Seasonal and spatial variation of floc size,settling velocity,and density on the inner Adriatic Shelf (Italy)

Measurements of floc sizes, floc settling velocities and effective floc densities were obtained at three locations on the inner Adriatic shelf (Italy) in February and May/June 2003 using the in situ size and settling column tripod INSSECT (Mikkelsen et al., 2004. INSSECT—an instrument platform for investigating floc properties close to the seabed. Limnology and Oceanography: Methods 2, 226–236). Measurements were carried out in a water depth of 8–12 m and the final data set comprised 2491 flocs. Relationships of observed floc size vs. floc settling velocity and floc size vs. effective floc density were similar to those observed by other authors working in similar settings. The raw data showed significant scatter around mean trends, indicating that only a relatively small fraction of variability in floc settling velocity and effective floc density was explained by floc size. For bin-averaged data, however, much of the variability in settling velocity and density was explained by floc size. On the Adriatic shelf mean floc settling velocities varied from 0.48 to 1.35 mm s⁻¹, while mean effective floc densities varied from 8.1 to 27.5 kg m⁻³; within the range reported by other authors. Analysis of variance showed significant differences in floc settling velocities, effective floc densities and floc size in space and time (seasons). Thus, floc settling velocities, effective floc densities and floc size on the inner Adriatic shelf could not be characterized by a common mean, but were more appropriately characterized by a range of values, varying in time and space.     

Particle fluxes and recent sediment accumulation on the Aquitanian margin of Bay of Biscay

As a part of the ANR-Forclim experiment, particle mass fluxes and sedimentation processes were investigated on the slope of Aquitanian margin of the Bay of Biscay, between the canyons of Cap-Breton and Cap-Ferret. Interface sediments were collected along a depth transect from 145 to 2000 m; simultaneously a mooring line was deployed at the deepest station (WH, 2000 m) with two traps (800 and 1700 m) for a 16-month period (June 2006–November 2007). ²¹⁰Pb activities of settling particles and of interface sediments were determined to study transport processes of particles. Sediment and mass accumulation rates, calculated from excess ²¹⁰Pb profiles in the sediment column, show the expected decreasing trend with depth, as usually observed on margins. Mean particulate mass fluxes at 800 and 1700-m depth at site WH are, respectively, 27 and 70 g m^?2 a^?1.The ²¹⁰Pb budget points out events of temporary high lateral input of particles. The comparison of mass and ²¹⁰Pb fluxes between the water column and the seabed indicates that lateral transport plays an important role in particle accumulation on the Aquitanian margin. Regarding the objectives of the ANR-Forclim program, which aims to improve significantly the interpretation of fossil foraminifera signals, as a proxy for hydrological changes in the North Atlantic ocean, these results highlight advection processes must be considered when interpreting fluxes of foraminifers on the Aquitanian margin.     

Spatio-temporal variability of size fractionated phytoplankton on the shelf adjacent to the Ebro river (NW Mediterranean)

The mesoscale distribution and seasonal variation of the size structure of phytoplankton biomass, as measured by chlorophyll a (chl a), was studied in the Ebro shelf area (NW Mediterranean) during three different seasons: autumn, winter and summer. In autumn and summer, when the water column was, respectively, slightly or strongly stratified and nutrient concentrations were low at surface, average total chl a values were 0.31 and 0.29 mg m⁻³, respectively. In winter, the intrusion of nutrients into the photic zone by intense vertical mixing and strong riverine inputs, produced an increase of the total autotrophic biomass (0.76 mg m⁻³). In the three seasons, the main contributor to total chl a was the picoplanktonic (<2 μm) size fraction (42% in winter and around 60% in autumn and summer). The nanophytoplankton (2–20 μm) contribution to total chl a showed the lowest variability amongst seasons (between 29% and 39%). The microplanktonic (>20 μm) chl a size fraction was higher in winter (27%) than in the other seasons (less than 13%). The maximum total chl a concentrations were found at surface in winter, at depths of 40 m in autumn and between 50 and 80 m in summer. The relative contribution of the <2 μm size fraction at these levels of the water column tended to be higher than at other depths in autumn and winter and lower in summer. In autumn and winter, nutrient inputs from Ebro river discharge and mixing processes resulted in an increase on the >2 μm contribution to total chl a in the coastal zone near the Ebro Delta area. In summer, the contribution of the <2 and >2 μm chl a size fractions was homogeneously distributed through the sampling area. In autumn and summer, when deep chl a maxima were observed, the total amount of the autotrophic biomass in the superficial waters (down to 10 m) of most offshore stations was less than 10% of the whole integrated chl a (down to 100 m or to the bottom). In winter, this percentage increased until 20% or 40%. The >2 μm chl a increased linearly with total chl a values. However, the <2 μm chl a showed a similar linear relationship only at total chl a values lower than 1 mg m⁻³ (in autumn and summer) or 2 mg m⁻³ (winter). At higher values of total chl a, the contribution of the <2 μm size fraction remained below an upper limit of roughly 0.5 mg m⁻³. Our results indicate that the picoplankton fraction of phytoplankton may show higher seasonal and mesoscale variability than is usually acknowledged.     

Two extraterrestrial dust horizons found in the Dome Fuji ice core,East Antarctica

Two silicate-rich dust layers were found in the Dome Fuji ice core in East Antarctica, at Marine Isotope Stages 12 and 13. Morphologies, textures, and chemical compositions of constituent particles reveal that they are high-temperature melting products and are of extraterrestrial origin. Because similar layers were found ～ 2000 km east of Dome Fuji, at EPICA (European Project for Ice Coring in Antarctica)-Dome C, particles must have rained down over a wide area 434 and 481 ka. The strewn fields occurred over an area of at least 3 × 10⁶ km². Chemical compositions of constituent phases and oxygen isotopic composition of olivines suggest that the upper dust layer was produced by a high-temperature interaction between silicate-rich melt and water vapor due to an impact explosion or an aerial burst of a chondritic meteoroid on the inland East Antarctic ice sheet. An estimated total mass of the impactor, on the basis of particle flux and distribution area, is at least 3 × 10⁹ kg. A possible parent material of the lower dust layer is a fragment of friable primitive asteroid or comet. A hypervelocity impact of asteroidal/cometary material on the upper atmosphere and an explosion might have produced aggregates of sub-μm to μm-sized spherules. Total mass of the parent material of the lower layer must exceed 1 × 10⁹ kg. The two extraterrestrial horizons, each a few millimeters in thickness, represent regional or global meteoritic events not identified previously in the Southern Hemisphere.     

The settling of resuspended lake sediment related to physicochemical properties of particles of different sizes: Implication for environmental remediation

Sediment resuspension is an important way for shallow lake internal pollution to interact with the overlying water column,and the pollution risks are reasonably related to the retention of resuspended sediment particles in overlying water.In the current study,the settling of resuspended sediment particles was comprehensively investigated under different disturbances using five urban lake sediments.The results show that the particle size distributions of resuspended sediment from different lakes exhibited similar variations during settling with disturbance,although varied settling times were observed under static conditions.During settling with and without disturbance,sediment particle sizes were mainly within 8-63μm at the initial stage,and were<8μm in the later stages of settling.Based on these settling characteristics,the sediment particle size was divided into sand(>63μm),silt(8-63μm),and very fine silt and clay(<8μm)fractions.Kinetic analysis suggested that sediment settling for different particle sizes could be well described by the first-and second-order kinetic equations,especially when settling was disturbed(r²=0.727-0.999).The retention of resuspended sediment could be enhanced as particle sizes decreased and disturbance intensities increased.Furthermore,a water elutriation method was successfully optimized,with separation efficiencies of 56.1%-83%,to separate sediment particles into the defined three particle size fractions.The chemical compositions of sediment were found to change with different particle sizes.Typically,calcium tended to form large-size sediment,while the total contents of aluminum,iron,magnesium,and manganese showed significantly negative correlations with sediment particle sizes(p<0.01)and tended to distribute in small-size particles(e.g.,<8μm).Overall,the sediment particle size related settling dynamics and physicochemical properties suggested the necessity on determining the pollution of resuspended sediment at different particle sizes for restoration of shallow lakes.     

Abrasion in pyroclastic density currents: Insights from tumbling experiments

During granular mass movements of any kind, particles may interact with one another. The degree of interaction is a function of several variables including; grain-size distribution, particle concentration, density stratification and degree of fluidisation. The impact of particle interaction is additionally influenced by the relative speed, impact angle and clast temperature. Thus, both source conditions and transport-related processes are expected to influence the flow dynamics of pyroclastic density currents and their subsequent deposition. Here, we use tumbling experiments to shed light on the susceptibility of porous clasts to abrasion.We investigated the abrasion of unaltered volcanic rocks (5.7–80 vol.% porosity) from Unzen (Japan), Bezymianny (Russia) and Santorini (Greece) volcanoes as well as one synthetic analogue material, an insulating material with the trade name Foamglas® (95 vol.% porosity). Each experiment started with angular fragments generated in a jaw crusher from larger clasts. Two experimental series were performed; on samples with narrow and broader grain-size distributions, respectively. The dry samples were subject to rotational movement at constant speed and ambient temperature in a gum rotational tumbler for durations of 15, 30, 45, 60 and 120 min. The amount of volcanic ash (particles <2 mm) generated was evaluated as a function of experimental duration and sample porosity. We term “abrasion” as the ash fraction generated during the experiments.The observed increase of “abrasion” with increasing sample porosity and experimental duration is initially non-linear but becomes linear for experiments of 30 min duration or longer. For any given sample, abrasion appears to be more effective for coarser samples and larger initial mass. The observed range of ash generated in our experiments is between 1 and 35 wt.%. We find that this amount generally increases with increasing initial clast size or increasing breadth of the initial grain-size distribution.Despite the limits in the complexity that is experimentally attainable in this simulation of ash generation, our results clearly testify the rapid and efficient generation of ash by abrasion, strongly influenced by the material properties (e.g., crystallinity, pore textures).     

Simulation of sediment motions using a discrete particle model in the inner surf and swash-zones

A volume-of-fluid Navier–Stokes solver (RIPPLE) was used to simulate inner surf and swash zone flow with a 3 s wave period and wave height of 0.14 m on a planar, 1:10 sloping beach (Iribarren number of 1.0). In addition to other hydrodynamic information, RIPPLE was used to provide high-resolution predictions of the pressure gradient and fluid velocity in the horizontal and vertical dimensions that served as forcing to a discrete particle model (DPM). Sediment transport processes in the inner surf and swash zones were simulated for a thin veneer of sediment particles over a 5 m test section in the DPM. Coupling between RIPPLE and the DPM was one-way such that particle–particle and fluid–particle interactions in the DPM did not provide feedback to alter the flow predicted by RIPPLE. The numerical simulation showed strong sediment suspension localized under vortices that reach the bed. Interestingly, the bulk of the sediment located in the small-scale vortex originated from locations nearly 0.2 m landward. These findings suggest that (1) sediment motion for a single swash event can be significant, (2) that sediment measured in suspension likely originates from locations other than the bed directly below the suspension plume suggesting the importance of sediment advection and (3) that sparse cross-shore measurements in the field will only sporadically capture localized suspension events.     

A LiDAR study of the effective size of cirrus ice crystals over Chung-Li,Taiwan

In this paper, we estimated the effective size of ice crystals in cirrus clouds using fall velocity derived from LiDAR (light detection and ranging) measurements at Chung-Li (24.58°N, 121.1°E), Taiwan. Nine shapes of the ice crystals, viz. hexagonal plates, hexagonal columns, rimed long columns, crystals with sector-like branches, broad-branched crystals, stellar crystal with broad arms, side planes, bullet rosettes and assemblages of planar poly-crystals of specific dimensions have been analyzed. The results show that the lidar derived most probable mean effective size of ice crystals is 340±180 μm with a dominant size range of 200–300 μm. The lidar derived mean effective size of cirrus crystals are parameterized in terms of cloud mid-height temperature as well as optical depth. The discussed method will be useful to study the most probable effective size distribution of ice crystals in cirrus cloud.     

The equivalent dose of different grain size quartz fractions from lakeshore sediments in the arid region of north China

Equivalent dose (D_e) values were measured by using medium aliquots of different grain size quartz fractions of five lakeshore sediments from the arid region of north China. There are two different relationships between D_e values and grain sizes of these five samples. The first relationship is that the D_e values obtained from various grain sizes are in agreement within 1 delta errors. The second relationship is that D_e values are similar to each other for fractions between 125 and 300 μm, while the D_e value of the 63–90 μm fraction is 40～55% smaller than others. For example, the D_e values obtained for sample #3 are 20.15 ± 1.19 Gy, 19.80 ± 0.83 Gy and 20.93 ± 1.06 Gy for fractions of 90–125, 125–150 and 250–300 μm respectively, but are 10.79 ± 0.84 Gy for the 63–90 μm fraction. The second relationship can't be interpreted by previous studies of both dosimetry and heterogeneous bleaching. It is deduced for sample #2, #3 and #6 that fine particles (<90 μm) intruded after the dominant sedimentation. Comparison of OSL ages from different grain size fractions of sample #2 with a radiocarbon age from the same lithologic layer supports that fractions coarser than 125 μm yield more reliable burial ages, while the fraction finer than 90 μm yields underestimated ages for some lakeshore sediments from this arid region.     

Short-term changes in the aerosol characteristics at Kharagpur (22°19′N, 87°19′E) during winter

In-situ measurements of number density, size distribution, and mass loading of near-surface aerosols were carried out at Kharagpur, a site on the eastern part of Indo-Gangetic Plains during the winter month of December 2004. The data have been used to investigate wintertime characteristics of aerosols and their effects on the occurrence of haze. The aerosol number density is found to be of the order of 10⁹ m^?3 and mass loading is ~265±70 μg m^?3 (5–8 times that reported from south Indian sites). The diurnal patterns and day-to-day variations in aerosol number density and mass loading are closely associated with atmospheric boundary layer height. During haze events, the number density of submicron particles is found to be 2–5 times higher than that during non-hazy period. This could be attributed to the enhanced concentration of anthropogenic aerosols, low atmospheric boundary layer height/ventilation coefficient and airflow convergence.     

Biosorption of heavy metals in polluted water,using different waste fruit cortex

The biosorption capacity of different cortex fruit wastes including banana (Musa paradisiaca), lemon (Citrus limonum) and orange (Citrus sinensis) peel were evaluated. In order to perform these experiments, grinded dried cortexes were used as package in 100 mm high, 10 mm i.d. columns. The grinded material was powdered in a mortar and passed through a screen in order to get two different particle sizes, 2 and 1 mm, for all powders. To estimate the biosorption capabilities of the tested materials, different heavy metals were passed through the columns and the elution filtrate reloaded different times to increase the retention of metals. The heavy metals used were prepared as synthetic samples at 10 mg/L of Pb(NO₃)₂, Cd(NO₃)₂, and Cu(NO₃)₂·6H₂O using primary standards. In preliminary experiments using banana cortex, it was found that material with 1 mm of particle size showed higher retention capability (up to12%) than the material with 2 mm of particle size. Considering these results, 1 mm particle size material was used in further experiments with the other waste materials. It was found that for Pb and Cu removal, lemon and orange cortex showed better biosorption capability when compared with banana cortex (up to 15% less for Pb and 48% less for Cu). For Cd, banana cortex showed better biosorption capability 57% (67.2 mg/g of cortex) more than orange (28.8 mg/g of cortex), and 82% more than lemon (12 mg/g of cortex). Reload of the columns with the filtrate after passing through the column improved the removal capability of all the materials tested from 10% to 50% depending on the cortex and metal tested.     

The statistical and numerical study of the global distribution of coronal plasma and magnetic field near 2.5 Rs over a 10-year period

The basic characteristics of the global distribution for the corona plasma and magnetic field near 2.5 Rs are analyzed with the statistical and numerical methods for 136 Carrington Rotations (CRs) covering four different phases of solar activity. By using the observational data and the velocity distribution model in the corona, the statistical average distribution of the magnetic field, density and the coronal mass outputs are analyzed for the four different phases. Then, a numerical study of the global distribution near 2.5 Rs has been made by solving a self-consistent MHD system. Finally, the solar wind speed at 1 AU is given by mapping the speed at 2.5 Rs to that near 1 AU, and the comparison of the numerical results with the observational measurements and the simulation result of the Wang–Sheeley–Arge (WSA) model are made during more than 5 years. The numerical results indicate that the global distributions on the source surface of 2.5 Rs at different phases of solar activity could be used to predict the change of the solar wind in interplanetary space.     

Interacting physical,chemical and biological forcing of phytoplankton thin-layer variability in Monterey Bay,California

During the 2005 Layered Organization in the Coastal Ocean (LOCO) field program in Monterey Bay, California, we integrated intensive water column surveys by an autonomous underwater vehicle (AUV) with satellite and mooring data to examine the spatiotemporal scales and processes of phytoplankton thin-layer development. Surveying inner to outer shelf waters repeatedly between August 18 and September 6, the AUV acquired 6841 profiles. By the criteria: [(1) thickness ≤3 m at the full-width half-maximum, (2) peak chlorophyll at least twice the local background concentrations, and (3) a corresponding peak in optical backscattering], thin layers were detected in 3978 (58%) of the profiles. Average layer thickness was 1.4 m, and average intensity was 13.5 μg l^?1 above (3.2x) background. Thin layers were observed at depths between 2.6 and 17.6 m, and their depths showed diurnal vertical migration of the layer phytoplankton populations. Horizontal scales of thin-layer patches ranged from <100 m to>10,000 m. A thin-layer index (TLI), computed from layer frequency, intensity and thinness, was highest in mid-shelf waters, coincident with a frontal zone between bay waters and an intrusion of low-salinity offshore waters. Satellite observations showed locally enhanced chlorophyll concentrations along the front, and in situ observations indicated that phytoplankton may have been affected by locally enhanced nutrient supply in the front and concentration of motile populations in a convergence zone. Minimum TLI was furthest offshore, in the area most affected by the intrusion of offshore, low-chlorophyll waters. Average thin-layer intensity doubled during August 25–29, in parallel with warming at the surface and cooling within and below the thermocline. During this apparent bloom of thin-layer populations, density oscillations in the diurnal frequency band increased by an order of magnitude at the shelfbreak and in near-bottom waters of the inner shelf, indicating the role of internal tidal pumping from Monterey Canyon onto the shelf. This nutrient transport process was mapped by the AUV. Peak TLI was observed on August 29 during a nighttime survey, when phytoplankton were concentrated in the nutricline. Empirical orthogonal function decomposition of the thin-layer particle size distribution data from this survey showed that throughout the inner to outer shelf survey domain, the layers were dominated by phytoplankton having a cross-section of ～50 μm. This is consistent with the size of abundant Akashiwo sanguinea cells observed microscopically in water samples. During a subsequent and stronger intrusion of low-salinity offshore waters, spatially-averaged vertical density stratification decreased by > 50%, and phytoplankton thin layers disappeared almost completely from the AUV survey domain.     

Phase functions of polar mesospheric cloud ice as observed by the CIPS instrument on the AIM satellite

The Cloud Imaging and Particle Size (CIPS) instrument on the Aeronomy of the Ice in the Mesosphere (AIM) spacecraft is a 4-camera nadir pointed imager with a bandpass centered at 265 nm and a field of view of 120°×80°. CIPS observes polar mesospheric clouds (PMCs) against the sunlit Rayleigh-scattered background. At individual polar locations approximately 5 km×5 km in area, CIPS observes the same volume of air seven times over a range of scattering angles from about 35° to 150°. These multi-angle observations allow the identification and extraction of the PMC scattered radiance from the Rayleigh-scattered background. We utilize the fact that the former has a highly asymmetric phase function about 90° scattering angle, while the latter has a phase function that is symmetric. The retrieved PMC phase function can then be interpreted to obtain PMC particle size distributions. We describe a technique for identification of PMCs in the CIPS observations through the separation of the Rayleigh and PMC radiances. PMC phase function results are shown for the first season of CIPS observations. Assuming the particles are oblate spheroids with an axial ratio of 2, and a Gaussian distribution of width 14 nm, we find the phase functions are consistent with mean radii between 50 and 60 nm. These results are similar to those discussed by Hervig et al. [2009. Interpretation of SOFIE PMC measurements: cloud identification and derivation of mass density, particle shape, and particle size. J. Atmos. Sol. Terr. Phys., in review.] in this issue from the Solar Occultation for Ice Experiment (SOFIE) which also flies on the AIM satellite.     

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.     

Selected trace metals (As,Cd and Hg) distribution and contamination in the coastal wetland sediment of the northern Beibu Gulf,South China Sea

Contamination with As, Cd and Hg, their spatial and temporal distribution are reported from the coastal wetland sediments of the northern Beibu Gulf, South China Sea. The content of As, Cd, Hg and TOC in surface sediments is 8.1 ± 5.8 μg g^?1, 0.08 ± 0.14 μg g^?1, 0.034 ± 0.028 μg g^?1 and 0.45 ± 0.39%, respectively. The mean sedimentation rates are 0.93–1.37 cm year^?1 during 1920s to 2008 determined by ²¹⁰Pb and ¹³⁷Cs dating in three cores. The vertical profiles of As, Cd and Hg content in the cores retrieved from Qin and Nanliu River estuaries show increasing trends during 1985–2008 due to anthropogenic impact caused by local economic development. Locally the surface sediments have potential ecological risk of As to benthos according to the NOAA sediment quality guidelines.     

Seasonal–latitudinal variations of PMC particle size from SME measurements for the northern 1983 season and SNOE measurements for the northern 2000 and southern 2000/2001 seasons

The ultraviolet spectrometers (UVS) on the solar mesosphere explorer (SME) and student nitric oxide explorer (SNOE) measured scattered limb radiance at small and large scattering angles from polar mesospheric clouds (PMCs). The SME data are for the northern summer hemisphere (NH) in 1983 and 1984. The SNOE measurements are for the NH in 2000 and for the southern hemisphere (SH) in the 2000/2001 season. From this database, we deduce the modal particle size from the measured scattering angle asymmetry in radiance. This quantity is determined as a function of time within the PMC season, and latitude, assuming several scattering models depending on the adopted size distribution and particle shape. For assumed spherical particles with a Gaussian distribution of width of 14 nm, the results for SME show mode particle sizes that vary from about 35 to 60 nm throughout the season. The results for SNOE under the same assumption show that for high latitudes in the NH the particle size grows systematically from the seasonal onset, from about 25 nm to a maximum of about 45 nm at 30 days after solstice. Lower latitudes show a similar time dependence, but with smaller particle sizes. SH PMC particle sizes display a more complicated seasonal variability. Generally, variability in measured cloud height is anti-correlated with particle size for the seasons analyzed here. Particle sizes in the SH are generally smaller than those in the NH, consistent with the northern bias in PMC brightness, and with previous satellite studies. These results are interpreted in terms of our understanding of PMC microphysics and inter-hemispheric differences in temperature and dynamics. Our quantitative results for mode radius depend on the assumption of a constant distribution width. If the width varies with latitude or time, our calculated gradients of mode radius would be different.     

Sulphate reduction in the sediment of the Venice canals (Italy)

The sulphur cycle in the sediment of the Venice canal network was investigated by considering the sulphate reduction rate (SRR) and the distribution of sulphur compounds, in both pore water and sediment. Sulphate reduction (SR) is the main process in the metabolism of the organic matter supplied to the network by untreated urban effluents. Although it might account for the decomposition of only a limited percentage of the total organic-C inputs, the estimated rates are among the highest observed in coastal sediments. Measured rates range from 0.26 to 0.99 μmol cm⁻³ d⁻¹, while mean annual values, estimated by a diagenetic model, vary from 0.16 to 0.43 μmol cm⁻³ d⁻¹. The speciation of S in the sediment reveals that pyrite-S is the most abundant component of the total reduced S pool, whereas acid volatile sulphides and elemental sulphur together account for less than 45%. A preliminary budget indicates that the rate of burial of solid-phase S is small compared to the S produced by SR (from 10 to 25%). A large amount of reduced S is then lost from the canal deposits to be re-oxidised at the sediment-water interface or in the overlying water column.     

The distribution of heavy metals including Pb,Cd and Cr in Kendari Bay surficial sediments

The surficial coastal sediments in Kendari Bay are sampled in the field to determine the concentration and pollution level of three heavy metals (Pb, Cd and Cr). Twenty-five sampling points ranging from the inner (Wanggu River) to the outer area of the bay have been chosen. The physicochemical properties, such as temperature, pH, salinity and TDS of the overlying water, as well as the sediment type and TOC of the surficial sediments, are also measured. The total concentrations of the Pb, Cd and Cr in the sediment samples are quantified using inductively-coupled plasma mass spectrometry (ICP-MS). The concentrations of the heavy metals (Pb, Cd and Cr) ranged from 0.84 to 17.02 μg/g, 0.02 to 0.17 μg/g and 1.92 to 40.11 μg/g (dry weight), respectively, following the Cr > Pb > Cd sequence. To assess the degree of contamination, a geoaccumulation index (I_geo) is measured. Kendari Bay is not a contaminated area regarding Pb, Cd and Cr.     

Phosphorus retention and release by sediments in the eutrophic Mai Po Marshes,Hong Kong

This study examined the phosphorus retention and release characteristics of sediments in the eutrophic Mai Po Marshes in Hong Kong. Results of chemical fractionation show that the sum of inorganic P pools exceeded 50% of the total sediment P content, with the redox-sensitive iron-bound P (Fe(OOH) ≈ P) being the dominant P fraction. Given the considerable average Fe(OOH) ≈ P concentration of 912 μg g⁻¹, Mai Po sediments demonstrated a great potential to release bioavailable P under low sediment redox potentials. This was further supported by the high mean anaerobic P flux of 31.8 mg m⁻² d⁻¹ recorded in Mai Po sediment cores, indicating the role of bottom sediments as a net P source. Although sediments in Mai Po had appreciable Langmuir adsorption maxima (1642–3582 mg kg⁻¹), the high zero equilibrium P concentrations (0.02–0.51 mg L⁻¹) obtained suggest that sediment sorption processes would contribute to sustaining the eutrophic conditions in overlying water column even with a further reduction in external P load. Concerted efforts should be made to reduce internal loading of P, especially under reducing conditions, to complement the implementation of zero discharge policy for Deep Bay for effective eutrophication abatement and long-term water quality improvement in the Mai Po Marshes.