Simulation of resuspended sediments resulting from dredging operations by a numerical flocculent transport model

Environmental remediations such as dredging operations cause contaminated sediments from the bottom of water bodies to become suspended into the water column. These resuspended particles are significant water quality concerns and cause adverse effects to aquatic organisms. In this paper, we present a vertically integrated two-dimensional flocculent sediment transport model to better model concentration changes of resuspended bottom sediments. The flocculent transport model has been applied to the Savannah River cutterhead dredge field study involving the resuspension of bottom sediments. The results showed that the model predictions correlate reasonably well with field data. These comparisons suggest that the flocculent sediment transport model can be used to predict the concentration profiles of a plume of toxic compounds resulting from cutterhead dredge operation.     

Evaluation of sequentially-coupled POP fluxes estimated from simultaneous measurements in multiple compartments of an air-water-sediment system

Bulk atmospheric deposition fluxes, air-water exchange fluxes, particle settling fluxes out of the upper water column, sediment trap fluxes in deep waters, and sediment burial fluxes of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were simultaneously measured in the Koster Fjord, eastern Skagerak, on the Swedish west coast. The aim of the study was to compare the magnitude and direction of the compound fluxes in the system in order to diagnose key fate processes. The PCB and PAH fluxes via net atmospheric deposition, settling particles out of the surface and through deep waters, as well as into the accreting underlying sediments were shown to be remarkably similar, agreeing within a factor of a few for any given target compound. Fluxes of all PCB and PAH target compounds remained fairly constant with water column depth. Thus there was no evidence for net desorption from sinking particles. The net unidirectional and near balancing of vertical fluxes suggests a net transport of PCBs and PAHs from the atmosphere to the continental shelf sediments in the Koster Fjord, which is consistent with the hypothesis that the shelf sediments are important sinks for these compounds.     

Sediment processes and mercury transport in a frozen freshwater fluvial lake (Lake St. Louis, QC, Canada)

An open-bottom and a closed-bottom mesocosm were developed to investigate the release of mercury from sediments to the water column in a frozen freshwater lake. The mesoscosms were deployed in a hole in the ice and particulate mercury (Hg_P) and total dissolved mercury (TDHg) were measured in sediments and in water column vertical profiles. In addition, dissolved gaseous mercury (DGM) in water and mercury water/airflux were quantified. Concentrations of TDHg, DGM, and mercury flux were all higher in the open-bottom mesocosm than in the closed-bottom mesocosm. In this paper we focus on the molecular diffusion of mercury from the sediment in comparison with the TDHg accumulation in the water column. We conclude that the molecular diffusion and sediment resuspension play a minor role in mercury release from sediments suggesting that solute release during ebullition is an important transport process for mercury in the lake.     

Horizontal and vertical variabilities of mercury concentration and speciation in sediments of the Gdansk Basin,Southern Baltic Sea

The mercury compounds introduced to the environment because of anthropogenic activity are accumulated, mainly, in marine sediments. Both distribution of mercury in the Baltic Sea and factors affecting it are remain largely unknown. Due to its complex chemistry and variable conditions in the Baltic Sea bottom sediments, mercury may be reemitted to the overlaying water, and thus to the environment.The aim of this study was twofold. Total mercury contents were measured in sediments of the Gdansk Basin along a Vistula mouth (main source)--Gdansk Deep (deposition area) transect in order to assess spatial distribution of the element. Soft and sandy bottom sediment cores were collected and cut into slices. The mercury measurements consisted of acid digestion followed by CV-AAS determination. A five-step sequential extraction procedure involving measurements of mercury species water soluble, bound to humic substances and insoluble, was employed in order to investigate mercury speciation. On the basis of speciation results stability and remobilisation potential was assessed. The second aim was demonstrating that mercury gradients in vertical profiles of the investigated sediment cores exist.Total mercury contents varied in range from 28 ng/g x dw to 844 ng/g. Mercury associated with organic matter and sulphides, (respectively 39% and 49%) were the dominant species of the element. The results indicated that the river run-off is a source of mercury in the area. Vertical gradients of both total content and speciation of mercury in the soft sediments were attributed to both remobilisation from sediments, and decreasing trend in the anthropogenic load of the element deposited to sediments.     

Polybrominated diphenyl ethers in sediments of the Daliao River Estuary, China: levels, distribution and their influencing factors

The concentrations, compositional profiles, possible sources of polybrominated diphenyl ethers (PBDEs) in sediments of the Daliao River Estuary as well as the factors influencing the distribution of PBDEs were investigated. The total concentrations of PBDEs ranged from 0.13 to 1.98 ng g⁻¹ d.w. BDE209 was the dominating congener in all sediment samples, indicating the pollution of PBDEs in the Daliao River Estuary mainly came from the use of deca-BDE commercial mixtures. The intrusion of sea waters promoted the deposition of the colloid-associated PBDEs in the estuary. There were significantly negative correlations between PBDE concentration in sediment with pH value and salinity in the bottom water. The higher river flow in the flood season (summer) obviously accelerated the transport of PBDEs, and thereby increased the risk of PBDE contamination to the deep ocean. Moreover, a positive correlation between TOC and PBDE distributions was observed, suggesting that TOC regulated the distributions of PBDEs in sediments of Daliao River Estuary.     

污染底泥及其间隙水分层特性的模拟实验研究

底泥冲刷沉降、再悬浮是作用于水环境内源污染的主要因素,而底泥间隙水的污染释放则是主要途径。通过底泥培养实验,研究了污染底泥及其间隙水的分层特性。结果表明,底泥及其污染物具有显著的分层特性。底泥间隙水中CODMn随深度的增加略有下降的趋势;底泥湿容重和干容重呈增大的趋势;含水率随底泥深度的增加而减小。底泥深度对底泥泥沙颗粒的级配有很大影响,在表层以细颗粒为主,随着深度的增加．底泥粒径增加,但趋势衰减较快。这对底泥冲刷作用下的再悬浮有很大影响。     

Sediment pollution and dynamic in the Mar Piccolo of Taranto (southern Italy): insights from bottom sediment traps and surficial sediments

Major and trace element, PAH, and PCB concentrations were measured in surface sediments and particles from sediment traps collected in the First and Second Basin of the Mar Piccolo (Gulf of Taranto) in two periods (June–July and August–September, 2013). The aim of the study was to evaluate pollution degree, sediment transport and particle redistribution dynamic within the area. Results confirm the higher contamination of sediments from the First Basin observed by previous researches, particularly for Cu, Hg, Pb, total PAHs, and total PCBs. Advective transport from the First to the Second Basin appears to be the leading transfer mechanism of particles and adsorbed contaminants, as evidenced by measured fluxes and statistical analyses of contaminant concentrations in surficial sediments and particles from sediment traps. Long-range selective transports of PAHs and microbial anaerobic degradation processes for PCBs have been also observed. These results are limited to a restricted time window but are consistent with the presence of transport fluxes at the bottom of the water column. This mechanism deserves further investigation and monitoring activities, potentially being the main responsible of pollutant delivering to the less contaminated sectors of the Mar Piccolo.     

Effects of taxonomy,sediment, and water column on C:N:P stoichiometry of submerged macrophytes in Yangtze floodplain shallow lakes,China

Carbon (C), nitrogen (N) and phosphorus (P) are the three most important essential elements limiting growth of primary producers. Submerged macrophytes generally absorb nutrients from sediments by root uptake. However, the C:N:P stoichiometric signatures of plant tissue are affected by many additional factors such as taxonomy, nutrient availability, and light availability. We first revealed the relative importance of taxonomy, sediment, and water column on plant C:N:P stoichiometry using variance partitioning based on partial redundancy analyses. Results showed that taxonomy was the most important factor in determining C:N:P stoichiometry, then the water column and finally the sediment. In this study, a significant positive relationship was found between community C concentration and macrophyte community biomass, indicating that the local low C availability in macrophytes probably was the main reason why submerged macrophytes declined in Yangtze floodplain shallow lakes. Based on our study, it is suggested that submerged macrophytes in Yangtze floodplain shallow lakes are primarily limited by low light levels rather than nutrient availability.

     

Effect of sediment properties on the sorption of C12-2-LAS in marine and estuarine sediments

Linear alkylbenzene sulfonates (LAS) are anionic high production volume surfactants used in the manufacture of cleaning products. Here, we have studied the effect of the characteristics of marine and estuarine sediments on the sorption of LAS. Sorption experiments were performed with single sediment materials (pure clays and sea sand), with sediments treated to reduce their organic carbon content, and with field marine and estuarine sediments. C₁₂-2-LAS was used as a model compound. Sorption to the clays montmorillonite and kaolinite resulted in non-linear isotherms very similar for both clays. When reducing the organic content, sorption coefficients decreased proportionally to the fraction removed in fine grain sediments but this was not the case for the sandy sediment. The correlation of the sediment characteristics with the sorption coefficients at different surfactant concentrations showed that at concentrations below 10 μg C₁₂-2-LAS/L, the clay content correlated better with sorption, while the organic fraction became more significant at higher concentrations.     

Persistence of residues in water and sediment op a fresh‐water lake after surface application of technical chlordane

Abstract

A fresh‐water lake, free from detectable pesticide residues before this study, was treated with a commercial formulation of technical chlordane. Water and sediment samples were analysed for chlordane residues 7, 24, 52, 279. and 421 days after treatment. Residues moved rapidly from the water to the lake bottom, supporting earlier results of a laboratory study with other organochlorines.

In water, α‐ and γ‐chlordane concentrations remained proportional to total chlordane concentrations, as determined by total‐peak area measurements of gas‐liquid chronatogrammes. But in bottom sediments, α‐ and γ‐chlordane were more persistent than other constituents of technical chlordane, supporting recent evidence that quantification of technical chlordane residues on the basis of γ‐chlordane quantification only (or that of a‐ and γ‐chlordane only), can lead to incorrect results and that this method, although simple and fast, should no longer be recommended.     

沉积物与水间相互作用的研究进展

本文综述了沉积物／水之间的相互作用的研究进展,主要讨论了污染物在沉积物／水界面间的物质传输：水体中污染物在颗粒物上的吸附作用;与沉积物相关的水质、健康和管理等方面的问题     

A scuba diving direct sediment sampling methodology on benthic transects in glacial lakes: procedure description,safety measures,and tests results

This work presents an in situ sediment sampling method on benthic transects, specifically intended for scientific scuba diver teams. It was originally designed and developed to sample benthic surface and subsurface sediments and subaqueous soils in glacial lakes up to a maximum depth of 25 m. Tests were conducted on the Sabocos and Baños tarns (i.e., cirque glacial lakes) in the Spanish Pyrenees. Two 100 m transects, ranging from 24.5 to 0 m of depth in Sabocos and 14 m to 0 m deep in Baños, were conducted. In each test, 10 sediment samples of 1 kg each were successfully collected and transported to the surface. This sampling method proved operative even in low visibility conditions (<2 m). Additional ice diving sampling tests were conducted in Sabocos and Truchas tarns. This sampling methodology can be easily adapted to accomplish underwater sampling campaigns in nonglacial lakes and other continental water or marine environments.     

Concentrations and profiles of PCDD/Fs in sediments of major Polish rivers and the Gdansk Basin--Baltic Sea

The present state of contamination of bottom sediments in southern part of the Baltic Sea with PCDD/Fs was compared to the findings made for the north-western and eastern Baltic Sea coastal areas of Finland, Sweden and Denmark. The extent of the study area--from marine the Gdańsk Basin, the lower Oder and Vistula Rivers up till W?oc?awek reservoir--allowed to obtain the sediment samples with diversified properties. Dioxin's concentrations in sediments examined in the Polish costal area allows us to evaluate this zone as relatively less contaminated. Higher dioxin concentration has been found in Wloclawek Dam Reservoir. Differences in congener patterns and temporal changes in marine sediment profiles were examined. The highest concentrations of tetra- and penta-congeners still remain in the surface layer of Gdansk Deep, whereas the decline in concentrations of these most toxic congeners, have been observed in the sediments from some other parts of the Baltic coast. Excess concentration of dioxins in sediments has a great impact on human being due to special ability of accumulation in the trophic chain as well as in water (fishes) and land (milk, meat).     

The deep-sea as a final global sink of semivolatile persistent organic pollutants? Part I: PCBs in surface and deep-sea dwelling fish of the north and south Atlantic and the Monterey Bay Canyon (California)

The understanding of the global environmental multiphase distribution of persistent organic pollutants (POPs) as a result of the physico-chemical properties of the respective compounds is well established. We have analysed the results of a vertical transport of POPs from upper water layers (0-200 m) to the deepwater region (> 800 m) in terms of the contamination of the biophase in both water layers. The contents of persistent organochlorine compounds like polychlorinated biphenyls (PCBs) in fish living in the upper water layers of the North Atlantic and the South Atlantic, and at the continental shelf of California (Marine Sanctuary Monterey Bay and its deep-sea Canyon) are compared to the levels in deep-sea or bottom dwelling fish within the same geographic area. The deep-sea biota show significantly higher burdens as compared to surface-living species of the same region. There are also indications for recycling processes of POPs--in this case the PCBs--in the biophase of the abyss as well. It can be concluded that the bio- and geo phase of the deep-sea may act similarly as the upper horizons of forest and grasslands on the continents as an ultimate global sink for POPs in the marine environment.     

Large-scale fires and time trends of PCDDS/DFs in sediments

Drastic increases in PCDDs/DFs concentrations were identified in the uppermost layers of a sediment core sample taken from the coastal area of Kobe City. As large-scale fires caused by the Great Hanshin-Awaji earthquake were deemed to be a possible cause, we performed additional sampling of sediment cores and surface sediment samples, estimating the total amount of PCDDs/DFs released from fires and presuming the load to sediments by individual transport routes, such as air and water, using an air diffusion model to investigate the influence of fires. The total amount of PCDDs/DFs released from fires was estimated at 2000 g-total PCDDs/DFs, 22 g-TEQ. Increases in PCDDs/DFs generated in fires were principally transported through water rather than air. If 20% of the total PCDDs/DFs formed in fires had entered water, it would correspond to the entire increase of PCDDs/DFs concentration in sediment cores.     

Equilibrium partitioning theory to predict the sediment toxicity of the anionic surfactant C(12)-2-LAS to Corophium volutator

The study of the effect of the sorption of linear alkylbenzene sulfonates (LAS) on the bioavailability to marine benthic organisms is essential to refine the environmental risk assessment of these compounds. According to the equilibrium partitioning theory (EqP), the effect concentration in water-only exposure will be similar to the effect concentration in the sediment pore water. In this work, sorption and desorption experiments with two marine sediments were carried out using the compound C₁₂-2-LAS. The effect of the sediment sorption on the toxicity of benthic organisms was studied in water-only and in sediment bioassays with the marine mud shrimp Corophium volutator. In addition, three common spiking methods were tested for its application in the toxicity tests, as well as the stability of the surfactant during the water-only and sediment-water test duration. LC50 values obtained from water-only exposure showed a good correspondence with the pore water concentrations calculated from the sorption and desorption isotherms in the spiked sediments.     

A laboratory study of sediment and contaminant release during gas ebullition

Significant quantities of gas are generated from labile organic matter in contaminated sediments. The implications for the gas generation and subsequent release of contaminants from sediments are unknown but may include enhanced direct transport such as pore water advection and diffusion. The behavior of gas in sediments and the resulting migration of a polyaromatic hydrocarbon, viz phenanthrene, were investigated in an experimental system with methane injection at the base of a sediment column. Hexane above the overlying water layer was used to trap any phenanthrene migrating out of the sediment layer. The rate of suspension of solid particulate matter from the sediment bed into the overlying water layer was also monitored. The experiments indicated that significant amounts of both solid particulate matter and contaminant can be released from a sediment bed by gas movement with the amount of release related to the volume of gas released. The effective mass transfer coefficient of gas bubble-facilitated contaminant release was estimated under field conditions, being around three orders of magnitude smaller than that of bioturbation. A thin sand-capping layer (2 cm) was found to dramatically reduce the amount of contaminant or particles released with the gas because it could prevent or at least reduce sediment suspension. Based on the experimental observations, gas bubble-facilitated contaminant transport pathways for both uncapped and capped systems were proposed. Sediment cores were sliced to obtain phenanthrene concentration. X-ray computed tomography (CT) was used to investigate the void space distribution in the sediment penetrated by gas bubbles. The results showed that gas bubble migration could redistribute the sediment void spaces and may facilitate pore water circulation in the sediment.     

Contamination status and potential release of trace metals in a mangrove forest sediment in Ho Chi Minh City,Vietnam

Can Gio district is located in the coastal area of Ho Chi Minh City, southern Vietnam. Discharge of wastewater from Ho Chi Minh City and neighboring provinces to the rivers of Can Gio has led to concerns about the accumulation of trace metals (As, Cu, Cr, Ni, Pb, and Zn) in the coastal sediments. The main objective of this study was to assess the distribution of As, Cu, Cr, Ni, Pb, and Zn in surface and core sediments and to evaluate the contamination status in relation to local background values, as well as the potential release of these selected trace metals from sediments to the water environment. Sediment characteristization, including determination of fine fraction, pH, organic matter, and major elements (Al, Fe, Ca, K, Mg, and S), was carried out to investigate which parameters affect the trace metal enrichment. Fine fraction and Al contents were found to be the controlling proxies affecting the distribution of trace metals while other sediment characteristics did not show any clear influence on trace metals’ distribution. Although As concentrations in the sediments were much higher compared to its reference value in other areas, the enrichment factor based on local background values suggests minor contamination of this element as well as for Cr, Cu, and Pb. Risk assessment suggested a medium to very high risk of Mn, Zn, and Ni under acidification. Of importance is also that trace metals in sediments were not easily mobilized by organic complexation based on their low extractabilities by ammonium-EDTA extraction.

     

Mathematical analysis of the whole core injection method accuracy for measuring phenanthrene biodegradation rates in undisturbed marine sediments

Rates of 14C-phenanthrene mineralization in contaminated, undisturbed marine sediments were measured using the whole core injection method to assess microbial natural attenuation activity as a function of sediment depth. Submerged sediments were sampled from Eagle Harbor, a marine superfund site in Puget Sound. Experiments show significant biodegradation activities (0.0012-0.0036 day(-1)) in the sediment horizons from 0 to 10 cm. The purpose and scope of this paper is to evaluate the range of experimental conditions giving valid results; a mathematical simulation described competing contaminant 14C-phenanthrene diffusion and simultaneous biodegradation (Monod kinetics), both retarded by sorption. The effect of aging was examined with two sorption models in presumed pseudo-homogenous sediments having effective properties. The simulation predictions provide quantitative guidelines for the successful use of the whole core injection method. (1) The effective Monod constant KS' in sediment is increased by a large partition coefficient KP between sediment and water and makes the apparent 14C-phenanthrene biodegradation approach first-order kinetics. (2) When KS'>1 mg(-1) l(-1), the measured 14C-phenanthrene biodegradation extent is biased by inadequately distributed injected tracer only when less than 7% of the sediment horizon is initially probed and mixed with injected tracer. (3) A short incubation time (<20 days) is necessary when a mobile indicator, e.g., gaseous 14CO2, is used. For longer incubation times, predictions show that a 14CO2 indicator diffuses to adjacent horizons, thus smearing the depth profile of biodegradation. (4) This method employing a radiolabeled tracer provides accurate biodegradation rates for freshly contaminated sediments, and represents an upper limit to the natural phenanthrene biodegradation extents if the contaminant is aged over 50 days.     

Factors influencing organotin distribution in different marine environmental compartments, and their potential health risk

Tributyltin (TBT) and triphenyltin (TPT) in different marine environmental compartments such as seawater, sediments, and inshore fishes were investigated in 21 Taiwanese harbors between 2001 and 2004 in order to determine the major factors influencing their distribution. The existence of major input sources and the limited water exchange rate inside the harbors were indicated by higher TBT concentrations in seawater from inner harbor than from outer harbor areas. The levels of TBT in sediments were found to be mainly affected by their geographic distribution, water exchange rates and shipping activity. No significant correlations in TBT concentrations between water, sediment and fish suggested TBT accumulation by fish might not result from water and sediment, but from their food. TPT were detected in most fish samples, but found in few sediment samples and none in seawater, indicating fish could be as a target element for monitoring contaminated levels of TPT in the aquatic environment. Mean concentrations of TBT in fish muscle higher than tolerable average residue levels (TARLs), and mean hazard indices of TBT and TPT higher than 1 suggested consumption of fishes from Taiwanese harbor areas might have potential high risk to human health.