Ratios In Sediments Research Articles

The visualization of geophysical and geomorphologic data from the area of Weddell Sea by the generic mapping tools

The paper concerns GMT application for studies of the geophysical and geomorphological settings of the Weddell Sea. Its western part is occupied by the back-arc basin developed during geologic evolution of the Antarctic. The mapping presents geophysical settings reflecting tectonic formation of the region, glaciomarine sediment distribution and the bathymetry. The GlobSed grid highlighted the abnormally large thickness of sedimentary strata resulted from the long lasting sedimentation and great subsidence ratio. The sediment thickness indicated significant influx (>13,000m) in the southern segment. Values of 6,000–7,000 m along the peninsula indicate stability of the sediments influx. The northern end of the Filchner Trough shows increased sediment supply. The topography shows variability -7,160–4,763 m. The ridges in the northern segment and gravity anomalies (>75 mGal) show parallel lines stretching NW-SE (10°–45°W, 60°–67°S) which points at the effects of regional topography. The basin is dominated by the slightly negative gravity >-30 mGal. The geoid model shows a SW-NE trend with the lowest values <18 m in the south, the highest values >20m in the NE and along the Coats Land. The ripples in the north follow the geometry of the submarine ridges and channels proving correlation with topography and gravitational equipotential surface.

Detonation nanodiamonds dispersed in polydimethylsiloxane as a novel electrorheological fluid: Effect of nanodiamonds surface

Using deagglomerated nanodiamond particles of 4–5 nm suspended in polydimethylsiloxane (PDMS) we have fabricated fluids demonstrated pronounced electrorheological effect. It has been revealed that the type of functional groups on nanodiamond particle surface plays a crucial role in the behavior of the suspensions under electric field. Suspension of hydrogenated nanodiamonds has demonstrated the most powerful electrorheogical effect. The high values of yield stress of the order of 80–90 Pa have been detected at extremely low concentrations of nanodiamond particles (3–4 wt%). The suspensions has outstanding sedimentation stability: the sedimentation ratio is more than 90% after 30 days. A power law dependence of the yield stress on the electric field, τ ∼ E1.0-1.5 indicates mainly the conduction mechanism of the effect. Suspensions of carboxylated nanodiamonds in PDMS reveal qualitatively different behavior and the electrophoresis occurs. The paper discusses the reasons of different rheological behavior depending on nanodiamond surface functionalization. The prospects of nanodiamonds application as filler for electrorheological fluids have been shown.

Tellurium in Late Permian‐Early Triassic Sediments as a Proxy for Siberian Flood Basalt Volcanism

AbstractWe measured the concentrations of trace elements in Late Permian to Early Triassic sediments from Spitsbergen. High mercury concentrations in sediments from the level of the Permo‐Triassic Mass Extinction (PTME) at this location were previously attributed to the emplacement of the Siberian Traps Large Igneous Province and used to link the timing of volcanism with the record of environmental change and extinction in these sediments. We investigated the use of the moderately to highly volatile, siderophile elements Ni, Zn, Cd, Sb, Te, Re, and Tl as proxies for the intensity of Siberian volcanism. These trace elements, like Hg, have high concentrations in volcanic gas compared to crustal rocks. Tellurium is highly enriched at the PTME, and Te/Th ratios increase by a factor of ∼20 across the PTME, similar to the variation in Hg/total organic carbon (TOC) in the same samples. Te/Th and Hg/TOC values imply that Siberian volcanism initiated at the onset of the PTME, coincident with the start of the δ13Corganic excursion and abrupt warming. Based on Te and Hg, most Siberian volcanism occurred between the two phases of the PTME boundary (a period of less than 100 ky), but also continued into the Early Triassic. The duration of Siberian volcanism inferred from Te/Th and Hg/TOC is shorter than that indicated by recent high‐precision U‐Pb ages of Siberian intrusive and extrusive rocks. Te concentrations and Te/Th ratios in sediments represent a useful new proxy for volcanism, which can be used to link the marine sedimentary record with large volcanic events on land.

Paleoclimatic indication of X-ray fluorescence core-scanned Rb/Sr ratios: A case study in the Zoige Basin in the eastern Tibetan Plateau

The X-ray fluorescence (XRF) core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change. However, some factors could affect Rb/Sr ratios, causing misinterpretation and limiting its application. In this study, we present a high-resolution XRF core-scanned Rb/Sr record of core ZB13-C1 from the Zoige Basin in the eastern Tibetan Plateau. To validate its application, we correlated this record with the chemical index of alteration (CIA) and other paleoclimatic proxies. Our results showed that (1) the core-scanned Rb/Sr ratios and CIA were reliable proxies of chemical weathering intensity in fine-grained sedimentary sequences; (2) the low values of core-scanned Rb/Sr ratios and CIA were significantly correlated with high total organic carbon content, arboreal pollen content, carbonate content, and C/N ratios, confirming its reliability as a proxy for the Asian summer monsoon intensity; (3) the core-scanned Rb/Sr ratios at core depths of 25–0.3 and 56–17 m were unable to reliably reflect chemical weathering intensity due to both the grain-size effect and the low test accuracy. Our study highlights the need for mutual verification of multiple indicators before accurately applying Rb/Sr as a paleoclimatic proxy in other similar study areas.

Characteristic analysis of phospholipid fatty acids (PLFAs) in typical nutrient polluted lake sediment in Wuhan

The process of urbanization aggravates the endogenous pollution of urban lake sediment, and polluted sediment may seriously affect the quality of the water in lakes. At present, it is difficult to distinguish the difference between sediment that is heavily polluted by nitrogen (N) and phosphorus (P) when using an analysis based on a physicochemical index classification. The current study applied phospholipid fatty acid (PLFA) technology to further analyze the sediment characteristics from the perspective of microbiology. Surface sediment from five urban lakes that are heavily polluted with N and P in Wuhan were sampled. Statistical approaches were used to analyze the microbial community structure in the sampled sediment, and to determine the correlations between the microorganisms and physicochemical indices. The most severely polluted lake sediment had similar PLFA structures, the highest saturated fatty-acid content, and bacteria as the dominant microorganism. However, there were differences between the microbial biomass of the various sediment samples, which may have been related to the degree of N and P pollution. Analysis of the microbial diversity in the sediment samples indicated that the bacteria were experiencing starvation and nutrient pressure, which may have been due to the dissolved oxygen concentration of the heavily polluted lake sediment. A correlation analysis showed that the endogenous N and P had different effects on the microbes of the polluted sediment. A redundancy analysis (RDA) demonstrated that the N/P ratio had the greatest influence on the PLFA species, accounting for 83% of the cumulative interpretation. To effectively promote the role of sediment microorganisms on circulating elements, it is necessary to regulate the N/P ratio of the sediment to some extent. When the N/P ratio in sediment exceeds 6, N pollution should be prioritized.

Preparation and characterization of icariin nanosuspension and lyophilized powder

The optimal process conditions for preparing icariin nanosuspension(ICA-NS) and lyophilized powder were determined to initially investigate their stability and characterize the prepared nanosuspension. The anti-solvent precipitation-high shear method was used in the experiment, and the particle size(size), polydispersity index(PDI), and sedimentation ratio(H_0/H) were used as indicators to determine the optimal process conditions of ICA-NS by single-factor test method. Lyophilized powder of nanosuspension was prepared by freeze-drying method, and its crystalline morphology was observed by transmission electron microscope. The equilibrium solubility of icariin, nanosuspension and lyophilized powder was determined by shake flask method and their stability was initially investigated. The crystal structure of nano-lyophilized powder was characterized by differential scanning calorimetry(DSC) and X-ray powder diffraction(XRD). Finally, the dissolution in vitro of nano-lyophilized powder was determined by the small cup method to prepare the ideal icariin nanoparticles. Soy lecithin(SPC) was used as the main stabilizer and povidone was used as the steric stabilizer. The prepared ICA-NS was nearly round in shape, uniform in size, and stable at room temperature. The average particle size was(62.51±7.11) nm. The drug loading was 16% and the solubility was 50 times higher than that of the original drug. Drugs in suspension and lyophilized powder were dispersed in nanoparticles in an amorphous state. The in vitro dissolution experiments showed that the cumulative release rate of nano-lyophilized powder reached 100% at 10 min, indicating that the dissolution rate of lyophilized powder was significantly increased after preparing into nano-lyophilized powder. Preparation of ICA-NS lyophilized powder by antisolvent precipitation-high shear method is simple, easy to operate, and can significantly improve its water solubility. However, the process conditions have some influence on its stability, which needs further study.

Spatial pattern and surface-specificity of particle and microorganism deposition and attachment: Modeling, analytic solution and experimental test

Hypothesis: Understanding microparticle and living cell deposition and attachment on surfaces from a flow is a long-standing surface-science problem, pivotal to developing antifouling strategies. Recent studies indicate a complex non-conservative and surface-specific nature of adhesion and mechanical contact forces that determine attachment kinetics. This requires new models and kinetic data, however, observed deposition rates (e.g., in parallel-plate flow chamber, PPFC) represent a superposition of attachment and bulk transport. Here, we propose to deduce attachment rates (as an appropriate rate constant) from spatial deposition profiles along PPFC and develop an analytical solution for the full problem, suitable for deposition data analysis and parameter fitting.Experiments: Analytical solution, validated by numerical simulations, reveals relation between the deposition profile along PPFC and key model parameter B, the ratio of sedimentation and attachment rates. Its use is demonstrated on experimental data obtained in a PPFC for particles and bacteria on various surfaces.Findings: Fitted B values highlight correlation with the particle/substrate nature and consistently explain the observed trends along PPFC, both decreasing and increasing. Thus derived attachment rates will serve as basis for future microscopic modelling that would relate attachment to appropriate surface and contact-mechanical characteristics of particles and substrate and flow conditions.

A novel α-(8-quinolinyloxy) monosubstituted zinc phthalocyanine nanosuspension for potential enhanced photodynamic therapy

Objective To prepare α-(8-quinolinyloxy) monosubstituted phthalocyanine zinc nanosuspension (ZnPc-NS) for photodynamic therapy by intravenous administration. Methods The formulation and preparation technology of ZnPc-NS were assessed by particle size using the precipitation-high pressure homogenization method. The efficacy of ZnPc-NS was evaluated based on particle size, zeta potential, sedimentation ratio, TEM imaging, stability assessment, photodynamic activity and safety. Results and discussion The content, average particle size, polydispersity and photodegradation constant of ZnPc-NS were 0.2 mg/ml, 219.7 ± 7.41 nm, 0.19 ± 0.02 and 0.006, respectively. The photosensitization rate of singlet oxygen (1O2) of the ZnPc-NS was three times higher than that of the ZnPc DMF solution. ZnPc-NS exhibited optimal antitumor activity in HepG2 cells under light exposure and low photo- and non-light-associated toxicity in HELFX cells. In addition, low hemolysis and vascular stimulation were evident in the experiments performed. Conclusion The ZnPc-NS exhibited optimal stability, faster photosensitization rate of 1O2, and optimal antitumor activity and safety than the ZnPc DMF solution, which could provide potential support for further research and development.

The distribution of (234U/238U) activity ratios in river sediments

Uranium (U) isotopes can be used to estimate the comminution age of sediments, i.e. the time elapsed from sediment production on continents, via weathering and physical erosion, to deposition in the sedimentary record. The calculation of this comminution age is based on measured (234U/238U) activity ratios in river sediments, and inferred time-dependent recoil effect, which leads to the preferential release of 234U from mineral lattices during erosion processes. In this study, we report on a large-scale (234U/238U) investigation of modern river sediments worldwide, with the aim to determine the extent to which parameters such as grain size, lithology, weathering, climate and geomorphology may influence the distribution of U isotopes in fine-grained sediments. Our extensive dataset (N = 64) includes U isotopic measurements for many of the world’s largest rivers, but also rivers draining particular climatic and geological settings. Our results indicate that sediments collected from river basins draining mostly igneous, metamorphic or volcanic rocks often display (234U/238U) ratios > 1, with clay-size fractions (<4 µm) being less depleted in 234U (higher 234U/238U) than corresponding silt-size fractions (4–63 µm). In contrast, sediments derived from multi-lithological basins or draining sedimentary rocks are typically characterized by (234U/238U) ratios <1, with clays generally exhibiting more depleted 234U signatures than silts. Taken together, these observations suggest that the formation of secondary clay minerals in soils from basins draining mostly igneous, metamorphic is accompanied by partial incorporation by recoil injection of 234U initially released during weathering processes, possibly from U-rich minerals, such as sphene or apatite. Instead, in multi-lithological catchments draining sedimentary rocks, we propose that the erosion of recycled sediments having experienced several cycles of weathering, possibly over glacial-interglacial timescales, could explain the much lower (234U/238U) ratios observed in clay-size fractions. While no direct relationships can be identified between sediment (234U/238U) ratios and lithology, weathering intensity, climatic or geomorphic parameters in corresponding river basins, we show that the catchment size probably plays an important role in controlling the distribution of (234U/238U) in river sediments, through its direct influence on the sediment residence time. Finally, a multiple regression analysis of our data, combining various environmental parameters for the lithology, climate and geomorphology of studied river basins, indicates predicted (234U/238U) values that are very similar to measured values (with R2 ∼ 0.8). This finding provides further support for the usefulness of (234U/238U) ratios in the sedimentary record for reconstructing past landscape changes and their effect on sediment transport and residence time in river basins.

Three-Disperse Magnetorheological Fluids Based on Ferrofluids Induced Modification of Sedimentation by Addition of Nanoparticles

The effect of mixing suspended nanoparticles into a bi-disperse magneto-rheological fluid on sedimentation phenomena is explored. A reference bi-disperse MRF has been modified using a ferrofluid containing magnetite nanoparticles of two shapes (spheres or hexagonal platelets) suspended in paraffin-oil as carrier fluid. The reference MRF was prepared with a mixture of two diameter sizes for the micrometric particles. The reference MRF was also prepared using two different grades of carbonyl-iron micrometric particles (herein these will be referred to as HARD and SOFT), which differ each other for their mechanical properties. The experiment monitored the evolution with time of the sediment-supernatant interface. This experiment showed that the presence of nanoparticles (particularly the spherical ones) slows down the sedimentation effects in terms of ratio and rate, independently of the other characteristics of the fluid. This study also showed that fluids based on SOFT carbonyl iron powders, in presence of nanospheres, are more stable than HARD carbonyl iron powder based fluids, since their sedimentation rate slows down in the long term. At the same time, HARD particle-based magnetorheological fluids show smaller sedimentation ratios than SOFT based fluids.

Clay minerals, Sr-Nd isotopes and provenance of sediments in the northwestern South China Sea

The clay mineralogy and Sr-Nd isotopic composition of sediments collected in the northwestern South China Sea (SCS) were investigated to understand sediment provenance and changes in the SCS since the Late Pleistocene. Our results show that the clay mineral assemblages of the surface sediments are characterized by high amounts of illite and smectite, and low amounts of kaolinite and chlorite. The 87Sr/86Sr ratios of the surface sediments vary from 0.709617 to 0.734416, and εNd values range from −11.6 to −8.3. The clay minerals and Sr-Nd isotope records suggest that sediments in the northwestern SCS are derived from multiple sources. The sediments deposited in the eastern shelf offshore of Hainan originate predominantly from Hainan Island and South China, whereas sediments in the western shelf offshore of Hainan are derived mainly from Indochina and Hainan Island. However, sediment source and transport mechanisms in the northwestern slope of the SCS are more complicated. Our results suggest that input from the west may be the major sediment source, but regions in the east (Taiwan and Luzon) also contribute part of the terrigenous materials. Downcore variations of Sr-Nd isotopic composition in core sediments show clear glacial–interglacial fluctuations. Higher 87Sr/86Sr ratios occur during glacial period, indicating that the input of terrigenous materials from old continental rocks becomes one of the important sediment sources during these periods. The exposure of continental shelf and southward migration of the coastline during the glacial sea-level lowstand led to an increase of terrigenous supply to the northwestern slope of the SCS. The paleo-Red River and Indochina are also potentially important contributors.

Triple oxygen isotopes of cherts through time

It has long been recognized that the stable oxygen isotope 18O/16O ratios of chemical sediments show a systematic decrease with increasing age. This continuous, 3.8 Ga long secular trend has been attributed to 80 °C hot early Earth oceans, a ~15‰ lower 18O/16O ratio of Archean seawater, or diagenetic obliteration of the original isotope signal. We demonstrate that high-precision triple oxygen isotope measurements including the rare third stable oxygen isotope 17O on silica rocks (cherts) can be used to shed light on this major problem in geochemistry. Our triple oxygen isotope data do not support 80 °C hot oceans in the Archean. The data also exclude that the 18O/16O of seawater was much lower in the Archean. Also, a simple freshwater-origin of cherts is not supported by the new data. We discuss the effects of diagenetic alteration on the triple oxygen isotope compositions of cherts and show that the Archean and Proterozoic cherts could have equilibrated with fluids with higher 18O/16O than today's oceans. For the Archean cherts, the high 18O/16O fluids required to explain the observations could reflect the composition of ambient seawater or of modified hydrothermal fluids. Oceans with higher 18O/16O ratio would be expected for an Archean “water world” without large continents. High 18O/16O fluids, however, could also have formed locally by reactions between seawater and the oceanic crust. Our study shows that high-precision triple oxygen isotope data provide new understandings of processes deep in time.

Quantification of Po-210 and Pb-210 as tracer of sediment resuspension rate in a shallow riverine system: Case study from southeast Michigan, USA

Polonium-210 and Pb-210 were measured in surficial benthic sediments and particulate matter collected in sediment traps deployed at five different locations in the Clinton River, a dynamic system, in Lake St. Clair in Southeast Michigan to quantify the sediment resuspension rates and determine the particle residence time. The mean 210Poxs/210Pbxs activity ratio of suspended trap and surficial bottom sediments were 0.72 ± 0.12 (n = 16, range: 0.42–0.89) and 0.79 ± 0.15 (n = 15, range: 0.40–1.00) indicating that a major fraction of trapped material is from resuspended bottom sediments. Sediment resuspension rate calculated using a single box model approach yielded a resuspension rate of 0.1–1.0 g cm−2 yr−1 using 210Po and 0.2–1.4 g cm−2 yr−1using 210Pb. Particle residence time varied from 0.3 to 3.9 days using 210Pb and 0.9–13.4 days for 210Po. This present study indicates that sediment resuspension is considerably high in Clinton River and thus any decision on remedial action towards the restoration such as dredging, natural attenuation is challenging. This present study has direct relevance to the transport and resuspension of other sulfur group elements (Se, O, etc) and lithogenic elements (e.g., Th).

Extent of zeolite synthesis via alkaline fusion from tailings dam sediments

Zeolite was synthesized via alkaline fusion from the tailings dam sediments of a sand mine in southern Brazil. The sediments are composed of a mixture of illite, kaolinite, vermiculite, quartz and K-feldspar yielding a silty-loam texture. The extent of zeolite synthesis was tested under varied NaOH:sediment ratio, temperature and fusion time. At the NaOH:sediment ratio of 8:5 and fusion temperature of 600 °C, all minerals were dissolved and converted in faujasite, except a quartz residue of less than 5 wt%. The synthetic faujasite shows intergrown octahedral habit, grain size < 2 µm, specific surface area of 760 m2 g−1 and cation exchange capacity of 4.6 cmol kg−1. Experiments at lower NaOH:sediment ratio produced lower amounts of zeolite from 6:5 to 5:5 and 4:5, faujasite fraction declined from 73 to 50 wt%. At an NaOH:sediment ratio of 3:5, the faujasite fraction dropped to 0.7 wt%, below which no faujasite was formed. By decreasing temperature from 550 to 250 °C, a smooth decrease in faujasite formation was observed, from 64 to 29 wt%. A synthetic analogous of ferrierite appeared in the runs at 300 and 250 °C. Experiments using prolonged heating (up to 12 h) at low temperatures (300, 200 °C) and low NaOH:sediment ratio (3:5) did not enhance zeolite formation. Kaolinite and vermiculite were dissolved in all runs, while residual illite was ubiquitous and residual quartz was present in all experiments.

Sediment transport and bed evolution in a 180∘curved channel with lateral intake: Numerical simulations using Eulerian and Discrete Phase models

Lateral intakes are hydraulic structures used for domestic, agricultural and industrial water conveyance, characterized by a very complex three-dimensional morphodynamic behavior: since streamlines near the lateral intake are deflected, some vortices form, pressure gradient, shear and centrifugal forces at the intake generate flow separation and a secondary movement, responsible for local scour and sediment deposition. On the other side, the modeling of flows, besides the sediment transport, in curved channels implies some more complications in comparison with straight channels. In this research, this complex process has been investigated experimentally and numerically, with the mechanism of sediment transport, bed topography evolution, flow pattern and their interactions. Experiments were performed in the Laboratory of Tarbiat Modares University, Iran, where a U-shaped channel with a lateral intake was installed and dry sediment was injected at constant rate into a steady flow. Due to the spiral flow, the bed topography changes significantly and the bed forms in turn affect the sediment entering the intake. Different from the previous works on this topic which were mainly based on laboratory experiments, here, Computational Fluid Dynamics (CFD) numerical simulations with FLUENT software were also performed, specifically with the two-phase Eulerian Model (EM) and Discrete Phase Model (DPM), at the aim of evaluating their performance in reproducing the observed physical processes. This software is used for a large variety of CFD problems, but not much for simulating sediment transport phenomena and bed topography evolution. The comparison of the results obtained through the two models against the laboratory experimental data proved a good performance of both the models in reproducing the main features of the flow, for example, the longitudinal and vertical streamlines and the mechanism of particles movement. However, the EM reveals a better performance than DPM in the prediction of the secondary flows and, consequently, of the bed topography evolution, whereas the DPM well depicts the particles pattern, predicts the location of trapped particles and determines the percentage of sediment entering the intake.The numerical models so calibrated and validated were applied to other cases with different positions of the intake in the bend. The results show that mechanism of sediment entrance into the intake varies in different position. If the intake is installed in the second half of the bend, the sediment accumulates along the inner bank of the bend and enters the intake from downstream edge of intake; on the other side, if it is placed in the first half of the bend, the sediment accumulates along both the inner and the outer bends and, therefore, more sediment enters the intake. Also the results of the simulations performed with the DPM model for different positions of the lateral intake show that for all discharge ratios, the position of 120∘is the one which guarantees the minimum ratio of sediment diverted to the intake (Gr).

Dredging in an estuary causes contamination by fluid mud on a tourist ocean beach. Evidence via REE ratios

Deposits of fluid mud on wave-dominated beaches are rare. Where they happen frequently and periodically, they can be associated with anthropic processes that bring fluid mud to the shoreface and surf zone. To determine the reason for the frequent deposition of fluid mud at Cassino Beach (Southern Brazil) in the 2014–2020 period, the La/Eu and Gd/Yb ratios in marine, beach, and adjacent Patos estuary sediments were investigated. Mud from the beach showed similar ratios of REE to dredged sediments from the harbor basin and navigation channel within the estuary. Industrial and port activity changes REE ratio in sediments of the navigation channel, and they are distinct from naturally deposited marine and estuarine sediments. We conclude that the mud deposition events at the beach are most likely associated with dredging processes in the estuary especially where overflow is the source of fluid mud on the beach shoreface.

Particle size distribution of sediment detached from rills under raindrop impact in semi-arid soils

Limited information is available on the role of raindrop impact (RI) in the particle size distribution of sediment (PSDs) and the homogeneous of sediment particles eroded in rills under slope gradients particularly in semi-arid soils. Toward this, a laboratory experiment was designed with three dominant semi-arid soils consist of loamy sand, clay and sandy clay, at four slope gradients (5, 10, 15, and 20%) under two soil surface conditions (SSC) i.e, with raindrop impact (RI) and without RI using a rainfall simulator with 90 mm h−1 in intensity for 30 min. Forty eight rainfall events were setted up to soil samples packed into the flumes with 0.4 m width by 4 m length. Runoff and sediment ratio for the two SSC was computed using the ratio of values with RI to their values without RI in each time interval from starting runoff. Based on the results, the soils appeared different behavior in runoff and sediment ratio during runoff generation time. In clay and sandy clay, contribution of RI in runoff and sediment increased during runoff generation in the rills which was associated to higher percentage of water-stable aggregates. The two soils produced higher runoff and sediment under RI with increasing slope gradient. The sediment selectivity by concentrated flow was determined using the comparison between PSDs in steady-state runoff and the PSD of original soil (PSDo). The PSDs curves of loamy sand were similar for the two SSC at slope gradients and overlapped almost with the PSDo, indicating lower importance of RI in the sediment transport selectivity in the soil with lower water-stable aggregates. Enrichment ratio of particles in sediment (ERs) varied with both soil texture and slope gradient. The contribution of RI in variation of ERs was more obvious in sand, indicating lower selectivity of sand to detachment by concentrated flow. The geometric mean diameter (dg) and standard deviation (δg) of the sediment particles were defined as a measure to determination of the homogeneity of sediment. Values of these indices increased under RI, indicating the contribution of RI in the transportability of all soil particles especially coarse particles. This study revealed that the RI is the major factor controlling runoff, sediment, the selectivity of soil particle by concentrated flow and sediment homogeneity in semi-arid soils. These variables can be quantified by PSDs, ERs, dg and δg for the two soil surface conditions and compared with the original soil.

Organic carbon accumulation and productivity over the past 130 years in Lake Kawaguchi (central Japan) reconstructed using organic geochemical proxies

Organic matter in lake sediments contains information that can be used to reconstruct lake environmental histories over decades or centuries. In this study, we used organic geochemical proxies (i.e., total organic carbon [TOC], TOC/total nitrogen [TN] atomic ratios [C/N], stable carbon isotope ratios of TOC [δ13CTOC] and palmitic acid [δ13CC16:0], and nitrogen isotope ratios of bulk sediment [δ15Nbulk]) in sediments from Lake Kawaguchi, Japan, to reconstruct detailed histories of the organic matter accumulation and lake productivity over the past 130 years. Vertical profiles of the mass accumulation rate (MAR) of TOC in the eastern lake basin (core KAW14-7A) showed parallel increases with the C/N ratio from the 1960s to the 1980s, indicating an accelerated delivery of terrestrial organic matter via anthropogenic land-use change. In contrast, the C/N ratios in the western and central basins (cores KAW14-1A and KAW14-4B, respectively) were almost constant prior to the 1980s, suggesting that the increasing trends in the TOC MAR values in these cores are most likely attributable to the onset of eutrophication associated with rapid economic growth after the mid-1950s. On the other hand, the δ15Nbulk showed a gradual increase from the late 1870s, providing evidence for anthropogenic nitrogen input to the lake prior to the apparent eutrophication. After the 1960s–1970s, the δ15Nbulk values rapidly increased, demonstrating water deterioration associated with the direct nutrient discharge into the lake from domestic wastewater. The δ13CC16:0 profiles displayed similar increasing trends to δ15Nbulk from the mid-1960s, demonstrating a close relationship between lake productivity and anthropogenic nitrogen input in Lake Kawaguchi. Our geochemical records as a whole clearly show high algal productivity and enhanced deposition of organic matter in recent decades, suggesting that the amelioration of the lake water is a likely consequence of the transfer of nutrients to the sediment by enhanced productivity, rather than a decrease in the amount of nutrient inflow into the lake.

A 23000 year old record of paleoclimatic and environmental changes from the eastern Arabian Sea

Abstract Climate of the eastern Arabian Sea is highly influenced by both global climate and Indian monsoon. We produced multi-proxy records of benthic foraminiferal biofacies and stable isotope ratio (δ13C and δ18O), planktic foraminifera and total organic carbon (wt%) content of sediments from core SK291/GC11 in the upper continental shelf off Mangalore, off eastern Arabian Sea (EAS) to decipher paleoenvironmental and paleoclimatic changes during the past ~23,000 years. The monsoon was weak during the Last Glacial Maximum ~23,000–18,000 calibrated years before Present (cal yr BP) when sea level was lower. Globigerinoides ruber populations fluctuate from 30 to 60% in the studied interval with a maximum during ~6000–5000 cal yr BP and a minimum during 19,000–17,000 cal yr BP. The δ18O values of benthic foraminifer Ammonia gaimardii suggest pronounced cooling phases during ~23,000–18,000 cal yr BP, and a short-term cooling at ~6000 cal yr BP. Several intervals of high organic productivity and low oxygen conditions were identified based on benthic foraminiferal biofacies during 23,247–682 cal yr BP. Wind-induced surface mixing was intense during 3200–530 cal yr BP as evidenced by high Globigerina bulloides abundances. The core was affected by moderate chemical weathering and solar variability appears to have been an important forcing factor in shaping climate of the region.

Plutonium in Southern Yellow Sea sediments and its implications for the quantification of oceanic-derived mercury and zinc

The spatial distributions of mercury (Hg) and zinc (Zn) concentration and the isotopic composition of plutonium (Pu) were investigated in surface sediments and sediment cores collected from the Southern Yellow Sea (SYS) during May 2014. The variation of the 240Pu/239Pu atom ratio (0.18–0.31) in the surface sediments of the SYS clearly indicated a signal of close-in fallout input from the Pacific Proving Ground (PPG). The buried 239+240Pu in the sediment of the SYS was estimated to be (4.7 ± 0.5) × 1010 Bq y−1 during the period from 2011 to 2014, of which ∼33% (1.5 × 1010 Bq y−1) was derived from the PPG by long-range transport via ocean currents (e.g., the North Equatorial Current and Kuroshio Current). The concentrations of Hg and Zn varied from 0.003 to 0.067 mg kg−1 and from 43.9 to 137 mg kg−1, respectively, and exhibited positive correlations with the 239+240Pu activity both in the surface sediments (0–1 cm) and upper layers (7 cm) of the sediment cores. Therefore, by using Pu as a tracer, we estimated that the oceanic input contributed 2.0 tons y−1 of Hg and 1.0 × 103 tons y−1 of Zn to the SYS sediments between 2011 and 2014, which accounted for 33% and 3% of total buried Hg and Zn, respectively. These findings indicate that environmental pollution control should also consider the oceanic contribution of some pollutants. The results of the present work help to elucidate the biogeochemical cycling of trace metals in marginal seas, and are helpful for managing environmental pollution in marine environments.