Cesium-137, metals and organic carbon in the sediments of the James River estuary,Virginia

A wide variety of sedimentary subenvironments are found within a 10-km stretch of James River including a flood dominated channel (Rocklanding Channel) and its bank (Rocklanding Shoal), a shoal with a water depth of 1 m separating two channels (Point of Shoals), an ebb-dominated channel (Burwell Bay Channel) and its bank (Burwell Bay Bank) and a tributary (Warwick River). The concentrations of Cs-137, Cu, Pb, Zn and organic carbon in the fine-grained sediments (i.e. < 63 μm) and the amount of fine-grained sediments in eight cores covering these subenvironments were determined. The sedimentation rates, estimated by Cs-137 geochronology, range from 0·4 to > 3 cm year^?1. The sedimentation rates in the Burwell Bay region are two or more, times those in the Point of Shoals and in the Rocklanding Channel and Shoal, reflecting the weaker currents in the Burwell Bay region. These sedimentation rates agree well with those obtained independently by measuring changes in the bathymetry of this area between 1873 and 1943. The concentrations of Cs-137, Cu, Pb, Zn and organic carbon in surface sediments vary by a factor of two to three. The concentrations are higher in the Burwell Bay region, probably as a result of the higher rates of accumulation of recently formed sediments in these subenvironments. The inventories of fine-grained sediments and of Cs-137, Cu, Pb, Zn and organic carbon accumulated since 1954 are also up to an order of magnitude higher in the Burwell Bay region. Although the concentrations of fine-grained sediments in three cores obtained in this region are similar, the inventories still vary by a factor of two to three. The inventories of Cs-137, Cu, Pb, Zn, organic carbon and fine-grained sediments correlate well with each other indicating that Cs-137 can be a useful tracer for studying the fate of these metals and organic carbon in estuarine environments. The inhomogeneity of the concentrations and inventories of the different elements along a 10-km segment of a river suggests that a closely-spaced sampling programme is essential for characterizing the sedimentary provinces within an estuary. The concentrations of Cs-137, metals and organic carbon in the coarse-grained sediments (i.e. > 63 μm) are considerably lower than those in fine-grained sediments. Thus, the contribution of coarse-grained sediments to the total inventory of these elements is small.     

The biology of the catfish Cnidoglanis macrocephalus (Plotosidae) in an Australian estuary

This paper describes the age structure, growth, diet and aspects of gonadal development in the cobbler, Cnidoglanis macrocephalus (Valenciennes), in the large Swan estuary in south-western Australia between August 1982 and June 1984. Analysis of otolith annuli showed that while the 0+ to 3+ age classes were regularly represented in monthly samples, the 4+ and more particularly the 5+ and 6+ were much less abundant. The weighted means for the back calculated lengths at the end of the first to fourth years of life were 181 mm (≡ 26 g), 314 mm (≡ 156 g), 418 mm (≡ 410 g) and 518 mm (≡ 833 g) respectively. The mean length at the end of the second year of life was similar to the minimum legal size for capture by commercial fishermen (320 mm). The von Bertlanffy growth curve calculated from the back calculated lengths was L_t = 917 [1 − e^{−0·20(t + 0·11)}]. The relative weight of mulluscs, crustaceans and polychaetes in the intestine varied markedly between small and large fish, apparently reflecting differences in the size of these prey. The large mean diameter of mature eggs ( ) was correlated with a low mean absolute fecundity (2078). Trends shown by egg size, gonadosomatic index and time of appearance of spent females indicate that spawning takes place between October and December. The attainment of sexual maturity is both age- and size-dependent. Although sexually maturing and occasionally spent fish were found in the lower estuary, meristic values, commercial catch statistics and other data indicate that the cobbler found in the Swan estuary are part of a population which typically spawns at sea.     

Fatty acid composition of surface sediments in the subtropical Pearl River estuary and adjacent shelf,Southern China

Surface sediments (10 cm) of the subtropical Pearl River estuary and adjacent shelf, Southern China were collected. Fatty acids and compound-specific carbon isotopic analyses were determined to infer their sources and biogeochemical cycle of this lipid in the subtropical Pearl River estuary and adjacent northern South China Sea (SCS). The total concentrations of fatty acids ranged from ∼1.28 to ∼42.25 μg g⁻¹ dry weight. The levels of polyunsaturated fatty acids (PUFA) were low (0.2–4.8% of total fatty acids), suggesting that fatty acids derived from algae were effectively recycled during the whole settling and depositing process. Bacterial fatty acids were significantly high and terrigenous fatty acids were low in the sediments. Principal component analysis (PCA) of the data also indicates that a clear separation of the biogeochemical sources can be seen. The δ¹³C values of bacterial fatty acids, i.e., i/aiC₁₅ (−22.9‰ to −29.4‰) suggest that bacteria within the sediments mainly utilize a labile pool of organic matter derived from algae for their growth in the subtropical Pearl River estuary system.     

Distribution and nature of organic matter in recent sediments of Lake Nokoué, Benin (West Africa)

The distribution and nature of organic matter clearly identify the principle sectors of the lagoon which vary according to hydrological and sedimentological conditions. The central area frequently includes coarse ancient fluviatile sediments. The rare organic matter there offers aliphatic and nitrogenous characters which may be derived from both the origin of organic matter (algae and meiofauna) and the level of oxygenation prevailing during deposition. In the southern sector, highly oxygenated conditions resulting from sea currents generated by the Cotonou outlet could cause the elimination of labile compounds, and hence be responsible for the high degradation state of organic matter. In the western sector, still water conditions allow fine sediments to be deposited. This frequently leads to the accumulation of organic matter showing such reducing conditions that they allow the integration of sulphur in humic compounds and a decrease of their solubility. In the northern area, the contribution of terrestrial material supplied by the Ouémé and Sô rivers is clearly indicated by the low average percentages of hydrolyzable fraction, C/N ratios ranging between 9 and 15, while H/C and N/C ratios are low in humic acids.     

闽江河口表层沉积物重矿物特征与物源示踪

对闽江河口近岸海域的230个表层沉积物样品和闽江20个表层沉积物样品进行重矿物分析,系统地研究了重矿物的分布特征及其物源指示。研究区共鉴定出重矿物27种,主要以普通角闪石、绿帘石、磁铁矿和黑云母为主。根据重矿物组合分布特征,将研究区分为两个矿物组合区,并划分为3个矿物组合亚区。闽江口近岸沉积区(Ⅰ-1区)矿物组合为普通角闪石-磁铁矿-绿帘石,受闽江物质影响很大;近岸混合沉积区(Ⅰ-2区)矿物组合为普通角闪石-磁铁矿-黑云母-绿帘石,受浙闽沿岸流携带物质和闽江物质共同影响沉积形成,闽江物质影响明显减弱;残留沉积区(Ⅱ区)矿物组合为普通角闪石-绿帘石-磁铁矿,主要为受后期改造的晚更新世海侵边界层。     

Seasonal phytoplankton composition, productivity and biomass in the Neuse River estuary, North Carolina

Phytoplankton community composition, productivity and biomass characteristics of the mesohaline lower Neuse River estuary were assessed monthly from May 1988 to February 1990. An incubation method which considered water-column mixing and variable light exposure was used to determine phytoplankton primary productivity. The summer productivity peaks in this shallow estuary were stimulated by increases in irradiance and temperature. However, dissolved inorganic nitrogen loading was the major factor controlling ultimate yearly production. Dynamic, unpredictable rainfall events determined magnitudes of seasonal production pulses through nitrogen loading, and helped determine phytoplankton species composition. Dinoflagellates occasionally bloomed but were otherwise present in moderate numbers; rainfall events produced large pulses of cryptomonads, and dry seasons and subsequent higher salinity led to dominance by small centric diatoms. Daily production was strongly correlated (r = 0·82) with nitrate concentration and inversely correlated (r = −0·73) with salinity, while nitrate and salinity were inversely correlated (r = −0·71), emphasizing the importance of freshwater input as a nutrient-loading source to the lower estuary. During 1989 mean daily areal phytoplankton production was 938 mgC m⁻², mean chlorophyll a was 11·8 mg m⁻³, and mean phytoplankton density was 1·56 × 10³ cells ml⁻¹. Estimated 1989 annual areal phytoplankton production for the lower estuary was 343 gC m⁻².     

Microphytobenthic biomass and species composition in intertidal flats of the Nakdong River estuary, Korea

Intertidal microphytobenthos (MPB) were investigated monthly from August 2006 to March 2008 at four different sites in the sand flats of Nakdong River estuary, Korea. Samples of surface sediment (ca. 1 cm) were collected, and chlorophyll a was extracted as biomass estimation. Species identification and enumeration were carried out by light microscopy, assisted where necessary by scanning electronic microscopy. Biomass varied between 0.47 and 16.58 μg cm⁻³, abundance changed from 5.25 to 414.75 × 10³ cells cm⁻³, while the Shannon diversity indexes ranged between 0.69 and 2.35 H′. Thirty-nine MPB taxa were identified, primarily composed of epipelic diatoms, among which Amphora and Navicula were the most abundant genera. Based on the biomass, abundance, species composition and their dynamics, MPB assemblages of sampling sites were grouped into three distinct communities corresponding to their sediment composition characteristics. Multivariate correlation analysis revealed that biomass was positively related to mud and very fine sand, negatively related to fine and medium sand, but not significantly related to environmental factors such as pore water nutrients, light intensity and salinity, which fluctuated rapidly during emersion period. Cluster analysis corroborated the division of MPB communities according to site types on seasonal scales, and also showed seasonality between sites by cluster of all summer groups. Principal component analysis identified that variability in species composition was significantly affected by mud, very fine sand, fine sand, light intensity, and sediment temperature. This study suggests that sediment composition plays an important role in the functioning of intertidal MPB communities in estuarine ecosystems.     

Factors affecting the distribution and abundance of Macrobrachium petersi (Hilgendorf) in the Keiskamma River and estuary,South Africa

A dry (1979–1980) and a wet (1980–1981) season had a marked effect on the freshwater inflow into the Keiskamma estuary. Under low inflow conditions, which results in elevated salinities in the upper reaches, an upstream migration of adult Macrobrachium petersi (Hilgendorf) to freshwater takes place. During periods of increased river inflow adult M. petersi move downstream to the more saline reaches of the estuary. These two migratory responses have been interpreted as (a) a breeding migration under high inflow conditions which ensures that larvae are in close proximity to salinities that favour growth and development, and (b) an adult upstream migration back to freshwater to escape elevated estuarine salinities as a result of the low freshwater inflow.     

The nitrogen isotopic composition of dissolved nitrate in the Yangtze River (Changjiang) estuary,China

The nitrogen isotopic composition of dissolved nitrate (δ¹⁵N-NO₃⁻) in surface water of the Yangtze River estuary was determined in four seasons of 2006. δ¹⁵N-NO₃⁻ ranged from 0.4‰ to 6.5‰ and varied with seasons and geographic regions, reflecting the dynamics of nitrogen cycling in the estuarine ecosystem. δ¹⁵N-NO₃⁻ was markedly lower in February than in other seasons and exhibited conservative mixing, which was probably attributed to the NO₃⁻ being sourced from the atmospheric deposition and agricultural fertilizer. In the upper estuary, the influence of riverine inputs was important during all surveys. In the turbidity maximum zone, nitrification was found with nitrate depleted in ¹⁵N in May, whereas denitrification resulting in heavy δ¹⁵N-NO₃⁻ played an important role in August. More enriched δ¹⁵N-NO₃⁻ values coinciding with losses of nitrate concentrations based on the conservative mixing model were found in the adjacent marine area in May, and may reflect obvious phytoplankton assimilation of dissolved nitrate. In this manner, δ¹⁵N-NO₃⁻ may be a sensitive indicator of nitrogen sources and biogeochemical processing existing in this estuary in conjunction with the variations of dissolved nitrate and other environmental factors.     

Transport of salt and suspended sediments in a curving channel of a coastal plain estuary: Satilla River, GA

This study describes the transport of salt and suspended sediment in a curving reach of a shallow mesotidal coastal plain estuary. Circulation data revealed a subtidal upstream bottom flow during neap tide, indicating the presence of a gravitational circulation mode throughout the channel. During spring tide, landward bottom flow weakened considerably at the upstream end of the channel and changed to seaward in the middle and downstream areas of the reach, suggesting the importance of tidal pumping. Salt flux near-bottom was landward at both ends of the channel during neap tide. At spring, however, the salt flux diverged along the bottom of the thalweg suggesting that tidal pumping caused a transfer of salt vertically and laterally into the intertidal zone. Thus, landward flux of salt is maintained even in the presence of subtidal seaward flow along the bottom at the downstream end of the channel.Landward bottom stress is greater than seaward stress, preferentially transporting suspended sediments upstream. Compared with salt, however, the weight of the suspended sediments causes less upward transfer of sediments into the intertidal zone. Flood flow carried more suspended sediments landward at the upstream end compared with the downstream end. We speculate that secondary flow in the curving channel picks up increasing amounts of suspended sediments along the sides during flood and adds them to the axial flow in the thalweg. Since the landward flow along the bottom of the thalweg weakens and even reverses during spring tide, there appears to be a complex re-circulation system for sediments re-suspended in curving channels that complicates the picture of a net transport of sediments landward.     

Kinetic and equilibrium studies of copper-dissolved organic matter complexation in water column of the stratified Krka River estuary (Croatia)

An interaction of dissolved natural organic matter (DNOM) with copper ions in the water column of the stratified Krka River estuary (Croatia) was studied. The experimental methodology was based on the differential pulse anodic stripping voltammetric (DPASV) determination of labile copper species by titrating the sample using increments of copper additions uniformly distributed on the logarithmic scale. A classical at-equilibrium approach (determination of copper complexing capacity, CuCC) and a kinetic approach (tracing of equilibrium reconstitution) of copper complexation were considered and compared. A model of discrete distribution of organic ligands forming inert copper complexes was applied. For both approaches, a home-written fitting program was used for the determination of apparent stability constants (K_i^equ), total ligands concentration (L_iT) and association/dissociation rate constants (k_i¹,k_i^- 1).A non-conservative behaviour of dissolved organic matter (DOC) and total copper concentration in a water column was registered. An enhanced biological activity at the freshwater–seawater interface (FSI) triggered an increase of total copper concentration and total ligand concentration in this water layer. The copper complexation in fresh water of Krka River was characterised by one type of binding ligands, while in most of the estuarine and marine samples two classes of ligands were identified. The distribution of apparent stability constants (log K₁^equ: 11.2–13.0, log K₂^equ:8.8–10.0) showed increasing trend towards higher salinities, indicating stronger copper complexation by autochthonous seawater organic matter.Copper complexation parameters (ligand concentrations and apparent stability constants) obtained by at-equilibrium model are in very good accordance with those of kinetic model. Calculated association rate constants (k₁¹:6.1–20 × 10³ (M s)^− 1, k₂¹: 1.3–6.3 × 10³ (M s)^− 1) indicate that copper complexation by DNOM takes place relatively slowly. The time needed to achieve a new pseudo-equilibrium induced by an increase of copper concentration (which is common for Krka River estuary during summer period due to the nautical traffic), is estimated to be from 2 to 4 h.It is found that in such oligotrophic environment (dissolved organic carbon content under 83 µM_C, i.e. 1 mg_CL^− 1) an increase of the total copper concentration above 12 nM could enhance a free copper concentration exceeding the level considered as potentially toxic for microorganisms (10 pM).     

Diel patterns of mysid drift (Crustacea: Mysidacea) in the Taieri River estuary,New Zealand

Drifting mysids were sampled to determine diel activity, and whether mysid numbers vary with respect to inflowing and outflowing tides. Samples of drifting mysids were collected at the mouth of the Taieri River, New Zealand, over one 24‐h cycle using five replicate conical drift nets in January 1999. One‐night and 1‐day ebb and flood tide were each sampled. Four species of mysid Tenagomysis macropsis, T. novae‐zealandiae, T. robusta, and an apparently undescribed species of Gastrosaccus sp., were collected over the sampling period. One species, T. robusta, has not previously been collected from estuarine or riverine systems. The undescribed Gastrosaccus sp. was the most abundant of the four species. All four species were more abundant at night, with T. robusta and Gastrosaccus sp. being considerably more abundant in the drift on outflowing tides. In contrast, roughly equal numbers of T. macropsis and T. novae‐zealandiae were observed drifting in and out of the estuary at night.     

中国黄渤海沉积物声速与物理性质研究

In order to investigate the correlation between a sound velocity and sediment bulk properties and explore the influence of frequency dependence of the sound velocity on the prediction of the sediment properties by the sound velocity,a compressional wave velocity is measured at frequencies of 25–250 k Hz on marine sediment samples collected from the Bohai Sea and the Yellow Sea in laboratory,together with the geotechnical parameters of sediments.The results indicate that the sound velocity ranges from 1.232 to 1.721 km/s for the collected sediment samples with a significant dispersion within the series measuring frequency.Poorly sorted sediments are highly dispersive nearly with a positive linear relationship.The porosity shows a better negative logarithmic correlation with the sound velocity compared with other geotechnical parameters.Generally,the sound velocity increases with the increasing of the average particle size,sand content,wet and dry bulk densities,and decreasing of the clay content,and water content.An important point should be demonstrated that the higher correlation can be obtained when the measuring frequency is low within the frequency ranges from 25 to 250 k Hz since the inhomogeneity of sediment properties has a more remarkably influence on the laboratory sound velocity measurement at the high frequency.     

长江口南部赤潮区春季表层沉积物中色素组成、含量与分布状况

为剖析长江口邻近海域春季硅藻藻华后期藻类沉降与底层水体缺氧现象之间的关系,作者于2011年春季,在长江口南部赤潮区采集了表层沉积物样品,并通过高效液相色谱法(HPLC),对浮游植物色素进行了分析。结果表明,硅藻藻华发生后,表层沉积物中叶绿素a(Chl a)、岩藻黄素(Fuco)和19’-丁酰氧基岩藻黄素(But-Fuco)含量有显著增加,高值区主要分布在调查海域东南侧50 m等深线外侧,与底层低氧水体分布区基本吻合。因此,硅藻藻华后沉降的藻类对于该海域夏季缺氧区的形成应具有一定作用,其具体过程和机制仍有待于研究。     

The PAH composition of surface sediments from Stagnone coastal lagoon, Marsala (Italy)

This paper examines the presence, distribution, nature and sources of 22 Aromatic Hydrocarbons (PAHs), which are important environmentally and toxicologically, in sediments from the Stagnone coastal lagoon at Marsala (Italy). Analysis was performed by gas chromatography/mass spectrometry (GC/MS) with selected ion monitoring (SIM). The total concentration of polycyclic aromatic hydrocarbons ranged from 72 to 18381 μg/kg of dry matrix. The relative standard deviation (RSD) of the replicates on the concentrations of individual compounds ranged from 5% to 20%. The accuracy of method was estimated by analyzing “blank” samples added of known quantities of analytes and the recover percentage was 88 ± 9%. The detection limit (LOD) of analytical procedure was less than 0.2 μg/kg d.w. for all analytes. The quantification limit (LOQ) of analytical procedure was less than 0.7 μg/kg d.w.The resulting distributions and weight ratios of specific compounds are discussed in terms of sampling location and origin of organic matter. A comparison with other studies of total PAHs suggests that the levels are within the concentration ranges already reported by other authors. From an eco-toxicological point of view, total PAH concentrations at seven out of the eight sites studied represent a relatively clean environment when compared to other sites.Organic matter content and PAH concentrations were found to be correlated and the compounds present in Stagnone sediments were shown to be mainly of pyrolitic origin, while a negligible quantity of PAHs may derive from biogenic sources since all the sediments contain perylene traces. There is no evidence of coal-tar contamination.Cluster analysis was carried out in order to discriminate between different PAH origins.     

Horizontal distribution and population dynamics of the dominant mysid Hyperacanthomysis longirostris along a temperate macrotidal estuary (Chikugo River estuary, Japan)

The estuarine turbidity maximum (ETM) that develops in the lower salinity areas of macrotidal estuaries has been considered as an important nursery for many fish species. Mysids are one of the dominant organisms in the ETM, serving as a key food source for juvenile fish. To investigate the horizontal distribution and population dynamics of dominant mysids in relation to the fluctuation of physical conditions (temperature, salinity, turbidity, and freshwater discharge), we conducted monthly sampling (hauls of a ring net in the surface water) along the macrotidal Chikugo River estuary in Japan from May 2005 to December 2006. Hyperacanthomysis longirostris was the dominant mysid in the estuary, usually showing peaks of density and biomass in or close to the ETM (salinity 1–10). In addition, intra-specific differences (life-cycle stage, sex, and size) in horizontal distribution were found along the estuary. Larger males and females, particularly gravid females, were distributed upstream from the center of distribution where juveniles were overwhelmingly dominant. Juveniles increased in size toward the sea in marked contrast with males and females. The findings suggest a possible system of population maintenance within the estuary; gravid females release juveniles in the upper estuary, juveniles grow during downstream transport, young males and females mature during the upstream migration. Density and biomass were primarily controlled by seasonal changes of temperature, being high at intermediate temperatures (ca. 15–25 °C in late spring and fall) and being low at the extreme temperatures (ca. 10 °C in midwinter and 30 °C in midsummer). High density (up to 666 ind. m⁻³) and biomass (up to 168 mg dry weight m⁻³) of H. longirostris were considered to be comparable with those of copepods in the estuary.     

Annual cycle and composition of the phytoplankton in the Quempillen River Estuary,southern Chile

Phytoplankton species and abundance were studied in the Quempillen River Estuary, from August 1979 to July 1980 in addition to some important environmental factors: salinity, temperature and dissolved oxygen. In order to determine the seasonal variations in cell density and biomass of the phytoplankton in this brackish aquatic environment, phytoplankton data obtained by the Uthermöhl (1958) technique were analysed.A total of 109 phytoplankton species were identified within the samples. Throughout the year there were two periods of population maxima, September and May, and one period of high biomass, February. The phytoflagellates were always present but only dominated the flora when diatoms were extremely reduced, especially during low tide periods.     

Neutron activation analysis(NAA) and geochemical studies of 38 elements in surface sediments from lower reach and estuary of Huanghe(Yellow) River

Using a neutron activation analysis technique, which involves gamma-spectrometry with a Ge(Li) detector coupled to a S40 multichannel analyzer and interfaced to a PDP-11 computer, we determined thirty-eight elements in sediments from the lower reach (downstream from Jinan) and estuary of Huanghe. The results are discussed in this paper.From inter-elemental correlations, it ts found that a large number of metals (Mn.As, Co, Cr.Cs, Rb, Sc, Ti, Ta, V and Zn) correlate positively with Fe. Ba and Ca correlate positively with Al. Whereas some elements (e. g. , Ti and lanthanides) show no correlation with either Fe or Al. On the other hand, Hf and Zr show a negative correlation with Fe. Elements which tend to be scavenged by Fe and Al colloids or suspended particles are enriched in sediments at the Huanghe Estuary relative to its lower reach. On the other hand, the contents of some elements (e. g. , Zr,Hf,U, Ba, etc. )are higher in sediments from the lower reach of Huanghe than in the estuarine sediments,which     

Aspects of larval,post-larval and juvenile ecology of Macrobrachium petersi (Hilgendorf) in the Keiskamma estuary,South Africa

Although Macrobrachium petersi has nine larval stages, only stage I and a minimal number of stage II M. petersi larvae were caught in the Keiskamma estuary. Stage I larvae undergo a vertical migration at night which is markedly influenced by salinity, especially under stratified conditions. Larvae remain in the water column on the ebb tide, a behavioural pattern which effectively carried them to favourable salinities for growth and development. Stage I larvae show an association with salt front regions. The sudden decline in larval abundance from stage I to stage II downstream from the front suggests a change from a pelagic to an epibenthic existence. Later larval stages failed to appear in the plankton. However, post-larvae were caught in the estuary and a juvenile migration from the estuary to freshwater was monitored.