Maximum Sedimentation Rate Research Articles

Sedimentation of bentonite suspensions under the influence of low molecular weight polymers based on amino ester salts

Among the available technologies for treating natural and wastewater from clay materials, coagulation/flocculation is the most common method due to its high efficiency, simplicity, and cost-effectiveness. Inorganic coagulants such as aluminum sulfate and ferric chloride, widely used as destabilizing agents for colloidal particles, have several significant drawbacks: low efficiency and toxicity. Organic reagents of both natural and synthetic origin are a good alternative. This work is devoted to the evaluation of the flocculation action of new reagents, which are low molecular weight polymers based on amino ester salts on clay suspensions, as well as the selection of their optimal concentration, providing the maximum sedimentation rate. Studies have shown that amino ester salts can be effectively used for the treatment of water-clay suspensions. An important factor is the nature of the anion used, which has a significant influence on the oagulation ability of esters. Thus, 40–50 % (wt.) aqueous solutions of amino ester chlorides added to clay suspensions in an amount not exceeding 0.1% (vol.) can be used to thicken clay suspensions. At the same time, aqueous solutions of amino ester bromides regardless of the concentration, introduced into bentonite suspensions of 0.1–0.4 % (vol.), contribute to improved sedimentation, reducing viscosity, and increasing filtration capacity. These results allow us to recommend the use of amino ester chlorides as athickener in the preparation of drilling muds for strengthening the walls of wells during drilling, and bromides – for flocculation of bentonite suspensions in oil production

Effect of pH value on effectiveness of biopolymer-based treatment of bauxite mine slurry

Effective dehydration and flocculation of mine slurries or sludge is important for nonferrous metal industries and environmental engineering. However, the mechanisms for the flocculation of slurry remain largely unclear. This paper presents the results of a series of flocculation tests, which was conducted on the slurry suspensions treated by xanthan gum (flocculant) at different pH values. It is shown that the settlement rate of mine slurry particles can be accelerated by adding xanthan gum, and the maximum sedimentation rate was obtained at a pH value of 5.9, and the final volume of flocs is significantly increased due to the addition of the flocculant. In addition, the settlement rates of xanthan gum-treated slurry suspensions at the pH values of 3, 5 and 7 decrease slightly compared with the reference slurry suspensions with pH=5.9, and the slurries remained stable as suspensions at the pH value of 9 and 11. The zeta potential measurement and SEM image analysis show that flocculation occurs primarily due to electrostatic attraction between slurry particles and the flocculants, and the bridging effect between the carboxylic groups in the side chains of xanthan gum molecule and the suspension particles.

Medium-term observations of salt marsh morphodynamics

Salt marshes play a key role in attenuating wave energy and promoting sedimentation necessary to potentially adapt to sea level rise. The changes in the soil surface elevation, as a result of spatially and temporally varied sedimentation pattern, affect the hydrodynamics, marsh edge extension and so the sedimentation rate. Little attention has yet been paid to the medium-term sedim\entation under the influence of marsh extension. To fill this gap, we performed a 6-year (from 2012 to 2018) field observation to obtain the soil surface elevation of the cross-shore tidal flats in the center Jiangsu Coast (China). The salt marsh edge is extracted from remote sensing images using NVDI technique, which allows us to quantify the seaward extension of salt marshes. Results highlight that soil surface elevation in the salt marsh region varies spatially and temporally as a function of marsh topography, inundation frequency and distance to the salt marsh edge. The sedimentation rate reduces linearly shoreward as a result of increasing soil surface elevation in the marsh region. At the transition of salt marshes and bare flats, the sedimentation rate follows a parabolic relationship with the increase in distance to the salt marsh edge but decreases linearly at the more landward sites. The maximum sedimentation rate is initially located around the mean high-water level and moves towards the edge of the salt marsh as a result of marsh extension and increasing soil surface elevation. Our field observations reveal these medium-term marsh dynamics and provide a unique dataset for development, testing and validation of numerical simulations to enhance predictions of the overall evolution of tidal flats.

The genetic relationship between paleoenvironment, mineral compositions and lithofacies in the Ordovician–Silurian Wufeng–Longmaxi sedimentary succession in the Sichuan Basin, SW China

• Five intervals (I–V) showing changes in minerals, lithofacies and paleoenvironment were identified. • High productivity and low detrital influx lead to the enrichment of nondetrital quartz in siliceous shale in Intervals I-II. • The enrichment of carbonate in calcareous shale in Interval III was due to high detrital influx. • High detrital influx and strong chemical weathering lead to an abundance of silt and clay minerals in silty–argillaceous shale and argillaceous shale in Intervals IV-V. Changes of sedimentary environments recorded in the Late Ordovician–Early Silurian sedimentary succession can be reflected in mineral composition and lithofacies of shales. Outcrops and cores from this set of shales in the Sichuan Basin, China, are analyzed. The results show that quartz, clay minerals, and carbonate are the main minerals. Five major lithofacies are developed. Based on the provenance proxies (Al 2 O 3 /TiO 2 , Th/Sc, and Zr/Sc ratios), chemical index of alteration (CIA), paleoproductivity proxies (Cu/Al and Ni/Al ratios), redox condition proxies (U/Th, V/Cr, and Ni/Co ratios), proxies of detrital influx (Ti and Al contents), and sedimentation rate (SR), the paleoenvironment is analyzed. The source rocks are dominated by felsic igneous rock. Comparison between five lithofacies revealed that the relatively low degree of chemical weathering, anoxic conditions, maximum paleoproductivity probably associated with the high frequency of volcanic activities, and minimum detrital influx and SR (0.60–5 m/Ma) led to the enrichment of nondetrital quartz and organic matter, which eventually formed siliceous shale. The moderate degree of chemical weathering, dysoxic–oxic conditions, decreasing paleoproductivity, and increasing detrital influx and SR (10–16.67 m/Ma) resulted in the increase in detrital quartz, clay minerals, and carbonate content, and the development of mixed shale and calcareous shale. Relatively strong chemical weathering, oxic conditions, minimum paleoproductivity, and maximum detrital influx and SR (100.74 m/Ma) favored the enrichment of silt and clay minerals, forming silty–argillaceous shale and argillaceous shale. This study provides an insight into the relationship between the environmental changes and shale mineral composition and lithofacies.

Microliter-stirred sample setup for X-ray spectroscopy analysis of nanomaterials in suspension

Analysis of samples in the liquid environment using X-ray spectroscopy techniques is a very attractive approach as it provides specimen characterization in its native conditions thanks to the penetrating properties of X-rays. However, very often due to challenging synthesis procedures and the high cost of specimens it is difficult to obtain a sample in quantities for optimal measurement. Additionally, nanoparticles (NPs) aqueous suspensions are often not stable and undergo agglomeration and sedimentation processes that can be avoided either by sonication or sample stirring. Relatively small sample volumes and intrinsic agglomeration processes make X-ray spectroscopy measurements challenging especially when long periods are needed for the collection of high-quality data. To address both issues, we developed dedicated sample system that allows measurements down to few tens of μL of the liquid sample with capability of continuous stirring of the suspension. The X-ray spectroscopy measurements of ZnO nanoparticles suspension in water showed a stable signal for hours of acquisition time. On the other hand, in the absence of stirring, agglomeration and subsequent sedimentation processes were visible already within few minutes with maximum sedimentation rate of 2.5% of concentration loss in the beam field per minute.

Effect of Exfoliated Graphene on Thermal Conductivity Enhancements of Graphene-Ironoxide Hybrid Nanofluids: Experimental Investigation and Effective Medium Theories

Reasoning of particular mechanism of anomalous thermal transport behaviours are not identified yet for the nanofluids. In this study, iron oxide (Maghemite: MH) and graphene (Gr) flake dispersed deionized water (DW) hybrid nanofluid system were developed for the first time to evaluate the thermal conductivity (TC) enhancements along with the analysis of anomalous TC behavior implementing modified effective medium theories (EMTs). A solvo-thermal two-step method was used to develop the MH nanoparticle and exfoliated Gr flake dispersed hybrid nanofluids with different compositions. Stability of as-prepared hybrid nanofluids were monitored using Ultraviolet-Visible (UV-Vis) spectroscopy. The maximum sedimentation rate was observed ~ 8.4 % after 600 hours. The results showed an overall maximum TC enhancement of ~ 43 % at 25 °C. EMTs were modified with the consideration of flat geometry of Gr flake. It is found that, modified EMTs with the crumpled factor (due to the non-flatness or crumple of Gr flake) of ~ 0.205 the predicted effective TC enhancements are agreed with the experimental TC’s of Gr-NMP/MH-DW hybrid nanofluids samples. The estimated crumple factor value of exfoliated Gr flakes using images analysis was also found nearly similar (~ 0.232). This agreement exposed that, Gr flake’s with negligible thickness compared to its extremely wide basal plane dimensions and its non-flatness or crumpled geometry in the nanofluids have the leading impacts on the effective TC properties of the Gr flake dispersed nanofluids. This modified model opens the new doors to analyse the insight of the thermophysical properties of various types of nanofluids by introducing potential other parameters.

Syndepositional processes in the pigmentation of oceanic red beds: evidence from the Basque–Cantabrian Basin (northern Spain)

AbstractOceanic red beds (ORBs) are present in Upper Cretaceous and Danian deep-marine deposits in the Basque–Cantabrian Basin of northern Spain. The presence and regularity of the succession of marl–limestone couplets is exceptional based on the macroscopic, microscopic and geochemical evidence collected. Five types of marl–limestone couplets are identified based on the colour, and a high maximum sedimentation rate (3.6 cm ka–1 ) is noted. The oxidizing activity of deep, cold-water masses is indicated by the oxygen isotope signal in the lower–upper Maastrichtian and Danian sections and the presence of the boreal inoceramidSpyridoceramus tegulatus.In theory, the variation in colour from grey to greenish-yellow, purple and pink up to red tones correlates with the Fe2+/(Fe2++Fe3+) ratio. It is interpreted as the possible palaeoenvironmental transit of particles that sediment out slowly in oxic environments when they circulate through cooler, oxidizing water masses. The colour is considered to be a depositional feature, and hematite, detected by X-ray diffraction, is the main staining agent, without discarding the possible redistribution of previous oxyhydroxides passing to hematite as a final product. The cell filling of the foraminifer shells does not incorporate appreciable amounts of Fe and Mg during diagenesis. Bacterial activity is detected using scanning electron microscopy images, both in the coccolith debris and in the detrital micas, although there is uncertainty as to its importance in the staining process.

Monitoring system of biophysical properties of the red blood cells of patients for medical diagnosis purposes

Modern medical diagnostics is impossible without high-tech means of collecting information about the patient's condition, in particular, the biochemical properties of blood and other tissues, physiological signals in the format of time series, and medical images as well. Extensive use of automatic methods of information processing and decision-making based on mathematical models, expert systems, and artificial intelligence is an integral part of the tomorrow’s medicine. Such approaches significantly increase the accuracy of diagnosis and the effectiveness of the prescribed treatment, but this requires the availability of properly structured databases with the results of both successful / unsuccessful treatments, and a complete set of necessary analyses and tests for each patient. This paper discusses the most important components of such database and public health monitoring system. The main issues are the standardization of data format, approaches, methods and laboratory equipment used to unify monitoring, diagnosis and control over the treatment. The importance of using additional physical parameters of blood cells and tissues to increase the efficiency of medical diagnostics with artificial intelligence is shown. The sedimentation curves corresponding to stable normal, stable increased and unstable erythrocyte aggregation rate are given. It is shown that the time to reach the maximum cell sedimentation rate can be calculated on a 2-phase model of blood suspension, indicators of which could be accumulated in the database, which will allow the extraction of additional diagnostic information using novel statistical and mathematical methods. Typical dependences of erythrocyte dielectric constant curves on temperature for oncology patients are given. It is shown that storage in the database the values of dielectric permittivity of red blood cells measured at different temperature and frequencies of electromagnetic fields applied in the dielectrometer, provides significant material for a more detailed study of the patterns of development of various diseases and finding the most sensitive indices for their timely detection.

Novel shortcut biological nitrogen removal method using an algae-bacterial consortium in a photo-sequencing batch reactor: Process optimization and kinetic modelling

This study evaluated a novel shortcut nitrogen removal method using a mixed consortium of microalgae, enriched ammonia oxidizing bacteria (AOB) and methanol utilizing denitrifier (MUD) in a photo-sequencing batch reactor (PSBR) for treating ammonium rich wastewater (ARWW). Alternating light and dark periods were followed to obtain complete biological nitrogen removal (BNR) without any external aeration and with the addition of methanol as the sole carbon source, respectively. The results showed that influent NH4+ was oxidized to NO2− by AOB during the light periods at a rate of 8.09 mg NH4+-N L−1h−1. Subsequently, NO2− was completely reduced during the dark period due to the action of MUD in presence of methanol. The high activities of ammonia monooxygenase (AMO) and nitrite reductase (NIR) enzymes revealed the strong role of AOB and MUD for achieving shortcut nitrogen removal from the wastewater. The reduced activities of nitrate reductase (NR) and nitrite oxidoreductase (NOR) at a high concentration of DO, NH4+ and NO2−in the system further confirmed the nitrogen removal pathway involved in the process. The biomass produced from these experiments showed good settling properties with a maximum sedimentation rate of 0.7–1.8 m h−1, a maximum sludge volume index (SVI) of 193 ml g−1- 256 ml g−1and floc size of 0.2–1.2 mm. In order to describe the growth and interaction among the algae, AOB and MUD for nitrogen removal in the system, the experimental results were fitted to four metabolic models, which revealed best fit of the experimental data due to the models based on algae-AOB and algae-AOB-MUD activities than with the other two models.

Basin filling evolution of the central basins of Mallorca since the Pliocene

AbstractA new compilation of data from 436 drill cores using decompaction and backstripping techniques was used to reconstruct the basin filling history from the Pliocene until the present day in the Palma, Inca and Sa Pobla Basins on the island of Mallorca (Spain). Calcareous rocks dominate the source area and provide a limited amount of clastic input to the basins that has resulted in an average accumulation rate of between 5 and 20 m/Ma during the last 5.3 Ma. Carbonate sediment production dominated the basin filling history during early‐mid Pliocene, but during the Quaternary, the sedimentation processes in the Palma Basin were probably enhanced by an evolution in the drainage network that increased the sediment supply and the accumulated thickness caused by stream capture. However, the maximum sedimentation rate filling the depocentres of the three basins has been decreasing since the Pliocene, showing that not only the catchment transport efficiency but also the relative sea level have been controlling the sediment accumulation in these carbonate basins. The isopach cross‐sections support the idea that a palaeorelief was generated during the Messinian sea level drop and that heterogeneities were filled in from the Pliocene to the Quaternary. We conclude that the central basins of Mallorca were filled heterogeneously due to tectonic and geomorphic processes that controlled sediment transport and production, resulting in different average sedimentation thicknesses that decreased since the Pliocene as the accommodation space became filled and the relative sea level dropped.

Investigation of sedimentation rates and sediment dynamics in Danube Delta lake system (Romania) by 210Pb dating method

Being a dynamic environment associated with complex costal, fluvial and marine processes, only a few studies regarding the evolution of the Danube Delta and the human impacts on its ecosystem have been carried out. Being a sensible to all processes occurring in its catchment area, information is stored in the deposited sediments, which can be used as tracers for natural and anthropogenic processes. The aim of this study is to determine a detailed reconstruction of the sedimentation rates in the last century by applying the 210Pb dating method validated by 137Cs profiles. Additionally, the impacts of the construction of river-regulating structures (mainly the Iron Gates Hydro-Energetic Power Plants) are investigated, along with the assessment of natural phenomena (floods, storms etc.). To achieve this, 26 sediment cores from seven lakes were collected. 210Pbsup and 137Cs were determined using gamma spectrometry, while 210Pbtot was measured via alpha spectrometry (210Po), using the CRS model for age determination. From the assessed lakes, the most affected was the Matița Lake with a maximum sedimentation rate of 10.93 g cm−2 yr−1 and the least affected was the Isac Lake. Average sedimentation rates are: 0.95 g cm−2 yr−1 for Cruhlig Lake, 0.70 g cm−2 yr−1 for Uzlina Lake, 0.44 g cm−2 yr−1 for Isac Lake, 0.47 g cm−2 yr−1 for Cuibida Lake, 0.51 g cm−2 yr−1 for Iacob Lake, 1.00 g cm−2 yr−1 for Matița Lake and 0.76 g cm−2 yr−1 for Merhei Lake. Physical parameters (water content, porosity and bulk density) and LOI (organic matter and inorganic carbon content) were determined for each core to differentiate organic and non-organic sedimentation. Beside the natural influences, it is difficult to track the effects of the Iron Gates and not all analysed lakes were suitable for this task. The 1940–1970 period and the following ten years were compared in means of sedimentation: a decrease in sedimentation can be observed in four of the lakes: 59% in Cruhlig Lake, 16% in Uzlina Lake, 10% in Iacob Lake and 42% in Isac Lake, leading to an average 32% for the four lakes. The other three lakes show increasing tendencies of 39% in this period: 87% in Matița Lake, 6% in Merhei Lake and 24% in Cuibida Lake. Sedimentation rates show growths of 3 times after 1989, the most affected being the two northern lakes (3 times increase in both Matița Lake and Merhei Lake) and the four central lakes (2 times in case of Cuibida Lake, 3 times in Iacob Lake, 3 times in Isac Lake and 4 times in Uzlina Lake) with an average increase of 3 times, while the southern one (Cruhlig Lake) 2 times.

RESEARCH ON METHODS OF HIGH COHERENT TARGET EXTRACTION IN URBAN AREA BASED ON PSINSAR TECHNOLOGY

Abstract. PSInSAR technology has been widely applied in ground deformation monitoring. Accurate identification of Persistent Scatterers (PS) is key to the success of PSInSAR data processing. In this paper, the theoretic models and specific algorithms of PS point extraction methods are summarized and the characteristics and applicable conditions of each method, such as Coherence Coefficient Threshold method, Amplitude Threshold method, Dispersion of Amplitude method, Dispersion of Intensity method, are analyzed. Based on the merits and demerits of different methods, an improved method for PS point extraction in urban area is proposed, that uses simultaneously backscattering characteristic, amplitude and phase stability to find PS point in all pixels. Shanghai city is chosen as an example area for checking the improvements of the new method. The results show that the PS points extracted by the new method have high quality, high stability and meet the strong scattering characteristics. Based on these high quality PS points, the deformation rate along the line-of-sight (LOS) in the central urban area of Shanghai is obtained by using 35 COSMO-SkyMed X-band SAR images acquired from 2008 to 2010 and it varies from −14.6 mm/year to 4.9 mm/year. There is a large sedimentation funnel in the cross boundary of Hongkou and Yangpu district with a maximum sedimentation rate of more than 14 mm per year. The obtained ground subsidence rates are also compared with the result of spirit leveling and show good consistent. Our new method for PS point extraction is more reasonable, and can improve the accuracy of the obtained deformation results.

Morphometric Temporal Change Analysis for the River Nile Forced Bends using RS/GIS Techniques: Case Study of Damietta Branch of the Nile River, Egypt

The River Nile is one of the world’s longest rivers. The Damietta branch in Egypt is important as a major source of irrigation and navigation path from Cairo to the Mediterranean Sea. Morphological changes in this branch of the Nile occurred following construction of the Aswan High Dam, which affected sedimentation and erosive flow, especially at bends in the river. In this study, morphometric temporal changes were investigated for the forced bends using Remote Sensing (RS) and Geographical Information System (GIS) techniques for a study period between 1987 and 2015. In addition, a comparative study was performed among three image classification techniques; onscreen digitizing, maximum likelihood classification and histogram thresholding techniques. A field map of the river banks for the year 2000 was used to verify morphometric behaviorof the forced bends extracted from the satellite images. The study showed that the maximum likelihood classification technique showed good performance in shoreline detection, with percentage error of only 0.42 % compared with observed data. Results show significant morphometric changes of the bank status for the forced bends studied. The forced bend named Sherpas was found to have the highest average annual rate of erosion, with a value of 1.62 m a-1. The maximum average annual rate of sedimentation was located at the inner bank of Sawalem forced bend, with a value of 1.0 m a-1. The maximum erosion and sedimentation rates achieved the greatest values within the period 1987 to 1998.

Consequences of the river valley bottom transformation after extreme flood (on the example of the Niida River, Japan)

Detailed study of different sections of floodplain was undertaken in the Niida River basin (Fukushima Prefecture) after an extreme flood event which occurred in the middle of September 2015. The upstream part of the basin is located in the area with very high level of radionuclide contamination after the accident at Fukushima Dai-ichi NPP. Field and GIS methods were used, including direct measurement of the depth of fresh sediment and its area, with soil descriptions for the typical floodplain sections, measurement of dose rates, interpretation of space images for a few time intervals (before and after flood event) with the following evaluation of spatial changes in deposition for different floodplain sections. In addition, results of quantitative assessment of sedimentation rates and soil radionuclide contamination were applied for understanding the effect of extreme flood on alluvial soils of the different sections. It was established that the maximum sedimentation rates (20-50 cm/event) occurred in the middle part of the lower reach of the Niida River and in some locations of the upper reaches. Dose rates had reduced considerably for all the areas with high sedimentation because the top soil layers with high radionuclide contamination were buried under fresh sediments produced mostly due to bank erosion and mass movements.

Mechanism of hydrolyzable metal ions effect on the zeta potential of fine quartz particles

ABSTRACTThe effects of ion species, cation valence, ionic strength, and hydrated ionic radius on the zeta potential of quartz have been systematically studied through the measurement of zeta potential, sedimentation rate, and aggregation observation. The results show that the interaction between hydrolysis components and quartz particles results in three critical points – CR1, CR2, and CR3. The results of sedimentation and aggregation observation are in good agreement with the changes of the zeta potential in 0.1 M MgCl2, the maximum sedimentation rate being 99.26% at pH 10.85. When the pH is around 6.25 or 10.00, the sedimentation rate is relatively lower and the size of aggregation smaller. The adsorption of hydrolyzable multivalent metal ions on the quartz surface is a combination of three adsorption forms, namely electrostatic adsorption, hydroxyl complex adsorption, and hydroxide precipitation adsorption. Then the hydrolysis properties of metal ions and the surrounding environment determine the action of the hydrolysis components and the main form of adsorption.

Natural attenuation of Fukushima-derived radiocesium in soils due to its vertical and lateral migration

Processes of vertical and lateral migration lead to gradual reduction in contamination of catchment soil, particularly its top layer. The reduction can be considered as natural attenuation. This, in turn, results in a gradual decrease of radiocesium activity concentrations in the surface runoff and river water, in both dissolved and particulate forms. The purpose of this research is to study the dynamics of Fukushima-derived radiocesium in undisturbed soils and floodplain deposits exposed to erosion and sedimentation during floods. Combined observations of radiocesium vertical distribution in soil and sediment deposition on artificial lawn-grass mats on the Niida River floodplain allowed us to estimate both annual mean sediment accumulation rates and maximum sedimentation rates corresponding to an extreme flood event during Tropical Storm Etau, 6-11 September 2015. Dose rates were reduced considerably for floodplain sections with high sedimentation because the top soil layer with high radionuclide contamination was eroded and/or buried under cleaner fresh sediments produced mostly due to bank erosion and sediments movements. Rate constants of natural attenuation on the sites of the Takase River and floodplain of Niida River was found to be in range 0.2–0.4 year−1. For the site in the lower reach of the Niida River, collimated shield dose readings from soil surfaces slightly increased during the period of observation from February to July 2016. Generally, due to more precipitation, steeper slopes, higher temperatures and increased biological activities in soils, self-purification of radioactive contamination in Fukushima associated with vertical and lateral radionuclide migration is faster than in Chernobyl. In many cases, monitored natural attenuation along with appropriate restrictions seems to be optimal option for water remediation in Fukushima contaminated areas.

Nonparametric Estimation to Reconstruct the Deformation History of an Active Fold in the Caspian Basin

The complete shape of an active fold in the western margin of the South Caspian Basin is established with a seismic section from a post-stacked cube migrated in depth. The structure is an open anticline, which deforms a thick sequence (more than 7 km) of Late Miocene to Pliocene sediments: the productive series (PS 5.9–3.1 Ma). A major erosive unconformity separates the most recent sediments with onlap and draping geometries towards the anticline culmination. Deformation is reconstructed using the complete fit of numerous reflections by the nonparametric regression method. This fold is detached above a weak, shale-rich unit located between 8 and 10 km depth dipping gently towards the E (7 $$^{\circ }$$ ). The fold geometry resembles a detachment fold, although it is reconstructed a long-lived history of basinward tilting accompanying sedimentation and folding, which diminished from 0.61 to 0.34 $$^{\circ }$$ /Ma during deposition of the PS. Fold growth started at 3.5 Ma within the upper PS with a shortening rate of 0.2 mm/year and coinciding with maximum sedimentation rates (3.24 mm/year). Folding continued up-to-Present under lower sedimentation rates (av. 0.66 ± 0.2 mm/year) and a shortening rate that increased slightly from 0.17 mm/year at 3.1 Ma to 0.29 mm/year during the last 1.6 Ma. The balance between sedimentation and shortening rates varies during folding, explaining the contrasting geometries observed in the growth sediments. It is also inferred that the possible occurrence of lateral flow of overpressured mud-rich sediments inflated the fold core during shortening, similarly to the upwelling process commonly described in salt-core anticlines.

Effects of electrolyte concentration and pH on the sedimentation rate of coagulated suspension of sodium montmorillonite

The sedimentation behavior of semi-dilute suspensions of sodium montmorillonite in the flocculation regime was studied as a function of ionic strength at pH 4.0 and 9.5 to elucidate the response of variation of macroscopic sedimentation behavior with microscopic particle association. The maximum velocity of the boundary between the supernatant and sediment and ultimate sediment height were chosen as indexes to evaluate the sedimentation behavior. Increment ratio of effective volume fraction of the particles (α) caused by the formation of flocs and hydrodynamic floc diameter were evaluated by Michaels and Bolger method on the basis of the Richardson⿿Zaki formula. The results clearly demonstrate that the maximum velocity of the boundary is strongly affected by both pH and salt concentration. The two observed patterns of variation of maximum sedimentation rate and ultimate sediment height can be clearly defined using 0.25⿿0.5M NaCl as an inflection range. This range is consistent with the transition point at 0.3M NaCl for the swelling behavior of sodium montmorillonite reported by Norrish. Below 0.25M NaCl, the effect of pH on the sedimentation rate is remarkably enhanced compared with that at higher salt concentration. This effect is ascribed to the dominant appearance of edge⿿face (EF) particle interactions, which can be regarded as negligible at higher salt concentration. The reason for this is that the breakage of weak EF bonds is induced by the dominant appearance of face⿿face particle interactions at higher salt concentrations. That is, the decrease of repulsion strengthening the attraction between neighboring particles is responsible for EF bond breakage. The small influence of pH on ultimate sediment height at high salt concentration can be ascribed to the residual strong EF bonds. The Michaels and Bolger method can be used qualitatively at range of NaCl greater than 0.5M.

Synchronizing Holocene lacustrine and marine sediment records using paleomagnetic secular variation

High sediment accumulation rates in lacustrine and shallow-marine archives around Iceland offer the potential to compare high-resolution paleoclimatic reconstructions from terrestrial and marine archives; however, direct comparisons are hampered by difficulties in stratigraphic correlation and in deriving accurate age models for lacustrine archives. Icelandic paleomagnetic secular variation (PSV) has the potential to synchronize these records. Here we compare Holocene PSV from a well-dated marine core on the North Iceland shelf with PSV from two lacustrine archives with comparable sediment-accumulation rates, HVT03–1A, a glacier-dominated lake, and HAK03–1B, in a nonglacial catchment. Geochemically characterized tephra layers combined with unique high-amplitude structures in the PSV records provide secure tie points every ∼200 yr. Once the records are synchronized, the chronology from the marine core can be reliably transferred to the two lacustrine records. The resultant lacustrine age models reveal large changes in sediment accumulation rate at submillennial scales that escape detection in conventional age models with independent dates every ∼1 k.y. Sediment accumulation rate changes occur at similar times in both lakes, despite very different catchment properties. Low and regular accumulation rates during the Holocene thermal maximum suggest regionally stable, vegetated catchments, followed by a stepped landscape destabilization during the transition into neoglaciation, culminating with maximum sedimentation rates during the Little Ice Age. PSV allows synchronization between multiple records from nearby marine and lacustrine archives, providing improved age models and a means of assessing leads and lags between marine and terrestrial environments.

Environmental impacts of dredging and other sediment disturbances on corals: A review

A review of published literature on the sensitivity of corals to turbidity and sedimentation is presented, with an emphasis on the effects of dredging. The risks and severity of impact from dredging (and other sediment disturbances) on corals are primarily related to the intensity, duration and frequency of exposure to increased turbidity and sedimentation. The sensitivity of a coral reef to dredging impacts and its ability to recover depend on the antecedent ecological conditions of the reef, its resilience and the ambient conditions normally experienced. Effects of sediment stress have so far been investigated in 89 coral species (∼10% of all known reef-building corals). Results of these investigations have provided a generic understanding of tolerance levels, response mechanisms, adaptations and threshold levels of corals to the effects of natural and anthropogenic sediment disturbances. Coral polyps undergo stress from high suspended-sediment concentrations and the subsequent effects on light attenuation which affect their algal symbionts. Minimum light requirements of corals range from <1% to as much as 60% of surface irradiance. Reported tolerance limits of coral reef systems for chronic suspended-sediment concentrations range from <10mgL−1 in pristine offshore reef areas to >100mgL−1 in marginal nearshore reefs. Some individual coral species can tolerate short-term exposure (days) to suspended-sediment concentrations as high as 1000mgL−1 while others show mortality after exposure (weeks) to concentrations as low as 30mgL−1. The duration that corals can survive high turbidities ranges from several days (sensitive species) to at least 5–6weeks (tolerant species). Increased sedimentation can cause smothering and burial of coral polyps, shading, tissue necrosis and population explosions of bacteria in coral mucus. Fine sediments tend to have greater effects on corals than coarse sediments. Turbidity and sedimentation also reduce the recruitment, survival and settlement of coral larvae. Maximum sedimentation rates that can be tolerated by different corals range from <10mgcm−2d−1 to >400mgcm−2d−1. The durations that corals can survive high sedimentation rates range from <24h for sensitive species to a few weeks (>4weeks of high sedimentation or >14days complete burial) for very tolerant species. Hypotheses to explain substantial differences in sensitivity between different coral species include the growth form of coral colonies and the size of the coral polyp or calyx. The validity of these hypotheses was tested on the basis of 77 published studies on the effects of turbidity and sedimentation on 89 coral species. The results of this analysis reveal a significant relationship of coral sensitivity to turbidity and sedimentation with growth form, but not with calyx size. Some of the variation in sensitivities reported in the literature may have been caused by differences in the type and particle size of sediments applied in experiments. The ability of many corals (in varying degrees) to actively reject sediment through polyp inflation, mucus production, ciliary and tentacular action (at considerable energetic cost), as well as intraspecific morphological variation and the mobility of free-living mushroom corals, further contribute to the observed differences. Given the wide range of sensitivity levels among coral species and in baseline water quality conditions among reefs, meaningful criteria to limit the extent and turbidity of dredging plumes and their effects on corals will always require site-specific evaluations, taking into account the species assemblage present at the site and the natural variability of local background turbidity and sedimentation.