A chemical investigation of the transport and fate of petroleum hydrocarbons in littoral and benthic environments: The TSESIS oil spill

The fate of saturated and aromatic hydrocarbons discharged into the coastal Baltic Sea environment from the TSESIS oil spill has been studied in the acute and postacute (one year) phases of the spill. Periodic samples of Mytilus edulis (mussels) from eight littoral zone stations and Macoma balthica from nine soft bottom stations were obtained as well as sediment trap samples and surface sediment samples. Glass capillary gas chromatography and gas chromatographic mass spectrometry were used as the analytical tools to determine saturated and aromatic hydrocarbon composition and concentrations in these samples.Sediment trap samples indicated that sizable quantities of chemically and microbially weathered oil were sedimented, and available for benthic uptake shortly after the spill. After initial uptake of sedimented oil (500 to 1000 μ/g dry weight), Macoma populations appear to have begun slow depuration through the first winter after the spill, but TSESIS oil was again introduced to the benthic stations studied during the following summer. Mytilus populations in the region were severely impacted by the oil. Initial depuration of spilled oil during the first month was rapid and nearly complete at all but the most heavily impacted stations one year after the spill. The post-spill depuration of assimilated hydrocarbons was characterised by a relative retention of alkylated dibenzothiophenes and alkylated phenanthrenes compared to their unsubstituted parent compounds and compared with the entire homologous naphthalene series.These data suggest that petroleum hydrocarbons from the TSESIS spill have become a chronic source of degraded saturated and aromatic hydrocarbons to the soft bottom benthic communities. Petroleum hydrocarbons in the benthic environment from this spill appear to reside in the difficulty sampled and mobile flucculent layer at the sediment/water interface and may affect epifaunal communities for an extended period of time.     

The long-term effects of crude oil on microbial processes in subarctic marine sediments

Subarctic marine sediments were exposed to fresh and ‘weathered’ crude oil from Cook Inlet, Alaska. The crude oil was thoroughly mixed with the sediment at various concentrations and some of the oil-sediment mixtures were placed on top of unamended sediments. Both sediments with added oil and those overlain by oiled sediments were investigated. These sediments were placed either in trays or aquaria. The trays were incubated in situ near the site from which the sediments were originally collected. The aquaria were maintained at simulated in situ conditions by maintaining a continuous flow of fresh seawater through them. The sediments were exposed to crude oil for periods up to 1.5 years. Sediments exposed to 50‰ fresh crude oil showed significant decreases in nitrogen fixation and denitrification rates and redox potentials. Also observed were increases in CO₂ production rates and methane concentrations. These same changes were observed in sediments exposed to 1‰. When ‘weathered’ crude oil was added to the sediments, the same changes were observed except there was no reduction in nitrogen fixation activity. In most cases, the observed effects were less marked when the sediments were amended with ‘weathered’ crude oil than with the same concentration of fresh crude oil. Untreated sediments that were overlain with treated sediments showed the same changes as those sediments that were thoroughly mixed with crude oil. The presence of fresh crude oil at 50‰ essentially eliminated burrowing activity of the benthic infauna. Under these conditions, there was an accumulation of detritus particles on the oiled sediments that was not present in the untreated controls.     

The composition and distribution of saturated and aromatic hydrocarbons in nearshore sediments, river sediments, and coastal peat of the Alaskan Beaufort Sea: Implications for detecting anthropogenic hydrocarbon inputs

A 3-year program, to determine spatial and temporal trends in sediment concentrations of hydrocarbons and metals from oil and gas exploration and development activities, was conducted in the US Beaufort Sea. Concentrations of saturated and aromatic hydrocarbons in sediments from the Beaufort Sea were elevated in comparison to non-polluted shelf-sediments from other regions of the US coast. Potential natural sources for hydrocarbons that were examined included riverine sediments and coastal peat. Significant quantities of fossil hydrocarbons characterize the surface sediments from the entire region. Sediment inputs from river discharges appear to account for this observation. The use of source-diagnostic ratios has allowed the differentiation of various sources in an area with high naturally-occurring hydrocarbon concentrations where effects due to oil and gas exploration and development activities may be obscured.     

Response of benthic communities in merl experimental ecosystems to low level, chronic additions of No. 2 fuel oil

The macrofauna and meiofauna of three oiled and three control experimental ecosystems at the Marine Ecosystems Research Laboratory (MERL) were followed for 25 weeks of semi-continuous additions of an oil-water dispersion of No. 2 fuel oil. Water column hydrocarbon levels were maintained at about 190 ppb, and after 20 weeks 109 sm/g dry weight fuel oil hydrocarbons were recorded in the top 2 cm of sediment.This simulated chronic oil pollution resulted in a highly significant decline in the number of macrofaunal and meiofaunal individuals in the experimental tanks compared with the controls. The effect was apparent on the numbers of individual macrofaunal species and on all metazoan meiofaunal groups.     

The process of sedimentation on the surface of a salt marsh

An unditched salt marsh-creek drainage basin (Holland Glade Marsh, Lewes, Delaware) has a sedimentation rate of 0·5 cm year^?1. During normal, storm-free conditions, the creek carries negligible amounts of sand and coarse silt. Of the material in the waters flooding the marsh surface, over 80% disappears from the floodwaters within 12 m of the creek. About one-half of the lost material is theoretically too fine to settle, even if flow were not turbulent; however, sediment found on Spartina stems can account for the loss.The quantity of suspended sediment that does reach the back marsh during these normal tides is inadequate to maintain the marsh surface against local sea level rise. This suspended sediment is also much finer than the deposited sediments. Additionally, remote sections of low marsh, sections flooded by only the highest spring tides, have 15–30 cm of highly inorganic marsh muds.This evidence indicates that normal tidal flooding does not produce sedimentation in Holland Glade. Study of the effects of two severe storms, of a frequency of once per year, suggests that such storms can deposit sufficient sediment to maintain the marsh.The actual deposition of fine-grained sediments (fine silt and clay) appears to result primarily from biological trapping rather than from settling. In addition, this study proposes that the total sedimentation on mature marshes results from a balance between tidal and storm sedimentation. Storms will control sediment supply and movement on micro- and meso-tidal marshes, and will have less influence on macro-tidal marshes.     

Effects of prudhoe bay crude oil-contaminated sediments on Protothaca staminea (mollusca: Pelecypoda): Hydrocarbon content,condition index,free amino acid level

Protothaca staminea and Macoma inquinata were exposed to sediment contaminated with 1237 ppm Prudhoe Bay crude oil in the field. Eighty-five per cent of the Protothaca and 17% of the Macoma survived 54 days' exposure. Body burdens of saturated and di- and tri-aromatic hydrocarbons were less than 2 ppm and quite variable. The condition index of Protothaca was reduced by 6% by exposure to oil. The level of free glycine in the mantle, gills and adductor muscle did not change significantly, but the taurine level fell, leading to a decrease in the taurine:glycine ratio. It was concluded that Protothaca, a filter feeder, is affected less severely by oil pollution than Macoma, a detritivore, perhaps because the feeding activity of filter feeders is less inhibited.     

Impact of crude oil on sulphate reduction and methane production in sediments impacted by the Amoco Cadiz oil spill

The activities of methane-producing and sulphate-reducing bacteria in intertidal sediments along the Brittany coast of France were examined in order to determine the effect of the Amoco Cadiz oil spill on sediment microbial processes. Porewater chemistry, methane production, sulphate rate and [2?¹⁴C]-acetate metabolism did not vary significantly between beach, estuary, and marsh sites, oiled or unoiled, after the Amoco Cadiz spill. Oiled sediments contained highly weathered oil of Amoco Cadiz origin, but unoiled comparison sites also contained hydrocarbons from anthropogenic sources. The additions of weathered Amoco Cadiz mousse, fresh and slightly weathered light Arabian crude oil, benzene or toluene to sediments from the oiled and unoiled marsh site did not significantly affect rates of sulphate reduction or methane production. The oxidation of [2?^14C]-acetate to ¹⁴CO₂, however, was significantly decreased when mousse, crude oil, benzene or toluene was added to sediments from the unoiled site. Inhibition seemed to be proportional to the extent of weathering. Sediments recently exposed to Amoco Cadiz crude oil were less affected by a second oiling, suggesting that the indigenous populations may have been replaced by organisms more resistant to oil toxicity. These results suggested that the Amoco Cadiz oil spill did not have major long-term effects on sulphate reduction or methane production.     

Hydrocarbons in the sediments of Port Valdez,Alaska: Consequences of five years' permitted discharge

Hydrocarbons have been investigated in the sediments of Port Valdez, Alaska after three to five years of oil terminal operation with a routine daily discharge of 170 kg of petroleum residue in an otherwise undeveloped area. Surficial benthic sediments (0–5 cm) and core segments down to 30 cm have been analyzed. Information about total hydrocarbons, unresolved complex mixture, normal alkanes, pristane, phytane, hopanes and polycyclic aromatic hydrocarbons indicates that petroleum, biogenic hydrocarbons, and combustion-derived aromatic hydrocarbons are present in sediments around the terminal at concentrations up to 218 μg g^?1 dry sediment. The vertical, horizontal and temporal distributions of anthropogenic hydrocarbons indicate that most of the sedimentary hydrocarbon accumulation has occurred within 1 km of the terminal. A simple calculation suggests that less than 3% of the total oil discharged during routine operations of the terminal has entered the sediments of Port Valdez. For comparison sediment hydrocarbon accumulation associated with a nearby small boat harbor was also examined.     

Evolution des hydrocarbures,des peuplements bacteriens et microphytiques dans les sediments des marais maritimes de l'iie grande pollues par l'amoco cadiz: 1, evolution des hydrocarbures et des bacteries

The evolution of hydrocarbons in sediments was studied from 1978 to 1980 at eight stations in the Ile Grande marshes (Brittany) polluted by the Amoco Cadiz oil spill. Generally, in 1980 (except for one heavily polluted site) the amounts of hydrocarbons were found to be far less important than in 1978 and sometimes biogenic hydrocarbons were found. In the superficial layer of the sediments biodegradation processes were generally important with the preferential degradation of n-alkanes. On the other hand, aromatic hydrocarbons seem not to have been altered after three years. Degradation of percolated hydrocarbons proceeds more slowly than in the surface layer. The number of degrading bacteria decreases when n-alkanes disappear.     

Distribution and transport of suspended sediments off the Yellow River (Huanghe) mouth and the nearby Bohai Sea

Hydrological and sedimentological investigations were carried out off the Yellow River (Huanghe) mouth and the nearby Bohai Sea during August–September 2007 to examine the distribution and transport of suspended sediments. Our data witnessed that suspended sediments from the Yellow River mouth primarily extend southerly and southeasterly during the flood season. High suspended sediment concentration (SSC) occurs as turbid plume on both sides of the river mouth, where it can reach >20 mg l^?1 in the surface water and >40 mg l^?1 in the bottom water. Accordingly, salinity varies from 25 to 29 psu, mean grain size (Dmz) is >200 μm, and volume concentration (VC) is >100 μl l^?1. High SSC was concentrated in the river mouth area as two muddy patches, i.e. the North Mud and South Mud, consisting mostly of fine-grained silt and clayey silt sediments. Our results have verified the larger extent of the South Mud than that of the North one, implicating south- and southeastward sediment dispersal paths that prevail near the river mouth area. The existing anti-clockwise and clockwise flows in the river mouth area were synthesized as the major hydrodynamics responsible for forming the two muddy patches. Tidal and residual currents are considered as the key hydrodynamic factors controlling the sediment distribution and transport in the region.     

Fate and effects of a heavy fuel oil spill on a Georgia salt marsh

Addition of a heavy oil to a Spartina salt marsh in the autumn resulted in high concentrations of polycyclic aromatic hydrocarbons in sediment and benthic animals. The highest concentrations of phenanthrene, chrysene and fluoranthene in the sediment were 112, 105 and 75 ng/g sediment, respectively. These concentrations rapidly decreased during the 20 week period following the spill. The times for these hydrocarbons to decrease to 50% of their highest values, i.e. half-life, were approximately 100, 70 and 30 days in sediment, mussels and oysters, respectively. Benthic macrofauna species showed three responses to oil addition which included no change, an increase, or a decrease in the population. No changes were noted in populations of fiddler crabs (Uca pugnax), oysters (Crassostrea virginica), and mussels (Modiolus demissus). Mud snails (Nassarius obsoleta) increased in density after the spill due to immigration of adult snails from untreated areas to scavenge on animals killed by the oil. Many of the adult periwinkles (Littorina irrorata) were killed by the oil. In the spring, juvenile periwinkles recolonised to oiled areas as a result of larvae settling.     

Organic geochemistry of sediments from chemosynthetic communities,Gulf of Mexico slope

We used a research submersible to obtain 33 sediment samples from chemosynthetic communities at 541–650 m water depths in the Green Canyon (GC) area of the Gulf of Mexico slope. Sediment samples from beneath an isolated mat of H₂S-oxidizing bacteria at GC 234 contain oil (mean = 5650 ppm) and C₁–C₅ hydrocarbons (mean = 12,979 ppm) that are altered by bacterial oxidation. Control cores away from the mat contain lower concentrations of oil (mean = 2966 ppm) and C₁–C₅ hydrocarbons (mean = 83.6 ppm). Bacterial oxidation of hydrocarbons depletes O₂ in sediments and triggers bacterial sulfate reduction to produce the H₂S required by the mats. Sediment samples from GC 185 (Bush Hill) contain high concentrations of oil (mean = 24,775 ppm) and C₁–C₅ hydrocarbons (mean = 11,037 ppm) that are altered by bacterial oxidation. Tube worm communities requiring H₂S occur at GC 185 where the sea floor has been greatly modified since the Pleistocene by accumulation of oil, thermogenic gas hydrates, and authigenic carbonate rock. Venting to the water column is suppressed by this sea-floor modification, enhancing bacterial activity in sediments. Sediments from an area with vesicomyid clams (GC 272) contain lower concentrations of oil altered by bacterial oxidation (mean = 1716 ppm) but C₁–C₅ concentrations are high (mean = 28,766 ppm). In contrast to other sampling areas, a sediment associated with the methanotrophic Seep Mytilid I (GC 233) is characterized by low concentration of oil (82 ppm) but biogenic methane (C₁) is present (8829 ppm).     

Analysis of a PAH-degrading bacterial population in subsurface sediments on the Mid-Atlantic Ridge

Little is known about the types and concentrations of polycyclic aromatic hydrocarbons (PAHs) existing in the deep-sea subsurface environment, which is believed to be cold, oligothrophic and of high static pressure. PAHs in the upper layers of the water column are unavoidably subjected to degradation while they are deposited to the sea floor and become embedded in the deep-sea sediment. In this report, a high concentration of PAHs was discovered in the sediment 2.7 m beneath the bottom surface at a water depth of 3962 m on the Mid-Atlantic Ridge (MAR). The total concentration of PAHs was 445 ng (g dry wt sediment)^-1. Among the seven detected PAHs, the concentrations of phenanthrene (222 ng g^-1) and fluorene (79 ng g^-1) were relatively high. In addition, PAH-degrading bacteria were found within the sediments. As in a previously detected site on the MAR, in the PAH-enriched region of this site, a bacterium of the genus Cycloclasticus was found to be the predominant isolate detected by PCR-DGGE analysis. In addition, bacteria of the Halomonas, Marinobacter, Alcanivorax, Thalassospira and Maricaulis genera, were also included in the PAH-degrading community. In summary, a high concentration of PAHs was detected in the subsurface of the deep-sea sediment, and once again, the Cycloclasticus bacterium was confirmed to be a ubiquitous marine PAH degrader even in the subsurface marine environment. Considering the abundance of PAHs therein, biodegradation is thus thought to be inactive, probably because of the low temperature, limited oxygen and/or limited nutrients.     

Simple estimation of penetration rate of light in intertidal sediments

A simple estimation of light penetration in tidal flat sediments was developed using various sediment size fractions and their attenuation rate of irradiance. The attenuation coefficients of the sediment size fractions of 63–125, 125–250, 250–500, 500–1000 μm and 1000–2000 μm were 8.10, 4.08, 2.92, 2.12 and 1.44 mm⁻¹, respectively. Using the average attenuation coefficient of the particle size fractions in the sediment, the calculated attenuation coefficient agreed well with the actual attenuation coefficient. The method presented gives a photo-parameter to predict productivity in intertidal sediments, given only the particle size fraction.     

长江口崇明东滩水域悬沙粒径组成和再悬浮作用特征

根据2006年10月在崇明东滩潮间带和潮下带两个站位的大小潮水文泥沙观测资料和悬沙水样的室内粒度分析资料,对悬沙粒径的时空分布特征及其与流速等的关系进行了分析,并对再悬浮特点进行了探讨,结果表明,大小潮期间的悬沙颗粒组成较细,平均粒径的均值仅为6μm;大潮时的悬沙粒径略粗于小潮的,潮间带的略粗于潮下带的;由底床向上悬沙粒径趋于减小。悬沙粒径与流速、悬沙含量无明显的统计学关系,底质粒径、再悬浮强度和再悬浮泥沙粒径的空间变化以及浮泥的悬浮作用等是主要的影响因素。由于底质粒径的空间分布复杂,在东滩水域再悬浮具有明显的空间变化。在底质平均粒径大于60μm的粗颗粒沉积区,大小潮的再悬浮作用微小,底质以推移质运动为主。在底质平均粒径介于5~11μm的细颗粒沉积区上,悬沙级配与底质级配基本相同,该区域是再悬浮的主要发生源地;悬沙级配的变化过程揭示,再悬浮对底层悬沙的贡献率平均为8%~20%,大潮时的再悬浮强度是小潮的5~10倍,由底质再悬浮产生的悬沙在底部水层中的平均含量约为0.03~0.47 kg/m3。     

Trends in the spatial and temporal distribution of metals (Cd,Cu, Zn and Pb) and organic compounds (PCBs and PAHs) in Dutch coastal zone sediments from 1981 to 1996: a model case study for Cd and PCBs

The spatial and temporal distribution of trace metals (Cd, Pb, Zn and Cu), polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) was studied to assess trends in the sediment of the Dutch coastal zone (<63-μm fraction) from 1981 to 1996. In general, the distributions showed a distinct zonation, with highest concentrations close to the coast near freshwater outlets and where dredged material had been dumped. Over time, the zone with high concentrations narrowed and moved towards the coast. The median of the percentage of the <63-μm fraction in the surface sediments did not change significantly in the Dutch coastal zone between 1981 and 1996. In that period, the median concentrations of Cd, Cu, Zn and Pb fell by 71, 38, 49 and 53%, respectively, in the area close to the coast (<20 km) north of the outlet of the Rhine. South of this outlet the median Cd, Cu and Zn concentrations fell by 45, 29 and 17%, respectively, and in the open sea area (>20 km offshore) the median concentrations for Cu and Zn fell by 35 and 18%, respectively. The largest reduction (80%) of the median concentration of PCBs occurred in the surface sediment in the open sea area (>20 km offshore) between 1986 and 1996. During this period the median PCBs concentration fell by nearly 70% close to the coast. The median PAH concentration fell by only 26% north of the outlet of the Rhine (<20 km from the coast) between 1986 and 1996. In the other areas there was no significant change. Possible reasons are that the main sources of PAHs are in the North Sea itself and that the load of PAHs from dredged material dumped in the Dutch coastal zone increased during the period studied. The reduction of the concentrations of metals and organic micropollutants in the surface sediments of the Dutch coastal zone is explained by a conservative physical mixing model, in which the previously polluted silt fraction in the surface sediments is replaced by less polluted suspended matter. There is a time lag of several years between the trend in the load of Cd and PCBs and the observed field concentration. The half life of the silt fraction and associated substances in the surface sediments is 1.9. Taking the uncertainties in the loads into account, the calculated surface sediment concentrations for Cd and PCBs agree fairly well with the field measurements. It is concluded that there are three main reasons for the decline in the metal, PCB and PAH concentrations in the highly dynamic surface sediments of the Dutch coastal zone: (1) the decrease in the load from various sources; (2) the sedimentation and mixing of less polluted suspended matter into the active sediment layer; and (3) the washing out of previously deposited more heavily polluted particles.     

Organic sedimentation in the water column in the Arabian Sea: Relationship between the lipid composition of small and large-size,surface and deep particles

Small and large-size particulates (>50 μm) have been collected during the ORGON IV cruise in the Arabian Sea (North-western Indian Ocean), using conventional metallic bottles and vertical near-surface (200-0 m) and deep (below 1000 m) plankton nets. This area presents remarkable conditions for studying organic sedimentation: a high superficial productivity, low oxygen content of seawater and low terrigenous inputs.Lipids have been quantified and analysed by gas-liquid chromatography and gas-liquid chromatography/mass spectrometry for fatty acids, saturated hydrocarbons and sterols. The distribution of biological species, size range and biological nature have been determined through microscopic examination.Principal results are presented in a geochemical context: small and large-size particles belong to two different reservoirs both for concentrations and chemical compositions.The comparison between the size range of particles and chemical characteristics observed through analyses of net and bottle samples emphasizes the importance of large-size particles in the geochemical process of material transfer between surface and sediment. For various lipids, this transfer concerns freshly biosynthesized molecules such as long-chain polyunsaturated fatty acids, pristane and sterols, compounds which are of high metabolic value for abyssal and pelagic organisms.The lipid fluxes, determined from in situ concentrations, and settling velocity estimated from the size range of deep particulate material, are compared to those reported by different authors using other sampling procedures for deep settling matter.     

Behaviour of no. 2 fuel oil in the water column of controlled ecosystems

Four experiments were carried out to determine the effect of different temperatures, light levels and biological activities on the residence times of petroleum hydrocarbons. No. 2 fuel oil was added as a seawater dispersion to give an initial concentration of 150 to 300 μg/litre in the water columns of large, outdoor marine microcosms. Hydrocarbons in water samples fractionated on passage through glass fibre filters (0·3 μm pore size) according to the solubilities, so that 80–90 % of the aromatics entered the filtrate while all of the saturates were trapped by the filter. The removal of oil compounds from the water columns was exponential, with rates which appeared to be determined chiefly by the temperature. The half life of total hydrocarbons varied from more than 10 days in March to ～30 h in July and September. Volatilisation was hypothesised to be an important removal mechanism for the 40–60% of the saturates which were not sedimented with suspended particulate matter. In warm water, the residence times of normal alkanes were increased up to 50 % by poisoning the water column, but no similar increase was noted for the bulk of the F₁ hydrocarbons. Aromatic (F₂) hydrocarbons appeared to be removed slowly volatilisation from cold water ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{> 200 h}$) and rapidly by biodegradation from warm water ($\text{t}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{< 40 h}$).     

A description of chloride cell and kidney tubule alterations in the flatfish Solea senegalensis exposed to moderately contaminated sediments from the Sado estuary (Portugal)

The effects of sediment-bound contaminants on kidney and gill chloride cells were surveyed in juvenile Solea senegalensis exposed to fresh sediments collected from three distinct sites of the Sado Estuary (Portugal) in a 28-day laboratorial assay. Sediments were analyzed for metallic contaminants, polycyclic aromatic hydrocarbons and organochlorines as well as for total organic matter, redox potential and fine fraction. The potential for causing adverse biological effects of each surveyed sediment was assessed by comparison of contaminant levels to available guidelines for coastal sediments, namely the Threshold Effects Level (TEL) and the Probable Effects Level (PEL). The Sediment Quality Guideline Quotient indices (SQGQ) were calculated to compare the overall contamination levels of the three stations. A qualitative approach was employed to analyze the histo/cytopathological traits in gill chloride cells and body kidney of fish exposed to each tested sediment for 0, 14 and 28 days. The results showed that sediment contamination can be considered low to moderate and that the least contaminated sediment (from a reference site, with the lowest SQGQ) caused lesser changes in the surveyed organs. However, the most contaminated sediment (by both metallic and organic xenobiotics, with highest SQGQ) was neither responsible for the highest mortality nor for the most pronounced lesions. Exposure to the sediment presenting an intermediate SQGQ, essentially contaminated by organic compounds, caused the highest mortality (48%) and the most severe damage to kidneys, up to full renal necrosis. Chloride cell alterations were similar in fish exposed to the two most contaminated sediments and consisted of a pronounced cellular hypertrophy, likely involving fluid retention and loss of mitochondria. It can be concluded that sediment contamination considered to be low or moderate may be responsible for severe injury to cells and parenchyma involved in the maintenance of osmotic balance, contributing for the high mortality levels observed. The results suggest that sediment-bound organic contaminants such as PAHs (polycyclic aromatic hydrocarbons) and PCBs (polychlorinated biphenyls) may be very toxic to the analyzed organs, especially the kidney, even when present in low-risk concentrations.     

夏季浙江沿岸陆架区泥沙输运机制

基于2014年夏季浙江沿岸陆架区的水文、泥沙、底质沉积物等实测资料,运用物质通量分析方法和Gao-Collins粒径趋势分析法,探讨了泥沙的输运通量、输运方向、动力机制及净输运趋势。夏季,近岸含沙量规律性较强,由西至东逐渐降低,由南至北逐渐升高,且与潮流有非常好的对应关系,呈现出明显的潮周期变化特征。研究区净悬沙通量自岸向外海迅速变小,悬沙输运中平流输运占主导地位,其次是垂向净环流对悬沙输运的影响,近岸海域表现为向海输沙,30 m以深海域表现为东北向输沙,同时台湾暖流的屏障作用也影响了悬沙向海扩散。粒径趋势分析显示浙江沿岸陆架表层沉积物的长期输运机制为由东北向西南输运,在流系以及海底地形的影响下,中部海域出现粒径趋势较弱的沉积中心。而在夏季,悬浮泥沙主要为平行岸线向东北输运,估算每天进入研究海域的净悬浮泥沙约为1.9×106 t。