Effects Of Sediment Characteristics Research Articles

Effects of sediment characteristics on the erosion of Pelton turbine

As Pelton turbines are increasingly used in high mountain regions because of their unique advantage of high-water head adaptability, the hydraulic characteristics and multi-phase flow behaviour in Pelton turbines have attracted the attention of many scholars. Most notably, the presence of solid particles such as sand exists in natural river systems, which end up in the turbines, causing erosion. This has become an international academic issue which has not been fully developed yet. In this study, three-phase simulations based on Eulerian–Lagrangian methodology are conducted to investigate the erosion phenomenon, especially in the bucket region. Sediment particle characteristics such as size and concentration in both the distribution system and buckets region are analysed. The innovation of this study is that, unlike other erosion investigations, it focuses on the impact angle of the jet flow as this is a unique characteristic of Pelton turbines. Furthermore, the sediment particle's flow characteristics at different bucket rotating angles and how they influence the erosion mechanism are also investigated. Results reveal that larger particles cause greater erosion on the bucket. In small particle and standard diameter conditions, the impact angle is mostly below 5 ∘ . Finally, this study presents the first successful attempt in using rotating angle to describe the erosion in a Pelton turbine. A corrected erosion model adapted to the Pelton turbine is given through regression and proves effective in predicting erosion.

Effects of sediment characteristics on the sediment transport capacity of overland flow

The transport of sediments is a crucial part of soil erosion. Accurately calculating the sediment transport capacity is key to the construction of soil erosion process models. Research on Tc has focused mainly on the dynamics of a single particle of sediment and hydraulic variables. There have been few studies of the impact of soil aggregates on the Tc. To clarify how sediment characteristics, including those for single particles and aggregates, affect the Tc of overland flow with no raindrop import, flume experiments were implemented at slope gradients varying from 5.24% to 26.80% and flow discharges ranging from 0.68 to 5.41 × 10−3 m2 s−1. The experimental materials were five typical soils in China. The results indicated that the correlation between the measured Tc and sediment mechanical composition indexes of the five soils was indistinctive in this study. The sediment settling velocity with aggregates has a significant correlation with the measured Tc. New equations, including for the sediment settling velocity with aggregates ωud75, were established to calculate the Tc. The empirical equation that included ωud75, slope gradient and unit discharge performed greatly in predicting Tc (R2 = 0.93, NSE = 0.90). ωud75 can effectively improve the calculation accuracy of Tc. The new equation including flow and sediment properties obtained through dimensional analysis performed well in predicting Tc (R2 = 0.99, NSE = 0.91), and the calculation accuracy was better than that of the empirical model derived in this study. These findings indicate that the sediment settling velocity is an important variable in the equation for predicting sediment transport capacity of overland flow.

Effects of Sediment Characteristics on Carbon Dioxide Fluxes Based on Interacting Factors in Unvegetated Tidal Flats

The contribution of unvegetated tidal flats to global net primary production is comparable to that of some vegetated coastal habitats. However, compared to carbon flux regulating factors in vegetated habitats, those in unvegetated tidal flats are not well understood, particularly in terms of their cause-effect relationships. Maximum gross primary production (GPPm), net primary production (NPP) and total respiration (TR) during emersion at noon when the irradiance level was at the saturation level for photosynthesis in nine unvegetated tidal flats across the Taiwan Strait in tropical and subtropical regions were determined in winter and summer from 2011 to 2016 to examine the direct and indirect relationships between sediment characteristics and carbon fluxes by using structural equation models (SEM). Most of the GPPm and NPP values were higher in winter than in summer. Conversely, the TR values were higher in summer than in winter. The NPP values at some sites shifted to negative values in summer, indicating the sites were carbon sources. The values of GPPm, TR and NPP for the tidal flats all increased significantly with increasing sediment mud content. The SEM results showed that the sediment mud content directly increased GPPm or indirectly increased GPPm via a compositional shift in benthic microalgae. The sediment mud content also directly increased TR or indirectly increased TR via increased organic matter content. The contribution of benthic microalgal and macrofaunal biomass to TR was relatively minor. This result suggests that primary production was stimulated mainly by the organic matter content rather than by increased microalgal biomass. With the integrated SEM framework, our results showed mechanistic evidence of how sediment mud content acted as a critical factor regulating carbon fluxes in unvegetated tidal flats.

The effect of sediment characteristics on bioturbation-mediated transfer of lead, in freshwater laboratory microcosms with Lumbriculus variegatus.

While it has been well established that sediment bioturbators can affect the fate of metals in aquatic systems and that the fate of metals there can depend on sediment characteristics, the interaction between these influences is not well known. The present study therefore investigated whether the influence of a sediment bioturbator on the fate of metals is affected by sediment characteristics. This was investigated using two laboratory microcosm experiments with lead-contaminated sediment and the oligochaete Lumbriculus variegatus. The first experiment used sediment collected from five Toledo Bend reservoir sites that differed in sediment characteristics, and analyses looked at the influence of sediment organic matter, sediment silt/clay content, sediment pH, and pore-water pH. In the second experiment, organic matter and silt/clay content of Toledo Bend reservoir sediment were varied experimentally using alpha-cellulose and clay, and Pb transfer to the water column and bioaccumulation were again quantified. Both experiments were conducted with sediment spiked with Pb to a concentration of 100 µg/g, at an oligochaete density of 6279 ind./m². In the first experiment, the Pb concentrations in the water column and those in the worms at the end of the 14-day experiment differed among sediment-collection sites. Silt/clay content and sediment pH were the two most important variables influencing Pb transfer from sediment to the water column. A multiple regression model with these variables explained 58% of the variability in this lead transfer. For Pb accumulation by the worms, sediment organic matter and pore-water pH were the two most important variables. This regression model explained 85% of the variability in tissue Pb levels. In the second experiment, where the individual effects of the organic matter and silt/clay content on Pb transport and distribution were assessed, the use of sediment with more organic matter resulted in a reduction in both the Pb transfer to the water column and the accumulation in worms. The increase in the sediment's silt/clay content resulted in a reduction in Pb bioaccumulation only. Overall, the results of the present study demonstrate that sediment pH, pore-water pH, organic matter, and silt/clay content influence the bioturbation-mediated transfer and the environmental distribution of Pb.

The Effect of Sediment Characteristics to Dispersion of Porous Cylinder Surrounded by Fluid

In order to study the effect of sediment characteristics to dispersion of porous cylinder surrounded by fluid, a model of porous cylinder surrounded by fluid is built. Based on the elastic-dynamic theory of liquid-saturated porous solid and numerical computation, the characteristic of dispersion of this structure are discussed. Combined with the HT suspension model, we explore the effect of the changes of the volume content and particle size to the dispersion. Results show that the dispersion is influenced by the changes of the volume content and particle size. With the increase of the volume content and particle size, the phase velocity of Stonely wave becomes larger. These conclusions will have potential application on the characteristics detection sediment and porous medium.

Salt marsh sediment characteristics as key regulators on the efficiency of hydrocarbons bioremediation by Juncus maritimus rhizospheric bacterial community.

Mitigation of petroleum hydrocarbons was investigated during a 5-month greenhouse experiment, to assess the rhizoremediation (RR) potential in sediments with different characteristics colonized by Juncus maritimus, a salt marsh plant commonly found in temperate estuaries. Furthermore, the efficiency of two bioremediation treatments namely biostimulation (BS) by the addition of nutrients, and bioaugmentation (BA) by addition of indigenous microorganisms, was tested in combination with RR. The effect of the distinct treatments on hydrocarbon degradation, root biomass weight, and bacterial community structure was assessed. Our result showed higher potential for hydrocarbon degradation (evaluated by total petroleum hydrocarbon analysis) in coarse rhizosediments with low organic matter (OM), than rhizosediments with high OM, and small size particles. Moreover, the bacterial community structure was shaped according to the rhizosediment characteristics, highlighting the importance of specific microbe-particle associations to define the structure of rhizospheric bacterial communities, rather than external factors, such as hydrocarbon contamination or the applied treatments. The potential for hydrocarbon RR seems to depend on root system development and bacterial diversity, since biodegradation efficiencies were positively related with these two parameters. Treatments with higher root biomass, and concomitantly with higher bacterial diversity yielded higher hydrocarbon degradation. Moreover, BS and BA did not enhance hydrocarbons RR. In fact, it was observed that higher nutrient availability might interfere with root growth and negatively influence hydrocarbon degradation performance. Therefore, our results suggested that to conduct appropriate hydrocarbon bioremediation strategies, the effect of sediment characteristics on root growth/exploration should be taken into consideration, a feature not explored in previous studies. Furthermore, strategies aiming for the recovery of bacterial diversity after oil spills may improve the efficiency of hydrocarbon biodegradation in contaminated salt marsh sediments.

Effects of Sediment Characteristics and Location on Polycyclic Aromatic Hydrocarbon (PAH) Associations

Polycyclic aromatic hydrocarbons (PAHs) distribution on aquatic particle sizes determines their transportation and degradation fate and hence their management performance for aquatic environment. Using thermal desorption (TD) extraction coupled to gas chromatography and mass spectrometer (GC-MS), we investigated PAH concentration variation in size-fractionated urban creek surface sediments. Sediment fractions were also investigated for their major material composition and chemical oxygen demand (COD). In general, the PAH’s concentrations and volatile content by particle sizes indicated bimodal distributions with smaller and larger particles enriched with constituents than with the intermediate sized sediment particles. However, most mass of the PAHs was associated with the smaller and intermediate-sized sediments. For smaller sediments, sediments affected by commercial area runoff showed higher concentrations of PAHs than that of non-commercial area runoff sediments. Linear correlations between sediment COD and PAH concentrations were obvious for highly volatile sediments than that of less volatile sediments.

Effect of sediment characteristics on sorption of 137Cs at the sediment-water interface

Effect of sediment characteristics on sorption of 137Cs at the sediment-water interface

Bioaccumulation of ivermectin from natural and artificial sediments in the benthic organism Lumbriculus variegatus

Although ivermectin is a widely used lipophilic parasiticide, data on its potential bioaccumulation in aquatic invertebrates are scarce. In this study, bioaccumulation patterns of radiolabeled 3H-ivermectin from sediments into tissues of the sediment-dwelling worm Lumbriculus variegatus were investigated and assessed. Two independent studies are described. In the first study, bioaccumulation kinetics of ivermectin in L. variegatus were investigated by following uptake, elimination, and biotransformation of the compound in worms exposed in artificial sediment. In the second study, possible effects of sediment characteristics on bioavailability of ivermectin were evaluated by comparing accumulation in worms exposed in three different natural sediments and one artificial sediment (organic carbon content 2% to 21%). During 28 days of exposure, ivermectin accumulated in worms exposed in all sediments with calculated bioaccumulation factors ranging from 0.2 to 11.0. Bioaccumulation factors correlated with total increase in biomass of worms during the exposure period and with organic carbon content of the sediments. Calculated biota–sediment accumulation factors ranged from 2.1 to 16.6, indicating that other variables, like quality of organic carbon and feeding behavior of the worms, may have influenced the bioavailability of ivermectin. Biotransformation products of ivermectin were only found in water, but not in sediment and worms. Results show that ivermectin has potential to bioaccumulate in L. variegatus, which could indicate a risk for biomagnification of the compound in the food chain.

A closer look at bioaccumulation of petroleum hydrocarbon mixtures in aquatic worms

Petroleum hydrocarbons (oils) are ubiquitous in the aquatic environment, and adequate risk assessment is thus essential. Bioaccumulation plays a key role in risk assessment, but the current knowledge on bioaccumulation of oils is limited. Therefore, this process was studied in detail, using the aquatic worm, Lumbriculus variegatus, and 14 field-contaminated sediments. The main focus during the present study was on uptake kinetics, the relationship between oil boiling point fraction and uptake, and effects of sediment characteristics. Uptake kinetics became slower with increasing boiling point fraction, but 70 to 90% of the equilibrium situation was reached within the standard exposure duration of 28 d. Worms accumulated sedimentary petroleum hydrocarbons in the range of C(10) to C(34), a range much wider than expected. Biota-to-sediment accumulation factors (BSAFs) for separate boiling point fractions were constant and around the proposed value of 1 to 2 up to C(22), but gradually decreased beyond this point. The decrease was probably caused by a combination of nonequilibrium conditions and enhanced sorption of higher boiling point fractions to sediments; the latter possibly due to the presence of strongly sorbing separate oil phases or black carbon. A negative relationship was observed between BSAF and oil concentration in sediment, which was explained by the presence of separate oil phases at high oil concentrations. These strongly sorbing phases may limit their own availability, particularly when being highly weathered; worms may also avoid them. The observed phenomena have obvious implications for bioaccumulation assessment of oils and suggest that the current risk assessment procedure for oils in sediments may lead to erroneous results.

Effect of sediment particle size on polycyclic aromatic hydrocarbon biodegradation: Importance of the sediment–water interface

Mechanisms for the effects of sediment on the biodegradation of organic compounds in the aquatic environment are not clear. In this research, effects of sediment characteristics on biodegradation kinetics of chrysene and benzo[a]pyrene were studied by inoculating polycyclic aromatic hydrocarbon (PAH)-degrading bacteria. Because water and PAHs can pass a polytetrafluoroethylene membrane yet bacteria and sediment cannot, a membrane experiment was performed to compare the biodegradation rates of PAHs in water and at the sediment-water interface, providing direct evidence that the PAH biodegradation rate is enhanced by the presence of sediment. Biodegradation of PAHs in water-sediment systems was fitted to zero-order kinetics; the order of biodegradation rate in water-sediment systems with different sediment was fine silt > clay > coarse silt. Biodegradation of PAHs in water-sediment systems occurred mainly at the sediment-water interface. According to membrane experiment results, when the biodegradation kinetics was fit to a zero-order equation, the maximum specific growth rates of bacteria (1/d) at the sediment-water interface were approximately three- to fourfold those in the water phase. Furthermore, the associated mechanisms regarding the effect of sediment characteristics were analyzed by investigating the process of bacterial growth and the distribution of bacteria and PAHs between water and sediment phases.

The effects of sediment characteristics and wave height on shape-parameter for representing equilibrium beach profiles

The shape parameter helps determining the shape of equilibrium beach profile in terms of offshore distance and water depth. The shape parameter therefore, should represent the effect of all the environmental factors involved in beach profile formation, such as wave climate and sediment properties. However, all the previous studies carried out to define shape parameter only consider the effects of sediment characteristics in their definitions. The aim of this study is to add the effect of wave climate also in the definition of shape parameter. This is achieved by integrating wave energy dissipation rate per unit volume at the surf zone. The result yields equilibrium wave energy dissipation rate that leads to theoretical definition of equilibrium beach profiles involving the effects of both the grain size and the wave climate parameters. It is found that the sediment grain size and the incoming wave height affect the value of shape parameter; whereas, the effects of wave period can be neglected. By means of energy equation, it is also possible to observe in macro scale the strength of wave energy on beach profile for different grain sizes. The findings also bring about the possibility of defining shape parameter such that any two arbitrary beach profiles owning the same sediment grain sizes can have the opportunity to have different beach profile formations. Finally, by adding the effect of wave height in the definition of shape parameter the graphical representation of the parameter, previously given by Moore (1982) is improved herein.

Effects of Sediment Characteristics on the Toxicity of Chromium(III) and Chromium(VI) to the Amphipod, Hyalella azteca

We evaluated the influence of sediment characteristics, acid-volatile sulfide (AVS) and organic matter (OM), on the toxicity of chromium (Cr) in freshwater sediments. We conducted chronic (28-42-d) toxicitytests with the amphipod Hyalella azteca exposed to Cr(VI) and Cr(III) in water and in spiked sediments. Waterborne Cr(VI) caused reduced survival of amphipods with a median lethal concentration (LC50) of 40 microg/L. Cr(VI) spiked into test sediments with differing levels of AVS resulted in graded decreases in AVS and sediment OM. Only Cr(VI)-spiked sediments with low AVS concentrations (< 1micromol/g) caused significant amphipod mortality. Waterborne Cr(III) concentrations near solubility limits caused decreased survival of amphipods at pH 7 and pH 8 but not at pH 6. Sediments spiked with high levels of Cr(III) did not affect amphipod survival but had minor effects on growth and inconsistent effects on reproduction. Pore waters of some Cr(III)-spiked sediments contained measurable concentrations of Cr(VI), but observed toxic effects did not correspond closely to Cr concentrations in sediment or pore waters. Our results indicate that risks of Cr toxicity are low in freshwater sediments containing substantial concentrations of AVS.

Sediment characteristics and colonization of soft-bottom benthos: a field manipulation experiment

A field manipulation experiment was carried out to test the effects of sediment characteristics (particle size and organic content) on colonization of soft-bottom benthos. Defaunated mud and sand in experimental trays were exposed at sub-tidal levels of two sites with sandy and muddy sea bottom, and retrieved monthly for examination of benthic composition. Seventy-eight out of the 107 species recorded, and 50% of the dominant species identified in the present study, were common in both the sand and mud trays. Classification analysis revealed higher faunal similarity of benthic composition in both sediment types within each of the two study sites. Results of three-way ANOVA (Sediment, Site and Time) showed that sediment effect was only significant for colonization of bivalves and gastropods, but not for polychaetes, amphipods, total species and individual numbers, or overall benthic diversity and evenness. This suggested that many of the benthic species can colonize both sediment types, and that factors other than sediment particle size and organic content may play a significant role in determining colonization of these species. The faunal composition of the same sediment type between sites was found to be different, indicating that the availability and abundance of benthic larvae/adults may be more important than sediment characteristics in determining benthic settlement. An increase in faunal similarity between mud and sand was observed over the study period, implying that the importance of sediment characteristics to benthic colonization decreased with exposure time.

Distribution and Abundance of Grapsid Crabs (Grapsidae) in a Mangrove Estuary: Effects of Sediment Characteristics, Salinity Tolerances, and Osmoregulatory Ability

Crabs (Grapsidae,Sesarma) are the dominant macrofaunal group of mangrove forest soils in northern Australia. Little is known about the ecology of these crabs or the factors that influence their distribution in mangrove forests. Pitfall traps were used to sample grapsid crabs in the Murray River estuary in north Queensland. Sampling was conducted at five sites along a salinity gradient from 35‰ at the river mouth. At each site, trapping was done in both low and high intertidal forests. We characterized the sediments at each site by measuring percent sand, silt, clay and organic matter, Eh, pH, and soil pore-water salinity. Four species of grapsids dominated the crab fauna along the Murray River (Sesarma semperi-longicristatum, S. messa, S. brevicristatum, andS. brevipes). Distinct zonation patterns were found along the salinity gradient and between high and low intertidal forests.S. messa was dominant in high intertidal, downstream forests, high and low intertidal forests in the middle to downstream portion of the river, and in low intertidal forests in the central reach of the river.S. brevipes was dominant in both low and high intertidal zone forests at low salinity upstream sites.S. brevicristatum was most abundant in the central reaches of the river and only in the high intertidal zone.S. semperi-longicristatum was found only in the low intertidal zone, downstream forest. Subsequently, tests of salinity tolerances of these crabs were carried out in the laboratory. These indicated very wide tolerances over salinities from completely fresh to hypersaline (60‰). The osmoregulatory abilities of the crabs were also found to vary. However, neither their salinity tolerance nor osmoregulatory ability adequately explain the zonation patterns were measured in the field. For example,S. brevicristatum had the most restricted distribution, but it had the second broadest salinity tolerance and osmoregulatory ability. Sediment characteristics explained a significant amount of the variation in abundance for two of the crab species. Pore-water salinity provided no explanatory power for any of the species. Individual species abundances are probably influenced by additional factors such as interspecific competition and predation.

The Distribution of Hydrobiids and the Effects of Sediment Characteristics on the Population Dynamics of Hydrobia ventrosa in a Coastal Region of the Southern Baltic

AbstractThe composition of the hydrobiid fauna in a coastal water of the southern Baltic was studied in 1990/91 at three stations with different sediment characteristics (grain size, organic content). Four species were found (Hydrobia ventrosa, H. ulvae, H. neglecta and Potamopyrgus jenkinsi). H. ventrosa was dominant at all stations. The mean hydrobiid abundances were 4,000 (stn. C), 18,000 (stn. B) and 40,000 (stn. A) ind./m2 respectively. Abundance was found to correlate with the organic content of the sediment. The reproduction and growth of H. ventrosa was studied. Two reproduction phases were observed, one in summer and the other in late autumn. The autumn reproduction peaks were staggered owing to the different growth rates at the various stations. Possible correlations between the differences in shell size of H. ventrosa at the various stations and both sediment characteristics and abundance are discussed.

Cadmium bioavailability to three estuarine animals in relation to geochemical fractions to sediments

The effects of sediment characteristics and geochemical fractions on the biological availability of cadmium to estuarine animals were studied. Grass shrimp (Palaemonetes pugio), blue mussels (Mytilus edulis) and a polychaete (Nereis virens) were exposed to Cd-treated sediment for 14 days. The test populations were evaluated for mortalities, oxygen consumption (exceptN. virens), and bioaccumulation of Cd. Sediment Cd was extracted sequentially to determine the exchangeable (EP), easily reducible (ERP), organic-sulfide (OSP), moderately reducible (MRP), and acid extractable (AEP) geochemical phases.

The effect of sediment characteristics on the distribution of two subtidal harpacticoid copepod species

Abundances of two harpacticoid copepod species, Enhydrosoma littorale Wells and Zausodes c.f. arenicolus Wilson, were significantly higher in one of two adjacent subtidal, soft-bottom habitats in St. George Sound, Florida (29°54′N : 84°37′48′′W). For Enhydrosoma littorale, a laboratory-preference experiment indicated that sediment-related factors caused the observed distribution. In a series of preference experiments, differences between the sediments of the two habitats in granulometry and organic matter were shown not to account for the preference. Rather, the preference results from differences in the microbes attached to the sediment particles in the two areas. In contrast, Zausodes c.f. arenicolus did nol prefer sediments from its area of high field abundance in laboratory preference experiments, indicating that factors external to the sediment i.e. hydrographic conditions or biological interactions, were responsible for this species' distribution.