화의 영향으로 집중호우 및 토사재해 발생빈도가 증가하고 있다. 이러한 토사재해로 인한 하도 내 피해예방 및 종합적인 토사 관리를 위해서는 정량적이고 시계열적인 토사이동량 파악이 필수적이다. 그러나 우리나라의 재래식관측기를 이용한 직접적인 측정방법은 실제 측정이 용이하지 않고 많은 비용과 인력, 시간이 소요된다. 특히 연속적인 측정이 거의 불가능한 상태에 있어 토사 이송에 관한 수문학적 요인과 메커니즘 관계를 정량적으로 분석한 연구는 부족한 실정에 있다. 따라서 본 연구에서는 하도 내 토사이동량 측정의 어려움을 개선하기 위해 실내수로실험에 하이드로폰을 활용하였고 하이드로폰의 인지능력을 파악하기 위해 충돌음향 계측 및 분석을 수행하였다. 연구결과 하이드로폰이 인지할 수 있는 개별입자별 main충돌시의 최소 임계치 기준은 공급유량과 토사입자의 크기가 커질수록 증가하는 것으로 나타났다.Due to recent climate change, the frequency of heavy rainfalls and sediment disasters is increasing. In order to prevent damages caused by sediment disaster and implement a comprehensive sediment control, a time-series analysis of sediment discharge data is essential. However, in South Korea, it is difficult to measure them directly as they use conventional meters as measurement, which prevents research from presenting a quantitative relationship between hydrological factors and mechanisms with regard to sediment transport. In this regard, the study attempted to overcome difficulties related to the measurement of soil particle transport in river channel. It used acoustic signals to recognize the transport of sediment particles and established an indoor waterway experiment equipment with a hydrophone. As a result, it is found that the minimum threshold value for the main collision of individual particles perceived by hydrophone increased as the supply flow rate and the size of sediment particles increased.

Provenances, distribution, and accumulation of organic matter in the southern Mariana Trench rim and slope: Implication for carbon cycle and burial in hadal trenches

It is generally accepted that organic matter content and accumulation rate at the seafloor attenuate with increasing water depth. However, hadal trenches, which represent the deepest portion of the hydrosphere on Earth, do not abide by this universal rule. It has been speculated that hadal trenches would serve as organic matter depocenters, where bacteria-mediated organic matter degradation intensifies. Here we examine the contents of total organic carbon (TOC) and total nitrogen (TN), as well as the δ13C values of TOC in three gravity cores, two box cores, and three grab samples with water depth from 4900 to 7118m, in order to reveal the provenances of organic matter, spatial distribution and accumulation rates of particulate organic carbon (POC) in the southern Mariana Trench rim and slope. Although the deepest area was not sampled, trench rim and slope is also of importance in terms of transportation and accumulation processes of organic matter. A vast majority of the sediment samples have bulk TOC/TN molar ratios and δ13C values of TOC ranging from 4.2 to 11 and from −21.8 to −18.9‰, respectively, implying that the organic matter was primarily sourced from marine algae. Two exceptions have been found at 101cm and 201cm depths of core GC05 with a possible input of terrestrial material suggested by an abrupt increase in TOC contents and TOC/TN molar ratios accompanied by marked decreases in δ13C values of TOC. Moreover, TOC contents in surface sediments basically increased with water depth. Based on the published excess 210Pb data and by assuming a simplified one-dimensional sediment loading despite of frequent occurrences of mass wasting transports in hadal trenches, the sedimentation rate in the southern Challenger Deep (6037m) was estimated to be 0.02cmyr−1. This much higher sedimentation rate compared to the globally averaged values in deep ocean sediments coupled with the trend of increasing in TOC contents with water depth may serve as evidence for the lateral transport of sediment particles induced by the funnel-like topography and localized current dynamics within the trench. The average POC accumulation rate within the southern Challenger Deep roughly amounts to 1.5×10−5gcm−2yr−1, equivalent to about a seventh of the globally averaged POC accumulation rate in deep-ocean seafloor. To our knowledge, POC accumulation in hadal trenches has been quantified for the first time, and we highlight that organic matter degradation in deep hadal trenches should not be neglected and may represent a significant component of the global carbon cycle.

Three-State Continuous-Time Markov Chain Model for Mixed-Size Sediment Particle Transport

AbstractIn this study, transport of mixed-size sediment particles under steady flow is described using the continuous-time Markov process. The continuous behavior of particle movement among the immobile bed material, bedload, and suspended load layer is modeled using a three-state continuous-time Markov process. Therefore, the probability of particles staying in each layer can be obtained by the proposed model, which can then be used to quantify the number of particles, and the bedload and suspended load transport rate, respectively. In addition, since the finer particles are more likely sheltered by coarse particles on the bed, mixed-size particles are considered in this paper to account for such an effect. The influence of dimensionless effective shear stress on the mean transient rates, representing the average rate of particle transitions among the immobile bed material, bedload layer, and suspended load layer, is quantified and discussed. The proposed model is verified against the experimental data w...

Indirect effects of non-lethal predation on bivalve activity and sediment reworking

Deposit-feeders are the dominant bioturbators of aquatic sediments, where they profoundly impact biogeochemical processes, but they are also vulnerable to both lethal and non-lethal predation by a large variety of predators. In this study, we performed a series of experiments to test the effects of predation avoidance on the feeding activity and sediment reworking intensity of the deposit-feeding bivalve Macoma balthica. Feeding activity at the sediment–water interface and sediment reworking intensity (vertical displacements of inert particle tracers) were monitored using image analysis techniques for treatments including and excluding the predatory shrimp, Crangon crangon. Detection of C. crangon by M. balthica resulted in an immediate retraction of the feeding siphon and a reduction in feeding activity. M. balthica also buried deeper into the sediment in the presence of C. crangon. This predator avoidance behaviour indirectly affected sediment reworking modes and rates, increasing the thickness of the bioturbated sediment layer as well as the non-local transport of sediment particles at depth. Conversely, feeding activity and sediment reworking processes remained unaffected when C. crangon was present, but isolated from the sediment, suggesting that predator perception in M. balthica is tactile (i.e. induced by direct encounter) rather than being chemosensory. Collectively, these results demonstrate that predatory avoidance behaviour by benthic infauna can significantly impact benthic bioturbation and the incorporation of organic matter into the benthic food web.

Stochastic Partial Differential Equation-Based Model for Suspended Sediment Transport in Surface Water Flows

A stochastic partial differential equation-based model has been derived based on the law of mass conservation and the Langevin equation of particle displacement to simulate suspended sediment transport in open-channel flows. In this model, the movement of any suspended sediment particle in turbulent flows is modeled as a stochastic diffusion process, which is composed of a drift term and a random term. The stochastic formula of fluid velocity is then substituted into the advection-diffusion (AD) equation to obtain the stochastic partial differential equation (SPDE) for suspended sediment transport. The lattice approximation is applied to solve the SPDE of suspended sediment transport in open channel flow. The proposed model, explicitly expressing the randomness of sediment concentration, has the advantage of capturing any randomly selected scenarios of particle movement and thus a more comprehensive quantitative description of sediment concentrations compared with the deterministic AD equation. As a result, the probability distribution of the sediment transport rate can be characterized based on a number of realizations obtained in the numerical experiments. It is found from the numerical experiments of particle trajectory that the transport of sediment particles is in the form of fully suspended load when the Rouse number is less than one. The ensemble mean sediment concentration of the proposed SPDE, obtained by the Monte Carlo simulation, agrees well with that of the deterministic AD equation.

Using a random displacement model to simulate turbulent particle motion in a baroclinic frontal zone: A new implementation scheme and model performance tests

Numerical artifacts can limit accurate simulation of turbulent particle motion when Lagrangian particle-tracking models are implemented in hydrodynamic models with stratified conditions like fronts. Yet, modeling of individual particle motion in frontal regions is critical for understanding sediment dynamics as well as the transport and retention of planktonic organisms. The objective of this research was to develop a numerical technique to accurately simulate turbulent particle motions in a particle-tracking model embedded within a hydrodynamic model of a frontal zone. A new interpolation scheme, the ‘water column profile’ scheme, was developed and used to implement a random displacement model for turbulent particle motions. A new interpolation scheme was necessary because linear interpolation schemes caused artificial aggregation of particles where abrupt changes in vertical diffusivity occurred. The new ‘water column profile’ scheme was used to fit a continuous function (a tension spline) to a smoothed profile of vertical diffusivities at the x– y particle location. The new implementation scheme was checked for artifacts and compared with a standard random walk model using (1) Well Mixed Condition tests, and (2) dye-release experiments. The Well Mixed Condition tests confirmed that the use of the ‘water column profile’ interpolation scheme for implementing the random displacement model significantly reduced numerical artifacts. In dye-release experiments, high concentrations of Eulerian tracer and Lagrangian particles were released at the same location up-estuary of the salt front and tracked for 4 days. After small differences in initial dispersal rates, tracer and particle distributions remained highly correlated ( r = 0.84 to 0.99) when a random displacement model was implemented in the particle-tracking model. In contrast, correlation coefficients were substantially lower ( r = 0.07 to 0.58) when a random walk model was implemented. In general, model performance tests indicated that the ‘water column interpolation’ scheme was an effective technique for implementing a random displacement model within a hydrodynamic model, and both could be used to accurately simulate diffusion in a highly baroclinic frontal region. The new implementation scheme has the potential to be a useful tool for investigating the influence of hydrodynamic variability on the transport of sediment particles and planktonic organisms in frontal zones.

Fractionation of 210Po and 210Pb in coastal waters of the NW Mediterranean continental margin

The natural radionuclides 210Po and 210Pb were analyzed in samples of surface sea water, rain and dry fallout, and river water collected along the NW Mediterranean coast as well as from a sediment trap moored 3 km south of Monaco. Using a box model calculation, the balances and fluxes of 210Po and 210Pb in the coastal waters of the NW Mediterranean were estimated. Atmospheric inputs of 210Po and 210Pb to Monaco coastal waters varied seasonally and were maximal in winter when storms and strong winds transfered continental 222Rn-rich air and aerosols of top soil particles to coastal surface waters, which in turn enhanced the 210Po and 210Pb input to these waters. The balance estimation using all fluxes in surface waters indicated that 210Pb was removed from surface water with residence times of 2.1, 0.40, and 2.7 years for dissolved, particulate, and total 210Pb, respectively. In the bottom water and surface sediments, additional excess 210Pb sinking and sedimentation fluxes were observed, suggesting a substantial down slope transport of sediment particles. Similarly, the residence times of 210Po in surface water were 1.2, 0.38, and 0.77 years for dissolved, particulate, and total 210Po, respectively; however, a deficit in the 210Po sinking flux in the bottom layer, compared to removal flux from the surface waters, suggested rapid degradation of 210Po-bearing biogenic particles during sinking following periods of low biological productivity.

Effects of environment on source water for desalination plants on the eastern coast of Saudi Arabia

A study was carried out in the sea adjacent to a major MSF plant where a new 24MGD SWRO plant is being commissioned. Data were collected on the topographical feature of the marine basin, water quality and plankton of the intake zone. The incidents of planktonic bloom, influx of invasive organisms like jellyfish and macrofouling organisms and ingress of marine algae were monitored regularly. The Intake Bay of the plant is a well designed man-made structure studded to the coast. The marine basin in Al-Jubail, is for geological reasons, a shallow gently sloping shelf while the bay proper is a dredged, deeper basin. The area outside the bay is a vast sea grass bed and the seafloor sediment is sandy. The drag of seawater maintained by the intake pumps facilitates the transport of sediment particles, uprooted algae and floating objects creating fouling problems inside the plant. Seawater temperatures, conductivity, pH, dissolved oxygen and trace metals were found to be very much benign to the trouble free operation of the plant. Influx of jellyfish, noticed during the summer, was not found to be very severe. Data on plankton showed the presence of many phyto and zooplankton organism of biofouling potential in the plant. Total suspended solids indicated the possibility of the intake bay becoming a source of elevated Silt Density Index (SDI) for the new SWRO plant. The paper considers the data in detail and discusses the effects of environment on the desalination plant in Al-Jubail and suggests certain strategies for the protection of seawater intakes and some points useful in the siting and design of coastal seawater intakes in the region.

QUASI-THREE-DIMENSIONAL MATHEMATICAL MODELING OF MORPHOLOGICAL PROCESSES BASED ON EQUILIBRIUM SEDIMENT TRANSPORT

A quasi-three-dimensional mathematical model has been developed to study the morphological processes based on equilibrium sediment transport method. The flow velocities are computed by a two-dimensional horizontal depth-averaged flow model (H2D) in combination with logarithmic velocity profiles. The transport of sediment particles by a flow water has been considered in the form of bed load and suspended load. The bed load transport rate is defined as the transport of particles by rolling and saltating along the bed surface and is given by the Van Rijn relationship (1987). The equilibrium suspended load transport is described in terms of an equilibrium sediment concentration profile (ce) and a logarithmic velocity (u). Based on the equilibrium transport, the bed change rate is given by integration of the sediment mass-balance equation. The model results have been compared with a Van Rijn results (equilibrium approach) and good agreement has been found.

Nepheloid structure and hydrographic control on the Barcelona continental margin, northwestern Mediterranean

Contemporary processes controlling the off-shelf transport of sediment particles on the Barcelona continental margin were identified using CTD/transmissometer profiles during three hydrographic surveys. A well defined pattern of particulate matter distribution consisting in surface, intermediate and near-bottom nepheloid layers related with topographic and hydrographic structures was observed. Suspended sediment supplied by rivers or resuspended on the shelf is transferred to the slope mainly through the bottom nepheloid layer. A detachment of this layer is produced at the shelf break generating an intermediate nepheloid layer that transports sediment from the shelf to the slope. This transport is observed along the whole shelf break, although the maximum transference takes place through the Foix submarine canyon. On the slope, an increase of particulate matter concentration has always been recorded along the 300–500 m isobaths associated with a permanent intermediate nepheloid layer. This slope nepheloid structure is controlled by the slope density front dynamics and by the associated geostrophic current. This pattern of particulate matter distribution had not been observed before in the study area, and shows some peculiarities different from any other continental margin that has been studied.

Organic and Trace Metal Pollution in the Sediments of the Kishon River (Israel) and Possible Influence on the Marine Environment

The sediments of the lower reach of the Kishon river, its harbors and estuary, sampled in 1989-1991, were highly polluted by trace metals and petroleum derived compounds released by the adjacent industries. The contamination was highest in the sediment deposition area of the Kishon fishing harbor and decreased seaward. River-borne pollution was also evident in Haifa Bay opposite the Kishon estuary. Contaminants trapped in the sediments of the lower Kishon river system can reach the marine environment through bottom transport of sediment particles and also as a result of disposal at sea of dredge spoils from the river channel and harbors. On the basis of the findings of the study, it was recommended to stop the long-time practice of dumping dredge spoils from the Kishon fishing harbor into the relatively clean Haifa Bay and to use instead an offshore deep water disposal site.

Lateral transport of sediment particles in the Okinawa Trough determined by natural radionuclides.

Settling particles at 640 m, 1390 m, and 1920 m depths in the Okinawa Trough and bottom sediments at six sites in the East China Sea were analyzed for U and Th isotopes, 210Pb, and 210Po. Concentrations of 212Th in the settling particles were higher than those observed in the open ocean and were relatively constant with depth compared with other radiogenic nuclides. Fluxes and concentrations of these radiogenic nuclides increased with depth and the measured fluxes were larger than those calculated from water column inventories. While sinking through the water column of 640-1390 m, the increases in 210Pb and unsupported 228Th fluxes originating intensively in the shelf region were much larger than the unsupported 230Th fluxes produced evenly in sea water. The 210Po/210Pb activity ratio in the settling particles was almost unity and the 228Th/230Th activity ratio of the radiogenic fraction was much smaller than the ratio of the production rates of these nuclides in the shelf water. These results suggest that a large fraction of the deeper settling particles, as well as the sediments in the trough zone originating in the continental shelf zone, are transported laterally and downward via the near bottom layer on a time scale of approximately 16 years on the average.