Sediment Plumes Research Articles

Hourly turbidity monitoring using Geostationary Ocean Color Imager fluorescence bands

The Geostationary Ocean Color imager (GOCI) is the first geostationary ocean color satellite sensor that collects hourly images eight times per day during daylight. This high frequency image acquisition makes it possible to study more detailed dynamics of red tide blooms, sediment plumes, and colored dissolved organic matter plumes, and can aid in the prediction of biophysical phenomena. We apply the red band difference and the fluorescence line height algorithms to GOCI imagery to separate waters with high algal and nonalgal particles and validate the results with the MODIS imagery. We also track optical features using hourly GOCI imagery and assess their movement through comparisons with predicted ocean currents derived from the navy coastal ocean model and tidal data.

Wave Glider Monitoring of Sediment Transport and Dredge Plumes in a Shallow Marine Sandbank Environment.

As human pressure on the marine environment increases, safeguarding healthy and productive seas increasingly necessitates integrated, time- and cost-effective environmental monitoring. Employment of a Wave Glider proved very useful for the study of sediment transport in a shallow sandbank area in the Belgian part of the North Sea. During 22 days, data on surface and water-column currents and turbidity were recorded along 39 loops around an aggregate-extraction site. Correlation with wave and tidal-amplitude data allowed the quantification of current- and wave-induced advection and resuspension, important background information to assess dredging impacts. Important anomalies in suspended particulate matter concentrations in the water column suggested dredging-induced overflow of sediments in the near field (i.e., dynamic plume), and settling of finer-grained material in the far field (i.e., passive plume). Capturing the latter is a successful outcome to this experiment, since the location of dispersion and settling of a passive plume is highly dependent on the ruling hydro-meteorological conditions and thus difficult to predict. Deposition of the observed sediment plumes may cause habitat changes in the long-term.

Evolution of sediment plumes in the Chesapeake bay and implications of climate variability.

Fluvial sediment transport impacts fisheries, marine ecosystems, and human health. In the upper Chesapeake Bay, river-induced sediment plumes are generally known as either a monotonic spatial shape or a turbidity maximum. Little is known about plume evolution in response to variation in streamflow and extreme discharge of sediment. Here we propose a typology of sediment plumes in the upper Chesapeake Bay using a 17 year time series of satellite-derived suspended sediment concentration. On the basis of estimated fluvial and wind contributions, we define an intermittent/wind-dominated type and a continuous type, the latter of which is further divided into four subtypes based on spatial features of plumes, which we refer to as Injection, Transport, Temporary Turbidity-Maximum, and Persistent Turbidity-Maximum. The four continuous types exhibit a consistent sequence of evolution within 1 week to 1 month following flood events. We also identify a "shift" in typology with increased frequency of Turbidity-Maximum types before and after Hurricane Ivan (2004), which implies that extreme events have longer-lasting effects upon estuarine suspended sediment than previously considered. These results can serve as a diagnostic tool to better predict distribution and impacts of estuarine suspended sediment in response to changes in climate and land use.

New methods for ADV measurements of turbulent sediment fluxes – application to a fine sediment plume

ABSTRACTNew methods have been developed to extract turbulent fluxes of momentum and fine sediments from Acoustic Doppler Velocimeter (ADV) data. The methods were validated with turbidity plume experiments. The ADV's backscatter amplitude signal was used to determine the sediment concentration and its turbulent fluctuations. However, different kinds of noise are found in the backscatter amplitude and the velocity signals, which are polluting the turbulent fluxes results. Therefore, spectral noise correction methods have been developed, which allow more accurate quantification of turbulent velocity and sediment concentration fluctuations. The techniques are applied to two benchmark cases of a vertical sediment-laden jet. Reynolds stresses, turbulent intensity of velocity and sediment concentration as well as turbulent sediment fluxes are shown to agree well with two-fluid plume measurements reported in the literature. The methods presented in this paper can be applied to the processing of measurements in cohesive sediment plumes, turbidity currents or mixing layers in the absence of, or in stable, flocculation.

Field experimental observations of highly graded sediment plumes

A field experiment in the waters off the south-eastern coast of Cyprus was carried out to study near-field formation of sediment plumes from dumping. Different loads of sediment were poured into calm and limpid waters one at the time from just above the sea surface. The associated plumes, gravitating towards the seafloor, were filmed simultaneously by four divers situated at different depths in the water column, and facing the plume at different angles. The processes were captured using GoPro-Hero-series cameras. The high-quality underwater footage from near-surface, mid-depth and near-bed positions gives unique insight into the dynamics of the descending plume and near-field dispersion processes, and enables good understanding of flow and sediment transport processes involved from-release-to-deposition of the load in a non-scaled environment. The high resolution images and footages are available through the link provided herein. Observations support the development of a detailed multi-fractional sediment plume model.

Air-Seawater Exchange of Organochlorine Pesticides along the Sediment Plume of a Large Contaminated River.

Gaseous exchange fluxes of organochlorine pesticides (OCPs) across the air-water interface of the coastal East China Sea were determined in order to assess whether the contaminated plume of the Yangtze River could be an important regional source of OCPs to the atmosphere. Hexachlorocyclohexanes (HCHs), chlordane compounds (CHLs), and dichlorodiphenyltrichloroethanes (DDTs) were the most frequently detected OCPs in air and water. Air-water exchange was mainly characterized by net volatilization for all measured OCPs. The net gaseous exchange flux ranged 10-240 ng/(m2·day) for γ-HCH, 60-370 ng/(m2·day) for trans-CHL, 97-410 ng/(m2·day) for cis-CHL, and ∼0 (e.g., equilibrium) to 490 ng/(m2·day) for p,p'-DDE. We found that the plume of the large contaminated river can serve as a significant regional secondary atmospheric source of legacy contaminants released in the catchment. In particular, the sediment plume represented the relevant source of DDT compounds (especially p,p'-DDE) sustaining net degassing when clean air masses from the open ocean reached the plume area. In contrast, a mass balance showed that, for HCHs, contaminated river discharge (water and sediment) plumes were capable of sustaining volatilization throughout the year. These results demonstrate the inconsistencies in the fate of HCHs and DDTs in this large estuarine system with declining primary sources.

A review of the physical impacts of sediment dispersion from aggregate dredging

The disturbance and subsequent dispersion of sediment arising from aggregate dredging results in increases in suspended sediment concentrations and, potentially, settlement of fine sediment or sand onto the bed, which may both cause adverse effects on local ecology. This subject is one area which has seen much research over many years and this paper sets out to synthesise some basic general conclusions for use when assessing the significance of planned operations. The literature detailing the dispersion of fine sediment plumes, and the longer term dispersion of sand released through the dredging process, is scrutinised, and in some cases re-evaluated, and used to identify an evidence-based footprint of potential impact.

Modeling the Temporal Evolution of Dredging-Induced Turbidity in the Far Field

AbstractA mathematical model of the transport of dredging-induced turbidity in the far field was developed in this study. Unlike the majority of the existing models, which assume a steady state, the present model retains the transient term, ∂c/∂t, to predict the temporal evolution of the spatial extent and concentration of the sediment plume. The unknown source strength is calibrated using field data. The appropriate turbulent diffusion coefficient in the longitudinal direction, Dx, is set to comply with the real situation with negligible longitudinal diffusion. The complete transient model formulation was then used to analyze the effects of key modeling parameters, such as the water depth, h, mean tidal current velocity, u, turbulent diffusion coefficients in the longitudinal and transverse directions, Dx and Dy, as well as the sediment-settling velocity, ws, on the model prediction, in particular the approach to the steady state and the ultimate suspended sediment concentration level at the steady state...

Spectral calibration of CBERS 2B multispectral satellite images to assess suspended sediment concentration

In this study, 11 CBERS 2B and 1 LANDSAT 5-TM satellite images from 2008 were used to estimate the suspended sediment concentration and the total suspended sediment load of the Parnaíba River (NE-Brazil). The calculation of the amount of sediment in suspension was performed using Tassan’s algorithm, which was originally developed for use on LANDSAT 5-TM images; therefore, the CBERS 2B images were spectrally calibrated using LANDSAT 5-TM at-satellite radiance. The application of atmospheric correction to the images was necessary to account for meteorological influence on the spectral data prior to the calculation of the suspended sediment concentration. Three types of dark object subtraction and the 6S model were tested, and one type of dark object subtraction was chosen as the appropriate atmospheric correction method. Tassan’s algorithm requires in situ calibration; therefore, suspended sediment concentrations measured in water samples from the Parnaíba River mouth were used to calibrate the algorithm. The results revealed that the variation of suspended sediment concentration was strongly influenced by seasonal precipitation. In 2008, the suspended sediment released by the Parnaíba River was approximately 2.54×106tons. The discharged sediment formed a sediment plume on the inner continental shelf. The extension of the plume depended on the specific hydrodynamic conditions that were forced mainly by the strength of river runoff, longshore currents, tidal currents and amplitudes, and wind and wave climate.

Ridge to reef modelling for use within land–sea planning under data‐limited conditions

ABSTRACT Soil erosion associated with land‐use change is considered one of the greatest human threats to coral reef ecosystems globally. To account for sediment runoff in land–sea planning, spatially and temporally dynamic models are needed that predict where soil loss is occurring, in addition to where sediments are travelling and settling in coastal marine areas. This assessment is particularly difficult given the complex three‐dimensional movement of sediment in water bodies. This study assessed the vulnerability of key marine resources to sedimentation in Raja Ampat, Indonesia, by developing a coupled terrestrial and marine model that relied primarily on global datasets. The model predicted the quantities of sediment at river mouths, and the spatial extent over where this sediment disperses in the ocean. In total, 1850 km2 of coral reefs, marine protected areas, dive sites, pearl farms, and other benthic habitats in Raja Ampat were found within sediment plumes with varying degrees of impact. Two hypothetical land‐use scenarios were created to illustrate the sensitivity of sedimentation on marine resources to development, and to compare future alternative management scenarios. The model provides a powerful tool for planners to understand how land management, and land‐use change might affect marine resources, particularly in data‐limited regions. Copyright © 2015 John Wiley & Sons, Ltd.

Investigating the use of oil platform marine fouling invertebrates as monitors of oil exposure in the Northern Gulf of Mexico

The concentration of 51 parent and alkylated PAHs was examined in oysters, Ostrea equestris, and corals, Tubastrea coccinea, collected from oil-rig structures off the coast of Louisiana during April and May 2011 to investigate their potential use as monitors for offshore contamination events. Corals and oysters collected from both sampling trips had lower PAH accumulation than most bivalves collected in previous studies near the shoreline of Louisiana and elsewhere in the Gulf of Mexico. In April, total PAH (TPAH) concentrations ranged from 8.73 to 15.17ngg−1 in corals and 2.52 to 22.04ngg−1 in oysters. In May, corals and oysters had elevated concentrations of TPAH ranging from 24.28 to 79.23ngg−1 and 7.18 to 95.55ngg−1, respectively. This increase could be a result of Mississippi River flooding that occurred during that time, as evidenced by the high perylene concentrations (3.92–41.49ngg−1) measured in May oysters. Oysters and corals collected in May from MC21B, the closest rig to the Mississippi River Delta, had the highest TPAH concentrations observed among all locations and the only rig to have predominantly petrogenic source inputs. Overall, given the low baseline of PAHs demonstrated in this study and the rapid accumulation of diagnostic chemicals in response to a possible contamination event (i.e. sediment plume from May flooding), oil-rig invertebrates could make excellent monitoring tools to examine the exposure to and recovery from oil (and oil-spill response options) in the offshore Northern Gulf of Mexico. Pre-spill baseline data of chemical and biological biomarkers of contamination is key to better estimating the impacts and recovery of oil exposure. Therefore, this screen of PAH accumulation represents a crucial first step in determining baseline contaminant levels in order to utilize these unique resources as monitors for offshore oil exposure in the Northern Gulf of Mexico.

Estimating source terms for far field dredge plume modelling

Far field modelling of dredging induced suspended sediment plumes is important while assessing the environmental aspects of dredging. Realistic estimation of source terms, that define the suspended sediment input for far field dredge plume modelling, is key to any assessment. This paper describes a generic method for source term estimation as it is used in practice in the dredging industry. It is based on soil characteristics and dredge production figures, combined with empirically derived, equipment and condition specific ‘source term fractions’. A source term fraction relates the suspended fine sediment that is available for dispersion, to the amount of fine sediment that is present in the soil and the way it is dredged. The use of source term fractions helps to circumvent modelling of complicated near field processes, at least initially, enabling quick assessments. When further detail is required and extra information is available, the applicability of the source term fractions can/should be evaluated by characterisation monitoring and/or near field modelling. An example of a fictitious yet realistic dredging project demonstrates how two different work methods can trigger two distinctly different types of stress to the environmental system in terms of sediment concentration and duration.

A review of impacts of marine dredging activities on marine mammals

AbstractMarine dredging is an excavation activity carried out worldwide by many industries. Concern about the impact dredging has on marine life, including marine mammals (cetaceans, pinnipeds, and sirenians) exists, but effects are largely unknown. Through consulting available literature, this review aims to expand on existing knowledge of the direct and indirect, negative and positive impacts on marine mammals. In terms of direct effects, collisions are possible, but unlikely, given the slow speed of dredgers. Noise emitted is broadband, with most energy below 1 kHz and unlikely to cause damage to marine mammal auditory systems, but masking and behavioural changes are possible. Sediment plumes are generally localized, and marine mammals reside often in turbid waters, so significant impacts from turbidity are improbable. Entrainment, habitat degradation, noise, contaminant remobilization, suspended sediments, and sedimentation can affect benthic, epibenthic, and infaunal communities, which may impact marine mammals indirectly through changes to prey. Eggs and larvae are at highest risk from entrainment, so dredging in spawning areas can be detrimental, but effects are minimized through the use of environmental windows. Sensitive environments such as seagrass beds are at risk from smothering, removal, or damage, but careful planning can reduce degradation. Assessing impacts of contaminant remobilization is difficult, but as long as contaminated sediments are disposed of correctly, remobilization is limited in space and time. Effects of suspended sediments and sedimentation are species-specific, but invertebrates, eggs, and larvae are most vulnerable. Positive effects, including an increase in food, result from greater nutrient loads, but are often short term. Dredging has the potential to impact marine mammals, but effects are species and location-specific, varying also with dredging equipment type. In general, evidence suggests that if management procedures are implemented, effects are most likely to be masking and short-term behavioural alterations and changes to prey availability.

THE EFFECTS OF WAVE-BREAKING-INDUCED TURBULENT COHERENT STRUCTURES ON BOTTOM STRESS AND SUSPENDED SEDIMENT TRANSPORT – A 3D NUMERICAL STUDY

To better understand the effect of wave-breaking-induced turbulence on nearshore sand transport, we carry out a 3D Large Eddy Simulation study of breaking solitary wave in spilling condition. Using a turbulence-resolving approach, we investigate the formation and evolution of wave-breaking-induced turbulent coherent structures, commonly known as obliquely descending eddies (ODEs), and how they may interact with the bed and enhance the suspended sediment transport. The numerical implementation is based on an open-source CFD library of solvers, called OpenFOAM®, where the incompressible 3D filtered Navier-Stokes equations for the water and the air phases are solved with a finite volume scheme. The evolution of the water-air interfaces are approximated with a Volume of Fluid (VOF) method. With the dynamic Smagorinsky closure, the numerical model results show good agreement with measured wave flume data of solitary wave breaking over a 1/50 sloping beach. Simulation results show that 3D hairpin vortices are generated under breaking wave, and they possess counter-rotating and downburst features, which are the key characteristics of obliquely descending eddies (ODEs) observed by earlier laboratory studies with Particle Image Velocimetry. A suspended sediment transport formulation (Liu and Garcia 2008) has been incorporated into the present hydrodynamic solver as part of the OpenFOAM® framework. Model results suggest that those ODEs that impinge onto the bed can cause significant bottom sediment suspension, and the location of the sediment plume is highly associated with the impinging points of ODEs but with notable time-lag.

THREE-DIMENSIONAL NUMERICAL ANALYSIS OF SEDIMENT TRANSPORT AROUND ABUTMENTS IN CHANNEL BEND

In this paper, the results for sediment transport simulation around bridge abutments in a channel bend are presented. Computational Fluid Dynamics code FANS3D is used to conduct the study, which solves three-dimensional Reynolds- Averaged Navier-Stokes equations with the finite analytic scheme. The two-layer turbulence model, which combines the one- and two-equation eddy-viscosity models, is utilized to resolve turbulence near smooth solid surfaces. The wall- function approach is adopted to take into account the roughness effects in case of sediment beds. For velocity-pressure coupling, PISO/SIMPLER algorithms are used. Chimera technique is utilized to embed non-matching blocks in the computational domain. The numerical model coupled with the sediment transport module was validated with experimental studies. For the present case, the transport of suspended sediment in a 90°-channel bend with abutments located in the middle was simulated. Sediment plume in a swirl was observed downstream of the abutments.

3D CFD simulations of trailing suction hopper dredger plume mixing: A parameter study of near-field conditions influencing the suspended sediment source flux

Frequency, duration and intensity of stresses like turbidity and sedimentation caused by dredging must be known to determine the environmental impact of dredging projects. These stresses depend on the amount of sediment spill from a dredger and on how much of this spill still is in suspension near environmentally sensitive areas. Near-field mixing close to a dredger influences the deposition behaviour of the sediment spill. This is investigated systematically with computational fluid dynamics simulations for 136 different conditions of trailing suction hopper dredger overflow sediment plume mixing. Most important influences are found for the ambient depth and the crossflow velocity (vector sum of the dredging speed and the ambient velocity), which can result in a completely different suspended sediment source flux behind the dredger. The simulation results are translated into mathematical relations to predict the suspended sediment source flux without computational effort.

Source to sink: Statistical identification of regional variations in the mineralogy of surface sediments in the western Nordic Seas (58°N–75°N; 10°W–40°W)

The non-clay and clay mineralogies of the < 2 mm sediment fraction from 157 seafloor samples in the western Nordic Seas is calculated by quantitative X-ray diffraction analysis. Our sample coverage includes the Iceland shelf, the ice-impacted East Greenland margin, and the Greenland, Iceland, and Irminger seas. The bedrock geology of source areas includes Precambrian basement rocks, Devonian red beds and younger marine and fluvial sediments, and large outcrops of early tertiary to recent flood basalts and other volcanic facies. Sediment erosion and transport in the area are associated with ice (sea ice and icebergs), and glacial meltwater and fluvial sediment plumes. We use Principal Component Analysis, fuzzy k-means clustering, and Discriminant Function Analysis to reduce the original 31 (minerals) × 157 (sites) matrix to more manageable 5 regional coherent clusters of sites, which are well discriminated by the weight % of six minerals, namely quartz, pyroxene, illites, magnetite and maghemite, amorphous silica (e.g. glass) and muscovite. The close spatial relationship between bedrock geology and discrete cluster membership stresses the importance of this variable and indicates that far-distant sediment transport by sea ice, icebergs, or other mechanisms, although occurring does not radically change the mineral composition of present-day sea-floor sediments. Our improved knowledge of the regional mineral assemblages allows for tracking distinct Eastern Greenland and Icelandic sources.

Characterization and sources analysis of polycyclic aromatic hydrocarbons in surface sediments in the Yangtze River Estuary

Eighteen polycyclic aromatic hydrocarbons (PAHs), including 16 PAHs selected as priorities for control by the US Environmental Protection Agency, 1-methylnaphthalene and 2-methylnaphthalene, were determined in sediment samples from the Yangtze River Estuary, including the intertidal marshes and the river plume area. Results showed the PAH concentrations in marsh sediments (316–792 ng g−1) were higher than those in the river plume sediment (98–391 ng g−1). Further analysis suggested the PAH concentrations are correlated with total organic carbon (r = 0.71, p < 0.05), as well as water current and industrial activities. However, particle size less affects distribution of PAHs in Yangtze River Estuary. Results also showed a difference in PAHs’ compositions between marsh and river plume sediments: PAHs with two rings were more abundant than other PAHs’ compositions in river plume sediments, while PAHs with 3–4 rings were dominated in marsh sediments. This distribution pattern suggested different contamination sources between marsh and river plume sediments. The diagnostic ratios of PAH isomers and principal component analysis further demonstrated the PAHs in the marsh sediment came from burning biomass or coal, and those from river plume sediments derived from a mixture of petrogenic and pyrolytic source. The concentrations of total PAHs in the sediments from Yangtze River Estuary were relatively low in comparison with other estuaries around the world. And ecological risk assessment also suggested that the PAHs in the Yangtze River Estuary sediments present little ecotoxicological risk. However, a risk assessment for chronic exposure to low PAH concentrations should be performed in a further study.

GOES Imager Shows Diurnal Changes of a &lt;italic&gt;Trichodesmium erythraeum&lt;/italic&gt; Bloom on the West Florida Shelf

The advantages of geostationary observations of sediment plumes and phytoplankton blooms have been reported for coastal waters in the southern North Sea and west Pacific. So far, similar observations have not been possible for the Gulf of Mexico where blooms of Trichodesmium erythraeum often occur. Here, using data collected by the Geostationary Operational Environmental Satellite (GOES) Imager, we document diurnal changes of a Trichodesmium bloom first identified by the Moderate Resolution Imaging Spectroradiometer (MODIS). Despite the low-signal-to-noise ratio ( ~ 46 : 1 for typical ocean radiance), the 550-750-nm band revealed clear patterns of Trichodesmium mats floating on the ocean surface and their temporal changes between 14:15 and 22:30 GMT on May 22, 2004. Normalization of the delineated bloom against the ocean background provided an effective atmospheric correction that enabled quantification of the changes in bloom size (i.e., area) and bloom intensity over the course of a day. The area coverage increased by about eightfold from midmorning (14-15 GMT) to reach its maximum around 18:30 GMT, whereas the mean intensity of the bloom area increased by ~ 22% from midmorning to 17:30 GMT. In the afternoon, while the bloom area remained relatively stable on the water surface, bloom intensity sharply decreased. These temporal patterns may be caused by physical aggregation and/or vertical migration of the Trichodesmium cells, and they agree well with the diurnal changes of a harmful algal bloom of the dinoflagellate Prorocentrum donghaiense in the East China Sea observed by the Geostationary Ocean Color Imager.

Lagrangian analysis of the transport and processing of agricultural runoff in the lower Maumee River and Maumee Bay

Lagrangian analyses is used to evaluate the processing of nutrients and sediments during storm runoff events as water moved from the Maumee River loading station at Waterville, OH through the lower river, Maumee Bay and into Lake Erie's western basin. Chemical signatures of storm water at Waterville were used in combination with frequent collections of water at transects along the flow paths to evaluate processing. These signatures consisted of the contrasting chemographs of conservative parameters (chloride and sulfate), dissolved nutrients (dissolved reactive phosphorus (DRP) and nitrate) and particulate substances (suspended solids (SS) and particulate phosphorus (PP)). During low flow, sharp drops in concentrations of chloride and sulfate indicated that mixing zones between river water and bay/lake water occurred at the river mouth. During high flows, the location of the mixing zone between riverine and bay/lake water was indicated by the margin of storm-event sediment plumes, with larger storms extending further into the lake. Steep concentration gradients of DRP and nitrate between high storm water concentrations and low bay/lake water concentrations were also present at the plume margin. The large areas of storm water inside the plume margin contained high DRP and nitrate concentrations but relatively low SS and PP concentrations, due to SS and PP deposition along the flow paths. Because this deposition occurred in water with high DRP concentrations, little of the bioavailable PP was likely to have been released prior to deposition. This storm runoff water provides excellent media for algal growth.