Trace organic contaminants and their sources in surface sediments of Santa Monica Bay,California, USA

Spatial distribution of selected contaminants in the surface sediments of Santa Monica Bay (SMB), California was investigated. Sediments were analyzed for DDTs (DDT and metabolites), polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), linear alkylbenzenes (LABs) and coprostanol. Effluent samples from the Hyperion Treatment Plant (HTP), which discharges treated municipal wastewater effluents into SMB, were also analyzed. The inter-correlation in the distribution trends of contaminants was examined. The concentrations of contaminants were interpolated in a geographic information system to visualize their spatial distribution in the Bay. Inventories of the contaminants were also estimated.The concentrations of coprostanol, LABs and PCBs are very high only in the vicinity of the sewage outfall whereas PAHs and DDTs occur widespread in the Bay. The poor correlation of DDTs with LABs, PAHs or coprostanol content confirms the historic origin of DDTs and their absence in the contemporary wastewaters. Moderate correlation of DDTs with PCBs implies historic deposits as a major origin of PCBs. There are hot spots of DDTs at water depths of 60 and 100 m and the inventory of DDTs in Bay sediments is insignificant compared to that estimated in the Palos Verdes Shelf which extends from the southern edge of Redondo Canyon around Palos Verdes Peninsula. The concentration of toxic contaminants was examined according to published sediment quality guidelines. About 20 stations contain p, p′-DDE and/or total DDTs above ERM and, PCBs between ERL and ERM indicating potential for adverse biological effects.     

Temporal and spatial distributions of contaminants in sediments of Santa Monica Bay,California

Contaminant inputs from wastewater discharge, a major source of contamination to Santa Monica Bay (SMB), have declined drastically during the last three decades as a result of improved treatment processes and better source control. To assess the concomitant temporal changes in the SMB sediments, a study was initiated in June 1997, in which 25 box cores were collected using a stratified random sampling design. Five sediment strata corresponding to the time intervals of 1890-1920, 1932-1963, 1965-1979, 1979-1989, and 1989-1997 were identified using (210)Pb dating techniques. Samples from each stratum were analyzed for metals, 1,1,1-Trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) and its metabolites (DDTs), polychlorinated biphenyls (PCBs), and total organic carbon (TOC). Samples from the 1965-1979, 1979-1989, and 1989-1997 strata were also analyzed for polycyclic aromatic hydrocarbons (PAHs) and linear alkylbenzenes (LABs). Sediment metal concentrations increased from 1890-1979 and were similar during the time intervals of 1965-1979, 1979-1989, and 1989-1997, although the mass emissions of trace metals from sewage inputs declined substantially during the same time period. Trace organic contamination in SMB was generally highest in sediments corresponding to deposition during the years of 1965-1979 or 1979-1989 and showed a decline in concentration in the 1989-1997 stratum. Temporal trends of contamination were greatest in sediments collected from areas near the Hyperion Treatment Plant (HTP) outfall system and on the slope of Redondo Canyon. The highest contaminant concentrations were present in sediments near the HTP 7-mile outfall in the 1965-1979 stratum. Elevated trace metal and organic concentrations were still present in the 1989-1997 stratum of most stations, suggesting that sediment contaminants have moved vertically in the sediment column since sludge discharges from the 7-mile outfall (a dominant source of contamination to the bay) ceased in 1987. The widespread distributions of DDTs and PCBs in SMB and highly confined distribution of LABs around the HTP outfall system were indicative of a dispersal mechanism remobilizing historically deposited contaminants to areas relatively remote from the point of discharge.     

Micropollutants and organic carbon concentrations in surface and deep sediments in the Tunisian coast near the city of Sousse.

A radioactive tracer was used to map the plume of the effluent of a municipal water treatment plant located on the Tunisian coast, close to the city of Sousse. A sampling campaign was programmed on the basis of the radioactivity distribution. The extent of sediment contamination was investigated to determine the impact of the plant effluent. Organic carbon and organic micropollutants (PCBs and chlorinated pesticides) were analysed on resuspendable particulate matter, on grab and core sediments. The area distributions of different compounds analysed were studied and relationships were investigated between radioactivity and organic carbon and micropollutant data. The study shows that sludge particles are deposited and accumulate in the zone south of the effluent outlet, contaminating sediments. Good correlations were found which demonstrate the efficiency of the technique used to plan the sampling and the link between organic carbon and organic micropollutants.     

Chlorinated hydrocarbons in the open mediterranean ecosystem and implications for mass balance calculations

Studies on the biogeochemical cycling of organic contaminants in the Mediterranean have demonstrated the importance of polychlorinated biphenyls (PCBs) as relatively stable markers of recent anthropogenic influence in ocean systems. This paper presents results of hydrocarbon analyses of deep water profiles, sediments and their associated surface flocculent layers, and zooplankton samples collected in the western basin. Seawater concentrations were higher than those previously reported for the eastern basin and were consistent with the presence of industrial sources in the northwestern segment. In the water column, the percent of PCBs associated with filterable particles was related to the ambient concentrations of total suspended matter, distance from coastal input sources and on depth. The occurrence of deep water residues primarily in the dissolved phase and observations of subsurface maxima in seawater concentrations during a season of high surface productivity were consistent with the predictions of vertical transport models based on residues associated with sinking particles and equilibrium partitioning. Flocculent layers at the sea/sediment interface contained two and three orders of magnitude, respectively, more PCBs and petroleum hydrocarbons (PHCs) than their associated surface sediments. The flocculent particles also contained several biogenic hydrocarbons presumably originating from plankton and relatively soluble and labile contaminants such as hexachlorohexane isomers (HCH) and hexachlorobenzene (HCB), thus confirming that the majority of the flux of hydrocarbons to sediments is carried on rapidly settling large particles. By combining the sediment and flocculents data with published sedimentation rates for the deep basins of the Mediterranean, a yearly flux rate of PCBs to the open sea sediments was estimated as 13 μg m⁻² yr⁻¹ or less than half of the rate measured in a coastal sediment trap experiment. Analytical results are placed in the context of other distribution data for PCBs and long-term flux studies to construct a partial mass balance budget for this semi-enclosed sea. The computed coastal inventory showed that about 35% remains suspended in the water column while the majority of residues are deposited in coastal sediments. However in the open sea, the deep water column may contain up to 70% of the total inventory and may be a continually increasing reservoir of stable organic contaminants reaching the ocean. The budget shows that priority for improved research and monitoring efforts in ocean systems should be given to continued advancement in techniques for the precise measurement of deep water concentrations and for measuring current atmospheric inputs and sedimentation rates in order to develop more accurate ocean flux models.     

Evaluation of the impacts of land-based contaminants on the benthic faunas of Jakarta Bay,Indonesia

To evaluate the impact of land-based contaminants on benthic faunas, as part of the Land-Ocean Contamination Study (LOCS), a study transect was established in Jakarta Bay, Indonesia during the 1996 southeasterly monsoon. The transect extended 72 km between the city's main port, Tanjung Priok, and the Pilau Seribu Island chain in the Java Sea. The dissolved concentrations of Pb, Cu, Zn, Cr and Ni in seawater, in suspended particulate matter (SPM) and surficial sea bed sediments were measured along the transect at nine sites. In addition, metal concentrations were measured in tissues of the corals Goniopora lobata and Lobophyllia hemprichii at five sites, and of the green mussel, Perna viridis at six sites. An assessment of the impact of contaminants on the faunas was made using a biomarker approach, employing coral community analysis and lysosomal stability with Perna viridis. The results of the study showed two main trends. The distributions of metals dissolved in seawater, in SPM, and in the coral and mussel tissues were similar, and failed to show a consistent graded response from inshore to offshore sites. This suggests that the concentration of metals in waters is the primary route for metal uptake by the coral and mussel tissues. By way of contrast, a clear offshore increase in coral generic diversity, coral cover, coral colony numbers and neutral-red retention time (lysosomal stability) was observed, suggesting increasing nearshore stress. Whilst the coral community stucture may reflect the seasonally-averaged metal distributions in the bay (shown by the metal content of sea bed sediments which increase shorewards), it is more likely that the coral community structure and lysosomal biomarker are responding principally to other nearshore stresses, such as sediment and nutrient loading of water (sewage) or, more likely, organic contaminants such as oils and other hydrocarbons.     

Organic matter origin and distribution in suspended particulate materials and surficial sediments from the western Adriatic Sea (Italy)

In this study, organic carbon (OC), total nitrogen (TN), stable carbon isotopic (δ¹³C_OC) and CuO reaction product compositions were used to identify the sources of organic matter (OM) and to quantify the relative importance of allochthonous and autochthonous contributions to the western Adriatic Sea, Italy. Suspended particulate material (195 samples) and surficial sediments (0–1 cm, 70 samples) from shallow cross-shelf transects were collected in February and May 2003, respectively. Vertical water column profiles were acquired along the same transects. Data include depth, potential temperature, salinity, density and chlorophyll fluorimetry.Along the western Adriatic shelf in the near-shore region, the phytoplankton growth was influenced by dynamics of the buoyant plumes from the Po and Appennine rivers. A small amount of very fine terrigenous material remained suspended within the coastal current and was exported southward along the shelf to the slope. High variability in the bulk composition was detected in the Po prodelta surficial sediments, whereas the western Adriatic shelf, although a larger area, exhibited a narrower range of values.A significant decoupling was observed between suspended particles in the water column and surficial deposits. The organic material collected in the water column was compositionally heterogeneous, with contributions from marine phytoplankton, riverine–estuarine phytoplankton and soil-derived OM. Frequent physical reworking of surficial sediments likely leads to the efficient oxidation of marine OC, resulting in the observed accumulation and preservation of refractory soil-derived OC delivered by the Po and Appennine rivers.     

Anthropogenic trace metals in sediment and settling particulate matter on a high-energy continental shelf (Sydney,Australia)

The anthropogenic contribution of trace metals to settling particulate matter (SPM) and surficial sediments was determined on the high-energy continental shelf adjacent to Sydney, Australia. Settling particulate matter and surficial sediment was collected in the vicinity of a major sewage outfall and at five control sites on the middle shelf (80-100 m water depth). Sediment traps were deployed on 10 occasions for up to 2 weeks during the summer and winter of 1995 and SPM was analyzed for Ag, Co, Cr, Cu, Fe, Mn, Ni, Pb and Zn. Cobalt, Fe, Mn and Ni act conservatively in SPM and in sediments regionally and are used as normalizing elements to determine anthropogenic enrichment. Surficial sediments and SPM are enriched in Ag, Cr, Cu, Pb and Zn near a major ocean outfall and at four of the five control sites, although sewage particles contribute < 5% of trace metals in the total sample. Silver is the most sensitive trace metal tracer for establishing the presence of sewage particulate matter. Sewage particulate matter flux near the outfall was estimated using a two end-member mixing model and is below 0.5 g m(-2) day(-1) during all deployment periods. The mean sewage particulate matter flux at sampling locations 30 km and 60 km north of the outfall are <0.13 g m(-2) day(-1) and <0.01 g m(-2) day(-1), respectively, indicating an efficient dispersal of anthropogenic material on this high energy continental shelf.     

Reconstruction of contaminant trends in a salt wedge estuary with sediment cores dated using a multiple proxy approach

The Taunton River is a partially mixed tidal estuary in southeastern Massachusetts (USA) which has received significant contaminant inputs, yet little information exists on the history of discharge and the subsequent fate of these contaminants. Three sediment cores taken along a transect were analyzed, reconstructing the spatial and temporal trends of pollution in the estuary. A combination of radiometric dating, contaminant markers, and storm layers from major hurricanes were used to establish age models and sedimentation rates. Age estimates obtained from the different dating methods compared well, establishing an accurate history of contaminant release to the estuary. Polycyclic aromatic hydrocarbons (PAHs) were present in one core at depths corresponding to the early 1860s, earlier than previously established dates of introduction. Temporal and spatial trends of Cr, Cu, Hg and Pb indicated multiple sources of varying input to the river. Polychlorinated biphenyls (PCBs) were present in each of the cores from the 1930s onward, with elevated levels still present in surficial sediments at several sites. A unique organic compound, Topanol, which was produced locally was used as a tracer to track contaminant transport in the river. Tracer data indicates that contaminants are still being transported and deposited to surficial sediments at high concentrations well after their discharge. This reconstruction demonstrates the utility of using multiple dating proxies where often the sole use of radiometric dating techniques is not an option and provides insights into the fate of contaminants discharged decades ago but continue to represent environmental risks.     

Municipal wastewater contamination in the southern california bight: Part I—metal and organic contaminants in sediments and organisms

Sediments and organisms were examined for concentrations of organic and metal contaminants from near the Los Angeles County (JWPCP) municipal outfall at Palos Verdes (PV) station 7-3, the Los Angeles City (Hyperion) municipal outfall at Santa Monica Bay (SMB) station 6-4 and reference station SMB 2–3 near Malibu Beach. Flows and mass emission rates of suspended solids, PCBs, Cd and Zn were similar at the two outfalls. Mass emission rate of copper was almost twice as high from Hyperion as from JWPCP, while mass emission rate of DDTs was an order or magnitude higher from JWPCP than from Hyperion.Surficial sediments at PV 7-3 were enriched in most contaminants relative to SMB 6-4 and relative to the mass emission rates of contaminants from the JGVPCP and Hyperion outfalls. Some of this enrichment could be accounted for by the greater accumulation of organic material, measured as total volatile solids, at PV 7-3 relative to SMB 6-4. Some might be accounted for by resurfacing of more contaminated historical deposits buried at PV 7-3. Some of the enrichment of DDTs relative to PCBs could be accounted for by the greater abundance of oxygenated metabolites of PCBs (PCBols) relative to DDTs (DDTols) in sediments.The degree of contamination of organisms by DDTs increased with proximity to PV 7-3 but contamination by PCBs was similar at PV 7-3 and SMB 6-4. DDT concentrations in fish livers ranged from 12 ± 4 ( ) mg/wet kg in longspine combfish from SMB 2–3 to 610 ± 105 (n = 5) mg/wet kg in Pacific sanddab from PV 7-3. DDT concentrations in fish gonads ranged from 0·003 ± 0·003 (n = 5) mg/wet kg in yellowchin sculpin from SMB 6-4 to 1.5 ± 6 (n = 3) mg/wet kg in Pacific sanddabs from PV 7-3. PCB concentrations in fish livers ranged from 1·2 ± 0·4 (n = 4) mg/wet kg in yellowchin sculpin from SMB 2–3 to 16 ± 3 (n = 6) in Pacific Sanddab from SMB 6-4. DDT and PCB concentrations in invertebrate hepatopancreas were only slightly lower than those in fish livers. DDTols and PCBoIs comprised an average of 91 % of the total of parent compounds and oxygenated metabolites in sediments and 66 % in livers and hepatopancreas. Trace metals were frequently decreased in livers and hepatopancreas from near outfalls even though they were highly elevated in sediments.Comparison of sediment and tissue chlorinated hydrocarbon data with that from Elliot and Commencement Bays, Puget Sound, indicated that none of the southern California coastal stations considered in this study were sufficiently lacking contamination to be considered as adequate control sites.     

Coprostanol levels and organic enrichment in sediments of the Bilbao estuary (north of Spain)

An assessment was made of the distribution of the faecal sterol coprostanol (COP) in sediments in the Bilbao estuary. Concentrations of COP ranged from 135.15 to 10.77 μg g⁻¹ dry weight, from the inner to the open estuary, with a mean value of 51.43 μg g⁻¹; the highest concentrations were found near the mouths of several tribularies flowing into the estuary. Comparisons with other published values indicate that sediments from the Bilbao estuary are affected by sewage pollution in a similar degree to that reported for other estuaries in the world. Organic enrichment and anaerobic sediment conditions prevail in three-fourths of its watercourse bed. Since the spatial distribution of several organic sedimentary parameters could be clearly correlated with COP levels, we can conclude the existence of major pollution by the addition of untreated sewage, coming from mainly domestic sources. The implementation of a sewerage treatment plan by the local water authority needs the monitoring of reliable sewage tracers, such as faccal sterols, to assess the effectiveness of the plan in reducing the effects of pollution.     

Linear alkyl benzenes (LABs) in sediments of Port Phillip Bay (Australia)

Linear alkyl benzenes (LABs), which have been proposed as markers of the hydrocarbon component of domestic wastes, were measured in sediments from three areas of Port Phillip Bay (Australia). The concentrations found (0–19 μg g⁻¹) were generally lower than those reported for other coastal sediments from the USA and Japan. This is thought to reflect the small quantity of domestic wastes entering Port Phillip Bay.Compositional profiles showed that both physical and biological processes had acted to remove LABs during deposition.At one site, unusual alkyl benzene compounds, but no conventional LABs, were detected. These compounds were probably synthesised terrestrially by the bacteria of a nearby sewage farm.     

Coprostanol in a Sediment Core from the Anoxic Tan-Shui Estuary, Taiwan

A short sediment core with a length of approximately 40 cm taken from the anoxic Tan-Shui estuary, Taiwan, was analysed for extractable and bound coprostanol (5β-cholestan-3β-ol), cholestanol (5α-cholestan-3β-ol) and cholesterol (cholest-5-en-3β-ol). Extractable Σcoprostanol and cholestanol concentrations exhibit an abrupt change at a depth of about 20 cm, which supposedly marks the time when a sewage treatment plant became operational in the estuary in 1980. The Σcoprostanol/cholesterol and cholestanol/cholesterol ratios are comparatively higher in sediment than in the sewage effluent, implying some degree of diagenesis in the extractable phase. Anoxicity must have played a crucial role in the preservation and diagenesis of the sterols. In the upper layer (c. top 20 cm), the concentrations of extractable Σcoprostanol, normalized to total organic carbon (TOC), increase down the core. Extractable cholestanol exhibits the same trend, but extractable cholesterol shows the opposite trend. This indicates cholesterol reduction to these two stanols. In addition, both bound Σcoprostanol/TOC and cholestanol/TOC display a decreasing trend with core depth and no pronounced concentration change at 20 cm depth. The averages of percent bound sterols are in the following order: cholesterol > coprostanol>cholestanol.     

Metal sources to the Baltic clam Macoma balthica (Mollusca: Bivalvia) in the southern Baltic Sea (the Gulf of Gdansk)

Metal concentrations of Cu, Fe, Mn, Ni, Pb and Zn in an infaunal facultative deposit-feeding bivalve, the Baltic clam Macoma balthica, in the Gulf of Gdansk (southern Baltic Sea) were assessed and compared to selected concentrations of metals in the environment. Between October 1996 and September 1997, dissolved and easy extractable (by 1M HCl) metal fractions of total suspended particulate matter (TPM) in the overlying water and of surficial sediments (<63 microm) were measured monthly at five sublittoral sites in the Gulf of Gdansk, and accumulated tissue metal concentrations in M. balthica were determined simultaneously. The study highlights the importance of sediment geochemistry as a factor modifying ambient trace metal bioavailabilities. Surficial sediments appeared to contribute most to the accumulation of Cu and Pb in M. balthica, reflecting the high metal availability in the Gulf. Assimilation of Cu from sediments is controlled by Mn components possibly through an inhibitory effect of Mn oxyhydroxides, while Pb accumulation from sediments depends on the organic content of the sediment. A dual metal uptake pathway, with a suspended particulate-bound fraction and surficial sediments, was apparent for Mn and Zn. Partitioning of Mn in sediments was related to the concentration of labile Fe, with increased levels of Fe tending to inhibit the accumulation of Mn by the clam. Tissue accumulated Zn might have been altered by the clam's internal regulation, making Zn tissue concentrations, to some degree, independent of its environmental level. The principal source of Ni accumulated by the clams exists in the soluble phase.     

A strategy for monitoring of contaminant distributions resulting from proposed sewage sludge disposal at the 106-mile ocean disposal site

It has been proposed that future ocean disposal of sewage sludge from the US east coast be done at a site beyond the edge of the continental shelf. In anticipation of that, a monitoring strategy has been developed to determine the average spatial distribution of contamination. The strategy is an iterative series of measurements developed from models of sludge dispersion and settling which are based on characteristics of the disposal site and sewage sludge. Once disposal is initiated at the site, the strategy requires sampling the upper mixed layer at 36 stations, mostly within 100 km of the site, and deployment of near-bottom sediment traps along a line extending 300 km away from the site. Based on initial results, subsequent sampling locations will be selected to refine estimates of the detectable extent of sludge-derived contamination. The sludge constituents which can be used to detect sludge in water at a dilution of 10⁶ and sludge in sediment traps when diluted by 100 with natural material include zinc, PCBs, coprostanol and spores of the bacterium Clostridium perfringens. Other synthetic organic compounds, besides PCB, may prove to be useful tracers.     

Diagenetic fate of organic contaminants on the Palos Verdes Shelf, California

Municipal wastes discharged through deepwater submarine outfalls since 1937 have contaminated sediments of the Palos Verdes Shelf. A site approximately 6–8 km downcurrent from the outfall system was chosen for a study of the diagenetic fate of organic contaminants in the waste-impacted sediments. Concentrations of three classes of hydrophobic organic contaminants (DDT+metabolites, polychlorinated biphenyls (PCBs), and the long-chain alkylbenzenes) were determined in sediment cores collected at the study site in 1981 and 1992. Differences between the composition of effluent from the major source of DDT (Montrose Chemical) and that found in sediments suggests that parent DDT was transformed by hydrolytic dehydrochlorination during the earliest stages of diagenesis. As a result, p,p′-DDE is the dominant DDT metabolite found in shelf sediments, comprising 60–70% of ΣDDT. The p,p-DDE/p,p′-DDMU concentration ratio decreases with increasing sub-bottom depth in sediment cores, indicating that reductive dechlorination of p,p′-DDE is occurring. Approximately 9–23% of the DDE inventory in the sediments may have been converted to DDMU since DDT discharges began ca. 1953. At most, this is less than half of the decline in p,p′-DDE inventory that has been observed at the study site for the period 1981–1995. Most of the observed decrease is attributable to remobilization by processes such as sediment mixing coupled to resuspension, contaminant desorption, and current advection. Existing field data suggest that the in situ rate of DDE transformation is 10²–10³ times slower than rates determined in recent laboratory microcosm experiments (Quensen, J.F., Mueller, S.A., Jain, M.K., Tiedje, J.M., 1998. Reductive dechlorination of DDE to DDMU in marine sediment microcosms. Science, 280, 722–724.). This explains why the DDT composition (i.e. o,p′-, p,p′-isomers of DDE, DDD, DDT) of sediments from this site have not changed significantly since at least 1972. Congener-specific PCB compositions in shelf sediments are highly uniform and show no evidence of diagenetic transformation. Apparently, the agents/factors responsible for reductive dechlorination of DDE are not also effecting alteration of the PCBs. Two types of long-chain alkylbenzenes were found in the contaminated sediments. Comparison of chain length and isomer distributions of the linear alkylbenzenes in wastewater effluent and surficial sediment samples indicate that these compounds undergo biodegradation during sedimentation. Further degradation of the linear alkylbenzenes occurs after burial despite relatively invariant isomer compositions. The branched alkylbenzenes are much more persistent than the linear alkylbenzenes, presumably due to extensive branching of the alkyl side chain. Based on these results, p,p′-DDE, PCBs, and selected branched alkylbenzenes are sufficiently persistent for use in molecular stratigraphy. The linear alkylbenzenes may also provide information on depositional processes. However, their application as quantitative molecular tracers should be approached with caution.     

Spatial Distribution of Polychlorinated Biphenyls （PCBs） Contaminants in the Tidal-flat Sediments of Yangtze Estuary

1 IntroductionYangtze River estuary is the biggest one in China, and there are domestic and manufactural rubbish disposal sites for Shanghai city in this tidal-flat. The Shanghai city, the whole Yangtze delta, or even all the Yangtze basin, will be PCBs contaminant sources of Yangtze estuary tidal-flat[1]. According to literatures so far, only two investigations for waters have included PCBs in the Yangtze estuary[2, 3]. No PCBs pollution of the tidal-flat sediments has been reported…     

Variation of reactivity of particulate and sedimentary organic matter along the Zhujiang River Estuary

To investigate organic matter source and reactivity in the Zhujiang River (Pearl River)Estuary and its adjacent areas, particulate organic carbon (POC), particulate hydrolysable amino acids (PHAA), and Chl a during two cruises in July 1999 and July 2000 were measured. The highest POC and PHAA concentration was observed in the waters with maximum Chl a. The spectra distribution,relative content (dry weight in milligram per gram), PHAA-C% POC and other indicators such as the ratios of amino acids vs. amino sugars (AA/AS) and glucosamine vs. galactosamine (Glum/Gal) suggested that particulate amino acids in the water column and sediments in the Zhujiang River Estuary were mainly derived from biogenic processes rather than transported from terrestrial erosion. In inner estuary where high turbidity was often observable, organic matter was mainly contributed by re-suspension of bottom sediments with revealed zooplankton, microbial reworked characteristics, which suggest that these organic matters were relatively “old“. In the estuarine brackish region, organic matter in water column is mainly contributed by relatively fresh, easily degradable phytoplankton derived organic matter.During physical - biological processes within the eastuary, organic matter derived from phytoplankton was subjected to alteration by zooplankton grazing and bacterial reworking.     

Nearshore sediment characteristics and formation of mudbanks along the Kerala coast,southwest India

In order to gain insight into the formation dynamics of mudbanks off the Kerala coast of India, extensive surveying of the nearshore bathymetry along with sediment characterization was undertaken. The textural and geotechnical properties of the surficial sediments of a mudbank were determined during pre-monsoon, monsoon, and post-monsoon periods. The mudbank sediments were clayey silts with high water and organic carbon contents, high Atterberg limits, and low bulk density, and therefore very susceptible to entrainment. During the monsoon, the mudbank regime was characterised by enhanced turbidity and a benthic fluff layer, triggered by the increasing swell of the early monsoon period. Re-suspension exposed a more consolidated, previously sub-bottom, layer which exhibited lower water content and greater shear strength than the pre-monsoon seabed. Texturally, the monsoon seabed was similar to the pre-monsoon seabed, with the same modal grain size, but the proportions of sand and coarse silt increased nearshore, while the proportions of fine and very fine silt increased offshore. There was a seaward-fining textural gradient at all times, but this became pronounced during the monsoon period. Paradoxically, the monsoonal seabed displayed greatly reduced wet bulk density. It is hypothesized that this was due to the presence of gas, probably methane, in the sediments (while the pre-monsoon sediments were fully saturated, the monsoon sediments were only 83% saturated). We speculate that the gas was forced into the surficial sediments either by wave pumping (at the onset of the monsoon) or by seaward-flowing subbottom freshwater (derived from monsoonal rains). With the waning of the monsoon, the benthic fluid mud layer rapidly disappeared and the seabed returned to its pre-monsoon state as suspended sediments were redeposited. The mudbank regime is therefore essentially an in situ phenomenon. It is suggested that the mudbanks are palimpsest, marshy, lagoonal deposits, rich in organic matter and derived gas, that were submerged after a marine transgression. The surficial sediment is annually entrained during the monsoon, but erosion is limited by the formation of the benthic fluid mud layer, which attenuates wave generated turbulence. Although some fine sediment disperses alongshore and offshore, most is returned to the seabed as the monsoon declines.     

有机污染物在不同沿海沉积环境中积累的差异性

以浙江沿海水域为研究区域,在系统地测定水体与沉积物中有机污染物种类的基础上,研究了表层沉积物中有机污染物的积累与沉积环境、沉积物矿物组成和排放环境因素之间的相互关系.结果显示,沿海水体和表层沉积物中主要存在的有机污染物有石油烷烃类化合物、邻苯二甲酸酯化合物、有机硅氧链类化合物、氯代苯酚类、苯醚类和胺类化合物等6大类,它们在表层沉积物中的积累强度呈现出河口大于沿岸大于强潮汐河沉积环境的趋势,但在相同沉积环境的沉积物中有机污染物的积累强度存在一定的差异,这说明有机污染物在沿海沉积物中的积累除与沉积环境有关外,还与区域有机污染物的排放特点有关.     

Sterols as markers of sewage contamination in a tropical urban estuary (Guanabara Bay, Brazil): space–time variations

Guanabara Bay, located adjacent to Rio de Janeiro in Brazil, is highly contaminated by substances derived from domestic and industrial effluents as well as from agricultural runoff. In the present work, sedimentary coprostanol and other faecal sterols were used to investigate historical trends in sewage contamination. Sediment cores were collected from eight different (and characterized) locations in the bay and were sectioned into dated segments. Organic carbon was determined by dry combustion and sterols were separated and quantified by GC/MS. The space-distribution of organic carbon and faecal sterol concentrations generally coincided with the presence of known pollution sources. Concentrations of coprostanol as high as 40 μg g⁻¹ were found, indicating areas of severe sewage contamination. Faecal sterol ratios, commonly used as tools to investigate contamination in temperate environments, however, were found to have limited applicability to this tropical estuarine system, probably due to the influence of intensive primary production and microbial processes.