Sediment Particle Size Fractions Research Articles

Particle-scale understanding sorption of phenanthrene on sediment fractions amended with black carbon and humic acid

Black carbon (BC) and humic acid (HA) have been proposed to dominate the sorption behavior of phenanthrene in sediment. Nevertheless, little is known about the sorption mechanism that related to particle-scale by spiking of BC and HA in sediment particle size fractions. In this study, sorption isotherms for phenanthrene were determined in four particle-size sediment fractions (<2 μm, 2–31 μm, 31–63 μm and >63 μm) that amended with BC and HA, or not. The fitting results by Freundlich model indicated that the sediment particle size fractions amended with BC increased the sorption capacity and affinity for phenanthrene. Sediment coarser size fractions (31–63 μm and >63 μm) by spiking of BC contributed higher to sorption capacity factor (KF) and nonlinearity factor (n) than the finer size fractions (2–31 μm and <2 μm). By contrast, the sediment particle size fractions amended with HA enhanced the sorption distribution coefficient (Kd), but reduced the sorption affinity for phenanthrene. All these phenomena are obviously affected by the distribution of heterogeneous organic matter that related to sediment particle-scale. Results of this work could help us better understand the impact of increased BC and HA content in sediments on the sorption of hydrophobic organic pollutants (HOCs) and predict the fate of HOCs in offshore sediments due to tidal action.

Influence of chemical charge on the fate of organic chemicals in sediment particle size fractions

In order to investigate the influence of differently sized particle fractions on the fate of ionic chemicals in water-sediment systems, we performed simulation studies following OECD guideline 308. We used 14C-labelled anionic (4-n-dodecylbenzenesulfonic acid sodium salt, ‘14C-DS-’), cationic (4-n-dodecylbenzyltrimethyl ammonium chloride, ‘14C-DA+‘) and non-ionic (4-n-dodecylphenol, ‘14C-DP’) organic chemicals. The sediment was subjected to particle size fractionation. For each particle fraction and test compound, water-sediment systems were prepared and incubated for 14 days. Across all particle fractions, higher amounts of applied radioactivity (AR) of 14C-DS- (in sand 60.1%, in silt 45.1%, in clay 57.0%) and of 14C-DP (sand: 31.8%, silt: 24.4%, clay: 29.2%) were mineralised compared to 14C-DA+ (sand: 5.1% AR, silt: 3.5% AR, clay: 2.4% AR). The highest bioavailability was observed for 14C-DS- followed by 14C-DP and 14C-DA+ across all particle fractions. Formation of non-extractable residues (NER) of 14C-DS- did not substantially differ between the particle fractions, whereas NER formation of 14C-DA+ was higher in the clay fraction (24.3% AR) than in silt (15.9% AR) and sand (8.4% AR). The same trend was observed for 14C-DP. We showed that differently sized particle fractions have an influence on the fate of ionic chemicals in water-sediment systems and conclude that this should be considered when simulation studies in soils and sediments with different textural compositions are performed. Since a positive charge of organic chemicals tends to form higher portions of NER in the clay fraction of sediments, these NER should be further investigated in terms of their nature and types of binding.

Distribution and adsorption of metals on different particle size fractions of sediments in a hydrodynamically disturbed canal

Sediment resuspension widely occurs in environments with hydrodynamic disturbances, where particles are sieved into different grain size groups. The particles of different grain size exhibit heterogeneity of their physical, chemical or biological features. This research addressed the association of metals on size fractional particles sieved by sediment resuspension in a canal of Taihu basin, a highly urbanized and human-impacted area. Surface sediment samples were collected from upstream to downstream sections of the canal to analyze the concentrations and fractionation of lead (Pb), zinc (Zn), and copper (Cu). One sediment sample was sieved into five different particle size groups (50–150 μm, 30–50 μm, 10–30 μm, 5–10 μm and <5 μm) through the wet sedimentation method. The strong adsorption ability of metals on fine particles is attributed to enrichment with organic matter and iron/aluminum (Fe/Al) oxides, with the increase in Pb, Zn, and Cu concentrations from 34.2 mg/kg, 263 mg/kg, and 32.5 mg/kg of 50–150 μm size group particles to 71.4 mg/kg, 698 mg/kg, and 137 mg/kg of <5 μm size group particles, respectively. The fine particles showed stronger sorption ability on Pb than Zn and Cu, with the Freundlich isotherm constant (Kf) values of the adsorption isotherms in the <10 μm size particle group ranging from 3.7 to 5.9 g/kg for Zn and Cu versus from 11 to 18 g/kg for Pb, probably causing difference on metals accumulation and releasing risk among metals in the downstream lakes with changeable environments.

Particle Size Specific Magnetic Properties Across the Norwegian‐Greenland Seas: Insights Into the Influence of Sediment Source and Texture on Bulk Magnetic Records

AbstractWe make fundamental observations of the particle size variability of magnetic properties from 71 core tops that span the southern Greenland and Norwegian Seas. These data provide the first detailed regional characterization of how bulk magnetic properties vary with sediment texture, sediment source, and sediment transport. Magnetic susceptibility (MS) and hysteresis parameters were measured on the bulk sediment and the five constituent sediment particle size fractions (clay, fine silt, medium silt, coarse silt, and sand). The median MS value of the medium silt size fraction is ~3–5 times higher than that of the sand and clay size fractions and results in a strong sensitivity of bulk MS to sediment texture. Hysteresis properties of the clay size fraction are relatively homogeneous and contrast that silt and sand size fractions which show regional differences across the study area. These coarser fractions are more transport limited and using medium silt hysteresis measurements and low temperature MS behavior we establish three endmembers that effectively explain the variability observed across the region. We model the response of bulk magnetic properties to changes in sediment texture and suggest that variations in sediment source are required to explain the bulk magnetic property variability observed in cores across the southern Greenland and Norwegian Seas. These findings imply that sediment source has a greater influence on driving bulk magnetic property variability across this region than has previously been assumed.

Trace metal distribution in the bed, bank and suspended sediment of the Ravensbourne River and its implication for sediment monitoring in an urban river

This study aims to identify a suitable sediment compartment for sediment quality monitoring by: (a) studying the concentration of trace metals (Cd, Cu, Ni, Pb and Zn) in the bed, bank and suspended sediment compartments of the Ravensbourne River to establish any differences in trace metal concentrations with compartment; (b) determining the influence of sediment particle size fractions ( 0.05) in the concentrations of metals between the suspended sediment and the < 63 μm bed sediment fraction, but there was a significant difference (p < 0.05) between the suspended sediment and the < 63 μm bank sediment fraction. There were also significant differences between the concentrations of metals in the < 63 μm and the 63 μm–2 mm fractions. Generally, the Ravensbourne River did not comply with the draft UK sediment quality guidelines for the metals analysed. This study shows the importance of identifying a suitable sediment compartment to sample for compliance with sediment quality standards. The bed and suspended sediments are the most widely used sediment compartments for sediment monitoring, but collecting sufficient mass of the < 63 μm sediment fraction for monitoring presents a challenge for urban gravel bed rivers like the Ravensbourne River. It seems appropriate to establish individual monitoring regimes for different rivers.

Distribution, diversity and abundance of bacterial laccase-like genes in different particle size fractions of sediments in a subtropical mangrove ecosystem.

This study investigated the diversity and abundance of bacterial lacasse-like genes in different particle size fractions, namely sand, silt, and clay of sediments in a subtropical mangrove ecosystem. Moreover, the effects of nutrient conditions on bacterial laccase-like communities as well as the correlation between nutrients and, both the abundance and diversity indices of laccase-like bacteria in particle size fractions were also studied. Compared to bulk sediments, Bacteroidetes, Caldithrix, Cyanobacteria and Chloroflexi were dominated in all 3 particle-size fractions of intertidal sediment (IZ), but Actinobacteria and Firmicutes were lost after the fractionation procedures used. The diversity index of IZ fractions decreased in the order of bulk > clay > silt > sand. In fractions of mangrove forest sediment (MG), Verrucomicrobia was found in silt, and both Actinobacteria and Bacteroidetes appeared in clay, but no new species were found in sand. The declining order of diversity index in MG fractions was clay > silt > sand > bulk. Furthermore, the abundance of lacasse-like bacteria varied with different particle-size fractions significantly (p < 0.05), and decreased in the order of sand > clay > silt in both IZ and MG fractions. Additionally, nutrient availability was found to significantly affect the diversity and community structure of laccase-like bacteria (p < 0.05), while the total organic carbon contents were positively related to the abundance of bacterial laccase-like genes in particle size fractions (p < 0.05). Therefore, this study further provides evidence that bacterial laccase plays a vital role in turnover of sediment organic matter and cycling of nutrients.

Particle-size fractions-dependent extracellular enzyme activity in sediments and implications for resource allocation in a subtropical mangrove ecosystem

The distribution of extracellular enzyme activities in particle-size fractions of sediments was investigated in a subtropical mangrove ecosystem. Five enzymes involved in carbon (C), nitrogen (N), and phosphorus (P) cycling were analyzed in the sand, silt, and clay of sediments. Among these fractions, the highest activities of phenol oxidase (PHO), β-D-glucosidase (GLU), and N-acetyl-glucosiminidase (NAG) were found in sand, and greater than bulk sediments of both intertidal zone (IZ) and mangrove forest (MG). This result implied that sand fractions might protect selective enzymes through the adsorption without affecting their activities. Additionally, the enzyme-based resource allocation in various particle-size fractions demonstrated that nutrients availability varied with different particle-size fractions and only sand fraction of MG with highest total C showed high N and P availability among fractions. Besides, the analysis between elemental contents and enzyme activities in particle size fractions suggested that enzymes could monitor the changes of nutrients availability and be good indicators of ecosystem responses to environmental changes. Thus, these results provided a means to assess the availability of different nutrients (C, N, and P) during decomposition of sediment organic matter (SOM), and thus helping to better manage the subtropical mangrove ecosystems to sequester C into SOM.

Distribution and fate of metals in the Montenegrin part of Lake Skadar

Skadar Lake, the largest lake on the Balkan Peninsula, is famous for a wide range of endemic and rare, or even endangered plant and animal species. Different anthropogenic pressures have, however, influenced the fragile equilibria of the lake ecosystem, with metal pollution as one of the primary concerns. Therefore, this study investigated spatial distribution of metal pollutants in the water and sediment phase of Skadar Lake, and anthropogenic and environmental factors affecting this distribution. A sieving analysis showed that sediment in Skadar Lake is mainly distributed in the three smallest fractions (colloid, clay and silt). Eleven metals were analyzed in the lake surface and bottom water, and only six of them were detected: potassium, magnesium, calcium, nickel, aluminum and manganese. They were all present at low concentrations. In contrast, sediments contained elevated levels of some metals with concentrations between 28.1-126.8 mg kg−1 for Ni, 23.6-79.2 mg kg−1 for Cr, 9.2-36.9 mg kg−1 for Cu, 199-878 mg kg−1 for Mn and 9.6-23.1 g kg−1 for Fe. Nickel exceeded consensus-based guidelines for safety towards freshwater dwelling organisms. The organic matter content of the sediment fluctuated between 4.7 and 21.5 %. No correlations were found between metal concentrations, organic matter and sediment particle size fractions, suggesting that the latter are not the main factors controlling metal accumulation in Skadar Lake.

Difference in organic carbon contents and distributions in particle-size fractions between soil and sediment on the Southern Loess Plateau, China

The purpose of this study was to assess the effect of long-term cultivation and water erosion on the soil organic carbon (OC) in particle-size fractions. The study site is located at Nihegou Watershed in the Southern Loess Plateau, China. The soil at this site is loess with loose and silty structure, and contains macropores. The results showed that the OC concentrations in sediments and in the particle-size fractions of sediments were higher than those in soils and in the particle-size fractions of soils. The OC concentration was highest in the clay particles and was lowest in the sand particles. Clay particles possessed higher OC enrichment ability than silt and sand particles. The proportions of OC in the silt fractions of soil and sediment were the highest (mean value of 53.87% and 58.48%, respectively), and the total proportion of OC in the clay and silt fractions accounted for 96% and 98% of the total OC in the soil and sediment, respectively. The loss of OC was highest in silt particles, with an average value of 0.16 Mg ha−1 y−1, and was lowest in the sand (0.003 Mg ha−1 y−1). This result suggests that the fine particle-size fraction in the removed sediment may be an important indicator to assess soil OC losses.

Distribution and bioavailability of heavy metals in different particle-size fractions of sediments in Taihu Lake, China

Taihu Lake is one of the most important water sources in the economically developed central-eastern part of China, and metal pollution is a major concern for the lake. The distribution and bioavailability of Cd, Cr, Cu, Pb, Sb and Zn were analysed in undifferentiated bottom sediments and in various particle-size fractions of the sediment from different parts of the lake. The average concentration of total metals in undifferentiated sediments ranged from 0.86 mg kg-1 (Cd) to 95.45 mg kg-1 (Zn) for the entire lake, with the highest concentrations in Zhushan Bay. The concentration of heavy metals was higher in extremely fine sands (0.064–0.125 mm) and fine sands (0.125–0.25 mm) than in other fractions. Sequential extractions showed that Cu, Zn and Cd were the most bioavailable accounting for 55.6%, 38.7% and 30.0% of their total concentration, respectively. However, the bioavailable proportion of many metals was not significantly different between grain grades except for Cu and Zn, which were higher in silts (<0.064 mm) than in other grades. Compared with the background values of local soils, the concentration of Zn, Cd, Cu, Pb and Sb was higher, indicating enrichment in the sediment. From ecological safety concerns, Zn, Cd and Cu should be examined closely because of their higher bioavailabilty in the sediment.

Cadmium concentration in sea bottom sediment and its potential risk in the upper Gulf of Thailand

Untreated or partially treated waste water discharge from industrial and domestic sources entering the Upper Gulf of Thailand have been reported to increase cadmium concentration in bottom sediment. This study was directed at providing a better understanding of cadmium transformation in the sediment from the area. Sediment samples collected from Chao Phraya River mouth (CPY), Bang Pakong River mouth (BPK) and Klong Dan estuary (KD) located in the Upper Gulf of Thailand were analyzed for cadmium concentration in various sediment particle size fractions. Using laboratory microcosms, cadmium release from sediment as affected by salinity and sediment redox condition was studied. A higher concentration of cadmium (0.2–0.6 μ g/g dry weight) was measured in finer sediment particle size fractions (< 0.075 mm) as compared to courser fractions at all sampling stations. Cadmium release from the sediment to water was influenced by both salinity and redox condition. Sediment was spiked with 10 ppm cadmium which is the cadmium level in sediment adopted by the Australia and New Zealand sediment quality guidelines which can cause adverse environmental impacts. Experiments conducted showed soluble cadmium concentration at sediment oxidation reduction conditions representative of bottom sediment were at levels that can adversely impact aquatic organisms, according to the PCADMIUM water quality guideline. In Thailand, there is no sediment quality guideline. Based on these experiments, 10 ppm of cadmium in sediment was recommended as a regulatory guidelines for allowable levels of cadmium in sediment in the study area.

Assessment of sediment toxicity by metal speciation in different particle-size fractions of river sediment

Mobility and toxicity of metals associated with sediments are generally affected by metal speciation and granular compositions. Due to the various speciation patterns of heavy metals in sediments, it is not reliable to assess the potential toxicity of heavy metals on the aquatic environment with the total concentrations of heavy metals in sediments. The purposes of this study were to investigate the distribution of metal speciation in different particle-size fractions of sediments collected from two rivers (the Ke-Ya River and Ell-Ren River) in Taiwan, and to assess their potential toxicity to the aquatic ecosystem. Metals in the exchangeable, carbonate-bound and Fe/Mn oxide-bound forms obtained by sequential extraction were considered to be mobile and related with anthropogenic pollution. The degree of metal pollution and potential toxicity of sediments were higher in the lower reaches of both rivers. The metal speciation in sediments had a bimodal distribution over particle-size fractions. Heavy metals were subject to accumulation in the silt/clay fraction (< 25 microm) and coarse sand (420-2,000 microm). By normalizing the sum of the exchangeable, carbonate-bound, and Fe/Mn oxide-bound metals, it suggested that the potential toxicity to the aquatic ecosystem was caused by the fine sediments as well as coarse sediments.

Distribution and reactivity of O2-reducing components in sediments from a layered aquifer.

The redox status of subsurface aqueous systems is controlled by the reactivity of solid redox-sensitive species and by the inflow of such species dissolved in groundwater. The reactivity toward molecular oxygen (O2) of solid reductants present in three particle size fractions of sediments from a pristine aquifer was characterized during 54 days. The stoichiometric relationships between carbon dioxide (CO2) production and O2 consumption was used in combination with sulfate production to discriminate between the contributions of sedimentary organic matter (0-87%), pyrite (6-100%), and siderite (0-43%) as the dominant reductants. The observed simultaneous oxidation of these reductants indicates that they are reactive on the same time scales. The measured reduction capacity 18-84 micromol O2/g) ranged from 8 to 42% of the total reduction capacity present as pyrite and organic carbon in the total sediment fraction (<2 mm). Fine fractions (<63 microm) were 10-250 times more reactive than their corresponding total fractions. Oxygen consumption rates decreased continuously during carbonate buffered conditions, due to a decreasing reactivity of reductants. Acidification accelerated pyrite oxidation but impeded SOM respiration. Our findings indicate that the geological history of aquifer sediments affects the amounts of organic matter, pyrite and siderite present, while environmental conditions, such as pH and microbial activity, are important in controlling the reactivity of these reductants. These controls should be considered when assessing the natural reduction activity of aquifer sediments in either natural or polluted systems.

Effect of sediment spatial variance and collection method on cladoceran toxicity and indigenous microbial activity determinations

AbstractQuantitative assessments of sediment quality frequently are based on data derived from sediments collected by grab sampling. Often only one sediment or one composited sediment is collected at a sample site, thereby preventing any determination of spatial variance. The significance of spatial variance and collection method on cladoceran toxicity and indigenous microbial activities was determined at a creosote contaminated site in the Little Scioto River in Marion County, Ohio. Replicate sediments were collected on two occasions from a horizontal sample grid (110 m2 and 1.4 m2) using an Ekman dredge and hand core. Sediment particle size fractions did not vary significantly between replicate grab samples. Survival of Daphnia magna and Ceriodaphnia dubia in 48‐h solid phase exposures varied, however, from 0 to 100% horizontally and vertically at the test site. Percent survival and β‐glucosidase activity decreased in sediment sections below a 4 to 5 cm depth. Dredged sediments produced less toxicity to the daphnids than did core collected samples. The coefficient of variance was high (&gt;40%) for both survival and hydrolase activities (alkaline phosphatase, β‐galactosidase and β‐glucosidase) between horizontal sediment replicates collected by either dredge or core. Subsample variance, however, was small (&lt;20%). These results highlight the important role that sediment heterogeneity and collection method have on sediment quality assessments.

The PAH and organic content of sediment particle size fractions

The relationship of nine Polycyclic Aromatic hydrocarbons (PAH) with organic matter present in various river sediment size fractions, from 63 μm to 1.0 to 2.0 mm, has been investigated. It is suggested that the PAH and organic matter content have bimodal distributions through the sediment size fractions which may be explained by the presence of two types of organic material in the sediment. Maxima in both factors are found in the two largest and the smallest size fractions. A positive linear relationship beween PAH concentration and organic matter has been demonstrated and the slope of this relationship has been used to identify sites where PAH pollution is generally high. The relative proportions of each PAH compound in the sediment remains relatively constant regardless of temporal and spatial differences in total PAH concentration and organic matter content and certain PAH compounds may be grouped together depending on their association with organic matter. Differing PAH compound availabilities, competition for adsorption sites and the reactivity of PAH compounds may all result in the unchanging sediment PAH profile seen in each size fraction. The organic material present in the sediment may have a similar affinity for all PAH's in a particular group.

Modelling magnetization data using SIMPLEX

Two new approaches to modelling magnetization data are described. The first approach models the magnetic properties of natural materials in terms of mixtures of possible source materials. The second approach models the magnetic properties of natural materials in terms of mixtures of magnetite and haematite crystals of varying concentrations and grain sizes. In the second approach the magnetic characteristics of magnetite and haematite and their variation with grain size are described by bicubic spline functions. The methods are applied to remanence, and susceptibility measurements on a suite of lake sediment particle size fractions and on a set of samples from a soil profile.