Spatial distribution and source apportionment of PAHs in surficial sediments of the Yangtze Estuary, China

Spatial distribution and source apportionment of polycyclic aromatic hydrocarbons (PAHs) in the surface sediments of the Yangtze Estuary, especially the North Branch, have been fully investigated. PAH concentrations increased with the descending distance from the inner estuary to the adjacent sea, and varied significantly in various estuarine regions. Water currents (e.g., river runoff and ocean current) greatly affected the distribution pattern. In addition, ambient sewage and traffic also contributed to the PAH pollution in the estuary. In the adjacent sea, PAH values along the -20m isobath were higher than those along the -10m isobath due to the "marginal filter" phenomenon formed by different water currents. In most sites, PAHs had poor correlations with sediment size, but had positive correlations with total organic carbon. Based on the qualitative and quantitative analysis results, PAH sources were proved to be mainly from a mixture of petroleum combustion, biomass, and coal combustion.     

Organic carbon and nitrogen stable isotopes in the intertidal sediments from the Yangtze Estuary, China

The natural isotopic compositions and C/N elemental ratios of sedimentary organic matter were determined in the intertidal flat of the Yangtze Estuary. The results showed that the ratios of carbon and nitrogen stable isotopes were respectively −29.8‰ to − 26.0‰ and 1.6‰–5.5‰ in the flood season (July), while they were −27.3‰ to − 25.6‰ and 1.7‰–7.8‰ in the dry season (February), respectively. The δ¹³C signatures were remarkably higher in July than in February, and gradually increased from the freshwater areas to the brackish areas. In contrast, there were relatively complex seasonal and spatial changes in stable nitrogen isotopes. It was also reflected that δ¹⁵N and C/N compositions had been obviously modified by organic matter diagenesis and biological processing, and could not be used to trace the sources of organic matter at the study area. In addition, it was considered that the mixing inputs of terrigenous and marine materials generally dominated sedimentary organic matter in the intertidal flat. The contribution of terrigenous inputs to sedimentary organic matter was roughly estimated according to the mixing balance model of stable carbon isotopes.     

Morphodynamic characteristics of the dextral diversion of the Yangtze River mouth,China: tidal and the Coriolis Force controls

This paper examines the morphological development of the Yangtze River mouth, which has been diverting southeasterly (dextrally), according to historical (150 years) chart‐based digital evolution model and on‐site measured tidal flow data. We reveal a significantly narrowing of the northern river mouth branch from formerly >30 km wide to presently 10 km wide due to rapid siltation. Net siltation there, however, decreases gradually, which largely contrasts with the fact that the siltation has shifted to the southern river mouth area, as shown by many newly‐emerged estuarine islands, sandy shoals and bifurcated branches. Our data have further demonstrated that the ebb flow that dominates in the study area changes its direction gradually from east to southeast from the inner to outer river mouth area, and its duration is much longer than the flood flow in the inner river mouth area, but nearly equal at the river mouth area. Accordingly, the sediment transport pathway has been diverted from east to southeast. We examine whether the Coriolis Force could explain the dextral diversion of the ebb flow and the altered morphodynamical processes. Although too weak to strengthen the tidal flows, the Coriolis Force can drag the ebb flow southeasterly, and so influence sediment transport paths at the estuarine scale. The Coriolis Force is limited in the inner river mouth, but substantial at and in the outer river mouth area when gradually free of estuarine topographic constraints. The Coriolis Force causes an offset in propagation of in‐out flow directions at the river mouth area to form a slack water setting prone to estuarine siltation. Using the present approach also enables explanation of the morphological development of the Holocene Yangtze delta‐coast that extends to the southeast. Copyright © 2010 John Wiley & Sons, Ltd.     

Longitudinal residual circulation in the South Passage of Yangtze Estuary:Combined influences from runoff,tide and bathymetry

Classical estuary circulation theory states that in the longitudinal direction of an estuary there exists a single circulation with landward,near-bottom,and sea...     

Phytoplankton dynamics in and near the highly eutrophic Pearl River Estuary,South China Sea

The dynamics of size-fractionated phytoplankton along the salinity gradient in the Pearl River Estuary and the adjacent near-shore oceanic water was investigated using microscopic, flow cytometric, and chlorophyll analyses in the early spring (March) and early autumn (September) of 2005. In the inner part of the estuary where salinity was less than 30, the phytoplankton community was dominated by micro- and nano-sized (3–200 μm) cells, particularly the diatom Skeletonema costatum, both in early spring and early autumn. In areas where salinity >30, including the mixing zone and nearshore oceanic water, micro- and nano-sized cell populations dominated the phytoplankton assemblage during early spring when influence of river discharge was minimal, whereas pico-sized (≤3 μm) cell populations were dominant during early autumn as a result of strong river discharge in the summer, with Synechococcus and pico-eukaryotes being predominant. Picophytoplankton were two orders of magnitude more abundant in early autumn (10⁶ cells mL⁻¹) than in early spring in the nearshore oceanic water. Nutrients delivered by freshwater input to the estuary were pushed toward high salinity (>30) areas as a result of short residence time, exerting a strong influence on phytoplankton abundance, especially picophytoplankton in the nearshore, otherwise oligotrophic, water. Influenced by high abundance of DIN and limitation in phosphorus, picophytoplankton in the adjacent nearshore oceanic water rose to prominence seasonally. Our results indicate that eutrophication in the Pearl River Estuary not only stimulates the growth of S. costatum in the nutrient-rich areas of the estuary but also appears to promote the growth of Synechococcus and pico-eukaryotes in the adjacent usually oligotrophic oceanic water at least during our autumn cruise.     

The joint influence of the Coriolis force and the stratification on stationary motions in the zonal model of equatorial atmosphere

Summary In the framework of a zonal model of the equatorial atmosphere, the joint influence of the Coriolis force and stratification on stationary motion is studied. In addition we assume a Boussinesq approximation and consider the equatorial region as a macrodisturbance localized round the Equator, against a background of an isothermal atmosphere with a zonal distribution. Exact analytical solutions of the system of equations (1)–(5) are obtained and analyzed. An interesting result is that the equatorial atmosphere could exist in different stationary states in each of them separately, as well as in a number of them simultaneously.     

Oblique sand ridges in confined tidal channels due to Coriolis and frictional torques

Ocean Dynamics - The role of the Coriolis effect in the initial formation of bottom patterns in a tidal channel is studied by means of a linear stability analysis. The key finding is that the...     

Hydrocarbons in surface sediments from the Changjiang (Yangtze River) Estuary, East China Sea

Sedimentary aliphatic (AH) and polycyclic aromatic hydrocarbons (PAHs) were studied in the Changjiang Estuary and the adjacent East China Sea. Total AH ranged from 2.20 to 11.82 μg g⁻¹ and consisted of n-alkanes and a dominant petroleum-related unresolved complex mixture (UCM). Within the n-alkanes, terrestrial plant wax compounds prevailed at nearly all stations. Of the PAHs, biogenic perylene dominated at stations receiving riverine inputs. Anthropogenic PAHs originating from combustion/pyrolysis processes varied from 17 to 157 ng g⁻¹, while fossil PAH concentrations ranged from 42 to 187 ng g⁻¹. Both biogenic and anthropogenic hydrocarbons are primarily derived from riverine discharges and accumulate at shallow-water stations. Distinct phase associations lead, nevertheless, to different sedimentation patterns. Fossil PAHs are enhanced at offshore stations where they are introduced directly by shipping activities. Biomarker fingerprints ascribe their source to Chinese crude oils. The overall levels of anthropogenic hydrocarbons are low compared to relevant areas worldwide and reveal a low/moderate level of hydrocarbon pollution.     

Suspended microplastics in the surface water of the Yangtze Estuary System,China: First observations on occurrence,distribution

Levels of microplastics (MPs) in China are completely unknown. This study characterizes suspended MPs quantitatively and qualitatively for the Yangtze Estuary and East China Sea. MPs were extracted via a floatation method. MPs were counted and categorized according to shape and size under a stereomicroscope. The MP densities were 4137.3 ± 2461.5 and 0.167 ± 0.138 n/m³, respectively, in the estuarine and the sea samples. Plastic abundances varied significantly in the estuary. Higher densities in three sea trawls confirmed that rivers were the important sources of MP to the marine environment. Plastic particles (>5 mm) were observed with a maximum size of 12.46 mm, but MPs (0.5–5 mm) constituted more than 90% by number of items. The most frequent geometries were fibres, followed by granules and films. Plastic spherules occurred sparsely. Transparent and coloured plastics comprised the majority of the particles. This study provides clues in understanding the fate and potential sources of MPs.     

Geochemical changes across the Ordovician-Silurian transition on the Yangtze Platform,South China

The trace element and rare earth element (REE) variations across the Ordovician-Silurian succession are presented from two outcrop sections on the Yangtze Platform: the Nanbazi section, Guizhou Province, deposited in a shallow platform interior setting, and the Wangjiawan section, Hubei Province, deposited in a deeper basinal environment. Geochemical analysis of closely spaced samples through three intervals, the Wufeng, Guanyinqiao and Longmaxi, revealed vast palaeoceanographic changes. Some geochemical proxies, including Th/U, Ni/Co, V/Cr, and V/(V+Ni) ratios, together with sedimentary facies and biotic data, indicate that an anoxic condition on the most of the Yangtze Platform during the Wufeng and Longmaxi intervals, but an oxic condition during the Guanyinqiao time. The shift of the anoxic to the oxic environment during the Guanyinqiao time coincided with a global sea-level lowstand, in parallel with the global glaciation. The Longmaxian anoxic environment was a result of a global sea-level rise, which may be synchronized with a mainly catastrophic event in the latest Ordovician. Although the two sections generally show similar variation patterns of trace and REE concentrations and some element ratios, a minor difference occurs between the Wangjiawan and Nanbazi sections, likely reflecting a difference in depositional setting during the accumulation. Such an oceanic oxygen-level variation may add a useful constraint to the current arguments on the cause and consequence of the latest Ordovician mass extinction. Supported by National Basic Research Program of China (Grant No. 2005CB422101)     

Coriolis’ force in the earth’s solid tidal dynamics

The Coriolis forces/accelerations due to the tidal deformations (shifts) have been estimated at points on the physical Earth’s surface. The maximum tidal accelerations occur in the direction of the prime vertical, i.e. in the prime vertical component of the deflection of the vertical. They amount to about 0.05 μGal (50 nGal). This is just about the accuracy level achieved recently by the best superconducting gravimeters (SG) exhibiting 0.1 μGal accuracy (nanoGal level). The main goal of the paper is to determine the necessity of Coriolis forces be taken into account in next future.     

Role of living environments in the accumulation characteristics of heavy metals in fishes and crabs in the Yangtze River Estuary, China

Correlation of heavy metals in the tissues of typical organisms (i.e., fishes and crabs) and those in their living environments (i.e., surface water, bottom water, and sediment) in Yangtze River Estuary has been qualitatively and quantitatively analyzed. Metal levels followed the trend: sediments > Eriocheir sinensis > Eriocheir leptognathus > benthic fish > pelagic fish > bottom water > surface water. Tissues in fishes and crabs of different species and sizes had diverse metal bioaccumulation characteristics, which was significantly affected by environment factors and their living habits. Metal levels in legs of crabs, and heads and skins of fishes showed significant correlations with those in their living environments. Collichthys lucidus is an effective bioindicator for assessing metal levels in water. No significant health risk was identified by the estimated daily intake and target hazard quotients analyses.     

Carbon isotope composition of the Lower Triassic marine carbonates, Lower Yangtze Region, South China

The Early Triassic is a critical period in earth his- tory. A series of events such as volcano eruptions[1,2], sea-level fluctuations, changes in environmental con- ditions[3], mass extinctions[4,5] as well as global negative carbon isotope excursions[6-9] have been discovered in the uppermost Permian or across the Permian-Triassic boundary. Large scale sea-level rise[10-12], restoration of environment conditions, re- covery of ecosystem[13], including gradual carbon iso- tope rise[14] occur…     

Opening time and filling pattern of the Neoproterozoic Kangdian Rift Basin, western Yangtze Continent, South China

The Neoproterozoic Kangdian Rift Basin is a continental rift basin in the western Yangtze Continent. Determining its time of opening and subsequent filling pattern is an important aspect of understanding the formation and evolution of the Yangtze Continent, South China. The Luliang Formation is the early filling in the eastern part of this rift basin, and its deposition age and filling sequence are significant for studies of the regional stratigraphic correlation, opening time, and filling pattern of this basin. Having been correlated to the upper part of the Mesoproterozoic Kunyang Group or to the Neoproterozoic Chengjiang Formation, the age and regional stratigraphic correlation of the Luliang Formation have long been uncertain. This is due to a lack of reliable absolute age constraints. To address this issue, the first zircon SHRIMP U-Pb geochronology has been established for this formation, yielding two high-precision isotopic ages of 818.6±9.2 and 805±14 Ma for the tuff layers at the bottoms of the lower and upper members of the Luliang Formation, respectively. Given the error factor, the bottom age of the lower member of the Luliang Formation can be interpreted as ca. 820 Ma, corresponding to the bottom age of the lower part of the Banxi Group, which is the early filling of the Neoproterozoic Xianggui Rift Basin, a representative basin of the Neoproterozoic rift basins in the Yangtze Continent, South China. The bottom age of the upper member of the Luliang Formation can be interpreted as ca. 800±5 Ma, corresponding to the bottom age of the Chengjiang Formation in the western part of the Neoproterozoic Kangdian Rift Basin and also corresponding to the bottom age of the upper part of the Banxi Group in the Neoproterozoic Xianggui Rift Basin. These ages indicate that the Neoproterozoic Kangdian Rift Basin shares the same opening time and filling sequences as those of the other Neoproterozoic rift basins in South China. Basin analysis shows that the Neoproterozoic Kangdian Rift Basin is a typical half-graben basin, with its main boundary fault in the west and basin center in the east. This basin consisted of mini unidirectional half-graben basins in its juvenile stage and simplified to become a large united half-graben basin in its mature stage, i.e., a supradetachment basin.     

Sedimentary record of polycyclic aromatic hydrocarbons in a sediment core from the Pearl River Estuary, South China

Owing to the hydrodynamic and sedimentation conditions, the western shoal of the Pearl River Estuary (PRE) is known to be an important sink of terrestrial substances including particle-associated pollutants from the Pearl River Delta (PRD) region. In this study, we report the sedimentary record of polycyclic aromatic hydrocarbons (PAHs) during the 20(th) century in a sediment core from the western shoal of the PRE. The summation PAH concentration ranged from 59 ng g(-1) to 330 ng g(-1) in the core with two distinct peaks. An initial increase of summation PAH concentration was found around the 1860s. The amounts of PAHs remained relatively constant for roughly 100 years, followed by the first peak in the 1950s. Then, there was a decrease in PAH concentration and flux in the 1960s and 1970s. A sharp increase of PAH concentration was observed in the early 1980s with a maximum concentration in the 1990s. The PAH diagnostic ratios indicated that the PAHs in the sediment core were mainly of pyrolytic origin, and that atmospheric deposition and land runoff may serve as the important pathways for PAHs input to the sediment. The Gross Domestic Product (GDP) was used as an index of socioeconomic development in the PRD region, which was correlated positively with the changes of PAH concentration and flux in the sediment core. The rapid increase in vehicle numbers and energy consumption in the region in the last two decades may have contributed to the rapid PAH increase since the early 1980s. The results clearly elucidated the impact of regional economic development on the estuarine environment.     

Influence of the Coriolis force on the formation of a seasonal thermocline

Large eddy simulation (LES) reveals that the Coriolis force plays an important role in seasonal thermocline formation. In the high-latitude ocean, a seasonal thermocline is formed at a certain depth, across which the downward transports of heat and momentum are prohibited. On the other hand, in the equatorial ocean, heat and momentum continue to propagate downward to the deeper ocean without forming a well-defined thermocline. Mechanism to clarify the latitudinal difference is suggested. The depth of a seasonal thermocline h is scaled in terms of both the Ekman length scale λ and the Monin–Obukhov length scale L, as h ??? 0.5(Lλ)^1/2, which is in contrast to the earlier suggestion as h?∝?L.     

拟静力试验中摩擦力的影响及去除方法

土木工程拟静力试验中经常会使用到加载与反力装置,当作动器施加荷载时,作动器与反力装置之间会产生摩擦力。摩擦力会对试验结果产生影响,特别是对拟动力和混合试验需要位移在线更新的试验影响更大。然而,关于摩擦力对抗震试验影响的研究鲜有报道且去除摩擦力的方法较少。为此,本文通过理论分析研究了摩擦力对抗震试验各参数的影响,并发展了从测量数据中去除摩擦力的方法,减小摩擦力对拟静力试验的影响。