Structure and chemistry of sediments in Belfast Lough,a semi-enclosed marine bay

In a study of the benthic environment of Belfast Lough the structure of the subtidal sediment was examined along with its content of organic matter and selected metals (Cr, Mn, Ni, Cu, Zn, Pb). A wide range of sediment types occurred within the lough but the mean grain sizes for individual sites lay predominantly within the size classes of fine sand, very fine sand and silt. The content of organic matter and metals in the sediments showed strong positive correlations with each other and with the content of silt/clay. Both organic matter and metals decreased in concentration in a seawards direction. The content of organic matter lay generally within the range of 1–5% which is normally associated with shelf sediments, but constituted up to 12% of the sediment in the docks area. Likewise, metals were usually within the range reported within other nearshore coastal waters of the U.K., but sediments in the docks area and inner lough were enriched with several metals. Cluster analysis identified four major subdivisions in the lough which were distinctly different in their contents of silt/clay, organic matter and metals.     

Characterization of minerals and organic phosphorus species in marine sediments using soft X-ray fluorescence spectromicroscopy

Phosphorus Near Edge X-ray Fluorescence Spectroscopy (P-NEXFS) data were collected on phosphorus containing phases including organic and inorganic compounds and minerals. Although phases containing P in the plus five oxidation state P(V) in a tetrahedral PO₄ structure have similar primary fluorescence peak positions, the size, shape, and positions of secondary spectral features are diagnostic for different compounds and minerals. In particular, calcium phosphates exhibited a notable post-peak shoulder at 2154.5 eV, while oxidized iron phosphates had a distinctive pre-peak feature at 2148 eV. Polyphosphates have a broad secondary peak located approximately 2 eV higher in energy than a similar feature in phosphate esters and diesters. Compounds containing P(V) in structures other than PO₄ tetrahedra such as phosphonates have a primary peak shifted about 1 eV lower than corresponding organo-phosphates. Organo-phosphates with P in the plus three oxidation state P(III) such as phosphines had primary fluorescence peaks shifted still further down in energy (2–3 eV). The substitution of aromatic carbon groups in close proximity to P structures in organic compounds generated both pre- and post-peak features as well as a number of secondary peaks. In addition, X-ray fluorescence mapping of P, Si, Al, Mg, and Na was conducted on a marine sediment sample with sub-micron spatial resolution. Phosphorus was heterogeneously distributed in the sample and not correlated on a broad scale with any other element examined. Much of the P present in the sample was located in small, 0.6–8 μm size, P-rich domains. Several P-rich regions were examined with P-NEXFS using a focused beam with 60 nm resolution and were found to consist of either calcium phosphate or polyphosphate phases. The presence of significant polyphosphate-dominated regions in a marine sediment sample supports the recent observations that such phases can play an important role in marine P cycling. The combination of fluorescence mapping and P-NEXFS data collection on fine particles provides a powerful new tool for environmental phosphorus studies.     

Chemistry of modern sediments in a hypersaline lagoon,north of Jeddah,Red Sea

Previous studies of modern peritidal sedimentary environments of the Red Sea, such as hypersaline lagoons and sea-marginal flats, have concentrated on its northern part, particularly in the Gulf of Aqaba. However, little is known about lagoon sediments in other localities along the Red Sea coastal stretches. This paper deals with the chemical characteristics of the sediments of a hypersaline (Ras Hatiba) lagoon, north of Jeddah, Saudi Arabia. The chemistry of hypersaline lagoon sediments is considerably changed following the modifications to the water chemistry by evaporation and precipitation.Ras Hatiba lagoon is a hypersaline elongated water body connected to the Red Sea by a narrow and shallow opening. The total area of the lagoon is c. 30 km².Coarse bioclastic sands are dominant in the lagoon and mostly surround lithified calcareous grounds. However, fine silt and clay sediments are present in separate patches. The sediments are rich in carbonates (average 78·5%) and organic carbon (average 7·3%), although they are negatively correlated. Calcium (average 25·1%) and magnesium (average 10·8‰) show a similar distribution pattern in the lagoon sediments. Strontium (average 5·2‰) is positively correlated with calcium. Sodium and potassium are relatively highly concentrated in the sediments (average 118 ppm and 173 ppm, respectively). Magnesium and strontium are of prime importance in the process of mineralization and diagenesis.The sabkha formation surrounding the lagoon is of low carbonate and organic carbon content, compared with the lagoon sediments, whilst it is characterized by high magnesium, sodium and potassium concentrations.Ras Hatiba lagoon sediments and sabkha resemble those of the northern Red Sea in the Gulfs of Aqaba and Suez and the Arabian Gulf in their major sedimentological and chemical characteristics.     

大鹏澳养殖区柱状沉积物中氮、磷的分布特征及污染状况研究

为研究海水养殖对海湾沉积物的累积影响, 对大亚湾的大鹏澳养殖区沉积物柱状样中总氮、总磷和有机碳的含量及剖面分布特征进行了研究, 并探讨了海水养殖区沉积物中氮、磷的污染状况。结果表明, 网箱养殖区、贝类养殖区和对照区等3个区域柱状样中总氮的含量范围分别为638.2—3803.9mg.kg-1、740.9—2152.1mg.kg-1和343.2—471.9mg.kg-1, 总磷的含量范围分别为344.7—3233.9mg.kg-1、297.9—497.5mg.kg-1和650.2—1327.2 mg.kg-1, 有机碳的含量范围分别为0.96%—2.22%、0.87%—1.13%和0.69%—0.95%。该三个因子的含量均从底层至表层呈增加趋势, 但网箱养殖区上层增加幅度最为剧烈, 贝类区次之, 对照区变化幅度最小。所有柱状样中, 总氮含量均超标, 但网箱养殖区总氮污染最为严重, 贝类养殖区次之, 对照区最轻; 网箱养殖区的总磷在上层的不同深度超标, 而贝类养殖区及对照区柱状样的总磷含量均未超标。     

Diagenetic sulfate reduction in marine sediments

The importance of interstitial pore water as a vehicle for transport of dissolved ions between sediment at depth and the overlying ocean reservoir may be overestimated. The major cause of this overestimation is the assumption that the rate of ionic diffusion through the sediment is of a similar magnitude to the rate of reaction occurring within the sediment column. Examples are given to indicate that the above assumption may not be correct, at least for diagenetic sulfate reduction. Closed-system modeling, although approximate, is shown to be consistent, both qualitatively and isotopically, with measured changes that are observed for several sedimentary environments.     

Acoustic impedance of marine sediments

A heavy walled steel tube has been used as an impedance tube for measuring the acoustic impedance of marine sediments. The acoustic characteristics of the water filled tube were found to be satisfactory for the measurements. Values of acoustic velocity and attenuation in the sediments were determined from the acoustic impedance measurements and found to agree with previously published data.     

Grain-size parameters of marine sediments

In their average grain-size parameters (K _d , K _dl), recent sediments of the northern Caspian Sea and the Barents Sea shelf are similar, while the sediments of the Norwegian Sea are closer to their counterparts of the World Ocean. Seaward, the content of the subcolloidal fraction increases against the background of the decreasing proportions of coarse-and medium-grained pelite matter.     

Sulfate reduction in deep coastal marine sediments

Sulfate reduction rates in sediments of four deep stations in the Saguenay Fjord and the Laurentian Trough, Gulf of St. Lawrence, are among the lowest reported for the coastal environment. Maximum rates were 0.4–7.0 nmol cm⁻³ day⁻¹. The low rates are due to relatively low sedimentation rates and continuously low temperatures. Regional differences in both integrated and maximum sulfate reduction rates in the sediment correlate with sediment trap measurements of sedimentation rate and organic carbon flux.Sulfate reduction accounts for the degradation of 5–26% of the estimated downward flux of organic matter to these sediments. Unlike the absolute rate of sulfate reduction, the relative proportion of the carbon flux that is degraded via sulfate reduction is not directly correlated with the sedimentation rate but is a function of organic matter composition, intensity of bioturbation, and the abundance of sub-oxic electron acceptors. Thus, the lowest proportion of carbon degradation via sulfate reduction occurred at a Gulf site, where a combination of low sedimentation and bioturbation rates allowed a long residence time for organic matter near the sediment surface and, in consequence, a low flux of labile carbon into the sulfate reduction zone. The highest proportion was observed at a station with a similar organic carbon flux but with higher rates of sedimentation and bioturbation. At a third site, with the highest rates of sulfate reduction as well as the highest rates of sedimentation and bioturbation, the contribution of sulfate reduction to organic matter degradation was only intermediate. This is attributable to the exhaustion of the supply of porewater sulfate. In deep coastal environments the proportion of organic matter degraded via sulfate reduction can be highly variable both spatially and temporally.     

Distribution of free gas in marine sediments: a global overview

To quantify the global distribution of free gas in shallow marine sediments, we have identified and indexed over 100 documented cases in the scientific and engineering literature. Our survey confirms previous assumptions, primarily that gas bubbles are ubiquitous in the organic-rich muds of coastal waters and shallow adjacent seas. Acoustic turbidity, as recorded during seismo-acoustic surveys, is the most frequently cited evidence used to infer the presence of seafloor gas. Biogenic methane predominates within these shallow subbottom deposits. Because of their global prevalence, growing interest in gassy marine sediments is understandable, as their presence can have profound scientific, engineering and environmental significance.     

Shear wave velocity measurements in marine sediments

Pulsed ultrasonic techniques for the measurement of sound speed are reliable and well documented. Extension of these techniques to the measurement of shear wave velocities in marine sediments, generally was unsuccessful. Recently developed shear wave transducers, based upon piezoelectric benders operated at sonic frequencies, provide significantly improved transducer-sample mechanical coupling. This improved coupling allows the application of pulsed techniques to the measurement of shear wave velocities in marine sediments, and the rapid determination of sediment dynamic elastic properties. Two types of bender-based shear wave transducer and preliminary data are described: 1) a probe configuration for box core samples, and 2) a modification to the Hamilton Frame Velocimeter for cut samples.     

Biodiversity patterns of free-living marine nematodes in a tropical bay: Cienfuegos, Caribbean Sea

Spatial and temporal biodiversity patterns of free-living marine nematodes were studied in Cienfuegos Bay, a tropical semi-enclosed basin in the Caribbean Sea. Taxonomic (to species level) and functional (biological trait) approaches were applied for describing the assemblage structure and relating it to abiotic environment based on a sampling scheme in six subtidal stations and three months. Biological trait approach added relevant information to species pattern regarding relationships between diversity patterns and the abiotic environment. The most common morphotypes were deposit feeding nematodes, with colonising abilities of 2–3 (in a scale from 1 to 5), tail conical cylindrical or filiforme and body slender; and their abundance were correlated with depth, organic matter and silt/clay fraction. In spite of a high turnover of species, functional diversity of assemblages did not change notably in space and time. A result probably due to sampling of the habitat pool of species and to low heterogeneity of the studied muddy bottoms. Chemical pollution (organic enrichment and heavy metals) and hydrodynamic regime possibly drove the biodiversity patterns. Spatial distribution of assemblages support the existence of two well differentiated basins inside the bay, the northern basin more polluted than the southern one. The low hydrodynamic regime would determine a poor dispersion of nematodes resulting in high spatial variance in the assemblage structure; and also the associated hypoxic conditions and pollutants in sediments can explain the dominance of tolerant nematode species such as Daptonema oxycerca, Sabatieria pulchra, Terschellingia gourbaultae, and Terschellingia longicaudata. A comparison of spatial–temporal patterns of biodiversity between Cienfuegos Bay and other semi-enclosed bays in temperate regions suggests several similarities: nematode assemblages are strongly influenced by anthropogenic disturbance, temporal trends are weak or overridden by spatial ones, and few cosmopolitan genera/species tolerant to pollution and hypoxic conditions are dominant.     

Geology and geotechnical characteristics of sediments in east bay area,Mississippi delta

Abstract

Deltaic sedimentation has produced an accumulation of clay and silt with a maximum thickness of 90 m in East Bay area. Sediments in the upper 50 m grade from interbedded sand, silt, and clay near South Pass and Southwest Pass to predominantly clay in the central part of the area. The variation in the types of sediments and rates of deposition greatly affected the engineering properties of these deposits. Sediments from boreholes in the central part of the area have shear strengths of less than 10 kPa to a depth of at least 50 m. Near the distributaries, shear strength increases with depth; values as high as 43 kPa were measured in sediments in the upper 50 m. These sediments are generally stronger and coarser, and have a lower water content and liquid limit than do sediments at comparable depths in the central part of the area.     

The consolidation of soft marine sediments

This paper outlines the governing relationships of nonlinear finite strain consolidation. A short review of current literature is presented. Nonlinear finite strain consolidation theory is applied to the analysis of the slow deposition of Gulf of Mexico Holocene sediments. It is shown that the conventional means of calculating rates of sediment accumulation are highly inaccurate. It is further shown that the state of effective stress and excess pore-water pressure, as calculated by nonlinear finite strain theory, is substantially different than when calculated by conventional Terzaghi-Frohlich theory.     

Mercury speciation in sediments at a municipal sewage sludge marine disposal site

Mercury speciation was performed in excess activated sewage sludge (ASS) and in marine sediments collected at the AAS disposal site off the Mediterranean coast of Israel in order to characterize the spatial and vertical distribution of different mercury species and assess their environmental impact. Total Hg (HgT) concentrations ranged between 0.19 and 1003ng/g at the polluted stations and 5.7 and 72.8ng/g at the background station, while the average concentration in ASS was 1181+/-273ng/g. Only at the polluted stations did HgT concentrations decrease exponentially with sediment depth, reaching background values at 16-20cm, the vertical distribution resulting from mixing of natural sediment with ASS solids and bioturbation by large populations of polycheates. Average Methyl Hg (MeHg) concentration in ASS was 39.7+/-7.1ng/g, ca. 3% of the HgT concentration, while the background concentrations ranged between 0.1 and 0.61ng/g. MeHg concentrations in surficial polluted sediments were 0.7-5.9ng/g (ca. 0.5% of the HgT) and decreased vertically, similar to HgT. A positive correlation between MeHg and Hg only at the polluted stations, higher MeHg concentrations at the surface of the sediment and not below the redoxline, and no seasonality in the concentrations suggest that the MeHg originated from the ASS and not from in situ methylation. By doing selective extractions, we found that ca. 80% of the total Hg in ASS and polluted sediments was strongly bound to amorphous organo-sulfur and to inorganic sulfide species that are not bioavailable. The fractions with potential bioaccessible Hg had maximal concentrations in the range in which biotic effects should be expected. Therefore, although no bioaccumulation was found in the biota in the area, the concentration in the polluted sediments are not negligible and should be carefully monitored.     

Interstitial water chemistry of villefranche bay sediments: Trace metal diagenesis

Pore water aliquots were taken with an in situ close interval sampler: the “Peeper”.We report here the pore water concentration profiles of TCO₂, SO₄, TH₂S, Ca and the trace metals Mn, Cu, Pb, Cd and Cr from sediments of a relatively polluted area, the Villefranche Bay, on the French Riviera (close to Nice).We investigated the major ion concentrations in order to establish geochemical mass balances of organic matter oxidation. ΔTCO₂/ΔSO₄ was <−2.0, reflecting the precipitation of calcite as confirmed by the calcium profile. Reduction of sulfate led to increasing sulfide concentrations with depth.Trace metal interstitial water concentrations decreased from 63 to 5 nM, 18 to 4 nM and 6.6 to less than 2 nM for Cu, Pb and Cr, respectively. Cd showed a different pattern with top and deep values of 0.7 nM and a minimum of 0.27 nM.Thermodynamic calculations were performed which suggest the potential formation of mineral phases such as sulfides.     

广东省典型海湾表层沉积有机质的来源和分布

于2009年对广东省3个典型海湾湛江港、深圳湾和流沙湾表层沉积物的稳定碳同位素进行了分析。结果显示,湛江港表层沉积物δ13C值的范围为25.9‰—23.9‰,平均值为25.2‰;深圳湾表层沉积物的δ13C值的范围为25.9‰—23.2‰,平均值为25.1‰;流沙湾表层沉积物的δ13C值的范围为23.2‰—20.0‰,平均值为20.9‰。根据经典二元模式计算,湛江港陆源有机质的贡献比例范围为0.57—0.90,平均为0.78;深圳湾陆源有机质的贡献比例范围为0.45—0.90,平均为0.76;而流沙湾表层沉积有机质中海洋有机质的贡献比例较大,陆源有机质的贡献比例很小。湛江港和深圳湾表层沉积有机质主要来源于陆架,可能是C3(光合作用最初产物为三碳化合物)植物和海洋浮游微藻的混合有机质,但起主导作用的是陆架C3植物;而流沙湾表层沉积有机质主要来源于大型海藻和贝类的排泄物。各海湾沉积有机质的分布没有明显的规律性,主要受大陆径流、航运和潮汐的影响,同时也受海域初级生产力和水产养殖业的影响。     

Toxicological effects of potash brine on bay of Fundy marine organisms

The acute lethality and sublethal heavy metal contamination potential to marine organisms of a waste brine solution from a potash mining operation were determined. The brine was acutely lethal to marine organisms of the Bay of Fundy, Canada, at concentrations between 47 and 55‰ salinity (96-h LC₅₀ values: threespine stickleback, Gasterosteus aculeatus, 47·7‰; polychaete worm, Nephtys incisa, 52·5‰; blue mussel, Mytilus edulis, lethal to whole animal and reduced ciliary activity of gills above 55‰).The brine diluted to sublethal concentrations (≤40‰) contained manganese (≤ 49·5 ×), copper and zinc (≤ 5·2 ×), lead (≤ 2·6 ×) and cadmium (≤ 0·7 ×) in decreasing order of enrichment relative to control seawater. Copper was accumulated in mussels exposed to these solutions over 44 days to the greatest degree (4 ·4 ×), followed by manganese and lead. Tissue lead concentration reached a steady value within 44 days and cadmium was not accumulated.     

Effects of daily nitrogen and phosphorus input on planktonic community metabolism in a semi-enclosed bay by mesocosm experiment

Planktonic metabolism plays an important role in affecting the energy transportation and carbon cycle of the marine ecosystem. However, its regulation mechanism remains unclear under the continuously exogenous nutrient inputs in nearshore waters. In this study, a mesocosm experiment was conducted in a semi-enclosed bay, the Daya Bay, to explore the responses of plankton metabolic balance and community structure to a concentration gradient of daily nitrogen and phosphorus inputs. The results showed that nutrient enrichments promoted phytoplankton biomass, total primary production, and community respiration, and the promoting effect enhanced alongwith the increase of nutrient concentration. However, the net community production fluctuated more violently between autotrophic and heterotrophic with the increase of nutrient inputs and tended to be more heterotrophic from the 5th day to the 10th day of the experiment. In addition, the daily flux of nitrogen and phosphorus, 2 μmol/(L·d) and 0.066 μmol/(L·d), respectively, could be regarded as a potential threshold for ecosystem stability and health, since most of the ecological characteristics related to plankton structure and function have undergone significant changes when the nutrient level is higher than that. In the nearshore enclosed or semi-enclosed waters, nutrient from continuous terrigenous input is likely to be concentrated and exceed this level, indicating the ecological risks due to the metabolic unbalance and the deterioration of plankton community structure.