Cross Validation of Two Partitioning-Based Sampling Approaches in Mesocosms Containing PCB Contaminated Field Sediment, Biota, and Activated Carbon Amendment.

PubMed

Schmidt, Stine N; Wang, Alice P; Gidley, Philip T; Wooley, Allyson H; Lotufo, Guilherme R; Burgess, Robert M; Ghosh, Upal; Fernandez, Loretta A; Mayer, Philipp

2017-09-05

The Gold Standard for determining freely dissolved concentrations (C free ) of hydrophobic organic compounds in sediment interstitial water would be in situ deployment combined with equilibrium sampling, which is generally difficult to achieve. In the present study, ex situ equilibrium sampling with multiple thicknesses of silicone and in situ pre-equilibrium sampling with low density polyethylene (LDPE) loaded with performance reference compounds were applied independently to measure polychlorinated biphenyls (PCBs) in mesocosms with (1) New Bedford Harbor sediment (MA, U.S.A.), (2) sediment and biota, and (3) activated carbon amended sediment and biota. The aim was to cross validate the two different sampling approaches. Around 100 PCB congeners were quantified in the two sampling polymers, and the results confirmed the good precision of both methods and were in overall good agreement with recently published LDPE to silicone partition ratios. Further, the methods yielded C free in good agreement for all three experiments. The average ratio between C free determined by the two methods was factor 1.4 ± 0.3 (range: 0.6-2.0), and the results thus cross-validated the two sampling approaches. For future investigations, specific aims and requirements in terms of application, data treatment, and data quality requirements should dictate the selection of the most appropriate partitioning-based sampling approach.

PROCEDURES FOR DERIVING EQUILIBRIUM PARTITIONING SEDIMENT BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISMS: METALS MIXTURES (CADMIUM, COPPER, LEAD, NICKEL, SILVER, AND ZINC)

EPA Science Inventory

This equilibrium partitioning sediment benchmark (ESB) document describes procedures to derive concentrations of metal mixtures in sediment which are protective of the presence of benthic organisms. The equilibrium partitioning (EqP) approach was chosen because it accounts for t...

PROCEDURES FOR THE DERIVATION OF EQUILIBRIUM PARTITIONING SEDIMENT BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISMS: COMPENDIUM OF TIER 2 VALUES FOR NONIONIC ORGANICS

EPA Science Inventory

This equilibrium partitioning sediment benchmark (ESB) document describes procedures to derive concentrations for 32 nonionic organic chemicals in sediment which are protective of the presence of freshwater and marine benthic organisms. The equilibrium partitioning (EqP) approach...

Probing receptor-ligand interactions by sedimentation equilibrium

NASA Astrophysics Data System (ADS)

Philo, John S.

1997-05-01

While sedimentation equilibrium is most commonly used to characterize the molecular weight and state of association of single proteins, this technique is also a very powerful tool for probing the interactions between two or more different proteins, and can characterize both the binding stoichiometry and the equilibrium constants. To resolve the complex binding interactions that can occur in such systems, it is crucial to globally fit data from many experiments to a common binding model, including samples made with different mixing ratios and a wide range of total concentration. It is often also essential to constrain the parameters during fitting so that the fits correctly reproduce the molar ratio of proteins used in making each sample. We have applied this methodology to probe mechanisms of receptor activation for a number of hematopoietic receptors and their cognate ligands, using receptor extracellular domains expressed as soluble proteins. Such data can potentially help in the design of improved or new protein therapeutics, as well as in efforts to create small- molecular mimetics of protein hormones through structure- based drug design. Sedimentation equilibrium has shown that stem cell factor, erythropoietin, and granulocyte-colony stimulating factor can each dimerize their respective receptors in solution, but the mechanism of ligand-induced receptor dimerization for these three systems are strikingly different.

Sediment transport through self-adjusting, bedrock-walled waterfall plunge pools

NASA Astrophysics Data System (ADS)

Scheingross, Joel S.; Lamb, Michael P.

2016-05-01

Many waterfalls have deep plunge pools that are often partially or fully filled with sediment. Sediment fill may control plunge-pool bedrock erosion rates, partially determine habitat availability for aquatic organisms, and affect sediment routing and debris flow initiation. Currently, there exists no mechanistic model to describe sediment transport through waterfall plunge pools. Here we develop an analytical model to predict steady-state plunge-pool depth and sediment-transport capacity by combining existing jet theory with sediment transport mechanics. Our model predicts plunge-pool sediment-transport capacity increases with increasing river discharge, flow velocity, and waterfall drop height and decreases with increasing plunge-pool depth, radius, and grain size. We tested the model using flume experiments under varying waterfall and plunge-pool geometries, flow hydraulics, and sediment size. The model and experiments show that through morphodynamic feedbacks, plunge pools aggrade to reach shallower equilibrium pool depths in response to increases in imposed sediment supply. Our theory for steady-state pool depth matches the experiments with an R2 value of 0.8, with discrepancies likely due to model simplifications of the hydraulics and sediment transport. Analysis of 75 waterfalls suggests that the water depths in natural plunge pools are strongly influenced by upstream sediment supply, and our model provides a mass-conserving framework to predict sediment and water storage in waterfall plunge pools for sediment routing, habitat assessment, and bedrock erosion modeling.

Pyrethroid sorption to Sacramento River suspended solids and bed sediments.

PubMed

Fojut, Tessa L; Young, Thomas M

2011-04-01

Sorption of pyrethroid insecticides to solid materials will typically dominate the fate and transport of these hydrophobic compounds in aquatic environments. Batch reactor isotherm experiments were performed with bifenthrin and λ-cyhalothrin with suspended material and bed sediment collected from the Sacramento River, California, USA. These batch reactor experiments were performed with low spiking concentrations and a long equilibration time (28 d) to be more relevant to environmental conditions. Sorption to suspended material and bed sediment was compared to examine the role of differential sorption between these phases in the environmental transport of pyrethroids. The equilibrium sorption data were fit to the Freundlich isotherm model and fit with r(2)  > 0.87 for all experiments. Freundlich exponents ranged from 0.72 ± 0.19 to 1.07 ± 0.050, indicating sorption nonlinearity for some of the experimental conditions and linearity for others over the concentration range tested. The Freundlich capacity factors were larger for the suspended solids than for the bed sediments, and the suspended material had a higher specific surface area and higher organic carbon content compared to the bed sediment. Calculated organic carbon-normalized distribution coefficients were larger than those previously reported in the literature, by approximately an order of magnitude, and ranged from 10(6.16) to 10(6.68) at an equilibrium aqueous concentration of 0.1 µg/L. Higher than expected sorption of pyrethroids to the tested materials may be explained by sorption to black carbon and/or mineral surfaces. Copyright © 2011 SETAC.

Response of a channel with alternate bars to a decrease in supple of mixed-size bedload: A flume experiment

Treesearch

Thomas E. Lisle; Fujiko Iseya; Hiroshi Ikeda

1993-01-01

The response of a channel with a topography and modeled bed material size typical of gravel bed rivers to reductions in sediment supply was investigated in a laboratory flume filled and fed with a sand-gravel mixture. After a series of quasi-stationary alternate bars were formed under equilibrium sediment transport, feed rate was reduced in two steps to one third and...

Experimental and theoretical investigation of the role of clay in subaqueous sediment flows and its effect on run-out distance

NASA Astrophysics Data System (ADS)

Hermidas, Navid; Luthi, Stefan; Eggenhuisen, Joris; Silva Jacinto, Ricardo; Toth, Ferenc; Pohl, Florian; de Leeuw, Jan

2016-04-01

Debris flows are driven by gravity, which in the tail region is overcome by the yield strength of the flow, forcing it to freeze. These flows are capable of achieving staggeringly large run-out distances on low gradients. The case in point, described in previous publications, is the flow which resulted in the deposit of Bed 5 of the Agadir megaslide on the north-west African margin. Debrites of this flow have been recorded several hundred kilometres away from the original landslide. Previous studies have attributed such long run-out distances to hydroplaning, low yield strength, and flow transformation. It is known that the net force acting on a volume of fluid in equilibrium is zero. In this work we show that clay-laden flows are capable of approaching equilibrium. The flows which can achieve the maximum run-out distance are cohesive enough to resist some of the surrounding disturbances, that can upset the equilibrium, and reach close to equilibrium conditions, yet are dilute enough to have low viscous stress, and relatively low yield strength and lose little sediment due to deposition. A flow that is not in equilibrium will always seek to approach equilibrium conditions by speeding up or slowing down, depositing sediment, eroding the substrate, contracting in the form of the tail approaching the head, stretching, entraining water and growing in height, or dewatering and collapsing. Here we present a theory that shows that two dimensional (2D) flows in equilibrium do not grow in height. 2D flume experiments were conducted on different mixtures of kaolinite, sand, silt, and water, on varying slopes and a transitionally rough bed (sand glued), and using various discharge rates, in order to map out different stages in the evolution of a density flow from a cohesive plug flow into a turbidity current. The following flow types were observed: high density turbidity currents, plug flows, and no flow. From the velocity profiles, certain runs demonstrated close to equilibrium behaviour. For these flows, very little flow height growth and velocity variation was observed over the length of the flume. In all cases the flow appeared to be laminar within the boundary layer with Kelvin-Helmholtz instabilities at the top which were suppressed to a large extent for higher sediment concentrations. A deposit consisting of thick muddy sand, with approximately uniform thickness, was observed for higher sediment concentrations, indicating relatively higher yield strength values, while a thinner more sandy deposit was observed for more dilute flows. It was concluded that high sediment concentrations on more moderate slopes result in slower moving plug flows which are capable of suppressing turbulence at the top, while lower sediment concentrations on steeper slopes result in faster moving, more turbulent currents. The flows which can achieve the largest run-out distance are located between these two extremes.

Sorption kinetics of Hg and HgCl[sub 2] on Kirkwood-Cohansey aquifer sediments from the New Jersey Coastal Plain

DOE Office of Scientific and Technical Information (OSTI.GOV)

MacLeod, C.; Peterson, J.

1992-01-01

Anomalously high Hg concentrations have been detected from domestic wells in the Kirkwood-Cohansey Aquifer System, New Jersey Coastal Plain. Mercury concentrations ranging from 0.2--83.0 [mu]g/l in relatively shallow wells ([lt] 100 feet) have been detected. Concentrations in excess of 2.0 [mu]g/l, (the USEPA Drinking Water Standard) have been detected in wells where the Cohansey Sand is overlain by the Bridgeton Formation; a fluvial iron-rich sand with some gravelly channel deposits containing goethite and gibbsite nodules. In this study, Bridgeton Fm. sediments were used to determine the sorption kinetics for solutions containing HgCl[sub 2] and for solutions containing dissolved elemental Hgmore » in order to assess the potential for the Bridgeton sediments to act as a conduit for Hg mobilized from the surface. Results of batch equilibrium experiments suggest that dissolved elemental Hg sorbs to Bridgeton sediments by a risk-order kinetic process. Sorption of the Hg proceeded exponentially and equilibrium was reached within 14 hours. The sorption kinetics for the HgCl[sub 2] solutions, however, appear to be of a second or higher order. For this compound sorption to the sediments begins exponentially, but after 6 hours desorption into the water begins to predominate followed by a slower exponential sorption step that requires nearly 36 hours to reach equilibrium. These experiments illustrate the necessity of determining the distribution coefficients of possible source compounds when attempting to evaluate mobilization potential of a contaminant in the unsaturated zone. Moreover, these data also suggest that HgCl[sub 2], a seed dressing for corn, medial bacteriacide, and embalming fluid ingredient, is more mobile in the environment than dissolved elemental Hg. Consequently, the ground water contamination potential appears to be greater for HgCl[sub 2] than for elemental Hg.« less

Equilibrium sampling of polychlorinated biphenyls in River Elbe sediments--Linking bioaccumulation in fish to sediment contamination.

PubMed

Schäfer, Sabine; Antoni, Catherine; Möhlenkamp, Christel; Claus, Evelyn; Reifferscheid, Georg; Heininger, Peter; Mayer, Philipp

2015-11-01

Equilibrium sampling can be applied to measure freely dissolved concentrations (cfree) of hydrophobic organic chemicals (HOCs) that are considered effective concentrations for diffusive uptake and partitioning. It can also yield concentrations in lipids at thermodynamic equilibrium with the sediment (clip⇌sed) by multiplying concentrations in the equilibrium sampling polymer with lipid to polymer partition coefficients. We have applied silicone coated glass jars for equilibrium sampling of seven 'indicator' polychlorinated biphenyls (PCBs) in sediment samples from ten locations along the River Elbe to measure cfree of PCBs and their clip⇌sed. For three sites, we then related clip⇌sed to lipid-normalized PCB concentrations (cbio,lip) that were determined independently by the German Environmental Specimen Bank in common bream, a fish species living in close contact with the sediment: (1) In all cases, cbio,lip were below clip⇌sed, (2) there was proportionality between the two parameters with high R(2) values (0.92-1.00) and (3) the slopes of the linear regressions were very similar between the three stations (0.297; 0.327; 0.390). These results confirm the close link between PCB bioaccumulation and the thermodynamic potential of sediment-associated HOCs for partitioning into lipids. This novel approach gives clearer and more consistent results compared to conventional approaches that are based on total concentrations in sediment and biota-sediment accumulation factors. We propose to apply equilibrium sampling for determining bioavailability and bioaccumulation potential of HOCs, since this technique can provide a thermodynamic basis for the risk assessment and management of contaminated sediments. Copyright © 2015 The Authors. Published by Elsevier Ltd.. All rights reserved.

PROCEDURES FOR DERIVING EQUILIBRIUM PARTITIONING BENCHMARKS (ESBS) FOR THE PROTECTION OF BENTHIC ORGANISM: PAH MIXTURES

EPA Science Inventory

This equilibrium partitioning sediment benchmark (ESB) document describes procedures to derive concentrations of PAH mixtures in sediment which are protective of the presence of benthic organisms. The equilibrium partitioning (EqP) approach was chosen because it accounts for t...

AN OVERVIEW OF THE DEVELOPMENT, STATUS, AND APPLICATION OF EQUILIBRIUM PARTITIONING SEDIMENT BENCHMARKS FOR PAH MIXTURES

EPA Science Inventory

This article provides an overview of the development, theoretical basis, regulatory status, and application of the U.S. Environmental Protection Agency's (USEPA's)< Equilibrium Partitioning Sediment Benchmarks (ESBs) for PAH mixtures. ESBs are compared to other sediment quality g...

Silicone passive equilibrium samplers as 'chemometers' in eels and sediments of a Swedish lake.

PubMed

Jahnke, Annika; Mayer, Philipp; McLachlan, Michael S; Wickström, Håkan; Gilbert, Dorothea; MacLeod, Matthew

2014-03-01

Passive equilibrium samplers deployed in two or more media of a system and allowed to come to equilibrium can be viewed as 'chemometers' that reflect the difference in chemical activities of contaminants between the media. We applied silicone-based equilibrium samplers to measure relative chemical activities of seven 'indicator' polychlorinated biphenyls (PCBs) and hexachlorobenzene in eels and sediments from a Swedish lake. Chemical concentrations in eels and sediments were also measured using exhaustive extraction methods. Lipid-normalized concentrations in eels were higher than organic carbon-normalized concentrations in sediments, with biota-sediment accumulation factors (BSAFs) of five PCBs ranging from 2.7 to 12.7. In contrast, chemical activities of the same pollutants inferred by passive sampling were 3.5 to 31.3 times lower in eels than in sediments. The apparent contradiction between BSAFs and activity ratios is consistent with the sorptive capacity of lipids exceeding that of sediment organic carbon from this ecosystem by up to 50-fold. Factors that may contribute to the elevated activity in sediments are discussed, including slower response of sediments than water to reduced emissions, sediment diagenesis and sorption to phytoplankton. The 'chemometer' approach has the potential to become a powerful tool to study the thermodynamic controls on persistent organic chemicals in the environment and should be extended to other environmental compartments.

Particle-scale measurement of PAH aqueous equilibrium partitioning in impacted sediments.

PubMed

Ghosh, Upal; Hawthorne, Steven B

2010-02-15

This research investigated the particle-scale processes that control aqueous equilibrium partitioning of PAHs in manufactured gas plant (MGP) site sediments. Dominant particle types in impacted sediments (sand, wood, coal/coke, and pitch) were physically separated under a microscope for equilibrium assessments. Solid-phase microextraction (SPME) combined with selected ion monitoring GC/MS and perdeuterated PAH internal standards were used to determine freely dissolved PAH concentrations in small (0.1-1 mL) water samples at concentrations as low as microg/L (for lower molecular weight PAHs) to ng/L (for higher molecular weight PAHs). For every particle class the initial release of PAHs into the aqueous phase was rapid, and an apparent equilibrium was reached in a matter of days. The average ratio of aqueous total PAH concentration for pitch vs coal/coke particles for eight sediment samples was 20. Thus, sediments that had aged in the field for many decades were not at equilibrium and were still going through a slow process of contaminant mass transfer between the different particle types. A possible consequence of this slow aging process is further lowering of the activity of the chemical as mass transfer is achieved to new sorption sites with time. This study also found that the presence of black carbon even at the level of (1)/(3) of sediment organic carbon does not necessarily imply a BC-dominated sorption behavior, rather source pitch particles if present may dominate PAH partitioning. To our knowledge this is the first report of equilibrium partitioning assessment conducted at the sediment particle scale.

How do changes in suspended sediment concentration alone influence the size of mud flocs under steady turbulent shearing?

NASA Astrophysics Data System (ADS)

Tran, Duc; Kuprenas, Rachel; Strom, Kyle

2018-04-01

Modeling the size and settling velocity of sediment under the influence of flocculation is crucial for the accurate prediction of mud movement and deposition in sediment transport modeling of environments such as agricultural streams, large coastal rivers, estuaries, river plumes, and turbidity currents. Yet, collecting accurate and high resolution data on mud flocs is difficult. As a result, models that account for the influence of flocculation on mud settling velocity are based on sparse data that often present non-congruent relationship in floc properties with basic influencers of flocculations such as suspended sediment concentration. This study examines the influence of suspended sediment concentration on floc size populations within a turbulent suspension. Specifically, the work investigates: (1) the relationship between the equilibrium floc size and suspended sediment concentration under conditions of steady concentration and turbulent shearing; and (2) the speed at which mature flocs adapt to an unsteady drop in the concentration when turbulent shear is constant. Two sets of experiments were used to investigate the target processes. All work was conducted in laboratory mixing tanks using a floc camera and a newly developed image acquisition method. The new method allows for direct imaging and sizing of flocs within turbulent suspensions of clay in concentrations ranging from 15 to 400 mg/L, so that no transfer of the sample to another settling column or imaging tank is needed. The primary conclusions from the two sets of experiments are: (1) that the equilibrium floc size in an energetic turbulent suspension is linearly and positively related to concentration over the range of C = 50 to 400 mg/L, yet with a smaller-than-expected slope based on previous data and models from low-energy environments; and (2) that floc sizes decrease quickly (with a time lag on the order of 1-15 min) to time-varying decreases in concentration at turbulent shearing of G = 50s-1 . Overall the data illustrate that equilibrium floc size is a positive function of concentration, but that the rate of increase is weaker than expected. The data also suggest that approximating the size or settling velocity of some muds with a simple equilibrium model might be appropriate if the time steps of interest are on the order of 10 min or larger. The data also shows the importance of calibrating historic mud settling velocity equations for accurate predictions.

Degradation of fipronil in anaerobic sediments and the effect on porewater concentrations.

PubMed

Brennan, Amanda A; Harwood, Amanda D; You, Jing; Landrum, Peter F; Lydy, Michael J

2009-09-01

The current study measured the degradation of fipronil in laboratory-spiked silt loam sediment under anaerobic conditions at different aging times. The half-life of fipronil in anaerobic sediments spiked at 5.8+/-0.049 and 21+/-1.4microg/kg dry weight (dw) was 21+/-0.22 and 15+/-0.11d, respectively. Fipronil-sulfide was the primary degradation product with fipronil-sulfone detected at lower concentrations. No degradation occurred to fipronil-sulfide and fipronil-sulfone over 200d in separate systems. A concurrent decline in sediment concentrations resulted in a decline of fipronil in sediment porewater with an increase in fipronil-sulfide and fipronil-sulfone measured by matrix-solid phase microextraction (matrix-SPME). Equilibrium among sediment, porewater, and matrix-SPME fiber occurred within 138d for fipronil and fipronil-sulfone; however, fipronil-sulfide did not reach equilibrium during the test, and modeling predicted upwards of 1083d to reach equilibrium. Regardless of the time to reach equilibrium, the rapid degradation of fipronil has little ecological significance given that fipronil-sulfide and fipronil-sulfone have equal or greater toxicity, and exhibit greater environmental stability in both the sediment and porewater, thereby becoming bioavailable.

Equilibrium Partitioning Sediment Benchmarks (ESBs) for the Protection of Benthic Organisms: Procedures for the Determination of the Freely Dissolved Interstitial Water Concentrations of Nonionic Organics

EPA Science Inventory

This document describes procedures to determine the concentrations of nonionic organic chemicals in sediment interstitial waters. In previous ESB documents, the general equilibrium partitioning (EqP) approach was chosen for the derivation of sediment benchmarks because it account...

Equilibrium Partitioning Sediment Benchmarks (ESBs) for the ...

EPA Pesticide Factsheets

This document describes procedures to determine the concentrations of nonionic organic chemicals in sediment interstitial waters. In previous ESB documents, the general equilibrium partitioning (EqP) approach was chosen for the derivation of sediment benchmarks because it accounts for the varying bioavailability of chemicals in different sediments and allows for the incorporation of the appropriate biological effects concentration. This provides for the derivation of benchmarks that are causally linked to the specific chemical, applicable across sediments, and appropriately protective of benthic organisms.  This equilibrium partitioning sediment benchmark (ESB) document was prepared by scientists from the Atlantic Ecology Division, Mid-Continent Ecology Division, and Western Ecology Division, the Office of Water, and private consultants. The document describes procedures to determine the interstitial water concentrations of nonionic organic chemicals in contaminated sediments. Based on these concentrations, guidance is provided on the derivation of toxic units to assess whether the sediments are likely to cause adverse effects to benthic organisms. The equilibrium partitioning (EqP) approach was chosen because it is based on the concentrations of chemical(s) that are known to be harmful and bioavailable in the environment.  This document, and five others published over the last nine years, will be useful for the Program Offices, including Superfund, a

Assembly of hard spheres in a cylinder: a computational and experimental study.

PubMed

Fu, Lin; Bian, Ce; Shields, C Wyatt; Cruz, Daniela F; López, Gabriel P; Charbonneau, Patrick

2017-05-14

Hard spheres are an important benchmark of our understanding of natural and synthetic systems. In this work, colloidal experiments and Monte Carlo simulations examine the equilibrium and out-of-equilibrium assembly of hard spheres of diameter σ within cylinders of diameter σ≤D≤ 2.82σ. Although phase transitions formally do not exist in such systems, marked structural crossovers can nonetheless be observed. Over this range of D, we find in simulations that structural crossovers echo the structural changes in the sequence of densest packings. We also observe that the out-of-equilibrium self-assembly depends on the compression rate. Slow compression approximates equilibrium results, while fast compression can skip intermediate structures. Crossovers for which no continuous line-slip exists are found to be dynamically unfavorable, which is the main source of this difference. Results from colloidal sedimentation experiments at low diffusion rate are found to be consistent with the results of fast compressions, as long as appropriate boundary conditions are used.

Molecular weight and oligomerization of rabbit thrombomodulin as assessed by sedimentation equilibrium

DOE Office of Scientific and Technical Information (OSTI.GOV)

Winnard, P.T.; Esmon, C.T.; Laue, T.M.

1989-02-15

Lubrol-solubilized rabbit thrombomodulin has been examined by equilibrium sedimentation in buffers that include sufficient D/sub 2/O to make the detergent neutrally buoyant. Data were acquired at rotor speeds from 12,000 to 28,000 rpm from two thrombomodulin preparations, at protein concentrations from 0.01 to 0.07%, and in buffer containing 0.01 to 0.23% Lubrol. Examination of the data from different rotor speeds shows that the thrombomodulin exists as a heterogeneous mixture containing monomer (Mr 65,000), trimer, and higher oligomers. The oligomers do not equilibrate over the time scale of the experiment. The weight fraction as monomer varies from preparation to preparation, andmore » appears to be independent of detergent concentration. Thus, experimenters should be cautious when interpreting binding or kinetic results obtained under similar buffer conditions.« less

Understanding the role of sediment waves and channel conditions over time and space

Treesearch

Thomas E. Lisle

1997-01-01

Abstract - Dynamic equilibrium in stream channels has traditionally been applied on the reach scale, where fluxes of water and sediment into a reach result in rapid but minor adjustments of channel dimensions, hydraulics or roughness (equilibrium), or aggradation and degradation (disequilibrium). Such an essentially one-dimensional spatial approach to sediment-channel...

Equilibrium Conditions of Sediment Suspending Flows on Earth, Mars and Titan

NASA Astrophysics Data System (ADS)

Amy, L. A.; Dorrell, R. M.

2016-12-01

Sediment entrainment, erosion and deposition by liquid water on Earth is one of the key processes controlling planetary surface evolution. Similar modification of planetary surfaces by liquids associated with a volatile cycle are also inferred to have occurred on other planets (e.g., water on Mars and methane-ethane on Titan). Here we explore conditions for equilibrium flow - the threshold between net sediment erosion and deposition - on different planets. We use a new theoretical model for particle erosion-suspension-deposition: this model shows a better fit to empirical data than comparative suspension criterions (e.g., Rouse Number) since it takes into account both flow competence and capacity, and particle size distribution effects. Shear stresses required to initially entrain sediment and maintain equilibrium flow vary significantly, being several times lower on Mars and more than ten times lower on Titan resulting principally from lower gravities. On all planets it is harder to maintain equilibrium flow as sediment mixtures become poorer sorted (higher shear stresses are needed as standard deviation increases). In comparison to large differences in critical shear stresses, critical slopes for equilibrium flow are similar for planets. Compared to Earth, equilibrium slopes on Mars should be slightly lower whilst those on Titan will be higher or lower for organic and ice particle systems, respectively. Particle size distribution has a similar, order of magnitude effect, on equilibrium slope on each planet. The results highlight that whilst reduced gravity on Titan and Mars significantly decreases the bed shear stress required for particle transport, it also proportionally effects the bed shear stress of moving fluid, such that similar slope gradients are required for equilibrium flow; minor variations in equilibrium slopes are related to differences in the particle-fluid density contrasts as well as fluid viscosities. These results help explain why planetary surfaces share striking similarities in their present or past landscapes and shows that particle size distribution is critical to sediment transport dynamics. Interestingly, particle distribution may vary between planets depending on the particle compositions and weathering regimes, imposing differences in equilibrium conditions.

Contamination of estuarine water, biota, and sediment by halogenated organic compounds: A field study

USGS Publications Warehouse

Pereira, W.E.; Rostad, C.E.; Chiou, C.T.; Brinton, T.I.; Barber, L.B.; Demcheck, D.K.; Demas, C.R.

1988-01-01

Studies conducted in the vicinity of an industrial outfall in the Calcasieu River estuary, Louisiana, have shown that water, bottom and suspended sediment, and four different species of biota are contaminated with halogenated organic compounds (HOC) including haloarenes. A "salting-out" effect in the estuary moderately enhanced the partitioning tendency of the contaminants into biota and sediments. Contaminant concentrations in water, suspended sediments, and biota were found to be far below the values predicted on the basis of the assumption of phase equilibria with respect to concentrations in bottom sediment. Relative concentration factors of HOC between biota (catfish) and bottom sediment increased with increasing octanol/estuarine water partition coefficients (Kow*), maximizing at log Kow* of about 5, although these ratios were considerably less than equilibrium values. In contrast, contaminant concentrations in water, biota, and suspended sediments were much closer to equilibrium values. Bioconcentration factors of HOC determined on the basis of lipid content for four different biotic species correlated reasonably well with equilibrium triolein/water partition coefficients (Ktw).

Large scale clear-water local pier scour experiments

USGS Publications Warehouse

Sheppard, D.M.; Odeh, M.; Glasser, T.

2004-01-01

Local clear-water scour tests were performed with three different diameter circular piles (0. 114, 0.305, and 0.914 m), three different uniform cohesionless sediment diameters (0.22, 0.80, and 2.90 mm) and a range of water depths and flow velocities. The tests were performed in the 6.1 m wide, 6.4 m deep, and 38.4 m long flume at the United States Geological Survey Conte Research Center in Turners Falls, Mass. These tests extend local scour data obtained in controlled experiments to prototype size piles and ratios of pile diameter to sediment diameter to 4,155. Supply water for this flow through flume was supplied by a hydroelectric power plant reservoir and the concentration of suspended fine sediment (wash load) could not be controlled. Equilibrium scour depths were found to depend on the wash load concentration. ?? ASCE.

Quantifying differences in the impact of variable chemistry on equilibrium uranium(VI) adsorption properties of aquifer sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Kent, Douglas B.; Zachara, John M.

2011-01-01

Uranium adsorption-desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500-1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO22+ + 2CO32- = >SOUO2(CO3HCO3)2-, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logKc) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logKc values. Using this approach, logKc values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (Kc uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors.

Effects of sediment supply on surface textures of gravel‐bed rivers

USGS Publications Warehouse

Buffington, John M.; Montgomery, David R.

1999-01-01

Using previously published data from flume studies, we test a new approach for quantifying the effects of sediment supply (i.e., bed material supply) on surface grain size of equilibrium gravel channels. Textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size (D50′). We find that surface median grain size (D50) varies inversely with sediment supply rate and systematically approaches the competent value (D50′) at low equilibrium transport rates. Furthermore, equilibrium transport rate is a power function of the difference between applied and critical shear stresses and is therefore a power function of the difference between competent and observed median grain sizes (D50′ and D50). Consequently, we propose that the difference between predicted and observed median grain sizes can be used to determine sediment supply rate in equilibrium channels. Our analysis framework collapses data from different studies toward a single relationship between sediment supply rate and surface grain size. While the approach appears promising, we caution that it has been tested only on a limited set of laboratory data and a narrow range of channel conditions.

Determination of adsorption and desorption of DNA molecules on freshwater and marine sediments.

PubMed

Xue, J; Feng, Y

2018-06-01

Free DNA and its adsorption by sediment in the aquatic environment lead to ambiguity in the identification of recent faecal pollution sources. The goal of this study was to understand the mechanisms of DNA adsorption and desorption on aquatic sediment under various conditions using quantitative polymerase chain reaction (qPCR). Both raw sewage (RS) DNA and purified PCR product (PPP) were used in adsorption and desorption experiments; autoclaved freshwater and marine sediments served as sorbents. Thirty-six hours were needed for adsorption to reach equilibrium. More DNA was adsorbed on both sediments in stream water than in 5 mmol l -1 NaCl and DNA adsorption increased in the presence of Ca 2+ and Mg 2+ . Successive desorption experiments showed that between 5% and 22% of adsorbed DNA was desorbed. Organic matter and clay played a significant role in determining the DNA adsorption capacity on sediment. The data suggest the presence of multilayer adsorption. DNA molecules on sediments were mostly adsorbed through ligand binding rather than electrostatic binding. Quantitative polymerase chain reaction assays provide a better way to investigate the DNA adsorption and desorption mechanisms by sediment. DNA desorption can potentially complicate the outcomes of microbial source tracking studies. © 2018 The Society for Applied Microbiology.

Modeling sediment transport with an integrated view of the biofilm effects

NASA Astrophysics Data System (ADS)

Fang, H. W.; Lai, H. J.; Cheng, W.; Huang, L.; He, G. J.

2017-09-01

Most natural sediment is invariably covered by biofilms in reservoirs and lakes, which have significant influence on bed form dynamics and sediment transport, and also play a crucial role in natural river evolution, pollutant transport, and habitat changes. However, most models for sediment transport are based on experiments using clean sediments without biological materials. In this study, a three-dimensional mathematical model of hydrodynamics and sediment transport is presented with a comprehensive consideration of the biofilm effects. The changes of the bed resistance mainly due to the different bed form dynamics of the biofilm-coated sediment (biosediment), which affect the hydrodynamic characteristics, are considered. Moreover, the variations of parameters related to sediment transport after the biofilm growth are integrated, including the significant changes of the incipient velocity, settling velocity, reference concentration, and equilibrium bed load transport rate. The proposed model is applied to evaluate the effects of biofilms on the hydrodynamic characteristics and sediment transport in laboratory experiments. Results indicate that the mean velocity increases after the biofilm growth, and the turbulence intensity near the river bed decreases under the same flow condition. Meanwhile, biofilm inhibits sediment from moving independently. Thus, the moderate erosion is observed for biosediment resulting in smaller suspended sediment concentrations. The proposed model can reasonably reflect these sediment transport characteristics with biofilms, and the approach to integration of the biological impact could also be used in other modeling of sediment transport, which can be further applied to provide references for the integrated management of natural aqueous systems.

Estuarine Facies Model Revisited: Conceptual Model of Estuarine Sediment Dynamics During Non-Equilibrium Conditions

NASA Astrophysics Data System (ADS)

Elliott, E. A.; Rodriguez, A. B.; McKee, B. A.

2017-12-01

Traditional models of estuarine systems show deposition occurs primarily within the central basin. There, accommodation space is high within the deep central valley, which is below regional wave base and where current energy is presumed to reach a relative minimum, promoting direct deposition of cohesive sediment and minimizing erosion. However, these models often reflect long-term (decadal-millennial) timescales, where accumulation rates are in relative equilibrium with the rate of relative sea-level rise, and lack the resolution to capture shorter term changes in sediment deposition and erosion within the central estuary. This work presents a conceptual model for estuarine sedimentation during non-equilibrium conditions, where high-energy inputs to the system reach a relative maximum in the central basin, resulting in temporary deposition and/or remobilization over sub-annual to annual timescales. As an example, we present a case study of Core Sound, NC, a lagoonal estuarine system where the regional base-level has been reached, and sediment deposition, resuspension and bypassing is largely a result of non-equilibrium, high-energy events. Utilizing a 465 cm-long sediment core from a mini-basin located between Core Sound and the continental shelf, a 40-year sub-annual chronology was developed for the system, with sediment accumulation rates (SAR) interpolated to a monthly basis over the 40-year record. This study links erosional processes in the estuary directly with sediment flux to the continental shelf, taking advantage of the highly efficient sediment trapping capability of the mini-basin. The SAR record indicates high variation in the estuarine sediment supply, with peaks in the SAR record at a recurrence interval of 1 year (+/- 0.25). This record has been compared to historical storm influence for the area. Through this multi-decadal record, sediment flushing events occur at a much more frequent interval than previously thought (i.e. annual rather than decadal timescales). This non-equilibrium estuarine model highlights moderate-energy events that impact the coast at least every year, in addition to high energy less frequent decadal to millennial events for modulating sediment and particulate matter erosion and transport through the estuary and delivery to the continental shelf.

The distribution dynamics and desorption behaviour of mobile pharmaceuticals and caffeine to combined sewer sediments.

PubMed

Hajj-Mohamad, M; Darwano, H; Duy, S Vo; Sauvé, S; Prévost, M; Arp, H P H; Dorner, S

2017-01-01

Pharmaceuticals are discharged to the environment from wastewater resource recovery facilities, sewer overflows, and illicit sewer connections. To understand the fate of pharmaceuticals, there is a need to better understand their sorption dynamics to suspended sediments (SS) and settled sediments (StS) in sewer systems. In this study, such sorption dynamics to both SS and StS were assessed using a batch equilibrium method under both static and dynamic conditions. Experiments were performed with natively occurring and artificially modified concentrations of sewer pharmaceuticals (acetaminophen, theophylline, carbamazepine, and a metabolite of carbamazepine) and caffeine. Differences in apparent distribution coefficients, K d,app , between SS and StS were related to differences in their organic carbon (OC) content, and the practice of artificially modifying the concentration. K d,app values of modified contaminant concentrations and high OC sediments were substantially higher. Pseudo-second order desorption rates for these mobile compounds were also quantified. Successive flushing events to simulate the addition of stormwater to sewer networks revealed that aqueous concentrations would not necessarily decrease, because the added water will rapidly return to equilibrium concentrations with the sediments. Sorption and desorption kinetics must be considered in addition to dilution, to avoid underestimating the influence of dilution on concentrations of pharmaceuticals discharged to the environment. Copyright © 2016 Elsevier Ltd. All rights reserved.

Selecting Performance Reference Compounds (PRCS)for Polyethylene Passive Samplers Deployed at Contaminated Sediment Sites

EPA Science Inventory

Use of equilibrium passive samplers for performing aquatic environmental monitoring at contaminated sediment sites, including Superfund sites, is becoming more common. However, a current challenge in passive sampling is determining when equilibrium is achieved between the sampl...

Riparian vegetation controls on the hydraulic geometry of streams

NASA Astrophysics Data System (ADS)

McBride, M.

2010-12-01

A synthesis of field measurements, remote observations, and numerical modeling techniques highlights the significance of riparian vegetation in determining the geometry of streams and impacting sediment transport dynamics in temperate, Piedmont regions. Specifically, forested and grassy riparian vegetation establish streams with significantly different widths and with different timescales for attaining a state of dynamic equilibrium. The interactions between riparian vegetation, channel form, and channel dynamics are scale dependent. Scale dependency arises because of variations in ratios of vegetation length scales and geomorphic scales (e.g., channel width and depth). Stream reaches with grassy vegetation experience more frequent overbank discharges, migrate more quickly, and exhibit a more classic dynamic equilibrium than forested reaches. These phenomena are relevant to current watershed management efforts that aim to reduce sediment and nutrient loads to receiving water bodies, such as the Chesapeake Bay. The reforestation of riparian buffers is a common restoration technique that intends to improve water quality, temperature regimes, and in-stream physical habitat. Passive reforestation of riparian areas along a tributary to Sleepers River in Danville, VT, USA caused an increase in channel width and cross-sectional area over a 40-year period. From a comparison of historical records and current cross-sectional dimensions, the channel widening resulted in the mobilization of approximately 85 kg/ha/yr of floodplain sediments. Long-term monitoring of suspended sediments in an adjacent watershed indicates that this sediment source may account for roughly 40 percent of the total suspended sediment load. In some instances, increased sediment loads associated with channel widening may be an unforeseen consequence that compromises riparian restoration efforts.

Simulated oil release from oil-contaminated marine sediment in the Bohai Sea, China.

PubMed

Yuan, Lingling; Han, Longxi; Bo, Wenjie; Chen, Hua; Gao, Wenshen; Chen, Bo

2017-05-15

There is a high degree of heavy oil partitioning into marine sediments when an oil spill occurs. Contaminated sediment, as an endogenous pollution source, can re-pollute overlying water slowly. In this study, a static oil release process and its effects in marine sediment was investigated through a series of experiments with reproductive heavy oil-contaminated marine sediment. The oil release process was accurately simulated with a Lagergren first-order equation and reached equilibration after 48h. The fitted curve for equilibrium concentration (C 0 ) and first-order rate constant (k 1 ) for sediment pollution levels exhibited a first-order log relationship. The instantaneous release rate (dC t dt) was also calculated. The C 0 increased with increases in temperature and dissolved organic matter (DOM), and decreasing salinity. The k 1 increased with temperature, but was not affected by DOM and salinity. These results can be used to better understand the fate of heavy oil in contaminated sediments of the Bohai Sea. Copyright © 2017. Published by Elsevier Ltd.

DEVELOPMENT AND APPLICATION OF EQUILIBRIUM PARTITIONING SEDIMENT GUIDELINES IN THE ASSESSMENT OF SEDIMENT PAH CONTAMINATION

EPA Science Inventory

The U.S. Environmental Protection Agency used insights and methods from its water quality criteria program to develop ESGs. The discovery that freely-dissolved contaminants were the toxic form led to equilibrium partitioning being chosen to model the distribution of contaminants...

Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

NASA Astrophysics Data System (ADS)

Baar, Anne W.; de Smit, Jaco; Uijttewaal, Wim S. J.; Kleinhans, Maarten G.

2018-01-01

Large-scale morphology, in particular meander bend depth, bar dimensions, and bifurcation dynamics, are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows. Overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology, while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream. However, existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes, and in practice models are calibrated on measured morphology. The objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near-bed flow conditions with varying secondary flow intensity, sediment sizes (0.17-4 mm), sediment transport mode, and bed state to test existing predictors. We conducted over 200 experiments in a rotating annular flume with counterrotating floor, which allows control of the secondary flow intensity separate from the streamwise flow velocity. Flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions. We isolated separate effects of all important parameters on the transverse slope. Resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on Shields number, and strongly depend on bed state and sediment transport mode. Fitted functions are provided for application in morphodynamic modeling.

Heat storage in the Hettangian aquifer in Berlin - results from a column experiment

NASA Astrophysics Data System (ADS)

Milkus, Chri(Sch)augott

2015-04-01

Aquifer Thermal Energy Storage (ATES) is a sustainable alternative for storage and seasonal availability of thermal energy. However, its impact on the subsurface flow regime is not well known. In Berlin (Germany), the Jurassic (Hettangian) sandstone aquifer with highly mineralized groundwater (TDS 27 g/L) is currently used for heat storage. The aim of this study was to examine the hydrogeochemical changes that are caused by the induced temperature shift and its effects on the hydraulic permeability of the aquifer. Column experiments were conducted, in which stainless steel columns were filled with sediment from the aquifer and flushed with native groundwater for several weeks. The initial temperature of the experiment was 20°C, comparable to the in-situ conditions within the aquifer. After reaching equilibrium between sediment and water, the temperature was increased to simulate heating of the aquifer. During the experiment, physical and chemical parameters (pH, ORP, dissolved oxygen and dissolved carbon dioxide) were measured at the outflow of the column and the effluent water was sampled. Using a Scanning Electron Microscope, the deposition of precipitated minerals and biofilm on sediment grains was analyzed. Changes in hydraulic properties of the sediment were studied by the use of tracer tests with Uranin.

Quantifying Differences in the Impact of Variable Chemistry on Equilibrium Uranium(VI) Adsorption Properties of Aquifer Sediments

PubMed Central

2011-01-01

Uranium adsorption–desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500–1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO22+ + 2CO32- = >SOUO2(CO3HCO3)2–, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logKc) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logKc values. Using this approach, logKc values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (<0.063 mm) of another could be demonstrated despite the fines requiring a different reaction stoichiometry. Estimates of logKc uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors. PMID:21923109

Quantifying differences in the impact of variable chemistry on equilibrium Uranium(VI) adsorption properties of aquifer sediments.

PubMed

Stoliker, Deborah L; Kent, Douglas B; Zachara, John M

2011-10-15

Uranium adsorption-desorption on sediment samples collected from the Hanford 300-Area, Richland, WA varied extensively over a range of field-relevant chemical conditions, complicating assessment of possible differences in equilibrium adsorption properties. Adsorption equilibrium was achieved in 500-1000 h although dissolved uranium concentrations increased over thousands of hours owing to changes in aqueous chemical composition driven by sediment-water reactions. A nonelectrostatic surface complexation reaction, >SOH + UO₂²⁺ + 2CO₃²⁻ = >SOUO₂(CO₃HCO₃)²⁻, provided the best fit to experimental data for each sediment sample resulting in a range of conditional equilibrium constants (logK(c)) from 21.49 to 21.76. Potential differences in uranium adsorption properties could be assessed in plots based on the generalized mass-action expressions yielding linear trends displaced vertically by differences in logK(c) values. Using this approach, logK(c) values for seven sediment samples were not significantly different. However, a significant difference in adsorption properties between one sediment sample and the fines (< 0.063 mm) of another could be demonstrated despite the fines requiring a different reaction stoichiometry. Estimates of logK(c) uncertainty were improved by capturing all data points within experimental errors. The mass-action expression plots demonstrate that applying models outside the range of conditions used in model calibration greatly increases potential errors.

A modified experimental setup for sedimentation equilibrium experiments with gels. Part 2: Technical developments.

PubMed

Cölfen, H; Borchard, W

1994-06-01

This part of the paper trilogy describes technical developments for an efficient experimental setup to investigate gels with equilibrium analytical ultracentrifugation. New 10-channel centerpieces for the Schlieren optics, a new programmable multiplexer, a modified Schlieren optical system, and a photo pickup with impulse transformer are introduced as major developments. Also, some new centerpieces suitable for equilibrium experiments with solutions using the Rayleigh interference and the uv-absorption optics are presented. These centerpieces allow the investigation of 10, 12, or even 26 samples per centerpiece. The problem to find suitable materials for cell centerpieces and windows in the case of adhering samples is discussed for the system gelatin/water. A phase volume calculation for circular sample channels as a correction for the case of broadened menisci is presented. The method described allows an accurate measurement of up to 70 samples simultaneously in an equilibrium experiment if the 8-hole rotor presented in part 1 of the trilogy is used. The number of samples is sufficient to characterize a gel/solvent system in the experimentally accessible range under identical conditions, which is not possible by means of any of the methods known before. All parts described are also applicable for the investigation of solutions.

DEVELOPMENT AND AVAILABILITY OF EQUILIBRIUM PARTITIONING SEDIMENT GUIDELINES (ESGS) FOR NONIONIC ORGANIC CONTAMINANTS, METALS MIXTURES, AND POLYCYCLIC AROMATIC HYDROCARBON (PAH) MIXTURES

EPA Science Inventory

Collaborative efforts between EPA's Office of Water and Office of Research and Development have resulted in the development of sediment guidelines based on equilibrium partitioning theory (EqP). The guidance available includes a technical support document, describing the derivat...

Ferric iron in sediments as a novel CO2 mineral trap: CO 2-SO2 reaction with hematite

USGS Publications Warehouse

Palandri, J.L.; Rosenbauer, R.J.; Kharaka, Y.K.

2005-01-01

Thermodynamic simulations of reactions among SO2-bearing CO 2-dominated gas, water and mineral phases predict that Fe III in sediments should be converted almost entirely to dissolved FeII and siderite (FeCO3), and that SO2 should simultaneously be oxidized to dissolved sulfate. The reactions are however, subject to kinetic constraints which may result in deviation from equilibrium and the precipitation of other metastable mineral phases. To test the prediction, a laboratory experiment was carried out in a well stirred hydrothermal reactor at 150??C and 300 bar with hematite, 1.0 m NaCl, 0.5 m NaOH, SO2 in quantity sufficient to reduce much of the iron, and excess CO2. The experiment produced stable siderite and metastable pyrite and elemental S. Changes in total dissolved Fe are consistent with nucleation of pyrite at ???17 h, and nucleation of siderite at ???600 h. Dissolution features present on elemental S at the conclusion of the experiment suggest nucleation early in the experiment. The experiment did not reach equilibrium after ???1400 h, as indicated by coexistence of hematite with metastable pyrite and elemental sulfur. However, the results confirm that FeIII can be used to trap CO2 in siderite if partly oxidized S, as SO2, is present to reduce the Fe with CO2 in the gas phase. ?? 2005 Elsevier Ltd. All rights reserved.

Sorption kinetics of TNT and RDX in anaerobic freshwater and marine sediments: Batch studies.

PubMed

Ariyarathna, Thivanka; Vlahos, Penny; Tobias, Craig; Smith, Richard

2016-01-01

Examination of the partitioning of explosives onto sediment in marine environments is critical to predict the toxicological impacts of worldwide explosive-contaminated sites adjacent to estuaries, wetlands, and the coastal ocean. Marine sediments have been identified as sites of enhanced munitions removal, yet most studies addressing these interactions focus on soils and freshwater sediments. The present study measured the kinetics of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) sorption onto 2 marine sediments of varying grain sizes (silt vs sand) and organic carbon (OC) content. Abiotic sediment sorption tests were performed at 23 °C, 15 °C, and 4 °C by spiking TNT and RDX solutions directly into anaerobic sediment slurries. Marine sediments showed significantly higher compound uptake rates (0.30-0.80 h(-1) ) than freshwater silt (0.0046-0.0065 h(-1) ) for both compounds, probably because of lower compound solubilities and a higher pH in marine systems. Equilibrium partition constants are on the same order of magnitude for marine silt (1.1-2.0 L kg(-1) sediment) and freshwater silt (1.4-3.1 L kg(-1) sediment) but lower for marine sand (0.72-0.92 L kg(-1) sediment). Total organic carbon content in marine sediments varied linearly with equilibrium partition constants for TNT and was moderately linear for RDX. Uptake rates and equilibrium constants of explosives are inversely correlated to temperature regardless of sediment type because of kinetic barriers associated with low temperatures. © 2015 SETAC.

Non-equilibrium flow and sediment transport distribution over mobile river dunes

NASA Astrophysics Data System (ADS)

Hoitink, T.; Naqshband, S.; McElroy, B. J.

2017-12-01

Flow and sediment transport are key processes in the morphodynamics of river dunes. During floods in several rivers (e.g., the Elkhorn, Missouri, Niobrara, and Rio Grande), dunes are observed to grow rapidly as flow strength increases, undergoing an unstable transition regime, after which they are washed out in what is called upper stage plane bed. This morphological evolution of dunes to upper stage plane bed is the strongest bed-form adjustment during non-equilibrium flows and is associated with a significant change in hydraulic roughness and water levels. Detailed experimental investigations, however, have mostly focused on fixed dunes limited to equilibrium flow and bed conditions that are rare in natural channels. Our understanding of the underlying sedimentary processes that result into the washing out of dunes is therefore very limited. In the present study, using the Acoustic Concentration and Velocity Profiler (ACVP), we were able to quantify flow structure and sediment transport distribution over mobile non-equilibrium dunes. Under these non-equilibrium flow conditions average dune heights were decreasing while dune lengths were increasing. Preliminary results suggest that this morphological behaviour is due to a positive phase lag between sediment transport maximum and topographic maximum leading to a larger erosion on the dune stoss side compared to deposition on dune lee side.

An experimental and modeling study of grain-scale uranium desorption from field-contaminated sediments and the potential influence of microporosity on mass-transfer

NASA Astrophysics Data System (ADS)

Stoliker, D.; Liu, C.; Kent, D. B.; Zachara, J. M.

2012-12-01

The aquifer below the 300-Area of the Hanford site (Richland, WA, USA) is plagued by a persistent plume of dissolved uranium (U(VI)) in excess of the Environmental Protection Agency drinking water maximum contamination level even after the removal of highly contaminated sediments. The aquifer sediments in the seasonally saturated lower vadose zone act as both a source and sink for uranium during stage changes in the nearby Columbia River. Diffusion limitation of uranium mass-transfer within these sediments has been cited as a potential cause of the plume's persistence. Equilibrium U(VI) sorption is a strong function of variable chemical conditions, especially carbonate, hydrogen, and uranyl ion activities. Field-contaminated sediments from the site require up to 1,000 hours to reach equilibrium in static batch reactors. Increases in U(VI) concentrations over longer time-scales result from changes in chemical conditions, which drive reactions with sediments that favor U(VI) desorption. Grain-scale U(VI) sorption/desorption rates are slow, likely owing to diffusion of U(VI) and other solutes through intra-granular pore domains. In order to improve understanding of the impact of intra-granular diffusion and chemical reactions controlling grain-scale U(VI) release, experiments were conducted on individual particle size fractions of a <8 mm composite of field-contaminated, lower vadose zone sediments. For each size fraction, equilibrium U(VI) sorption/desorption in static batch reactors was well-described by surface complexation models over a range of chemical conditions applicable to the field site. Desorption rates from individual size fractions in flow-through batch reactors, examined under a single set of constant chemical conditions with multiple stop-flow events, were similar for all size fractions <2 mm. Kinetic U(VI) desorption in flow-through batch reactors was modeled using a multi-rate surface complexation approach, where sorption/desorption rates were assumed to be proportional to the displacement from equilibrium and multiple diffusion domains were described with a two-parameter lognormal distribution of mass-transfer rate coefficients. Parameters describing mass transfer were the same for all size fractions <2 mm but differed for the largest (2-8 mm) size fraction. The evolution of pH, along with dissolved cation and carbonate concentrations, was modeled using equilibrium cation exchange, rate-limited calcite dissolution, aerobic respiration, and silica dissolution. Desorption and chemical reaction models calibrated with individual size fractions predicted U(VI) and chemical composition as a function of time for the bulk sediment sample. Volumes of pores less than 2.4 nm, quantified using nitrogen adsorption-desorption isotherms, were the same for all size fractions < 2 mm, nearly double that of the 2-8 mm size fraction. Similarity in the observed pore volumes and multi-rate mass-transfer parameters across all size fractions <2 mm suggest the importance of pores in this size class in controlling slow grain-scale U(VI) desorption rates. Models like these provide a means for testing the influence of grain-scale mass-transfer on the persistence of U(VI) plume at the site.

The unbearable heaviness of colloids: facts, surprises, and puzzles in sedimentation

NASA Astrophysics Data System (ADS)

Piazza, Roberto; Buzzaccaro, Stefano; Secchi, Eleonora

2012-07-01

Sedimentation has played a key role in the development of colloid science. In fact, it is because of the celebrated experiments by Perrin, yielding a concrete demonstration of molecular reality and giving strong support to Einstein’s theory of Brownian motion, that colloids enter the realm of basic physics. Subsequent investigations have shown that a lot more can be learnt both from sedimentation equilibrium and from particle settling dynamics. These advances, together with new experimental approaches, will be reviewed in this paper. Yet, we shall also show that inquiring about gravity settling is far from being a closed matter: for instance, the concept of buoyancy for a settling colloidal mixture is far from being obvious. Moreover, sedimentation holds novel surprises, such as colloidal inflations and settling disasters, showing that a simple external field like gravity may induce mind-boggling, and theoretically challenging effects.

Microbially assisted recording of the Earth's magnetic field in sediment.

PubMed

Zhao, Xiangyu; Egli, Ramon; Gilder, Stuart A; Müller, Sebastian

2016-02-11

Sediments continuously record variations of the Earth's magnetic field and thus provide an important archive for studying the geodynamo. The recording process occurs as magnetic grains partially align with the geomagnetic field during and after sediment deposition, generating a depositional remanent magnetization (DRM) or post-DRM (PDRM). (P)DRM acquisition mechanisms have been investigated for over 50 years, yet many aspects remain unclear. A key issue concerns the controversial role of bioturbation, that is, the mechanical disturbance of sediment by benthic organisms, during PDRM acquisition. A recent theory on bioturbation-driven PDRM appears to solve many inconsistencies between laboratory experiments and palaeomagnetic records, yet it lacks experimental proof. Here we fill this gap by documenting the important role of bioturbation-induced rotational diffusion for (P)DRM acquisition, including the control exerted on the recorded inclination and intensity, as determined by the equilibrium between aligning and perturbing torques acting on magnetic particles.

Massive units deposited by bedload transport in sheet flow mode

NASA Astrophysics Data System (ADS)

Viparelli, E.; Hernandez Moreira, R. R.; Jafarinik, S.; Sanders, S.; Huffman, B.; Parker, G.; Kendall, C.

2017-12-01

A sandy massive (structureless) unit overlying a basal erosional surface and underlying a parallel or cross-laminated unit often characterizes turbidity current and coastal storm deposits. The basal massive units are thought to be the result of relatively rapid deposition of suspended sediment. However, suspension-based models fail to explain how basal massive units can be emplaced for long distances, far away from the source and can contain gravel particles as floating clasts. Here we present experimental results that can significantly change the understanding of the processes forming turbidity current and coastal storm deposits. The experiments were performed in open channel flow mode in the Hydraulics Laboratory at the University of South Carolina. The sediment was a mixture of sand size particles with a geometric mean diameter of 0.95 mm and a geometric standard deviation of 1.65. Five experiments were performed with a flow rate of 30 l/s and sediment feed rates varying between 1.5 kg/min and 20 kg/min. Each experiment was characterized by two phases, 1) the equilibration phase, in which we waited for the system to reach equilibrium condition, and 2) the aggradation phase, in which we slowly raised the water surface base level to induce channel bed aggradation under the same transport conditions observed over the equilibrium bed. Our experiments show that sandy massive units can be the result of deposition from a thick bedload layer of colliding grains, the sheet flow layer. The presence of this sheet flow layer explains how a strong, sustained current can emplace extensive massive units containing gravel clasts. Although our experiments were conducted in open-channel mode, observations of bedload driven by density underflows suggest that our results are directly applicable to sheet flows driven by deep-sea turbidity currents. More specifically, we believe that this mechanism offers an explanation for massive turbidites that heretofore have been identified as the deposits of "high density" turbidity currents.

Modeling the sediment transport induced by deep sea mining in the Pacific Ocean

NASA Astrophysics Data System (ADS)

Purkiani, Kaveh; Paul, André; Schulz, Michael; Vink, Annemiek; Walter, Maren

2017-04-01

A numerical modeling study is conducted in the German license area in northeastern Pacific Ocean to investigate the sediment dispersal of mining exploitation. A sediment transport module is implemented in a hydrodynamic model. All differently sized particles can aggregate and break up until equilibrium floc sizes are obtained. A nested model approach using the MITgcm (Massachusetts Institute of Technology general circulation model) is applied and validated against hydrographic and hydrodynamic measurements obtained in this region. Two different sediment discharge scenarios have been examined to investigate the effect of flocculation on sediment transport distribution in the deep ocean. The suspended sediment is mainly influenced by a dominant SW current far away from the sediment discharge location. Independent of initial particle size all initial particles larger than 30 μm attain similar floc size equilibrium. In contrast to coastal seas and estuaries where floc size equilibrium can be obtained in a few hours, due to low shear rate (G) the flocculation process at deep ocean is completed within 1˜2 days. Considering temporal evolution of the floc size in the model, an increase in floc sinking velocity consequently enhances the sediment deposition at seafloor. The analysis of different sediment concentration scenarios suggests that floc sinking velocity increases at higher suspended sediment concentration (SSC). The presence of a dominant current in this region induces a fine sediment plume in SW direction. The dispersed SSC plume at 20 km downstream the discharge location is able to form the flocculation process and induces a spatial variation of floc size and floc sinking velocity.

Allowance for effects of thermodynamic nonideality in sedimentation equilibrium distributions reflecting protein dimerization.

PubMed

Wills, Peter R; Scott, David J; Winzor, Donald J

2012-03-01

This reexamination of a high-speed sedimentation equilibrium distribution for α-chymotrypsin under slightly acidic conditions (pH 4.1, I(M) 0.05) has provided experimental support for the adequacy of nearest-neighbor considerations in the allowance for effects of thermodynamic nonideality in the characterization of protein self-association over a moderate concentration range (up to 8 mg/mL). A widely held but previously untested notion about allowance for thermodynamic nonideality effects is thereby verified experimentally. However, it has also been shown that a greater obstacle to better characterization of protein self-association is likely to be the lack of a reliable estimate of monomer net charge, a parameter that has a far more profound effect on the magnitude of the measured equilibrium constant than any deficiency in current procedures for incorporating the effects of thermodynamic nonideality into the analysis of sedimentation equilibrium distributions reflecting reversible protein self-association. Copyright © 2011 Elsevier Inc. All rights reserved.

Mechanistic Sediment Quality Guidelines Based on Contaminant Bioavailability: Equilibrium Partitioning Sediment Benchmarks

EPA Science Inventory

Globally, billions of metric tons of contaminated sediments are present in aquatic systems representing a potentially significant ecological risk. Estimated costs to manage (i.e., remediate and monitor) these sediments are in the billions of U.S. dollars. Biologically-based app...

Bioavailability Assessment of a Contaminated Field Sediemtn from Patrick Bayou, Texas: TIE and Equilibrium Partitioning

EPA Science Inventory

Contaminated sediments are commonly found in urbanized harbors. Remediation is often necessary and diagnosing the cause of sediment toxicity becomes imperative. In the present study, sediments from Patrick Bayou, Texas were subjected to initial toxicity testing. All sediments ...

Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

NASA Astrophysics Data System (ADS)

Li, M.; Whelan, M. J.; Wang, G.; White, S. M.

2012-12-01

The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO4 from Ca2+ and HPO42- when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC0) vary from 0.014 mg l-1 to 0.061 mg l-1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC0 and linear sorption coefficients (K) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC0 and K increase with increasing temperature, indicating a higher P buffering capacity at high temperatures.

Phosphorus sorption and buffering mechanisms in suspended sediments from the Yangtze Estuary and Hangzhou Bay, China

NASA Astrophysics Data System (ADS)

Li, M.; Whelan, M. J.; Wang, G. Q.; White, S. M.

2013-05-01

The adsorption isotherm and the mechanism of the buffering effect are important controls on phosphorus (P) behaviors in estuaries and are important for estimating phosphate concentrations in aquatic environments. In this paper, we derive phosphate adsorption isotherms in order to investigate sediment adsorption and buffering capacity for phosphorus discharged from sewage outfalls in the Yangtze Estuary and Hangzhou Bay near Shanghai, China. Experiments were also carried out at different temperatures in order to explore the buffering effects for phosphate. The results show that P sorption in sediments with low fine particle fractions was best described using exponential equations. Some P interactions between water and sediment may be caused by the precipitation of CaHPO4 from Ca2+ and HPO42- when the phosphate concentration in the liquid phase is high. Results from the buffering experiments suggest that the Zero Equilibrium Phosphate Concentrations (EPC0) vary from 0.014 mg L-1 to 0.061 mg L-1, which are consistent with measured phosphate concentrations in water samples collected at the same time as sediment sampling. Values of EPC0 and linear sorption coefficients (K) in sediments with high fine particle and organic matter contents are relatively high, which implies that they have high buffering capacity. Both EPC0 and K increase with increasing temperature, indicating a higher P buffering capacity at high temperatures.

Molecular weight of Escherichia coli β-galactosidase in concentrated solutions of guanidine hydrochloride

PubMed Central

Erickson, Robert P.

1970-01-01

The molecular weight of Escherichia coli β-galactosidase was determined in 6m- and 8m-guanidine hydrochloride by meniscus-depletion sedimentation equilibrium, sedimentation velocity and viscosity. Sedimentation equilibrium revealed heterogeneity with the smallest component having a molecular weight of about 50000. At lower speeds, the apparent weight-average molecular weight is about 80000. By use of a calculation based on an empirical correlation for proteins that are random coils in 6m-guanidine hydrochloride, sedimentation velocity gave a molecular weight of 91000, and the intrinsic viscosity indicated a viscosity-average molecular weight of 84000. Heating in 6m-guanidine hydrochloride lowered the viscosity of β-galactosidase in a variable manner. PMID:4924171

Hydrated calcareous oil-shale ash as potential filter media for phosphorus removal in constructed wetlands.

PubMed

Kaasik, Ago; Vohla, Christina; Mõtlep, Riho; Mander, Ulo; Kirsimäe, Kalle

2008-02-01

The P-retention in hydrated calcareous ash sediment from oil-shale burning thermal power plants in Estonia was studied. Batch experiments indicate good (up to 65 mg P g(-1)) P-binding capacity of the hydrated oil-shale ash sediment, with a removal effectiveness of 67-85%. The high phosphorus sorption potential of hydrated oil-shale ash is considered to be due to the high content of reactive Ca-minerals, of which ettringite Ca6Al2(SO4)3(OH)12.26H2O and portlandite Ca(OH)2 are the most important. The equilibrium dissolution of ettringite provides free calcium ions that act as stable nuclei for phosphate precipitation. The precipitation mechanism of phosphorus removal in hydrated ash plateau sediment is suggested by Ca-phosphate formation in batch experiments at different P-loadings. Treatment with a P-containing solution causes partial-to-complete dissolution of ettringite and portlandite, and precipitation of Ca-carbonate and Ca-phosphate phases, which was confirmed by X-ray diffraction (XRD) and scanning electron microscope (SEM)-EDS studies. Thus, the hydrated oil-shale ash sediment can be considered as a potential filtration material for P removal in constructed wetlands for wastewater treatment.

An Arabidopsis E3 Ligase, SHOOT GRAVITROPISM9, Modulates the Interaction between Statoliths and F-Actin in Gravity Sensing[W][OA

PubMed Central

Nakamura, Moritaka; Toyota, Masatsugu; Tasaka, Masao; Morita, Miyo Terao

2011-01-01

Higher plants use the sedimentation of amyloplasts in statocytes as statolith to sense the direction of gravity during gravitropism. In Arabidopsis thaliana inflorescence stem statocyte, amyloplasts are in complex movement; some show jumping-like saltatory movement and some tend to sediment toward the gravity direction. Here, we report that a RING-type E3 ligase SHOOT GRAVITROPISM9 (SGR9) localized to amyloplasts modulates amyloplast dynamics. In the sgr9 mutant, which exhibits reduced gravitropism, amyloplasts did not sediment but exhibited increased saltatory movement. Amyloplasts sometimes formed a cluster that is abnormally entangled with actin filaments (AFs) in sgr9. By contrast, in the fiz1 mutant, an ACT8 semidominant mutant that induces fragmentation of AFs, amyloplasts, lost saltatory movement and sedimented with nearly statically. Both treatment with Latrunculin B, an inhibitor of AF polymerization, and the fiz1 mutation rescued the gravitropic defect of sgr9. In addition, fiz1 decreased saltatory movement and induced amyloplast sedimentation even in sgr9. Our results suggest that amyloplasts are in equilibrium between sedimentation and saltatory movement in wild-type endodermal cells. Furthermore, this equilibrium is the result of the interaction between amyloplasts and AFs modulated by the SGR9. SGR9 may promote detachment of amyloplasts from AFs, allowing the amyloplasts to sediment in the AFs-dependent equilibrium of amyloplast dynamics. PMID:21602290

3D-Printing for Analytical Ultracentrifugation

PubMed Central

Desai, Abhiksha; Krynitsky, Jonathan; Pohida, Thomas J.; Zhao, Huaying

2016-01-01

Analytical ultracentrifugation (AUC) is a classical technique of physical biochemistry providing information on size, shape, and interactions of macromolecules from the analysis of their migration in centrifugal fields while free in solution. A key mechanical element in AUC is the centerpiece, a component of the sample cell assembly that is mounted between the optical windows to allow imaging and to seal the sample solution column against high vacuum while exposed to gravitational forces in excess of 300,000 g. For sedimentation velocity it needs to be precisely sector-shaped to allow unimpeded radial macromolecular migration. During the history of AUC a great variety of centerpiece designs have been developed for different types of experiments. Here, we report that centerpieces can now be readily fabricated by 3D printing at low cost, from a variety of materials, and with customized designs. The new centerpieces can exhibit sufficient mechanical stability to withstand the gravitational forces at the highest rotor speeds and be sufficiently precise for sedimentation equilibrium and sedimentation velocity experiments. Sedimentation velocity experiments with bovine serum albumin as a reference molecule in 3D printed centerpieces with standard double-sector design result in sedimentation boundaries virtually indistinguishable from those in commercial double-sector epoxy centerpieces, with sedimentation coefficients well within the range of published values. The statistical error of the measurement is slightly above that obtained with commercial epoxy, but still below 1%. Facilitated by modern open-source design and fabrication paradigms, we believe 3D printed centerpieces and AUC accessories can spawn a variety of improvements in AUC experimental design, efficiency and resource allocation. PMID:27525659

Large sized non-uniform sediment transport at high capacity on steep slopes

NASA Astrophysics Data System (ADS)

Fu, X.; Zhang, L.; Duan, J. G.

2015-12-01

Transport of large-sized particles such as cobbles in steep streams still remains poorly understood in spite of its importance in mountain stream morphdynamics. Here we explored the law of cobble transport and the effect of cobble existence on gravel bed material transport, using flume experiments with a steep slope (4.9%) and water and sediment constantly supplying. The experiments were conducted in an 8 m long and 0.6 m wide circulating flume with the maximal size up to 90 mm and cobble concentrations in the sediment bed ranging from 22 percent to 6 percent. The sediment transport rate is on the order of 1000 g/m/s, which could be taken as high rate transport compared with existing researches. Bed load transport rate and flow variables were measured after the flume reached an equilibrium state. Bed surface topography was also measured by applying Kinect range camera before and after each run in order to analyze the fractal characteristics of the bed surface under different flow conditions. Critical shear stress of each size friction was estimated from the reference transport method (RTM) and a new hiding function was recommended. Preliminary results show that the bed was nearly in an equal mobility transport regime. We then plot dimensionless fractional transport rate versus dimensionless shear stress and assess the existing bed load transport formulas of non-uniform sediments for their applicability at high sediment transport capacity. This study contributes to the comprehension of high rate sediment transport on steep slopes.

Comparison of Methods for Characterizing Nonideal Solute Self-Association by Sedimentation Equilibrium

PubMed Central

Scott, David J.; Winzor, Donald J.

2009-01-01

Abstract We have examined in detail analytical solutions of expressions for sedimentation equilibrium in the analytical ultracentrifuge to describe self-association under nonideal conditions. We find that those containing the radial dependence of total solute concentration that incorporate the Adams-Fujita assumption for composition-dependence of activity coefficients reveal potential shortcomings for characterizing such systems. Similar deficiencies are shown in the use of the NONLIN software incorporating the same assumption about the interrelationship between activity coefficients for monomer and polymer species. These difficulties can be overcome by iterative analyses incorporating expressions for the composition-dependence of activity coefficients predicted by excluded volume considerations. A recommendation is therefore made for the replacement of current software packages by programs that incorporate rigorous statistical-mechanical allowance for thermodynamic nonideality in sedimentation equilibrium distributions reflecting solute self-association. PMID:19651047

Bioavailability Assessment of a Contaminated Field Sediment from Patrick Bayou, Texas, USA: Toxicity Identification Evaluation and Equilibrium Partitioning

EPA Science Inventory

Contaminated sediments are commonly found in urbanized harbors. At sufficiently high contaminant levels, sediments can cause toxicity to aquatic organisms and impair benthic communities. As a result, remediation is necessary and diagnosing the cause of sediment toxicity become...

Effect of sediment transport boundary conditions on the numerical modeling of bed morphodynamics

USDA-ARS?s Scientific Manuscript database

Experimental sediment transport studies in laboratory flumes can use two sediment-supply methods: an imposed feed at the upstream end or recirculation of sediment from the downstream end to the upstream end. These methods generally produce similar equilibrium bed morphology, but temporal evolution c...

Fertilizers mobilization in alluvial aquifer: laboratory experiments

NASA Astrophysics Data System (ADS)

Mastrocicco, M.; Colombani, N.; Palpacelli, S.

2009-02-01

In alluvial plains, intensive farming with conspicuous use of agrochemicals, can cause land pollution and groundwater contamination. In central Po River plain, paleo-channels are important links between arable lands and the underlaying aquifer, since the latter is often confined by clay sediments that act as a barrier against contaminants migration. Therefore, paleo-channels are recharge zones of particular interest that have to be protected from pollution as they are commonly used for water supply. This paper focuses on fertilizer mobilization next to a sand pit excavated in a paleo-channel near Ferrara (Italy). The problem is approached via batch test leaking and columns elution of alluvial sediments. Results from batch experiments showed fast increase in all major cations and anions, suggesting equilibrium control of dissolution reactions, limited availability of solid phases and geochemical homogeneity of samples. In column experiments, early elution and tailing of all ions breakthrough was recorded due to preferential flow paths. For sediments investigated in this study, dispersion, dilution and chemical reactions can reduce fertilizers at concentration below drinking standards in a reasonable time frame, provided fertilizer loading is halted or, at least, reduced. Thus, the definition of a corridor along paleo-channels is recommended to preserve groundwater quality.

Hydromorphodynamic effects of the width ratio and local tributary widening on discordant confluences

NASA Astrophysics Data System (ADS)

Guillén-Ludeña, S.; Franca, M. J.; Alegria, F.; Schleiss, A. J.; Cardoso, A. H.

2017-09-01

River training works performed in the last couple of centuries constrained the natural dynamics of channel networks in locations that include the confluences between tributaries and main channels. As a result, the dynamics of these confluences are currently characterized by homogeneous flow depths, flow velocities, and morphologic conditions, which are associated with impoverished ecosystems. The widening of river reaches is seen as a useful measure for river restoration, as it enhances the heterogeneity in flow depths, flow velocities, sediment transport, and bed substrates. The purpose of this study is to analyze the effects of local widening of the tributary mouth as well as the effects of the ratio between the width of the tributary and that of the main channel on the flow dynamics and bed morphology of river confluences. For that purpose, 12 experiments were conducted in a 70° laboratory confluence. In these experiments, three unit-discharge ratios were tested (qr = 0.37, 0.50, and 0.77) with two width ratios and two tributary configurations. The unit-discharge ratio is defined as the unit discharge in the tributary divided by that of the main channel, measured upstream of the confluence. The width ratio, which is defined as the width of the tributary divided by that of the main channel, was modified by changing the width of the main channel from 0.50 to 1.00 m (corresponding to Br = 0.30 and 0.15 respectively). The tributary configurations consisted of (i) a straight reach with a constant width (the so-called reference configuration) and (ii) a straight reach with a local widening at the downstream end (the so-called widened configuration). During the experiments, a uniform sediment mixture was continuously supplied to both channels. This experimental setup is novel among existing experimental studies on confluence dynamics, as it addresses new confluence configurations and includes a continuous sediment supply to both channels. The experiments were run until the outgoing sediment rate was nearly the same as the incoming; i.e., equilibrium had been achieved. The bed topography and water surface were then recorded in both channels. The results reveal that the width ratio and the locally widened tributary reach influence the dynamics of the confluence. The different width ratios influenced the size of the bank-attached bar at equilibrium, which was wider and longer for Br = 0.15 than for Br = 0.30. Other morphological differences were observed at equilibrium for the different width ratios, such as deeper scour holes and increased penetration of the tributary into the main channel. These differences were attributed to the different values of the ratio between the unit momentum-flux of the tributary and that of the main channel that were noted at equilibrium for the different width ratios. The local widening of the downstream reach of the tributary significantly enhanced the heterogeneity in flow depth, flow velocity, and bed morphology within the widened reach. This heterogeneity contrasts with the homogeneity observed in the tributary without widening (reference configuration). Additionally, the effects of the local tributary widening were limited to the tributary, with minor or negligible effects on the main channel.

Changes in Bedform Shape at the Transition Between Upper Plane-Bed and Sheet-Flow Bedload Transport Regimes

NASA Astrophysics Data System (ADS)

Hernandez Moreira, R. R.; Huffman, B.; Vautin, D.; Viparelli, E.

2015-12-01

The interactions between flow hydrodynamics and bedform characteristics at the transition between upper plane-bed bedload transport regime and sheet-flow have not yet been thoroughly described and still remain poorly understood. The present study focuses on the experimental study of this transition in open channel mode. The experiments were performed in the hydraulic laboratory of the Department of Civil and Environmental Engineering of the University of South Carolina in a sediment-feed flume, 9-m long by 19-cm wide with uniform material sediment of geometric mean grain size diameter of 1.11 mm. Sediment feed rates ranged between 0.5 kg/min and 20 kg/min with two different flow rates of 20 l/s and 30 l/s. We recorded periodic measurements of water surface and bed elevation to estimate the global flow parameters, e.g. mean flow velocity and bed shear stress, and to determine when the flow and the sediment transport reached conditions of mobile bed equilibrium. We define mobile bed equilibrium as a condition in which the mean bed elevation does not change in time. At equilibrium, measurements of bed elevation fluctuations were taken with an ultrasonic transducer system at six discrete locations. In the runs with low and medium feed rates, i.e. smaller than ~12 kg/min, the long wavelength and small amplitude bedforms typical of the upper plane bed regime, which were observed in previous experimental work, formed and migrated downstream. In particular, with increasing feed rates, the amplitude of the bedforms decreases and their geometry changes, from well-defined triangular shapes, to rounded shapes to flat bed with very small amplitude, long wavelength undulations. The decrease in amplitude corresponds to a decrease in form drag and an increase in the thickness of the bedload layer. The ultrasonic measurements are analyzed to statistically describe the observed transition in terms of probability distribution functions of the bed elevation fluctuations.

Transport of U(VI) through sediments amended with phosphate to induce in situ uranium immobilization.

PubMed

Mehta, Vrajesh S; Maillot, Fabien; Wang, Zheming; Catalano, Jeffrey G; Giammar, Daniel E

2015-02-01

Phosphate amendments can be added to U(VI)-contaminated subsurface environments to promote in situ remediation. The primary objective of this study was to evaluate the impacts of phosphate addition on the transport of U(VI) through contaminated sediments. In batch experiments using sediments (<2 mm size fraction) from a site in Rifle, Colorado, U(VI) only weakly adsorbed due to the dominance of the aqueous speciation by Ca-U(VI)-carbonate complexes. Column experiments with these sediments were performed with flow rates that correspond to a groundwater velocity of 1.1 m/day. In the absence of phosphate, the sediments took up 1.68-1.98 μg U/g of sediments when the synthetic groundwater influent contained 4 μM U(VI). When U(VI)-free influents were then introduced with and without phosphate, substantially more uranium was retained within the column when phosphate was present in the influent. Sequential extractions of sediments from the columns revealed that uranium was uniformly distributed along the length of the columns and was primarily in forms that could be extracted by ion exchange and contact with a weak acid. Laser induced fluorescence spectroscopy (LIFS) analysis along with sequential extraction results suggest adsorption as the dominant uranium uptake mechanism. The response of dissolved uranium concentrations to stopped-flow events and the comparison of experimental data with simulations from a simple reactive transport model indicated that uranium adsorption to and desorption from the sediments was not always at local equilibrium. Copyright © 2014 Elsevier Ltd. All rights reserved.

Morphodynamic Modeling of the Lower Yellow River, China: Flux (Equilibrium) Form or Entrainment (Nonequilibrium) Form of Sediment Mass Conservation?

NASA Astrophysics Data System (ADS)

An, C.; Parker, G.; Ma, H.; Naito, K.; Moodie, A. J.; Fu, X.

2017-12-01

Models of river morphodynamics consist of three elements: (1) a treatment of flow hydraulics, (2) a formulation relating some aspect of sediment transport to flow hydraulics, and (3) a description of sediment conservation. In the case of unidirectional river flow, the Exner equation of sediment conservation is commonly described in terms of a flux-based formulation, in which bed elevation variation is related to the streamwise gradient of sediment transport rate. An alternate formulation of the Exner equation, however, is the entrainment-based formulation in which bed elevation variation is related to the difference between the entrainment rate of bed sediment into suspension and the deposition rate of suspended sediment onto the bed. In the flux-based formulation, sediment transport is regarded to be in a local equilibrium state (i.e., sediment transport rate locally equals sediment transport capacity). However, the entrainment-based formulation does not require this constraint; the sediment transport rate may lag in space and time behind the changing flow conditions. In modeling the fine-grained Lower Yellow River, it is usual to treat sediment conservation in terms of an entrainment-based (nonequilibrium) rather than a flux-based (equilibrium) formulation with the consideration that fine-grained sediment may be entrained at one place but deposited only at some distant location downstream. However, the differences in prediction between the two formulations are still not well known, and the entrainment formulation may not always be necessary for the Lower Yellow River. Here we study this problem by comparing the results of flux-based and entrainment-based morphodynamics under conditions typical of the Yellow River, using sediment transport equations specifically designed for the Lower Yellow River. We find, somewhat unexpectedly, that in a treatment of a 200-km reach using uniform sediment, there is little difference between the two formulations unless the sediment fall velocity is arbitrarily greatly reduced. A consideration of sediment mixtures, however, shows that the two formulations give very different patterns of grain sorting. We explain this in terms of the structures of the two Exner equations for sediment mixtures, and define conditions for applicability of each formulation.

Development and evaluation of consensus-based sediment effect concentrations for polychlorinated biphenyls

USGS Publications Warehouse

MacDonald, Donald D.; Dipinto, Lisa M.; Field, Jay; Ingersoll, Christopher G.; Long, Edward R.; Swartz, Richard C.

2000-01-01

Sediment-quality guidelines (SQGs) have been published for polychlorinated biphenyls (PCBs) using both empirical and theoretical approaches. Empirically based guidelines have been developed using the screening-level concentration, effects range, effects level, and apparent effects threshold approaches. Theoretically based guidelines have been developed using the equilibrium-partitioning approach. Empirically-based guidelines were classified into three general categories, in accordance with their original narrative intents, and used to develop three consensus-based sediment effect concentrations (SECs) for total PCBs (tPCBs), including a threshold effect concentration, a midrange effect concentration, and an extreme effect concentration. Consensus-based SECs were derived because they estimate the central tendency of the published SQGs and, thus, reconcile the guidance values that have been derived using various approaches. Initially, consensus-based SECs for tPCBs were developed separately for freshwater sediments and for marine and estuarine sediments. Because the respective SECs were statistically similar, the underlying SQGs were subsequently merged and used to formulate more generally applicable SECs. The three consensus-based SECs were then evaluated for reliability using matching sediment chemistry and toxicity data from field studies, dose-response data from spiked-sediment toxicity tests, and SQGs derived from the equilibrium-partitioning approach. The results of this evaluation demonstrated that the consensus-based SECs can accurately predict both the presence and absence of toxicity in field-collected sediments. Importantly, the incidence of toxicity increases incrementally with increasing concentrations of tPCBs. Moreover, the consensus-based SECs are comparable to the chronic toxicity thresholds that have been estimated from dose-response data and equilibrium-partitioning models. Therefore, consensus-based SECs provide a unifying synthesis of existing SQGs, reflect causal rather than correlative effects, and accurately predict sediment toxicity in PCB-contaminated sediments.

Influence of variable chemical conditions on EDTA-enhanced transport of metal ions in mildly acidic groundwater

USGS Publications Warehouse

Kent, D.B.; Davis, J.A.; Joye, J.L.; Curtis, G.P.

2008-01-01

Adsorption of Ni and Pb on aquifer sediments from Cape Cod, Massachusetts, USA increased with increasing pH and metal-ion concentration. Adsorption could be described quantitatively using a semi-mechanistic surface complexation model (SCM), in which adsorption is described using chemical reactions between metal ions and adsorption sites. Equilibrium reactive transport simulations incorporating the SCMs, formation of metal-ion-EDTA complexes, and either Fe(III)-oxyhydroxide solubility or Zn desorption from sediments identified important factors responsible for trends observed during transport experiments conducted with EDTA complexes of Ni, Zn, and Pb in the Cape Cod aquifer. Dissociation of Pb-EDTA by Fe(III) is more favorable than Ni-EDTA because of differences in Ni- and Pb-adsorption to the sediments. Dissociation of Ni-EDTA becomes more favorable with decreasing Ni-EDTA concentration and decreasing pH. In contrast to Ni, Pb-EDTA can be dissociated by Zn desorbed from the aquifer sediments. Variability in adsorbed Zn concentrations has a large impact on Pb-EDTA dissociation.

Passive sampling methods for contaminated sediments: Scientific rationale supporting use of freely dissolved concentrations

PubMed Central

Mayer, Philipp; Parkerton, Thomas F; Adams, Rachel G; Cargill, John G; Gan, Jay; Gouin, Todd; Gschwend, Philip M; Hawthorne, Steven B; Helm, Paul; Witt, Gesine; You, Jing; Escher, Beate I

2014-01-01

Passive sampling methods (PSMs) allow the quantification of the freely dissolved concentration (Cfree) of an organic contaminant even in complex matrices such as sediments. Cfree is directly related to a contaminant's chemical activity, which drives spontaneous processes including diffusive uptake into benthic organisms and exchange with the overlying water column. Consequently, Cfree provides a more relevant dose metric than total sediment concentration. Recent developments in PSMs have significantly improved our ability to reliably measure even very low levels of Cfree. Application of PSMs in sediments is preferably conducted in the equilibrium regime, where freely dissolved concentrations in the sediment are well-linked to the measured concentration in the sampler via analyte-specific partition ratios. The equilibrium condition can then be assured by measuring a time series or a single time point using passive samplers with different surface to volume ratios. Sampling in the kinetic regime is also possible and generally involves the application of performance reference compounds for the calibration. Based on previous research on hydrophobic organic contaminants, it is concluded that Cfree allows a direct assessment of 1) contaminant exchange and equilibrium status between sediment and overlying water, 2) benthic bioaccumulation, and 3) potential toxicity to benthic organisms. Thus, the use of PSMs to measure Cfree provides an improved basis for the mechanistic understanding of fate and transport processes in sediments and has the potential to significantly improve risk assessment and management of contaminated sediments. Integr Environ Assess Manag 2014;10:197–209. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC. PMID:24288295

Equilibrium Partitioning: What's it Good for and How do you Know if it Works?

EPA Science Inventory

Much has been written about the use of equilibrium partitioning (EqP) as an approach for deriving sediment quality guidelines, and about whether guidelines so derived “work.” The purpose of this presentation is to discuss issues relevant to judging whether equilibrium partitioni...

Sedimentation equilibrium analysis of protein interactions with global implicit mass conservation constraints and systematic noise decomposition.

PubMed

Vistica, Jennifer; Dam, Julie; Balbo, Andrea; Yikilmaz, Emine; Mariuzza, Roy A; Rouault, Tracey A; Schuck, Peter

2004-03-15

Sedimentation equilibrium is a powerful tool for the characterization of protein self-association and heterogeneous protein interactions. Frequently, it is applied in a configuration with relatively long solution columns and with equilibrium profiles being acquired sequentially at several rotor speeds. The present study proposes computational tools, implemented in the software SEDPHAT, for the global analysis of equilibrium data at multiple rotor speeds with multiple concentrations and multiple optical detection methods. The detailed global modeling of such equilibrium data can be a nontrivial computational problem. It was shown previously that mass conservation constraints can significantly improve and extend the analysis of heterogeneous protein interactions. Here, a method for using conservation of mass constraints for the macromolecular redistribution is proposed in which the effective loading concentrations are calculated from the sedimentation equilibrium profiles. The approach is similar to that described by Roark (Biophys. Chem. 5 (1976) 185-196), but its utility is extended by determining the bottom position of the solution columns from the macromolecular redistribution. For analyzing heterogeneous associations at multiple protein concentrations, additional constraints that relate the effective loading concentrations of the different components or their molar ratio in the global analysis are introduced. Equilibrium profiles at multiple rotor speeds also permit the algebraic determination of radial-dependent baseline profiles, which can govern interference optical ultracentrifugation data, but usually also occur, to a smaller extent, in absorbance optical data. Finally, the global analysis of equilibrium profiles at multiple rotor speeds with implicit mass conservation and computation of the bottom of the solution column provides an unbiased scale for determining molar mass distributions of noninteracting species. The properties of these tools are studied with theoretical and experimental data sets.

Surfactant-enhanced remediation of a trichloroethene-contaminated aquifer. 1. Transport of triton X-100

USGS Publications Warehouse

Smith, J.A.; Sahoo, D.; Mclellan, H.M.; Imbrigiotta, T.E.

1997-01-01

Transport of a nonionic surfactant (Triton X-100) at aqueous concentrations less than 400 mg/L through a trichloroethene-contaminated sand-and-gravel aquifer at Picatinny Arsenal, NJ, has been studied through a series of laboratory and field experiments. In the laboratory, batch and column experiments were conducted to quantify the rate and amount of Triton X-100 sorption to the aquifer sediments. In the field, a 400 mg/L aqueous Triton X-100 solution was injected into the aquifer at a rate of 26.5 L/min for a 35-d period. The transport of Triton X-100 was monitored by sampling and analysis of groundwater at six locations surrounding the injection well. Equilibrium batch sorption experiments showed that Triton X-100 sorbs strongly and nonlinearly to the field soil with the sharpest inflection point of the isotherm occurring at an equilibrium aqueous Triton X-100 concentration close to critical micelle concentration. Batch, soil column, and field experimental data were analyzed with zero-, one-, and two- dimensional (respectively) transient solute transport models with either equilibrium or rate-limited sorption. These analyses reveal that Triton X- 100 sorption to the aquifer solids is slow relative to advective and dispersive transport and that an equilibrium sorption model cannot simulate accurately the observed soil column and field data. Comparison of kinetic sorption parameters from batch, column, and field transport data indicate that both physical heterogeneities and Triton X-100 mass transfer between water and soil contribute to the kinetic transport effects.Transport of a nonionic surfactant (Triton X-100) at aqueous concentrations less than 400 mg/L through a trichloroethene-contaminated sand-and-gravel aquifer was studied. Equilibrium batch sorption experiments showed that Triton X-100 sorbs strongly and nonlinearly to the field soil with the sharpest inflection point of the isotherm occurring at an equilibrium aqueous Triton X-100 concentration close to critical micelle concentration. Batch, soil column, and field experimental data were analyzed with zero-, one-, and two-dimensional transient solute transport models with either equilibrium or rate-limited sorption. These analyses revealed that Triton X-100 sorption to the aquifer solids was slow relative to advective and dispersive transport.

Mechanisms linking sediment supply and bar morphology: Results from a straight flume with alternate bars

NASA Astrophysics Data System (ADS)

Braudrick, C. A.; Minear, J. T.; Dietrich, W. E.; Dehart, M.; Sklar, L. S.

2008-12-01

One of the largest uncertainties in routing sediment through drainage networks is predicting the degree to which changes in sediment supply are mitigated by changes in sediment storage in bars. We hypothesize that changes in topographic steering link sediment supply and bar morphology. This hypothesis posits that increased sediment supply would enhance topographic steering over the bar, causing the bar to advance laterally into the pool. Contrarily, decreased supply would diminish topographic steering, causing bars to shrink laterally and pools to expand. We examined this hypothesis in a 28-m long, 0.86-m wide flume with a constant discharge of 5.4 l/s and sand with a median grain size of 0.8 mm. The conditions were sufficient to support alternate bars downstream of the upper 8-10 m, and the flume was run for approximately 65 hours at a constant discharge and sediment feed. The equilibrium slope was 0.0033. Once the channel reached equilibrium, the sediment feed was turned off while the discharge was held constant. During the first 25 hours after the feed was stopped, the sediment transport rate at the downstream end of the flume increased from 9.8 to 10.5 kg/hr as sediment was provided by incision at the upstream end of the flume. Because the bed was the only sediment source, sediment supply increased with distance down the flume. Once the feed was shut off, bar response differed between the upstream and downstream portions of the flume. Bars at the downstream end of the flume, where sediment supply increased relative to equilibrium conditions, swelled into the pool. These changes in bar morphology were accompanied by a decrease in surface grain size. Further upstream, where sediment supply was lower, the bars shrunk. These results suggest that there may be a linkage between topographic steering, bar morphology, and sediment supply, but further numerical tests and experimental manipulations are necessary to verify this linkage and to account for the effect of the decreased surface grain size of the bars.

Temperature-dependent sorption of naphthalene, phenanthrene, and pyrene to low organic carbon aquifer sediments

USGS Publications Warehouse

Piatt, Joseph J.; Backhus, Debera A.; Capel, Paul D.; Eisenreich, Steven J.

1996-01-01

Sorption experiments were conducted with naphthalene, phenanthrene, and pyrene on low organic carbon sediments at 4 and 26 °C using batch and column techniques. Experimental controls ensured the absence of biologic and photolytic activity and colloid-free solution supernatants. Equilibrium distribution coefficients (Kd) increased 1.1−1.6 times with a decrease in temperature of 22 °C. Fraction instantaneous sorption (F) values did not change significantly with a decrease in temperature of 22 °C. Desorption rate constants (k2) decreased 1.2−2.6 times with a decrease in temperature of 22 °C. Times to equilibrium were at least 40 h. The magnitude of observed Kd and k2 values and the effect of temperature on Kd (e.g., low enthalpy of sorption) are consistent with sorbate partitioning between the aqueous phase and small amounts of organic matter (foc = 0.02%) on the sediments. The temperature dependence of Kd and k2 may be small as compared to the effects of heterogeneities in field-scale aquifer systems. Thus, thermal gradients may not be of major importance in most saturated subsurface regimes when predicting solute transport. However, aquifer remediation pump-and-treat times could be decreased because increased temperature decreases both retardation and tailing.

Control of Sediment Availability on the Path of Channel Recovery in Bedload-Dominated Rivers

NASA Astrophysics Data System (ADS)

Doyle, H.; Renshaw, C. E.; Magilligan, F. J.

2015-12-01

Following a disturbance, a channel can recover to an equilibrium form by adjusting its slope, width, depth, grain size, or some combination of these dimensions that define the recovery path. In this study we relate the channel recovery path to the quantity and caliber of sediment introduced due to dam construction/removal or erosion caused by flooding. We suggest that the recovery path of a channel depends on the availability of sediment of a size that is transported as bedload during bankfull flows (the "mobile fraction"). We define a ratio, S*, of the sediment volume added to the channel because of the disturbance to the average annual sediment flux. We compare S* values to the recovery path of New England gravel-bedded streams following two dam emplacements and removals and flooding related to Tropical Storm Irene. Pelham Dam in Pelham, MA (removed 2012) and Kendrick Dam in Pittsford, VT (removed 2014) were on similar streams: drainage areas ~25 km2, slopes 1-2%, and bankfull widths ~10 m. Sediment was excavated from both impoundments prior to removal, resulting in lower S* values. Irene-affected study sites are on ~10 gravel-bedded streams in VT, NH, and MA. Sediment input at these sites is due to bank failures and landslides, many of which continue to supply sediment to the channel four years after flooding. To track recovery we collected annual topographic and sediment size data and calculated Shields numbers to determine if channels had reached an equilibrium form. We define equilibrium for bedload rivers as Shields numbers at bankfull discharge equal to that required to initiate bedload transport. Following dam emplacements the channels failed to recover because mobile sediment was unavailable. Fining dominated the recovery at Irene-affected sites (~10% reduction in sediment size) and dam removal sites (up to 30-60% reduction) with little post-disturbance change in channel geometry, possibly due to the limited mobile fraction.

Sorption of albendazole in sediments and soils: Isotherms and kinetics.

PubMed

Mutavdžić Pavlović, Dragana; Glavač, Antonija; Gluhak, Mihaela; Runje, Mislav

2018-02-01

Albendazole is a broad-spectrum anthelmintic drug effective against gastrointestinal parasites in humans and animals. Despite the fact that it has been detected in environment (water, sediment and soil), there is no information on its fate in the environment. So, in order to understand the sorption process of albendazole in environment, the sorption mechanism and kinetic properties were investigated through sorption equilibrium and sorption rate experiments. For that purpose, batch sorption of albendazole on five sediment samples and five soil samples from Croatia's region with different physico-chemical properties was investigated. Except physico-chemical properties of used environmental solid samples, the effects of various parameters such as contact time, initial concentration, ionic strength and pH on the albendazole sorption were studied. The K d parameter from linear sorption model was determined by linear regression analysis, while the Freundlich and Langmuir sorption models were applied to describe the equilibrium isotherms. The estimated K d values varied from 29.438 to 104.43 mLg -1 at 0.01 M CaCl 2 and for natural pH value of albendazole solution (pH 6.6). Experimental data showed that the best agreement was obtained with the linear model (R 2  > 0.99), while the rate of albendazole sorption is the best described with the kinetic model of pseudo-second-order. Obtained results point to a medium or even strong sorption of albendazole for soil or sediment particles, which is particularly dependent on the proportion of organic matter, pH, copper and zinc in them. Copyright © 2017 Elsevier Ltd. All rights reserved.

Sedimentation equilibrium of a small oligomer-forming membrane protein: effect of histidine protonation on pentameric stability.

PubMed

Surya, Wahyu; Torres, Jaume

2015-04-02

Analytical ultracentrifugation (AUC) can be used to study reversible interactions between macromolecules over a wide range of interaction strengths and under physiological conditions. This makes AUC a method of choice to quantitatively assess stoichiometry and thermodynamics of homo- and hetero-association that are transient and reversible in biochemical processes. In the modality of sedimentation equilibrium (SE), a balance between diffusion and sedimentation provides a profile as a function of radial distance that depends on a specific association model. Herein, a detailed SE protocol is described to determine the size and monomer-monomer association energy of a small membrane protein oligomer using an analytical ultracentrifuge. AUC-ES is label-free, only based on physical principles, and can be used on both water soluble and membrane proteins. An example is shown of the latter, the small hydrophobic (SH) protein in the human respiratory syncytial virus (hRSV), a 65-amino acid polypeptide with a single α-helical transmembrane (TM) domain that forms pentameric ion channels. NMR-based structural data shows that SH protein has two protonatable His residues in its transmembrane domain that are oriented facing the lumen of the channel. SE experiments have been designed to determine how pH affects association constant and the oligomeric size of SH protein. While the pentameric form was preserved in all cases, its association constant was reduced at low pH. These data are in agreement with a similar pH dependency observed for SH channel activity, consistent with a lumenal orientation of the two His residues in SH protein. The latter may experience electrostatic repulsion and reduced oligomer stability at low pH. In summary, this method is applicable whenever quantitative information on subtle protein-protein association changes in physiological conditions have to be measured.

Drivers of Microbial Metabolic Activity, Biogeochemical Cycling and Associated Greenhouse Gas Production in Streambed Sediments

NASA Astrophysics Data System (ADS)

Comer-Warner, S.; Krause, S.; Gooddy, D.; Blaen, P.; Brekenfeld, N.; Wexler, S.; Kaiser, J.

2017-12-01

Hotspots of enhanced biogeochemical reactivity are produced where groundwater and surface water mixes in streambed sediments. This enhanced reactivity is due to elevated residence times and nutrient concentrations found in these areas, leading to increased rates of microbial metabolic activity. Streambed sediments, therefore, may be important in reducing catchment-wide nutrient concentrations through increased cycling. However, they also have the potential to produce high concentrations of greenhouse gases (CO2, CH4 and N2O), as end-products of respiration and intermediate products of denitrification. The hydrological and biogeochemical drivers of streambed C and N cycling, are still insufficiently understood. Here we present results from biogeochemical sampling and tracer experiments in an agricultural sandstone stream in the UK. Nutrient, DOC and greenhouse gas concentrations, as well as d13CCO2, were measured in the streambed sediment in multilevel piezometers, and nutrient concentrations, as well as d15NNO3 and d18ONO3, were measured in Diffusive Equilibrium in Thin-film Gels. Tracer experiments using both conservative (Fluorescein and NaCl) and smart (Resazurin-Resorufin) tracers were performed to determine in-stream metabolism, transient storage and solute transport times in sub-reaches of the stream. Our results show large differences in nutrient and greenhouse gas concentrations between sub-reaches dominated by gravel sediments and those dominated by sandy sediments, as well as seasonally. This suggests temperature, sediment type and residence time are key controls on streambed nutrient cycling and greenhouse gas production. The results of this study have important implications for future greenhouse gas estimates from streams and rivers, particularly as the contribution of sediment greenhouse gas production is recognised as increasingly significant.

Fine sediment trapping in river lateral cavities

NASA Astrophysics Data System (ADS)

Juez, C.; Maechler, G.; Schleiss, A. J.; Franca, M. J.

2016-12-01

River restoration is nowadays a major issue in the field of hydraulics. The natural course and geometry of the rivers have been artificially changed by human activities for different purposes (land gaining, flood protection, agriculture). From a morphologic point of view, channelized rivers often display a straight path and monotonous river banks. This is in contradiction with natural morphology, where a high diversity can be found across the channel path (meanders) and the banks (pools, riffles). One way to restore rivers consist of transforming the artificial banks by adding macro-roughness elements in the lateral river banks (also called cavities and lateral embayments). The creation of irregularities on the banks causes new flow patterns that diversify the river habitat. However, these lateral cavities may be also responsible of the change of the river morphology, since they may trap the fine sediments travelling within the water. This is particularly important in glacier-fed streams such as the upper Rhone River in Switzerland. These are charged with fine sediments resulting from the erosion of the underlying glaciers bottom. The creation of lateral cavities may affect the sediment and morphological equilibrium of the river since these may trap sediments. This work aims to study the influence of the lateral cavities on the transport of fine sediments in the main channel. A set of laboratory experiments were done which covered a wide range of rectangular cavity configurations. Key parameters such as the flow discharge, the aspect ratio of the cavities and the initial sediment concentration were tested. Surface PIV, sediment samples and turbidity temporal records were collected during the experiments. The trapping efficiency of the cavities and the associated flow patterns were analyzed. The resulting conclusions provide a useful information for the future design of river restoration projects.

Assessing bioavailability of DDT and metabolites in marine sediments using solid-phase microextraction with performance reference compounds.

PubMed

Bao, Lian-Jun; Jia, Fang; Crago, J; Zeng, Eddy Y; Schlenk, D; Gan, Jay

2013-09-01

Solid-phase microextraction (SPME) has often been used to estimate the freely dissolved concentration (Cfree ) of organic contaminants in sediments. A significant limitation in the application of SPME for Cfree measurement is the requirement for attaining equilibrium partition, which is often difficult for strongly hydrophobic compounds such as DDT. A method was developed using SPME with stable isotope-labeled analogues as performance reference compounds (PRCs) to measure Cfree of DDT and metabolites (DDTs) in marine sediments. Six (13) C-labeled or deuterated PRCs were impregnated into polydimethylsiloxane (PDMS) fiber before use. Desorption of PRCs from PDMS fibers and absorption of DDTs from sediment were isotropic in a range of sediments evaluated ex situ under well-mixed conditions. When applied to a historically contaminated marine sediment from a Superfund site, the PRC-SPME method yielded Cfree values identical to those found by using a conventional equilibrium SPME approach (Eq-SPME), whereas the time for mixing was reduced from 9 d to only 9 h. The PRC-SPME method was further evaluated against bioaccumulation of DDTs by Neanthes arenaceodentata in the contaminated sediment with or without amendment of activated carbon or sand. Strong correlations were consistently found between the derived equilibrium concentrations on the fiber and lipid-normalized tissue residues for DDTs in the worms. Results from the present study clearly demonstrated the feasibility of coupling PRCs with SPME sampling to greatly shorten sampling time, thus affording much improved flexibility in the use of SPME for bioavailability evaluation. Copyright © 2013 SETAC.

Assessing Bioavailability of DDT and Metabolites in Marine Sediments using Solid-Phase Microextraction with Performance Reference Compounds

PubMed Central

Bao, Lian-Jun; Jia, Fang; Crago, J.; Zeng, Eddy Y.; Schlenk, D.; Gan, Jay

2014-01-01

Solid-phase microextraction (SPME) has often been used to estimate the freely dissolved concentration (Cfree) of organic contaminants in sediments. A significant limitation in the application of SPME for Cfree measurement is the requirement for attaining equilibrium partition, which is often difficult for strongly hydrophobic compounds such as DDT. A method was developed using SPME with stable isotope-labeled analogues as performance reference compounds (PRCs) to measure Cfree of DDT and metabolites (DDTs) in marine sediments. Six 13C-labeled or deuterated PRCs were impregnated into polydimethylsiloxane (PDMS) fiber before use. Desorption of PRCs from PDMS fibers and absorption of DDTs from sediment were isotropic in a range of sediments evaluated ex situ under well-mixed conditions. When applied to a historically contaminated marine sediment from a Superfund site, the PRC-SPME method yielded Cfree values identical to those found by using a conventional equilibrium SPME approach (Eq-SPME), wherease the time for mixing was reduced from 9 d to only 9 h. The PRC-SPME method was further evaluated against bioaccumulation of DDTs by Neanthes arenaceodentata in the contaminated sediment with or without amendment of activated carbon or sand. Strong correlations were consistently found between the derived equilibrium concentrations on the fiber and lipid-normalized tissue residues for DDTs in the worms. Results from the present study clearly demonstrated the feasibility of coupling PRCs with SPME sampling to greatly shorten sampling time, thus affording much improved flexibility in the use of SPME for bioavailability evaluation. Environ Toxicol Chem 2013;32:1946–1953. PMID:23661411

Exchangeable Phosphorus Pools and Equilibrium Characteristics for River Sediment as a Function of Particle Size

DTIC Science & Technology

2010-10-01

Zea mays L .). Can J Soil Sci 75:361-367. Zhang, T. Q., A. F. MacKenzie, B. C. Liang, and C. F. Drury. 2004. Soil test phosphorus and phosphorus...particulate exchangeable P fractions (as a fractional percentage), respectively, Cs is the suspended sediment concentration (M L -3), and Kd is the...groundwater) amended with P to a concentration of 0.120 mg L -1 to maintain in situ P equilibrium conditions (reported in James and Larson 2008

Sensitivity and spin-up times of cohesive sediment transport models used to simulate bathymetric change: Chapter 31

USGS Publications Warehouse

Schoellhamer, D.H.; Ganju, N.K.; Mineart, P.R.; Lionberger, M.A.; Kusuda, T.; Yamanishi, H.; Spearman, J.; Gailani, J. Z.

2008-01-01

Bathymetric change in tidal environments is modulated by watershed sediment yield, hydrodynamic processes, benthic composition, and anthropogenic activities. These multiple forcings combine to complicate simple prediction of bathymetric change; therefore, numerical models are necessary to simulate sediment transport. Errors arise from these simulations, due to inaccurate initial conditions and model parameters. We investigated the response of bathymetric change to initial conditions and model parameters with a simplified zero-dimensional cohesive sediment transport model, a two-dimensional hydrodynamic/sediment transport model, and a tidally averaged box model. The zero-dimensional model consists of a well-mixed control volume subjected to a semidiurnal tide, with a cohesive sediment bed. Typical cohesive sediment parameters were utilized for both the bed and suspended sediment. The model was run until equilibrium in terms of bathymetric change was reached, where equilibrium is defined as less than the rate of sea level rise in San Francisco Bay (2.17 mm/year). Using this state as the initial condition, model parameters were perturbed 10% to favor deposition, and the model was resumed. Perturbed parameters included, but were not limited to, maximum tidal current, erosion rate constant, and critical shear stress for erosion. Bathymetric change was most sensitive to maximum tidal current, with a 10% perturbation resulting in an additional 1.4 m of deposition over 10 years. Re-establishing equilibrium in this model required 14 years. The next most sensitive parameter was the critical shear stress for erosion; when increased 10%, an additional 0.56 m of sediment was deposited and 13 years were required to re-establish equilibrium. The two-dimensional hydrodynamic/sediment transport model was calibrated to suspended-sediment concentration, and despite robust solution of hydrodynamic conditions it was unable to accurately hindcast bathymetric change. The tidally averaged box model was calibrated to bathymetric change data and shows rapidly evolving bathymetry in the first 10-20 years, though sediment supply and hydrodynamic forcing did not vary greatly. This initial burst of bathymetric change is believed to be model adjustment to initial conditions, and suggests a spin-up time of greater than 10 years. These three diverse modeling approaches reinforce the sensitivity of cohesive sediment transport models to initial conditions and model parameters, and highlight the importance of appropriate calibration data. Adequate spin-up time of the order of years is required to initialize models, otherwise the solution will contain bathymetric change that is not due to environmental forcings, but rather improper specification of initial conditions and model parameters. Temporally intensive bathymetric change data can assist in determining initial conditions and parameters, provided they are available. Computational effort may be reduced by selectively updating hydrodynamics and bathymetry, thereby allowing time for spin-up periods. reserved.

Solid-phase Microextraction (SPME) with Stable Isotope Calibration for Measuring Bioavailability of Hydrophobic Organic Contaminants

PubMed Central

Cui, Xinyi; Bao, Lianjun; Gan, Jay

2014-01-01

Solid-phase microextraction (SPME) is a biomimetic tool ideally suited for measuring bioavailability of hydrophobic organic compounds (HOCs) in sediment and soil matrices. However, conventional SPME sampling requires the attainment of equilibrium between the fiber and sample matrix, which may take weeks or months, greatly limiting its applicability. In this study, we explored the preloading of polydimethylsiloxane fiber with stable isotope labeled analogs (SI-SPME) to circumvent the need for long sampling time, and evaluated the performance of SI-SPME against the conventional equilibrium SPME (Eq-SPME) using a range of sediments and conditions. Desorption of stable isotope-labeled analogs and absorption of PCB-52, PCB-153, bifenthrin and cis-permethrin were isotropic, validating the assumption for SI-SPME. Highly reproducible preloading was achieved using acetone-water (1:4, v/v) as the carrier. Compared to Eq-SPME that required weeks or even months, the fiber concentrations (Cf) under equilibrium could be reliably estimated by SI-SPME in 1 d under agitated conditions or 20 d under static conditions in spiked sediments. The Cf values predicted by SI-SPME were statistically identical to those determined by Eq-SPME. The SI-SPME method was further applied successfully to field sediments contaminated with PCB 52, PCB 153, and bifenthrin. The increasing availability of stable isotope labeled standards and mass spectrometry nowadays makes SI-SPME highly feasible, allowing the use of SPME under non-equilibrium conditions with much shorter or flexible sampling time. PMID:23930601

Equilibrium Partitioning Approach for Assessing Toxicity of Contaminants in Sediments: Linking Measured Concentrations to Effects

EPA Science Inventory

A variety of approaches exist for assessing the degree, extent and/or risk of metals contamination in sediments. Selection of the “correct” approach depends on the nature of the question being asked (e.g., the degree of metals contamination in marine sediments may be estimated by...

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wei Chen; Kan, A.T.; Tomson, M.B.

Both the adsorption and the desorption processes play important roles in the transport and fate of organic contaminants in water-sediments and groundwater systems. The adsorption-desorption processes are shown to be influenced by a number of factors, including sediments organic carbon content, contaminant aqueous solubility, aqueous-phase concentration as well as some natural environmental factors such as pH, pE, ionic strength and temperature. External mechanical forces, such as sediment perturbation, and repeated dredging will also have finite effect on the microscopic interparticle forces that control bonds between large and small grain particles. The objective of this research is to study the influencesmore » of various environmental effects on the equilibrium or non-equilibrium desorption behavior of nonpolar organic pollutants in historically contaminated natural sediments of Lake Charles, LA. Differences of desorption behavior between freshly and historically contaminated sediments will be compared in order to evaluated the desorption mechanism. The influences of particle size, mineral composition, organic matter concentration, and aqueous phase matrix composition on desorption behaviour will also be evaluated.« less

Experimental Investigation and Analysis of HEC-6 River Morphological Model

NASA Astrophysics Data System (ADS)

Tingsanchali, Tawatchai; Supharatid, Seree

1996-05-01

Only comparatively few experimental studies have been carried out to investigate the performance of the HEC-6 river morphological model. The model was developed by the Hydrologic Engineering Center of the US Army Corps of Engineers. In this study, experiments were carried out in a 20 m long concrete flume 0.6 m wide with varying rectangular cross-sections. The channel bed is paved with uniform sand of D50 = 0.9 mm and D90 = 1.2 mm within the test reach of 12 m. Two types of experiments were carried out with sediment transport, one under steady uniform flow and another under steady non-uniform flow conditions. Nine steady uniform flow experiments were carried out to compare the measured equilibrium relationship of flow and sediment transport rate with two bedload formulae, namely, Du Boys and Meyer-Peter and Muller, and with three total load formulae, namely, Toffaleti, Laursen and Yang. It was found that even though the sediment transport consists of a certain portion of bedload, the total load formulae give satisfactory results and better agreement than the two bedload formulae. Five steady non-uniform flow experiments were carried out under various conditions of varying bed profile and channel width and also with sediment addition and withdrawal. The measured transient water surface and bed profiles are compared with the computed results from the HEC-6 model. It was found that the Toffaleti and Yang total load formulae used in the HEC-6 model give the most satisfactory prediction of actual bed profiles under various conditions of non-uniform flow and sediment transport. The effects of Manning's n, variations of sediment inflow, various sediment transport formulae, sediment grain size and the model numerical parameters, i.e. distance interval x and numerical weighting factor, on the computed water surface and bed profiles were determined. It was found that the selection of the sediment transport formulae has the most significant effect on the computed results. It can be concluded that the HEC-6 model can predict satisfactorily a long-term average pattern of local scour and deposition along a channel with either a small abrupt change in geometry or gradually varying cross-sections. However, the accuracy of the model prediction is reduced in the regions where highly non-uniform flow occurs.

Sediment Equilibrium and Diffusive Fluxes in Relation to Phosphorus Dynamics in the Turbid Minnesota River

DTIC Science & Technology

2009-01-01

extractable P and K in a sandy clay loam soil under continuous corn ( Zea mays L .). Can J Soil Sci 75:361-367. Zhang, T. Q., A. F. MacKenzie, B. C...diffusive P flux from deposited sediment stored in river channels may also play a role in soluble P control. Ranges in equilibrium partitioning between...largest plants in the State of Minnesota, discharge (average discharge = 1.8 m3 s-1) at effluent P concentrations of 1.5 mg L -1 or less. A 538-megawatt

Observations and modelling of shoreline and multiple sandbar behaviour on a high-energy meso-tidal beach

NASA Astrophysics Data System (ADS)

Splinter, Kristen D.; Gonzalez, Maria V. G.; Oltman-Shay, Joan; Rutten, Jantien; Holman, Robert

2018-05-01

This contribution describes 10 years of observed sandbar and shoreline cross-shore position variability at a meso-tidal, high energy, multiple sandbar beach. To examine relationships between the temporal variability in shoreline/sandbar position with offshore wave forcing, a simple equilibrium model is applied to these data. The analysis presented in this paper shows that the equilibrium model is skilled at predicting the alongshore-averaged, time-varying position of the shoreline (R = 0.82) and the outer sandbar position (R = 0.75), suggesting that these end members of the nearshore sediment system are most strongly influenced by offshore wave forcing in a predictable, equilibrium-forced manner. The middle and inner bars are hypothesized to act as sediment transport pathways between the shoreline and the outer bar. Prediction of these more transient features by an equilibrium model was less skilful. Model coefficients reveal that these two end members (outer bar and shoreline) in the sediment system act in opposite directions to changes in the annual offshore wave forcing. During high wave events, sediment is removed from the shoreline and deposited in the nearshore sediment system with simultaneous landward retreat of the shoreline and offshore migration of the outer sandbar. While both end member features have cycles at annual and inter-annual scales, their respective equilibrium response factor differs by almost a factor of 10, with the shoreline responding around an inter-annual mean (ϕ = 1000 days) and the outer bar responding around a seasonal mean (ϕ = 170 days). The model accurately predicts shoreline response to both mild (e.g. 2004/05, 2008/09) and extreme (e.g. 2005/06, 2009/10) winter storms, as well as their summer recovery. The more mobile and dynamic outer sandbar is well-modelled during typical winters. Summer onshore sandbar migration of the outer bar in 2005 and 2006 is under-predicted as the system transitioned between a triple (winter) and double (summer) sandbar system. The changing of the number of bars present in the system is something that this simple model cannot predict. Analysis of the data suggests that this multi-bar system adjusts its cross-shore seasonal movement when there is a significant change in the sediment supply to the system (e.g., nourishment projects, severe storms).

Radioactive equilibrium in ancient marine sediments

USGS Publications Warehouse

Breger, I.A.

1955-01-01

Radioactive equilibrium in eight marine sedimentary formations has been studied by means of direct determinations of uranium, radium and thorium. Alpha-particle counting has also been carried out in order to cross-calibrate thick-source counting techniques. The maximum deviation from radioactive equilibrium that has been noted is 11 per cent-indicating that there is probably equilibrium in all the formations analyzed. Thick-source alpha-particle counting by means of a proportional counter or an ionization chamber leads to high results when the samples contain less than about 10 p.p.m. of uranium. For samples having a higher content of uranium the results are in excellent agreement with each other and with those obtained by direct analytical techniques. The thorium contents that have been obtained correspond well to the average values reported in the literature. The uranium content of marine sediments may be appreciably higher than the average values that have been reported for sedimentary rocks. Data show that there is up to fourteen times the percentage of uranium as of thorium in the formations studied and that the percentage of thorium never exceeds that of uranium. While the proximity of a depositional environment to a land mass may influence the concentration of uranium in a marine sediment, this is not true with thorium. ?? 1955.

Treatment of atrazine in nursery irrigation runoff by a constructed wetland.

PubMed

Runes, Heather B; Jenkins, Jeffrey J; Moore, James A; Bottomley, Peter J; Wilson, Bruce D

2003-02-01

To investigate the treatment capability of a surface flow wetland at a container nursery near Portland, Oregon, atrazine was introduced during simulated runoff events. Treatment efficiency was evaluated as the percent atrazine recovered (as percent of applied) in the water column at the wetland's outlet. Atrazine treatment efficiency at the outlet of the constructed wetland during a 7-d period ranged from 18-24% in 1998 (experiments 1-3) and 16-17% in 1999 (experiments 4 and 5). Changes in total flow, or frequency and intensity of runoff events did not affect treatment. For experiment 6 in 1999, where the amount, frequency, and duration of runoff events exceeded all other experiments, treatment was compromised. For all experiments, deethylatrazine (DEA) and deisopropylatrazine (DIA) accounted for 13-21% of the initial application. Hydroxyatrazine (HA) was rarely detected in the water. Organic carbon adsorption coefficients (Koc) were determined from batch equilibrium sorption isotherms with wetland sediment, and they decreased in the order of HA > DIA > atrazine > DEA. Static water-sediment column experiments indicated that sorption is an important mechanism for atrazine loss from water passing through the constructed wetland. The results of the MPN assay indicated the existence in the wetland of a low-density population of microorganisms with the potential to mineralize atrazine's ethyl side chain.

How vegetation and sediment transport feedbacks drive landscape change in the Everglades and wetlands worldwide

USGS Publications Warehouse

Larsen, Laurel G.; Harvey, Judson W.

2010-01-01

Mechanisms reported to promote landscape self‐organization cannot explain vegetation patterning oriented parallel to flow. Recent catastrophic shifts in Everglades landscape pattern and ecological function highlight the need to understand the feedbacks governing these ecosystems. We modeled feedback between vegetation, hydrology, and sediment transport on the basis of a decade of experimentation. Results from more than 100 simulations showed that flows just sufficient to redistribute sediment from sparsely vegetated sloughs to dense ridges were needed for an equilibrium patterned landscape oriented parallel to flow. Surprisingly, although vegetation heterogeneity typically conveys resilience, in wetlands governed by flow/sediment feedbacks it indicates metastability, whereby the landscape is prone to catastrophic shifts. Substantial increases or decreases in flow relative to the equilibrium condition caused an expansion of emergent vegetation and loss of open‐water areas that was unlikely to revert upon restoration of the equilibrium hydrology. Understanding these feedbacks is critical in forecasting wetland responses to changing conditions and designing management strategies that optimize ecosystem services, such as carbon sequestration or habitat provision. Our model and new sensitivity analysis techniques address these issues and make it newly apparent that simply returning flow to predrainage conditions in the Everglades may not be sufficient to restore historic landscape patterns and processes.

PROCEDURES FOR THE DERIVATION OF EQUILIBRIUM ...

EPA Pesticide Factsheets

This equilibrium partitioning sediment benchmark (ESB) document describes procedures to derive concentrations for 32 nonionic organic chemicals in sediment which are protective of the presence of freshwater and marine benthic organisms. The equilibrium partitioning (EqP) approach was chosen because it accounts for the varying biological availability of chemicals in different sediments and allows for the incorporation of the appropriate biological effects concentration. This provides for the derivation of benchmarks that are causally linked to the specific chemical, applicable across sediments, and appropriately protective of benthic organisms. EqP can be used to calculate ESBs for any toxicity endpoint for which there are water-only toxicity data; it is not limited to any single effect endpoint. For the purposes of this document, ESBs for 32 nonionic organic chemicals, including several low molecular weight aliphatic and aromatic compounds, pesticides, and phthalates, were derived using Final Chronic Values (FCV) from Water Quality Criteria (WQC) or Secondary Chronic Values (SCV) derived from existing toxicological data using the Great Lakes Water Quality Initiative (GLI) or narcosis theory approaches. These values are intended to be the concentration of each chemical in water that is protective of the presence of aquatic life. For nonionic organic chemicals demonstrating a narcotic mode of action, ESBs derived using the GLI approach specifically for fres

Equilibrium sampling informs tissue residue and sediment remediation for pyrethroid insecticides in mariculture: A laboratory demonstration.

PubMed

Li, Juan-Ying; Shi, Wenxuan; Li, Zhenhua; Chen, Yiqin; Shao, Liu; Jin, Ling

2018-03-01

Mariculture product safety in relation to sediment quality has attracted increasing attention because of the accumulation of potentially hazardous chemicals, including pyrethroid insecticides, in sediment. Passive sampling has been widely used to assess the bioavailability of sediment-associated hydrophobic organic contaminants and predict their body residue in benthic organisms. Therefore, in this study, we introduced polydimethylsiloxane (PDMS) polymer as a biomimetic "chemometer" for freely-dissolved concentrations (C free ) to assess the efficacy of different carbon sorbents in reducing the bioavailability of pyrethroids in the process of sediment remediation. Black carbon (BC)-based materials (e.g., charcoal, biochar, and activated carbon) showed the advantageous sorption capacity over humic substance-based peat soil based on both C free and tissue residue in exposed clams. Of the tested BC-type materials, biochar appeared to be an ideal one in the remediation of pyrethroid-contaminated sediment. The predictive value of the PDMS chemometer approach to informing tissue residue was confirmed by a good agreement between the measured lipid-normalized concentrations of pyrethroids in clams and the lipid-based equilibrium concentrations calculated from C free via lipid-water partition coefficients. The quantitative inter-compartmental relationship underlying the laboratory system of sediment-pore water-PDMS-biota was also cross-validated by a mechanistically-based bioaccumulation model, thus confirming the validity of C free as a predictive intermediate to alert for tissue residue and guide sediment remediation. The present study revealed a great promise of sensing C free by polymer-based equilibrium sampling in predicting tissue residue of chemicals applied in mariculture against regulatory guidelines, and, in turn, informing remediation measures when needs arise. In situ demonstration is warranted in the future to ascertain the field applicability of this approach in real mariculture systems. Copyright © 2017 Elsevier B.V. All rights reserved.

Deposition and simulation of sediment transport in the Lower Susquehanna River reservoir system

USGS Publications Warehouse

Hainly, R.A.; Reed, L.A.; Flippo, H.N.; Barton, G.J.

1995-01-01

The Susquehanna River drains 27,510 square miles in New York, Pennsylvania, and Maryland and is the largest tributary to the Chesapeake Bay. Three large hydroelectric dams are located on the river, Safe Harbor (Lake Clarke) and Holtwood (Lake Aldred) in southern Pennsylvania, and Conowingo (Conowingo Reservoir) in northern Maryland. About 259 million tons of sediment have been deposited in the three reservoirs. Lake Clarke contains about 90.7 million tons of sediment, Lake Aldred contains about 13.6 million tons, and Conowingo Reservoir contains about 155 million tons. An estimated 64.8 million tons of sand, 19.7 million tons of coal, 112 million tons of silt, and 63.3 million tons of clay are deposited in the three reservoirs. Deposition in the reservoirs is variable and ranges from 0 to 30 feet. Chemical analyses of sediment core samples indicate that the three reservoirs combined contain about 814,000 tons of organic nitrogen, 98,900 tons of ammonia as nitrogen, 226,000 tons of phosphorus, 5,610,000 1tons of iron, 2,250,000 tons of aluminum, and about 409,000 tons of manganese. Historical data indicate that Lake Clarke and Lake Aldred have reached equilibrium, and that they no longer store sediment. A comparison of cross-sectional data from Lake Clarke and Lake Aldred with data from Conowingo Reservoir indicates that Conowingo Reservoir will reach equilibrium within the next 20 to 30 years. As the Conowingo Reservoir fills with sediment and approaches equilibrium, the amount of sediment transported to the Chesapeake Bay will increase. The most notable increases will take place when very high flows scour the deposited sediment. Sediment transport through the reservoir system was simulated with the U.S. Army Corps of Engineers' HEC-6 computer model. The model was calibrated with monthly sediment loads for calendar year 1987. Calibration runs with options set for maximum trap efficiency and a "natural" particle-size distribution resulted in an overall computed trap efficiency of 34 percent for 1987, much less than the measured efficiency of 71 percent.

Role of naturally occurring gas hydrates in sediment transport

DOE Office of Scientific and Technical Information (OSTI.GOV)

McIver, R.D.

1982-06-01

Naturally occurring gas hydrates have the potential to store enormous volumes of both gas and water in semi-solid form in ocean-bottom sediments and then to release that gas and water when the hydrate's equilibrium condition are disturbed. Therefore, hydrates provide a potential mechanism for transporting large volumes of sediments. Under the combined low bottom-water temperatures and moderate hydrostatic pressures that exist over most of the continental slopes and all of the continental rises and abyssal plains, hydrocarbon gases at or near saturation in the interstitial waters of the near-bottom sediments will form hydrates. The gas can either be autochthonous, microbiallymore » produced gas, or allochthonous, catagenic gas from deeper sediments. Equilibrium conditions that stabilize hydrated sediments may be disturbed, for example, by continued sedimentation or by lowering of sea level. In either case, some of the solid gas-water matrix decomposes. Released gas and water volume exceeds the volume occupied by the hydrate, so the internal pressure rises - drastically if large volumes of hydrate are decomposed. Part of the once rigid sediment is converted to a gas- and water-rich, relatively low density mud. When the internal pressure, due to the presence of the compressed gas or to buoyancy, is sufficiently high, the overlying sediment may be lifted and/or breached, and the less dense, gas-cut mud may break through. Such hydrate-related phenomena can cause mud diapirs, mud volcanos, mud slides, or turbidite flows, depending on sediment configuration and bottom topography. 4 figures.« less

Effects of sediment supply on surface textures of gravel-bed rivers

Treesearch

John M. Buffington; David R. Montgomery

1999-01-01

Using previously published data from flume studies, we test a new approach for quantifying the effects of sediment supply (i.e., bed material supply) on surface grain size of equilibrium gravel channels. Textural response to sediment supply is evaluated relative to a theoretical prediction of competent median grain size (D’50). We find that surface median grain size (...

Network-scale dynamics of sediment mixtures: how do tectonics affect surface bed texture and channel slope?

NASA Astrophysics Data System (ADS)

Gasparini, N. M.; Bras, R. L.; Tucker, G. E.

2003-04-01

An alluvial channel's slope and bed texture are intimately linked. Along with fluvial discharge, these variables are the key players in setting alluvial transport rates. We know that both channel slope and mean grain size usually decrease downstream, but how sensitive are these variables to tectonic changes? Are basin concavity and downstream fining drastically disrupted during transitions from one tectonic regime to another? We explore these questions using the CHILD numerical landscape evolution model to generate alluvial networks composed of a sand and gravel mixture. The steady-state and transient patterns of both channel slope and sediment texture are investigated. The steady-state patterns in slope and sediment texture are verified independently by solving the erosion equations under equilibrium conditions, i.e. the case when the erosion rate is equal to the uplift rate across the entire landscape. The inclusion of surface texture as a free parameter (as opposed to just channel slope) leads to some surprising results. In all cases, an increase in uplift rate results in channel beds which are finer at equilibrium (for a given drainage area). Higher uplift rates imply larger equilibrium transport rates; this leads to finer channels that have a smaller critical shear stress to entrain material, and therefore more material can be transported for a given discharge (and channel slope). Changes in equilibrium slopes are less intuitive. An increase in uplift rates can cause channel slopes to increase, remain the same, or decrease, depending on model parameter values. In the surprising case in which equilibrium channel slopes decrease with increasing uplift rates, we suggest that surface texture changes more than compensate for the required increase in transport rates, causing channel slopes to decrease. These results highlight the important role of sediment grain size in determining transport rates and caution us against ignoring this important variable in fluvial networks.

Internal loading of phosphate in Lake Erie Central Basin.

PubMed

Paytan, Adina; Roberts, Kathryn; Watson, Sue; Peek, Sara; Chuang, Pei-Chuan; Defforey, Delphine; Kendall, Carol

2017-02-01

After significant reductions in external phosphorus (P) loads, and subsequent water quality improvements in the early 1980s, the water quality of Lake Erie has declined considerably over the past decade. The frequency and magnitude of harmful algal blooms (primarily in the western basin) and the extent of hypoxic bottom waters in the central basin have increased. The decline in ecosystem health, despite meeting goals for external P loads, has sparked a renewed effort to understand P cycling in the lake. We use pore-water P concentration profiles and sediment cores incubation experiments to quantify the P flux from Lake Erie central basin sediments. In addition, the oxygen isotopes of phosphate were investigated to assess the isotopic signature of sedimentary phosphate inputs relative to the isotopic signature of phosphate in lake water. Extrapolating the total P sediment flux based on the pore-water profiles to the whole area of the central basin ranged from 300 to 1250metric tons per year and using the flux based on core incubation experiments an annual flux of roughly 2400metric tons of P is calculated. These estimates amount to 8-20% of the total external input of P to Lake Erie. The isotopic signature of phosphate in the extractable fraction of the sediments (~18‰) can explain the non-equilibrium isotope values of dissolved phosphate in the deep water of the central basin of Lake Erie, and this is consistent with sediments as an important internal source of P in the Lake. Copyright © 2016 Elsevier B.V. All rights reserved.

Mineral paragenesis on Mars: The roles of reactive surface area and diffusion

PubMed Central

Gil‐Lozano, Carolina; Uceda, Esther R.; Losa‐Adams, Elisabeth; Davila, Alfonso F.; Gago‐Duport, Luis

2017-01-01

Abstract Geochemical models of secondary mineral precipitation on Mars generally assume semiopen systems (open to the atmosphere but closed at the water‐sediment interface) and equilibrium conditions. However, in natural multicomponent systems, the reactive surface area of primary minerals controls the dissolution rate and affects the precipitation sequences of secondary phases, and simultaneously, the transport of dissolved species may occur through the atmosphere‐water and water‐sediment interfaces. Here we present a suite of geochemical models designed to analyze the formation of secondary minerals in basaltic sediments on Mars, evaluating the role of (i) reactive surface areas and (ii) the transport of ions through a basalt sediment column. We consider fully open conditions, both to the atmosphere and to the sediment, and a kinetic approach for mineral dissolution and precipitation. Our models consider a geochemical scenario constituted by a basin (i.e., a shallow lake) where supersaturation is generated by evaporation/cooling and the starting point is a solution in equilibrium with basaltic sediments. Our results show that cation removal by diffusion, along with the input of atmospheric volatiles and the influence of the reactive surface area of primary minerals, plays a central role in the evolution of the secondary mineral sequences formed. We conclude that precipitation of evaporites finds more restrictions in basaltic sediments of small grain size than in basaltic sediments of greater grain size. PMID:29104844

Mineral paragenesis on Mars: The roles of reactive surface area and diffusion.

PubMed

Fairén, Alberto G; Gil-Lozano, Carolina; Uceda, Esther R; Losa-Adams, Elisabeth; Davila, Alfonso F; Gago-Duport, Luis

2017-09-01

Geochemical models of secondary mineral precipitation on Mars generally assume semiopen systems (open to the atmosphere but closed at the water-sediment interface) and equilibrium conditions. However, in natural multicomponent systems, the reactive surface area of primary minerals controls the dissolution rate and affects the precipitation sequences of secondary phases, and simultaneously, the transport of dissolved species may occur through the atmosphere-water and water-sediment interfaces. Here we present a suite of geochemical models designed to analyze the formation of secondary minerals in basaltic sediments on Mars, evaluating the role of (i) reactive surface areas and (ii) the transport of ions through a basalt sediment column. We consider fully open conditions, both to the atmosphere and to the sediment, and a kinetic approach for mineral dissolution and precipitation. Our models consider a geochemical scenario constituted by a basin (i.e., a shallow lake) where supersaturation is generated by evaporation/cooling and the starting point is a solution in equilibrium with basaltic sediments. Our results show that cation removal by diffusion, along with the input of atmospheric volatiles and the influence of the reactive surface area of primary minerals, plays a central role in the evolution of the secondary mineral sequences formed. We conclude that precipitation of evaporites finds more restrictions in basaltic sediments of small grain size than in basaltic sediments of greater grain size.

Field-scale reduction of PCB bioavailability with activated carbon amendment to river sediments.

PubMed

Beckingham, Barbara; Ghosh, Upal

2011-12-15

Remediation of contaminated sediments remains a technological challenge because traditional approaches do not always achieve risk reduction goals for human health and ecosystem protection and can even be destructive for natural resources. Recent work has shown that uptake of persistent organic pollutants such as polychlorinated biphenyls (PCBs) in the food web is strongly influenced by the nature of contaminant binding, especially to black carbon surfaces in sediments. We demonstrate for the first time in a contaminated river that application of activated carbon to sediments in the field reduces biouptake of PCBs in benthic organisms. After treatment with activated carbon applied at a dose similar to the native organic carbon of sediment, bioaccumulation in freshwater oligochaete worms was reduced compared to preamendment conditions by 69 to 99%, and concentrations of PCBs in water at equilibrium with the sediment were reduced by greater than 93% at all treatment sites for up to three years of monitoring. By comparing measured reductions in bioaccumulation of tetra- and penta-chlorinated PCB congeners resulting from field application of activated carbon to a laboratory study where PCBs were preloaded onto activated carbon, it is evident that equilibrium sorption had not been achieved in the field. Although other remedies may be appropriate for some highly contaminated sites, we show through this pilot study that PCB exposure from moderately contaminated river sediments may be managed effectively through activated carbon amendment in sediments.

Prospective Environmental Risk Assessment for Sediment-Bound Organic Chemicals: A Proposal for Tiered Effect Assessment.

PubMed

Diepens, Noël J; Koelmans, Albert A; Baveco, Hans; van den Brink, Paul J; van den Heuvel-Greve, Martine J; Brock, Theo C M

A broadly accepted framework for prospective environmental risk assessment (ERA) of sediment-bound organic chemicals is currently lacking. Such a framework requires clear protection goals, evidence-based concepts that link exposure to effects and a transparent tiered-effect assessment. In this paper, we provide a tiered prospective sediment ERA procedure for organic chemicals in sediment, with a focus on the applicable European regulations and the underlying data requirements. Using the ecosystem services concept, we derived specific protection goals for ecosystem service providing units: microorganisms, benthic algae, sediment-rooted macrophytes, benthic invertebrates and benthic vertebrates. Triggers for sediment toxicity testing are discussed.We recommend a tiered approach (Tier 0 through Tier 3). Tier-0 is a cost-effective screening based on chronic water-exposure toxicity data for pelagic species and equilibrium partitioning. Tier-1 is based on spiked sediment laboratory toxicity tests with standard benthic test species and standardised test methods. If comparable chronic toxicity data for both standard and additional benthic test species are available, the Species Sensitivity Distribution (SSD) approach is a more viable Tier-2 option than the geometric mean approach. This paper includes criteria for accepting results of sediment-spiked single species toxicity tests in prospective ERA, and for the application of the SSD approach. We propose micro/mesocosm experiments with spiked sediment, to study colonisation success by benthic organisms, as a Tier-3 option. Ecological effect models can be used to supplement the experimental tiers. A strategy for unifying information from various tiers by experimental work and exposure-and effect modelling is provided.

Effect of temperature and salinity on phosphate sorption on marine sediments.

PubMed

Zhang, Jia-Zhong; Huang, Xiao-Lan

2011-08-15

Our previous studies on the phosphate sorption on sediments in Florida Bay at 25 °C in salinity 36 seawater revealed that the sorption capacity varies considerably within the bay but can be attributed to the content of sedimentary P and Fe. It is known that both temperature and salinity influence the sorption process and their natural variations are the greatest in estuaries. To provide useful sorption parameters for modeling phosphate cycle in Florida Bay, a systematic study was carried out to quantify the effects of salinity and temperature on phosphate sorption on sediments. For a given sample, the zero equilibrium phosphate concentration and the distribution coefficient were measured over a range of salinity (2-72) and temperature (15-35 °C) conditions. Such a suite of experiments with combinations of different temperature and salinity were performed for 14 selected stations that cover a range of sediment characteristics and geographic locations of the bay. Phosphate sorption was found to increase with increasing temperature or decreasing salinity and their effects depended upon sediment's exchangeable P content. This study provided the first estimate of the phosphate sorption parameters as a function of salinity and temperature in marine sediments. Incorporation of these parameters in water quality models will enable them to predict the effect of increasing freshwater input, as proposed by the Comprehensive Everglades Restoration Plan, on the seasonal cycle of phosphate in Florida Bay.

Sorption of selected pharmaceuticals and pesticides on different river sediments.

PubMed

Radović, Tanja T; Grujić, Svetlana D; Kovačević, Srđan R; Laušević, Mila D; Dimkić, Milan A

2016-12-01

In the present work, the sorption ability of 17 pharmaceutical compounds, two metabolites, and 15 pesticides (34 target compounds in total) onto four different river sediments was investigated separately. Selected compounds present the most frequently prescribed pharmaceuticals in human and animal medicine and the most frequently used pesticides in agriculture. Their presence into the surface, ground, and waste waters was confirmed into the numerous papers in literature, as well as their presence into the river sediments (for some of them). However, investigations of their sorption onto the river sediments, as major natural protection from potential pollution of ground water by them is missing. Sorption in this study was investigated onto river sediments taken from rivers in the Republic of Serbia, where only less than 10 % of total generated waste water passes through mainly basic treatment processes. Experiments were based on batch equilibrium procedures and obtained solutions were analyzed by previously developed and validated sensitive high performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analytical methods. All results were modeled by Freundlich isotherms. Obtained results have shown that Kf coefficient values are in correlation with organic carbon content. Kd sorption coefficient values were relatively low and ranged in wide ranges for almost all compounds and sediments. That implicates on the conclusion that capacities of the investigated sorbents are not large for those compounds.

Sedimentation Equilibrium of a Small Oligomer-forming Membrane Protein: Effect of Histidine Protonation on Pentameric Stability

PubMed Central

Surya, Wahyu; Torres, Jaume

2015-01-01

Analytical ultracentrifugation (AUC) can be used to study reversible interactions between macromolecules over a wide range of interaction strengths and under physiological conditions. This makes AUC a method of choice to quantitatively assess stoichiometry and thermodynamics of homo- and hetero-association that are transient and reversible in biochemical processes. In the modality of sedimentation equilibrium (SE), a balance between diffusion and sedimentation provides a profile as a function of radial distance that depends on a specific association model. Herein, a detailed SE protocol is described to determine the size and monomer-monomer association energy of a small membrane protein oligomer using an analytical ultracentrifuge. AUC-ES is label-free, only based on physical principles, and can be used on both water soluble and membrane proteins. An example is shown of the latter, the small hydrophobic (SH) protein in the human respiratory syncytial virus (hRSV), a 65-amino acid polypeptide with a single α-helical transmembrane (TM) domain that forms pentameric ion channels. NMR-based structural data shows that SH protein has two protonatable His residues in its transmembrane domain that are oriented facing the lumen of the channel. SE experiments have been designed to determine how pH affects association constant and the oligomeric size of SH protein. While the pentameric form was preserved in all cases, its association constant was reduced at low pH. These data are in agreement with a similar pH dependency observed for SH channel activity, consistent with a lumenal orientation of the two His residues in SH protein. The latter may experience electrostatic repulsion and reduced oligomer stability at low pH. In summary, this method is applicable whenever quantitative information on subtle protein-protein association changes in physiological conditions have to be measured.   PMID:25867485

Entropy production in a fluid-solid system far from thermodynamic equilibrium.

PubMed

Chung, Bong Jae; Ortega, Blas; Vaidya, Ashwin

2017-11-24

The terminal orientation of a rigid body in a moving fluid is an example of a dissipative system, out of thermodynamic equilibrium and therefore a perfect testing ground for the validity of the maximum entropy production principle (MaxEP). Thus far, dynamical equations alone have been employed in studying the equilibrium states in fluid-solid interactions, but these are far too complex and become analytically intractable when inertial effects come into play. At that stage, our only recourse is to rely on numerical techniques which can be computationally expensive. In our past work, we have shown that the MaxEP is a reliable tool to help predict orientational equilibrium states of highly symmetric bodies such as cylinders, spheroids and toroidal bodies. The MaxEP correctly helps choose the stable equilibrium in these cases when the system is slightly out of thermodynamic equilibrium. In the current paper, we expand our analysis to examine i) bodies with fewer symmetries than previously reported, for instance, a half-ellipse and ii) when the system is far from thermodynamic equilibrium. Using two-dimensional numerical studies at Reynolds numbers ranging between 0 and 14, we examine the validity of the MaxEP. Our analysis of flow past a half-ellipse shows that overall the MaxEP is a good predictor of the equilibrium states but, in the special case of the half-ellipse with aspect ratio much greater than unity, the MaxEP is replaced by the Min-MaxEP, at higher Reynolds numbers when inertial effects come into play. Experiments in sedimentation tanks and with hinged bodies in a flow tank confirm these calculations.

An examination of the rheology of flocculated clay suspensions

NASA Astrophysics Data System (ADS)

Spearman, Jeremy

2017-04-01

A dense cohesive sediment suspension, sometimes referred to as fluid mud, is a thixotropic fluid with a true yield stress. Current rheological formulations struggle to reconcile the structural dynamics of cohesive sediment suspensions with the equilibrium behaviour of these suspensions across the range of concentrations and shear. This paper is concerned with establishing a rheological framework for the range of sediment concentrations from the yield point to Newtonian flow. The shear stress equation is based on floc fractal theory, put forward by Mills and Snabre (1988). This results in a Casson-like rheology equation. Additional structural dynamics is then added, using a theory on the self-similarity of clay suspensions proposed by Coussot (1995), giving an equation which has the ability to match the equilibrium and time-dependent viscous rheology of a wide range of suspensions of different concentration and mineralogy.

The Graded Alluvial River: Variable Flow and the Dominant Discharge

NASA Astrophysics Data System (ADS)

Blom, A.; Arkesteijn, L.; Viparelli, E.

2016-12-01

We derive analytical formulations for the graded or equilibrium longitudinal profile of a mixed-sediment alluvial river under variable flow. The formulations are applicable to reaches upstream from the backwater zone. The model is based on the conservation equations for the mass of two distinct sediment modes, sand and gravel, at the bed surface to account for the effects of grain size selective transport and abrasion of gravel particles. The effects of a variable flow rate are included by (a) treating the flow as a continuously changing yet steady water discharge (i.e. here termed an alternating steady discharge) and (b) assuming the time scale of changes in channel slope and bed surface texture to be much larger than the one of changes in flow rate. The equations are simplified realizing that at equilibrium the river profile finds itself in a dynamic steady state with oscillations around constant mean values of channel slope and bed surface texture. A generalized sediment transport relation representing the stochastic nature of sediment transport allows for explicit or analytical solutions to the streamwise decrease of both the channel slope and the bed surface mean grain size under variable flow for reaches unaffected by backwater effects. This modelling approach also provides a definition of a channel-forming or dominant water discharge, i.e., that steady water discharge that is equivalent in its effect on the equilibrium channel slope to the full hydrograph.

Morphological resilience to flow fluctuations of fine sediment deposits in bank lateral cavities

NASA Astrophysics Data System (ADS)

Juez, C.; Thalmann, M.; Schleiss, A. J.; Franca, M. J.

2018-05-01

Lateral cavities are built in the banks of rivers for several purposes: to create harbors, to capture sediment, to keep a central navigable channel (i.e., Casiers de Girardon in the Rhone river) or to promote the formation of aquatic habitats if a limited amount of sediment is captured, providing hydraulic and morphologic diversity (i.e., the case of Japanese Wandos). This work is focused on this latter purpose: promotion of hydraulic and morphologic diversity. In these scenarios, an increase in the flow discharge in the main channel may, however, re-mobilize the deposit of sediment inside these lateral embayments and cause a sudden increase of the sediment concentration and turbidity in the main channel. It is thus of interest to characterize the resistance and resilience of these sedimentary deposits when the main channel is subjected to high flow or flushing events. Laboratory tests were carried out for five different normalized geometries of the cavities installed in the banks of an open channel and for five hydrographs with different levels of unsteadiness. Water depth, sediment deposit mass, sediment concentration and area covered by the settled sediments were recorded throughout each experiment. Although sediment deposits established at equilibrium before the flushing events are different depending on the geometry of the cavities, generally, they are recovered after being flushed by the high flow events. It is shown that the resistance and resilience of the sediment deposits are strongly dependent on the flow field and the mass exchange between the main channel and the cavities. This mass exchange is governed by the geometry of the cavities and the magnitude of the hydrographs applied.

[Mechanism of phosphorus adsorption and immobility by sediments in innercity heavily polluted canal].

PubMed

Li, Da-Peng; Huang, Yong; Yuan, Yan; Fan, Cheng-Xin

2011-01-01

The mechanisms of phosphorus (P) adsorption and immobility were investigated in laboratory experiments. The sediments and waters used were taken from an inner-city heavily polluted canal. Addition of KH2PO4 into the operated experimental units, with and without (i.e., static) intermittent sediment resuspension, were made similar to the external P input and carried out periodically. The results show that the amount of the accumulative P adsorption onto the sediments was up to 363.4 mg x kg(-1) under the conditions of sediment disturbance over a 39-day period, and it was evidently higher than that (213.2 mg x kg(-1)) under static conditions. Sequential fractionation indicated that most of the incorporated P was accounted for in the Fe/Al-P. There were over 61% in the case of intermittent sediment disturbance and up to 83% in the case of static conditions. Based on the bioavailability of Fe/Al-P, 40.6% of the incorporated P was accounted for in non-occluded Fe/Al-P of the sediments under intermittent sediment disturbance conditions. This value increased to 59.5% under static conditions. In addition, more than 23% of the incorporated P was accounted for in HCl-P of the sediments under intermittent sediment disturbance conditions, on the other hand, the concentration of HCl-P kept relatively constant under static conditions. After 39 d of P adsorption by the both sediments, the values of the maximum sorption capacity (S(max)) decreased,while zero equilibrium P concentration (EPC0) and P saturation P(%) increased. However, the extent of EPC0 and P% under intermittent sediment disturbance conditions was obviously lower than that under static conditions. It was hopefully suggested that intermittent sediment disturbance can not only accelerate the P adsorption but also enhance the P retention by sediments.

Microbial production of isotopically light iron(II) in a modern chemically precipitated sediment and implications for isotopic variations in ancient rocks

USGS Publications Warehouse

Tangalos, G.E.; Beard, B.L.; Johnson, C.M.; Alpers, Charles N.; Shelobolina, E.S.; Xu, H.; Konishi, H.; Roden, E.E.

2012-01-01

The inventories and Fe isotope composition of aqueous Fe(II) and solid-phase Fe compounds were quantified in neutral-pH, chemically precipitated sediments downstream of the Iron Mountain acid mine drainage site in northern California, USA. The sediments contain high concentrations of amorphous Fe(III) oxyhydroxides [Fe(III)am] that allow dissimilatory iron reduction (DIR) to predominate over Fe–S interactions in Fe redox transformation, as indicated by the very low abundance of Cr(II)-extractable reduced inorganic sulfur compared with dilute HCl-extractable Fe. δ56Fe values for bulk HCl- and HF-extractable Fe were ≈ 0. These near-zero bulk δ56Fe values, together with the very low abundance of dissolved Fe in the overlying water column, suggest that the pyrite Fe source had near-zero δ56Fe values, and that complete oxidation of Fe(II) took place prior to deposition of the Fe(III) oxide-rich sediment. Sediment core analyses and incubation experiments demonstrated the production of millimolar quantities of isotopically light (δ56Fe ≈ -1.5 to -0.5‰) aqueous Fe(II) coupled to partial reduction of Fe(III)am by DIR. Trends in the Fe isotope composition of solid-associated Fe(II) and residual Fe(III)am are consistent with experiments with synthetic Fe(III) oxides, and collectively suggest an equilibrium Fe isotope fractionation between aqueous Fe(II) and Fe(III)am of approximately -2‰. These Fe(III) oxide-rich sediments provide a model for early diagenetic processes that are likely to have taken place in Archean and Paleoproterozoic marine sediments that served as precursors for banded iron formations. Our results suggest pathways whereby DIR could have led to the formation of large quantities of low-δ56Fe minerals during BIF genesis.

Cross Validation of Two Partitioning-Based Sampling Approaches in Mesocosms Containing PCB Contaminated Field Sediment, Biota, and Activated Carbon Amendment

EPA Science Inventory

The Gold Standard for determining freely dissolved concentrations (Cfree) of hydrophobic organic compounds in sediment interstitial water would be in situ deployment combined with equilibrium sampling, which is generally difficult to achieve. In the present study, ex situ equilib...

g Dependent particle concentration due to sedimentation

NASA Astrophysics Data System (ADS)

Haranas, Ioannis; Gkigkitzis, Ioannis; Zouganelis, George D.

2012-11-01

Sedimentation of particles in a fluid has long been used to characterize particle size distribution. Stokes' law is used to determine an unknown distribution of spherical particle sizes by measuring the time required for the particles to settle a known distance in a fluid of known viscosity and density. In this paper, we study the effects of gravity on sedimentation by examining the resulting particle concentration distributed in an equilibrium profile of concentration C m, n above the bottom of a container. This is for an experiment on the surface of the Earth and therefore the acceleration of gravity had been corrected for the oblateness of the Earth and its rotation. Next, at the orbital altitude of the spacecraft in orbit around Earth the acceleration due to the central field is corrected for the oblateness of the Earth. Our results show that for experiments taking place in circular or elliptical orbits of various inclinations around the Earth the concentration ratio C m, n / C m, ave , the inclination seems to be the most ineffective in affecting the concentration among all the orbital elements. For orbital experiment that use particles of diameter d p =0.001 μm the concentration ratios for circular and slightly elliptical orbits in the range e=0-0.1 exhibit a 0.009 % difference. The concentration ratio increases with the increase of eccentricity, which increases more for particles of larger diameters. Finally, for particles of the same diameter concentration ratios between Earth and Mars surface experiments are related in the following way C_{(m,n)_{mathit{Earth}}} = 0.99962 C_{(m,n)_{mathit{Mars}}}.

Laboratory investigation on effects of flood intermittency on river delta dynamics

NASA Astrophysics Data System (ADS)

Miller, K. L.; Kim, W.

2015-12-01

In order to simplify the complex hydrological variability of flow conditions, experiments modeling delta evolution are often conducted using a representative "channel-forming" flood flow and then relate results to field settings using an intermittency factor, defined as the fraction of total time at flood conditions. Although this intermittency factor makes it easier to investigate how variables, such as relative base level and/or sediment supply, affect delta dynamics, little is known about how this generalization to a single flow condition affects delta processes. We conducted a set of laboratory experiments with periodic flow conditions to determine the effects of intermittent discharges on delta evolution. During the experiment, flood with a set water discharge and sediment supply, cycles between periods of normal flow where the water flux is halved and the sediment discharge is turned off. For each run, the magnitude of the flood is held constant, but the duration is assigned differently, thus varying the intermittency between 1 and 0.2. We find that as the intermittency factor decreases (duration of each flood period decreases), the delta topset has a larger, more elongated area with a shallower slope as a result of reworking on the delta topset during normal flow conditions. During periods of normal flow, the system adjusts towards a new equilibrium state that then in turn acts as the initial condition for the subsequent flood period. Furthermore, the natural delta avulsion cycle becomes obscured by the flood cycles as the flood duration becomes shorter than the autogenic behavior. These results suggest that the adjustment timescale for differing flow conditions is a factor in determining the overall shape of the delta and behavior of the fluviodeltaic channels. We conclude, periods of normal flow when topset sediment is reworked, may be just as important to delta dynamics as periods of flood when sediment is supplied to the system.

Adsorption Processes of Lead Ions on the Mixture Surface of Bentonite and Bottom Sediments.

PubMed

Hegedűsová, Alžbeta; Hegedűs, Ondrej; Tóth, Tomáš; Vollmannová, Alena; Andrejiová, Alena; Šlosár, Miroslav; Mezeyová, Ivana; Pernyeszi, Tímea

2016-12-01

The adsorption of contaminants plays an important role in the process of their elimination from a polluted environment. This work describes the issue of loading environment with lead Pb(II) and the resulting negative impact it has on plants and living organisms. It also focuses on bentonite as a natural adsorbent and on the adsorption process of Pb(II) ions on the mixture of bentonite and bottom sediment from the water reservoir in Kolíňany (SR). The equilibrium and kinetic experimental data were evaluated using Langmuir isotherm kinetic pseudo-first and pseudo-second-order rate equations the intraparticle and surface diffusion models. Langmuir isotherm model was successfully used to characterize the lead ions adsorption equilibrium on the mixture of bentonite and bottom sediment. The pseudo second-order model, the intraparticle and surface (film) diffusion models could be simultaneously fitted the experimental kinetic data.

Bottom-sediment chemistry in Devil's Lake, northeast North Dakota

USGS Publications Warehouse

Komor, S.C.

1994-01-01

High magnesium calcite 8 mole percent MgCO3 is the most abundant carbonate at the sediment surface. With increasing depth abundances of high magnesium carbonate decrease and abundances of low magnesium calcite aragonite and dolomite increase. Carbon isotope compositions of bulk carbonates range from δ13C = -0.7 to +0.5%. These values are close to equilibrium with dissolved inorganic carbon in lake water (δ13C = -2%) but far from equilibrium with dissolved inorganic carbon in pore water (δ13C = -16.3- -10/0%). Disequilibrium between pore water and carbonates suggests that the carbonates did not recrystallize substantially in the presence of pore water. Therefore the change of carbonate mineral proportions with depth in the sediments is due mainly to temporal changes in the proportions of endogenic, detrital, and biologic carbonates that were deposited on the lake bottom rather than postdepositional carbonate diagenesis.

Benthic fluxes of cadmium, lead, copper and nitrogen species in the northern Adriatic Sea in front of the River Po outflow, Italy.

PubMed

Zago, C; Capodaglio, G; Ceradini, S; Ciceri, G; Abelmoschi, L; Soggia, F; Cescon, P; Scarponi, G

2000-02-10

Trace heavy metal (Cd, Pb and Cu) and nitrogen species (N-NO3, N-NO2 and N-NH4) fluxes between sediment and water were examined for approximately 4 days, in a coastal marine station located in the northern Adriatic Sea in front of the River Po outflow. An in situ benthic chamber, equipped with electronic devices for monitoring and adjustment of oxygen and pH and with a temperature detector, was used. The benthic chamber experiment enabled study of the temporal trend of metals and nutrients when oxygen concentration varied in a controlled environment. Although particular care was devoted to chamber deposition and parameter control, sediment resuspension occurred at the beginning of the experiment and O2 fluctuations were observed during the course of the experiment. Pb concentration was affected by both resuspension and oxic conditions in bottom water, which prevented determination of any reasonable Pb flux value. Cd and Cu, not influenced by oxygen fluctuations, reached an equilibrium phase in a short period with initial positive fluxes from sediment of 0.68 (S.D. = 0.07) and 6.9 (S.D. = 5.6) pmol cm(-2) h(-1), respectively. With regard to nitrogen species, the highest positive flux was that of N-NH4 (10.5, S.D. = 2.4, nmol cm(-2) h(-1)) whose concentration increased in the chamber, while nitrate concentration (initial flux of -5.7, S.D. = 1.5, nmol cm(-2) h(-1)) immediately decreased after the beginning of the experiment. Nitrite concentration was almost constant throughout the experiment and its flux was generally low (initial flux 0.1, S.D. = 0.9, nmol cm(-2) h(-1)).

Hydrogeochemical and mineralogical effects of sustained CO2 contamination in a shallow sandy aquifer: A field-scale controlled release experiment

NASA Astrophysics Data System (ADS)

Cahill, Aaron G.; Marker, Pernille; Jakobsen, Rasmus

2014-02-01

A shallow aquifer CO2 contamination experiment was performed to investigate evolution of water chemistry and sediment alteration following leakage from geological storage by physically simulating a leak from a hypothetical storage site. In a carbonate-free aquifer, in western Denmark, a total of 1600 kg of gas phase CO2 was injected at 5 and 10 m depth over 72 days through four inclined injection wells into aeolian and glacial sands. Water chemistry was monitored for pH, EC, and dissolved element evolution through an extensive network of multilevel sampling points over 305 days. Sediment cores were taken pre and postinjection and analyzed to search for effects on mineralogy and sediment properties. Results showed the simulated leak to evolve in two distinct phases; an advective elevated ion pulse followed by increasing persistent acidification. Spatial and temporal differences in evolution of phases suggest separate chemical mechanisms and geochemical signatures. Dissolved element concentrations developed exhibiting four behaviors: (1) advective pulse (Ca, Mg, Na, Si, Ba, and Sr), (2) pH sensitive abundance dependent (Al and Zn), (3) decreasing (Mn and Fe), and (4) unaffected (K). Concentration behaviors were characterized by: (1) a maximal front moving with advective flow, (2) continual increase in close proximity to the injection plane, (3) removal from solution, and (4) no significant change. Only Al was observed to exceed WHO guidelines, however significantly so (10-fold excess). The data indicate that pH is controlled by equilibrium with gibbsite which is again coupled to cation exchange processes. Pre and postinjection sediment analysis indicated alteration of sediment composition and properties including depletion of reactive mineral species.

Reversible and irreversible sorption of perfluorinated compounds (PFCs) by sediments of an urban reservoir.

PubMed

Chen, Huiting; Reinhard, Martin; Nguyen, Viet Tung; Gin, Karina Yew-Hoong

2016-02-01

Uncertainty about the extent to which contaminant sorption by suspended solids and bed sediments is irreversible is a major impediment for modeling and managing the water quality of surface water resources. This study examined reversible and irreversible sorption of several perfluorinated compounds (PFCs) to bed sediments from an urban reservoir. PFCs investigated include C4, C6, C8, C9 and C10 perfluoroalkanoate homologues (PFBA, PFHxA, PFOA, PFNA and PFDA, respectively) and perfluorooctane and hexane sulfonate (PFOS and PFHxS, respectively). Although sorption branches of the PFOS, PFNA and PFDA isotherms were nearly linear (implying a partitioning-like process), desorption experiments indicated that a fraction of the sorbed PFCs were entrapped and resistant to desorption. The hysteretic desorption branches were approximately linear. Irreversibility increased with chain length and was nearly complete for PFDA (thermodynamic irreversibility index (TII) 0.98). For the weakly sorbing PFOA and PFHxS, sorption was largely reversible. Data suggest that (1) for the strongly sorbing PFCs, e.g. PFNA, PFDA and PFOS, bed sediments acted predominantly as irreversible sinks, (2) aqueous concentrations of the moderately sorbing PFCs (PFOA and PFHxS) are buffered by reversibly sorbing suspended solids, and (3) the short-chain PFCs (PFBA and PFHxA) are not significantly sorbed and therefore not expected to be significantly influenced by sediment transport. Situations in which highly contaminated particles entering relatively clean water bodies, equilibrium is approached from the reverse (desorption) direction. For irreversibly sorbed contaminants field-based K(D) values will be higher than the K(D) values derived from laboratory sorption data obtained from forward sorption experiments. Copyright © 2015 Elsevier Ltd. All rights reserved.

Controls on sediment cover in bedrock-alluvial channels of the Henry Mountains, Utah

NASA Astrophysics Data System (ADS)

Hodge, R. A.; Yager, E.; Johnson, J. P.; Tranmer, A.

2017-12-01

The location and extent of sediment cover in bedrock-alluvial channels influences sediment transport rates, channel incision and instream ecology. However, factors affecting sediment cover and how it responds to changes in relative sediment supply have rarely been quantitatively evaluated in field settings. Using field surveys and SFM analysis of channel reach topography, we quantified sediment cover and channel properties including slope, width, grain size distributions, and bedrock and alluvial roughness in North Wash and Chelada Creek in the Henry Mountains, Utah. Along reaches where upstream sediment supply does not appear to be restricted, we find that the fraction of local bedrock exposure increases as a function of local relative transport capacity . In a downstream section of Chelada Creek, decadal-scale sediment supply has been restricted by an upstream culvert that has caused a backwater effect and corresponding upstream deposition. In this section, alluvial cover is uncorrelated with local stream power. To test the impact of relative sediment supply on sediment cover, a 1D sediment transport model was used to predict the equilibrium sediment cover in Chelada Creek under varying flow and sediment supply conditions. Sediment transport in each model section was predicted using the partial cover model of Johnson (2015), which accounts for differences in bedrock and alluvial roughness on critical shear stress and flow resistance. Model runs in which sediment supply was approximately equal to mean transport capacity produced a pattern of sediment cover which best matched the field observations upstream of the culvert. However, runs where sediment supply was under-capacity produced the pattern most similar to field observations downstream of the culvert, consistent with our field-based interpretations. Model results were insensitive to initial sediment cover, and equilibrium was relatively quickly reached, suggesting that the channel is responsive to changes in imposed conditions. Overall, our results suggest that alluvial cover fractions may be predictable at spatial scales relevant for landscape evolution modelling, but that local bed roughness and thresholds in relative sediment supply may need to be accounted for.

Reactive solute transport in streams: 2. Simulation of a pH modification experiment

USGS Publications Warehouse

Runkel, Robert L.; McKnight, Diane M.; Bencala, Kenneth E.; Chapra, Steven C.

1996-01-01

We present an application of an equilibrium-based solute transport model to a pH-modification experiment conducted on the Snake River, an acidic, metal-rich stream located in the Rocky Mountains of Colorado. During the experiment, instream pH decreased from 4.2 to 3.2, causing a marked increase in dissolved iron concentrations. Model application requires specification of several parameters that are estimated using tracer techniques, mass balance calculations, and geochemical data. Two basic questions are addressed through model application: (1) What are the processes responsible for the observed increase in dissolved iron concentrations? (2) Can the identified processes be represented within the equilibrium-based transport model? Simulation results indicate that the increase in iron was due to the dissolution of hydrous iron oxides and the photoreduction of ferric iron. Dissolution from the streambed is represented by considering a trace compartment consisting of freshly precipitated hydrous iron oxide and an abundant compartment consisting of aged precipitates that are less soluble. Spatial variability in the solubility of hydrous iron oxide is attributed to heterogeneity in the streambed sediments, temperature effects, and/or variability in the effects of photoreduction. Solubility products estimated via simulation fall within a narrow range (pKsp from 40.2 to 40.8) relative to the 6 order of magnitude variation reported for laboratory experiments (pKsp from 37.3 to 43.3). Results also support the use of an equilibrium-based transport model as the predominate features of the iron and pH profiles are reproduced. The model provides a valuable tool for quantifying the nature and extent of pH-dependent processes within the context of hydrologic transport.

Reactive Solute Transport in Streams: 2. Simulation of a pH Modification Experiment

NASA Astrophysics Data System (ADS)

Runkel, Robert L.; McKnight, Diane M.; Bencala, Kenneth E.; Chapra, Steven C.

1996-02-01

We present an application of an equilibrium-based solute transport model to a pH-modification experiment conducted on the Snake River, an acidic, metal-rich stream located in the Rocky Mountains of Colorado. During the experiment, instream pH decreased from 4.2 to 3.2, causing a marked increase in dissolved iron concentrations. Model application requires specification of several parameters that are estimated using tracer techniques, mass balance calculations, and geochemical data. Two basic questions are addressed through model application: (1) What are the processes responsible for the observed increase in dissolved iron concentrations? (2) Can the identified processes be represented within the equilibrium-based transport model? Simulation results indicate that the increase in iron was due to the dissolution of hydrous iron oxides and the photoreduction of ferric iron. Dissolution from the streambed is represented by considering a trace compartment consisting of freshly precipitated hydrous iron oxide and an abundant compartment consisting of aged precipitates that are less soluble. Spatial variability in the solubility of hydrous iron oxide is attributed to heterogeneity in the streambed sediments, temperature effects, and/or variability in the effects of photoreduction. Solubility products estimated via simulation fall within a narrow range (pKsp from 40.2 to 40.8) relative to the 6 order of magnitude variation reported for laboratory experiments (pKsp from 37.3 to 43.3). Results also support the use of an equilibrium-based transport model as the predominate features of the iron and pH profiles are reproduced. The model provides a valuable tool for quantifying the nature and extent of pH-dependent processes within the context of hydrologic transport.

Influence of competing inorganic cations on the ion exchange equilibrium of the monovalent organic cation metoprolol on natural sediment.

PubMed

Niedbala, Anne; Schaffer, Mario; Licha, Tobias; Nödler, Karsten; Börnick, Hilmar; Ruppert, Hans; Worch, Eckhard

2013-02-01

The aim of this study was to systematically investigate the influence of the mono- and divalent inorganic ions Na(+) and Ca(2+) on the sorption behavior of the monovalent organic cation metoprolol on a natural sandy sediment at pH=7. Isotherms for the beta-blocker metoprolol were obtained by sediment-water batch tests over a wide concentration range (1-100000 μg L(-1)). Concentrations of the competing inorganic ions were varied within freshwater relevant ranges. Data fitted well with the Freundlich sorption model and resulted in very similar Freundlich exponents (n=0.9), indicating slightly non-linear behavior. Results show that the influence of Ca(2+) compared to Na(+) is more pronounced. A logarithmic correlation between the Freundlich coefficient K(Fr) and the concentration or activity of the competing inorganic ions was found allowing the prediction of metoprolol sorption on the investigated sediment at different electrolyte concentrations. Additionally, the organic carbon of the sediment was completely removed for investigating the influence of organic matter on the sorption of metoprolol. The comparison between the experiments with and without organic carbon removal revealed no significant contribution of the organic carbon fraction (0.1%) to the sorption of metoprolol on the in this study investigated sediment. Results of this study will contribute to the development of predictive models for the transport of organic cations in the subsurface. Copyright © 2012 Elsevier Ltd. All rights reserved.

PREFERENTIAL PARTITIONING OF A PAH AND PCB TO A MARINE SEDIMENT AMENDED WITH SEVERAL SOURCES OF SOOT CARBON

EPA Science Inventory

Over the last decade, several studies reported that the partitioning of PAHs to sediments, in some cases, did not follow predictions based on equilibrium partitioning theory. One explanation for these differences is the presence of a second sedimentary phase with partitioning cha...

Biodynamic modeling of PCB uptake by Macoma balthica and Corbicula fluminea from sediment amended with activated carbon

USGS Publications Warehouse

McLeod, Pamela B.; Luoma, S.N.; Luthy, R.G.

2008-01-01

Activated carbon amendment was assessed in the laboratory as a remediation strategy for freshwater sediment contaminated with polychlorinated biphenyls (PCBs) from the Grasse River (near Massena, NY). Three end points were evaluated: aqueous equilibrium PCB concentration, uptake into semipermeable membrane devices (SPMDs), and 28-day bioaccumulation in the clam Corbicula fluminea. PCB uptake by water, SPMDs, and clams followed similar trends, with reductions increasing as a function of carbon dose. Average percent reductions in clam tissue PCBs were 67, 86, and 95% for activated carbon doses of 0.7, 1.3, and 2.5% dry wt, respectively. A biodynamic model that incorporates sediment geochemistry and dietary and aqueous uptake routes was found to agree well with observed uptake by C. fluminea in our laboratory test systems. Results from this study were compared to 28-day bioaccumulation experiments involving PCB-contaminated sediment from Hunters Point Naval Shipyard (San Francisco Bay, CA) and the clam Macoma balthica. Due to differences in feeding strategy, M. balthica deposit-feeds whereas C. fluminea filter-feeds, the relative importance of the aqueous uptake route is predicted to be much higher for C. fluminea than for M. balthica. Whereas M. balthica takes up approximately 90% of its body burden through sediment ingestion, C. fluminea only accumulates approximately 45% via this route. In both cases, results strongly suggest that it is the mass transfer of PCBs from native sediment to added carbon particles, not merely reductions in aqueous PCB concentrations, that effectively reduces PCB bioavailability and uptake by sediment-dwelling organisms. ?? 2008 American Chemical Society.

Flow characteristics and longitudinal sorting patterns associated with stable alluvial-bedrock and bedrock-alluvial transitions

NASA Astrophysics Data System (ADS)

Jafarinik, S.; Viparelli, E.

2017-12-01

Recent research recognized the existence of bedrock channels in low-slope rivers, but little is known about the morphodynamics of bedrock-alluvial and alluvial-bedrock transitions in these systems. Bedrock-alluvial and alluvial-bedrock transitions are fluvial features separating bedrock and alluvial reaches. In the bedrock reach the river bed is partially covered with alluvium. An increase in sediment supply to an alluvial reach results in channel bed aggradation. An increase in sediment supply to a bedrock reach, on the other hand, results in a reduction of the exposed bedrock. Mathematical modeling of the alluvial morphodynamics of bedrock reaches reveals that these transitions can characterize transient or equilibrium conditions. Model results show that the magnitude of the alluvial equilibrium slope and the depth of the bedrock surface relative to the downstream water surface base level have a primary control on the equilibrium conditions. Further, numerical results show that when a stable bedrock-alluvial transition forms, the bed material transport capacity in bedrock reach decreases in the flow direction. On the contrary, when a stable alluvial-bedrock transition forms the bed material transport capacity in the bedrock reach increases in the flow direction. These spatial changes in bed material transport capacity are associated with spatial changes in alluvial cover and flow hydrodynamics. Here we present a one-dimensional formulation of alluvial morphodynamics that accounts for the non-uniformity of the bed material and for the spatial change in flow resistances associated with the spatial and temporal changes in flow hydrodynamics of the bedrock reaches. This change in flow resistances can be associated with 1) changes in skin friction due to longitudinal changes in the grain size distribution of the bed surface, and/or 2) changes in bedform geometry associated with the interaction between the alluvial cover and the underlying bedrock. The model has been validated against laboratory experiments with stable alluvial-bedrock transitions and is applied to describe the spatial changes in flow characteristics and sediment sorting patterns upstream of a stable bedrock-alluvial transition.

Equilibrium and kinetic modeling of contaminant immobilization by activated carbon amended to sediments in the field.

PubMed

Rakowska, Magdalena I; Kupryianchyk, Darya; Koelmans, Albert A; Grotenhuis, Tim; Rijnaarts, Huub H M

2014-12-15

Addition of activated carbons (AC) to polluted sediments and soils is an attractive remediation technique aiming at reducing pore water concentrations of hydrophobic organic contaminants (HOCs). In this study, we present (pseudo-)equilibrium as well as kinetic parameters for sorption of a series of PAHs and PCBs to powdered and granular activated carbons (AC) after three different sediment treatments: sediment mixed with powdered AC (PAC), sediment mixed with granular AC (GAC), and addition of GAC followed by 2 d mixing and subsequent removal ('sediment stripping'). Remediation efficiency was assessed by quantifying fluxes of PAHs towards SPME passive samplers inserted in the sediment top layer, which showed that the efficiency decreased in the order of PAC > GAC stripping > GAC addition. Sorption was very strong to PAC, with Log KAC (L/kg) values up to 10.5. Log KAC values for GAC ranged from 6.3-7.1 and 4.8-6.2 for PAHs and PCBs, respectively. Log KAC values for GAC in the stripped sediment were 7.4-8.6 and 5.8-7.7 for PAH and PCB. Apparent first order adsorption rate constants for GAC (kGAC) in the stripping scenario were calculated with a first-order kinetic model and ranged from 1.6 × 10(-2) (PHE) to 1.7 × 10(-5) d(-1) (InP). Sorption affinity parameters did not change within 9 months post treatment, confirming the longer term effectiveness of AC in field applications for PAC and GAC. Copyright © 2014. Published by Elsevier Ltd.

Rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium distribution coefficients of a surficial sediment at the Idaho National Engineering Laboratory, Idaho

USGS Publications Warehouse

Bunde, R.L.; Rosentreter, J.J.; Liszewski, M.J.

1998-01-01

The rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium sorption were measured as part of an investigation to determine strontium chemical transport properties of a surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. Batch experimental techniques were used to determine the rate of strontium sorption and strontium distribution coefficients (K(d)s) between aqueous and solid phases. Rate experiments indicate that strontium in solution reached an apparent equilibrium with the sediment in 26 h. K(d)s were derived using the linear isotherm model at initial sodium concentrations from 100 to 5,000 mg/l and initial potassium concentrations from 2 to 150 mg/l. K(d)s ranged from 56 ?? 2 to 62 ?? 3 ml/g at initial aqueous concentrations of sodium and potassium equal to or less than 300 and 150 mg/l, respectively. K(d)s hinged from 4.7 ?? 0.2 to 19 ?? 1 ml/g with initial aqueous concentrations of sodium between 1,000 and 5,000 mg/l. These data indicate that sodium concentrations greater than 300 mg/l in wastewater increase the availability of strontium for transport beneath waste disposal ponds at the INEL by decreasing strontium sorption on the surficial sediment. Wastewater concentrations of sodium and potassium less than 300 and 150 mg/l, respectively, have little effect on the availability of strontium for transport.The rate of strontium sorption and the effects of variable aqueous concentrations of sodium and potassium on strontium sorption were measured as part of an investigation to determine strontium chemical transport properties of a surficial sediment at the Idaho National Engineering Laboratory (INEL), Idaho. Batch experimental techniques were used to determine the rate of strontium sorption and strontium distribution coefficients (Kds) between aqueous and solid phases. Rate experiments indicate that strontium in solution reached an apparent equilibrium with the sediment in 26 h. Kds were derived using the linear isotherm model at initial sodium concentrations from 100 to 5,000 mg/l and initial potassium concentrations from 2 to 150 mg/l. Kds ranged from 56??2 to 62??3 ml/g at initial aqueous concentrations of sodium and potassium equal to or less than 300 and 150 mg/l, respectively. Kds ranged from 4.7??0.2 to 19??1 ml/g with initial aqueous concentrations of sodium between 1,000 and 5,000 mg/l. These data indicate that sodium concentrations greater than 300 mg/l in wastewater increase the availability of strontium for transport beneath waste disposal ponds at the INEL by decreasing strontium sorption on the surficial sediment. Wastewater concentrations of sodium and potassium less than 300 and 150 mg/l, respectively, have little effect on the availability of strontium for transport.

A simple shear limited, single size, time dependent flocculation model

NASA Astrophysics Data System (ADS)

Kuprenas, R.; Tran, D. A.; Strom, K.

2017-12-01

This research focuses on the modeling of flocculation of cohesive sediment due to turbulent shear, specifically, investigating the dependency of flocculation on the concentration of cohesive sediment. Flocculation is important in larger sediment transport models as cohesive particles can create aggregates which are orders of magnitude larger than their unflocculated state. As the settling velocity of each particle is determined by the sediment size, density, and shape, accounting for this aggregation is important in determining where the sediment is deposited. This study provides a new formulation for flocculation of cohesive sediment by modifying the Winterwerp (1998) flocculation model (W98) so that it limits floc size to that of the Kolmogorov micro length scale. The W98 model is a simple approach that calculates the average floc size as a function of time. Because of its simplicity, the W98 model is ideal for implementing into larger sediment transport models; however, the model tends to over predict the dependency of the floc size on concentration. It was found that the modification of the coefficients within the original model did not allow for the model to capture the dependency on concentration. Therefore, a new term within the breakup kernel of the W98 formulation was added. The new formulation results is a single size, shear limited, and time dependent flocculation model that is able to effectively capture the dependency of the equilibrium size of flocs on both suspended sediment concentration and the time to equilibrium. The overall behavior of the new model is explored and showed align well with other studies on flocculation. Winterwerp, J. C. (1998). A simple model for turbulence induced flocculation of cohesive sediment. .Journal of Hydraulic Research, 36(3):309-326.

Morphodynamics of semi-alluvial streams in northern Fennoscandia: a flume experiment to determine bedform self-organization

NASA Astrophysics Data System (ADS)

Polvi, Lina

2017-04-01

Streams in northern Fennoscandia have two characteristics that complicate a process-based understanding of sediment transport affecting channel form: (1) they are typically semi-alluvial, in that they contain coarse glacial legacy sediment, and (2) numerous mainstem lakes buffer sediment and water fluxes. Systematic studies of these streams are complicated because natural reference sites are lacking due to over a century of widespread channel simplification to aid timber-floating. This research is part of a larger project to determine controls on channel geometry and sediment transport at: (1) the catchment scale, examining downstream hydraulic geometry, (2) the reach scale, examining sediment transport, and (3) the bedform scale, examining the potential for predictable bedform formation. The objective of the current study, targeting the bedform scale, was to use a flume experiment to determine whether sediment self-organizes and creates bedforms in semi-alluvial channels. The prototype channels, tributaries to the unregulated Vindel River in northern Sweden that are being restored after timber-floating, contain coarse sediment (D16: 55 mm, D50:250 mm, D84:620 mm) with moderately steep slopes (2-5%) and typically experience snowmelt-flooding and flooding due to ice jams. Using a scaling factor of 8 for Froude number similitude, an 8-m long, 1.1 m wide fixed-bed flume was set up at the Colorado State University Engineering Research Center with a scaled-down sediment distribution analogous to the prototype channels. For two flume setups, with bed slopes of 2% and 5%, four runs were conducted with flows analogous to QBF, Q2, Q10 and Q50 flows in the prototype channels until equilibrium conditions were reached. Digital elevation models (DEMs) of bed topography were constructed before and after each run using structure-from-motion photogrammetry. To examine self-organization of sediment, DEMs of difference between pre-flow conditions and after each flow were created; scour and deposition in relation to large immobile clasts were examined. Preliminary results show that at high flows at the lower slope (2%), fine sediment was deposited above immobile clasts and scour was common below. High flows at the higher slope (5%) caused scour above and occasionally directly below immobile clasts, with fine sediment deposited nearby scour zones above immobile clasts. These results indicate that these channels experience a shielding effect by large immobile clasts, inhibiting bedload transport and creating pockets of fine sediment upstream of large boulders. Additionally, pools downstream of immobile boulders may experience velocity reversals, causing scour instead of deposition in low-velocity zones. In addition, the combined aggradation and degradation between the Q50 and Q10 flows was less than between the Q10 and Q2 flows. This is most likely because the snowmelt-dominated flow regime of northern Sweden with buffering capacity of lakes precludes extremely high flows, causing a small difference in intermediate- and high-recurrence interval flow magnitudes. Therefore, flows with an intermediate recurrence interval likely do the most geomorphic work, but major sediment self-organization as seen in alluvial mountain streams is unlikely barring an extreme event. In conclusion, classical slope-dependent bedform relationships found in alluvial gravel-bed streams may not be applicable in semi-alluvial channels in northern Fennoscandia.

Sediment depositions upstream of open check dams: new elements from small scale models

NASA Astrophysics Data System (ADS)

Piton, Guillaume; Le Guern, Jules; Carbonari, Costanza; Recking, Alain

2015-04-01

Torrent hazard mitigation remains a big issue in mountainous regions. In steep slope streams and especially in their fan part, torrential floods mainly result from abrupt and massive sediment deposits. To curtail such phenomenon, soil conservation measures as well as torrent control works have been undertaken for decades. Since the 1950s, open check dams complete other structural and non-structural measures in watershed scale mitigation plans1. They are often built to trap sediments near the fan apexes. The development of earthmoving machinery after the WWII facilitated the dredging operations of open check dams. Hundreds of these structures have thus been built for 60 years. Their design evolved with the improving comprehension of torrential hydraulics and sediment transport; however this kind of structure has a general tendency to trap most of the sediments supplied by the headwaters. Secondary effects as channel incision downstream of the traps often followed an open check dam creation. This sediment starvation trend tends to propagate to the main valley rivers and to disrupt past geomorphic equilibriums. Taking it into account and to diminish useless dredging operation, a better selectivity of sediment trapping must be sought in open check dams, i.e. optimal open check dams would trap sediments during dangerous floods and flush them during normal small floods. An accurate description of the hydraulic and deposition processes that occur in sediment traps is needed to optimize existing structures and to design best-adjusted new structures. A literature review2 showed that if design criteria exist for the structure itself, little information is available on the dynamic of the sediment depositions upstream of open check dams, i.e. what are the geomorphic patterns that occur during the deposition?, what are the relevant friction laws and sediment transport formula that better describe massive depositions in sediment traps?, what are the range of Froude and Shields numbers that the flows tend to adopt? New small scale model experiments have been undertaken focusing on depositions processes and their related hydraulics. Accurate photogrammetric measurements allowed us to better describe the deposition processes3. Large Scale Particle Image Velocimetry (LS-PIV) was performed to determine surface velocity fields in highly active channels with low grain submersion4. We will present preliminary results of our experiments showing the new elements we observed in massive deposit dynamics. REFERENCES 1.Armanini, A., Dellagiacoma, F. & Ferrari, L. From the check dam to the development of functional check dams. Fluvial Hydraulics of Mountain Regions 37, 331-344 (1991). 2.Piton, G. & Recking, A. Design of sediment traps with open check dams: a review, part I: hydraulic and deposition processes. (Accepted by the) Journal of Hydraulic Engineering 1-23 (2015). 3.Le Guern, J. Ms Thesis: Modélisation physique des plages de depot : analyse de la dynamique de remplissage.(2014) . 4.Carbonari, C. Ms Thesis: Small scale experiments of deposition processes occuring in sediment traps, LS-PIV measurments and geomorphological descriptions. (in preparation).

Isotherm, kinetic, and thermodynamic study of ciprofloxacin sorption on sediments.

PubMed

Mutavdžić Pavlović, Dragana; Ćurković, Lidija; Grčić, Ivana; Šimić, Iva; Župan, Josip

2017-04-01

In this study, equilibrium isotherms, kinetics and thermodynamics of ciprofloxacin on seven sediments in a batch sorption process were examined. The effects of contact time, initial ciprofloxacin concentration, temperature and ionic strength on the sorption process were studied. The K d parameter from linear sorption model was determined by linear regression analysis, while the Freundlich and Dubinin-Radushkevich (D-R) sorption models were applied to describe the equilibrium isotherms by linear and nonlinear methods. The estimated K d values varied from 171 to 37,347 mL/g. The obtained values of E (free energy estimated from D-R isotherm model) were between 3.51 and 8.64 kJ/mol, which indicated a physical nature of ciprofloxacin sorption on studied sediments. According to obtained n values as measure of intensity of sorption estimate from Freundlich isotherm model (from 0.69 to 1.442), ciprofloxacin sorption on sediments can be categorized from poor to moderately difficult sorption characteristics. Kinetics data were best fitted by the pseudo-second-order model (R 2  > 0.999). Thermodynamic parameters including the Gibbs free energy (ΔG°), enthalpy (ΔH°) and entropy (ΔS°) were calculated to estimate the nature of ciprofloxacin sorption. Results suggested that sorption on sediments was a spontaneous exothermic process.

Transport of bisphenol-A in sandy aquifer sediment: Column experiment.

PubMed

Zakari, Sissou; Liu, Hui; Tong, Lei; Wang, Yan; Liu, Jianfeng

2016-02-01

The present paper aims to study the transport behavior of bisphenol-A (BPA) in sandy aquifer so as to provide important parameters for the prediction and control of contaminant plume in aquifer. Miscible displacement experiments were conducted and the breakthrough curves (BTCs) were simulated using HYDRUS-1D software. The effects of pore-water velocity (10-52 cm h(-1)) and initial concentration (2.5-40 mg L(-1)) on the sorption were also investigated. The BTCs of BPA fit the linear first-order non-equilibrium two-site model. The parameters such as partition coefficient (K(d)), the fraction of instantaneous adsorption on "Type-1" sites (F), the first order sorption rate coefficient for the kinetic non-equilibrium (type-2) sites (α), the retardation coefficient (R), and sorption capacity (q(column)) were computed. Results showed that BPA transported 0.11-0.83 m with various pore water velocity in sandy sediment column when water flowed 1 m. The sorption of BPA was mainly caused by the instantaneous surface adsorption as F varied from 0.596 to 0.908. The transport velocity of BPA was affected by pore water velocity (v) and followed the linear equation 1/R = 0.0600 + 0.0110v (r(2) = 0.9724). The parameter K(d) were also closely related to v and followed the equation LnK(d) = 1.0023-0.0482v (r(2) = 0.9690). The sorption capacity was more related to the initial BPA concentration (C0) and followed the linear equation q(column) = 0.265 + 0.253C0 (r(2) = 0.9727). The parameter α was affected by both v and C0 whereas F was not dramatically affected by both. Copyright © 2015 Elsevier Ltd. All rights reserved.

Can coarse surface layers in gravel-bedded rivers be mobilized by finer gravel bedload?

NASA Astrophysics Data System (ADS)

Venditti, J. G.; Dietrich, W. E.; Nelson, P. A.; Wydzga, M. A.; Fadde, J.; Sklar, L.

2005-12-01

In response to reductions in sediment supply, gravel-bed rivers undergo a coarsening of the sediments that comprise the river's bed and, over some longer time scale, a river's grade may also be reduced as sediments are depleted from upstream reaches. Coarse, degraded river reaches are commonly observed downstream of dams across the Western United States. Following dam closure, these riverbeds become immobile under the altered flow and sediment supply regimes, leading to a reduction in the available salmon spawning and rearing habitat. Gravel augmentation to these streams is now common practice. This augmentation is typically seen as resurfacing the static coarse bed. As an alternative, we propose that the addition of appropriately finer gravels to these channels may be capable of mobilizing an otherwise immobile coarse surface layer, creating the potential to release fine material trapped beneath the surface. A series of laboratory experiments are being undertaken to test this hypothesis in a 30 m long and 0.86 m wide gravel-bedded flume channel using a constant discharge and a unimodal bed sediment with a median grain size of 8 mm and no sand present. The channel width-to-depth ratio of ~4 suppresses the development of lateral topography and allows us to focus on grain-to-grain interactions. Experiments proceed by maintaining a constant sediment feed until an equilibrium grade and transport rate are established, starving the flume of sediment for at least 24 hours, and then adding narrowly graded gravel over a period of one to two hours at a rate that is ~4x the bedload rate observed prior to terminating the sediment supply. The bed prior to sediment addition has an armor median grain size that is typically twice that of the subsurface and feed size distribution. The volume and median grain size of the resulting pulses are varied. Pulses move downstream rapidly with well-defined fronts in the form of bedload sheets and cause peaks in the sediment flux approximately equal to the supply rate. Once the pulse has passed through the flume, bedload flux rapidly drops to background values, leaving few introduced grains on the bed. When the sediment feed is the median grain size of the subsurface bed material mixture, few armor grains are mobilized, although there is some exchange between the surface and bedload. Pulses composed of the fine tail of the surface grain size distribution are capable of mobilizing all grain sizes in the armor (including the largest grains) as finer bedload fills the interstices of the coarse surface layer. This suggests that gravel augmentation using fine gravel may provide an effective means of improving bed mobility conditions. Further experiments are underway to explore the effects of repeated fine gravel addition on bed state.

Sedimentation of a two-dimensional colloidal mixture exhibiting liquid-liquid and gas-liquid phase separation: a dynamical density functional theory study.

PubMed

Malijevský, Alexandr; Archer, Andrew J

2013-10-14

We present dynamical density functional theory results for the time evolution of the density distribution of a sedimenting model two-dimensional binary mixture of colloids. The interplay between the bulk phase behaviour of the mixture, its interfacial properties at the confining walls, and the gravitational field gives rise to a rich variety of equilibrium and non-equilibrium morphologies. In the fluid state, the system exhibits both liquid-liquid and gas-liquid phase separation. As the system sediments, the phase separation significantly affects the dynamics and we explore situations where the final state is a coexistence of up to three different phases. Solving the dynamical equations in two-dimensions, we find that in certain situations the final density profiles of the two species have a symmetry that is different from that of the external potentials, which is perhaps surprising, given the statistical mechanics origin of the theory. The paper concludes with a discussion on this.

Modelling the fate of micropollutants in the marine environment using passive sampling.

PubMed

Claessens, Michiel; De Laender, Frederik; Monteyne, Els; Roose, Patrick; Janssen, Colin R

2015-07-15

Polydimethylsiloxane sheets were used to determine freely dissolved concentrations (C(diss)) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in the Belgian coastal zone. Equilibrium models were used to predict the whole water concentrations (C(ww)) of these compounds as well as their concentrations in sediment, suspended particulate matter (SPM) and biota. In general, contaminant concentrations were predicted well for whole water and biota. C(ww) was increasingly underpredicted as K(oc) increased, possibly because of the presence of black carbon. Concentrations in biota were overestimated by the equilibrium approach when logK(ow) exceeded 6.5, suggesting an increasing role of transformation processes. Concentrations of PAHs and PCBs in sediment and SPM were consistently underpredicted although a good correlation between measured and predicted values was observed. This was potentially due to the use of experimental K(oc) values which have been found to underestimate partitioning of hydrophobic substances to sediment in field studies. Copyright © 2015 Elsevier Ltd. All rights reserved.

Processes of nickel and cobalt uptake by a manganese oxide forming sediment in Pinal Creek, Globe mining district, Arizona

USGS Publications Warehouse

Kay, J.T.; Conklin, M.H.; Fuller, C.C.; O'Day, P. A.

2001-01-01

A series of column experiments was conducted using manganese oxide coated sediments collected from the hyporheic zone in Pinal Creek (AZ), a metal-contaminated stream, to study the uptake and retention of Mn, Ni, and Co. Experimental variables included the absence (abiotic) and presence (biotic) of active Mn-oxidizing bacteria, the absence and presence of dissolved Mn, and sediment manganese oxide content. Uptake of Mn under biotic conditions was between 8 and 39% higher than under abiotic conditions. Continuous uptake of Mn due to biotic oxidation was evident from extraction of column sediments. Manganese uptake is hypothesized to initially occur as adsorption, which led to subsequent surface and/or microbial oxidation. Complete breakthrough of Ni within 100 pore volumes indicated no process of continuous uptake and was modeled as an equilibrium adsorption process. Nickel uptake in the presence of dissolved Mn was 67-100% reversible. Sediment extractions suggest that Ni uptake occurred through weak and strong adsorption. Continuous uptake of cobalt increased with sediment manganese oxide content, and Co uptake was up to 75% greater under biotic than abiotic conditions. Cobalt uptake was controlled by both existing and newly formed manganese oxides. Only a small amount of Co uptake was reversible (10-25%). XANES spectral analysis indicated that most Co(II) was oxidized to Co(III) and probably incorporated structurally into manganese oxides. Although manganese oxides were the primary phase controlling uptake and retention of Mn, Ni, and Co, the mechanisms varied among the metals.

Methods for Estimating Adsorbed Uranium(VI) and Distribution Coefficients of Contaminated Sediments

USGS Publications Warehouse

Kohler, M.; Curtis, G.P.; Meece, D.E.; Davis, J.A.

2004-01-01

Assessing the quantity of U(VI) that participates in sorption/desorption processes in a contaminated aquifer is an important task when investigating U migration behavior. U-contaminated aquifer sediments were obtained from 16 different locations at a former U mill tailings site at Naturita, CO (U.S.A.) and were extracted with an artificial groundwater, a high pH sodium bicarbonate solution, hydroxylamine hydrochloride solution, and concentrated nitric acid. With an isotopic exchange method, both a KD value for the specific experimental conditions as well as the total exchangeable mass of U(VI) was determined. Except for one sample, KD values determined by isotopic exchange with U-contaminated sediments that were in equilibrium with atmospheric CO2 agreed within a factor of 2 with KD values predicted from a nonelectrostatic surface complexation model (NEM) developed from U(VI) adsorption experiments with uncontaminated sediments. The labile fraction of U(VI) and U extracted by the bicarbonate solution were highly correlated (r2 = 0.997), with a slope of 0.96 ?? 0.01. The proximity of the slope to one suggests that both methods likely access the same reservoir of U(VI) associated with the sediments. The results indicate that the bicarbonate extraction method is useful for estimating the mass of labile U(VI) in sediments that do not contain U(IV). In-situ KD values calculated from the measured labile U(VI) and the dissolved U(VI) in the Naturita alluvial aquifer agreed within a factor of 3 with in-situ K D values predicted with the NEM and groundwater chemistry at each well.

Remediation of organochlorine pesticides contaminated lake sediment using activated carbon and carbon nanotubes.

PubMed

Hua, Shan; Gong, Ji-Lai; Zeng, Guang-Ming; Yao, Fu-Bing; Guo, Min; Ou, Xiao-Ming

2017-06-01

Organochlorine pesticides (OCPs) in sediment were a potential damage for humans and ecosystems. The aim of this work was to determine the effectiveness of carbon materials remedy hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethanes (DDTs) in sediment. Two different carbon materials including activated carbon (AC) and multi-walled carbon nanotubes (MWCNTs) were used in the present research. Sediment treated with 2 wt% AC and MWCNTs after 150 d contact showed 97%, and 75% reduction for HCH, and 93% and 59% decrease for DDTs in aqueous equilibrium concentration, respectively. Similarly, the reduction efficiencies of DDT and HCH uptake by semipermeable membrane devices (SPMDs) treated with AC (MWCNTs) were 97% (75%) and 92% (63%), respectively under the identical conditions. Furthermore, for 2 wt% AC (MWCNTs) system, a reduction of XAD beads uptake up to 87% (52%) and 73% (67%) was obtained in HCH and DDT flux to overlying water in quiescent system. Adding MWCNTs to contaminated sediment did not significantly decrease aqueous equilibrium concentration and DDTs and HCH availability in SPMDs compared to AC treatment. A series of results indicated that AC had significantly higher remediation efficiency towards HCH and DDTs in sediment than MWCNTs. Additionally, the removal efficiencies of two organic pollutants improved with increasing material doses and contact times. The greater effectiveness of AC was attributed to its greater specific surface area, which was favorable for binding contaminants. These results highlighted the potential for using AC as in-situ sorbent amendments for sediment remediation. Copyright © 2017 Elsevier Ltd. All rights reserved.

A gel probe equilibrium sampler for measuring arsenic porewater profiles and sorption gradients in sediments: II. Field application to Haiwee reservoir sediment

USGS Publications Warehouse

Campbell, K.M.; Root, R.; O'Day, P. A.; Hering, J.G.

2008-01-01

Arsenic (As) geochemistry and sorption behavior were measured in As- and iron (Fe)-rich sediments of Haiwee Reservoir by deploying undoped (clear) polyacrylamide gels and hydrous ferric oxide (HFO)-doped gels in a gel probe equilibrium sampler, which is a novel technique for directly measuring the effects of porewater composition on As adsorption to Fe oxides phases in situ. Arsenic is deposited at the sediment surface as As(V) and is reduced to As(III) in the upper layers of the sediment (0-8 cm), but the reduction of As(V) does not cause mobilization into the porewater. Dissolved As and Fe concentrations increased at depth in the sediment column driven by the reductive dissolution of amorphous Fe(III) oxyhydroxides and conversion to a mixed Fe(II, III) green rust-type phase. Adsorption of As and phosphorous (P) onto HFO-doped gels was inhibited at intermediate depths (10-20 cm), possibly due to dissolved organic or inorganic carbon, indicating that dissolved As concentrations were at least partially controlled by porewater composition rather than surface site availability. In sediments that had been recently exposed to air, the region of sorption inhibition was not observed, suggesting that prior exposure to air affected the extent of reductive dissolution, porewater chemistry, and As adsorption behavior. Arsenic adsorption onto the HFO-doped gels increased at depths >20 cm, and the extent of adsorption was most likely controlled by the competitive effects of dissolved phosphate. Sediment As adsorption capacity appeared to be controlled by changes in porewater composition and competitive effects at shallower depths, and by reductive dissolution and availability of sorption sites at greater burial depths. ?? 2008 American Chemical Society.

Observations of Near-Bed Deposition and Resuspension Processes at the Fluvial-Tidal Transition Using High Resolution Adcp, Adv, and Lisst

NASA Astrophysics Data System (ADS)

Haught, D. R.; Stumpner, P.

2012-12-01

Processes that determine deposition and resuspension of sediment in fluvial and tidal systems are complicated and difficult to predict because of turbulence-sediment interaction. In fluvial systems net sediment deposition rates near the bed are determined by shear stresses that occur when turbulence interacts with the bed and the entrained sediment above. In tidal systems, processes are driven primarily by the confounding factors of slack water and reversing flow. In this study we investigate near-bed sediment fluxes, settling velocities and sediment size distributions during a change from a fluvial signal to a tidal signal. In order to examine these processes a high resolution, high frequency ADCP, ADV, water quality sonde and LISST data were collocated at the fluvial-tidal transition in the Sacramento River at Freeport, CA. Data were collected at 15-30 minute increments for a month`. Data were dissevered into fluvial and tidal components. Acoustic backscatterence was used as a surrogate to sediment concentration and sediment flux () was calculated from the turbulence properties. Settling velocities were computed from the diffusion-advection equation assuming equilibrium of settling and re-suspension fluxes. Particle density was back-calculated from median particle diameter and calculated settling velocities (Reynolds number<0.5) using Stokes' law. Preliminary results suggest that during peak fluvial discharge that the diffusion-advection gives poor estimates of settling velocities as inferred from particle densities above 3500 kg/m3. During the transition from fluvial to tidal signal and throughout the tidal signal particle densities range from 2650 kg/m3 to 1000 kg/m3, suggesting that settling velocities were accurately estimated. Thus the equilibrium assumption appears poor during high fluvial discharge and reasonable during low fluvial discharge when tidal signal is dominant.

Vertical suspsended sediment fluxes observed from ocean gliders

NASA Astrophysics Data System (ADS)

Merckelbach, Lucas; Carpenter, Jeffrey

2016-04-01

Many studies trying to understand a coastal system in terms of sediment transport paths resort to numerical modelling - combining circulation models with sediment transport models. Two aspects herein are crucial: sediment fluxes across the sea bed-water column interface, and the subsequent vertical mixing by turbulence. Both aspects are highly complex and have relatively short time scales, so that the processes involved are implemented in numerical models as parameterisations. Due to the effort required to obtain field observations of suspended sediment concentrations (and other parameters), measurements are scarce, which makes the development and tuning of parameterisations a difficult task. Ocean gliders (autonomous underwater vehicles propelled by a buoyancy engine) provide a platform complementing more traditional methods of sampling. In this work we present observations of suspended sediment concentration (SSC) and dissipation rate taken by two gliders, each equipped with optical sensors and a microstructure sensor, along with current observations from a bottom mounted ADCP, all operated in the German Bight sector of the North Sea in Summer 2014. For about two weeks of a four-week experiment, the gliders were programmed to fly in a novel way as Lagrangian profilers to water depths of about 40 m. The benefit of this approach is that the rate of change of SSC - and other parameters - is local to the water column, as opposed to an unknown composition of temporal and spatial variability when gliders are operated in the usual way. Therefore, vertical sediment fluxes can be calculated without the need of the - often dubious - assumption that spatial variability can be neglected. During the experiment the water column was initially thermally stratified, with a cross-pycnocline diffusion coefficient estimated at 7\\cdot10-5 m2 s-1. Halfway through the experiment the remnants of tropical storm Bertha arrived at the study site and caused a complete mixing of the water column. An analysis of the data showed that resuspension and deposition were solely tidally-driven and in equilibrium prior to the arrival of the storm, with an averaged resuspension rate of 3-4 g m-2 s-1. During the storm the effect of surface waves increased the resuspension rate by an order of magnitude. The data suggest that after the passing of the storm, when the tide was the main driver again, resuspension rates are generally higher than before the storm. This provides a further indication that although a (Summer) storm might be a short-term event, its effects on sediment transport may be felt on much longer time scales.

Modeling Paragenesis: Erosion Opposite to Gravity in Cave Channels

NASA Astrophysics Data System (ADS)

Cooper, M. P.; Covington, M. D.

2017-12-01

Sediment plays an important role in bedrock channels, providing both tools and cover that influence patterns of bed erosion. It has also been shown that sediment load influences bedrock channel width, with increased sediment leading to wider channels. A variety of models have been developed to explore these effects. In caves, it is hypothesized that sediments covering the floors of fully flooded channels that are forming beneath the water table (phreatic zone) can force dissolution upwards towards the water table, leading to upward erosion balanced by gradual deposition of sediment within the channel bottom. This strange process is termed paragenesis, and while there are conceptual and experimental models of the process, no prior mathematical models of cave passage evolution has captured these effects. Consequently, there is little quantitative understanding of the processes that drive paragenesis and how they link to the morphology of the cave channels that develop. We adapt a previously developed algorithm for estimating boundary shear stress within channels with free-surface flows to enable calculation of boundary shear stress in pipe-full conditions. This model successfully duplicates scaling relationships in surface channels, and geometries of caves formed in the phreatic zone such as phreatic tubes. Once sediment flux is incorporated the model successfully duplicates the hypothesized processes of paragenetic gallery formation: the cover effect prevents dissolution in the direction of gravity; passages are enlarged upwards reducing the sediment transport capacity; sediment is deposited and the process drives a continuing feedback loop. Simulations reveal that equilibrium paragenetic channel widths scale with both sediment flux and discharge. Unlike in open channel settings, increased sediment load actually narrows paragenetic channels. The cross section evolution model also reveals that the existence of equilibrium widths in such galleries requires erosion to scale with shear stress, suggesting a role of either mechanical erosion or transport limited dissolution. These types of erosion contrast with current numerical models of speleogenesis, where chemically limited dissolution, a process independent of shear stress, is predicted to occur in most turbulent flow settings.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kayzar, Theresa M.; Villa, Adam C.; Lobaugh, Megan L.

The uranium concentrations and isotopic compositions of waters, sediment leachates and sediments from Red Rock Creek in the Stanislaus National Forest of California were measured to investigate the transport of uranium from a point source (the Juniper Uranium Mine) to a natural surface stream environment. Furthermore, we alter the (234U)/(238U) composition of Red Rock Creek downstream of the Juniper Mine. As a result of mine-derived contamination, water (234U)/(238U) ratios are 67% lower than in water upstream of the mine (1.114–1.127 ± 0.009 in the contaminated waters versus 1.676 in the clean branch of the stream), and sediment samples have activitymore » ratios in equilibrium in the clean creek and out of equilibrium in the contaminated creek (1.041–1.102 ± 0.007). Uranium concentrations in water, sediment and sediment leachates are highest downstream of the mine, but decrease rapidly after mixing with the clean branch of the stream. Uranium content and compositions of the contaminated creek headwaters relative to the mine tailings of the Juniper Mine suggest that uranium has been weathered from the mine and deposited in the creek. The distribution of uranium between sediment surfaces (leachable fraction) and bulk sediment suggests that adsorption is a key element of transfer along the creek. In clean creek samples, uranium is concentrated in the sediment residues, whereas in the contaminated creek, uranium is concentrated on the sediment surfaces (~70–80% of uranium in leachable fraction). Furthermore, contamination only exceeds the EPA maximum contaminant level (MCL) for drinking water in the sample with the closest proximity to the mine. Isotopic characterization of the uranium in this system coupled with concentration measurements suggest that the current state of contamination in Red Rock Creek is best described by mixing between the clean creek and contaminated upper branch of Red Rock Creek rather than mixing directly with mine sediment.« less

Geochronology of recent sediments from the Cariaco Trench (Venezuela) by Alpha Spectrometry of {sup 210}Pb ({sup 210}Po)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arriojas, A.; Barros, H.; Palacios, D.

2010-08-04

210Pb concentration in marine sediments of the Cariaco Trench (North-East of Venezuela) was measured through the analysis of 210Po alpha emissions, which can be assumed to be in secular equilibrium with 210Pb. The analysed sediment core has a length of 1.9 m. The results allowed to apply the CF:CS dating model (Constant Flux and Constant Supply). The sedimentation rate was estimated to be 0.25 cm/y. As far as we know this is the first {alpha}- dating carried out in the country, performed with an alpha spectrometer recently funded by the IAEA.

Understanding bioavailability and toxicity of sediment-associated contaminants by combining passive sampling with in vitro bioassays in an urban river catchment.

PubMed

Li, Juan-Ying; Tang, Janet Yat Man; Jin, Ling; Escher, Beate I

2013-12-01

Bioavailable and bioaccessible fractions of sediment-associated contaminants are considered as better dose metrics for sediment-quality assessment than total concentrations. The authors applied exhaustive solvent extraction and nondepletive equilibrium sampling techniques to sediment samples collected along the Brisbane River in South East Queensland, Australia, which range from pristine environments to urban and industry-impacted areas. The wide range of chemicals expected prevents comprehensive chemical analysis, but a battery of cell-based bioassays sheds light on mixture effects of chemicals in relation to various modes of toxic action. Toxic effects were expressed as bioanalytical equivalent concentrations (BEQs) normalized to the organic carbon content of each sediment sample. Bioanalytical equivalent concentrations from exhaustive extraction agreed fairly well with values estimated from polydimethylsiloxane passive sampling extracts via the constant organic carbon to polydimethylsiloxane partition coefficient. Agreement was best for bioassays indicative of photosynthesis inhibition and oxidative stress response and discrepancy within a factor of 3 for the induction of the aryl hydrocarbon receptor. For nonspecific cytotoxicity, BEQ from exhaustive extraction were 1 order of magnitude higher than values from equilibrium sampling, possibly because of coextraction of bioactive natural organic matter that led to an overestimation of toxicity in the exhaustive extracts, which suggests that passive sampling is better suited in combination with bioanalytical assessment than exhaustive extraction. © 2013 SETAC.

Evolution of Holocene tidal systems along the Dutch coast: effects of rivers, coastal boundary conditions, eco-engineering species, inherited relief and human interference

NASA Astrophysics Data System (ADS)

Haas, T. D.; Pierik, H. J.; van der Spek, A.; Cohen, K.; van Maanen, B.; Kleinhans, M. G.

2016-12-01

Estuaries and tidal basins are partly enclosed coastal bodies of water with a free connection to the open sea at their tidal inlet and with no to marginal riverine input (tidal basins) or substantial riverine input (estuaries). Their tidal inlets can only remain open over Holocene timescales when (1) the formation of accommodation space exceeds infilling or (2) the inlet system is in dynamic equilibrium (sediment input equals output). Physical and numerical modelling suggest that estuaries and tidal basins develop toward a dynamic equilibrium under constant boundary conditions and remain open over long timescales, whereas many natural estuaries and tidal basins have filled up and were closed off or became deltas during the Holocene. This raises the question if and how tidal inlets can remain open over long timescales? And what is the effect of river inflow and sediment supply thereon? Here we compare the Holocene evolution of tidal systems along the Dutch coast to empirically identify the most important factors that control their long-term evolution. Along the coast of the Netherlands estuaries and tidal basins were formed during the middle Holocene driven by rapid relative sea-level rise and during the late Holocene driven by natural and human-induced subsidence in coastal plain peatlands. During the Holocene tidal inlets connected to rivers (estuaries) were able to persist and attain dynamic equilibrium while tidal basins without or with a very marginal riverine inflow were unstable and closed off under abundant sediment supply. There are many examples of long-lived tidal inlets that rapidly closed off after upstream river avulsion leading to a decrease and finally loss of riverine input. Long-term net import of sediment from the sea into Dutch tidal basins is favoured by strong, flood-dominated, tidal asymmetry along the Dutch coast, the shallow sand-rich floor of the North Sea and the abundance of mud in the coastal area supplied by the Rhine and Meuse rivers. While sandy tidal basins may obtain dynamic equilibrium and remain open over long timescales, we hypothesize that an abundance of mud and eco-engineering species often culminates in continuous basin filling with fine sediment and the growth of intertidal and supratidal areas, eventually resulting in closure of the basin.

Run-of-River Impoundments Can Remain Unfilled While Transporting Gravel Bedload: Numerical Modeling Results

NASA Astrophysics Data System (ADS)

Pearson, A.; Pizzuto, J. E.

2015-12-01

Previous work at run-of-river (ROR) dams in northern Delaware has shown that bedload supplied to ROR impoundments can be transported over the dam when impoundments remain unfilled. Transport is facilitated by high levels of sand in the impoundment that lowers the critical shear stresses for particle entrainment, and an inversely sloping sediment ramp connecting the impoundment bed (where the water depth is typically equal to the dam height) with the top of the dam (Pearson and Pizzuto, in press). We demonstrate with one-dimensional bed material transport modeling that bed material can move through impoundments and that equilibrium transport (i.e., a balance between supply to and export from the impoundment, with a constant bed elevation) is possible even when the bed elevation is below the top of the dam. Based on our field work and previous HEC-RAS modeling, we assess bed material transport capacity at the base of the sediment ramp (and ignore detailed processes carrying sediment up and ramp and over the dam). The hydraulics at the base of the ramp are computed using a weir equation, providing estimates of water depth, velocity, and friction, based on the discharge and sediment grain size distribution of the impoundment. Bedload transport rates are computed using the Wilcock-Crowe equation, and changes in the impoundment's bed elevation are determined by sediment continuity. Our results indicate that impoundments pass the gravel supplied from upstream with deep pools when gravel supply rate is low, gravel grain sizes are relatively small, sand supply is high, and discharge is high. Conversely, impoundments will tend to fill their pools when gravel supply rate is high, gravel grain sizes are relatively large, sand supply is low, and discharge is low. The rate of bedload supplied to an impoundment is the primary control on how fast equilibrium transport is reached, with discharge having almost no influence on the timing of equilibrium.

Human alterations, dynamic equilibrium, and riparian ecosystem responses along selected rivers in Tuscany, Italy (Invited)

NASA Astrophysics Data System (ADS)

Hupp, C. R.; Rinaldi, M.

2010-12-01

Many, if not most, streams have been mildly to severely affected by human disturbance, which complicates efforts to understand riparian ecosystems. Mediterranean regions have a long history of human influences including: dams, stream channelization, mining of sediment, and levee /canal construction. Typically these alterations reduce the ecosystem services that functioning floodplains provide and may negatively impact the natural ecology of floodplains through reductions in suitable habitats, biodiversity, and nutrient cycling. Additionally, human alterations typically shift affected streams away from a state of natural dynamic equilibrium, where net sediment deposition is approximately in balance with net erosion. Lack of equilibrium typically affects the degree to which floodplain ecosystems are connected to streamflow regime. Low connectivity, usually from human- or climate-induced incision, may result in reduced flow on floodplains and lowered water tables. High connectivity may result in severe sediment deposition. Connectivity has a direct impact on vegetation communities. Riparian vegetation distribution patterns and diversity relative to various fluvial geomorphic channel patterns, landforms, and processes are described and interpreted for selected rivers of Tuscany, Central Italy; with emphasis on channel evolution following human impacts. Multivariate analysis reveals distinct quantitative vegetation patterns related to six fluvial geomorphic surfaces. Analysis of vegetation data also shows distinct associations of plants with adjustment processes related to the stage of channel evolution. Plant distribution patterns coincide with disturbance/landform/soil moisture gradients. Species richness increases from channel bed to terrace and on heterogeneous riparian areas, while species richness decreases from moderate to intense incision and from low to intense narrowing. As a feedback mechanism, woody vegetation in particular may facilitate geomorphic recovery of floodplains by affecting sedimentation dynamics. Identification and understanding of critical fluvial parameters related to floodplain connectivity (e.g. stream gradient, grain-size, and hydrography) and spatial and temporal sediment deposition/erosion process trajectories should facilitate management efforts to retain and/or regain important ecosystem services.

Analysis of equivalent widths of alluvial channels and application for instream habitat in the Rio Grande

Treesearch

Claudia A. Leon

2003-01-01

Rivers are natural systems that adjust to variable water and sediment discharges. Channels with spatial variability in width that are managed to maintain constant widths over a period of time are able to transport the same water and sediment discharges by adjusting the bed slope. Methods developed to de ne equilibrium hydraulic geometry characteristics of alluvial...

Hydrodynamics of the VanA-type VanS histidine kinase: an extended solution conformation and first evidence for interactions with vancomycin

PubMed Central

Phillips-Jones, Mary K.; Channell, Guy; Kelsall, Claire J.; Hughes, Charlotte S.; Ashcroft, Alison E.; Patching, Simon G.; Dinu, Vlad; Gillis, Richard B.; Adams, Gary G.; Harding, Stephen E.

2017-01-01

VanA-type resistance to glycopeptide antibiotics in clinical enterococci is regulated by the VanSARA two-component signal transduction system. The nature of the molecular ligand that is recognised by the VanSA sensory component has not hitherto been identified. Here we employ purified, intact and active VanSA membrane protein (henceforth referred to as VanS) in analytical ultracentrifugation experiments to study VanS oligomeric state and conformation in the absence and presence of vancomycin. A combination of sedimentation velocity and sedimentation equilibrium in the analytical ultracentrifuge (SEDFIT, SEDFIT-MSTAR and MULTISIG analysis) showed that VanS in the absence of the ligand is almost entirely monomeric (molar mass M = 45.7 kDa) in dilute aqueous solution with a trace amount of high molar mass material (M ~ 200 kDa). The sedimentation coefficient s suggests the monomer adopts an extended conformation in aqueous solution with an equivalent aspect ratio of ~(12 ± 2). In the presence of vancomycin over a 33% increase in the sedimentation coefficient is observed with the appearance of additional higher s components, demonstrating an interaction, an observation consistent with our circular dichroism measurements. The two possible causes of this increase in s – either a ligand induced dimerization and/or compaction of the monomer are considered. PMID:28397853

Planview Geometry and morphological characteristics of pocket beaches on the Catalan coast (Spain)

NASA Astrophysics Data System (ADS)

Bowman, D.; Guillén, J.; López, L.; Pellegrino, V.

2009-07-01

Coastal planform studies are a relevant initial stage before launching detailed dynamic field experiments. The aim of this study is to define the planform characteristics of 72 Catalan pocket beaches, natural and man-made, and to determine their sheltering effect, embaymentization and their status of equilibrium. Planform measurements were performed on SIGPAC, 1:5000 orthophoto sets and wave climate was provided by Puertos del Estado (Wana model). Planform parameters were applied and coastal planview indexes were determined. The study shows that the Catalan pocket beaches display a wide range of indentation, suggesting that no single structural, tectonic or morphological control dominates their planform. The man-made pocket beaches typically display indentations which are smaller than those shown by natural pocket beaches. Headland spacing and beach area are positively correlated. The more indented bays are, the shorter their beaches become. Low-indented pocket beaches are the widest and the longest ones. Deep indentation contributes towards beach protection and energy dissipation which counteracts rip efficiency and inhibits the formation of mega-rips. Pocket beaches often show gradual and moderate alongshore changes in texture and beach morphology. One third of the Catalan pocket beaches are "sediment starved", i.e., 60% and more of their embayed shorelines are deprived of beach sediments. Examination of the status of equilibrium demonstrates that most of the Catalan pocket beaches are in an unstable mode, with indentation ratios that are unrelated to the wave obliquity.

Turbidity Current Head Mixing

NASA Astrophysics Data System (ADS)

Hernandez, David; Sanchez, Miguel Angel; Medina, Pablo

2010-05-01

A laboratory experimental set - up for studying the behaviour of sediment in presence of a turbulent field with zero mean flow is compared with the behaviour of turbidity currents [1] . Particular interest is shown on the initiation of sediment motion and in the sediment lift - off. The behaviour of the turbidity current in a flat ground is compared with the zero mean flow oscilating grid generated turbulence as when wave flow lifts off suspended sediments [2,3]. Some examples of the results obtained with this set-up relating the height of the head of the turbidity current to the equilibrium level of stirred lutoclines are shown. A turbulent velocity u' lower than that estimated by the Shield diagram is required to start sediment motion. The minimum u' required to start sediment lift - off, is a function of sediment size, cohesivity and resting time. The lutocline height depends on u', and the vorticity at the lutocline seems constant for a fixed sediment size [1,3]. Combining grid stirring and turbidty current head shapes analyzed by means of advanced image analysis, sediment vertical fluxes and settling speeds can be measured [4,5]. [1] D. Hernandez Turbulent structure of turbidity currents and sediment transport Ms Thesis ETSECCPB, UPC. Barcelona 2009. [2] A. Sánchez-Arcilla; A. Rodríguez; J.C. Santás; J.M. Redondo; V. Gracia; R. K'Osyan; S. Kuznetsov; C. Mösso. Delta'96 Surf-zone and nearshore measurements at the Ebro Delta. A: International Conference on Coastal Research through large Scale Experiments (Coastal Dynamics '97). University of Plymouth, 1997, p. 186-187. [3] P. Medina, M. A. Sánchez and J. M. Redondo. Grid stirred turbulence: applications to the initiation of sediment motion and lift-off studies Physics and Chemistry of the Earth, Part B: Hydrology, Oceans and Atmosphere. 26, Issue 4, 2001, Pages 299-304 [4] M.O. Bezerra, M. Diez, C. Medeiros, A. Rodriguez, E. Bahia., A. Sanchez-Arcilla and J.M. Redondo. Study on the influence of waves on coastal diffusion using image analysis. Applied Scientific Research 59,.191-204. 1998. [5] J.M. Redondo. Turbulent mixing in the Atmosphere and Ocean. Fluid Physics. 584-597. World Scientific. New York. 1994

Passive PE Sampling in Support of In Situ Remediation of Contaminated Sediments

DTIC Science & Technology

2015-08-01

control RPD relative percent difference RSD relative standard deviation SERDP Strategic Environmental Research and Development Program SOPs...sediments from 2 stations, each at 4 PCB spike levels, for four individual congeners was 22 ± 6 % relative standard deviation ( RSD ). Also, comparison of... RSD (Table 3). However, larger congeners (e.g., congeners #153 and 180) whose approach to equilibrium is less certain, based on small fractions of

Freshwater mussel response to bedform movement: experimental stream studies

NASA Astrophysics Data System (ADS)

Kozarek, J. L.; MacGregor, K. R.; Hornbach, D.; Hove, M.

2017-12-01

Freshwater mussels are intrinsically linked to near-bed sediment dynamics, but it remains unclear how mussels respond to changing sediment loads across spatial and temporal scales. The interactions between mussels and sediment transport are complex and often involve feedback loops. Mussels are filter feeders removing suspended particles from the water column and the physical presence of mussels can have significant impacts on the structure of riverbed habitat. We investigated the feedbacks between mussels, flow, and migrating bedforms during flood experiments in the St. Anthony Falls Laboratory Outdoor StreamLab (OSL) at the University of Minnesota. The OSL is a field-scale sand-bed meandering stream channel with independent control over sediment feed (recirculated) and water flow (diverted from the Mississippi River). Mussel location, orientation to flow, and protrusion from sediment was surveyed immediately before, after, and one and two days after each flood event. Flow fields, bed shear stress, bedform migration, and bar topography were measured during each flooding event with and without mussels present (density = 4/m2 and 8/m2) to quantify the influence of mussels on channel morphology and bedform migration. Mobile bedforms (up to 14 cm high) were present for all flood events with quasi-equilibrium, aggrading, and degrading bed conditions. Mussels moved little horizontally during all flood events, but were shown to move quickly to deeper water after the flood receded. However, mussels moved vertically, burrowing or being buried under mobile bedforms, during each flood event. The research presented here will focus on feedbacks between three mussel species with different shell sculptures, flow conditions, and migrating bedforms during flooding events. These results reveal how freshwater mussels respond to and affect flow and sediment transport during flood events that are difficult to observe in the field.

Supercoiled circular DNA of an insect granulosis virus

PubMed Central

Tweeten, Kathleen A.; Bulla, Lee A.; Consigli, Richard A.

1977-01-01

The DNA of the granulosis virus of the Indian meal moth, Plodia interpunctella, was characterized by physical chemical and electron microscopic techniques. Twenty-five percent of the DNA extracted from purified virus was isolated as supercoiled circular molecules. The remaining 75% consisted of relaxed circular molecules. These molecular forms were indicated by the production of two radioactive bands during sedimentation of 3H-labeled granulosis virus DNA in alkaline sucrose gradients or in equilibrium density gradients of neutral cesium chloride/propidium iodide. Electron microscopic visualization of the DNA that banded at the higher density in the latter gradients revealed supercoiled structures whereas that of DNA that banded at the lower density demonstrated relaxed circular molecules. The superhelical molecules were converted to relaxed circles by treatment with pancreatic DNase. The molecular weight of the viral DNA was calculated to be 81 × 106 by sedimentation in neutral sucrose and 78 × 106 by sedimentation in alkaline sucrose. The molecular weight estimated from length measurements in electron micrographs was 76 × 106. The buoyant density of the granulosis virus DNA was 1.703 g/cm3 and that of its insect host DNA was 1.697 g/cm3. Equilibrium sedimentation in cesium chloride and thermal denaturation indicated G + C contents of 44% and 39% for the viral and host DNA, respectively. Images PMID:198791

Fibulin 5 Forms a Compact Dimer in Physiological Solutions*

PubMed Central

Jones, Richard P. O.; Wang, Ming-Chuan; Jowitt, Thomas A.; Ridley, Caroline; Mellody, Kieran T.; Howard, Marjorie; Wang, Tao; Bishop, Paul N.; Lotery, Andrew J.; Kielty, Cay M.; Baldock, Clair; Trump, Dorothy

2009-01-01

Fibulin 5 is a 52-kDa calcium-binding epidermal growth factor (cbEGF)-rich extracellular matrix protein that is essential for the formation of elastic tissues. Missense mutations in fibulin 5 cause the elastin disorder cutis laxa and have been associated with age-related macular degeneration, a leading cause of blindness. We investigated the structure, hydrodynamics, and oligomerization of fibulin 5 using small angle x-ray scattering, EM, light scattering, circular dichroism, and sedimentation. Compact structures for the monomer were determined by small angle x-ray scattering and EM, and are supported by close agreement between the theoretical sedimentation of the structures and the experimental sedimentation of the monomer in solution. EM showed that monomers associate around a central cavity to form a dimer. Light scattering and equilibrium sedimentation demonstrated that the equilibrium between the monomer and the dimer is dependent upon NaCl and Ca2+ concentrations and that the dimer is dominant under physiological conditions. The dimerization of fragments containing just the cbEGF domains suggests that intermolecular interactions between cbEGFs cause dimerization of fibulin 5. It is possible that fibulin 5 functions as a dimer during elastinogenesis or that dimerization may provide a method for limiting interactions with binding partners such as tropoelastin. PMID:19617354

Supercoiled circular DNA of an insect granulosis virus.

PubMed

Tweeten, K A; Bulla, L A; Consigli, R A

1977-08-01

The DNA of the granulosis virus of the Indian meal moth, Plodia interpunctella, was characterized by physical chemical and electron microscopic techniques. Twenty-five percent of the DNA extracted from purified virus was isolated as supercoiled circular molecules. The remaining 75% consisted of relaxed circular molecules. These molecular forms were indicated by the production of two radioactive bands during sedimentation of (3)H-labeled granulosis virus DNA in alkaline sucrose gradients or in equilibrium density gradients of neutral cesium chloride/propidium iodide. Electron microscopic visualization of the DNA that banded at the higher density in the latter gradients revealed supercoiled structures whereas that of DNA that banded at the lower density demonstrated relaxed circular molecules. The superhelical molecules were converted to relaxed circles by treatment with pancreatic DNase. The molecular weight of the viral DNA was calculated to be 81 x 10(6) by sedimentation in neutral sucrose and 78 x 10(6) by sedimentation in alkaline sucrose. The molecular weight estimated from length measurements in electron micrographs was 76 x 10(6). The buoyant density of the granulosis virus DNA was 1.703 g/cm(3) and that of its insect host DNA was 1.697 g/cm(3). Equilibrium sedimentation in cesium chloride and thermal denaturation indicated G + C contents of 44% and 39% for the viral and host DNA, respectively.

Polyoxymethylene passive samplers to assess the effectiveness of biochar by reducing the content of freely dissolved fipronil and ethiprole.

PubMed

Li, Shasha; Wang, Pingping; Liu, Xingang; Wu, Xiaohu; Dong, Fengshou; Xu, Jun; Zheng, Yongquan

2018-07-15

An equilibrium passive sampler based on polyoxymethylene (POM) was used to determine the freely dissolved concentrations (C free ) of fipronil and ethiprole. The sorption equilibrium times of fipronil and ethiprole in POM were 14.2d and 24.0d, respectively. The POM-water partitioning coefficients (logK POM-water ) were 2.6 for fipronil and 1.4 for ethiprole. The method was further used to evaluate the sorption behavior of biochars which produced by pyrolysis of Magnolia wood (Magnolia denudata) at 300°C, 500°C and 700°C. The amounts of target compounds adsorbed increased with increasing pyrolysis temperature of the biochars. Biochars characterized by a low polarity index had better sorption capacity for the target compounds. The additions of biochars to sediment were effective in reducing C free , and the enhancement was found to be more pronounced with high biochar content. C free in sediment with more organic matter was significantly higher after biochar addition. Increasing the sediment-biochar contact time from 7 to 30d resulted in an increase in sorption of the compounds. We conclude that Magnolia wood biochar effectively reduces the content of freely dissolved fipronil and ethiprole content in sediment. Copyright © 2018. Published by Elsevier B.V.

Investigating uranium distribution in surface sediments and waters: a case study of contamination from the Juniper Uranium Mine, Stanislaus National Forest, CA.

PubMed

Kayzar, Theresa M; Villa, Adam C; Lobaugh, Megan L; Gaffney, Amy M; Williams, Ross W

2014-10-01

The uranium concentrations and isotopic compositions of waters, sediment leachates and sediments from Red Rock Creek in the Stanislaus National Forest of California were measured to investigate the transport of uranium from a point source (the Juniper Uranium Mine) to a natural surface stream environment. The ((234)U)/((238)U) composition of Red Rock Creek is altered downstream of the Juniper Mine. As a result of mine-derived contamination, water ((234)U)/((238)U) ratios are 67% lower than in water upstream of the mine (1.114-1.127 ± 0.009 in the contaminated waters versus 1.676 in the clean branch of the stream), and sediment samples have activity ratios in equilibrium in the clean creek and out of equilibrium in the contaminated creek (1.041-1.102 ± 0.007). Uranium concentrations in water, sediment and sediment leachates are highest downstream of the mine, but decrease rapidly after mixing with the clean branch of the stream. Uranium content and compositions of the contaminated creek headwaters relative to the mine tailings of the Juniper Mine suggest that uranium has been weathered from the mine and deposited in the creek. The distribution of uranium between sediment surfaces (leachable fraction) and bulk sediment suggests that adsorption is a key element of transfer along the creek. In clean creek samples, uranium is concentrated in the sediment residues, whereas in the contaminated creek, uranium is concentrated on the sediment surfaces (∼70-80% of uranium in leachable fraction). Contamination only exceeds the EPA maximum contaminant level (MCL) for drinking water in the sample with the closest proximity to the mine. Isotopic characterization of the uranium in this system coupled with concentration measurements suggest that the current state of contamination in Red Rock Creek is best described by mixing between the clean creek and contaminated upper branch of Red Rock Creek rather than mixing directly with mine sediment. Published by Elsevier Ltd.

Investigating uranium distribution in surface sediments and waters: a case study of contamination from the Juniper Uranium Mine, Stanislaus National Forest, CA

DOE PAGES

Kayzar, Theresa M.; Villa, Adam C.; Lobaugh, Megan L.; ...

2014-06-07

The uranium concentrations and isotopic compositions of waters, sediment leachates and sediments from Red Rock Creek in the Stanislaus National Forest of California were measured to investigate the transport of uranium from a point source (the Juniper Uranium Mine) to a natural surface stream environment. Furthermore, we alter the (234U)/(238U) composition of Red Rock Creek downstream of the Juniper Mine. As a result of mine-derived contamination, water (234U)/(238U) ratios are 67% lower than in water upstream of the mine (1.114–1.127 ± 0.009 in the contaminated waters versus 1.676 in the clean branch of the stream), and sediment samples have activitymore » ratios in equilibrium in the clean creek and out of equilibrium in the contaminated creek (1.041–1.102 ± 0.007). Uranium concentrations in water, sediment and sediment leachates are highest downstream of the mine, but decrease rapidly after mixing with the clean branch of the stream. Uranium content and compositions of the contaminated creek headwaters relative to the mine tailings of the Juniper Mine suggest that uranium has been weathered from the mine and deposited in the creek. The distribution of uranium between sediment surfaces (leachable fraction) and bulk sediment suggests that adsorption is a key element of transfer along the creek. In clean creek samples, uranium is concentrated in the sediment residues, whereas in the contaminated creek, uranium is concentrated on the sediment surfaces (~70–80% of uranium in leachable fraction). Furthermore, contamination only exceeds the EPA maximum contaminant level (MCL) for drinking water in the sample with the closest proximity to the mine. Isotopic characterization of the uranium in this system coupled with concentration measurements suggest that the current state of contamination in Red Rock Creek is best described by mixing between the clean creek and contaminated upper branch of Red Rock Creek rather than mixing directly with mine sediment.« less

Post-tsunami beach recovery in Thailand: A case for punctuated equilibrium in coastal dynamics

NASA Astrophysics Data System (ADS)

Switzer, Adam D.; Gouramanis, Chris; Bristow, Charles; Yeo, Jeffrey; Kruawun, Jankaew; Rubin, Charles; Sin Lee, Ying; Tien Dat, Pham

2017-04-01

A morpho-geophysical investigation of two beaches in Thailand over the last decade shows that they have completely recovered from the 2004 Indian Ocean tsunami (IOT) without any human intervention. Although the beach systems show contrasting styles of recovery in both cases natural processes have reconstructed the beaches to comparable pre-tsunami morphologies in under a decade, demonstrating the existence of punctuated equilibrium in coastal systems and the resilience of natural systems to catastrophic events. Through a combination of remote sensing, field surveys and shallow geophysics we reconstruct the post-event recovery of beaches at Phra Thong Island, a remote, near pristine site that was severely impacted by the IOT. We identify periods of aggradation, progradation and washover sedimentation that match with local events including a storm in November 2007. The rapid recovery of these systems implies that majority of sediment scoured by the tsunami was not transported far offshore but remained in the littoral zone within reach of fair-weather waves that returned it (the sediment) to the beach naturally.

Simulating the evolution of coastal morphology and stratigraphy with a new morphological-behaviour model (GEOMBEST)

USGS Publications Warehouse

Stolper, D.; List, J.H.; Thieler, E.R.

2005-01-01

A new morphological-behaviour model is used to simulate evolution of coastal morphology associated with cross-shore translations of the shoreface, barrier, and estuary. The model encapsulates qualitative principles drawn from established geological concepts that are parameterized to provide quantitative predictions of morphological change on geological time scales (order 10 3 years), as well as shorter time scales applicable for long-term coastal management (order 101 to 102 years). Changes in sea level, and sediment volume within the shoreface, barrier, and estuary, drive the model behaviour. Further parameters, defining substrate erodibility, sediment composition, and time-dependent shoreface response, constrain the evolution of the shoreface towards an equilibrium profile. Results from numerical experiments are presented for the low-gradient autochthonous setting of North Carolina and the steep allochthonous setting of the Washington shelf. Simulations in the Currituck region of North Carolina examined the influence of sediment supply, substrate composition, and substrate erodibility on barrier transgression. Results demonstrate that the presence of a lithified substrate reduces the rate of barrier transgression compared to scenarios where an erodible, sand-rich substrate exists. Simulations of the Washington coast, 20 km north of the Columbia River, confirmed that the model can reproduce complex stratigraphy involving regressive and transgressive phases of coastal evolution. Results suggest that the first major addition of sediment to the shelf occurred around 12 900 years ago and resulted from the rapid addition of sediment volume from the Columbia River attributed to the Missoula floods. This was followed by a period where little or no sediment was added (12 400-9100 BP) and a third period when most sediment was added to the shelf (9100 BP to present) from the Columbia River. Comparing results from each setting demonstrates an indirect control that substrate slope has on shoreface transgression rates. Shoreface transgression is shown to be sensitive to the rate of estuarine sedimentation, with the sensitivity increasing as substrate slope decreases. 

Interactions between globular proteins and F-actin in isotonic saline solution.

PubMed

Lakatos, S; Minton, A P

1991-10-05

Solutions of each of three different globular proteins (cytochrome c, chromophorically labeled serum albumin, and chromophorically labeled aldolase), mixed with another unlabeled globular protein or with fibrous actin, were prepared in pH 8.0 Tris-HCl buffer containing 0.15 M NaCl. Each solution was centrifuged at low speed, at 5 degrees C, until unassociated globular protein in solution achieved sedimentation equilibrium. Individual absorbance gradients of both macrosolutes in the mixtures subsequent to centrifugation were obtained via optical scans of the centrifuge tubes at two wavelengths. The gradients of each macrosolute in mixtures of two globular proteins revealed no association of globular proteins under the conditions of these experiments, but perturbation of the gradients of serum albumin, aldolase, and cytochrome c in the presence of F-actin indicated association of all three globular proteins with F-actin. Perturbation of actin gradients in the presence of serum albumin and aldolase suggested partial depolymerization of the F-actin by the globular protein. Analysis of the data with a simple phenomenological model relating free globular protein, bound globular protein, and total actin concentration provided estimates of the respective equilibrium constants for association of serum albumin and aldolase with F-actin, under the conditions of these experiments, of the order of 0.1 microM-1.

Characterizing particle-scale equilibrium adsorption and kinetics of uranium(VI) desorption from U-contaminated sediments

USGS Publications Warehouse

Stoliker, Deborah L.; Liu, Chongxuan; Kent, Douglas B.; Zachara, John M.

2013-01-01

Rates of U(VI) release from individual dry-sieved size fractions of a field-aggregated, field-contaminated composite sediment from the seasonally saturated lower vadose zone of the Hanford 300-Area were examined in flow-through reactors to maintain quasi-constant chemical conditions. The principal source of variability in equilibrium U(VI) adsorption properties of the various size fractions was the impact of variable chemistry on adsorption. This source of variability was represented using surface complexation models (SCMs) with different stoichiometric coefficients with respect to hydrogen ion and carbonate concentrations for the different size fractions. A reactive transport model incorporating equilibrium expressions for cation exchange and calcite dissolution, along with rate expressions for aerobic respiration and silica dissolution, described the temporal evolution of solute concentrations observed during the flow-through reactor experiments. Kinetic U(VI) desorption was well described using a multirate SCM with an assumed lognormal distribution for the mass-transfer rate coefficients. The estimated mean and standard deviation of the rate coefficients were the same for all <2 mm size fractions but differed for the 2–8 mm size fraction. Micropore volumes, assessed using t-plots to analyze N2 desorption data, were also the same for all dry-sieved <2 mm size fractions, indicating a link between micropore volumes and mass-transfer rate properties. Pore volumes for dry-sieved size fractions exceeded values for the corresponding wet-sieved fractions. We hypothesize that repeated field wetting and drying cycles lead to the formation of aggregates and/or coatings containing (micro)pore networks which provided an additional mass-transfer resistance over that associated with individual particles. The 2–8 mm fraction exhibited a larger average and standard deviation in the distribution of mass-transfer rate coefficients, possibly caused by the abundance of microporous basaltic rock fragments.

Phase Equilibrium, Chemical Equilibrium, and a Test of the Third Law: Experiments for Physical Chemistry.

ERIC Educational Resources Information Center

Dannhauser, Walter

1980-01-01

Described is an experiment designed to provide an experimental basis for a unifying point of view (utilizing theoretical framework and chemistry laboratory experiments) for physical chemistry students. Three experiments are described: phase equilibrium, chemical equilibrium, and a test of the third law of thermodynamics. (Author/DS)

Cesium migration in Hanford sediment: a multisite cation exchange model based on laboratory transport experiments.

PubMed

Steefel, Carl I; Carroll, Susan; Zhao, Pihong; Roberts, Sarah

2003-12-01

Cs+ transport experiments carried out in columns packed with uncontaminated Hanford formation sediment from the SX tank farm provide strong support for the use of a multisite, multicomponent cation exchange model to describe Cs+ migration in the Hanford vadose zone. The experimental results indicate a strong dependence of the effective Cs+ Kd on the concentrations of other cations, including Na+ that is present at high to extremely high concentrations in fluids leaking from the Hanford SX tanks. A strong dependence of the Cs+ Kd on the aqueous Cs+ concentration is also apparent, with retardation of Cs+ increasing from a value of 41 at a Cs+ concentration of 10(-4) M in the feed solution to as much as 282 at a Cs+ concentration of 5x10(-7) M, all in a background of 1 M NaNO3. The total cation exchange capacity (CEC) of the Hanford sediment was determined using 22Na isotopic equilibrium exchange in a flow-through column experiment. The value for the CEC of 120 microeq/g determined with this method is compatible with a value of 121.9 microeq/g determined by multi-cation elution. While two distinct exchange sites were proposed by Zachara et al. [Geochim. Cosmochim. Acta 66 (2002) 193] based on binary batch exchange experiments, a third site is proposed in this study to improve the fit of the Cs+-Na+ and Cs+-Ca+ exchange data and to capture self-sharpened Cs+ breakthrough curves at low concentrations of Cs+. Two of the proposed exchange sites represent frayed edge sites (FES) on weathered micas and constitute 0.02% and 0.22% of the total CEC. Both of the FES show a very strong selectivity for Cs+ over Na+ (K(Na-Cs)=10(7.22) and 10(4.93), respectively). The third site, accounting for over 99% of the total CEC, is associated with planar sites on expansible clays and shows a smaller Na+-Cs+ selectivity coefficient of 10(1.99). Parameters derived from a fit of binary batch experiments alone tend to under predict Cs+ retardation in the column experiments. The transport experiments indicate 72-90% of the Cs+ sorbed in experiments targeting exchange on FES was desorbed over a 10- and 24-day period, respectively. At high Cs+ concentrations, where sorption is controlled primarily by exchange on planar sites, 95% of the Cs+ desorption was desorbed. Most of the difficulty in desorbing Cs+ from FES is a result of the extremely high selectivity of these sites for Cs+, although truly irreversible sorption as high as 23% was suggested in one experiment. The conclusion that Cs+ exchange is largely reversible in a thermodynamic sense is supported by the ability to match Cs+ desorption curves almost quantitatively with an equilibrium reactive transport simulation. The model for Cs+ retardation developed here qualitatively explains the behavior of Cs+ in the Hanford vadose zone underneath a variety of leaking tanks with differing salt concentrations. The high selectivity of FES for Cs+ implies that future desorption and migration is very unlikely to occur under natural recharge conditions.

Soil erosion and effluent particle size distribution under different initial conditions and rock fragment coverage

NASA Astrophysics Data System (ADS)

Jomaa, S.; Barry, D. A.; Brovelli, A.; Heng, B. C. P.; Sander, G. C.; Parlange, J.-Y.

2012-04-01

It is well known that the presence of rock fragments on the soil surface and the soil's initial characteristics (moisture content, surface roughness, bulk density, etc.) are key factors influencing soil erosion dynamics and sediment delivery. In addition, the interaction of these factors increases the complexity of soil erosion patterns and makes predictions more difficult. The aim of this study was (i) to investigate the effect of soil initial conditions and rock fragment coverage on soil erosion yields and effluent particle size distribution and (ii) to evaluate to what extent the rock fragment coverage controls this relationship. Three laboratory flume experiments with constant precipitation rate of 74 mm/h on a loamy soil parcel with a 2% slope were performed. Experiments with duration of 2 h were conducted using the 6-m × 2-m EPFL erosion flume. During each experiment two conditions were considered, a bare soil and a rock fragment-protected (with 40% coverage) soil. The initial soil surface state was varied between the three experiments, from a freshly re-ploughed and almost dry condition to a compacted soil with a well-developed shield layer and high moisture content. Experiments were designed so that rain splash was the primary driver of soil erosion. Results showed that the amount of eroded mass was highly controlled by the initial soil conditions and whether the steady-state equilibrium was un-, partially- or fully- developed during the previous event. Additionally, results revealed that sediment yields and particle size composition in the initial part of an erosion event are more sensitive to the erosion history than the long-time behaviour. This latter appears to be mainly controlled by rainfall intensity. If steady-state was achieved for a previous event, then the next event consistently produced concentrations for each size class that peaked rapidly, and then declined gradually to steady-state equilibrium. If steady state was not obtained, then different and more complex behaviour was observed in the next event, with large differences found between fine, medium and coarse size classes. The presence of rock fragments on the topsoil reduced the time needed to reach steady state compared with the bare soil. This was attributed to the reduction of rain splash erosion caused by the rapid development of the overland flow, as a result of rock fragments reducing the flow cross-sectional area.

Copper isotope signatures in modern marine sediments

NASA Astrophysics Data System (ADS)

Little, Susan H.; Vance, Derek; McManus, James; Severmann, Silke; Lyons, Timothy W.

2017-09-01

The development of metal stable isotopes as tools in paleoceanography requires a thorough understanding of their modern marine cycling. To date, no Cu isotope data has been published for modern sediments deposited under low oxygen conditions. We present data encompassing a broad spectrum of hydrographic and redox regimes, including continental margin and euxinic (sulphide-containing) settings. Taken together with previously published data from oxic settings, these data indicate that the modern oceanic sink for Cu has a surprisingly homogeneous isotopic composition of about +0.3‰ (δ65Cu, relative to NIST SRM976). We suggest that this signature reflects one of two specific water-column processes: (1) an equilibrium isotope fractionation between soluble, isotopically heavy, Cu complexed to strong organic ligands and an isotopically light pool sorbed to particles that deliver Cu to the sediment, or (2) an equilibrium isotope fractionation between the same isotopically heavy ligand-bound pool and the particle reactive free Cu2+ species, with the latter being scavenged by particulates and thereby delivered to the sediment. An output flux of about +0.3‰ into sediments is isotopically light relative to the known inputs to the ocean (at around +0.6‰) and the seawater value of +0.6 to +0.9‰, suggesting the presence of an as yet unidentified isotopically light source of Cu to the oceans. We hypothesize that this source may be hydrothermal, or may result from the partial dissolution of continentally derived particles.

The effect of biological cohesion on current ripple development

NASA Astrophysics Data System (ADS)

Malarkey, Jonathan; Baas, Jaco H.; Hope, Julie

2014-05-01

Results are presented from laboratory experiments examining the role of biological cohesion, associated with Extra Polymeric Substances, on the development of current ripples. The results demonstrate the importance of biological cohesion compared to the effect of physical cohesion associated with clays in an otherwise sandy bed. FURTHER INFORMATION In fluvial and marine environments sediment transport is mainly dependent on the nature of the bed surface (rippled or flat) and the nature of cohesion in the bed. Cohesion can be either physical, as a result of the presence of clays, or biological as a result of the presence of organisms. In the case of the latter, biological cohesion occurs as a result of the presence of Extra Polymeric Substances (EPS) secreted by microorganisms. While it is known that EPS can dramatically increase the threshold of motion (Grant and Gust, 1987), comparatively little is known about the effect of EPS on ripple formation and development. The experiments described here seek to fill this gap. They also allow the effect of biological cohesion to be compared with that of physical cohesion from previous experiments (Baas et al., 2013). The experiments, which were conducted in a 10m flume at Bangor University, involved a current over a bed made of fine sand, with a median diameter of 0.148mm, and various amounts of xanthan gum, a proxy for naturally occurring EPS (Vardy et al., 2007). The hydrodynamic experimental conditions were matched very closely to those of Baas et al. (2013). The ripple dimensions were recorded through the glass side wall of the tank using time lapse photography. In the physical cohesion experiments of Baas et al. (2013) for clay contents up to 12%, the clay was very quickly winnowed out of the bed, leaving essentially clay-free ripples that developed at more or less the same rate as clean sand ripples. The resulting equilibrium ripples were essentially the same length as the clean sand ripples but reduced in height. By contrast, the biological cohesion experiments resulted in a drastic slowing down in ripple development, for much smaller amounts of xanthan (< 1/8%), but resulted in equilibrium ripples with the same dimensions as abiotic sand. This difference in effect for biological and physical cohesion is thought to be related to differences in the nature of the binding. In particular, sand grains with biological cohesion are inhibited from moving independently, which is crucial to ripple development. This work has profound implications for sediment transport studies and emphasises the importance of considering biology as well as clays in sediments. ACKNOWLEDGEMENTS This work was funded by the UK Natural Environment Research Council (NERC) under the 'COHBED' project (NE/1027223/1). REFERENCES Baas, J.H., Davies, A.G. and Malarkey, A.G. (2013) Bedform development in mixed sand-mud: the contrasting role of cohesive forces in flow and bed. Geomorphology, 182, 19-32. Grant, J. and Gust, G. (1987) Prediction of coastal sediment stability from photopigment content of mats of purple sulfur bacteria. Nature, 330, 244-246. Vardy, S., Saunders, J.E., Tolhurst, T.J., Davies, P.A., and Paterson, D.M. (2007) Calibration of the high-pressure cohesive strength meter (CSM). Continental Shelf Research, 27, 1190-1199.

Attenuation of landfill leachate by UK Triassic sandstone aquifer materials. 1. Fate of inorganic pollutants in laboratory columns

NASA Astrophysics Data System (ADS)

Thornton, Steven F.; Tellam, John H.; Lerner, David N.

2000-05-01

The attenuation of inorganic contaminants in acetogenic and methanogenic landfill leachate by calcareous and carbonate-deficient, oxide-rich Triassic sandstone aquifer materials from the English Midlands was examined in laboratory columns. Aqueous equilibrium speciation modelling, simple transport modelling and chemical mass balance approaches are used to evaluate the key processes and aquifer geochemical properties controlling contaminant fate. The results indicate that leachate-rock interactions are dominated by ion-exchange processes, acid-base and redox reactions and sorption/precipitation of metal species. Leachate NH 4 is attenuated by cation exchange with the aquifer sediments; however, NH 4 migration could be described with a simple model using retardation factors. Organic acids in the acetogenic leachate buffered the system pH at low levels during flushing of the calcareous aquifer material. In contrast, equilibrium with Al oxyhydroxide phases initially buffered pH (˜4.5) during flushing of the carbonate-deficient sandstone with methanogenic leachate. This led to the mobilisation of sorbed and oxide-bound heavy metals from the aquifer sediment which migrated as a concentrated pulse at the leachate front. Abiotic reductive dissolution of Mn oxyhydroxides on each aquifer material by leachate Fe 2+ maintains high concentrations of dissolved Mn and buffers the leachate inorganic redox system. This feature is analogous to the Mn-reducing zones found in leachate plumes and in the experiments provides a sink for the leachate Fe load and other heavy metals. The availability of reactive solid phase Mn oxyhydroxides limits the duration of redox buffering and Fe attenuation by these aquifer sediments. Aquifer pH and redox buffering capacity exert a fundamental influence on leachate inorganic contaminant fate in these systems. The implications for the assessment of aquifer vulnerability at landfills are discussed and simple measurements of aquifer properties which may improve the prediction of contaminant attenuation are outlined.

Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea†

PubMed Central

Duplisea, Daniel E; Jennings, Simon; Malcolm, Stephen J; Parker, Ruth; Sivyer, David B

2001-01-01

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5–65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage. PMID:16759420

Modelling potential impacts of bottom trawl fisheries on soft sediment biogeochemistry in the North Sea.

PubMed

Duplisea, D E; Jennings, S; Malcolm, S J; Parker, R; Sivyer, D B

2001-12-19

Bottom trawling causes physical disturbance to sediments particularly in shelf areas. The disturbance due to trawling is most significant in deeper areas with softer sediments where levels of natural disturbance due to wave and tidal action are low. In heavily fished areas, trawls may impact the same area of seabed more than four times per year. A single pass of a beam trawl, the heaviest gear routinely used in shelf sea fisheries, can kill 5-65% of the resident fauna and mix the top few cm of sediment. We expect that sediment community function, carbon mineralisation and biogeochemical fluxes will be strongly affected by trawling activity because the physical effects of trawling are equivalent to those of an extreme bioturbator, and yet, unlike bioturbating macrofauna, trawling does not directly contribute to community metabolism. We used an existing box-model of a generalised soft sediment system to examine the effects of trawling disturbance on carbon mineralisation and chemical concentrations. We contrasted the effects of a natural scenario, where bioturbation is a function of macrobenthos biomass, with an anthropogenic impact scenario where physical disturbance results from trawling rather than the action of bioturbating macrofauna. Simulation results suggest that the effects of low levels of trawling disturbance will be similar to those of natural bioturbators but that high levels of trawling disturbance prevent the modelled system from reaching equilibrium due to large carbon fluxes between oxic and anoxic carbon compartments. The presence of macrobenthos in the natural disturbance scenario allowed sediment chemical storage and fluxes to reach equilibrium. This is because the macrobenthos are important carbon consumers in the system whose presence reduces the magnitude of available carbon fluxes. In soft sediment systems, where the level physical disturbance due to waves and tides is low, model results suggest that intensive trawling disturbance could cause large fluctuations in benthic chemical fluxes and storage.

Polycyclic aromatic hydrocarbon (PAH)-phase associations in Washington coastal sediment

NASA Astrophysics Data System (ADS)

Prahl, Fredrick G.; Carpenter, Roy

1983-06-01

Polycyclic aromatic (PAH) and aliphatic hydrocarbon compositions, organic carbon, nitrogen and lignin contents were determined in whole, unfractionated sediment from the Washington continental shelf and in discrete sediment fractions separated by particle size and density. At least 20 to 25% of perylene and PAH derived from pyrolytic processes and 50% of the retene measured in whole sediment are contained within organic C- and lignin-rich panicles of density ≤ 1.9 g/cc. These particles, which include primarily vascular plant remains and bits of charcoal, comprise less than 1% of the total sediment weight. In contrast, a series of methylated phenanthrene homologs, possibly of fossil origin, are concentrated in some component of the more dense, lithic matrix of the sediment. Equilibrium models of PAH sorption/desorption from aqueous phase onto small particles of high surface area do not appear applicable to the behavior of the major PAH types identified in this aquatic environment.

A Non-Equilibrium Sediment Transport Model for Coastal Inlets and Navigation Channels

DTIC Science & Technology

2011-01-01

exchange of water , sediment, and nutrients between estuaries and the ocean. Because of the multiple interacting forces (waves, wind, tide, river...in parallel using OpenMP. The CMS takes advantage of the Surface- water Modeling System (SMS) interface for grid generation and model setup, as well...as for plotting and post- processing (Zundel, 2000). The circulation model in the CMS (called CMS-Flow) computes the unsteady water level and

Reversible dimer formation and stability of the anti-tumour single-chain Fv antibody MFE-23 by neutron scattering, analytical ultracentrifugation, and NMR and FT-IR spectroscopy.

PubMed

Lee, Yie Chia; Boehm, Mark K; Chester, Kerry A; Begent, Richard H J; Perkins, Stephen J

2002-06-28

MFE-23 is a single chain Fv (scFv) antibody molecule used to target colorectal cancer through its high affinity for the tumour marker carcinoembryonic antigen (CEA). ScFv molecules are formed from peptide-linked antibody V(H) and V(L) domains, and many of these form dimers. Our recent crystal structure for MFE-23 showed that this formed an unusual symmetric back-to-back association of two monomers that is consistent with a domain-swapped diabody structure. Neutron scattering and modelling fits showed that MFE-23 existed as compact V(H)-V(L)-linked monomers at therapeutically relevant concentrations below 1 mg/ml. Size-exclusion gel chromatography showed that the monomeric and dimeric forms of MFE-23 could be separated, and that the proportions of these two forms depended on the starting MFE-23 concentration. Sedimentation equilibrium experiments by analytical ultracentrifugation at nine concentrations of MFE-23 indicated a reversible monomer-dimer self-association equilibrium with an association constant of 1.9x10(3)-2.2x10(3) M(-1). Sedimentation velocity experiments using the time derivative g(s(*)) method showed that MFE-23-His has a concentration-dependent weight average sedimentation coefficient that increased from 1.8 S for the monomer to about 3-6 S for the dimer. Both values agreed with those calculated from the MFE-23 crystal structure. In relation to the thermal stability of MFE-23, denaturation experiments by (1)H NMR and FT-IR spectroscopy showed that the molecule is stable up to 47 degrees C, after which denaturation was irreversible. MFE-23 dimerisation is discussed in terms of a new model for diabody structures, in which the V(H) and V(L) domains in the monomer are able to dissociate and reassociate to form a dimer, or diabody, but in which symmetric back-to-back contacts between the two monomers are formed. This dimerisation in solution is attributed to the complementary nature of the C-terminal surface of the MFE-23 monomer. Crystal structures for seven other scFv molecules have shown that, while the contact residues for symmetric back-to-back dimer formation in MFE-23 are not fully conserved, in principle, back-to-back contacts can be formed in these too. This offers possibilities for the creation of other forms of scFv molecules. (c) 2002 Elsevier Science Ltd.

Headwater peatland channels in south-eastern Australia; the attainment of equilibrium

NASA Astrophysics Data System (ADS)

Nanson, R. A.; Cohen, T. J.

2014-05-01

Many small headwater catchments (< 50 km2) in temperate south-eastern Australia store sediment in valley fills. While accumulation in some of these systems commenced up to 30,000 years ago, most did not commence filling with peat or clastic material until at least the mid Holocene. In such headwater settings, many clastic valley fills develop cut-and-fill channels, which contrast to some peatland settings where sinuous equilibrium channels have evolved. Four peatland systems within this dataset demonstrate stable channel systems which span nearly the full spectrum of observed valley-floor slopes. We assess new and published longitudinal data from these four channels and demonstrate that each of these channels has achieved equilibrium profiles. New and published flow and survey data are synthesised to demonstrate how these peatland systems have attained equilibrium. Low rates of sediment supply and exceptionally high bank strengths have resulted in low width to depth ratios which accommodate rapid changes in flow velocity and depth with changes in discharge. In small peatland channels, planform adjustments have been sufficient to counter the energy provided by these hydraulically efficient cross-sections and have enabled the achievement of regime energy-slopes. In larger and higher energy peatland channels, large, armoured, stable, bedforms have developed. These bedforms integrate with planform adjustments to maintain a condition of minimum variance in energy losses as represented by the slope profiles and, therefore, a uniform increase in downstream entropy.

Simulation of the mobility of metal - EDTA complexes in groundwater: The influence of contaminant metals

USGS Publications Warehouse

Friedly, J.C.; Kent, D.B.; Davis, J.A.

2002-01-01

Reactive transport simulations were conducted to model chemical reactions between metal - EDTA (ethylenediaminetetraacetic acid) complexes during transport in a mildly acidic quartz - sand aquifer. Simulations were compared with the results of small-scale tracer tests wherein nickel-, zinc-, and calcium - EDTA complexes and free EDTA were injected into three distinct chemical zones of a plume of sewage-contaminated groundwater. One zone had a large mass of adsorbed, sewage-derived zinc; one zone had a large mass of adsorbed manganese resulting from mildly reducing conditions created bythe sewage plume; and one zone had significantly less adsorbed manganese and negligible zinc background. The chemical model assumed that the dissolution of iron(III) from metal - hydroxypolymer coatings on the aquifer sediments by the metal - EDTA complexes was kinetically restricted. All other reactions, including metal - EDTA complexation, zinc and manganese adsorption, and aluminum hydroxide dissolution were assumed to reach equilibrium on the time scale of transport; equilibrium constants were either taken from the literature or determined independently in the laboratory. A single iron(III) dissolution rate constant was used to fit the breakthrough curves observed in the zone with negligible zinc background. Simulation results agreed well with the experimental data in all three zones, which included temporal moments derived from breakthrough curves at different distances downgradient from the injections and spatial moments calculated from synoptic samplings conducted at different times. Results show that the tracer cloud was near equilibrium with respect to Fe in the sediment after 11 m of transport in the Zn-contaminated region but remained far from equilibrium in the other two zones. Sensitivity studies showed that the relative rate of iron(III) dissolution by the different metal - EDTA complexes was less important than the fact that these reactions are rate controlled. Results suggest that the published solubility for ferrihydrite reasonably approximates the Fe solubility of the hydroxypolymer coatings on the sediments. Aluminum may be somewhat more soluble than represented by the equilibrium constant for gibbsite, and its dissolution may be rate controlled when reacting with Ca - EDTA complexes.

Hydrodynamics and morphodynamics of a mobile bed confluence under equilibrium conditions for different values of the flow discharge ratio

NASA Astrophysics Data System (ADS)

Birjukova Canelas, Olga; Lage Ferreira, Rui Miguel; Heleno Cardoso, António

2017-04-01

Under steady water and sediment feeding in laboratory conditions, sediment fluxes tend to reach a steady state and bed morphology tends to equilibrium. This laboratory study states two objectives: i) to provide a detailed three-dimensional characterization of the flow field at a movable bed confluence and ii) to contribute to the characterization of the effect of the flow discharge ratio (Qr = Qt/Qm, Qt - tributary flow discharge and Qm - main channel flow discharge) on the flow field. While the junction angle between the main channel and the tributary as well as the sediment discharge ratio were kept constant, two scenarios corresponding to two different flow discharge ratios with dominant main channel flow discharge (Qm > Qt) were analyzed. Prior to the flow velocity measurements, both channels were fed with water and sand mixtures and tests were run until the equilibrium condition was reached, i.e. until the moment where the difference between the total supplied sand discharge and the total outgoing sand discharge was smaller than ± 5%. During the experiments, bed topography was systematically recorded. Then, the flow was stopped, the water was slowly drained and the bed was carefully fixed with a cement and vernix coat and allowed to dry to guarantee that it remained stable from there on, while the clear water (free of sand) discharges were fed again to the fixed bed converging channels. A 3D side looking Acoustic Doppler Velocimeter (ADV), installed on a remotely controlled and precisely positioned (± 0.1 mm) robotic arm, was used to measure the instantaneous velocities at a very dense mesh. Once the velocities measured and recorded, the water surface levels were surveyed. For the case with more dominant tributary flow (Qr = 0.17), as expected, the scour hole formed at the tributary mouth is much deeper and larger and extends towards the outer bank of the post-confluence channel, as well as upstream the junction corner. The avalanche slopes are, consequently, steeper. On the other hand, for the case with a weaker tributary flow (Qr = 0.08), no erosion is observed immediately upstream the junction. Moreover, the bank-attached sediment bar downstream the junction is considerably more developed in longitudinal and vertical directions. In both scenarios, a strong horizontal vortical structure was observed immediately downstream the junction. More detailed analysis of the origin and the characteristics of these and other flow patterns is still under investigation. Acknowledgements This research as partially supported by Portuguese and European funds, within programs COMPETE2020 and PORL-FEDER, through project PTDC/ECM-HID/6387/2014 granted by the National Foundation for Science and Technology (FCT).

Experimental study on unsteady open channel flow and bedload transport based on a physical model

NASA Astrophysics Data System (ADS)

Cao, W.

2015-12-01

Flow in a nature river are usually unsteady, while nearly all the theories about bedload transport are on the basis of steady, uniform flow, and also with supposed equilibrium state of sediment transport. This is may be one of the main reasons why the bedload transport formulas are notoriously poor accuracy to predict the bedload. The aim of this research is to shed light on the effect of unsteadiness on the bedload transport based on experimental studies. The novel of this study is that the experiments were not carried out in a conventional flume but in a physical model, which are more similar to the actual river. On the other hand, in our experiments, multiple consecutive flood wave were reproduced in the physical model, and all the flow and sediment parameters are based on a large number of data obtained from many of identical flood waves. This method allow us to get more data for one flood, efficiently avoids the uncertainty of bedload rate only for one single flood wave, due to the stochastic fluctuation of the bedload transport. Three different flood waves were selected in the experiments. During each run of experiment, the water level of five different positions along the model were measured by ultrasonic water level gauge, flow velocity at the middle of the channel were measured by two dimensional electromagnetic current meter. Moreover, the bedload transport rate was measured by a unique automatic trap collecting and weighing system at the end of the physical model. The results shows that the celerity of flood wave propagate varies for different flow conditions. The velocity distribution was approximately accord with log-law profile during the entire rising and falling limb of flood. The bedload transport rate show intensity fluctuation in all the experiments, moreover, for different flood waves, the moment when the shear stress reaches its maximum value is not the exact moment when the sediment transport rate reaches its maximum value, which indicates that the movement of flow and the sediment are not always synchronous during the flood processes. Comparing the bedload transport rate with the existing results of steady flows shows that the bedload transport capacity in unsteady flow is greater than that of the steady flow with same bed shear stresses. (Supported by KPNST(2013BAB12B01; 2012BAB04B01) and NSFC(11472310))

Passive sampling methods for contaminated sediments: State of the science for organic contaminants

PubMed Central

Lydy, Michael J; Landrum, Peter F; Oen, Amy MP; Allinson, Mayumi; Smedes, Foppe; Harwood, Amanda D; Li, Huizhen; Maruya, Keith A; Liu, Jingfu

2014-01-01

This manuscript surveys the literature on passive sampler methods (PSMs) used in contaminated sediments to assess the chemical activity of organic contaminants. The chemical activity in turn dictates the reactivity and bioavailability of contaminants in sediment. Approaches to measure specific binding of compounds to sediment components, for example, amorphous carbon or specific types of reduced carbon, and the associated partition coefficients are difficult to determine, particularly for native sediment. Thus, the development of PSMs that represent the chemical activity of complex compound–sediment interactions, expressed as the freely dissolved contaminant concentration in porewater (Cfree), offer a better proxy for endpoints of concern, such as reactivity, bioaccumulation, and toxicity. Passive sampling methods have estimated Cfree using both kinetic and equilibrium operating modes and used various polymers as the sorbing phase, for example, polydimethylsiloxane, polyethylene, and polyoxymethylene in various configurations, such as sheets, coated fibers, or vials containing thin films. These PSMs have been applied in laboratory exposures and field deployments covering a variety of spatial and temporal scales. A wide range of calibration conditions exist in the literature to estimate Cfree, but consensus values have not been established. The most critical criteria are the partition coefficient between water and the polymer phase and the equilibrium status of the sampler. In addition, the PSM must not appreciably deplete Cfree in the porewater. Some of the future challenges include establishing a standard approach for PSM measurements, correcting for nonequilibrium conditions, establishing guidance for selection and implementation of PSMs, and translating and applying data collected by PSMs. Integr Environ Assess Manag 2014;10:167–178. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC. PMID:24307344

Effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene.

PubMed

Wang, Peng; Hua, Zulin; Cai, Yunjie; Shen, Xia; Li, Qiongqiong; Liu, Xiaoyuan

2015-08-01

The sorption behaviors of pollutants affected by hydrodynamic conditions were confirmed in natural water environment. The effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene were investigated. The particle entrainment simulator (PES) was used to simulate varied bottom shear stresses. The batch equilibrium method was applied to the experiments with the stress levels and the action time controlled at 0.2-0.5 N/m(2) and 24 h, respectively. The findings indicated that apparent partition coefficient of aniline on sediment increased with the shear stress significantly, while decreased with nitrobenzene concentration. On the contrary, both the sorption amount of aniline on suspended particulate matter (Q s) and the effect of nitrobenzene concentration on Q s declined as the shear stress increased. The sorption kinetic results showed that the sorption process followed the pseudo-second-order kinetics equation, and the process included two stages: fast sorption stage and slow sorption stage, among which the average sorption rate of fast stage was 7.5-9.5 times that of slow one. The effect of shear stress on the average sorption rate of aniline was enhanced with the increase of nitrobenzene concentration. And shear stress weakened the disturbance of cosolute on main solute sorption process. In addition, experiment results of sorption kinetic show that only the initial sorption rate was affected by shear stress and cosolute concentration. In the first 5 min, shear stress had positive effects on the sorption rate. After that, the sorption rate barely changed with shear stress and cosolute concentration.

Degradation of rizazole in water-sediment systems.

PubMed

Zhang, Changpeng; Zhao, Hua; Ping, Lifeng; Cai, Xiaoming; Wu, Min; He, Hongmei; Zhang, Chunrong; Zhu, Yahong; Li, Zhen

2013-01-01

This study investigated the degradation of rizazole in water-sediment systems (West Lake system, WL; Beijing-Hangzhou Grand Canal system, BG) with two different types of sediments under aerobic and anaerobic conditions. The half-lives of rizazole in the WL water phase (14.59-15.13 d) were similar to those in the BG water phase (15.90-16.46 d). Within 3-7 d, the rizazole concentration in the sediments reached the maximum values, i.e., equilibrium. Rizazole dissipation was faster in the WL sediment phase with higher organic matter content (T(1/2) = 18.99-19.09 d) compared with the BG sediment phase (T(1/2) = 31.08-33.32 d). Rizazole degradation was slightly faster in the West Lake water-sediment system (WL system) (T(1/2) = 17.11-18.05 d) than in the Beijing-Hangzhou Grand Canal water-sediment system (BG system) (T(1/2) = 20.51-25.02 d). The aerobic degradation of rizazole was similar to its anaerobic degradation in the water-sediment system. The findings are useful to understand the behavior of pesticide in environment.

Mechanical analysis of statolith action in roots and rhizoids

NASA Astrophysics Data System (ADS)

Todd, Paul

1994-08-01

Published observations on the response times following gravistimulation (horizontal positioning) of Chara rhizoids and developing roots of vascular plants with normal and ``starchless'' amyloplasts were reviewed and compared. Statolith motion was found to be consistent with gravitational sedimentation opposed by elastic deformation of an intracellular material. The time required for a statolith to sediment to equilibrium was calculated on the basis of its buoyant density and compared with observed sedimentation times. In the examples chosen, the response time following gravistimulation (from horizontal positioning to the return of downward growth) could be related to the statolith sedimentation time. Such a relationship implies that the transduction step is rapid in comparison with the perception steo following gravistimulation of rhizoids and developing roots.

Mechanical analysis of statolith action in roots and rhizoids.

PubMed

Todd, P

1994-01-01

Published observations on the response times following gravistimulation (horizontal positioning) of Chara rhizoids and developing roots of vascular plants with normal and "starchless" amyloplasts were reviewed and compared. Statolith motion was found to be consistent with gravitational sedimentation opposed by elastic deformation of an intracellular material. The time required for a statolith to sediment to equilibrium was calculated on the basis of its buoyant density and compared with observed sedimentation times. In the examples chosen, the response time following gravistimulation (from horizontal positioning to the return of downward growth) could be related to the statolith sedimentation time. Such a relationship implies that the transduction step is rapid in comparison with the perception step following gravistimulation of rhizoids and developing roots.

Study on the sorption behaviour of estrone on marine sediments.

PubMed

Zhang, Jing; Yang, Gui-Peng; Li, Quan; Cao, Xiaoyan; Liu, Guangxing

2013-11-15

The sorption behaviour of estrone (E1) on marine sediments treated by different methods was systematically investigated. About 22 h was required for sorption equilibrium of E1. Sorption isotherms of E1 were well fitted with Freundlich model. The sorption behaviour of E1 on HCl-treatment and H2O-treatment sediments related significantly with the sediment organic carbon contents. Additionally, clay minerals and surface areas of sediments played dominant roles in the sorption of E1 on H2O2-treatment sediments. Some external factors which could affect sorption behaviour of E1 were also investigated. Our results showed that the sorption capacity of E1 on the sediments increased with the increasing concentrations of cationic surfactant cetyltrimethylammonium bromide (CTAB), nonionic surfactant polyoxyethylene (80) sorbitan esters (Tween 80) and salinity of seawater. In contrast, the sorption capacity of E1 decreased with the increasing concentration of anionic surfactant sodium dodecylbenzene sulfonate (SDBS), pH value and temperature of seawater. Copyright © 2013 Elsevier Ltd. All rights reserved.

Experimental observations of granular debris flows

NASA Astrophysics Data System (ADS)

Ghilardi, P.

2003-04-01

Various tests are run using two different laboratory flumes with rectangular cross section and transparent walls. The grains used in a single experiment have an almost constant grain sizes; mean diameter ranges from 5 mm to 20 mm. In each test various measurements are taken: hydrograms, velocity distribution near the transparent walls and on the free surface, average flow concentration. Concentration values are measured taking samples. Velocity distributions are obtained from movies recorded by high speed video cameras capable of 350 frames per second; flow rates and depth hydrograms are computed from the same velocity distributions. A gate is installed at the beginning of one of the flumes; this gate slides normally to the bed and opens very quickly, reproducing a dam-break. Several tests are run using this device, varying channel slope, sediment concentration, initial mixture thickness before the gate. Velocity distribution in the flume is almost constant from left to right, except for the flow sections near the front. The observed discharges and velocities are less than those given by a classic dam break formula, and depend on sediment concentration. The other flume is fed by a mixture with constant discharge and concentration, and is mainly used for measuring velocity distributions when the flow is uniform, with both rigid and granular bed, and to study erosion/deposition processes near debris flow dams or other mitigation devices. The equilibrium slope of the granular bed is very close to that given by the classical equilibrium formulas for debris flow. Different deposition processes are observed depending on mixture concentration and channel geometry.

Equilibrium Partitioning Sediment Guidelines (ESGs) for the ...

EPA Pesticide Factsheets

... PLC = partial life-cycle ... 5 ii mini iiiiiiiii iiiiiii mi 1 1 iii mini ii i B : - Benthic vs WQC i— w ~_ ~ _ o° _ -0 ° - - - ii mini iiiiiiiii iiiiiii iiiiiiiii mini ii 0.1 ... PhD thesis. ...

The equilibrium sedimentation of hyaluronic acid and of two synthetic polymers

PubMed Central

Nichol, L. W.; Ogston, A. G.; Preston, B. N.

1967-01-01

1. The method of equilibrium sedimentation has been investigated as an alternative to osmotic-pressure measurement for determining thermodynamic properties of polymer solutions at relatively high concentrations. 2. The simplifications that must be made in the theoretical treatment are discussed. 3. Measurements have been made on samples of polyethylene glycol, neutralized polymethacrylic acid and hyaluronic acid. With the first and third, values of the `non-ideality coefficients' have been obtained that agree with those obtained from osmotic measurements on the same materials. 4. Evidence has been obtained of the presence in hyaluronic acid preparations of a fraction that has either a lower degree of thermodynamic non-ideality or a higher density increment than the bulk of the sample. This fraction is not protein. ImagesFig. 3.Fig. 4.Fig. 5.Fig. 7.Fig. 8.Fig. 9.Fig. 11.Fig. 12.Fig. 13.Fig. 14. PMID:6029600

Analytical Model of Inlet Growth and Equilibrium Cross-Sectional Area

DTIC Science & Technology

2016-04-01

performance in a real-world setting. BACKGROUND: Long-term inlet stability in bar-built systems is determined by the tidal and wave forces that...across the node was limited due to convergence of the two incoming tidal waves . As such, the equivalent bay area was calculated using the midpoint as a...sediment transport is driven by tides and does not incorporate other forcing and associated sediment pathways. The ratio of wave to tidal energy is an

dSED: A database tool for modeling sediment early diagenesis

NASA Astrophysics Data System (ADS)

Katsev, S.; Rancourt, D. G.; L'Heureux, I.

2003-04-01

Sediment early diagenesis reaction transport models (RTMs) are becoming powerful tools in providing kinetic descriptions of the metal and nutrient diagenetic cycling in marine, lacustrine, estuarine, and other aquatic sediments, as well as of exchanges with the water column. Whereas there exist several good database/program combinations for thermodynamic equilibrium calculations in aqueous systems, at present there exist no database tools for classification and analysis of the kinetic data essential to RTM development. We present a database tool that is intended to serve as an online resource for information about chemical reactions, solid phase and solute reactants, sorption reactions, transport mechanisms, and kinetic and equilibrium parameters that are relevant to sediment diagenesis processes. The list of reactive substances includes but is not limited to organic matter, Fe and Mn oxides and oxyhydroxides, sulfides and sulfates, calcium, iron, and manganese carbonates, phosphorus-bearing minerals, and silicates. Aqueous phases include dissolved carbon dioxide, oxygen, methane, hydrogen sulfide, sulfate, nitrate, phosphate, some organic compounds, and dissolved metal species. A number of filters allow extracting information according to user-specified criteria, e.g., about a class of substances contributing to the cycling of iron. The database also includes bibliographic information about published diagenetic models and the reactions and processes that they consider. At the time of preparing this abstract, dSED contained 128 reactions and 12 pre-defined filters. dSED is maintained by the Lake Sediment Structure and Evolution (LSSE) group at the University of Ottawa (www.science.uottawa.ca/LSSE/dSED) and we invite input from the geochemical community.

The Piedmont landscape of Maryland: a new look at an old problem.

USGS Publications Warehouse

Costa, J.E.; Cleaves, E.T.

1984-01-01

Both equilibrium and episodic erosion features can be recognized in the modern landscape. An equilibrium condition is suggested by adjustment of first and second order streams to rock structure and lithology, entrenchment of some streams against gneiss domes, altitudinal zonation of rock types around gneiss domes, correlation of lithology with overburden thickness on uplands, etc. The long-term episodic character of erosion is suggested by clastic wedges on the adjacent Coastal Plain, an upland of low relief that truncates non-carbonate rocks of different lithologies, isovolumetric chemical weathering of alumino-silicate rocks, clastic deposition in marble valleys, and weathering profile truncation by modern drainage. The upland surface preserved in the eastern Piedmont developed by the Late Cretaceous. In the interval from the Late Cretaceous to the Late Miocene, low input of terrigenous sediments to the Coastal Plain, dominance of marine sedimentation, and spotty evidence of saprolite formation on crystalline rocks, suggest that the Maryland Piedmont was an area of low relief undergoing intense weathering. Incised valleys were formed during a cycle of erosion probably initiated in the Late Miocene and extensive colluvial sediments were deposited on hillslopes by periglacial processes during the Pleistocene.-after Authors

A centennial tribute to G.K. Gilbert's Hydraulic Mining Débris in the Sierra Nevada

NASA Astrophysics Data System (ADS)

James, L. A.; Phillips, J. D.; Lecce, S. A.

2017-10-01

G.K. Gilbert's (1917) classic monograph, Hydraulic-Mining Débris in the Sierra Nevada, is described and put into the context of modern geomorphic knowledge. The emphasis here is on large-scale applied fluvial geomorphology, but other key elements-e.g., coastal geomorphology-are also briefly covered. A brief synopsis outlines key elements of the monograph, followed by discussions of highly influential aspects including the integrated watershed perspective, the extreme example of anthropogenic sedimentation, computation of a quantitative, semidistributed sediment budget, and advent of sediment-wave theory. Although Gilbert did not address concepts of equilibrium and grade in much detail, the rivers of the northwestern Sierra Nevada were highly disrupted and thrown into a condition of nonequilibrium. Therefore, concepts of equilibrium and grade-for which Gilbert's early work is often cited-are discussed. Gilbert's work is put into the context of complex nonlinear dynamics in geomorphic systems and how these concepts can be used to interpret the nonequilibrium systems described by Gilbert. Broad, basin-scale studies were common in the period, but few were as quantitative and empirically rigorous or employed such a range of methodologies as PP105. None demonstrated such an extreme case of anthropogeomorphic change.

River discharge controlling a tidal delta: the interplay between monsoon input and tidal reworking in SW Bangladesh

NASA Astrophysics Data System (ADS)

Hale, R. P.; Goodbred, S. L., Jr.; Bain, R. L.; Wilson, C.; Best, J.; Reed, M. J.

2015-12-01

The Ganges-Brahmaputra-Meghna River system (GBM) is among the world's largest in terms of both annual water and sediment discharge. The subaerial delta (110,000 km2) is home to ~160 million people, in addition to the ecologically and economically critical Sundarbans National Forest (SNF). Recent sediment budgets suggest that ~15% of the 1 x 109 t yr-1 sediment load carried by the GBM is subsequently advected along shore and inland via tidal activity, to the otherwise-abandoned SW portion of the delta. A unit-scale estimate based on observed offshore suspended sediment concentrations (SSC) >1.0 g L-1 suggests that sufficient sediment is available in the system to maintain the elevation of the subaerial delta plain, even under current relative sea-level-rise rates. Recent work measuring sedimentation within SNF corroborates this finding, and understanding these sediment delivery dynamics will be critical for protecting the future of nearby regions that are heavily populated, but drastically altered by human activities. Cross-channel hydrodynamic surveys were conducted to estimate what fraction of the water (and sediment) is diverted from the major tidal channels toward the SNF interior. Measurements including profiles of velocity and SSC were collected on spring and neap tides during the dry and monsoon seasons, along transects bracketing major conduit channels into the SNF. During the dry season, we observe water flux at the southern end of the study area to be in approximate equilibrium regardless of tidal range, with SSC <0.3 g L-1 during neap tides, and <1.0 g L-1 during spring tides. North of the SNF conduit channels, we observe equilibrium water discharge and similarly low SSC during neap tides, but a modest ebb dominance and surface SSC >1.0 g L-1 during spring tides. This suggests the possibility of additional inputs of water and sediment from an adjacent tidal channel, as well as a potential source for the deposition observed on the Sundarbans platform during spring-tide flooding. Within channels in SNF, near-bed SSC increase by >5x from neap to spring tides, to a peak of ~1.0 g L-1. Sediment grab samples collected in a distributary channel show a moderate fining trend with distance from the major conduit, which has implications for the sedimentation rates observed on the tidal delta plain.

Interaction of Strontium-90 in Sediment and Porewater in a Stream Near Chernobyl

NASA Astrophysics Data System (ADS)

Freed, R.; Smith, L.; Bugai, D.

2002-12-01

We investigated the interaction of 90Sr in sediments and pore waters of wetlands and stream hyporheic zones at a stream near Chernobyl. A non-dimensional activity ratio was formulated, the ratio of 90Sr in the pore waters compared with exchangeable 90Sr in the sediment on a volume basis. The average activity ratio for the wetland and channel sediments was 0.028 +/- 0.005. The activity ratio decreased when the sediment and porewaters were not in equilibrium. The change in the activity ratio was documented during two observational periods in a wetland: initially during a time when groundwater was discharging to the wetland (snowmelt, 2000) and subsequently at a time of near-stagnant groundwater flow (late fall in 2001 after a dry three month period). In both the discharge and stagnant periods, the exchangeable 90Sr concentration in sediment increased with depth by a factor of five to a peak concentration at 10 cm. In contrast, the 90Sr concentration in porewater differed significantly in the two observational periods. During the groundwater discharge period, the porewater concentration was relatively constant over the 30 cm depth of observation (120 +/-12 Bq/L) and surface water concentrations were similar. During the near-stagnant period, the porewater concentration increased with depth from 20+/-2 Bq/L in surface waters to 400 +/-40 Bq/L at a depth of 10 cm. We hypothesize that during discharge periods, the porewaters in the wetland represent the 90Sr concentration of advecting groundwater while during stagnant periods, the porewaters represent the concentration of 90Sr in equilibrium with the sediment. This proposed explanation is supported using PHREEQC in a dual porosity mode. Using independent estimates of the model parameters, the concentration profiles could be successfully matched with the assumption of advective transport during the discharge period and diffusive transport of 90Sr during near-stagnant conditions.

Littoral transport in the surf zone elucidated by an Eulerian sediment tracer.

USGS Publications Warehouse

Duane, D.B.; James, W.R.

1980-01-01

An Eulerian, or time integration, sand tracer experiment was designed and carried out in the surf zone near Pt. Mugu, California on April 19, 1972. Data indicate that conditions of stationarity and finite boundaries required for proper application of Eulerian tracer theory exist for short time periods in the surf zone. Grain counts suggest time required for tracer sand to attain equilibrium concentration is on the order of 30-60 minutes. Grain counts also indicate transport (discharge) was strongly dependent upon grain size, with the maximum rate occurring in the size 2.5-2.75 phi, decreasing to both finer and coarser sizes. The measured instantaneous transport was at the annual rate of 2.4 x 106 m3/yr.- Authors

Sedimentation equilibrium and the generalized Archimedes' principle.

PubMed

Parola, Alberto; Buzzaccaro, Stefano; Secchi, Eleonora; Piazza, Roberto

2013-03-21

The buoyancy concept is critically re-examined for applications to dispersions of nano-particles, such as colloids, proteins, or macromolecules. It is shown that when the size of the buoyant particle is not too different (say, at most a factor of ten) from the size of the dispersed particles, new intriguing phenomena emerge, leading to the violation of the Archimedes' principle. The resulting buoyancy force depends not only on the volume of the particle and on the mass density of the dispersion, but also on the relative size of the particles, on their geometry, and on the interactions between the buoyant particle and the fluid. Explicit expressions for such a generalized Archimedes' principle are obtained and the results are tested against targeted experiments in colloidal dispersions.

Sedimentation equilibrium and the generalized Archimedes' principle

NASA Astrophysics Data System (ADS)

Parola, Alberto; Buzzaccaro, Stefano; Secchi, Eleonora; Piazza, Roberto

2013-03-01

The buoyancy concept is critically re-examined for applications to dispersions of nano-particles, such as colloids, proteins, or macromolecules. It is shown that when the size of the buoyant particle is not too different (say, at most a factor of ten) from the size of the dispersed particles, new intriguing phenomena emerge, leading to the violation of the Archimedes' principle. The resulting buoyancy force depends not only on the volume of the particle and on the mass density of the dispersion, but also on the relative size of the particles, on their geometry, and on the interactions between the buoyant particle and the fluid. Explicit expressions for such a generalized Archimedes' principle are obtained and the results are tested against targeted experiments in colloidal dispersions.

PAHs in the Great Barrier Reef Lagoon reach potentially toxic levels from coal port activities

NASA Astrophysics Data System (ADS)

Burns, Kathryn A.

2014-05-01

In view of the controversy over expanding the coastal coal ports bordering the Great Barrier Reef (GBR) Lagoon and the World Heritage Area, I re-evaluated the data published in Burns and Brinkman (2011). I used the US EPA procedures for the determination of Equilibrium Partitioning Sediment Benchmarks (ESBs) for the protection of benthic organisms (Hansen et al., 2003), and the new proposed ANZECC/ARMCANZ (2013) sediment quality guidelines (Simpson et al., 2013) and determined that the coastal sediments offshore from the Hay Point coal terminal and suspended sediments caught in sediment traps inshore and at the offshore coral reefs contained levels of PAHs that approach the estimates for toxicity to benthic and water column organisms. This result is discussed in relation to risks posed to the GBR ecosystem by the port practices and the imminent expansion of the Abbott Point, Hay Point and other coal terminals.

Laminar laboratory rivers

NASA Astrophysics Data System (ADS)

Seizilles, Grégoire; Devauchelle, Olivier; Lajeunesse, Éric; Métivier, François

2014-05-01

A viscous fluid flowing over fine plastic grains spontaneously channelizes into a few centimeters-wide river. After reaching its equilibrium shape, this stable laboratory flume is able to carry a steady load of sediments, like many alluvial rivers. When the sediment discharge vanishes, the river size, shape and slope fit the threshold theory proposed by Glover and Florey (1951), which assumes that the Shields parameter is critical on the channel bed. As the sediment discharge is increased, the river widens and flattens. Surprisingly, the aspect ratio of its cross section depends on the sediment discharge only, regardless of the water discharge. We propose a theoretical interpretation of these findings based on the balance between gravity, which pulls particles towards the center of the channel, and the diffusion of bedload particles, which pushes them away from areas of intense bedload.

Hydrologic data on channel adjustments, 1970 to 1975, on the Rio Grande downstream from Cochiti Dam, New Mexico before and after closure

USGS Publications Warehouse

Dewey, Jack D.; Roybal, F.E.; Funderburg, D.E.

1979-01-01

Cross-section channel profiles, sediment transport and hydrologic data have been observed and computed for a series of pre-dam and post-dam investigations from 1970 to 1975 at 37 cross sections established along a 59-mile study reach from Cochiti Dam to Isleta Diversion Dam, New Mexico. Cochiti Dam began impounding water in November 1973. Because the dam will trap virtually all of the sediment load originating upstream and water discharge will be controlled, it is expected that equilibrium values of channel width, depth, slope and sediment-transport capability in the existing main stem of the Rio Grande will change. Changes in cross sections with time and space and changes in size distribution of sediments are documented. (Woodard-USGS).

In Situ Immobilization of Selenium in Sediment

DOE Office of Scientific and Technical Information (OSTI.GOV)

Moore, Robert C.; Stewart, Thomas Austin

2014-09-01

This project focused on the use of a sorbent, carbonated apatite, to immobilize selenium in the environment. It is know that apatite will sorb selenium and based on the mechanism of sorption it is theorized that carbonated apatite will be more effective that pure apatite. Immobilization of selenium in the environment is through the use of a sorbent in a permeable reactive barrier (PRB). A PRB can be constructed by trenching and backfill with the sorbent or in the case of apatite as the sorbent formed in situ using the apatite forming solution of Moore (2003, 2004). There is verymore » little data on selenium sorption by carbonated apatite in the literature. Therefore, in this work, the basic sorptive properties of carbonated apatite were investigated. Carbonated apatite was synthesized by a precipitation method and characterized. Batch selenium kinetic and equilibrium experiments were performed. The results indicate the carbonated apatite contained 9.4% carbonate and uptake of selenium as selenite was rapid; 5 hours for complete uptake of selenium vs. more than 100 hours for pure hydroxyapatite reported in the literature. Additionally, the carbonated apatite exhibited significantly higher distribution coefficients in equilibrium experiments than pure apatite under similar experimental conditions. The next phase of this work will be to seek additional funds to continue the research with the goal of eventually demonstrating the technology in a field application.« less

Arsenic Attenuation By Oxidized Aquifer Sediments in Bangladesh

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stollenwerk, K.G.; Breit, G.N.; Welch, A.H.

2007-07-13

Recognition of arsenic (As) contamination of shallow fluvio-deltaic aquifers in the Bengal Basin has resulted in increasing exploitation of groundwater from deeper aquifers that generally contain low concentrations of dissolved As. Pumping-induced infiltration of high-As groundwater could eventually cause As concentrations in these aquifers to increase. This study investigates the adsorption capacity for As of sediment from a low-As aquifer near Dhaka, Bangladesh. A shallow, chemically-reducing aquifer at this site extends to a depth of 50 m and has maximum As concentrations in groundwater of 900 {micro}g/L. At depths greater than 50 m, geochemical conditions are more oxidizing and groundwatermore » has < 5 {micro}g/L As. There is no thick layer of clay at this site to inhibit vertical transport of groundwater. Arsenite [As(III)] is the dominant oxidation state in contaminated groundwater; however, data from laboratory batch experiments show that As(III) is oxidized to arsenate [As(V)] by manganese (Mn) minerals that are present in the oxidized sediment. Thus, the long-term viability of the deeper aquifers as a source of water supply is likely to depend on As(V) adsorption. The adsorption capacity of these sediments is a function of the oxidation state of As and the concentration of other solutes that compete for adsorption sites. Arsenite that was not oxidized did adsorb, but to a much lesser extent than As(V). Phosphate (P) caused a substantial decrease in As(V) adsorption. Increasing pH and concentrations of silica (Si) had lesser effects on As(V) adsorption. The effect of bicarbonate (HCO{sub 3}) on As(V) adsorption was negligible. Equilibrium constants for adsorption of As(V), As(III), P, Si, HCO3, and H were determined from the experimental data and a quantitative model developed. Oxidation of As(III) was modeled with a first-order rate constant. This model was used to successfully simulate As(V) adsorption in the presence of multiple competing solutes. Results from these experiments show that oxidized sediments have a substantial but limited capacity for removal of As from groundwater.« less

Arsenic attenuation by oxidized aquifer sediments in Bangladesh

USGS Publications Warehouse

Stollenwerk, K.G.; Breit, G.N.; Welch, A.H.; Yount, J.C.; Whitney, J.W.; Foster, A.L.; Uddin, M.N.; Majumder, R.K.; Ahmed, N.

2007-01-01

Recognition of arsenic (As) contamination of shallow fluvio-deltaic aquifers in the Bengal Basin has resulted in increasing exploitation of groundwater from deeper aquifers that generally contain low concentrations of dissolved As. Pumping-induced infiltration of high-As groundwater could eventually cause As concentrations in these aquifers to increase. This study investigates the adsorption capacity for As of sediment from a low-As aquifer near Dhaka, Bangladesh. A shallow, chemically-reducing aquifer at this site extends to a depth of 50??m and has maximum As concentrations in groundwater of 900????g/L. At depths greater than 50??m, geochemical conditions are more oxidizing and groundwater has < 5????g/L As. There is no thick layer of clay at this site to inhibit vertical transport of groundwater. Arsenite [As(III)] is the dominant oxidation state in contaminated groundwater; however, data from laboratory batch experiments show that As(III) is oxidized to arsenate [As(V)] by manganese (Mn) minerals that are present in the oxidized sediment. Thus, the long-term viability of the deeper aquifers as a source of water supply is likely to depend on As(V) adsorption. The adsorption capacity of these sediments is a function of the oxidation state of As and the concentration of other solutes that compete for adsorption sites. Arsenite that was not oxidized did adsorb, but to a much lesser extent than As(V). Phosphate (P) caused a substantial decrease in As(V) adsorption. Increasing pH and concentrations of silica (Si) had lesser effects on As(V) adsorption. The effect of bicarbonate (HCO3) on As(V) adsorption was negligible. Equilibrium constants for adsorption of As(V), As(III), P, Si, HCO3, and H were determined from the experimental data and a quantitative model developed. Oxidation of As(III) was modeled with a first-order rate constant. This model was used to successfully simulate As(V) adsorption in the presence of multiple competing solutes. Results from these experiments show that oxidized sediments have a substantial but limited capacity for removal of As from groundwater.

Evaluating the Relationship between Equilibrium Passive Sampler Uptake and Aquatic Organism Bioaccumulation.

EPA Science Inventory

For decades, biomonitoring organisms have been used to assess the bioavailability of hydrophobic organic contaminants (HOCs) at contaminated sediment Superfund sites across the country. Specific applications include evaluating remedy effectiveness and pre- and post-remediation l...

Emerging investigator series: development and application of polymeric electrospun nanofiber mats as equilibrium-passive sampler media for organic compounds.

PubMed

Qian, Jiajie; Jennings, Brandon; Cwiertny, David M; Martinez, Andres

2017-11-15

We fabricated a suite of polymeric electrospun nanofiber mats (ENMs) and investigated their performance as next-generation passive sampler media for environmental monitoring of organic compounds. Electrospinning of common polymers [e.g., polyacrylonitrile (PAN), polymethyl methacrylate (PMMA), and polystyrene (PS), among others] yielded ENMs with reproducible control of nanofiber diameters (from 50 to 340 nm). The ENM performance was investigated initially with model hydrophilic (aniline and nitrobenzene) and hydrophobic (selected PCB congeners and dioxin) compounds, generally revealing fast chemical uptake into all of these ENMs, which was well described by a one compartment, first-order kinetic model. Typical times to reach 90% equilibrium (t 90% ) were ≤7 days under mixing conditions for all the ENMs and <0.5 days for the best performing materials under static (i.e., no mixing) conditions. Collectively, these short equilibrium timescales suggest that ENMs may be used in the field as an equilibrium-passive sampler, at least for our model compounds. Equilibrium partitioning coefficients (K ENM-W , L kg -1 ) averaged 2 and 4.7 log units for the hydrophilic and hydrophobic analytes, respectively. PAN, PMMA and PS were prioritized for additional studies because they exhibited not only the greatest capacity for simultaneous uptake of the entire model suite (log K ENM-W ∼1.5-6.2), but also fast uptake. For these optimized ENMs, the rates of uptake into PAN and PMMA were limited by aqueous phase diffusion to the nanofiber surface, and the rate-determining step for PS was analyte specific. Sorption isotherms also revealed that the environmental application of these optimized ENMs would occur within the linear uptake regime. We examined the ENM performance for the measurement of pore water concentrations from spiked soil and freshwater sediments. Soil and sediment studies not only yielded reproducible pore water concentrations and comparable values to other passive sampler materials, but also provided practical insights into ENM stability and fouling in such systems. Furthermore, fast uptake for a suite of structurally diverse hydrophilic and moderately hydrophobic compounds was obtained for PAN and PS, with t 90% ranging from 0.01 to 4 days with mixing and K ENM-W values ranging from 1.3 to 3.2 log units. Our findings show promise for the development and use of ENMs as equilibrium-passive samplers for a range of organic pollutants across soil/sediment and water systems.

Landscape self organisation: Modelling Sediment trains

NASA Astrophysics Data System (ADS)

Schoorl, J. M.; Temme, A. J. A. M.; Veldkamp, A.

2012-04-01

Rivers tend to develop towards an equilibrium length profile, independently of exogenous factors. In general, although still under debate, this so-called self-organisation is assumed to be caused by simple feedbacks between sedimentation and erosion. Erosion correlates positively with gradient and discharge and sedimentation negatively. With the LAPSUS model, which was run for the catchment of the Sabinal, a small river in the South of Spain, this interplay of erosion and sedimentation results in sediment pulses (sequences of incision and sedimentation through time). These pulses are visualised in a short movie ( see http://www.youtube.com/watch?v=V5LDUMvYZxU). In this case the LAPSUS model run did not take climate, base level nor tectonics into account. Therefore, these pulses can be considered independent of them. Furthermore, different scenarios show that the existence of the pulses is independent of precipitation, erodibility and sedimentation rate, although they control the number and shape of the pulses. A fieldwork check showed the plausibility of the occurrence of these sediment pulses. We conclude that the pulses as modelled with LAPSUS are indeed the consequence of the feedbacks between erosion and sedimentation and are not depending on exogenous factors. Keywords: Landscape self-organisation, Erosion, Deposition, LAPSUS, Modelling

Estuarine Sediment Deposition during Wetland Restoration: A GIS and Remote Sensing Modeling Approach

NASA Technical Reports Server (NTRS)

Newcomer, Michelle; Kuss, Amber; Kentron, Tyler; Remar, Alex; Choksi, Vivek; Skiles, J. W.

2011-01-01

Restoration of the industrial salt flats in the San Francisco Bay, California is an ongoing wetland rehabilitation project. Remote sensing maps of suspended sediment concentration, and other GIS predictor variables were used to model sediment deposition within these recently restored ponds. Suspended sediment concentrations were calibrated to reflectance values from Landsat TM 5 and ASTER using three statistical techniques -- linear regression, multivariate regression, and an Artificial Neural Network (ANN), to map suspended sediment concentrations. Multivariate and ANN regressions using ASTER proved to be the most accurate methods, yielding r2 values of 0.88 and 0.87, respectively. Predictor variables such as sediment grain size and tidal frequency were used in the Marsh Sedimentation (MARSED) model for predicting deposition rates for three years. MARSED results for a fully restored pond show a root mean square deviation (RMSD) of 66.8 mm (<1) between modeled and field observations. This model was further applied to a pond breached in November 2010 and indicated that the recently breached pond will reach equilibrium levels after 60 months of tidal inundation.

Effect of organic matter on CO(2) hydrate phase equilibrium in phyllosilicate suspensions.

PubMed

Park, Taehyung; Kyung, Daeseung; Lee, Woojin

2014-06-17

In this study, we examined various CO2 hydrate phase equilibria under diverse, heterogeneous conditions, to provide basic knowledge for successful ocean CO2 sequestration in offshore marine sediments. We investigated the effect of geochemical factors on CO2 hydrate phase equilibrium. The three-phase (liquid-hydrate-vapor) equilibrium of CO2 hydrate in the presence of (i) organic matter (glycine, glucose, and urea), (ii) phyllosilicates [illite, kaolinite, and Na-montmorillonite (Na-MMT)], and (iii) mixtures of them was measured in the ranges of 274.5-277.0 K and 14-22 bar. Organic matter inhibited the phase equilibrium of CO2 hydrate by association with water molecules. The inhibition effect decreased in the order: urea < glycine < glucose. Illite and kaolinite (unexpandable clays) barely affected the CO2 hydrate phase equilibrium, while Na-MMT (expandable clay) affected the phase equilibrium because of its interlayer cations. The CO2 hydrate equilibrium conditions, in the illite and kaolinite suspensions with organic matter, were very similar to those in the aqueous organic matter solutions. However, the equilibrium condition in the Na-MMT suspension with organic matter changed because of reduction of its inhibition effect by intercalated organic matter associated with cations in the Na-MMT interlayer.

Origin of Slope Failure in the Ursa Region, Northern Gulf of Mexico

NASA Astrophysics Data System (ADS)

Stigall, J.; Dugan, B.

2008-12-01

We use one-dimensional fluid flow and stability models to predict the evolution of overpressure and stability conditions of IODP Expedition Sites U1322 and U1324 in the Ursa region, northern Gulf of Mexico. Simulations of homogenous mud deposited at 3 and 12 mm/yr for Sites U1322 and U1324, with permeability (k) on the order of 10-17m2 and bulk compressibility of .4 /MPa, predict overpressures up to .45MPa and 1MPa in shallow sediments (<200m below sea floor). With limit equilibrium calculations for an infinite slope, these overpressures equate to a factor of safety (FS) greater than 10 and 4.5 for a internal friction angle of 26° and a seafloor slope of 2°. This implies stability throughout the last 50,000 years. Seismic and core observations, however, document major slope failures that span the entire Ursa region. Permeability in this region is well constrained by laboratory experiments, so we investigate how pulsed (high-to-low) sedimentation rates could have created unstable conditions, FS <1. Models with periods of high sedimentation generate overpressure that create unstable conditions while maintaining the time-averaged sedimentation rates. Other factors which are not possible to simulate in one dimension, such as a complex basin geometry, also influence the conditions that caused the past failures. A two-dimensional model linking lateral flow between the sites with the interpreted geometry from seismic stratigraphy gives a better picture of the flow field and instability within the basin. Asymmetrical loading of permeable sediments could have created a lateral difference in pore pressures which would have driven lateral flow from Site U1324 to Site U1322 where overpressures are higher than our one-dimensional models suggest. We anticipate that two-dimensional models with transient sedimentation patterns will enhance our understanding of flow in marginally stable environments and triggers of slope failures in passive margin systems.

Morphodynamics: Rivers beyond steady state

NASA Astrophysics Data System (ADS)

Church, M.; Ferguson, R. I.

2015-04-01

The morphology of an alluvial river channel affects the movement of water and sediment along it, but in the longer run is shaped by those processes. This interplay has mostly been investigated empirically within the paradigm of Newtonian mechanics. In rivers, this has created an emphasis on equilibrium configurations with simple morphology and uniform steady flow. But transient adjustment, whether between equilibrium states or indefinitely, is to be expected in a world in which hydrology, sediment supply, and base level are not fixed. More fundamentally, water flows and all the phenomena that accompany them are inherently unsteady, and flows in natural channels are characteristically nonuniform. The morphodynamics of alluvial river channels is the striking consequence. In this paper, we develop the essential connection between the episodic nature of bed material transport and the production of river morphology, emphasizing the fundamental problems of sediment transport, the role of bar evolution in determining channel form, the role of riparian vegetation, and the wide range of time scales for change. As the key integrative exercise, we emphasize the importance of physics-based modeling of morphodynamics. We note consequences that can be of benefit to society if properly understood. These include the possibility to better be able to model how varying flows drive morphodynamic change, to understand the influence of the sediments themselves on morphodynamics, and to recognize the inherent necessity for rivers that transport bed material to deform laterally. We acknowledge pioneering contributions in WRR and elsewhere that have introduced some of these themes.

Estimation of apparent rate coefficients for radionuclides interacting with marine sediments from Novaya Zemlya.

PubMed

Børretzen, P; Salbu, B

2000-10-30

To assess the impact of radionuclides entering the marine environment from dumped nuclear waste, information on the physico-chemical forms of radionuclides and their mobility in seawater-sediment systems is essential. Due to interactions with sediment components, sediments may act as a sink, reducing the mobility of radionuclides in seawater. Due to remobilisation, however, contaminated sediments may also act as a potential source of radionuclides to the water phase. In the present work, time-dependent interactions of low molecular mass (LMM, i.e. species < 10 kDa) radionuclides with sediments from the Stepovogo Fjord, Novaya Zemlya and their influence on the distribution coefficients (Kd values) have been studied in tracer experiments using 109Cd2+ and 60Co2+ as gamma tracers. Sorption of the LMM tracers occurred rapidly and the estimated equilibrium Kd(eq)-values for 109Cd and 60Co were 500 and 20000 ml/g, respectively. Remobilisation of 109Cd and 60Co from contaminated sediment fractions as a function of contact time was studied using sequential extraction procedures. Due to redistribution, the reversibly bound fraction of the gamma tracers decreased with time, while the irreversibly (or slowly reversibly) associated fraction of the gamma tracers increased. Two different three-compartment models, one consecutive and one parallel, were applied to describe the time-dependent interaction of the LMM tracers with operationally defined reversible and irreversible (or slowly reversible) sediment fractions. The interactions between these fractions were described using first order differential equations. By fitting the models to the experimental data, apparent rate constants were obtained using numerical optimisation software. The model optimisations showed that the interactions of LMM 60Co were well described by the consecutive model, while the parallel model was more suitable to describe the interactions of LMM 109Cd with the sediments, when the squared sum of residuals were compared. The rate of sorption of the irreversibly (or slowly reversibly) associated fraction was greater than the rate of desorption of the reversibly bound fractions (i.e. k3 > k2) for both radionuclides. Thus, the Novaya Zemlya sediment are supposed to act as a sink for the radionuclides under oxic conditions, and transport to the water phase should mainly be attributed to resuspended particles.

Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska.

PubMed

Gulick, Sean P S; Jaeger, John M; Mix, Alan C; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L; Berbel, Glaucia B B; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Kioka, Arata; Konno, Susumu; LeVay, Leah J; März, Christian; Matsuzaki, Kenji M; McClymont, Erin L; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R; Ridgway, Kenneth D; Romero, Oscar E; Slagle, Angela L; Stoner, Joseph S; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D; Worthington, Lindsay L; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M

2015-12-08

Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼ 2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼ 100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale.

Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

PubMed Central

Jaeger, John M.; Mix, Alan C.; Asahi, Hirofumi; Bahlburg, Heinrich; Belanger, Christina L.; Berbel, Glaucia B. B.; Childress, Laurel; Cowan, Ellen; Drab, Laureen; Forwick, Matthias; Fukumura, Akemi; Ge, Shulan; Gupta, Shyam; Konno, Susumu; LeVay, Leah J.; März, Christian; McClymont, Erin L.; Moy, Chris; Müller, Juliane; Nakamura, Atsunori; Ojima, Takanori; Ribeiro, Fabiana R.; Ridgway, Kenneth D.; Romero, Oscar E.; Slagle, Angela L.; Stoner, Joseph S.; St-Onge, Guillaume; Suto, Itsuki; Walczak, Maureen D.; Worthington, Lindsay L.; Bailey, Ian; Enkelmann, Eva; Reece, Robert; Swartz, John M.

2015-01-01

Erosion, sediment production, and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of the Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 My, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes show that erosion accelerated in response to Northern Hemisphere glacial intensification (∼2.7 Ma) and that the 900-km-long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8–1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (∼100-ky) glacial cycles in the mid-Pleistocene climate transition (1.2–0.7 Ma). Since then, erosion and transport of material out of the orogen has outpaced tectonic influx by 50–80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2-My mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the timescale of orogenic wedge response (millions of years). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and of the possible influence of climate-driven erosive processes that diverge from equilibrium on the million-year scale. PMID:26598689

Decadal to Millennial Sedimentation Patterns of the Hudson River Estuary

NASA Astrophysics Data System (ADS)

Jones, M.; McHugh, C. M.; Burckle, L.; Pekar, S.; Pereira, G.; Ryan, W. B.; Bell, R.; Carbotte, S.

2002-12-01

The Hudson River Estuary (HRE) is adjacent to large metropolitan areas including New York City. Understanding the variable energy conditions for transporting sediments is key to deal with environmental pollution such as the controversial burial and dredging of PCB's in the HRE. We studied sediment transport in the HRE by examining more than 150 cores and grab samples interpreted within the framework of acoustic images. The HRE sedimentary environments were defined based on quantitative estimates of grain size, sedimentary structures, bioturbation, and sedimentation rates and were divided into: channel, channel banks, subtidal flats, tributaries, and islands. Diatom assemblages were used to determine the extent of salt-water intrusion and sediment reworking in the estuary. Along a longitudinal profile, the estuary can be subdivided into: (1) sandy inner fluvial (furthest upstream), (2) muddy central portions, and (3) sandy outer marine. We classified sedimentary facies for the central and fluvial parts of the system (1 and 2). The HRE basin is nearly filled with sediment and tidal energy is focused within the channel and its banks. In the central basin where the estuary is wide (up to 4 km), flood currents are more energetic along the eastern channel bank and the ebb currents lead to minor sediment deposition on the western bank, but only where the system is out of equilibrium with its sediment load. The energy of the tides is accentuated along narrow segments of the estuary that are locally constrained by gorges of the Hudson Valley Highlands leading to erosion and the trapping of sediments. Beyond the banks of the channel, the subtidal flats that were filled with sediment by 0.5 to 3ka, are tranquil environments where the sediment is homogenized by bioturbation and reworked by waves as the estuary shallowed. Occasional high-energy events, (possibly flood-related) eroded the subtidal flats sediment as shown by rare rip-up clasts found in the cores. The inner fluvial part of the estuary is filling with sediments above sea-level forming islands. Here, the energy of tidal currents is strong as evidenced by the sand-mud rhythmic alternations of the sediments. Tributaries contribute a generally low sediment budget, but only on a seasonal basis and the fluvial energy is not strong enough to transport the gravel-size components that remain near the mouths of the tributaries forming localized deltas. The fluvial sands, form waves that migrate along the channel floor, but this coarser-grained bedload is rarely transported south of Kingston, New York, resulting in a muddy estuarine bottom further downstream. Results show that tidal energy is a dominant force in the transport and deposition of HRE sediments and that only fine-grained sediments are transported throughout most of the studied areas. Because the HRE basin is nearly filled, most sediment bypasses the system with only localized areas of sediment trapping where the estuary is out of equilibrium with its sediment load, and in the estuarine turbidity maxima, an area previously shown to contain high sediment concentrations.

Electrostatic and hydrodynamics effects in a sedimented magnetorheological suspension.

PubMed

Domínguez-García, P; Pastor, J M; Melle, Sonia; Rubio, Miguel A

2009-08-01

We present experimental results on the equilibrium microstructure of a sedimented magnetorheological suspension, namely, an aqueous suspension of micron-sized superparamagnetic particles. We develop a study of the electrical interactions on the suspension by processing video-microscopy images of the sedimented particles. We calculate the pair distribution function, g(r), which yields the electrostatic pair potential u(r), showing an anomalous attractive interaction for distances on the order of twice the particle diameter, with characteristic parameters whose values show a dependence with the two-dimensional concentration of particles. The repulsive body of the potential is adjusted to a DLVO expression in order to calculate the Debye screening length and the effective surface charge density. Influence of confinement and variations on the Boltzmann sedimentation profile because of the electrostatic interactions appear to be essential for the interpretation of experimental results.

Effects of nutrient loading on the carbon balance of coastal wetland sediments

USGS Publications Warehouse

Morris, J.T.; Bradley, P.M.

1999-01-01

Results of a 12-yr study in an oligotrophic South Carolina salt marsh demonstrate that soil respiration increased by 795 g C m-2 yr-1 and that carbon inventories decreased in sediments fertilized with nitrogen and phosphorus. Fertilized plots became net sources of carbon to the atmosphere, and sediment respiration continues in these plots at an accelerated pace. After 12 yr of treatment, soil macroorganic matter in the top 5 cm of sediment was 475 g C m-2 lower in fertilized plots than in controls, which is equivalent to a constant loss rate of 40 g C m-2 yr-1. It is not known whether soil carbon in fertilized plots has reached a new equilibrium or continues to decline. The increase in soil respiration in the fertilized plots was far greater than the loss of sediment organic matter, which indicates that the increase in soil respiration was largely due to an increase in primary production. Sediment respiration in laboratory incubations also demonstrated positive effects of nutrients. Thus, the results indicate that increased nutrient loading of oligotrophic wetlands can lead to an increased rate of sediment carbon turnover and a net loss of carbon from sediments.

Evaluation of toxicity to the amphipod, Hyalella azteca, and to the midge, Chironomus dilutus; and bioaccumulation by the oligochaete, Lumbriculus variegatus, with exposure to PCB-contaminated sediments from Anniston, Alabama

USGS Publications Warehouse

Ingersoll, Christopher G.; Steevens, Jeffery A.; MacDonald, Donald D.; Brumbaugh, William G.; Coady, Matthew R.; Farrar, J. Daniel; Lotufo, Guilherme R.; Kemble, Nile E.; Kunz, James L.; Stanley, Jacob K.; Sinclair, Jesse A.; Ingersoll, Christopher G.; Steevens, Jeffery A.; MacDonald, Donald D.

2014-01-01

The U.S. Environmental Protection Agency (USEPA) requested that as part of the remedial investigation for the Anniston, Alabama Polychlorinated Biphenyl (PCB) Site (Anniston PCB Site), that Pharmacia Corporation and Solutia Inc. (P/S) perform long-term reproduction toxicity tests with the amphipod, Hyalella azteca, and the midge, Chironomus dilutus, and bioaccumulation tests with the oligochaete, Lumbriculus variegatus, using sediment samples collected from reference locations and from Operable Unit 4 of the Anniston PCB Site. The sediment toxicity testing and sediment bioaccumulation results will be used by ARCADIS U.S., Inc. (ARCADIS) as part of a weight-of-evidence assessment to evaluate risks and establish sediment remediation goals for contaminants to sediment-dwelling organisms inhabiting the Anniston PCB Site. The goal of this study was to characterize relations between sediment chemistry and sediment toxicity and relations between sediment chemistry and sediment bioaccumulation in samples of sediments collected from the Anniston PCB Site. A total of 32 samples were evaluated from six test sites and one reference site to provide a wide range in concentrations of chemicals of potential concern (COPCs) including PCBs in samples of whole sediment. The goal of this study was not to determine the extent of sediment contamination across the Anniston PCB Site. Hence, the test sites or samples collected from within a test site were not selected to represent the spatial extent of sediment contamination across the Anniston PCB Site. Sediment chemistry, pore-water chemistry, and sediment toxicity data were generated for 26 sediment samples from the Anniston PCB Site. All of the samples were evaluated to determine if they qualified as reference sediment samples. Those samples that met the chemical selection criteria and biological selection criteria were identified as reference samples and used to develop the reference envelope for each toxicity test endpoint. Physical characterization of samples of whole sediment included analyses of grain size, TOC, and nutrients. Organic chemical characterization of samples of whole sediment included PCB homologs and select (13) PCB congeners, parent and alkylated polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, and polychlorinated dibenzo-p-dioxins; and dibenzofurans. The PCB aroclors analyzed included 1016, 1221, 1232, 1242, 1248, 1254, 1260, 1262 and 1268. Analyses of whole sediment also included total metals, simultaneously extracted metals, and acid volatile sulfide. Chemical characterization of samples of pore water isolated from samples of whole sediment at the start of the sediment toxicity exposures or at the start of the sediment bioaccumulation exposures included metals, major cations, major anions, dissolved organic carbon, and additional water-quality characteristics. Concentrations of metals or PCBs in pore water during the sediment toxicity exposures or during sediment bioaccumulation exposures also were determined using peeper samples (for metals) or solid-phase microextraction (SPME) samplers (for PCBs). The bioavailability and bioaccumulation of PCBs in 14 sediment samples were investigated using SPME passive samplers and the 28-d L. variegatus whole-sediment bioaccumulation exposures In general the accumulation of PCBs consistently was predicted through the use of organic carbon normalization and equilibrium partitioning. In these sediments, PCB homologs were accumulated differently based on bioavailability and potential to accumulate in oligochaetes. As part of this assessment homolog specific biota sediment accumulation factor values were developed that could be applied across the larger site to predict tissue levels of PCBs. The whole-sediment toxicity tests done with H. azteca and C. dilutus met the established ASTM and USEPA test acceptability criteria. The most responsive H. azteca endpoints were day 42 survival normalized young per female and day 28 biomass and that the most responsive C. dilutus endpoints were adult biomass and percent adult emergence. Overall, between the two species, the most responsive endpoint assessed for these two species was H. azteca survival-normalized young per female (67 percent of the samples classified as toxic). Concentration-response models (CRMs) and site-specific sediment toxicity thresholds (TTs) were generated with matching sediment chemistry and sediment toxicity data. Sediment chemistry, pore-water chemistry, and sediment toxicity data were evaluated for as many as 26 sediment samples from the Anniston PCB Site. The reference-envelope approach was used to identify the sediment samples that were toxic to benthic invertebrates. This procedure involved identification of reference sediment samples, normalizing the toxicity data to reflect control responses, developing a reference envelope for each toxicity test endpoint, and designating each sediment sample as toxic or not toxic for each toxicity test endpoint, for each species, and for all species combined. These results demonstrated percent emergence of adult C. dilutus, biomass of adult C. dilutus, and reproduction of H. azteca normalized to percent survival were among the most responsive endpoints that were evaluated. Therefore, these endpoints were selected for CRM development. The site-specific TTs for whole sediment provide a reliable basis for identifying toxic and not toxic sediment samples in the Anniston PCB Site (that is, for correctly classifying the sediment samples used to derive the TTs as toxic or not toxic, for the endpoint used to derive the TTs). Among the 69 TTs for sediment, the TTLRs for total PCB homologs [499 to 1,870 micrograms per kilogram dry weight (μg/kg DW)] and for lead [(9.48 to 10.3 milligrams per kilogram (mg/kg) DW] based on reproduction of H. azteca or based on emergence or biomass of adult C. dilutus, were the most reliable. Such TTs had low rates of false negative errors (that is, only 0 to 11 percent of the samples below the TT were toxic to benthic invertebrates), low rates of false positive errors (only 0 to 6 percent of the samples greater than the TT were not toxic to benthic invertebrates), and high rates of correct classification (that is, 92 to 96 percent). The site-specific TTs for PCBs and other COPCs derived in this study also were compared to empirically based sediment quality guidelines (SQGs), to equilibrium-partitioning based SQGs, and to the results of spiked-sediment toxicity tests. The results of this evaluation indicated that the site-specific sediment TTs for PCBs were comparable to the consensus-based SQGs that were derived for PCBs. In addition, the site-specific sediment TTs for PCBs are well within the range of SQGs derived using the equilibrium partitioning approach. The site-specific sediment TTs for PCBs also are consistent with the results of chronic TTs that have been estimated for benthic invertebrates using the results of spiked-sediment toxicity tests. As the site-specific sediment TTs for PCBs are consistent with empirically based SQGs, equilibrium-partitioning based SQGs, and results of sediment-spiking studies, these site- specific sediment TTs likely represent the concentrations of PCBs that are sufficient to cause toxicity to benthic invertebrates (as opposed to simply being correlated with adverse effects on the survival, weight, or reproduction of benthic invertebrates). Importantly, such site-specific sediment TTs have been demonstrated to accurately classify sediment samples as toxic or not toxic to benthic invertebrates at the Anniston PCB Site. In contrast, the TTs for metals, PAHs, and organochlorine pesticides were generally lower than consensus-based SQGs (that is, probable effect concentrations), and LC50s (median lethal effect concentrations) generated in spiked-sediment toxicity tests, indicating that these COPCs are likely not the main contributors to the observed toxicity of the site sediments evaluated in this study. The reproduction endpoint for H. azteca provided lower TTs compared to the day 28 biomass endpoint for H. azteca and the emergence or biomass endpoints for adult C. dilutus provided lower TTs compared to the day 13 biomass endpoint for C. dilutus.

Watershed safety and quality control by safety threshold method

NASA Astrophysics Data System (ADS)

Da-Wei Tsai, David; Mengjung Chou, Caroline; Ramaraj, Rameshprabu; Liu, Wen-Cheng; Honglay Chen, Paris

2014-05-01

Taiwan was warned as one of the most dangerous countries by IPCC and the World Bank. In such an exceptional and perilous island, we would like to launch the strategic research of land-use management on the catastrophe prevention and environmental protection. This study used the watershed management by "Safety Threshold Method" to restore and to prevent the disasters and pollution on island. For the deluge prevention, this study applied the restoration strategy to reduce total runoff which was equilibrium to 59.4% of the infiltration each year. For the sediment management, safety threshold management could reduce the sediment below the equilibrium of the natural sediment cycle. In the water quality issues, the best strategies exhibited the significant total load reductions of 10% in carbon (BOD5), 15% in nitrogen (nitrate) and 9% in phosphorus (TP). We found out the water quality could meet the BOD target by the 50% peak reduction with management. All the simulations demonstrated the safety threshold method was helpful to control the loadings within the safe range of disasters and environmental quality. Moreover, from the historical data of whole island, the past deforestation policy and the mistake economic projects were the prime culprits. Consequently, this study showed a practical method to manage both the disasters and pollution in a watershed scale by the land-use management.

Modeling tidal marsh distribution with sea-level rise: evaluating the role of vegetation, sediment, and upland habitat in marsh resiliency.

PubMed

Schile, Lisa M; Callaway, John C; Morris, James T; Stralberg, Diana; Parker, V Thomas; Kelly, Maggi

2014-01-01

Tidal marshes maintain elevation relative to sea level through accumulation of mineral and organic matter, yet this dynamic accumulation feedback mechanism has not been modeled widely in the context of accelerated sea-level rise. Uncertainties exist about tidal marsh resiliency to accelerated sea-level rise, reduced sediment supply, reduced plant productivity under increased inundation, and limited upland habitat for marsh migration. We examined marsh resiliency under these uncertainties using the Marsh Equilibrium Model, a mechanistic, elevation-based soil cohort model, using a rich data set of plant productivity and physical properties from sites across the estuarine salinity gradient. Four tidal marshes were chosen along this gradient: two islands and two with adjacent uplands. Varying century sea-level rise (52, 100, 165, 180 cm) and suspended sediment concentrations (100%, 50%, and 25% of current concentrations), we simulated marsh accretion across vegetated elevations for 100 years, applying the results to high spatial resolution digital elevation models to quantify potential changes in marsh distributions. At low rates of sea-level rise and mid-high sediment concentrations, all marshes maintained vegetated elevations indicative of mid/high marsh habitat. With century sea-level rise at 100 and 165 cm, marshes shifted to low marsh elevations; mid/high marsh elevations were found only in former uplands. At the highest century sea-level rise and lowest sediment concentrations, the island marshes became dominated by mudflat elevations. Under the same sediment concentrations, low salinity brackish marshes containing highly productive vegetation had slower elevation loss compared to more saline sites with lower productivity. A similar trend was documented when comparing against a marsh accretion model that did not model vegetation feedbacks. Elevation predictions using the Marsh Equilibrium Model highlight the importance of including vegetation responses to sea-level rise. These results also emphasize the importance of adjacent uplands for long-term marsh survival and incorporating such areas in conservation planning efforts.

Turbulent coagulation of particles smaller than the length scales of turbulence and equilibrium sorption of phenanthrene to clay: Implications for pollutant transport in the estuarine water column

NASA Astrophysics Data System (ADS)

Brunk, Brett Kenneth

1997-11-01

Pollutant and particle transport in estuaries is affected by a multitude of physical, chemical and biological processes. In this research the importance of equilibrium sorption and turbulent coagulation were studied. Sorption in estuaries was modeled using phenanthrene, bacterial extracellular polymer and kaolinite clay as surrogates for a hydrophobic organic pollutant, dissolved organic matter and inorganic suspended sediment, respectively. Experiments over a range of estuarine salinities showed that ionic strength had the largest effect on the extent of sorption, while the effect of extracellular polymer coatings on the mineral surfaces was insignificant. Further calculations using typical estuarine suspended sediment concentrations indicated that equilibrium sorption could not fully account for the solid/solution phase distribution of hydrophobic organic compounds in the estuarine water column. For particles that are small compared to the length scales of turbulence, the rate of coagulation is related to the dynamics of the smallest turbulent eddies since they have the highest shear rate. Experimental and theoretical effort focused on determining the coagulation rate of spherical particles in isotropic turbulence. A pair diffusion approximation valid for rapidly fluctuating flows was used to calculate the rate of coagulation in a randomly varying isotropic linear flow field. Dynamic simulations of particle coagulation in Gaussian turbulence were computed over a range of representative values of particle-particle interactions (i.e, hydrodynamic interactions and van der Waals attraction) and total strain (i.e., the product of the strain rate and its time scale). The computed coagulation rates for isotropic turbulence differed from analytical approximations valid at large and small total strain. As expected, particle interactions were found to be significant. Experimental measurements of coagulation in grid-generated turbulence were obtained by measuring the loss of singlet particles from an initially monodisperse suspension as a function of turbulence intensity. Model predictions based on the particle Hamaker constant and spatial distribution of turbulence in the reactor agreed well with the experiments without the use of any fitting parameters. The close agreement of simulations and observations indicate the numerical model has successfully captured the relevant physics that governs the aggregation of colloidal particles in turbulent flows. This work is the first successful description of turbulent coagulation. Given the ubiquity of turbulent suspensions in engineered and natural systems, the ability to quantitatively describe particle behavior under these conditions is expected to have considerable utility.

Purification of biomaterials by phase partitioning

NASA Technical Reports Server (NTRS)

Harris, J. M.

1984-01-01

A technique which is particularly suited to microgravity environments and which is potentially more powerful than electrophoresis is phase partitioning. Phase partitioning is purification by partitioning between the two immiscible aqueous layers formed by solution of the polymers poly(ethylene glycol) and dextran in water. This technique proved to be very useful for separations in one-g but is limited for cells because the cells are more dense than the phase solutions thus tend to sediment to the bottom of the container before reaching equilibrium with the preferred phase. There are three phases to work in this area: synthesis of new polymers for affinity phase partitioning; development of automated apparatus for ground-based separations; and design of apparatus for performing simple phase partitioning space experiments, including examination of mechanisms for separating phases in the absence of gravity.

New polymers for low-gravity purification of cells by phase partitioning

NASA Technical Reports Server (NTRS)

Harris, J. M.

1983-01-01

A potentially powerful technique for separating different biological cell types is based on the partitioning of these cells between the immiscible aqueous phases formed by solution of certain polymers in water. This process is gravity-limited because cells sediment rather than associate with the phase most favored on the basis of cell-phase interactions. In the present contract we have been involved in the synthesis of new polymers both to aid in understanding the partitioning process and to improve the quality of separations. The prime driving force behind the design of these polymers is to produce materials which will aid in space experiments to separate important cell types and to study the partitioning process in the absence of gravity (i.e., in an equilibrium state).

The Equilibrium Constant for Bromothymol Blue: A General Chemistry Laboratory Experiment Using Spectroscopy

ERIC Educational Resources Information Center

Klotz, Elsbeth; Doyle, Robert; Gross, Erin; Mattson, Bruce

2011-01-01

A simple, inexpensive, and environmentally friendly undergraduate laboratory experiment is described in which students use visible spectroscopy to determine a numerical value for an equilibrium constant, K[subscript c]. The experiment correlates well with the lecture topic of equilibrium even though the subject of the study is an acid-base…

Resolved 12CH2D2 and 13CH3D in CH4 as Sensitive Indicators of Disequilibrium and Equilibrium during Microbial Methane Cycling

NASA Astrophysics Data System (ADS)

Ash, J. L.; Egger, M.; Slomp, C. P.; Kohl, I. E.; Treude, T.; Rumble, D.; Young, E. D.

2016-12-01

The ability to measure the relative concentrations of at least two doubly-substituted rare isotopologues of gases with biogeochemical relevance provides new constraints on sources and sinks of these gases. In particular, as shown recently for O2, the use of two independent, rare isotopologues allows for detection of thermodynamic intra-species equilibrium and disequilibrium. Here, we report the first measurements of fully resolved 13CH3D and 12CH2D2 from natural samples of microbial methane gas. A suite of sedimentary methane samples from the Bornholm Basin in the Baltic Sea was collected during IODP Exp. 347. Sample depths range from 2-20 meters below seafloor (mbsf). Methane concentrations decrease with depth, and mcrA (a marker for methanogenesis and methanotropy) is present throughout. See Figure. Both Δ13CH3D and Δ12CH2D2 increase with depth as methane concentrations decrease with the shallowest samples exhibiting disequilibrium by up to 2‰ in Δ13CH3D and 13‰ in Δ12CH2D2 while the deepest samples approach isotopic thermodynamic equilibrium (marked by grey bars in Figure). The Fe-mediated anaerobic oxidation of methane (Fe-AOM) has been inferred in these sediments by geochemical modeling . Slow methane cycling by methanogensis and methanotrophy is likely responsible for the approach to isotopic bond order equilibrium in CH4 with depth, consistent with Fe-AOM. While axenic culturing experiments generate methane with large deficits in 12CH2D2 (reported at this meeting), these data from the Baltic Sea demonstrate that isotopic equilibrium can be achieved during microbial recycling of methane. In the absence of Δ12CH2D2, the Δ13CH3D values alone could be misinterpreted as representing gradients in temperature due perhaps to exothermic organic matter degradation. The combination of both mass-18 rare isotopologues of methane provides the means to distinguish equilibrium from disequilibrium and probe microbial methane cycling even where Δ13CH3D suggests reasonable temperatures.

DESORPTION OF PYRETHROIDS FROM SUSPENDED SOLIDS

PubMed Central

Fojut, Tessa L.; Young, Thomas M.

2014-01-01

Pyrethroid insecticides have been widely detected in sediments at concentrations that can cause toxicity to aquatic organisms. Desorption rates play an important role in determining the bioavailability of hydrophobic organic compounds, such as pyrethroids, because these compounds are more likely to be sorbed to solids in the environment and times to reach sorptive equilibrium can be long. In this study, sequential Tenax desorption experiments were performed with three sorbents, three aging times, and four pyrethroids. A biphasic rate model was fit to the desorption data with r2 > 0.99 and the rapid and slow compartment desorption rate constants and compartment fractions are reported. Suspended solids from irrigation runoff water collected from a field that had been sprayed with permethrin one day prior were used in the experiments to compare desorption rates for field-applied pyrethroids to those for laboratory-spiked materials. Suspended solids were used in desorption experiments because suspended solids can be a key source of hydrophobic compounds to surface waters. The rapid desorption rate parameters of field-applied permethrin were not statistically different than those of laboratory spiked permethrin, indicating that the desorption of the spiked pyrethroids is comparable to those added and aged in the field. Sorbent characteristics had the greatest effect on desorption rate parameters; as organic carbon content of the solids increased, the rapid desorption fractions and rapid desorption rate constants both decreased. The desorption rate constant of the slow compartment for sediment containing permethrin aged for 28 d was significantly different from those aged 1 d and 7 d, while desorption in the rapid and slow compartments did not differ between these treatments. PMID:21538493

Evaluation and use of a diffusion-controlled sampler for determining chemical and dissolved oxygen gradients at the sediment-water interface

USGS Publications Warehouse

Simon, N.S.; Kennedy, M.M.; Massoni, C.S.

1985-01-01

Field and laboratory evaluations were made of a simple, inexpensive diffusion-controlled sampler with ports on two sides at each interval which incorporates 0.2-??m polycarbonate membrane to filter samples in situ. Monovalent and divalent ions reached 90% of equilibrium between sampler contents and the external solution within 3 and 6 hours, respectively. Sediment interstitial water chemical gradients to depths of tens of centimeters were obtained within several days after placement. Gradients were consistent with those determined from interstitial water obtained by centrifugation of adjacent sediment. Ten milliliter sample volumes were collected at 1-cm intervals to determine chemical gradients and dissolved oxygen profiles at depth and at the interface between the sediment and water column. The flux of dissolved species, including oxygen, across the sediment-water interface can be assessed more accurately using this sampler than by using data collected from benthic cores. ?? 1985 Dr W. Junk Publishers.

A general mixture model and its application to coastal sandbar migration simulation

NASA Astrophysics Data System (ADS)

Liang, Lixin; Yu, Xiping

2017-04-01

A mixture model for general description of sediment laden flows is developed and then applied to coastal sandbar migration simulation. Firstly the mixture model is derived based on the Eulerian-Eulerian approach of the complete two-phase flow theory. The basic equations of the model include the mass and momentum conservation equations for the water-sediment mixture and the continuity equation for sediment concentration. The turbulent motion of the mixture is formulated for the fluid and the particles respectively. A modified k-ɛ model is used to describe the fluid turbulence while an algebraic model is adopted for the particles. A general formulation for the relative velocity between the two phases in sediment laden flows, which is derived by manipulating the momentum equations of the enhanced two-phase flow model, is incorporated into the mixture model. A finite difference method based on SMAC scheme is utilized for numerical solutions. The model is validated by suspended sediment motion in steady open channel flows, both in equilibrium and non-equilibrium state, and in oscillatory flows as well. The computed sediment concentrations, horizontal velocity and turbulence kinetic energy of the mixture are all shown to be in good agreement with experimental data. The mixture model is then applied to the study of sediment suspension and sandbar migration in surf zones under a vertical 2D framework. The VOF method for the description of water-air free surface and topography reaction model is coupled. The bed load transport rate and suspended load entrainment rate are all decided by the sea bed shear stress, which is obtained from the boundary layer resolved mixture model. The simulation results indicated that, under small amplitude regular waves, erosion occurred on the sandbar slope against the wave propagation direction, while deposition dominated on the slope towards wave propagation, indicating an onshore migration tendency. The computation results also shows that the suspended load will also make great contributions to the topography change in the surf zone, which is usually neglected in some previous researches.

PEaCH4 v.2.0: A modelling platform to predict early diagenetic processes in marine sediments with a focus on biogenic methane - Case study: Offshore Namibia

NASA Astrophysics Data System (ADS)

Arning, Esther T.; Häußler, Steffen; van Berk, Wolfgang; Schulz, Hans-Martin

2016-07-01

The modelling of early diagenetic processes in marine sediments is of interest in marine science, and in the oil and gas industry, here, especially with respect to methane occurrence and gas hydrate formation as resources. Early diagenesis in marine sediments evolves from a complex web of intertwining (bio)geochemical reactions. It comprises microbially catalysed reactions and inorganic mineral-water-gas interactions. A model that will describe and consider all of these reactions has to be complex. However, it should be user-friendly, as well as to be applicable for a broad community and not only for experts in the field of marine chemistry. The presented modelling platform PeaCH4 v.2.0 combines both aspects, and is Microsoft Excel©-based. The modelling tool is PHREEQC (version 2), a computer programme for speciation, batch-reaction, one-dimensional transport, and inverse geochemical calculations. The conceptual PEaCH4 model is based on the conversion of sediment-bound degradable organic matter. PEaCH4 v.2.0 was developed to quantify and predict early diagenetic processes in marine sediments with the focus on biogenic methane formation and its phase behaviour, and allows carbon mass balancing. In regard to the irreversible degradation of organic matter, it comprises a "reaction model" and a "kinetic model" to predict methane formation. Both approaches differ in their calculations and outputs as the "kinetic model" considers the modelling time to integrate temperature dependent biogenic methane formation in its calculations, whereas the "reaction model" simply relies on default organic matter degradation. With regard to the inorganic mineral-water-gas interactions, which are triggered by irreversible degradation of organic matter, PEaCH4 v.2.0 is based on chemical equilibrium thermodynamics, appropriate mass-action laws, and their temperature dependent equilibrium constants. The programme is exemplarily presented with the example of upwelling sediments off Namibia, ODP Leg 175, Site 1082. The application demonstrates that the modelling platform PEaCH4 v.2.0 provides a user-friendly, but complex scientific tool that delivers retraceable information about early diagenetic processes and products in marine sediments.

Effect of adsorbed metals ions on the transport of Zn- and Ni-EDTA complexes in a sand and gravel aquifer

USGS Publications Warehouse

Kent, D.B.; Davis, J.A.; Anderson, L.C.D.; Rea, B.A.; Coston, J.A.

2002-01-01

Adsorption, complexation, and dissolution reactions strongly influenced the transport of metal ions complexed with ethylenediaminetetraacetic acid (EDTA) in a predominantly quartz-sand aquifer during two tracer tests conducted under mildly reducing conditions at pH 5.8 to 6.1. In tracer test M89, EDTA complexes of zinc (Zn) and nickel (Ni), along with excess free EDTA, were injected such that the lower portion of the tracer cloud traveled through a region with adsorbed manganese (Mn) and the upper portion of the tracer cloud traveled through a region with adsorbed Zn. In tracer test S89, Ni- and Zn-EDTA complexes, along with excess EDTA complexed with calcium (Ca), were injected into a region with adsorbed Mn. The only discernable chemical reaction between Ni-EDTA and the sediments was a small degree of reversible adsorption leading to minor retardation. In the absence of adsorbed Zn, the injected Zn was displaced from EDTA complexes by iron(III) [Fe(III)] dissolved from the sediments. Displacement of Zn by Fe(III) on EDTA became increasingly thermodynamically favorable with decreasing total EDTA concentration. The reaction was slow compared to the time-scale of transport. Free EDTA rapidly dissolved aluminum (Al) from the sediments, which was subsequently displaced slowly by Fe. In the portion of tracer cloud M89 that traveled through the region contaminated with adsorbed Zn, little displacement of Zn complexed with EDTA was observed, and Al was rapidly displaced from EDTA by Zn desorbed from the sediments, in agreement with equilibrium calculations. In tracer test S89, desorption of Mn dominated over the more thermodynamically favorable dissolution of Al oxyhydroxides. Comparison with results from M89 suggests that dissolution of Al oxyhydroxides in coatings on these sediment grains by Ca-EDTA was rate-limited whereas that by free EDTA reached equilibrium on the time-scale of transport. Rates of desorption are much faster than rates of dissolution of Fe oxyhydroxides from sediment-grain surfaces and, therefore, adsorbed metal ions can strongly influence the speciation of ligands like EDTA in soils and sediments, especially over small temporal and spatial scales. Copyright ?? 2002 Elsevier Science Ltd.

Vegetation ecogeomorphology, dynamic equilibrium, and disturbance: chapter 7

USGS Publications Warehouse

Hupp, Cliff R.

2013-01-01

Early ecologists understood the need to document geomorphic form and process to explain plant species distributions. Although this relationship has been acknowledged for over a century, with the exception of a few landmark papers, only the past few decades have experienced intensive research on this interdisciplinary topic. Here the authors provide a summary of the intimate relations between vegetation and geomorphic/process on hillslopes and fluvial systems. These relations are separated into systems (primarily fluvial) in dynamic equilibrium and those that are in nonequilibrium conditions including the impacts of various human disturbances affecting landforms, geomorphic processes, and interrelated, attendant vegetation patterns and processes. The authors conclude with a conceptual model of stream regime focusing on sediment deposition, erosion, and equilibrium that can be expanded to organize and predict vegetation patterns and life history strategies.

Turbidity Currents With Equilibrium Basal Driving Layers: A Mechanism for Long Runout

NASA Astrophysics Data System (ADS)

Luchi, R.; Balachandar, S.; Seminara, G.; Parker, G.

2018-02-01

Turbidity currents run out over 100 km in lakes and reservoirs, and over 1,000 km in the ocean. They do so without dissipating themselves via excess entrainment of ambient water. Existing layer-averaged formulations cannot capture this. We use a numerical model to describe the temporal evolution of a turbidity current toward steady state under condition of zero net sediment flux at the bed. The flow self-partitions itself into two layers. The lower "driving layer" approaches an invariant flow thickness, velocity profile, and suspended sediment concentration profile that sequesters nearly all of the suspended sediment. This layer can continue indefinitely at steady state over a constant bed slope. The upper "driven layer" contains a small fraction of the suspended sediment. The devolution of the flow into these two layers likely allows the driving layer to run out long distances.

Effect of Mantle Wedge Hybridization by Sediment Melt on Geochemistry of Arc Magma and Arc Mantle Source - Insights from Laboratory Experiments at High Pressures and Temperatures

NASA Astrophysics Data System (ADS)

Mallik, A.; Dasgupta, R.; Tsuno, K.; Nelson, J. M.

2015-12-01

Generation of arc magmas involves metasomatism of the mantle wedge by slab-derived H2O-rich fluids and/or melts and subsequent melting of the modified source. The chemistry of arc magmas and the residual mantle wedge are not only regulated by the chemistry of the slab input, but also by the phase relations of metasomatism or hybridization process in the wedge. The sediment-derived silica-rich fluids and hydrous partial melts create orthopyroxene-rich zones in the mantle wedge, due to reaction of mantle olivine with silica in the fluid/melt [1,2]. Geochemical evidence for such a reaction comes from pyroxenitic lithologies coexisting with peridotite in supra-subduction zones. In this study, we have simulated the partial melting of a parcel of mantle wedge modified by bulk addition of sediment-derived melt with variable H2O contents to investigate the major and trace element chemistry of the magmas and the residues formed by this process. Experiments at 2-3 GPa and 1150-1300 °C were conducted on mixtures of 25% sediment-derived melt and 75% lherzolite, with bulk H2O contents varying from 2 to 6 wt.%. Partial reactive crystallization of the rhyolitic slab-derived melt and partial melting of the mixed source produced a range of melt compositions from ultra-K basanites to basaltic andesites, in equilibrium with an orthopyroxene ± phlogopite ± clinopyroxene ± garnet bearing residue, depending on P and bulk H2O content. Model calculations using partition coefficients (from literature) of trace elements between experimental minerals and silicate melt suggest that the geochemical signatures of the slab-derived melt, such as low Ce/Pb and depletion in Nb and Ta (characteristic slab signatures) are not erased from the resulting melt owing to reactive crystallization. The residual mineral assemblage is also found to be similar to the supra-subduction zone lithologies, such as those found in Dabie Shan (China) and Sanbagawa Belt (Japan). In this presentation, we will also compare the major and trace element characteristics of bulk rock and minerals found in orthopyroxenites from supra-subduction zones with the residua formed in our experiments, to differentiate between melt versus fluid, and sediment- versus basalt-derived flux in the mantle wedge. [1] Mallik et al. (2015) CMP169(5) [2] Sekine & Wyllie (1982) CMP 81(3)

Trends in the sediment yield of the Sacramento River, California, 1957-2001

USGS Publications Warehouse

Wright, Scott A.; Schoellhamer, David H.

2004-01-01

Human activities within a watershed, such as agriculture, urbanization, and dam building, may affect the sediment yield from the watershed. Because the equilibrium geomorphic form of an estuary is dependent in part on the sediment supply from the watershed, anthropogenic activities within the watershed have the potential to affect estuary geomorphology. The Sacramento River drains the northern half of California’s Central Valley and is the primary source of sediment to San Francisco Bay. In this paper, it is shown that the delivery of suspended-sediment from the Sacramento River to San Francisco Bay has decreased by about one-half during the period 1957 to 2001. Many factors may be contributing to the trend in sediment yield, including the depletion of erodible sediment from hydraulic mining in the late 1800s, trapping of sediment in reservoirs, riverbank protection, altered land-uses (such as agriculture, grazing, urbanization, and logging), and levees. This finding has implications for planned tidal wetland restoration activities around San Francisco Bay, where an adequate sediment supply will be needed to build subsided areas to elevations typical of tidal wetlands as well as to keep pace with projected sea-level rise. In a broader context, the study underscores the need to address anthropogenic impacts on watershed sediment yield when considering actions such as restoration within downstream depositional areas.

POLANYI-BASED MODELS FOR THE COMPETITIVE SORPTION OF LOW-POLARITY ORGANIC CONTAMINANTS ON A NATURAL SORBENT. (R825406)

EPA Science Inventory

The development of appropriate equilibrium sorption relationships for anthropogenic organic contaminants with soils and sediments is essential to predicting the extents and rates of solid-water interactions in the environment. In this context, we previously reported results that ...

Supporting Documentation Used in the Derivation of Selected Freshwater Tier 2 ESBs

EPA Science Inventory

Compilation of toxicity data used to derive secondary chronic values (SCVs) and tier 2 equilibrium partitioning sediment benchmarks (ESBs) for a selection of nonionic organic chemicals. The values are used in the following U.S. EPA document: U.S. EPA. 2008. Procedures for th...

Variability of in situ sediment strength and pore pressure behavior of tidal estuary surface sediments

NASA Astrophysics Data System (ADS)

Lucking, Greg; Stark, Nina; Lippmann, Thomas; Smyth, Stephen

2017-10-01

Tidal estuaries feature spatially and temporally varying sediment dynamics and characteristics. Particularly, the variability of geotechnical sediment parameters is still poorly understood, limiting the prediction of long-term sediment stability and dynamics. This paper presents results from an in situ investigation of surficial sediments (≤50 cm) in a tidal estuary in New Hampshire (USA), using a portable free fall penetrometer. The aim is to investigate variations in sediment strength and pore pressure behavior with regard to sediment type and seabed morphology. The study also provides a detailed analysis of high velocity impact pore pressure data to derive information about sediment type and permeability. The penetrometer was deployed 227 times, and the findings are correlated to 78 sediment samples. Differences in sediment strength and type were found when transitioning from tidal flats to the deeper channels. Finer-grained sediments located predominantly on the tidal flats appeared well consolidated with noticeable and spatially consistent sediment strength (reflected in an estimate of quasi-static bearing capacity qsbcmax 10 kPa). Sediments with higher sand content (>75%) showed more variations in strength relating to differences in gradation, and likely represent loose and poorly consolidated sands (qsbcmax 10-55 kPa). The rate at which the recorded excess pore pressures approached equilibrium after penetration was classified and related to sediment type. The data indicate that the development of excess pore pressures upon impact and during penetration may provide additional insight into the nature and layering of bed material, such as identifying a desiccated or over-consolidated dilative surficial layer. In summary, with varying sediment grain size distributions, bulk densities and morphology, sediment strength and pore pressure behavior can vary significantly within a tidal estuary.

Pocomoke Sound Sedimentary and Ecosystem History

USGS Publications Warehouse

Cronin, Thomas M.

2004-01-01

Summary of Results: Pocomoke Sound Sediment and Sediment Processes Transport of sediment from coastal marshes. Analyses of pollen and foraminifera from surface sediments in Pocomoke Sound suggest that neither the upstream forested wetlands nor coastal marshes bordering the sound have contributed appreciably to particulate matter in the 10- to 1000-micron size range that is currently being deposited in the sound. Sediment processes derived from short-lived isotope. Analyses of beryllium-7, cesium-137 and lead-210 and redox sensitive elements from Pocomoke sediments showed that there has been a significant increase in anthropogenic elements since the late 1940's when the Delmarva Peninsula became more accessible from the Baltimore-Washington region. Cesium-137 was found to be a useful tool to determine changes in sedimentation within the system. Three major stages of sedimentation occurred. Before 1950, the system was equilibrium with the agriculture activity in the watershed, whereas urbanization and agricultural activity changes during and immediately preceding World War II resulted in increased sediment flux. Around 1970, the sediment flux diminished and there was an apparent increase in bank erosion sediment to the deeper parts of the system. Rates of sediment deposition. Radiocarbon, lead-210, and pollen dating of sediment cores from Pocomoke Sound indicate relatively continuous deposition of fine-grained sediments in the main Pocomoke channel at > ~7 m water depths. Mean sediment accumulation rates during the past few centuries were relatively high (>1 cm yr -1 ). The ages of coarser-grained sediments (sands) blanketing the shallow (4.0 cm yr -1 ) at most sites throughout the Sound in post-Colonial time. These results confirm those from other regions of the bay that land-clearance increased the flux of river-borne sediment to certain r

In situ passive sampling of sediments in the Lower Duwamish Waterway Superfund site: Replicability, comparison with ex situ measurements, and use of data.

PubMed

Apell, Jennifer N; Gschwend, Philip M

2016-11-01

Superfund sites with sediments contaminated by hydrophobic organic compounds (HOCs) can be difficult to characterize because of the complex nature of sorption to sediments. Porewater concentrations, which are often used to model transport of HOCs from the sediment bed into overlying water, benthic organisms, and the larger food web, are traditionally estimated using sediment concentrations and sorption coefficients estimated using equilibrium partitioning (EqP) theory. However, researchers have begun using polymeric samplers to determine porewater concentrations since this method does not require knowledge of the sediment's sorption properties. In this work, polyethylene passive samplers were deployed into sediments in the field (in situ passive sampling) and mixed with sediments in the laboratory (ex situ active sampling) that were contaminated with polychlorinated biphenyls (PCBs). The results show that porewater concentrations based on in situ and ex situ sampling generally agreed within a factor of two, but in situ concentrations were consistently lower than ex situ porewater concentrations. Imprecision arising from in situ passive sampling procedures does not explain this bias suggesting that field processes like bioirrigation may cause the differences observed between in situ and ex situ polymeric samplers. Copyright © 2016 Elsevier Ltd. All rights reserved.

Large-scale risk assessment of polycyclic aromatic hydrocarbons in shoreline sediments from Saudi Arabia: environmental legacy after twelve years of the Gulf war oil spill.

PubMed

Bejarano, Adriana C; Michel, Jacqueline

2010-05-01

A large-scale assessment of polycyclic aromatic hydrocarbons (PAHs) from the 1991 Gulf War oil spill was performed for 2002-2003 sediment samples (n = 1679) collected from habitats along the shoreline of Saudi Arabia. Benthic sediment toxicity was characterized using the Equilibrium Partitioning Sediment Benchmark Toxic Unit approach for 43 PAHs (ESBTU(FCV,43)). Samples were assigned to risk categories according to ESBTU(FCV,43) values: no-risk (< or = 1), low (>1 - < or = 2), low-medium (>2 - < or = 3), medium (>3 - < or = 5) and high-risk (>5). Sixty seven percent of samples had ESBTU(FCV,43) > 1 indicating potential adverse ecological effects. Sediments from the 0-30 cm layer from tidal flats, and the >30 - <60 cm layer from heavily oiled halophytes and mangroves had high frequency of high-risk samples. No-risk samples were characterized by chrysene enrichment and depletion of lighter molecular weight PAHs, while high-risk samples showed little oil weathering and PAH patterns similar to 1993 samples. North of Safaniya sediments were not likely to pose adverse ecological effects contrary to sediments south of Tanaqib. Landscape and geomorphology has played a role on the distribution and persistence in sediments of oil from the Gulf War. Copyright 2009 Elsevier Ltd. All rights reserved.

Long-term Kinetics of Uranyl Desorption from Sediments Under Advective Conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shang, Jianying; Liu, Chongxuan; Wang, Zheming

2014-02-15

Long-term (> 4 months) column experiments were performed to investigate the kinetics of uranyl (U(VI)) desorption in sediments collected from the Integrated Field Research Challenge (IFRC) site at the US Department of Energy (DOE) Hanford 300 Area. The experimental results were used to evaluate alternative multi-rate surface complexation reaction (SCR) approaches to describe the short- and long-term kinetics of U(VI) desorption under flow conditions. The SCR stoichiometry, equilibrium constants, and multi-rate parameters were independently characterized in batch and stirred flow-cell reactors. Multi-rate SCR models that were either additively constructed using the SCRs for individual size fractions (e.g., Shang et al.,more » 2011), or composite in nature could effectively describe short-term U(VI) desorption under flow conditions. The long-term desorption results, however, revealed that using a labile U concentration measured by carbonate extraction under-estimated desorbable U(VI) and the long-term rate of U(VI) desorption. An alternative modeling approach using total U as the desorbable U(VI) concentration was proposed to overcome this difficulty. This study also found that the gravel size fraction (2-8 mm), which is typically treated as non-reactive in modeling U(VI) reactive transport because of low external surface area, can have an important effect on the U(VI) desorption in the sediment. This study demonstrates an approach to effectively extrapolate U(VI) desorption kinetics for field-scale application, and identifies important parameters and uncertainties affecting model predictions.« less

Tracking channel-floodplain sediment exchange with conservative and non-conservative geochemical tracers

NASA Astrophysics Data System (ADS)

Belmont, Patrick; Stout, Justin

2013-04-01

Fine sediment is routed through landscapes and channel networks in a highly unsteady and non-uniform manner, potentially experiencing deposition and re-suspension many times during transport from source to sink. Developing a better understanding of sediment routing at the landscape scale is an intriguing challenge from a modeling perspective because it requires consideration of a multitude of processes that interact and vary in space and time. From an applied perspective, an improved understanding of sediment routing is essential for predicting how conservation and restoration practices within a watershed will influence water quality, to support land and water management decisions. Two key uncertainties in predicting sediment routing at the landscape scale are 1) determining the proportion of suspended sediment that is derived from terrestrial (soil) erosion versus channel (bank) erosion, and 2) constraining the proportion of sediment that is temporarily stored and re-suspended within the channel-floodplain complex. Sediment fingerprinting that utilizes a suite of conservative and non-conservative geochemical tracers associated with suspended sediment can provide insight regarding both of these key uncertainties. Here we present a model that tracks suspended sediment with associated conservative and non-conservative geochemical tracers. The model assumes that particle residence times are described by a bimodal distribution wherein some fraction of sediment is transported through the system in a relatively short time (< 1 year) and the remainder experiences temporary storage (of variable duration) within the channel-floodplain complex. We use the model to explore the downstream evolution of non-conservative tracers under equilibrium conditions (i.e., exchange between the channel and floodplain is allowed, but no net change in channel-floodplain storage can occur) to illustrate how the process of channel-floodplain storage and re-suspension can potentially bias interpretation of sediment fingerprinting results. We then apply the model to explain measurements of meteoric Beryllium-10, Lead-210, and Cesium-137 associated with suspended sediment in two very different rivers, one incising (Le Sueur River, south-central Minnesota, USA) and the other aggrading (Root River, southeastern Minnesota, USA) in response to base level fall and rise, respectively. The Le Sueur River exhibits a remarkably narrow range of tracer concentrations in source areas, which include agricultural fields, alluvial banks, and bluffs. Suspended sediment samples collected immediately above and below the 30 km long incising reach show a systematic shift in terrestrial sources in the downstream direction, indicated by changes in Beryllium-10 concentrations. The Root River indicates a more variable erosion history, with significant variability of Beryllium-10 concentrations in source areas (agricultural fields, forested hillslopes, and alluvial floodplains and terraces) and inverted Beryllium-10 depth profiles (higher concentrations at depth, suggesting unsteady erosion and significant storage of legacy sediment). Both rivers show a systematic disparity in normalized concentrations of conservative versus non-conservative tracers, indicating that significant storage and re-suspension occurs in both systems as the sediment is routed through the channel-floodplain complex.

Experiments on Bedrock Cover in a Highly Sinuous Channel

NASA Astrophysics Data System (ADS)

Parker, G.; Fernandez, R.; Stark, C. P.

2015-12-01

One of several mechanisms by which bedrock rivers can incise is abrasion of the bedrock surface by colliding sediment particles. This effect has been captured in terms of a "cover factor" corresponding to the areal fraction p of the bed that is covered with sediment. According to this formulation, a value of p equal to 1 corresponds to complete alluvial cover: sediment particles strike each other and no bedrock abrasion is accomplished. Correspondingly, a value of p equal to 0 corresponds to the absence of sediment: no particles are available to strike the bed, and again no bedrock abrasion is accomplished. Thus the condition 0 < p < 1 is hypothesized to be the condition for incision driven by abrasion. At the microscopic level, however, p can take only the binary values 0 and 1: either a point on the bedrock surface is covered or is not covered. Therefore, the value of p that enters into any morphodynamic formulation of cover must represent an average over some spatiotemporal window. Here we consider the case of a highly sinuous meandering flume. The bed is set in concrete to take the topography corresponding to purely alluvial mobile-bed equilibrium. The recirculation of sediment over this bed at below-capacity conditions leads to a complex pattern of free and forced bars that only partially cover the bed. At certain locations, such as near the inside of bends, the bed is always covered, where at other locations, such as right near the apexes of the very tight bends in the flume, the bed is almost never covered. At other locations, the instantaneous cover fluctuates between the binary values 0 and 1, reflecting the migration of bars of various sizes over the bedrock surface. The averaging of these binary values over appropriate time windows allows determination of the local spatial variation of p that can serve as input to a numerical model of the evolution of bedrock meandering channels.

Using DoD Maps to Examine the Influence of Large Wood on Channel Morphodynamics

NASA Astrophysics Data System (ADS)

MacKenzie, L. C.; Eaton, B. C.

2012-12-01

Since the advent of logging and slash burning, many streams in British Columbia have experienced changes to the amount of large wood added to or removed from these systems, which has, in turn, influenced the storage and movement of sediment within these channels. This set of flume experiments examines and quantifies the impacts of large wood on the reach-scale morphodynamics. Understanding the relation between the wood load and channel morphodynamics is important when assessing the quality of the aquatic habitat of a stream. The experiments were conducted using a fixed-bank, mobile bed Froude-scaled physical model of Fishtrap Creek, British Columbia, built in a shallow flume that is 1.5 m wide and 11 m long. The stream table was run without wood until it reached equilibrium at which point wood pieces of varying sizes were added to the channel. The bed morphology was surveyed using a laser profiling system at five-hour intervals. The laser profiles were then interpolated to create digital elevation models (DEM) from which DEM of difference (DoD) maps were produced. Analysis of the DoD maps focused on quantifying and locating differences in the distribution of sediment storage, erosion, and deposition between the runs as well as those induced by the addition of large wood into the stream channel. We then assessed the typical influence of individual pieces and of jams on pool frequency, size and distribution along the channels.

SEDFIT-MSTAR: Molecular weight and molecular weight distribution analysis of polymers by sedimentation equilibrium in the ultracentrifuge

PubMed Central

Schuck, Peter; Gillis, Richard B.; Besong, Tabot M.D.; Almutairi, Fahad; Adams, Gary G.; Rowe, Arthur J.; Harding, Stephen E.

2014-01-01

Sedimentation equilibrium (analytical ultracentrifugation) is one of the most inherently suitable methods for the determination of average molecular weights and molecular weight distributions of polymers, because of its absolute basis (no conformation assumptions) and inherent fractionation ability (without the need for columns or membranes and associated assumptions over inertness). With modern instrumentation it is also possible to run up to 21 samples simultaneously in a single run. Its application has been severely hampered because of difficulties in terms of baseline determination (incorporating estimation of the concentration at the air/solution meniscus) and complexity of the analysis procedures. We describe a new method for baseline determination based on a smart-smoothing principle and built into the highly popular platform SEDFIT for the analysis of the sedimentation behavior of natural and synthetic polymer materials. The SEDFIT-MSTAR procedure – which takes only a few minutes to perform - is tested with four synthetic data sets (including a significantly non-ideal system) a naturally occurring protein (human IgG1) and two naturally occurring carbohydrate polymers (pullulan and λ–carrageenan) in terms of (i) weight average molecular weight for the whole distribution of species in the sample (ii) the variation in “point” average molecular weight with local concentration in the ultracentrifuge cell and (iii) molecular weight distribution. PMID:24244936

Denitrification in sediments from the hyporheic zone adjacent to a small forested stream

USGS Publications Warehouse

Duff, J.H.; Triska, F.J.

1990-01-01

Denitrifying potentials increased with increasing distance from the stream channel. Dissolved oxygen was 100% of the concentration expected in equilibrium with the atmosphere in water obtained from monitoring wells immediately adjacent to the stream but was as low as 7% of the expected value in water 11.4 m inland. Both nitrate and dissolved organic carbon decreased over summer in wells at the base of the alder-forested slope. A 48-h injection of nitrate-amended stream water into hyporheic water 8.4 m inland stimulated nitrous oxide production in the presence of acetylene. Nitrous oxide was generated as nitrate and acetylene were co-transported to a well 13 m down-gradient. Acetylene-block experiments coupled with the chemistry data suggest that denitrification can modify the chemistry of water during passage through the hyporheic zone. -from Authors

Polycyclic aromatic hydrocarbons (PAHs) and alkylated PAHs in the coastal seawater, surface sediment and oyster from Dalian, Northeast China.

PubMed

Hong, Wen-Jun; Jia, Hongliang; Li, Yi-Fan; Sun, Yeqing; Liu, Xianjie; Wang, Luo

2016-06-01

A total of 46 polycyclic aromatic hydrocarbons (PAHs, 21 parent and 25 alkylated) were determined in seawater, surface sediment and oyster from coastal area of Dalian, North China. The concentration of Σ46PAHs in seawater, sediment, and oyster were 136-621 ng/L, 172-4700 ng/g dry weight (dw) and 60.0-129 ng/g wet weight (ww) in winter, and 65.0-1130 ng/L, 71.1-1090 ng/g dw and 72.8-216 ng/g ww in summer, respectively. High PAH levels were found in industrial area both in winter and summer. Selected PAH levels in sediments were compared with Sediments Quality Guidelines (ERM-ERL, TEL-PEL indexes) for evaluation probable toxic effects on marine organism and the results indicate that surface sediment from all sampling sites have a low to medium ecotoxicological risk. Daily intake of PAHs via oyster as seafood by humans were estimated and the results indicated that oyster intake would not pose a health risk to humans even 30 days after a oil spill accident near by. Water-sediment exchange analysis showed that, both in winter and summer, the fluxes for most high molecular weight PAHs were from seawater to sediment, while for low molecular weight PAHs, an equilibrium was reached between seawater and sediment. Copyright © 2016 Elsevier Inc. All rights reserved.

Deriving sediment Interstitial Water Remediation Goals ...

EPA Pesticide Factsheets

Background/Objectives. Passive sampling is becoming a frequently used measurement technique at Superfund sites with contaminated sediments. Passive sampling measures the concentrations of freely dissolved chemicals (Cfrees) in the sediment interstitial water. The freely dissolved chemical is a good surrogate for and a very practical means for estimating the concentrations of bioavailable chemical in the sediments. Building from this approach, a methodology is proposed to derive sediment Interstitial Water Remediation Goals (IWRGs) for the protection of benthic organisms from direct toxicity using Cfrees measured with passive sampling.Approach/Activities. In the early 2000s, EPA developed and released Equilibrium Partitioning Sediment Benchmarks (ESBs) for a series of chemicals. ESBs are intended to be chemical concentrations below which unacceptable toxicity to benthic organisms does not occur. The ESBs (expressed with the units of ug/g OC) were derived using the equations:ESB= K_OC×FCV where K_OC=0.00028+0.983K_OWThe KOC is the organic carbon normalized sediment-water chemical partition coefficient, FCV is the Final Chronic Value from EPA’s ambient water quality criteria for the protection of aquatic life, and KOW is the n-octanol/water partition coefficient for the chemical. At a specific site, the remedial goal (CS:ESB µg/kg-dw) in sediment are then derived using the site-specific fraction of organic carbon in the sediment (fOC:SS) at the site:C_

Equilibrium concentration profiles and sedimentation kinetics of colloidal gels under gravitational stress

NASA Astrophysics Data System (ADS)

Buzzaccaro, S.; Secchi, E.; Brambilla, G.; Piazza, R.; Cipelletti, L.

2012-07-01

We study the sedimentation of colloidal gels by using a combination of light scattering, polarimetry and video imaging. The asymptotic concentration profiles φ(z,t → ∞) exhibit remarkable scaling properties: profiles for gels prepared at different initial volume fractions and particle interactions can be superimposed onto a single master curve by using suitable reduced variables. We show theoretically that this behavior stems from a power law dependence of the compressive elastic modulus versus φ, which we directly test experimentally. The sedimentation kinetics comprises an initial latency stage, followed by a rapid collapse where the gel height h decreases at constant velocity and a final compaction stage characterized by a stretched exponential relaxation of h toward a plateau. Analogies and differences with previous works are briefly discussed.

Direct atmospheric deposition of 210Pb to rivers determined through 210Pb (210Po) disequilibrium and implications to sediment source apportionment

NASA Astrophysics Data System (ADS)

Blumentritt, D. J.; Shottler, S.; Engstrom, D. R.

2011-12-01

Atmospheric radioisotopes such as 210Pb can be an effective tool for determining sediment source types in rivers and streams. Pb-210 is ubiquitous in deposition from atmospheric washout and is highly particle reactive, so sediments derived from a surface with prolonged exposure to rainfall, such as farm fields, are enriched in atmospheric 210Pb. Conversely, sediment sources that are not readily exposed to rainfall (i.e. streambanks) are absent of any appreciable 210Pb. Many sediment source apportionment studies have used 210Pb to quantify the proportion of sediment loads from the two source types, field and non-field. These studies, however, primarily take place in smaller watersheds where 210Pb that falls directly onto the surface of the water is assumed negligible. Lake Pepin is a riverine lake located in southeastern Minnesota with a 122,000 km2 watershed composed of three major rivers, the Minnesota, headwaters Mississippi, and St. Croix. The sediment load in Lake Pepin has increased by an order of magnitude since Euro-American settlement in the region. Most of the sediment (>80%) is transported to Lake Pepin from the highly agricultural Minnesota River basin. Extensive sediment fingerprinting work has been done on Lake Pepin sediments, but a source of significant uncertainty still exists: How much of the 210Pb measured in Lake Pepin is directly deposited to the surface of the contributing water bodies and did not enter on eroded particles? To answer this important question, we have developed a method to quantify the amount of directly deposited 210Pb. Alpha spectrometry is used to measure 210Po, a daughter product of 210Pb decay. Because 210Po has a short half-life (138 days), it takes approximately one year to reach equilibrium with 210Pb on sediment particles. If deposition of 210Pb directly from the atmosphere to the water surface is significant, there will be disequilibrium between the two radioisotopes and the activity of 210Po will increase as an inverse exponential function, with respect to time, following sample collection. The magnitude of this increase is the amount of directly deposited 210Pb. Samples were collected at four locations, corresponding to gauging stations, on the Minnesota/Mississippi River system above Lake Pepin. Three measurements were made on each sample over the course of a year after collection. Based on those three measurements, the activity of 210Po was modeled for time zero and for the equilibrium concentration, revealing the amount of 210Pb from direct atmospheric deposition. These estimates were flow-weighted over the course of the year, providing a critical correction to the source apportionment model.

Tracing the sources and cycling of phosphorus in river sediments using oxygen isotopes: Methodological adaptations and first results from a case study in France.

PubMed

Pistocchi, Chiara; Tamburini, Federica; Gruau, Gerard; Ferhi, André; Trevisan, Dominique; Dorioz, Jean-Marcel

2017-03-15

An essential aspect of eutrophication studies is to trace the ultimate origin of phosphate ions (P-PO 4 ) associated with the solid phase of river sediments, as certain processes can make these ions available for algae. However, this is not a straightforward task because of the diversity of allochthonous and autochthonous sources that can supply P-PO 4 to river sediments as well as the existence of in-stream processes that can change the speciation of these inputs and obscure the original sources. Here, we present the results of a study designed to explore the potentials, limitations and conditions for the use of the oxygen isotope composition of phosphate (δ 18 Op) extracted from river sediments for this type of tracing. We first tested if the method commonly applied to soils to purify P-PO 4 and to measure their δ 18 Op concentrations could be adapted to sediments. We then applied this method to a set of sediments collected in a river along a gradient of anthropogenic pressure and compared their isotopic signatures with those from samples that are representative of the potential P-PO 4 inputs to the river system (soils and riverbank material). The results showed that following some adaptations, the purification method could be successfully transposed to river sediments with a high level of P-PO 4 purification (>97%) and high δ 18 Op measurement repeatability and accuracy (<0.4‰). The values for the potential allochthonous sources varied from 11.8 to 18.3‰, while the δ 18 Op value for the river sediments ranged from 12.2 to 15.8‰. Moreover, a sharp increase (>3‰) in the sediment δ 18 Op value immediately downstream from the discharge point revealed the strong impact of municipal wastewater. The calculation of the theoretical equilibrium δ 18 O p values using the river water temperature and δ 18 O w showed that the downstream sediments were in equilibrium, which was not the case for the upstream sediments. This difference could be related to the contrast between the short residence time of the transfer system in the catchment head, which can preserve the isotopic variability of the source materials, and the longer residence times and higher P bioavailability in the lower catchment, possibly fostering the recycling of P-PO 4 by the biota and the equilibration of the oxygen isotope signature in P-PO 4 . These results demonstrate the potential of the isotopic approach to assess the sources and in-stream turnover of sedimentary P in river systems. Copyright © 2016 Elsevier Ltd. All rights reserved.

Erosion characteristics and horizontal variability for small erosion depths in the Sacramento-San Joaquin River Delta, California, USA

NASA Astrophysics Data System (ADS)

Schoellhamer, David H.; Manning, Andrew J.; Work, Paul A.

2017-06-01

Erodibility of cohesive sediment in the Sacramento-San Joaquin River Delta (Delta) was investigated with an erosion microcosm. Erosion depths in the Delta and in the microcosm were estimated to be about one floc diameter over a range of shear stresses and times comparable to half of a typical tidal cycle. Using the conventional assumption of horizontally homogeneous bed sediment, data from 27 of 34 microcosm experiments indicate that the erosion rate coefficient increased as eroded mass increased, contrary to theory. We believe that small erosion depths, erosion rate coefficient deviation from theory, and visual observation of horizontally varying biota and texture at the sediment surface indicate that erosion cannot solely be a function of depth but must also vary horizontally. We test this hypothesis by developing a simple numerical model that includes horizontal heterogeneity, use it to develop an artificial time series of suspended-sediment concentration (SSC) in an erosion microcosm, then analyze that time series assuming horizontal homogeneity. A shear vane was used to estimate that the horizontal standard deviation of critical shear stress was about 30% of the mean value at a site in the Delta. The numerical model of the erosion microcosm included a normal distribution of initial critical shear stress, a linear increase in critical shear stress with eroded mass, an exponential decrease of erosion rate coefficient with eroded mass, and a stepped increase in applied shear stress. The maximum SSC for each step increased gradually, thus confounding identification of a single well-defined critical shear stress as encountered with the empirical data. Analysis of the artificial SSC time series with the assumption of a homogeneous bed reproduced the original profile of critical shear stress, but the erosion rate coefficient increased with eroded mass, similar to the empirical data. Thus, the numerical experiment confirms the small-depth erosion hypothesis. A linear model of critical shear stress and eroded mass is proposed to simulate small-depth erosion, assuming that the applied and critical shear stresses quickly reach equilibrium.

Erosion characteristics and horizontal variability for small erosion depths in the Sacramento-San Joaquin River Delta, California, USA

USGS Publications Warehouse

Schoellhamer, David H.; Manning, Andrew J.; Work, Paul A.

2017-01-01

Erodibility of cohesive sediment in the Sacramento-San Joaquin River Delta (Delta) was investigated with an erosion microcosm. Erosion depths in the Delta and in the microcosm were estimated to be about one floc diameter over a range of shear stresses and times comparable to half of a typical tidal cycle. Using the conventional assumption of horizontally homogeneous bed sediment, data from 27 of 34 microcosm experiments indicate that the erosion rate coefficient increased as eroded mass increased, contrary to theory. We believe that small erosion depths, erosion rate coefficient deviation from theory, and visual observation of horizontally varying biota and texture at the sediment surface indicate that erosion cannot solely be a function of depth but must also vary horizontally. We test this hypothesis by developing a simple numerical model that includes horizontal heterogeneity, use it to develop an artificial time series of suspended-sediment concentration (SSC) in an erosion microcosm, then analyze that time series assuming horizontal homogeneity. A shear vane was used to estimate that the horizontal standard deviation of critical shear stress was about 30% of the mean value at a site in the Delta. The numerical model of the erosion microcosm included a normal distribution of initial critical shear stress, a linear increase in critical shear stress with eroded mass, an exponential decrease of erosion rate coefficient with eroded mass, and a stepped increase in applied shear stress. The maximum SSC for each step increased gradually, thus confounding identification of a single well-defined critical shear stress as encountered with the empirical data. Analysis of the artificial SSC time series with the assumption of a homogeneous bed reproduced the original profile of critical shear stress, but the erosion rate coefficient increased with eroded mass, similar to the empirical data. Thus, the numerical experiment confirms the small-depth erosion hypothesis. A linear model of critical shear stress and eroded mass is proposed to simulate small-depth erosion, assuming that the applied and critical shear stresses quickly reach equilibrium.

Three-Dimensional Sediment Dynamics in Well-Mixed Estuaries: Importance of the Internally Generated Overtide, Spatial Settling Lag, and Gravitational Circulation

NASA Astrophysics Data System (ADS)

Wei, Xiaoyan; Kumar, Mohit; Schuttelaars, Henk M.

2018-02-01

To investigate the dominant sediment transport and trapping mechanisms, a semi-analytical three-dimensional model is developed resolving the dynamic effects of salt intrusion on sediment in well-mixed estuaries in morphodynamic equilibrium. As a study case, a schematized estuary with a converging width and a channel-shoal structure representative for the Delaware estuary is considered. When neglecting Coriolis effects, sediment downstream of the estuarine turbidity maximum (ETM) is imported into the estuary through the deeper channel and exported over the shoals. Within the ETM region, sediment is transported seaward through the deeper channel and transported landward over the shoals. The largest contribution to the cross-sectionally integrated seaward residual sediment transport is attributed to the advection of tidally averaged sediment concentrations by river-induced flow and tidal return flow. This contribution is mainly balanced by the residual landward sediment transport due to temporal correlations between the suspended sediment concentrations and velocities at the M2 tidal frequency. The M2 sediment concentration mainly results from spatial settling lag effects and asymmetric bed shear stresses due to interactions of M2 bottom velocities and the internally generated M4 tidal velocities, as well as the salinity-induced residual currents. Residual advection of tidally averaged sediment concentrations also plays an important role in the landward sediment transport. Including Coriolis effects hardly changes the cross-sectionally integrated sediment balance, but results in a landward (seaward) sediment transport on the right (left) side of the estuary looking seaward, consistent with observations from literature. The sediment transport/trapping mechanisms change significantly when varying the settling velocity and river discharge.

Is “morphodynamic equilibrium” an oxymoron?

USGS Publications Warehouse

Zhou, Zeng; Coco, Giovanni; Townend, Ian; Olabarrieta, Maitane; van der Wegen, Mick; Gong, Zheng; D'Alpaos, Andrea; Gao, Shu; Jaffe, Bruce E.; Gelfenbaum, Guy R.; He, Qing; Wang, Yaping; Lanzoni, Stefano; Wang, Zhengbing; Winterwerp, Han; Zhang, Changkuan

2017-01-01

Morphodynamic equilibrium is a widely adopted yet elusive concept in the field of geomorphology of coasts, rivers and estuaries. Based on the Exner equation, an expression of mass conservation of sediment, we distinguish three types of equilibrium defined as static and dynamic, of which two different types exist. Other expressions such as statistical and quasi-equilibrium which do not strictly satisfy the Exner conditions are also acknowledged for their practical use. The choice of a temporal scale is imperative to analyse the type of equilibrium. We discuss the difference between morphodynamic equilibrium in the “real world” (nature) and the “virtual world” (model). Modelling studies rely on simplifications of the real world and lead to understanding of process interactions. A variety of factors affect the use of virtual-world predictions in the real world (e.g., variability in environmental drivers and variability in the setting) so that the concept of morphodynamic equilibrium should be mathematically unequivocal in the virtual world and interpreted over the appropriate spatial and temporal scale in the real world. We draw examples from estuarine settings which are subject to various governing factors which broadly include hydrodynamics, sedimentology and landscape setting. Following the traditional “tide-wave-river” ternary diagram, we summarize studies to date that explore the “virtual world”, discuss the type of equilibrium reached and how it relates to the real world.

From rationality to cooperativeness: The totally mixed Nash equilibrium in Markov strategies in the iterated Prisoner's Dilemma.

PubMed

Menshikov, Ivan S; Shklover, Alexsandr V; Babkina, Tatiana S; Myagkov, Mikhail G

2017-01-01

In this research, the social behavior of the participants in a Prisoner's Dilemma laboratory game is explained on the basis of the quantal response equilibrium concept and the representation of the game in Markov strategies. In previous research, we demonstrated that social interaction during the experiment has a positive influence on cooperation, trust, and gratefulness. This research shows that the quantal response equilibrium concept agrees only with the results of experiments on cooperation in Prisoner's Dilemma prior to social interaction. However, quantal response equilibrium does not explain of participants' behavior after social interaction. As an alternative theoretical approach, an examination was conducted of iterated Prisoner's Dilemma game in Markov strategies. We built a totally mixed Nash equilibrium in this game; the equilibrium agrees with the results of the experiments both before and after social interaction.

Fluorescence lifetime components reveal kinetic intermediate states upon equilibrium denaturation of carbonic anhydrase II

NASA Astrophysics Data System (ADS)

Nemtseva, Elena V.; Lashchuk, Olesya O.; Gerasimova, Marina A.; Melnik, Tatiana N.; Nagibina, Galina S.; Melnik, Bogdan S.

2018-01-01

In most cases, intermediate states of multistage folding proteins are not ‘visible’ under equilibrium conditions but are revealed in kinetic experiments. Time-resolved fluorescence spectroscopy was used in equilibrium denaturation studies. The technique allows for detecting changes in the conformation and environment of tryptophan residues in different structural elements of carbonic anhydrase II which in its turn has made it possible to study the intermediate states of carbonic anhydrase II under equilibrium conditions. The results of equilibrium and kinetic experiments using wild-type bovine carbonic anhydrase II and its mutant form with the substitution of leucine for alanine at position 139 (L139A) were compared. The obtained lifetime components of intrinsic tryptophan fluorescence allowed for revealing that, the same as in kinetic experiments, under equilibrium conditions the unfolding of carbonic anhydrase II ensues through formation of intermediate states.

Fluorescence lifetime components reveal kinetic intermediate states upon equilibrium denaturation of carbonic anhydrase II.

PubMed

Nemtseva, Elena V; Lashchuk, Olesya O; Gerasimova, Marina A; Melnik, Tatiana N; Nagibina, Galina S; Melnik, Bogdan S

2017-12-21

In most cases, intermediate states of multistage folding proteins are not 'visible' under equilibrium conditions but are revealed in kinetic experiments. Time-resolved fluorescence spectroscopy was used in equilibrium denaturation studies. The technique allows for detecting changes in the conformation and environment of tryptophan residues in different structural elements of carbonic anhydrase II which in its turn has made it possible to study the intermediate states of carbonic anhydrase II under equilibrium conditions. The results of equilibrium and kinetic experiments using wild-type bovine carbonic anhydrase II and its mutant form with the substitution of leucine for alanine at position 139 (L139A) were compared. The obtained lifetime components of intrinsic tryptophan fluorescence allowed for revealing that, the same as in kinetic experiments, under equilibrium conditions the unfolding of carbonic anhydrase II ensues through formation of intermediate states.

From rationality to cooperativeness: The totally mixed Nash equilibrium in Markov strategies in the iterated Prisoner’s Dilemma

PubMed Central

Myagkov, Mikhail G.

2017-01-01

In this research, the social behavior of the participants in a Prisoner's Dilemma laboratory game is explained on the basis of the quantal response equilibrium concept and the representation of the game in Markov strategies. In previous research, we demonstrated that social interaction during the experiment has a positive influence on cooperation, trust, and gratefulness. This research shows that the quantal response equilibrium concept agrees only with the results of experiments on cooperation in Prisoner’s Dilemma prior to social interaction. However, quantal response equilibrium does not explain of participants’ behavior after social interaction. As an alternative theoretical approach, an examination was conducted of iterated Prisoner's Dilemma game in Markov strategies. We built a totally mixed Nash equilibrium in this game; the equilibrium agrees with the results of the experiments both before and after social interaction. PMID:29190280

SEDIMENT-AIR EQUILIBRIUM PARTITIONING OF SEMI-VOLATILE HYDROPHOBIC ORGANIC COMPOUNDS. PART 1. METHOD DEVELOPMENT AND WATER VAPOR SORPTION ISOTHERM. (R825513C017)

EPA Science Inventory

The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Concl...

Bed topography and sand transport responses to a step change in discharge and water depth

USDA-ARS?s Scientific Manuscript database

Ephemeral streams with sand and gravel beds may inherit bed topography caused by previous flow events, resulting in bed topography that is not in equilibrium with flow conditions, complicating the modeling of flow and sediment transport. Major flow events, resulting from rainfall with high intensity...

Gas hydrate property measurements in porous sediments with resonant ultrasound spectroscopy

NASA Astrophysics Data System (ADS)

McGrail, B. P.; Ahmed, S.; Schaef, H. T.; Owen, A. T.; Martin, P. F.; Zhu, T.

2007-05-01

Resonant ultrasound spectroscopy was used to characterize a natural geological core sample obtained from the Mallik 5L-38 gas hydrate research well at high pressure and subambient temperatures. Using deuterated methane gas to form gas hydrate in the core sample, it was discovered that resonance amplitudes are correlated with the fraction of the pore space occupied by the gas hydrate crystals. A pore water freezing model was developed that utilizes the known pore size distribution and pore water chemistry to predict gas hydrate saturation as a function of pressure and temperature. The model showed good agreement with the experimental measurements and demonstrated that pore water chemistry is the most important factor controlling equilibrium gas hydrate saturations in these sediments when gas hydrates are formed artificially in laboratory pressure vessels. With further development, the resonant ultrasound technique can provide a rapid, nondestructive, field portable means of measuring the equilibrium P-T properties and dissociation kinetics of gas hydrates in porous media, determining gas hydrate saturations, and may provide new insights into the nature of gas hydrate formation mechanisms in geologic materials.

A pre-dam-removal assessment of sediment transport for four dams on the Kalamazoo River between Plainwell and Allegan, Michigan

USGS Publications Warehouse

Syed, Atiq U.; Bennett, James P.; Rachol, Cynthia M.

2005-01-01

Four dams on the Kalamazoo River between the cities of Plainwell and Allegan, Mich., are in varying states of disrepair. The Michigan Department of Environmental Quality (MDEQ) and U.S. Environmental Protection Agency (USEPA) are considering removing these dams to restore the river channels to pre-dam conditions. This study was initiated to identify sediment characteristics, monitor sediment transport, and predict sediment resuspension and deposition under varying hydraulic conditions. The mathematical model SEDMOD was used to simulate streamflow and sediment transport using three modeling scenarios: (1) sediment transport simulations for 730 days (Jan. 2001 to Dec. 2002), with existing dam structures, (2) sediment transport simulations based on flows from the 1947 flood at the Kalamazoo River with existing dam structures, and (3) sediment transport simulations based on flows from the 1947 flood at the Kalamazoo River with dams removed. Sediment transport simulations based on the 1947 flood hydrograph provide an estimate of sediment transport rates under maximum flow conditions. These scenarios can be used as an assessment of the sediment load that may erode from the study reach at this flow magnitude during a dam failure. The model was calibrated using suspended sediment as a calibration parameter and root mean squared error (RMSE) as an objective function. Analyses of the calibrated model show a slight bias in the model results at flows higher than 75 m3/s; this means that the model-simulated suspended-sediment transport rates are higher than the observed rates; however, the overall calibrated model results show close agreement between simulated and measured values of suspended sediment. Simulation results show that the Kalamazoo River sediment transport mechanism is in a dynamic equilibrium state. Model results during the 730-day simulations indicate significant sediment erosion from the study reach at flow rates higher than 55 m3/s. Similarly, significant sediment deposition occurs during low to average flows (monthly mean flows between 25.49 m3/s and 50.97 m3/s) after a high-flow event. If the flow continues to stay in the low to average range the system shifts towards equilibrium, resulting in a balancing effect between sediment deposition and erosion rates. The 1947 flood-flow simulations show approximately 30,000 m3 more instream sediments erosion for the first 21 days of the dams removed scenario than for the existing-dams scenario, with the same initial conditions for both scenarios. Application of a locally weighted regression smoothing (LOWESS) function to simulation results of the dams removed scenario indicates a steep downtrend with high sediment transport rates during the first 21 days. In comparison, the LOWESS curve for the existing-dams scenario shows a smooth transition of sediment transport rates in response to the change in streamflow. The high erosion rates during the dams-removed scenario are due to the absence of the dams; in contrast, the presence of dams in the existing-dams scenario helps reduce sediment erosion to some extent. The overall results of 60-day simulations for the 1947 flood show no significant difference in total volume of eroded sediment between the two scenarios, because the dams in the study reach have low heads and no control gates. It is important to note that the existing-dams and dams-removed scenarios simulations are run for only 60 days; therefore, the simulations take into account the changes in sediment erosion and deposition rates only during that time period. Over an extended period, more erosion of instream sediments would be expected to occur if the dams are not properly removed than under the existing conditions. On the basis of model simulations, removal of dams would further lower the head in all the channels. This lowering of head could produce higher flow velocities in the study reach, which ultimately would result in accelerated erosion rates.

Cycling of mercury across the sediment-water interface in seepage lakes: Chapter 13, Advances in Chemistry

USGS Publications Warehouse

Hurley, James P.; Krabbenhoft, David P.; Babiarz, Christopher L.; Andren, Anders

1994-01-01

The magnitude and direction of Hg fluxes across the sediment—water interface were estimated by groundwater, dry bulk sediment, sediment pore water, sediment trap, and water-column analyses in two northern Wisconsin seepage lakes. Little Rock Lake (Treatment Basin) received no groundwater discharge during the study period (1988—1990), and Follette Lake received continuous groundwater discharge. In Little Rock Lake, settling of particulate matter accounted for the major Hg delivery mechanism to the sediment—water interface. Upward diffusion of Hg from sediment pore waters below 2—4-cm sediment depth was apparently a minor source during summer stratification. Time-series comparisons suggested that the observed buildup of Hg in the hypolimnion of Little Rock Lake was attributable to dissolution and diffusion of Hg from recently fallen particulate matter close to the sediment—water interface. Groundwater inflow represented an important source of new Hg, and groundwater outflow accounted for significant removal of Hg from Pallette Lake. Equilibrium speciation calculations revealed that association of Hg with organic matter may control solubility in well-oxygenated waters, whereas in anoxic environments sulfur (polysulfide and bisulfide) complexation governs dissolved total Hg levels.

Formation of natural gas hydrates in marine sediments. Gas hydrate growth and stability conditioned by host sediment properties

USGS Publications Warehouse

Clennell, M.B.; Henry, P.; Hovland, M.; Booth, J.S.; Winters, W.J.; Thomas, M.

2000-01-01

The stability conditions of submarine gas hydrates (methane clathrates) are largely dictated by pressure, temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of the host sediments also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our model presumes that gas hydrate behaves in a way analogous to ice in the pores of a freezing soil, where capillary forces influence the energy balance. Hydrate growth is inhibited within fine-grained sediments because of the excess internal phase pressure of small crystals with high surface curvature that coexist with liquid water in small pores. Therefore, the base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature, and so nearer to the seabed than would be calculated from bulk thermodynamic equilibrium. The growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, sheets, and lenses in muds; cements in sand and ash layers) can be explained by a requirement to minimize the excess of mechanical and surface energy in the system.

Comparative phosphorus sorption by marine sediments and agricultural soils in a tropical environment.

PubMed

Fox, Robert L; Fares, Ali; Wan, Y; Evensen, Carl I

2006-01-01

The influence of soil phosphorus (P) sources on P sorption characteristics of marine sediments was investigated for Pearl Harbor and off shore Molokai in Hawaii. Estuary sediments were sampled in seven locations; these represented different soils and on-shore activities. The soil samples included nine major soils that contributed sediment to the Harbor and coastal sediments near the island of Molokai. Sediment and soil samples were equilibrated for 6 days in 0.01 M CaCl(2) solution and synthetic seawater containing differing amounts of P. Phosphorus sorption curves were constructed. The equilibrated solution P, with no P added, ranged from 0.01 to 0.2 mg L(-1); P sorption by sediments at standard solution concentration 0.2 mg L(-1), ranged from 0 to 230 mg kg(-1). Sediment P sorption corresponded closely with soil sorption characteristics. Soils contributing sediments to the west reach of Pearl Harbor are highly weathered Oxisols with high standard P sorption values while those in the southeast of the Harbor were Vertisols and Mollisols which sorb little P. The influence of source materials on sediment P sorption was also observed for off-shore sediments near Molokai. Sediments serve as both source and sink for P in Pearl Harbor and in this role can be a stabilizing influence on P concentration in the water column. Phosphorus sorption curves in conjunction with water quality data can help to understand P dynamics between sediments and the water column and help evaluate concerns about P loading to a water body. For Pearl Harbor, solution P in equilibrium with sediments from the Lochs was 0.021 mg L(-1); a value unlikely to produce an algal bloom. (Measured total P in the water columns (mean) was 0.060.).

A screening level probabilistic ecological risk assessment of PAHs in sediments of San Francisco Bay

DOE Office of Scientific and Technical Information (OSTI.GOV)

Febbo, E.J.; Arnold, W.R.; Biddinger, G.R.

1995-12-31

As part of the Regional Monitoring Program administered by the San Francisco Estuary Institute (SFEI), sediment samples were collected at 20 stations in San Francisco Bay and analyzed to determine concentrations of 43 PAHs. These data were obtained from SFEI and used to calculate the potential risk to aquatic organisms using probabilistic modeling and Monte Carlo statistical procedures. Sediment chemistry data were used in conjunction with a sediment equilibrium model, a bioconcentration model, biota-sediment accumulation factors, and critical body burden effects concentrations to assess potential risk to bivalves. Bivalves were the chosen receptors because they lack a well-developed enzymatic systemmore » for metabolizing PAHs. Thus, they more readily accumulate PAHs and represent a species at greater risk than other taxa, such as fish and crustaceans. PAHs considered in this study span a broad range of octanol-water partition coefficients. Results indicate that risk of non-polar narcotic effects from PAHs was low in the Northern Bay Area, but higher in the South Bay near the more urbanized sections of the drainage basin.« less

Tetracyclic diterpenoid hydrocarbons in some Australian coals, sediments and crude oils

NASA Astrophysics Data System (ADS)

Noble, Rohinton A.; Alexander, Robert; Kagi, Robert Ian; Knox, John

1985-10-01

Tetracyclic diterpenoid hydrocarbons (diterpanes) based on the ent-beyerane, phyllocladane and ent-kaurane skeletons have been identified in the hydrocarbon extracts of some Australian coals, sediments and crude oils. Structures were assigned to the geological diterpanes by comparison with synthetically prepared reference compounds. Studies of a sample suite consisting of low-rank coals and sediments indicate that the ratios of C-16 epimers of phyllocladane and ent-kaurane are maturity dependent, and that the relative proportion of the thermodynamically preferred 16β (H)-compounds increases with increasing thermal maturity. Thermodynamic equilibrium for the interconversion reactions is attained in sediments before the onset of crude oil generation. The most likely natural product precursors for the tetracyclic diterpanes are considered to be the tetracyclic diterpene hydrocarbons which occur widely in the leaf resins of conifers. Tetracyclic diterpanes have been identified in sediments and coals of Permian age or younger, suggesting that these compounds are markers for both modern and extinct families of conifers. In particular, phyllocladane is proposed as a marker for the Podocarpaceae family of conifers.

Conductivity dependence of seismoelectric wave phenomena in fluid-saturated sediments

NASA Astrophysics Data System (ADS)

Block, Gareth I.; Harris, John G.

2006-01-01

Seismoelectric phenomena in sediments arise from acoustic wave-induced fluid motion in the pore space, which perturbs the electrostatic equilibrium of the electric double layer on the grain surfaces. Experimental techniques and the apparatus built to study the conductivity dependence of the electrokinetic (EK) effect are described, and outcomes for studies in loose glass microspheres and medium-grain sand are presented. By varying the NaCl concentration in the pore fluid, we measured the conductivity dependence of two kinds of EK behavior: (1) the electric fields generated within the samples by the passage of transmitted acoustic waves and (2) the electromagnetic waves produced at the fluid-sediment interface by the incident acoustic wave. Both phenomena are caused by relative fluid motion in the sediment pores; this feature is characteristic of poroelastic (Biot) media but is not predicted by either viscoelastic fluid or solid models. A model of plane wave reflection from a fluid-sediment interface using EK-Biot theory leads to theoretical predictions that compare well to the experimental data for both loose glass microspheres and medium-grain sand.

Geochemical controls on lead concentrations in stream water and sediments

USGS Publications Warehouse

Hem, J.D.

1976-01-01

The equilibrium distribution of lead in solution and adsorbed on cation exchange sites in sediment theoretically may be calculated from equations representing selectivities of substrate for lead over H+, Ca2+ and Na+, and the stabilities of lead solute species. Such calculations include consideration of total concentrations of major ions, cation exchange capacity (CEC) of substrate, and pH, at values expected in various natural systems. Measurements of CEC and selectivity coefficients were made for synthetic halloysite, a finely divided amorphous 1:1 clay prepared by precipitation from a mixture of solutions of aluminum and silica. Where suspended sediment having the same properties is present in concentrations of 10-1,000 mg/1 at pH 6-8, more than 90% of the lead present can be adsorbed on sediment surfaces. The cation exchange behavior of lead and other minor cationic species in natural systems could be predicted by this type of model if enough other supporting information were available. Information of the type needed describing natural stream sediments, however, is presently inadequate for accurate predictions. ?? 1976.

Influence of the sediment transport threshold on a river network (Invited)

NASA Astrophysics Data System (ADS)

Devauchelle, O.; Petroff, A.; Seybold, H. F.; Rothman, D.

2010-12-01

In order to transport sediment as bedload, a river must impose a sufficient shear stress on its bed. Conversely, a river far above the threshold for bedload would quickly erode its bed and decrease its slope, thus returning towards the threshold. In 1961, F. M. Henderson first used this hypothesis to derive theoretically Lacey's law (which states that the width of a river scales with the square root of its discharge). His reasoning can be extended to demonstrate that, under similar conditions, the product of the water discharge with the square of its slope is constant (Q S2 = const.), the value of this constant depending on the sediment properties. The steephead ravines of the Florida panhandle, formed by seepage erosion in a homogeneous sand plateau, fall remarkably close to Henderson's equilibrium. Thanks to the uniformity of the sediment and to the steady input of groundwater, the hundreds of streams which drain this landscape are ideal field cases to understand how the quasi-equilibrium hypothesis constrains the network structure. Indeed, both Lacey's equation and the above discharge-slope relation are satisfied in the field. The slope-discharge relation Q S2 = const. is a boundary condition for both the aquifer and the landscape itself, as it relates the flux of water drained by the streams to their longitudinal profile. A direct illustration of this coupling is the shape of the longitudinal profile of rivers in the neighborhood of their springs, which we predict theoretically. The boundary condition Q S2 = const. also holds further downstream, and raises delicate theoretical questions concerning the architecture of the entire network. In particular, we address the limitation of the distance between a spring and the first confluence of a stream.

Primary sources and toxicity of PAHs in Milwaukee-area streambed sediment

USGS Publications Warehouse

Baldwin, Austin K.; Corsi, Steven R.; Lutz, Michelle A.; Ingersoll, Christopher G.; Dorman, Rebecca A.; Magruder, Christopher; Magruder, Matthew

2017-01-01

High concentrations of polycyclic aromatic hydrocarbons (PAHs) in streams can be a significant stressor to aquatic organisms. To understand the likely sources and toxicity of PAHs in Milwaukee-area streams, streambed sediment samples from 40 sites and parking lot dust samples from 6 sites were analyzed for 38 parent PAHs and 25 alkylated PAHs. Diagnostic ratios, profile correlations, principal components analysis, source-receptor modeling, and mass fractions analysis were used to identify potential PAH sources to streambed sediment samples, and land-use analysis was used to relate streambed sediment PAH concentrations to different urban-related land uses. On the basis of this multiple lines-of-evidence approach, coal-tar pavement sealant was indicated as the primary source of PAHs in a majority of streambed sediment samples, contributing an estimated 77% of total PAHs to samples, on average. Comparison to the Probable Effect Concentrations and (or) the Equilibrium Partitioning Sediment Benchmark indicates that 78% of stream sediment samples are likely to cause adverse effects to benthic organisms. Laboratory toxicity tests on a 16-sample subset of the streambed sites using the amphipod Hyalella azteca (28-day) and the midge Chironomus dilutus (10-day) measured significant reductions in one or more biological endpoints, including survival, in 75% of samples, with H. azteca more responsive than C. dilutus.

Three model space experiments on chemical reactions. [Gibbs adsorption, equilibrium shift and electrodeposition

NASA Technical Reports Server (NTRS)

Grodzka, P.; Facemire, B.

1977-01-01

Three investigations conducted aboard Skylab IV and Apollo-Soyuz involved phenomena that are of interest to the biochemistry community. The formaldehyde clock reaction and the equilibrium shift reaction experiments conducted aboard Apollo Soyuz demonstrate the effect of low-g foams or air/liquid dispersions on reaction rate and chemical equilibrium. The electrodeposition reaction experiment conducted aboard Skylab IV demonstrate the effect of a low-g environment on an electrochemical displacement reaction. The implications of the three space experiments for various applications are considered.

Assessment of the bioavailability and phytotoxicity of sediment spiked with polycyclic aromatic hydrocarbons.

PubMed

Rončević, Srđan; Spasojević, Jelena; Maletić, Snežana; Jazić, Jelena Molnar; Isakovski, Marijana Kragulj; Agbaba, Jasmina; Grgić, Marko; Dalmacija, Božo

2016-02-01

Large amounts of sediment are dredged globally every year. This sediment is often contaminated with low concentrations of metals, polycyclic aromatic hydrocarbons, pesticides and other organic pollutants. Some of this sediment is disposed of on land, creating a need for risk assessment of the sediment disposal method, to minimize the degradation of environmental quality and prevent risks to human health. Evaluating the available fractions of certain polycyclic aromatic hydrocarbons is very important, as in the presence of various organisms, they are believed to be easily subject to the processes of bioaccumulation, biosorption and transformation. In order to determine the applicability of applying these methods for the evaluation of pollutant bioavailability in sediments, the desorption kinetics from the sediment of various polycyclic aromatic hydrocarbons in the presence of Tenax and XAD4 were examined over the course of 216 h. Changes in the PAH concentrations in dredged sediments using five different seed plants during a short time of period (10 days) were also followed. Using chemical extraction techniques with Tenax and XAD4, a time of around 24 h is enough to achieve equilibrium for all four PAHs. Results showed good agreement between the seed accumulation and PAH extraction methods with both agents. If we compare the two extraction techniques, XAD4 gave better results for phenanthrene, pyrene and benzo(a)pyrene, and Tenax gave better results for chrysene.

Can Wet Rocky Granular Flows Become Debris Flows Due to Fine Sediment Production by Abrasion?

NASA Astrophysics Data System (ADS)

Arabnia, O.; Sklar, L. S.; Bianchi, G.; Mclaughlin, M. K.

2015-12-01

Debris flows are rapid mass movements in which elevated pore pressures are sustained by a viscous fluid matrix with high concentrations of fine sediments. Debris flows may form from coarse-grained wet granular flows as fine sediments are entrained from hillslope and channel material. Here we investigate whether abrasion of the rocks within a granular flow can produce sufficient fine sediments to create debris flows. To test this hypothesis experimentally, we used a set of 4 rotating drums ranging from 0.2 to 4.0 m diameter. Each drum has vanes along the boundary ensure shearing within the flow. Shear rate was varied by changing drum rotational velocity to maintain a constant Froude Number across drums. Initial runs used angular clasts of granodiorite with a tensile strength of 7.6 MPa, with well-sorted coarse particle size distributions linearly scaled with drum radius. The fluid was initially clear water, which rapidly acquired fine-grained wear products. After each 250 m tangential distance, we measured the particle size distributions, and then returned all water and sediment to the drums for subsequent runs. We calculate particle wear rates using statistics of size and mass distributions, and by fitting the Sternberg equation to the rate of mass loss from the size fraction > 2mm. Abundant fine sediments were produced in the experiments, but very little change in the median grain size was detected. This appears to be due to clast rounding, as evidenced by a decrease in the number of stable equilibrium resting points. We find that the growth in the fine sediment concentration in the fluid scales with unit drum power. This relationship can be used to estimate fine sediment production rates in the field. We explore this approach at Inyo Creek, a steep catchment in the Sierra Nevada, California. There, a significant debris flow occurred in July 2013, which originated as a coarse-grained wet granular flow. We use surveys to estimate flow depth and velocity where super-elevation occurred, to calculate a unit power of 4.5 KW/m2. From this we predict that 14% of the coarse mass is converted to fine sediment by abrasion per km. At that rate, the increase in fines concentration may have been sufficient to cause a wet granular flow to evolve into a debris flow within the first 1 km of its > 4km travel distance.

Basin scale controls on CO2 and CH4 emissions from the Upper Mississippi River

USGS Publications Warehouse

Crawford, John T.; Loken, Luke C.; Stanley, Emily H.; Stets, Edward G.; Dornblaser, Mark M.; Striegl, Robert G.

2016-01-01

The Upper Mississippi River, engineered for river navigation in the 1930s, includes a series of low-head dams and navigation pools receiving elevated sediment and nutrient loads from the mostly agricultural basin. Using high-resolution, spatially resolved water quality sensor measurements along 1385 river kilometers, we show that primary productivity and organic matter accumulation affect river carbon dioxide and methane emissions to the atmosphere. Phytoplankton drive CO2to near or below atmospheric equilibrium during the growing season, while anaerobic carbon oxidation supports a large proportion of the CO2 and CH4 production. Reductions of suspended sediment load, absent of dramatic reductions in nutrients, will likely further reduce net CO2emissions from the river. Large river pools, like Lake Pepin, which removes the majority of upstream sediments, and large agricultural tributaries downstream that deliver significant quantities of sediments and nutrients, are likely to persist as major geographical drivers of greenhouse gas emissions.

DNA from lake sediments reveals long-term ecosystem changes after a biological invasion.

PubMed

Ficetola, Gentile Francesco; Poulenard, Jérôme; Sabatier, Pierre; Messager, Erwan; Gielly, Ludovic; Leloup, Anouk; Etienne, David; Bakke, Jostein; Malet, Emmanuel; Fanget, Bernard; Støren, Eivind; Reyss, Jean-Louis; Taberlet, Pierre; Arnaud, Fabien

2018-05-01

What are the long-term consequences of invasive species? After invasion, how long do ecosystems require to reach a new equilibrium? Answering these questions requires long-term, high-resolution data that are vanishingly rare. We combined the analysis of environmental DNA extracted from a lake sediment core, coprophilous fungi, and sedimentological analyses to reconstruct 600 years of ecosystem dynamics on a sub-Antarctic island and to identify the impact of invasive rabbits. Plant communities remained stable from AD 1400 until the 1940s, when the DNA of invasive rabbits was detected in sediments. Rabbit detection corresponded to abrupt changes of plant communities, with a continuous decline of a dominant plant species. Furthermore, erosion rate abruptly increased with rabbit abundance. Rabbit impacts were very fast and were stronger than the effects of climate change during the 20th century. Lake sediments can allow an integrated temporal analysis of ecosystems, revealing the impact of invasive species over time and improving our understanding of underlying mechanisms.

Molecular controls on Cu and Zn isotopic fractionation in Fe-Mn crusts

NASA Astrophysics Data System (ADS)

Little, S. H.; Sherman, D. M.; Vance, D.; Hein, J. R.

2014-06-01

The isotopic systems of the transition metals are increasingly being developed as oceanic tracers, due to their tendency to be fractionated by biological and/or redox-related processes. However, for many of these promising isotope systems the molecular level controls on their isotopic fractionations are only just beginning to be explored. Here we investigate the relative roles of abiotic and biotic fractionation processes in controlling modern seawater Cu and Zn isotopic compositions. Scavenging to Fe-Mn oxides represents the principal output for Cu and Zn to sediments deposited under normal marine (oxic) conditions. Using Fe-Mn crusts as an analogue for these dispersed phases, we investigate the phase association and crystal chemistry of Cu and Zn in such sediments. We present the results of an EXAFS study that demonstrate unequivocally that Cu and Zn are predominantly associated with the birnessite (δ-MnO2) phase in Fe-Mn crusts, as previously predicted from sequential leaching experiments (e.g., Koschinsky and Hein, 2003). The crystal chemistry of Cu and Zn in the crusts implies a reduction in coordination number in the sorbed phase relative to the free metal ion in seawater. Thus, theory would predict equilibrium fractionations that enrich the heavy isotope in the sorbed phase (e.g., Schauble, 2004). In natural samples, Fe-Mn crusts and nodules are indeed isotopically heavy in Zn isotopes (at ∼1‰) compared to deep seawater (at ∼0.5‰), consistent with the predicted direction of equilibrium isotopic fractionation based on our observations of the coordination environment of sorbed Zn. Further, ∼50% of inorganic Zn‧ is chloro-complexed (the other ∼50% is present as the free Zn2+ ion), and complexation by Cl- is also predicted to favour equilibrium partitioning of light Zn isotopes into the dissolved phase. The heavy Zn isotopic composition of Fe-Mn crusts and nodules relative to seawater can therefore be explained by an inorganic fractionation during uptake. However, Cu in Fe-Mn crusts is isotopically light (at ∼0.3 to 0.5‰) compared to the dissolved phase in seawater (at ∼0.9‰). We suggest that this is because dissolved Cu in the oceans is overwhelmingly complexed to strong organic ligands, which are better competitors for the heavy isotope.

In Situ Rates of Sulfate Reduction in Response to Geochemical Perturbations

USGS Publications Warehouse

Kneeshaw, T.A.; McGuire, J.T.; Cozzarelli, I.M.; Smith, E.W.

2011-01-01

Rates of in situ microbial sulfate reduction in response to geochemical perturbations were determined using Native Organism Geochemical Experimentation Enclosures (NOGEEs), a new in situ technique developed to facilitate evaluation of controls on microbial reaction rates. NOGEEs function by first trapping a native microbial community in situ and then subjecting it to geochemical perturbations through the introduction of various test solutions. On three occasions, NOGEEs were used at the Norman Landfill research site in Norman, Oklahoma, to evaluate sulfate-reduction rates in wetland sediments impacted by landfill leachate. The initial experiment, in May 2007, consisted of five introductions of a sulfate test solution over 11 d. Each test stimulated sulfate reduction with rates increasing until an apparent maximum was achieved. Two subsequent experiments, conducted in October 2007 and February 2008, evaluated the effects of concentration on sulfate-reduction rates. Results from these experiments showed that faster sulfate-reduction rates were associated with increased sulfate concentrations. Understanding variability in sulfate-reduction rates in response to perturbations may be an important factor in predicting rates of natural attenuation and bioremediation of contaminants in systems not at biogeochemical equilibrium. Copyright ?? 2011 The Author(s). Journal compilation ?? 2011 National Ground Water Association.

Numerical Experiments Based on the Catastrophe Model of Solar Eruptions

NASA Astrophysics Data System (ADS)

Xie, X. Y.; Ziegler, U.; Mei, Z. X.; Wu, N.; Lin, J.

2017-11-01

On the basis of the catastrophe model developed by Isenberg et al., we use the NIRVANA code to perform the magnetohydrodynamics (MHD) numerical experiments to look into various behaviors of the coronal magnetic configuration that includes a current-carrying flux rope used to model the prominence levitating in the corona. These behaviors include the evolution in equilibrium heights of the flux rope versus the change in the background magnetic field, the corresponding internal equilibrium of the flux rope, dynamic properties of the flux rope after the system loses equilibrium, as well as the impact of the referential radius on the equilibrium heights of the flux rope. In our calculations, an empirical model of the coronal density distribution given by Sittler & Guhathakurta is used, and the physical diffusion is included. Our experiments show that the deviation of simulations in the equilibrium heights from the theoretical results exists, but is not apparent, and the evolutionary features of the two results are similar. If the flux rope is initially locate at the stable branch of the theoretical equilibrium curve, the flux rope will quickly reach the equilibrium position in the simulation after several rounds of oscillations as a result of the self-adjustment of the system; and the flux rope lose the equilibrium if the initial location of the flux rope is set at the critical point on the theoretical equilibrium curve. Correspondingly, the internal equilibrium of the flux rope can be reached as well, and the deviation from the theoretical results is somewhat apparent since the approximation of the small radius of the flux rope is lifted in our experiments, but such deviation does not affect the global equilibrium in the system. The impact of the referential radius on the equilibrium heights of the flux rope is consistent with the prediction of the theory. Our calculations indicate that the motion of the flux rope after the loss of equilibrium is consistent with which is predicted by the Lin-Forbes model and observations. Formation of the fast mode shock ahead of the flux rope is observed in our experiments. Outward motions of the flux rope are smooth, and magnetic energy is continuously converted into the other types of energy because both the diffusions are considered in calculations, and magnetic reconnection is allowed to occur successively in the current sheet behind the flux rope.

Sediments influence accumulation of two macroalgal species through novel but differing interactions with nutrients and herbivory

NASA Astrophysics Data System (ADS)

Clausing, Rachel J.; Bittick, Sarah Joy; Fong, Caitlin R.; Fong, Peggy

2016-12-01

Despite increasing concern that sediment loads from disturbed watersheds facilitate algal dominance on tropical reefs, little is known of how sediments interact with two primary drivers of algal communities, nutrients and herbivory. We examined the effects of sediment loads on the thalli of two increasingly abundant genera of macroalgae, Galaxaura and Padina, in a bay subject to terrestrial sediment influx in Mo'orea, French Polynesia. Field experiments examining (1) overall effects of ambient sediments and (2) interacting effects of sediments (ambient/removal) and herbivores (caged/uncaged) demonstrated that sediments had strong but opposite effects on both species' biomass accumulation. Sediment removal increased accumulation of Padina boryana Thivy 50% in the initial field experiment but had no effect in the second; rather, in a novel interaction, herbivores overcompensated for increases in tissue nutrient stores that occurred with sediments loads, likely by preferential consumption of nutrient-rich meristematic tissues. Despite negative effects of sediments on biomass, Padina maintained rapid growth across treatments in both experiments. In contrast, positive growth in Galaxaura divaricata Kjellman only occurred with ambient sediment loads. In mesocosm experiments testing interactions of added nutrients and sediments on growth, Galaxaura grew at equivalent rates with sediments (collected from thalli on the reef) as with additions of nitrate and phosphate, suggesting sediments provide a nutrient subsidy. For Padina, however, the only effect was a 50% reduction in growth with sediment. Overall, retention of thallus sediments creates a positive feedback that Galaxaura appears to require to sustain net growth, while Padina merely tolerates sediments. These results indicate that sediments can modify nutrient and herbivore control of algae in ways that differ among species, with the potential for strong and unexpected effects on the abundance and composition of tropical reef macroalgae.

Potentially Toxic Element Uptake by Bacillus jeotgali Strain U3: A Natural Attenuation Mechanism in polluted sediments from Estero de Urías Coastal Lagoon (SE Gulf of California)?

NASA Astrophysics Data System (ADS)

Green-Ruiz, C. R.; Rodríguez-Tirado, V. A.; Carrasco-Valenzuela, A. C.; Gómez-Gil, B.

2007-05-01

In addition to an increased flux of potentially toxic elements (PTE's) into aquatic ecosystems, toxicity, bioavailability and persistency of these pollutants have led to critical localized pollution sites around the world, and the risk for the environment and the health of organism, including humans, has been increased. Clean-up technologies for the treatment of huge volumes of water, sediments and soils contaminated with these elements are needed. Use of bacteria as concentrators of PTE's can become a good tool for the remediation of man- impacted coastal ecosystems. A subtropical estuarine bacterium was isolate from surface sediments from Estero de Urías coastal lagoon, Mazatlán, Mexico, which is an aquatic ecosystem surrounded by several anthropogenic that release PTE's into the environment. This bacterial strain (U3) was ascertained (16s rRNA analysis) to belong to the Bacillus jeotgali specie. Batch experiments with different bacterial biomass and PTE (Cd, Cu, Hg, Pb and Zn) concentrations, pH and temperature were carried out in order to evaluate the biosorption capacity of Bacillus jeotgali strain U3. Except data from Zn experiments, all values were fitted to the adsorption Langmuir model. The maximum adsorption capacities (qmax) were 58 mg Cd g-1, 27 mg Cu g-1, 191 mg Hg g-1 (viable biomass), 21 mg Hg g-1 (non-viable biomass), 90 mg Pb g-1. Adsorption of Zn was 350 mg g-1, when equilibrium concentration in solution was 130 mg Zn l-1. According our data, Bacillus jeotgali strain U3 is considered as a suitable adsorbent and the presence of this microorganism in Estero de Urías coastal lagoon can produce a natural attenuation of potentially toxic elements pollution.

Effects of Urechis unicinctus juveniles on chemical characteristics of organically contaminated coastal sediment

NASA Astrophysics Data System (ADS)

Kang, Kyoung Ho; Zhang, Zhifeng; Kim, Jae Min; Seon, Seung Chun; Shao, Mingyu

2010-03-01

Biological activities of marine benthos such as burrowing and feeding may change sediment characteristics. We conducted three experiments to examine the potential of using juveniles of a spoon worm Urechis unicinctus to improve the quality of organically contaminated coastal sediment. Sediment samples were collected from a site that was heavily contaminated with organic matter (Seonso) and two sites that were clean (Myo-do, Dolsan-do). Urechis juveniles, obtained by artificial fertilization and cultured in the laboratory, were introduced to the sediment (weight 3 kg, depth 10 cm) at a density of 500 individuals per aquarium (length 50 cm, width 35 cm, height 30 cm) (Experiment 1), or at densities ranging from 100 to 900 individuals per beaker (Experiment 2). To examine how sediment contamination can be modified by the effects of Urechis, 500 individuals (per aquarium) were exposed to the Seonso contaminated sediment that had been mixed with 0-100% clean sand (Experiment 3). Each experiment lasted two months and sediment samples were collected every 15 d to determine the several indexes of sediment quality, which included acid volatile sulfide (AVS), chemical oxygen demand (COD) and total ignition loss (TIL). In Experiment 1, the existence of Urechis did not result in significant changes in quality indexes in the sediments collected from Myo-do, Dolsan-do. However, AVS, COD and TIL of the Seonso sediment all decreased significantly after co-incubation with Urechis juveniles for 30 to 45 d. Experiment 2 showed that a density of at least 300 juveniles per beaker was necessary to significantly reduce all three quality indexes, and the magnitude of reduction was positively correlated with juvenile density. Experiment 3 revealed that Urechis juveniles were effective in reducing the AVS, COD and TIL of the Seonso sediment that had been mixed with 60%, 80%, and 80% of clean sand, respectively. The results of the present study therefore indicated that juveniles of this spoon worm have the potential to be used to improve the quality of organically contaminated sediment in coastal waters.

Development and application of a three dimensional numerical model for predicting pollutant and sediment transport using an Eulerian-Lagrangian marker particle technique

NASA Technical Reports Server (NTRS)

Pavish, D. L.; Spaulding, M. L.

1977-01-01

A computer coded Lagrangian marker particle in Eulerian finite difference cell solution to the three dimensional incompressible mass transport equation, Water Advective Particle in Cell Technique, WAPIC, was developed, verified against analytic solutions, and subsequently applied in the prediction of long term transport of a suspended sediment cloud resulting from an instantaneous dredge spoil release. Numerical results from WAPIC were verified against analytic solutions to the three dimensional incompressible mass transport equation for turbulent diffusion and advection of Gaussian dye releases in unbounded uniform and uniformly sheared uni-directional flow, and for steady-uniform plug channel flow. WAPIC was utilized to simulate an analytic solution for non-equilibrium sediment dropout from an initially vertically uniform particle distribution in one dimensional turbulent channel flow.

Spatial variation in sediment-water exchange of phosphorus in Florida Bay: AMP as a model organic compound.

PubMed

Huang, Xiao-Lan; Zhang, Jia-Zhong

2010-10-15

Dissolved organic phosphorus (DOP) has been recognized as dominant components in total dissolved phosphorus (TDP) pools in many coastal waters, and its exchange between sediment and water is an important process in biogeochemical cycle of phosphorus. Adenosine monophosphate (AMP) was employed as a model DOP compound to simulate phosphorus exchange across sediment-water interface in Florida Bay. The sorption data from 40 stations were fitted to a modified Freundlich equation and provided a detailed spatial distribution both of the sediment's zero equilibrium phosphorus concentration (EPC(0-T)) and of the distribution coefficient (K(d-T)) with respect to TDP. The K(d-T) was found to be a function of the index of phosphorus saturation (IPS), a molar ratio of the surface reactive phosphorus to the surface reactive iron oxide content in the sediment, across the entire bay. However, the EPC(0-T) was found to correlate to the contents of phosphorus in the eastern bay only. Sediment in the western bay might act as a source of the phosphorus in the exchange process due to their high EPC(0-T) and low K(d-T), whereas sediments in the eastern bay might act as a sink because of their low EPC(0-T) and high K(d-T). These results strongly support the hypothesis that both phosphorus and iron species in calcareous marine sediments play a critical role in governing the sediment-water exchange of both phosphate and DOP in the coastal and estuarine ecosystems.

The effect of activated carbon on partitioning, desorption, and biouptake of native polychlorinated biphenyls in four freshwater sediments.

PubMed

Sun, Xueli; Ghosh, Upal

2008-11-01

The present study evaluated the effect of activated carbon amendment in four freshwater sediments from the Great Lakes (North America) areas of concern with a wide range of sediment geochemical characteristics (0.83-5.1% total organic carbon) and polychlorinated biphenyl (PCB) concentrations (0.33-84.7 microg/g). The work focused on understanding the impact of activated carbon amendment on PCB aqueous partitioning, PCB desorption characteristics, and PCB biouptake in a freshwater oligochaete (Lumbriculus variegatus). The results showed that PCB aqueous equilibrium concentrations, rapid desorption fractions, and biouptake by the oligochaete were reduced after activated carbon amendment. Addition of activated carbon at a dose of 0.5-fold native organic carbon reduced PCB bioaccumulation by 42% for Niagara River sediment, 85% for Grasse River sediment, 74% for Milwaukee River sediment 1, and 70% for Milwaukee River sediment 2. A linear relationship was observed between log biota-sediment accumulation factor and the first 6-h desorption fractions for each PCB homologue for treated and untreated sediments. Water-lipid bioconcentration factors for PCB congeners were largely conserved after amendment with activated carbon. Our present results suggest that at steady state, changes in the aqueous PCB concentrations can be used to predict changes in PCB bioaccumulation in deposit-feeding organisms. Thus, use of advanced pore-water measurement techniques, such as solid-phase extraction passive samplers, may be suitable for long-term monitoring of treatment performance.

Variation laws and release characteristics of phosphorus on surface sediment of Dongting Lake.

PubMed

Zhu, Guangrui; Yang, Ying

2018-05-01

The variation trend and growth rate of P were analyzed by the concentration of the phosphorus fraction on surface sediment of Dongting Lake from 2012 to 2016, to reveal the cumulative effect of P in the actual environment. Meanwhile, the adsorption kinetics and adsorption isotherm were employed to examine the P-release possibility of sediment, which predicts the yearly released sediment phosphorus in Dongting Lake. The actual growth rate of TP (Total Phosphorus) is 53 mg·(kg·year) -1 in East Dongting Lake, 39 mg·(kg·year) -1 in South Dongting Lake, and 29 mg·(kg·year) -1 in West Dongting Lake, while the sum of the phosphorus fraction growth rates has little difference from the rate of TP in sediments of the three areas of Dongting Lake. Furthermore, the Elovich model and the Langmuir crossover-type equations are established to present the adsorption characteristic of sediment in Dongting Lake; the result shows that the sediments play a source role for phosphorus in East and South Dongting Lake from zero equilibrium phosphorus concentration (EPC 0 ) in the present situation, but an adsorption effect on TP is shown in West Dongting Lake. When the conditions of environment change are ignored, the maximum P-sorption level in sediments of East Dongting Lake will reach in 2040 according to the actual growth rate of sediments, while that in West Dongting Lake and South Dongting Lake will be in 2046 and 2061, respectively.

Protein associations and analytical ultracentrifugation

NASA Astrophysics Data System (ADS)

Laue, Tom

2010-03-01

Analytical ultracentrifugation (AUC) is a first principle method for characterizing the thermodynamics of macromolecules in solution. Since AUC directly assesses mass, it is particularly useful for characterizing both reversible and irreversible binding interactions between macromolecules. The principle measurement in AUC is the concentration as a function of radial position, which may be provided by either absorbance, interference or fluorescence detection. Each of these three different detectors may be used to characterize protein associations using either sedimentation equilibrium or sedimentation velocity analysis. Examples will be shown for characterizing irreversible (aggregate) formation, high-accuracy reversible association analysis, and the detection of protein interactions in complex and concentrated fluids (e.g. serum, cell cytosol).

Demonstrating Phase Changes.

ERIC Educational Resources Information Center

Rohr, Walter

1995-01-01

Presents two experiments that demonstrate phase changes. The first experiment explores phase changes of carbon dioxide using powdered dry ice sealed in a piece of clear plastic tubing. The second experiment demonstrates an equilibrium process in which a crystal grows in equilibrium with its saturated solution. (PVD)

Constraints on Subduction Zone Temperatures and Chemical Fluxes from Accessory Phase Saturation in Subducted Sediments (Invited)

NASA Astrophysics Data System (ADS)

Blundy, J.; Skora, S.

2009-12-01

A global correlation between the incompatible trace element chemistry of subducted sediments and that of magmas erupted through the overlying plate testifies to the important role that sediments play in controlling magmagenesis. We report new experimental data on the high pressure (3 GPa) and temperature (700-1300 °C) phase relations of hydrous red clay to evaluate the role of residual accessory phases in controlling the incompatible trace element chemistry of sediment-derived fluids. A particular focus is monazite, which preferentially incorporates LREE and Th, exerting a powerful control on the fluid Th/LREE ratio. Given that arc magmas appear to inherit the Th/LREE ratio of the associated subducting sediment, understanding monazite solubility and stability has the potential to provide new constraints on temperature at the slab surface, a parameter that is notoriously hard to pin down by other means. Experiments on red clay with H2O structurally bound in hydrous minerals (<2 wt%) produced negligible melt fractions for any reasonable temperatures. Experiments with 7-15 wt% added H2O produced copious melting at temperatures only 50-100°C above the solidus (c. 720 °C), e.g. with 15 wt% added H2O, the red clay is >50% molten at 800 °C. Irrespective of the amount of added H2O the residual assemblage comprised garnet and kyanite up to the liquidus (1250 °C with 7 wt% H2O). Phengite is present ≤800 °C; ilmenite and rutile persist to c. 1000 °C; quartz/coesite-out temperature decreases from 1000 °C with 7 wt% H2O to 800 °C with 15%. Monazite was stable to 950 °C in the Th- and LREE-doped starting materials that we used. The trace element contents of the residual melts in equilibrium with monazite-thorite solid solutions were used, in conjunction with published data, to develop a thermodynamic model of LREE and Th solubility in sediment-derived fluids. These models were used to calculate the stability of monazite in a red clay with natural LREE and Th levels. For the case of 7 wt% added H2O, monazite is exhausted at 825 °C; it disappears at 780 °C with 15 wt% added H2O. In our experiments monazite fractionates LREE from Th, such that fluids preserving the original sedimentary ratio must be generated at or above monazite-out temperatures in subducted slabs where red clay is the dominant sedimentary lithology. We propose that the subducted sedimentary signature is imparted by fluxing of H2O derived from hydrated (e.g. serpentinised) portions of the deeper subducting slab, triggering copious “flash melting” of the sediment at the point were its temperature exceeds ~800 °C. Without the addition of H2O sediment melting is too restricted to allow any appreciable fluid release into the overlying mantle. Moreover, under such conditions the Th/LREE ratio is strongly fractionated due to the abundance of residual monazite. The availability of H2O in hydrated portions of subducted slabs, e.g. in the vicinity of fracture zones, may exercise an important control on the spatial distribution of subduction zone magmatism.

Wave-induced ripple development in mixed clay-sand substrates

NASA Astrophysics Data System (ADS)

Wu, Xuxu; Parsons, Daniel; Baas, Jaco H.; Mouazé, Dominique; McLelland, Stuart; Amoudry, Laurent; Eggenhuisen, Jorris; Cartigny, Matthieu; Ruessink, Gerben

2016-04-01

This paper reports on a series of experiments that aim to provide a fuller understanding of ripple development within clay-sand mixture substrates under oscillatory flow conditions. The work was conducted in the Total Environment Simulator at the University of Hull and constituted 6 separate runs, in which 5 runs were conducted under identical sets of regular waves (an additional run was conducted under irregular waves, but is not discussed in present paper). The bed content was systematically varied in its composition ranging from a pure sand bed through to a bed comprising 7.4% clay. A series of state-of-the-art measurements were employed to quantify interactions of near-bed hydrodynamics, sediment transport, and turbulence over rippled beds formed by wave action, during and after, each run. The experimental results demonstrate the significant influence of the amount of cohesive clay materials in the substrate on ripple evolution under waves. Most importantly, addition of clay in the bed dramatically slowed down the rate of ripple development and evolution. The equilibrium time of each run increased exponentially from 30 minutes under the control conditions of a pure sand bed, rising to ~350 minutes for the bed with the highest fraction of clay. The paper discusses the slower ripple growth rates with higher cohesive fractions, via an influence on critical shear, but highlights that the end equilibrium size of ripples is found to be independent of increasing substrate clay fraction. The suspended particles mass (SPM) concentration indicates that clay particles were suspended and winnowed by wave action. Additionally, laser granulometry of the final substrates verified that ripple crests were composed of pure sand layers that were absent at ripple troughs, reflecting a relatively higher winnowing efficiency at wave ripples crest. The winnowing process and its efficiency is inexorably linked to wave ripple development and evolution. The implications of the results for sediment dynamics in mixed-bed substrates are highlighted and discussed.

Microgravity combustion of dust suspensions

NASA Technical Reports Server (NTRS)

Lee, John H. S.; Peraldi, Olivier; Knystautas, Rom

1993-01-01

Unlike the combustion of homogeneous gas mixtures, there are practically no reliable fundamental data (i.e., laminar burning velocity, flammability limits, quenching distance, minimum ignition energy) for the combustion of heterogeneous dust suspensions. Even the equilibrium thermodynamic data such as the constant pressure volume combustion pressure and the constant pressure adiabatic flame temperature are not accurately known for dust mixtures. This is mainly due to the problem of gravity sedimentation. In normal gravity, turbulence, convective flow, electric and acoustic fields are required to maintain a dust in suspension. These external influences have a dominating effect on the combustion processes. Microgravity offers a unique environment where a quiescent dust cloud can in principle be maintained for a sufficiently long duration for almost all combustion experiments (dust suspensions are inherently unstable due to Brownian motion and particle aggregation). Thus, the microgravity duration provided by drop towers, parabolic flights, and the space shuttle, can all be exploited for different kinds of dust combustion experiments. The present paper describes some recent studies on microgravity combustion of dust suspension carried out on the KC-135 and the Caravelle aircraft. The results reported are obtained from three parabolic flight campaigns.

Characterization of redox conditions in groundwater contaminant plumes

NASA Astrophysics Data System (ADS)

Christensen, Thomas H.; Bjerg, Poul L.; Banwart, Steven A.; Jakobsen, Rasmus; Heron, Gorm; Albrechtsen, Hans-Jørgen

2000-10-01

Evaluation of redox conditions in groundwater pollution plumes is often a prerequisite for understanding the behaviour of the pollutants in the plume and for selecting remediation approaches. Measuring of redox conditions in pollution plumes is, however, a fairly recent issue and yet relative few cases have been reported. No standardised or generally accepted approach exists. Slow electrode kinetics and the common lack of internal equilibrium of redox processes in pollution plumes make, with a few exceptions, direct electrochemical measurement and rigorous interpretation of redox potentials dubious, if not erroneous. Several other approaches have been used in addressing redox conditions in pollution plumes: redox-sensitive compounds in groundwater samples, hydrogen concentrations in groundwater, concentrations of volatile fatty acids in groundwater, sediment characteristics and microbial tools, such as MPN counts, PLFA biomarkers and redox bioassays. This paper reviews the principles behind the different approaches, summarizes methods used and evaluates the approaches based on the experience from the reported applications.

Satellite monitoring of sea surface pollution

NASA Technical Reports Server (NTRS)

Fielder, G.; Telfer, D. J. (Principal Investigator)

1979-01-01

The author has identified the following significant results. Image processing techniques developed are well adapted to the exploration and isolation of local areas which exhibit small temperature differences between themselves and their surroundings. In the worst case of imagery of small areal extent of sea surface having no coastal boundary in the area, there is yet no method of distinguishing unambiguously an oil spill from fog, cloud, the effect produced by shallow sediments, or the effects of naturally occuring thermal fronts. In the case of uniform slicks of liquid North Sea oil in still air, laboratory simulation experiments show that, for oil thicknesses in excess of 1 or 2 mm, there is, under equilibrium conditions, little dependence of oil surface temperature on the thickness of the oil layer. The surface temperature of oil is consistently higher than that of water, the difference being about 1 K at low values of relative humidity, but tending to increase as the relative humidity increases.

Isolation and purification of a granulosis virus from infected larvae of the Indian meal moth, Plodia interpunctella.

PubMed

Tweeten, K A; Bulla, L A; Consigli, R A

1977-09-01

A procedure was developed for purification of a granulosis virus inclusion body produced in vivo in the Indian meal moth, Plodia interpunctella (Hübner). Purification was accomplished by differential centrifugation, treatment with sodium deoxycholate, and velocity sedimentation in sucrose gradients. The adequacy of the procedure was confirmed by mixing experiments in which uninfected, radioactively labeled larvae were mixed with infected, unlabeled larvae. After purification, the virus was shown to be free of host tissue, to retain its physical integrity, and to be highly infectious per os. Preparations of purified virus consisted of homogeneous populations of intact inclusion bodies (210 by 380 nm) whose buoyant density was 1.271 g/cm3 when centrifuged to equilibrium in sucrose gradients. Electron microscopy of thin-sectioned virus or of virus sequentially disrupted on electron microscope grids demonstrated three components: protein matrix, envelope, and nucleocapsid.

Isolation and purification of a granulosis virus from infected larvae of the Indian meal moth, Plodia interpunctella.

PubMed Central

Tweeten, K A; Bulla, L A; Consigli, R A

1977-01-01

A procedure was developed for purification of a granulosis virus inclusion body produced in vivo in the Indian meal moth, Plodia interpunctella (Hübner). Purification was accomplished by differential centrifugation, treatment with sodium deoxycholate, and velocity sedimentation in sucrose gradients. The adequacy of the procedure was confirmed by mixing experiments in which uninfected, radioactively labeled larvae were mixed with infected, unlabeled larvae. After purification, the virus was shown to be free of host tissue, to retain its physical integrity, and to be highly infectious per os. Preparations of purified virus consisted of homogeneous populations of intact inclusion bodies (210 by 380 nm) whose buoyant density was 1.271 g/cm3 when centrifuged to equilibrium in sucrose gradients. Electron microscopy of thin-sectioned virus or of virus sequentially disrupted on electron microscope grids demonstrated three components: protein matrix, envelope, and nucleocapsid. Images PMID:334076

Biological and chemical characterization of metal bioavailability in sediments from Lake Roosevelt, Columbia River, Washington, USA

USGS Publications Warehouse

Besser, J.M.; Brumbaugh, W.G.; Ivey, C.D.; Ingersoll, C.G.; Moran, P.W.

2008-01-01

We studied the bioavailability and toxicity of copper, zinc, arsenic, cadmium, and lead in sediments from Lake Roosevelt (LR), a reservoir on the Columbia River in Washington, USA that receives inputs of metals from an upstream smelter facility. We characterized chronic sediment toxicity, metal bioaccumulation, and metal concentrations in sediment and pore water from eight study sites: one site upstream in the Columbia River, six sites in the reservoir, and a reference site in an uncontaminated tributary. Total recoverable metal concentrations in LR sediments generally decreased from upstream to downstream in the study area, but sediments from two sites in the reservoir had metal concentrations much lower than adjacent reservoir sites and similar to the reference site, apparently due to erosion of uncontaminated bank soils. Concentrations of acid-volatile sulfide in LR sediments were too low to provide strong controls on metal bioavailability, and selective sediment extractions indicated that metals in most LR sediments were primarily associated with iron and manganese oxides. Oligochaetes (Lumbriculus variegatus) accumulated greatest concentrations of copper from the river sediment, and greatest concentrations of arsenic, cadmium, and lead from reservoir sediments. Chronic toxic effects on amphipods (Hyalella azteca; reduced survival) and midge larvae (Chironomus dilutus; reduced growth) in whole-sediment exposures were generally consistent with predictions of metal toxicity based on empirical and equilibrium partitioning-based sediment quality guidelines. Elevated metal concentrations in pore waters of some LR sediments suggested that metals released from iron and manganese oxides under anoxic conditions contributed to metal bioaccumulation and toxicity. Results of both chemical and biological assays indicate that metals in sediments from both riverine and reservoir habitats of Lake Roosevelt are available to benthic invertebrates. These findings will be used as part of an ongoing ecological risk assessment to determine remedial actions for contaminated sediments in Lake Roosevelt. ?? 2007 Springer Science+Business Media, LLC.

Channel responses to varying sediment input: A flume experiment modeled after Redwood Creek, California

USGS Publications Warehouse

Madej, Mary Ann; Sutherland, D.G.; Lisle, T.E.; Pryor, B.

2009-01-01

At the reach scale, a channel adjusts to sediment supply and flow through mutual interactions among channel form, bed particle size, and flow dynamics that govern river bed mobility. Sediment can impair the beneficial uses of a river, but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing. We use a flume experiment, coupled with field measurements in a gravel-bed river, to explore sediment transport, storage, and mobility relations under various sediment supply conditions. Our flume experiment modeled adjustments of channel morphology, slope, and armoring in a gravel-bed channel. Under moderate sediment increases, channel bed elevation increased and sediment output increased, but channel planform remained similar to pre-feed conditions. During the following degradational cycle, most of the excess sediment was evacuated from the flume and the bed became armored. Under high sediment feed, channel bed elevation increased, the bed became smoother, mid-channel bars and bedload sheets formed, and water surface slope increased. Concurrently, output increased and became more poorly sorted. During the last degradational cycle, the channel became armored and channel incision ceased before all excess sediment was removed. Selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored. Our flume results of changes in bed elevation, sediment storage, channel morphology, and bed texture parallel those from field surveys of Redwood Creek, northern California, which has exhibited channel bed degradation for 30??years following a large aggradation event in the 1970s. The flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur, but the channel may return to a state of balancing sediment supply and transport capacity.

The influence of fish feed pellets on the stability of seabed sediment: A laboratory flume investigation

NASA Astrophysics Data System (ADS)

Neumeier, Urs; Friend, Patrick L.; Gangelhof, Uffe; Lunding, Jens; Lundkvist, Morten; Bergamasco, Alessandro; Amos, Carl L.; Flindt, Mogens

2007-11-01

Superfluous fish food settling below fish farms can have a negative impact on the seabed. To aid in the assessment of this impact a series of flume experiments, designed to mimic seabed conditions below a fish farm, was conducted with the aim of examining the effects of fish pellets on the stability of fine sediments. Artificial beds, with varying quantities of fish pellets incorporated both within the sediment matrix and lying on the sediment surface, were allowed to consolidate for different periods of time ranging from 1 to 10 days, and then subjected to erosion experiments. In flume experiments containing fish pellets, a bacterial biofilm developed at the sediment-water interface after a few days. In the control experiments (no fish pellets), a diatom biofilm caused extensive stabilisation of the surface sediment. The erosion experiments showed that the addition of fish pellets reduced the surface erosion threshold by more than 50%. The stability decrease was more pronounced in the experiments with greater amounts of pellets. Evidence of drag reduction due to high suspended sediment concentration was also observed. This phenomenon is discussed and a correction formula is proposed for the effective shear stress experienced by the bed.

Geochemical behavior and dissolved species control in acid sand pit lakes, Sepetiba sedimentary basin, Rio de Janeiro, SE - Brazil

NASA Astrophysics Data System (ADS)

Marques, Eduardo D.; Sella, Sílvia M.; Bidone, Edison D.; Silva-Filho, Emmanoel V.

2010-12-01

This work shows the influence of pluvial waters on dissolved components and mineral equilibrium of four sand pit lakes, located in the Sepetiba sedimentary basin, SE Brazil. The sand mining activities promote sediment oxidation, lowering pH and increasing SO 4 contents. The relatively high acidity of these waters, similar to ore pit lakes environment and associated acid mine drainage, increases weathering rate, especially of silicate minerals, which produces high Al concentrations, the limiting factor for fish aquaculture. During the dry season, basic cations (Ca, Mg, K and Na), SiO 2 and Al show their higher values due to evapoconcentration and pH are buffered. In the beginning of the wet season, the dilution factor by rainwater increases SO 4 and decreases pH values. The aluminum monomeric forms (Al(OH) 2+ and Al(OH) 2+), the most toxic species for aquatic organisms, occur during the dry season, while AlSO 4+ species predominate during the wet season. Gibbsite, allophane, alunite and jurbanite are the reactive mineral phases indicated by PHREEQC modeling. During the dry season, hydroxialuminosilicate allophane is the main phase in equilibrium with the solution, while the sulphate salts alunite and jurbanite predominate in the rainy season due to the increasing of SO 4 values. Gibbsite is also in equilibrium with sand pit lakes waters, pointing out that hydrolysis reaction is a constant process in the system. Comparing to SiO 2, sulphate is the main Al retriever in the pit waters because the most samples (alunite and jurbanite) are in equilibrium with the solution in both seasons. This Al hydrochemical control allied to some precaution, like pH correction and fertilization of these waters, allows the conditions for fishpond culture. Equilibrium of the majority samples with kaolinite (Ca, Mg, Na diagrams) and primary minerals (K diagram) points to moderate weathering rate in sand pit sediments, which cannot be considered for the whole basin due to the anomalous acidification of the studied waters.

In situ determination of heat flow in unconsolidated sediments

USGS Publications Warehouse

Sass, J.H.; Kennelly, J.P.; Wendt, W.E.; Moses, T.H.; Ziagos, J.P.

1979-01-01

Subsurface thermal measurements are the most effective, least ambiguous tools for identifying and delineating possible geothernml resources. Measurements of thermal gradient in the upper few tens of meters generally are sufficient to outline the major anomalies, but it is always desirable to combine these gradients with reliable estimates of thermal conductivity to provide data on the energy flux and to constrain models for the heat sources responsible for the observed, near-surface thermal anomalies. The major problems associated with heat-flow measurements in the geothermal exploration mode are concerned with the economics of casing and/or grouting holes, the repeated site visits necessary to obtain equilibrium temperature values, the possible legal liability associated with the disturbance of underground aquifers, the surface hazards presented by pipes protruding from the ground, and the security problems associated with leaving cased holes open for periods of weeks to months. We have developed a technique which provides reliable 'real-time' determinations of temperature, thermal conductivity, and hence, of heat flow during the drilling operation in unconsolidated sediments. A combined temperature, gradient, and thermal conductivity experiment can be carried out, by driving a thin probe through the bit about 1.5 meters into the formation in the time that would otherwise be required for a coring trip. Two or three such experiments over the depth range of, say, 50 to 150 meters provide a high-quality heat-flow determination at costs comparable to those associated with a standard cased 'gradient hole' to comparable depths. The hole can be backfilled and abandoned upon cessation of drilling, thereby eliminating the need for casing, grouting, or repeated site visits.

Numerical Modeling of River Fluxes Under Changing Environmental Conditions (Invited)

NASA Astrophysics Data System (ADS)

Simpson, G.

2013-12-01

High frequency climate cycles have a major impact on landscapes, but it remains uncertain if alluvial rivers can transfer the resulting sediment pulses downstream to sedimentary basins. Stratigraphic records located near the mouth of rivers exhibit cyclicity consistent with orbital forcing. However, in some cases, the sediment supply from rivers appears to have remained remarkably constant despite changes in climate, which has been interpreted to indicate that rivers dampen rapid variability. Here, we employ a physically-based numerical model to resolve this outstanding problem. Our simulations show that rivers forced with water flux cycles exhibit highly pulsed sediment outflux records, even when the period of forcing is several orders of magnitude shorter than river response times. This non-linear amplified system response characterised by positive feedback is related to the strong negative correlation between water flux and the equilibrium slope of a river. We also show that the apparent stability of sediment fluxes based on time-averaged data is an artifact of integrating highly episodic records over multiple cycles rather than a signature of diffusive floodplain processes. We conclude that marine sedimentary basins may record sediment-flux cycles resulting from discharge (and ultimately climate) variability, whereas they may be relatively insensitive to pure sediment-flux perturbations (such as for example those induced by tectonics).

A Unified Kinetics and Equilibrium Experiment: Rate Law, Activation Energy, and Equilibrium Constant for the Dissociation of Ferroin

ERIC Educational Resources Information Center

Sattar, Simeen

2011-01-01

Tris(1,10-phenanthroline)iron(II) is the basis of a suite of four experiments spanning 5 weeks. Students determine the rate law, activation energy, and equilibrium constant for the dissociation of the complex ion in acid solution and base dissociation constant for phenanthroline. The focus on one chemical system simplifies a daunting set of…

Different partition of polycyclic aromatic hydrocarbon on environmental particulates in freshwater: Microplastics in comparison to natural sediment.

PubMed

Wang, Wenfeng; Wang, Jun

2018-01-01

Microplastics pollution in the aquatic ecosystems has aroused increasing concerns in recent years. Though microplastics are known to sorb organic contaminants from water, the interaction mechanisms between microplastics and organic chemicals are not yet well understood. Here we investigated the partition characteristics of phenanthrene (Phe) in three mass-produced plastic particles, including polyethylene (PE), polystyrene (PS) and polyvinylchloride (PVC)， and one natural sediment, as a comparison. The sorption kinetics of Phe onto microplastics and natural sediment were successfully described by the pseudo-second-order model (R 2 > 0.992), while the equilibrium data were best-fitted to the Langmuir isotherm (R 2 > 0.995). Compared with natural sediment, microplastics exhibited higher capacities for Phe which followed an order of PE > PS > PVC. As the aqueous concentration of pyrene (Pyr) increased, both uptakes and distribution coefficients (K d ) of Phe within the solids decreased, with natural sediment giving the largest decline. Although proportions of Phe desorbed from the contaminated microplastics were low, due to the high Phe uptake, microplastics released larger amounts of the sorbed Phe to water than the natural sediment during the desorption process. Given their minimal abundance relative to natural sediment, microplastics may play a less important role in the transport of organic pollutants in a natural aquatic environment. Copyright © 2017 Elsevier Inc. All rights reserved.

Formation Mechanisms for Spur and Groove Features on Fringing Reefs

NASA Astrophysics Data System (ADS)

Bramante, J. F.; Ashton, A. D.; Perron, J. T.

2016-12-01

Spur and groove systems (SAGs) are ubiquitous morphological features found on fore-reef slopes globally. SAGs consist of parallel, roughly shore-normal ridges of actively growing coral and coralline algae (spurs) separated by offshore-sloping depressions typically carpeted by a veneer of sediment (grooves). Although anecdotal observations and recent statistical analyses have reported correlations between wave exposure and the distribution of SAGs on fore-reef slopes, the physical mechanisms driving SAG formation remain poorly understood. For example, there remains significant debate regarding the importance of coral growth versus bed erosion for SAG formation. Here we investigate a hypothesis that SAG formation is controlled by feedbacks between sediment production and diffusion and coral growth. Using linear stability analysis, we find that sediment production, coral growth, and the feedbacks between them are unable to produce stable periodic structures without a sediment sink. However, if incipient grooves act as conduits for sediment transport offshore, a positive feedback can develop as the groove bed erodes through wave-driven abrasion during offshore transport. Eventually a negative feedback slows groove deepening when the groove bed is armored by sediment, and the groove bed relaxes to a sediment-veneered equilibrium profile analogous to sediment-rich shorefaces. To test this hypothesis, we apply a numerical model that incorporates coral growth and sediment production, sediment diffusion, non-linear wave-driven abrasion, and sediment advection offshore. This model produces the periodic, linear features characteristic of SAG morphology. The relative magnitude of growth, production, diffusion, abrasion, and advection rates affect periodic spacing or wavelength of the modeled SAGs. Finally, we evaluate the ability of the model to replicate geographical variability in SAG characteristics using previously published datasets and reanalysis wave data.

Interaction of sigma factor sigmaN with Escherichia coli RNA polymerase core enzyme.

PubMed

Scott, D J; Ferguson, A L; Gallegos, M T; Pitt, M; Buck, M; Hoggett, J G

2000-12-01

The equilibrium binding and kinetics of assembly of the DNA-dependent RNA polymerase (RNAP) sigma(N)-holoenzyme has been investigated using biosynthetically labelled 7-azatryptophyl- (7AW)sigma(N). The spectroscopic properties of such 7AW proteins allows their absorbance and fluorescence to be monitored selectively, even in the presence of high concentrations of other tryptophan-containing proteins. The 7AWsigma(N) retained its biological activity in stimulating transcription from sigma(N)-specific promoters, and in in vitro gel electrophoresis assays of binding to core RNAP from Escherichia coli. Furthermore, five Trp-->Ala single mutants of sigma(N) were shown to support growth under conditions of nitrogen limitation, and showed comparable efficiency in activating the sigma(N)-dependent nifH promoter in vivo, indicating that none of the tryptophan residues were essential for activity. The equilibrium binding of 7AWsigma(N) to core RNAP was examined by analytical ultracentrifugation. In sedimentation equilibrium experiments, absorbance data at 315 nm (which reports selectively on the distribution of free and bound 7AWsigma(N)) established that a 1:1 complex was formed, with a dissociation constant lower than 2 microM. The kinetics of the interaction between 7AWsigma(N) and core RNAP was investigated using stopped-flow spectrofluorimetry. A biphasic decrease in fluorescence intensity was observed when samples were excited at 280 nm, whereas only the slower of the two phases was observed at 315 nm. The kinetic data were analysed in terms of a mechanism in which a fast bimolecular association of sigma(N) with core RNAP is followed by a relatively slow isomerization step. The consequences of these findings on the competition between sigma(N) and the major sigma factor, sigma(70), in Escherichia coli are discussed.

Interaction of sigma factor sigmaN with Escherichia coli RNA polymerase core enzyme.

PubMed Central

Scott, D J; Ferguson, A L; Gallegos, M T; Pitt, M; Buck, M; Hoggett, J G

2000-01-01

The equilibrium binding and kinetics of assembly of the DNA-dependent RNA polymerase (RNAP) sigma(N)-holoenzyme has been investigated using biosynthetically labelled 7-azatryptophyl- (7AW)sigma(N). The spectroscopic properties of such 7AW proteins allows their absorbance and fluorescence to be monitored selectively, even in the presence of high concentrations of other tryptophan-containing proteins. The 7AWsigma(N) retained its biological activity in stimulating transcription from sigma(N)-specific promoters, and in in vitro gel electrophoresis assays of binding to core RNAP from Escherichia coli. Furthermore, five Trp-->Ala single mutants of sigma(N) were shown to support growth under conditions of nitrogen limitation, and showed comparable efficiency in activating the sigma(N)-dependent nifH promoter in vivo, indicating that none of the tryptophan residues were essential for activity. The equilibrium binding of 7AWsigma(N) to core RNAP was examined by analytical ultracentrifugation. In sedimentation equilibrium experiments, absorbance data at 315 nm (which reports selectively on the distribution of free and bound 7AWsigma(N)) established that a 1:1 complex was formed, with a dissociation constant lower than 2 microM. The kinetics of the interaction between 7AWsigma(N) and core RNAP was investigated using stopped-flow spectrofluorimetry. A biphasic decrease in fluorescence intensity was observed when samples were excited at 280 nm, whereas only the slower of the two phases was observed at 315 nm. The kinetic data were analysed in terms of a mechanism in which a fast bimolecular association of sigma(N) with core RNAP is followed by a relatively slow isomerization step. The consequences of these findings on the competition between sigma(N) and the major sigma factor, sigma(70), in Escherichia coli are discussed. PMID:11085949

Bubble Shuttle: A newly discovered transport mechanism, which transfers microorganisms from the sediment into the water column

NASA Astrophysics Data System (ADS)

Schmale, O.; Stolle, C.; Leifer, I.; Schneider von Deimling, J.; Kiesslich, K.; Krause, S.; Frahm, A.; Treude, T.

2013-12-01

The diversity and abundance of methanotrophic microorganisms is well studied in the aquatic environment, indicating their importance in biogeochemical cycling of methane in the sediment and the water column. However, whether methanotrophs are distinct populations in these habitats or are exchanged between benthic and pelagic environments, remains an open question. Therefore, field studies were conducted at the 'Rostocker Seep' site (Coal Oil Point seep area, California, USA) to test our hypothesis that methane-oxidizing microorganisms can be transported by gas bubbles from the sediment into the water column. The natural methane emanating location 'Rostocker Seep' showed a strong surface water oversaturation in methane with respect to the atmospheric equilibrium. Catalyzed Reporter Deposition Fluorescence In Situ Hybridization (CARD-FISH) analyzes were performed to determine the abundance of aerobic and anaerobic methanotrophic microorganisms. Aerobic methane oxidizing bacteria were detected in the sediment and the water column, whereas anaerobic methanotrophs were detected exclusively in the sediment. The key device of the project was the newly developed "Bubble Catcher" used to collect naturally emanating gas bubbles at the sea floor together with particles attached to the bubble surface rim. Bubble Catcher experiments were carried out directly above a natural bubble release spot and on a reference site at which artificially released gas bubbles were caught, which had no contact with the sediment. CARD-FISH analyzes showed that aerobic methane oxidizing bacteria were transported by gas bubbles from the sediment into the water column. In contrast anaerobic methanotrophs were not detected in the bubble catcher. Further results indicate that this newly discovered Bubble Shuttle transport mechanism might influence the distribution pattern of methanotrophic microorganisms in the water column and even at the air-sea interface. Methane seep areas are often characterized by an elevated abundance of methane-oxidizing microorganisms, which consume a considerable amount of methane before it escapes into the atmosphere. Based on our study we hypothesize that the Bubble Shuttle transport mechanism contributes to this pelagic methane sink by a sediment-water column transfer of methane oxidizing microorganisms. Furthermore, this Bubble Shuttle may influence the methanotrophic community in the water column after massive short-term submarine inputs of methane (e.g. release of methane from bore holes). Especially in deep-sea regions, where the abundance of methane oxidizing microorganisms in the water column is low in general, Bubble Shuttle may inject a relevant amount of methane oxidizing microorganisms into the water column during massive inputs, supporting indirectly the turnover of this greenhouse active trace gas in the submarine environment.

Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments

USGS Publications Warehouse

Yin, J.; Haggerty, R.; Stoliker, D.L.; Kent, D.B.; Istok, J.D.; Greskowiak, J.; Zachara, J.M.

2011-01-01

In the 300 Area of a U(VI)-contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real-time change of local groundwater chemistry. Copyright 2011 by the American Geophysical Union.

Transient groundwater chemistry near a river: Effects on U(VI) transport in laboratory column experiments

USGS Publications Warehouse

Yin, Jun; Haggerty, Roy; Stoliker, Deborah L.; Kent, Douglas B.; Istok, Jonathan D.; Greskowiak, Janek; Zachara, John M.

2011-01-01

In the 300 Area of a U(VI)-contaminated aquifer at Hanford, Washington, USA, inorganic carbon and major cations, which have large impacts on U(VI) transport, change on an hourly and seasonal basis near the Columbia River. Batch and column experiments were conducted to investigate the factors controlling U(VI) adsorption/desorption by changing chemical conditions over time. Low alkalinity and low Ca concentrations (Columbia River water) enhanced adsorption and reduced aqueous concentrations. Conversely, high alkalinity and high Ca concentrations (Hanford groundwater) reduced adsorption and increased aqueous concentrations of U(VI). An equilibrium surface complexation model calibrated using laboratory batch experiments accounted for the decrease in U(VI) adsorption observed with increasing (bi)carbonate concentrations and other aqueous chemical conditions. In the column experiment, alternating pulses of river and groundwater caused swings in aqueous U(VI) concentration. A multispecies multirate surface complexation reactive transport model simulated most of the major U(VI) changes in two column experiments. The modeling results also indicated that U(VI) transport in the studied sediment could be simulated by using a single kinetic rate without loss of accuracy in the simulations. Moreover, the capability of the model to predict U(VI) transport in Hanford groundwater under transient chemical conditions depends significantly on the knowledge of real-time change of local groundwater chemistry.

The subunit structure of horse spleen apoferritin: the molecular weight of the oligomer and its stability to dissociation by dilution (Short Communication)

PubMed Central

Crichton, Robert R.; Eason, Robert; Barclay, Allan; Bryce, Charles F. A.

1973-01-01

The oligomer molecular weight of horse spleen apoferritin was determined by sedimentation-equilibrium techniques and a value of 443000 found. It is concluded that the apoferritin molecule consists of 24 subunits. At concentrations as low as 0.01μm there is no evidence of subunit dissociation. PMID:4737327

In situ redox manipulation of subsurface sediments from Fort Lewis, Washington: Iron reduction and TCE dechlorination mechanisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

JE Szecsody; JS Fruchter; DS Sklarew

2000-03-21

Pacific Northwest National Laboratory (PNNL) conducted a bench-scale study to determine how effective chemically treated Ft. Lewis sediments can degrade trichloroethylene (TCE). The objectives of this experimental study were to quantify: (1) sediment reduction and oxidation reactions, (2) TCE degradation reactions, and (3) other significant geochemical changes that occurred. Sediment reduction and oxidation were investigated to determine the mass of reducible iron in the Ft. Lewis sediments and the rate of this reduction and subsequent oxidation at different temperatures. The temperature dependence was needed to be able to predict field-scale reduction in the relatively cold ({approximately}11 C) Ft. Lewis aquifer.more » Results of these experiments were used in conjunction with other geochemical and hydraulic characterization to design the field-scale injection experiment and predict barrier longevity. For example, the sediment reduction rate controls the amount of time required for the dithionite solution to fully react with sediments. Sediment oxidation experiments were additionally conducted to determine the oxidation rate and provide a separate measure of the mass of reduced iron. Laboratory experiments that were used to meet these objectives included: (1) sediment reduction in batch (static) systems, (2) sediment reduction in 1-D columns, and (3) sediment oxidation in 1-D columns. Multiple reaction modeling was conducted to quantify the reactant masses and reaction rates.« less

Depth and temperature of permafrost on the Alaskan Arctic Slope; preliminary results

USGS Publications Warehouse

Lachenbruch, Arthur H.; Sass, J.H.; Lawver, L.A.; Brewer, M.C.; Moses, T.H.

1982-01-01

As permafrost is defined by its temperature, the only way to determine its depth is to monitor the return to equilibrium of temperatures in boreholes that penetrate permafrost. Such measurements are under way in 25 wells on the Alaskan Arctic Slope; 21 are in Naval Petroleum Reserve Alaska (NPRA), and 4 are in the foothills to the east. Near-equilibrium results indicate that permafrost thickness in NPRA generally ranges between 200 and 400 m (compared to 600+ m at Prudhoe Bay); there are large local variations and no conspicuous regional trends. By contrast the long-term mean temperature of the ground surface (one factor determining permafrost depth) varies systematically from north to south in a pattern modified by the regional topography. The observed variation in permafrost temperature and depth cannot result primarily from effects of surface bodies of water or regional variations in heat flow; they are consistent, however, with expectable variations in the thermal conductivity of the sediments. It remains to be determined (with conductivity measurements) whether certain sites with anomalously high local gradients have anomalously high heat flow; if they do, they might indicate upwelling of interstitial fluids in the underlying basin sediments.

Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China.

PubMed

Tang, Qiang; Bao, Yuhai; He, Xiubin; Fu, Bojie; Collins, Adrian L; Zhang, Xinbao

2016-04-01

Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems. Copyright © 2016 Elsevier B.V. All rights reserved.

Transferring mixtures of chemicals from sediment to a bioassay using silicone-based passive sampling and dosing.

PubMed

Mustajärvi, Lukas; Eriksson-Wiklund, Ann-Kristin; Gorokhova, Elena; Jahnke, Annika; Sobek, Anna

2017-11-15

Environmental mixtures of chemicals consist of a countless number of compounds with unknown identity and quantity. Yet, chemical regulation is mainly built around the assessment of single chemicals. Existing frameworks for assessing the toxicity of mixtures require that both the chemical composition and quantity are known. Quantitative analyses of the chemical composition of environmental mixtures are however extremely challenging and resource-demanding. Bioassays may therefore serve as a useful approach for investigating the combined toxicity of environmental mixtures of chemicals in a cost-efficient and holistic manner. In this study, an unknown environmental mixture of bioavailable semi-hydrophobic to hydrophobic chemicals was sampled from a contaminated sediment in a coastal Baltic Sea area using silicone polydimethylsiloxane (PDMS) as an equilibrium passive sampler. The chemical mixture was transferred to a PDMS-based passive dosing system, and its applicability was demonstrated using green algae Tetraselmis suecica in a cell viability assay. The proportion of dead cells increased significantly with increasing exposure level and in a dose-response manner. At an ambient concentration, the proportion of dead cells in the population was nearly doubled compared to the control; however, the difference was non-significant due to high inter-replicate variability and a low number of replicates. The validation of the test system regarding equilibrium sampling, loading efficiency into the passive dosing polymer, stability of the mixture composition, and low algal mortality in control treatments demonstrates that combining equilibrium passive sampling and passive dosing is a promising tool for investigating the toxicity of bioavailable semi-hydrophobic and hydrophobic chemicals in complex environmental mixtures.

Trimeric transmembrane domain interactions in paramyxovirus fusion proteins: roles in protein folding, stability, and function.

PubMed

Smith, Everett Clinton; Smith, Stacy E; Carter, James R; Webb, Stacy R; Gibson, Kathleen M; Hellman, Lance M; Fried, Michael G; Dutch, Rebecca Ellis

2013-12-13

Paramyxovirus fusion (F) proteins promote membrane fusion between the viral envelope and host cell membranes, a critical early step in viral infection. Although mutational analyses have indicated that transmembrane (TM) domain residues can affect folding or function of viral fusion proteins, direct analysis of TM-TM interactions has proved challenging. To directly assess TM interactions, the oligomeric state of purified chimeric proteins containing the Staphylococcal nuclease (SN) protein linked to the TM segments from three paramyxovirus F proteins was analyzed by sedimentation equilibrium analysis in detergent and buffer conditions that allowed density matching. A monomer-trimer equilibrium best fit was found for all three SN-TM constructs tested, and similar fits were obtained with peptides corresponding to just the TM region of two different paramyxovirus F proteins. These findings demonstrate for the first time that class I viral fusion protein TM domains can self-associate as trimeric complexes in the absence of the rest of the protein. Glycine residues have been implicated in TM helix interactions, so the effect of mutations at Hendra F Gly-508 was assessed in the context of the whole F protein. Mutations G508I or G508L resulted in decreased cell surface expression of the fusogenic form, consistent with decreased stability of the prefusion form of the protein. Sedimentation equilibrium analysis of TM domains containing these mutations gave higher relative association constants, suggesting altered TM-TM interactions. Overall, these results suggest that trimeric TM interactions are important driving forces for protein folding, stability and membrane fusion promotion.

Trimeric Transmembrane Domain Interactions in Paramyxovirus Fusion Proteins

PubMed Central

Smith, Everett Clinton; Smith, Stacy E.; Carter, James R.; Webb, Stacy R.; Gibson, Kathleen M.; Hellman, Lance M.; Fried, Michael G.; Dutch, Rebecca Ellis

2013-01-01

Paramyxovirus fusion (F) proteins promote membrane fusion between the viral envelope and host cell membranes, a critical early step in viral infection. Although mutational analyses have indicated that transmembrane (TM) domain residues can affect folding or function of viral fusion proteins, direct analysis of TM-TM interactions has proved challenging. To directly assess TM interactions, the oligomeric state of purified chimeric proteins containing the Staphylococcal nuclease (SN) protein linked to the TM segments from three paramyxovirus F proteins was analyzed by sedimentation equilibrium analysis in detergent and buffer conditions that allowed density matching. A monomer-trimer equilibrium best fit was found for all three SN-TM constructs tested, and similar fits were obtained with peptides corresponding to just the TM region of two different paramyxovirus F proteins. These findings demonstrate for the first time that class I viral fusion protein TM domains can self-associate as trimeric complexes in the absence of the rest of the protein. Glycine residues have been implicated in TM helix interactions, so the effect of mutations at Hendra F Gly-508 was assessed in the context of the whole F protein. Mutations G508I or G508L resulted in decreased cell surface expression of the fusogenic form, consistent with decreased stability of the prefusion form of the protein. Sedimentation equilibrium analysis of TM domains containing these mutations gave higher relative association constants, suggesting altered TM-TM interactions. Overall, these results suggest that trimeric TM interactions are important driving forces for protein folding, stability and membrane fusion promotion. PMID:24178297

Scaling laws for perturbations in the ocean-atmosphere system following large CO2 emissions

NASA Astrophysics Data System (ADS)

Towles, N.; Olson, P.; Gnanadesikan, A.

2015-01-01

Scaling relationships are derived for the perturbations to atmosphere and ocean variables from large transient CO2 emissions. Using the carbon cycle model LOSCAR (Zeebe et al., 2009; Zeebe, 2012b) we calculate perturbations to atmosphere temperature and total carbon, ocean temperature, total ocean carbon, pH, and alkalinity, marine sediment carbon, plus carbon-13 isotope anomalies in the ocean and atmosphere resulting from idealized CO2 emission events. The peak perturbations in the atmosphere and ocean variables are then fit to power law functions of the form γDαEbeta, where D is the event duration, E is its total carbon emission, and γ is a coefficient. Good power law fits are obtained for most system variables for E up to 50 000 PgC and D up to 100 kyr. However, these power laws deviate substantially from predictions based on simplified equilibrium considerations. For example, although all of the peak perturbations increase with emission rate E/D, we find no evidence of emission rate-only scaling α + β =0, a prediction of the long-term equilibrium between CO2 input by volcanism and CO2 removal by silicate weathering. Instead, our scaling yields α + β ≃ 1 for total ocean and atmosphere carbon and 0< α + β < 1 for most of the other system variables. The deviations in these scaling laws from equilibrium predictions are mainly due to the multitude and diversity of time scales that govern the exchange of carbon between marine sediments, the ocean, and the atmosphere.

Transport and fate of viruses in sediment and stormwater from a Managed Aquifer Recharge site

NASA Astrophysics Data System (ADS)

Sasidharan, Salini; Bradford, Scott A.; Šimůnek, Jiří; Torkzaban, Saeed; Vanderzalm, Joanne

2017-12-01

Enteric viruses are one of the major concerns in water reclamation and reuse at Managed Aquifer Recharge (MAR) sites. In this study, the transport and fate of bacteriophages MS2, PRD1, and ΦX174 were studied in sediment and stormwater (SW) collected from a MAR site in Parafield, Australia. Column experiments were conducted using SW, stormwater in equilibrium with the aquifer sediment (EQ-SW), and two pore-water velocities (1 and 5 m day-1) to encompass expected behavior at the MAR site. The aquifer sediment removed >92.3% of these viruses under all of the considered MAR conditions. However, much greater virus removal (4.6 logs) occurred at the lower pore-water velocity and in EQ-SW that had a higher ionic strength and Ca2+ concentration. Virus removal was greatest for MS2, followed by PRD1, and then ΦX174 for a given physicochemical condition. The vast majority of the attached viruses were irreversibly attached or inactivated on the solid phase, and injection of Milli-Q water or beef extract at pH = 10 only mobilized a small fraction of attached viruses (<0.64%). Virus breakthrough curves (BTCs) were successfully simulated using an advective-dispersive model that accounted for rates of attachment (katt), detachment (kdet), irreversible attachment or solid phase inactivation (μs), and blocking. Existing MAR guidelines only consider the removal of viruses via liquid phase inactivation (μl). However, our results indicated that katt > μs > kdet > μl, and katt was several orders of magnitude greater than μl. Therefore, current microbial risk assessment methods in the MAR guideline may be overly conservative in some instances. Interestingly, virus BTCs exhibited blocking behavior and the calculated solid surface area that contributed to the attachment was very small. Additional research is therefore warranted to study the potential influence of blocking on virus transport and potential implications for MAR guidelines.

Connecting Solubility, Equilibrium, and Periodicity in a Green, Inquiry Experiment for the General Chemistry Laboratory

ERIC Educational Resources Information Center

Cacciatore, Kristen L.; Amado, Jose; Evans, Jason J.; Sevian, Hannah

2008-01-01

We present a novel first-year chemistry laboratory experiment that connects solubility, equilibrium, and chemical periodicity concepts. It employs a unique format that asks students to replicate experiments described in different sample lab reports, each lacking some essential information, rather than follow a scripted procedure. This structure is…

Reciprocal interactions between fluvial processes and riparian plants at multiple scales: ecogeomorphic feedbacks drive coevolution of floodplain morphology and vegetation communities

NASA Astrophysics Data System (ADS)

Stella, J. C.; Kui, L.; Diehl, R. M.; Bywater-Reyes, S.; Wilcox, A. C.; Shafroth, P. B.; Lightbody, A.

2017-12-01

Fluvial forces interact with woody riparian plants in complex ways to influence the coevolution of river morphology and floodplain plant communities. Here, we report on an integrated suite of multi-disciplinary studies that contrast the responses of plants with different morphologies, tamarisk (Tamarix spp.) and cottonwood (Populus fremontii) in terms of (1) differences in vulnerability to scour and burial during floods; (2) interactions and feedbacks between plants and river morphodynamics; and (3) long-term coevolution of river floodplains and riparian communities following flow regulation from dams. The focus of these studies is sand-bed rivers in arid-land regions where invasion by tamarisk has strongly influenced riverine plant communities and geomorphic processes. We complemented a suite of field-scale flume experiments using live seedlings to quantify the initial stages of plant-river interactions with an analysis of long-term vegetation and geomorphic changes along the dammed Bill Williams River (AZ, USA) using time-series air photographs. Vegetation-fluvial interactions varied with plant characteristics, river hydraulics and sediment conditions, across the wide range of scales we investigated. In the flume studies, tamarisk's denser crowns and stiffer stems induced greater sedimentation compared to cottonwood. This resulted in tamarisk's greater mortality from burial as small seedlings under sediment equilibrium conditions but higher relative survival in larger floods under sediment deficit scenarios, in which more cottonwoods were lost to root scour. Sediment deficit conditions, as occurs downstream of dams, induced both greater scour and greater plant loss. With larger size and at higher densities, plants' vulnerability diminished due to greater root anchoring and canopy effects on hydraulics. At the corridor scale, we observed a pattern of plant encroachment during five decades of flow regulation, in which channel narrowing and simplification was more associated with tamarisk-dominated reaches compared with native woodlands. Together, these multi-scale plant-river dynamics help explain the persistence of tamarisk along regulated rivers where catastrophic floods have been reduced and also highlight limitations of using flow releases for invasive species management.

Erosion of an ancient mountain range, the Great Smoky Mountains, North Carolina and Tennessee

USGS Publications Warehouse

Matmon, A.; Bierman, P.R.; Larsen, J.; Southworth, S.; Pavich, M.; Finkel, R.; Caffee, M.

2003-01-01

Analysis of 10Be and 26Al in bedrock (n=10), colluvium (n=5 including grain size splits), and alluvial sediments (n=59 including grain size splits), coupled with field observations and GIS analysis, suggest that erosion rates in the Great Smoky Mountains are controlled by subsurface bedrock erosion and diffusive slope processes. The results indicate rapid alluvial transport, minimal alluvial storage, and suggest that most of the cosmogenic nuclide inventory in sediments is accumulated while they are eroding from bedrock and traveling down hill slopes. Spatially homogeneous erosion rates of 25 - 30 mm Ky-1 are calculated throughout the Great Smoky Mountains using measured concentrations of cosmogenic 10Be and 26Al in quartz separated from alluvial sediment. 10Be and 26Al concentrations in sediments collected from headwater tributaries that have no upstream samples (n=18) are consistent with an average erosion rate of 28 ?? 8 mm Ky-1, similar to that of the outlet rivers (n=16, 24 ?? 6 mm Ky-1), which carry most of the sediment out of the mountain range. Grain-size-specific analysis of 6 alluvial sediment samples shows higher nuclide concentrations in smaller grain sizes than in larger ones. The difference in concentrations arises from the large elevation distribution of the source of the smaller grains compared with the narrow and relatively low source elevation of the large grains. Large sandstone clasts disaggregate into sand-size grains rapidly during weathering and downslope transport; thus, only clasts from the lower parts of slopes reach the streams. 26Al/10Be ratios do not suggest significant burial periods for our samples. However, alluvial samples have lower 26Al/10Be ratios than bedrock and colluvial samples, a trend consistent with a longer integrated cosmic ray exposure history that includes periods of burial during down-slope transport. The results confirm some of the basic ideas embedded in Davis' geographic cycle model, such as the reduction of relief through slope processes, and of Hack's dynamic equilibrium model such as the similarity of erosion rates across different lithologies. Comparing cosmogenic nuclide data with other measured and calculated erosion rates for the Appalachians, we conclude that rates of erosion, integrated over varying time periods from decades to a hundred million years are similar, the result of equilibrium between erosion and isostatic uplift in the southern Appalachian Mountains.

Slip slidin' away: A post-glacial environmental history of the Waipaoa River basin

NASA Astrophysics Data System (ADS)

Gomez, Basil; Rosser, Brenda J.

2018-04-01

The dramatic changes that occurred to the post-glacial landscape in the headwaters of the Waipaoa River basin are a consequence of perturbations about the equilibrium that exists between the rate of tectonic uplift and fluvial incision. At times when the amount of coarse sediment delivered to channels exceeds the capacity of streams to remove it, the channel bed rises at the rate of tectonic uplift. Once bedload overcapacity is replaced by undercapacity and the alluvial cover is depleted, streams reestablish contact with bedrock and recuperate the time lost to fluvial incision. The first major perturbation occurred during the final phase of the last glaciation (ca. 33-17.5 cal. ka), when aggradation was driven by a climate-forced variation in the relative supplies of sediment and water. We suggest that the subsequent transformation of channels in the headwaters of the Waipaoa River basin, from alluvial to bedrock, occurred as the atmospheric and oceanic circulation converged on their contemporary patterns ca. 12 cal. ka. A second major perturbation that continues to the present began ca. 1910-1912 CE, when a massive increase in sediment load was accompanied by a modest increase in water discharge after the native vegetation cover in the headwaters was replaced by pasture. The processes of terrace creation and incision are inherently unsteady, and in five interim cases incision was arrested by a transient increase in the thickness of the alluvial cover that was a response to climatic forcing. Events that disrupted the native vegetation cover in the headwaters also modulated patterns of sediment dispersal and accumulation in other parts of the fluvial system and caused rapid, storm-driven infilling of the Poverty Bay Flats. Tectonic subsidence dictates the course of the Waipaoa River across Poverty Bay Flats which, because the modern rate of floodplain construction by vertical accretion is rapid relative to the amount of destruction by lateral channel migration, has remained virtually unchanged for the past 100 years. During this time the channel assumed a narrower, deeper form that is in equilibrium with the contemporary supply of sediment and hydraulic regime.

Ecological risk assessment of boreal sediments affected by metal mining: Metal geochemistry, seasonality, and comparison of several risk assessment methods.

PubMed

Väänänen, Kristiina; Kauppila, Tommi; Mäkinen, Jari; Leppänen, Matti T; Lyytikäinen, Merja; Akkanen, Jarkko

2016-10-01

The mining industry is a common source of environmental metal emissions, which cause long-lasting effects in aquatic ecosystems. Metal risk assessment is challenging due to variations in metal distribution, speciation, and bioavailability. Therefore, seasonal effects must be better understood, especially in boreal regions in which seasonal changes are large. We sampled 4 Finnish lakes and sediments affected by mining for metals and geochemical characteristics in autumn and late winter, to evaluate seasonal changes in metal behavior, the importance of seasonality in risk assessment, and the sensitivity and suitability of different risk assessment methods. We compared metal concentrations in sediment, overlying water, and porewater against environmental quality guidelines (EQGs). We also evaluated the toxicity of metal mixtures using simultaneously extracted metals and an acid volatile sulfides (SEM-AVS) approach together with water quality criteria (US Environmental Protection Agency equilibrium partitioning benchmarks). Finally, site-specific risks for 3 metals (Cu, Ni, Zn) were assessed using 2 biotic ligand models (BLMs). The metal concentrations in the impacted lakes were elevated. During winter stratification, the hypolimnetic O2 saturation levels were low (<6%) and the pH was acidic (3.5-6.5); however, abundant O2 (>89%) and neutral pH (6.1-7.5) were found after the autumnal water overturn. Guidelines were the most conservative benchmark for showing an increased risk of toxicity in the all of the lakes. The situation remained stable between seasons. On the other hand, SEM-AVS, equilibrium partition sediment benchmarks (ESBs), and BLMs provided a clearer distinction between lakes and revealed a seasonal variation in risk among some of the lakes, which evidenced a higher risk during late winter. If a sediment risk assessment is based on the situation in the autumn, the overall risk may be underestimated. It is advisable to carry out sampling and risk assessment during periods in which metals are assumed to be the most environmentally harmful. Integr Environ Assess Manag 2016;12:759-771. © 2015 SETAC. © 2015 SETAC.

Use of ecocores in estimating the biodegradation potential of 4-nonylphenol in freshwater sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dawson, T.D.; Liber, K.

1995-12-31

Ecocores, a type of sediment microcosm used to estimate biodegradation rates in sediments, were used in conjunction with a full-scale mesocosm study to help determine the possible mechanism of degradation of 4-nonylphenol in freshwater sediments. Ecocore and mesocosm sediments displayed very similar nonylphenol concentrations over the duration of the 8-week experiment; neither revealed any signs of nonylphenol degradation. Average nonylphenol concentrations at the beginning of the experiment were not significantly different from concentrations measured at the end of the experiment for both field (9.2 vs. 10.2 {micro}g/g) and ecocore (3.2 vs. 6.4 {micro}g/g) sediments. Mean nonylphenol concentrations remained relatively constantmore » over the duration of the 55-d incubation period in both viable (6.4 {+-} 3.9 {micro}g/g) and sterilized (8.0 {+-} 7.7 {micro}g/g) ecocore sediments. The observation of stable bacterial densities in this study is consistent with the lack of biodegradation of nonylphenol in the sediments of the test system. Ecocores worked well in conjunction with a mesocosm experiment where contaminant loads to the sediment were defined and to some extent controlled. This study indicated that sediment associated 4-nonylphenol is very resistant to microbial degradation within the experimental conditions and 8-week time frame used here.« less

Deltas as Ecomorphodynamic Systems: Effects of Vegetation Gradients on Sediment Trapping and Channel Dynamics

NASA Astrophysics Data System (ADS)

Piliouras, A.; Kim, W.; Goggin, H.

2014-12-01

Understanding the feedbacks between water, sediment, and vegetation in deltas is an important part of understanding deltas as ecomorphodynamic systems. We conducted a set of laboratory experiments using alfalfa (Medicago sativa) as a proxy for delta vegetation to determine (1) the effects of plants on delta growth and channel dynamics and (2) the influence of fine material on delta evolution. Vegetated experiments were compared to a control run without plants to isolate the effects of vegetation, and experiments with fine sediment were compared to a set of similar experiments with only sand. We found that alfalfa increased sediment trapping on the delta topset, and that the plants were especially effective at retaining fine material. Compared to the control run, the vegetated experiments showed an increased retention of fine sediment on the floodplain that resulted in increased delta relief and stronger pulses of shoreline progradation when channel avulsion and migration occurred. In other words, a higher amount of sediment storage with the addition of vegetation corresponded to a higher amount of sediment excavation during channelization events. In natural systems, dense bank vegetation is typically expected to help confine flow. We seeded our delta uniformly, which eliminated typical vegetation density gradients from riverbank to island center and therefore diminished the gradient in overbank sedimentation that best confines channels by creating levees. Dense clusters of alfalfa throughout the interior of the floodplain and delta islands were therefore able to induce flow splitting, where channels diverged around a stand of plants. This created several smaller channels that were then able to more widely distribute sediment at the delta front compared to unvegetated experiments. We conclude that plants are efficient sediment trappers that change the rate and amount of sediment storage in the delta topset, and that gradients in vegetation density are an important factor in determining how channel behavior may change.

EVALUATION OF CHLORPYRIFOS UPTAKE IN STERILIZED AND NON-STERILIZED SEDIMENT

EPA Science Inventory

In order to evaluate chemical interactions in sediment, initial experiments were designed to assess the role of microbial activitiy on chemical fate of chlorpyrifos. In these initial experiments, sediment uptake of chlorpyrifos was evaluated using Enzyme Linked Immunosorbent Assa...

How does sediment affect the hydraulics of bedrock-alluvial rivers?

NASA Astrophysics Data System (ADS)

Hodge, Rebecca; Hoey, Trevor; Maniatis, George; Leprêtre, Emilie

2016-04-01

Relationships between flow, sediment transport and channel morphology are relatively well established in coarse-grained alluvial channels. Developing equivalent relationships for bedrock-alluvial channels is complicated by the two different components that comprise the channel morphology: bedrock and sediment. These two components usually have very different response times to hydraulic forcing, meaning that the bedrock morphology may be inherited from previous conditions. The influence of changing sediment cover on channel morphology and roughness will depend on the relative magnitudes of the sediment size and the spatial variations in bedrock elevation. We report results from experiments in a 0.9m wide flume designed to quantify the interactions between flow and sediment patch morphology using two contrasting bedrock topographies. The first topography is a plane bed with sand-scale roughness, and the second is a 1:10 scale, 3D printed, model of a bedrock channel with spatially variable roughness (standard deviation of elevations = 12 mm in the flume). In all experiments, a sediment pulse was added to the flume (D50 between 7 and 15 mm) and sediment patches were allowed to stabilise under constant flow conditions. The flow was then incrementally increased in order to identify the discharges at which sediment patches and isolated grains were eroded. In the plane bed experiments ˜20% sediment cover is sufficient to alter the channel hydraulics through the increased roughness of the bed; this impact is expressed as the increased discharge at which isolated grains are entrained. In the scaled bed experiments, partial sediment cover decreased local flow velocities on a relatively smooth area of the bed. At the scale of the entire channel, the bed morphology, and the hydraulics induced by it, was a primary control on sediment cover stability at lower sediment inputs. At higher inputs, where sediment infilled the local bed topography, patches were relatively more stable, suggesting an increased impact on the hydraulics and the role of grain-grain interactions. We draw together these experiments using a theoretical framework to express the impact of sediment cover on channel roughness and hence hydraulics.

Development and application of freshwater sediment-toxicity benchmarks for currently used pesticides

USGS Publications Warehouse

Nowell, Lisa H.; Norman, Julia E.; Ingersoll, Christopher G.; Moran, Patrick W.

2016-01-01

Sediment-toxicity benchmarks are needed to interpret the biological significance of currently used pesticides detected in whole sediments. Two types of freshwater sediment benchmarks for pesticides were developed using spiked-sediment bioassay (SSB) data from the literature. These benchmarks can be used to interpret sediment-toxicity data or to assess the potential toxicity of pesticides in whole sediment. The Likely Effect Benchmark (LEB) defines a pesticide concentration in whole sediment above which there is a high probability of adverse effects on benthic invertebrates, and the Threshold Effect Benchmark (TEB) defines a concentration below which adverse effects are unlikely. For compounds without available SSBs, benchmarks were estimated using equilibrium partitioning (EqP). When a sediment sample contains a pesticide mixture, benchmark quotients can be summed for all detected pesticides to produce an indicator of potential toxicity for that mixture. Benchmarks were developed for 48 pesticide compounds using SSB data and 81 compounds using the EqP approach. In an example application, data for pesticides measured in sediment from 197 streams across the United States were evaluated using these benchmarks, and compared to measured toxicity from whole-sediment toxicity tests conducted with the amphipod Hyalella azteca (28-d exposures) and the midge Chironomus dilutus (10-d exposures). Amphipod survival, weight, and biomass were significantly and inversely related to summed benchmark quotients, whereas midge survival, weight, and biomass showed no relationship to benchmarks. Samples with LEB exceedances were rare (n = 3), but all were toxic to amphipods (i.e., significantly different from control). Significant toxicity to amphipods was observed for 72% of samples exceeding one or more TEBs, compared to 18% of samples below all TEBs. Factors affecting toxicity below TEBs may include the presence of contaminants other than pesticides, physical/chemical characteristics of sediment, and uncertainty in TEB values. Additional evaluations of benchmarks in relation to sediment chemistry and toxicity are ongoing.

Field application of activated carbon amendment for in-situ stabilization of polychlorinated biphenyls in marine sediment.

PubMed

Cho, Yeo-Myoung; Ghosh, Upal; Kennedy, Alan J; Grossman, Adam; Ray, Gary; Tomaszewski, Jeanne E; Smithenry, Dennis W; Bridges, Todd S; Luthy, Richard G

2009-05-15

We report results on the first field-scale application of activated carbon (AC) amendment to contaminated sediment for in-situ stabilization of polychlorinated biphenyls (PCBs). The test was performed on a tidal mud flat at South Basin, adjacent to the former Hunters Point Naval Shipyard, San Francisco Bay, CA. The major goals of the field study were to (1) assess scale up of the AC mixing technology using two available, large-scale devices, (2) validate the effectiveness of the AC amendment at the field scale, and (3) identify possible adverse effects of the remediation technology. Also, the test allowed comparison among monitoring tools, evaluation of longer-term effectiveness of AC amendment, and identification of field-related factors that confound the performance of in-situ biological assessments. Following background pretreatment measurements, we successfully incorporated AC into sediment to a nominal 30 cm depth during a single mixing event, as confirmed by total organic carbon and black carbon contents in the designated test plots. The measured AC dose averaged 2.0-3.2 wt% and varied depending on sampling locations and mixing equipment. AC amendment did not impact sediment resuspension or PCB release into the water column over the treatment plots, nor adversely impactthe existing macro benthic community composition, richness, or diversity. The PCB bioaccumulation in marine clams was reduced when exposed to sediment treated with 2% AC in comparison to the control plot Field-deployed semi permeable membrane devices and polyethylene devices showed about 50% reduction in PCB uptake in AC-treated sediment and similar reduction in estimated pore-water PCB concentration. This reduction was evident even after 13-month post-treatment with then 7 months of continuous exposure, indicating AC treatment efficacy was retained for an extended period. Aqueous equilibrium PCB concentrations and PCB desorption showed an AC-dose response. Field-exposed AC after 18 months retained a strong stabilization capability to reduce aqueous equilibrium PCB concentrations by about 90%, which also supports the long-term effectiveness of AC in the field. Additional mixing during or after AC deployment, increasing AC dose, reducing AC-particle size, and sequential deployment of AC dose will likely improve AC-sediment contact and overall effectiveness. The reductions in PCB availability observed with slow mass transfer under field conditions calls for predictive models to assess the long-term trends in pore-water PCB concentrations and the benefits of alternative in-situ AC application and mixing strategies.

The temporal evolution of magnesium isotope fractionation during hydromagnesite dissolution, precipitation, and at equilibrium

NASA Astrophysics Data System (ADS)

Oelkers, Eric H.; Berninger, Ulf-Niklas; Pérez-Fernàndez, Andrea; Chmeleff, Jérôme; Mavromatis, Vasileios

2018-04-01

This study provides experimental evidence of the resetting of the magnesium (Mg) isotope signatures of hydromagnesite in the presence of an aqueous fluid during its congruent dissolution, precipitation, and at equilibrium at ambient temperatures over month-long timescales. All experiments were performed in batch reactors in aqueous sodium carbonate buffer solutions having a pH from 7.8 to 9.2. The fluid phase in all experiments attained bulk chemical equilibrium within analytical uncertainty with hydromagnesite within several days, but the experiments were allowed to continue for up to 575 days. During congruent hydromagnesite dissolution, the fluid first became enriched in isotopically light Mg compared to the dissolving hydromagnesite, but this Mg isotope composition became heavier after the fluid attained chemical equilibrium with the mineral. The δ26Mg composition of the fluid was up to ∼0.35‰ heavier than the initial dissolving hydromagnesite at the end of the dissolution experiments. Hydromagnesite precipitation was provoked during one experiment by increasing the reaction temperature from 4 to 50 °C. The δ26Mg composition of the fluid increased as hydromagnesite precipitated and continued to increase after the fluid attained bulk equilibrium with this phase. These observations are consistent with the hypothesis that mineral-fluid equilibrium is dynamic (i.e. dissolution and precipitation occur at equal, non-zero rates at equilibrium). Moreover the results presented in this study confirm (1) that the transfer of material from the solid to the fluid phase may not be conservative during stoichiometric dissolution, and (2) that the isotopic compositions of carbonate minerals can evolve even when the mineral is in bulk chemical equilibrium with its coexisting fluid. This latter observation suggests that the preservation of isotopic signatures of carbonate minerals in the geological record may require a combination of the isolation of fluid-mineral system from external chemical input and/or the existence of a yet to be defined dissolution/precipitation inhibition mechanism.

Phenomenological Partial Specific Volumes for G-Quadruplex DNAs

PubMed Central

Hellman, Lance M.; Rodgers, David W.; Fried, Michael G.

2009-01-01

Accurate partial specific volume (ν̄) values are required for sedimentation velocity and sedimentation equilibrium analyses. For nucleic acids, the estimation of these values is complicated by the fact that ν̄ depends on base composition, secondary structure, solvation and the concentrations and identities of ions in the surrounding buffer. Here we describe sedimentation equilibrium measurements of the apparent isopotential partial specific volume φ′ for two G-quadruplex DNAs and a single-stranded DNA of similar molecular weight and base composition. The G-quadruplex DNAs are a 22 nucleotide fragment of the human telomere consensus sequence and a 27 nucleotide fragment from the human c-myc promoter. The single-stranded DNA is 26 nucleotides long and is designed to have low propensity to form secondary structures. Parallel measurements were made in buffers containing NaCl and in buffers containing KCl, spanning the range 0.09M ≤ [salt] ≤ 2.3M. Limiting values of φ′, extrapolated to [salt] = 0M, were: 22-mer (NaCl-form), 0.525 ± 0.004 mL/g; 22-mer (KCl-form), 0.531 ± 0.006 mL/g; 27-mer (NaCl-form), 0.548 ± 0.005 mL/g; 27-mer (KCl-form), 0.557 ± 0.006 mL/g; 26-mer (NaCl-form), 0.555 ± 0.004 mL/g; 26-mer (KCl-form), 0.564 ± 0.006 mL/g. Small changes in φ′ with [salt] suggest that large changes in counterion association or hydration are unlikely to take place over these concentration ranges. PMID:19238377

Estimating aquatic toxicity as determined through laboratory tests of great lakes sediments containing complex mixtures of environmental contaminants

USGS Publications Warehouse

1996-01-01

We developed and evaluated a total toxic units modeling approach for predicting mean toxicity as measured in laboratory tests for Great Lakes sediments containing complex mixtures of environmental contaminants (e.g., polychlorinated biphenyls, polycyclic aromatic hydrocarbons, pesticides, chlorinated dioxins, and metals). The approach incorporates equilibrium partitioning and organic carbon control of bioavailability for organic contaminants and acid volatile sulfide (AVS) control for metals, and includes toxic equivalency for planar organic chemicals. A toxic unit is defined as the ratio of the estimated pore-water concentration of a contaminant to the chronic toxicity of that contaminant, as estimated by U.S. Environmental Protection Agency Ambient Water Quality Criteria (AWQC). The toxic unit models we developed assume complete additivity of contaminant effects, are completely mechanistic in form, and were evaluated without any a posteriori modification of either the models or the data from which the models were developed and against which they were tested. A linear relationship between total toxic units, which included toxicity attributable to both iron and un-ionized ammonia, accounted for about 88% of observed variability in mean toxicity; a quadratic relationship accounted for almost 94%. Exclusion of either bioavailability components (i.e., equilibrium partitioning control of organic contaminants and AVS control of metals) or iron from the model substantially decreased its ability to predict mean toxicity. A model based solely on un-ionized ammonia accounted for about 47% of the variability in mean toxicity. We found the toxic unit approach to be a viable method for assessing and ranking the relative potential toxicity of contaminated sediments.

Payload specialists Patrick Baudry conducts equilibrium experiments

NASA Technical Reports Server (NTRS)

1985-01-01

Payload specialists Patrick Baudry participates in an experiment involving equilibrium and vertigo. He is anchored to the orbiter floor by foot restraints and is wearing a device over his eyes to measure angular head movement and up and down eye movement.

UXO Burial Prediction Fidelity: A Summary

DTIC Science & Technology

2017-07-01

should not be construed as representing the official position of either the Department of Defense or the sponsoring organization. For More Information ...equilibrium. Any complete picture of munition evolution in sediment would need to account for these effects. More relevant to the present topic: these...of adds uncertainty to predictions of munition fate, and assessments of risk probabilities would need to account for the statistical distribution of

Numerical modelling of bedload sediment transport

NASA Astrophysics Data System (ADS)

Langlois, Vincent J.

2010-05-01

We present a numerical study of sediment transport in the bedload regime. Classical bedload transport laws only describe the variation of the vertically integrated flux of grains as a function of the Shields number. However, these relations are only valid if the moving layer of the bed is at equilibrium with the external flow. Besides, they do not contain enough information for many geomorphological applications. For instance, understanding inertial effects in the moving bed requires models that are able to account for the variability of hydrodynamical conditions, and the discrete nature of the sediment material. We developped a numerical modelling of the behaviour of a three-dimensional bed of grains sheared by a unidirectional fluid flow. These simulations are based on a combination of discrete and continuum approaches: sediment particles are modelled by hard spheres interacting through simple contact forces, whereas the fluid flow is described by a 'mean field' model. Both the drag exerted on grains by the fluid and the retroactive effect of the presence of grains on the flow are accounted for, allowing the system to converge to its equilibrium state (no assumption is made on the fluid velocity profile inside the layer of moving grains). Above the motion threshold, the variation of the flux of grains in the steady state is found to vary like the cube of the Shields number (as predicted by Bagnold). Besides, our simulations allow us to obtain new insights into the detailed mechanisms of bedload transport, by giving access to non-integral quantities, such as the trajectories of each individual grains, the detailed velocity and packing fraction profiles inside the granular bed, etc. It is therefore possible to investigate some effects that are not accounted for in usual continuum models, such as the polydispersity of grains, the ageing of the bed, the response to a variation of the flowrate, etc.

Landscape disequilibrium on 1000-10,000 year scales Marsyandi River, Nepal, central Himalaya

NASA Astrophysics Data System (ADS)

Pratt-Sitaula, Beth; Burbank, Douglas W.; Heimsath, Arjun; Ojha, Tank

2004-03-01

In an actively deforming orogen, maintenance of a topographic steady state requires that hillslope erosion, river incision, and rock uplift rates are balanced over timescales of 10 5-10 7 years. Over shorter times, <10 5 years, hillslope erosion and bedrock river incision rates fluctuate with changes in climate. On 10 4-year timescales, the Marsyandi River in the central Nepal Himalaya has oscillated between bedrock incision and valley alluviation in response to changes in monsoon intensity and sediment flux. Stratigraphy and 14C ages of fill terrace deposits reveal a major alluviation, coincident with a monsoonal maximum, ca. 50-35 ky BP. Cosmogenic 10Be and 26Al exposure ages define an alluviation and reincision event ca. 9-6 ky BP, also at a time of strong South Asian monsoons. The terrace deposits that line the Lesser Himalayan channel are largely composed of debris flows which originate in the Greater Himalayan rocks up to 40 km away. The terrace sequences contain many cubic kilometers of sediment, but probably represent only 2-8% of the sediments which flushed through the Marsyandi during the accumulation period. At ˜10 4-year timescales, maximum bedrock incision rates are ˜7 mm/year in the Greater Himalaya and ˜1.5 mm/year in the Lesser Himalayan Mahabarat Range. We propose a model in which river channel erosion is temporally out-of-phase with hillslope erosion. Increased monsoonal precipitation causes an increase in hillslope-derived sediment that overwhelms the transport capacity of the river. The resulting aggradation protects the bedrock channel from erosion, allowing the river gradient to steepen as rock uplift continues. When the alluvium is later removed and the bedrock channel re-exposed, bedrock incision rates probably accelerate beyond the long-term mean as the river gradient adjusts downward toward a more "equilibrium" profile. Efforts to document dynamic equilibrium in active orogens require quantification of rates over time intervals significantly exceeding the scale of these millennial fluctuations in rate.

Sediment trapping efficiency of adjustable check dam in laboratory and field experiment

NASA Astrophysics Data System (ADS)

Wang, Chiang; Chen, Su-Chin; Lu, Sheng-Jui

2014-05-01

Check dam has been constructed at mountain area to block debris flow, but has been filled after several events and lose its function of trapping. For the reason, the main facilities of our research is the adjustable steel slit check dam, which with the advantages of fast building, easy to remove or adjust it function. When we can remove transverse beams to drain sediments off and keep the channel continuity. We constructed adjustable steel slit check dam on the Landow torrent, Huisun Experiment Forest station as the prototype to compare with model in laboratory. In laboratory experiments, the Froude number similarity was used to design the dam model. The main comparisons focused on types of sediment trapping and removing, sediment discharge, and trapping rate of slit check dam. In different types of removing transverse beam showed different kind of sediment removal and differences on rate of sediment removing, removing rate, and particle size distribution. The sediment discharge in check dam with beams is about 40%~80% of check dam without beams. Furthermore, the spacing of beams is considerable factor to the sediment discharge. In field experiment, this research uses time-lapse photography to record the adjustable steel slit check dam on the Landow torrent. The typhoon Soulik made rainfall amounts of 600 mm in eight hours and induced debris flow in Landow torrent. Image data of time-lapse photography demonstrated that after several sediment transport event the adjustable steel slit check dam was buried by debris flow. The result of lab and field experiments: (1)Adjustable check dam could trap boulders and stop woody debris flow and flush out fine sediment to supply the need of downstream river. (2)The efficiency of sediment trapping in adjustable check dam with transverse beams was significantly improved. (3)The check dam without transverse beams can remove the sediment and keep the ecosystem continuity.

Physical characterization of plakophilin 1 reconstituted with and without zinc.

PubMed

Hofmann, I; Mücke, N; Reed, J; Herrmann, H; Langowski, J

2000-07-01

Plakophilin 1 (PKP1) belongs to the arm-repeat protein family which is characterized by the presence of a conserved 42-amino-acid motif. Despite individual members of the family containing a similar type of structural domain, they exhibit diverse cellular functions. PKP1 is ubiquitously expressed in human tissues and, depending on the type of cell, found prominently in the karyoplasm and/or in desmosomes. In surface plasmon resonance detection experiments, we noticed that PKP1 specifically bound zinc but not calcium or magnesium. Therefore we have used circular dichroism spectroscopy, limited proteolysis, analytical ultracentrifugation, electron microscopy and dynamic light scattering to establish the physical properties of recombinant PKP1 depending on the presence or absence of zinc. The alpha helix content of PKP1 was considerably higher when reconstituted with zinc than without. By atomic absorption spectroscopy 7.3 atoms zinc were shown to be tightly associated with one molecule of wild-type PKP1. The zinc-reconstituted protein formed globular particles of 21.9 +/- 8.4 nm diameter, as measured by electron microscopy after glycerol spraying/rotary metal shadowing. In parallel, the average sedimentation coefficient (s20, w) for zinc-containing PKP1 was 41S and its diffusion coefficient, as obtained by dynamic light scattering, 1.48 x 10-7 cm2.s-1. The molecular mass of 2.44 x 106 obtained from s and D yields an average stoichiometry of 30 for the PKP1 oligomer. In contrast, PKP1, reconstituted without zinc, contained no significant amount of zinc, sedimented with 4.6S, and was present in monomeric form as determined by sedimentation equilibrium centrifugation.

Relation of Mercury to Other Chemical Constituents in Ground Water in the Kirkwood-Cohansey Aquifer System, New Jersey Coastal Plain, and Mechanisms for Mobilization of Mercury from Sediments to Ground Water

USGS Publications Warehouse

Barringer, Julia L.; MacLeod, Cecilia L.

2001-01-01

Water from 265 domestic wells that tap the unconfined Kirkwood-Cohansey aquifer system in the Coastal Plain of New Jersey contained concentrations of mercury that are equal to or exceed the U.S. Environmental Protection Agency maximum contaminant level (MCL) of 2 ug/L (micrograms per liter). The wells range in depth from 50 to 200 feet, and are located in 32 discrete, mostly residential, areas that were developed primarily on former agricultural land during the 1950?s through the 1970?s. Concentrations in two other areas exceeded 1 ug/L. Naturally occurring mercury concentrations in ground water from the Kirkwood-Cohansey aquifer system typically are less than 0.01 ug/L, but concentrations in water from some wells were as much as 42 ug/L. No evidence currently exists that conclusively links known point sources such as landfills, industrial operations, or commercial enterprises to most of the elevated concentrations of mercury in ground water in the residential areas. Possible sources of the mercury include pesticides and atmospheric deposition. Analysis of water from wells in 6 of the 34 areas for other constituents indicates that nitrate concentrations also commonly are elevated above background levels (which typically are undetectable at 0.01 milligrams per liter), and exceed the MCL of 10 milligrams per liter in some samples. Several volatile organic compounds (VOCs), including chloroform, also have been measured in water from wells at many of the 34 sites. Analytical results for water samples collected at several depths from boreholes at 2 of the 34 sites indicate elevated concentrations of calcium, magnesium, barium, strontium, nitrate, and chloride, which may be related to both agricultural chemical applications and septic-system effluent. Determinations of tritium and helium concentrations indicate that water containing elevated concentrations of mercury recharged the aquifer between 9.4 and 79 years ago, which includes the period during which many of the 34 sites were undergoing a change from agricultural or undeveloped to residential land use. Batch equilibrium experiments were used to measure adsorption of dissolved mercury, mercuric chloride, and phenylmercuric acetate by aquifer sediments at pH 3.5-4.0, 4.5-5.0, and 5.5-6.0. In nearly all cases, 55 to 95 percent of the mercury added to the sediments was adsorbed. Mercury mobilization from aquifer sediments inoculated with mercury was investigated by leaching the sediments with two concentrations of nitric acid (a component of acid rain), a sodium chloride solution (simulating road salt), and three fertilizer solutions. A solution of 20-20-20 (nitrogenphosphorous-potassium) fertilizer removed virtually all of the mercury with which the sediments had been inoculated. The sodium chloride solution was moderately effective in removing applied mercury from the sediments, as was a solution of nitric acid. A more dilute nitric acid solution and two sodium nitrate fertilizer solutions were less effective. Results of these experiments indicate that mercury adsorbs to aquifer sediments, but that varying amounts can be removed by infiltrating solutions, some of which can be related to specific land uses. Land-use history at the 34 sites generally indicates a change from agricultural or undeveloped settings to residential settings. Whatever the source of mercury to these sites, a change in the geochemical environment of the soil and aquifer brought about by land-use change probably provides mechanisms for mobilizing the mercury from soils and sediments to ground water.

Criticality in a non-equilibrium, driven system: charged colloidal rods (fd-viruses) in electric fields.

PubMed

Kang, K; Dhont, J K G

2009-11-01

Experiments on suspensions of charged colloidal rods (fd-virus particles) in external electric fields are performed, which show that a non-equilibrium critical point can be identified. Several transition lines of field-induced phases and states meet at this point and it is shown that there is a length- and time-scale which diverge at the non-equilibrium critical point. The off-critical and critical behavior is characterized, with both power law and logarithmic divergencies. These experiments show that analogous features of the classical, critical divergence of correlation lengths and relaxation times in equilibrium systems are also exhibited by driven systems that are far out of equilibrium, related to phases/states that do not exist in the absence of the external field.

Evaluation of simulated dredging to control internal phosphorus release from sediments: Focused on phosphorus transfer and resupply across the sediment-water interface.

PubMed

Yu, Juhua; Ding, Shiming; Zhong, Jicheng; Fan, Chengxin; Chen, Qiuwen; Yin, Hongbin; Zhang, Lei; Zhang, Yinlong

2017-08-15

Sediment dredging is an effective restoration method to control the internal phosphorus (P) loading of eutrophic lakes. However, the core question is that the real mechanism of dredging responsible for sediment internal P release still remains unclear. In this study, we investigated the P exchange across the sediment-water interface (SWI) and the internal P resupply ability from the sediments after dredging. The study is based on a one-year field simulation study in Lake Taihu, China, using a Rhizon soil moisture sampler, high-resolution dialysis (HR-Peeper), ZrO-Chelex diffusive gradients in thin film (ZrO-Chelex DGT), and P fractionation and adsorption isotherm techniques. The results showed low concentration of labile P in the pore water with a low diffusion potential and a low resupply ability from the sediments after dredging. The calculated flux of P from the post-dredged sediments decreased by 58% compared with that of non-dredged sediments. Furthermore, the resupply in the upper 20mm of the post-dredged sediments was reduced significantly after dredging (P<0.001). Phosphorus fractionation analysis showed a reduction of 25% in the mobile P fractions in the post-dredged sediments. Further analysis demonstrated that the zero equilibrium P concentration (EPC 0 ), partitioning coefficient (K p ), and adsorption capacity (Q max ) on the surface sediments increased after dredging. Therefore, dredging could effectively reduce the internal P resupply ability of the sediments. The reasons for this reduction are probably the lower contributions of mobile P fractions, higher retention ability, and the adsorption capacity of P for post-dredged sediments. Overall, this investigation indicated that dredging was capable of effectively controlling sediment internal P release, which could be ascribed to the removal of the surface sediments enriched with total phosphorus (TP) and/or organic matter (OM), coupled with the inactivation of P to iron (Fe) (hydr)oxides in the upper 20mm active layer. Copyright © 2017 Elsevier B.V. All rights reserved.

Longitudinal variation in lateral trapping of fine sediment in tidal estuaries: observations and a 3D exploratory model

NASA Astrophysics Data System (ADS)

Chen, Wei; de Swart, Huib E.

2018-03-01

This study investigates the longitudinal variation of lateral entrapment of suspended sediment, as is observed in some tidal estuaries. In particular, field data from the Yangtze Estuary are analysed, which reveal that in one cross-section, two maxima of suspended sediment concentration (SSC) occur close to the south and north sides, while in a cross-section 2 km down-estuary, only one SSC maximum on the south side is present. This pattern is found during both spring tide and neap tide, which are characterised by different intensities of turbulence. To understand longitudinal variation in lateral trapping of sediment, results of a new three-dimensional exploratory model are analysed. The hydrodynamic part contains residual flow due to fresh water input, density gradients and Coriolis force and due to channel curvature-induced leakage. Moreover, the model includes a spatially varying eddy viscosity that accounts for variation of intensity of turbulence over the spring-neap cycle. By imposing morphodynamic equilibrium, the two-dimensional distribution of sediment in the domain is obtained analytically by a novel procedure. Results reveal that the occurrence of the SSC maxima near the south side of both cross-sections is due to sediment entrapment by lateral density gradients, while the second SSC maximum near the north side of the first cross-section is by sediment transport due to curvature-induced leakage. Coriolis deflection of longitudinal flow also contributes the trapping of sediment near the north side. This mechanism is important in the upper estuary, where the flow due to lateral density gradients is weak.

Toxicity of smelter slag-contaminated sediments from Upper Lake Roosevelt and associated metals to early life stage White Sturgeon (Acipenser transmontanus Richardson, 1836)

USGS Publications Warehouse

Little, E.E.; Calfee, R.D.; Linder, G.

2014-01-01

The toxicity of five smelter slag-contaminated sediments from the upper Columbia River and metals associated with those slags (cadmium, copper, zinc) was evaluated in 96-h exposures of White Sturgeon (Acipenser transmontanus Richardson, 1836) at 8 and 30 days post-hatch. Leachates prepared from slag-contaminated sediments were evaluated for toxicity. Leachates yielded a maximum aqueous copper concentration of 11.8 μg L−1 observed in sediment collected at Dead Man's Eddy (DME), the sampling site nearest the smelter. All leachates were nonlethal to sturgeon that were 8 day post-hatch (dph), but leachates from three of the five sediments were toxic to fish that were 30 dph, suggesting that the latter life stage is highly vulnerable to metals exposure. Fish maintained consistent and prolonged contact with sediments and did not avoid contaminated sediments when provided a choice between contaminated and uncontaminated sediments. White Sturgeon also failed to avoid aqueous copper (1.5–20 μg L−1). In water-only 96-h exposures of 35 dph sturgeon with the three metals, similar toxicity was observed during exposure to water spiked with copper alone and in combination with cadmium and zinc. Cadmium ranging from 3.2 to 41 μg L−1 or zinc ranging from 21 to 275 μg L−1 was not lethal, but induced adverse behavioral changes including a loss of equilibrium. These results suggest that metals associated with smelter slags may pose an increased exposure risk to early life stage sturgeon if fish occupy areas contaminated by slags.

Relationship of geological and geothermal field properties: Midcontinent area, USA, an example

USGS Publications Warehouse

Forster, A.; Merriam, D.F.; Brower, J.C.

1993-01-01

Quantitative approaches to data analysis in the last decade have become important in basin modeling and mineral-resource estimation. The interrelation of geological, geophysical, geochemical, and geohydrological variables is important in adjusting a model to a real-world situation. Revealing the interdependences of variables can contribute in understanding the processes interacting in sedimentary basins. It is reasonably simple to compare spatial data of the same type but more difficult if different properties are involved. Statistical techniques, such as cluster analysis or principal components analysis, or some algebraic approaches can be used to ascertain the relations of standardized spatial data. In this example, structural configuration on five different stratigraphic horizons, one total sediment thickness map, and four maps of geothermal data were copared. As expected, the structural maps are highly related because all had undergone about the same deformation with differing degrees of intensity. The temperature gradients derived (1) from shallow borehole logging measurements under equilibrium conditions with the surrounding rock, and (2) from non-equilibrium bottom-hole temperatures (BHT) from deeper depths are mainly independent of each other. This was expected and confirmed also for the two temperature maps at 1000 ft which were constructed using both types of gradient values. Thus, it is evident that the use of a 2-point (BHT and surface temperature) straightline calculation of a mean temperature gradient gives different information about the geothermal regime than using gradients from temperatures logged under equilibrium conditions. Nevertheless, it is useful to determine to what a degree the larger dataset of nonequilibrium temperatures could reflect quantitative relationships to geologic conditions. Comparing all maps of geothermal information vs. the structural and the sediment thickness maps, it was determined that all correlations are moderately negative or slightly positive. These results are clearly shown by the cluster analysis and the principal components. Considering a close relationship between temperature and thermal conductivity of the sediments as observed for most of the Midcontinent area and relatively homogeneous heat-flow density conditions for the study area these results support the following assumptions: (1) undifferentiated geothermal gradients, computed from temperatures of different depth intervals and differing sediment properties, cannot contribute to an improved understanding of the temperature structure and its controls within the sedimentary cover, and (2) the quantitative approach of revealing such relations needs refined datasets of temperature information valid for the different depth levels or stratigraphic units. ?? 1993 International Association for Mathematical Geology.

Considerations of erosion and storage of carbon, focusing on tropical landscapes in Puerto Rico and Panama (Invited)

NASA Astrophysics Data System (ADS)

Stallard, R. F.

2013-12-01

Humid tropical regions are particularly good settings to examine the terrestrial carbon and nutrient cycles because the high average temperatures combined with abundant water and frequent intense storms promote rapid biological activity, weathering, and physical erosion. In studying the human-modified carbon or nutrient cycles on particular landscapes, assessments of the impact of human activities must be compared to prior states of those landscapes with regard to (1) biogeochemical reservoir sizes on the landscape, (2) rates of transport through and out of the landscape, and (3) ultimate fate of the material exported. Ongoing studies in small catchments and larger adjacent watersheds in Puerto Rico (PR) and Panama (PTY) assess which biological, hydrologic, and geomorphic mechanisms have been affected by human activities. The catchments are on older volcanic rocks (6, 2 in PR), granitic rocks (3, all in PR), and one in PTY on limey sediments. Three of the volcanic catchments and one granitic catchment are agricultural. In all these landscapes, landslides, rather than surficial erosion, appear to be the largest regional sediment source, and the biggest landslide-producing storms occur once every few decades. Both landslide-related and surficial erosion are greater in agricultural catchments compared to forested catchments on the same lithology, and granitic landscapes are eroding far more rapidly than volcanic landscapes. Physical erosion on the granitic landscapes appears to be greatly in excess of reasonable equilibrium rates based on mass balances and estimates based on Be-10. The particulate-organic-carbon (POC) yields exceed combined dissolved organic (DOC) and inorganic (DIC) carbon yields in the granitic watersheds, but they are considerably less than the DOC+DIC yields in the volcanic watersheds. Annual yields of DIC and DOC relate linearly to annual runoff, whereas POC has a steep exponential-style increase with increasing runoff, indicating a strong sensitivity to climate change, compared to a linear response. POC yields are tied to sediment yields that are, in turn, far in excess of equilibrium yields. This excess implies that much of the present carbon transport in eastern PR is the result of erosion in excess of equilibrium. In essence, soils that have developed for thousands of years are eroding more rapidly than they are now forming. Carbon accumulation in soil is rapid, and in a landslide scar, which can endure thousands of years, half of the carbon is regenerated in 80 years and all of it in about 200 years. Thus, eroding carbon is being replaced with carbon from the atmosphere. In PR, sediments are delivered to reservoirs or the ocean; in PTY deposition is in reservoirs. These reservoirs are strongly coupled sinks for carbon and nutrients. After landslides, huge quantities of sediment are deposited along with considerable wood and other organic debris. Sediment that deposits in the crenulated arms of the reservoirs is quite rich in organic matter derived from lake productivity that has been greatly augmented by nutrients derived from agricultural lands and domestic wastes. Carbon storage in reservoirs exceeds forest storage, and unlike forests, increases with time.

Nitrogen-assisted Three-phase Equilibrium in Hydrate Systems Composed of Water, Methane, Carbon Dioxide, and Nitrogen

NASA Astrophysics Data System (ADS)

Darnell, K.; Flemings, P. B.; DiCarlo, D. A.

2016-12-01

In June 2016, seawater samples at sediment-seawater interface and sediment samples were collected by the he Jiaolong, China's manned submersible, at four sampling sites located in the Yap Trench. Seawater samples from different depths of the trench were also collected by CTD. Chemical parameters, including pH, alkanility, concentrations of dissolved inorganic carbon, dissolved and total organic carbon, methane, dimethylsulfoniopropionate, nutrients, carbohydrates, and amino acids were analyzed in the seawater samples. Concentrations of total organic carbon, six constant elements and nine trace elements were determined in the sediment samples. All the vertical profiles of the chemical parameters in the seawater have unique characteristics. Our resluts also showed that the carbonate compensation depth (CCD) was between 4500 m and 5000 m in the trench. The hadal sediment at 6500 m depth under the CCD line was siliceous ooze favored for the burial of orgaic carbon, attributed to accumulation of surface sediment by gravity flow. The abyssal sediment at the 4500 m depth was calcareous ooze. Various microfossils, such as discoasters and diatoms, were identified in different sediment layers of the sediment samples.Based on the ratios of Fe/Al and Ti/Al, and the correlation between different elements, the sediment in the Yap Trench were derived from biogenic, terrestrial, volcanic and autogenic sources. The ratios of Ni/Co and V/Cr showed that the deposition environment of the trench should be oxidative, arributed to inflow of the Antractic bottom oxygen-rich seawater.The high concentraiont of Ca in the sediment from the station 371-Yap-S02 below 4 cm depth indicated that there was no large-scale volcanic eruption in the research area and the volcanic materials in the sediment might orginated from the Mariana Volcanic Arc, and the Carolyn Ridge has been slowly sinking on the east side of the trench due to plate subduction. This study is the first systematic study of chemical characteristics in the seawater and sediment of the Yap Trench.

Physical phenomena and the microgravity response

NASA Technical Reports Server (NTRS)

Todd, Paul

1989-01-01

The living biological cell is not a sack of Newtonian fluid containing systems of chemical reactions at equilibrium. It is a kinetically driven system, not a thermodynamically driven system. While the cell as a whole might be considered isothermal, at the scale of individual macromolecular events there is heat generated, and presumably sharp thermal gradients exist at the submicron level. Basic physical phenomena to be considered when exploring the cell's response to inertial acceleration include particle sedimentation, solutal convection, motility electrokinetics, cytoskeletal work, and hydrostatic pressure. Protein crystal growth experiments, for example, illustrate the profound effects of convection currents on macromolecular assembly. Reaction kinetics in the cell vary all the way from diffusion-limited to life-time limited. Transport processes vary from free diffusion, to facilitated and active transmembrane transport, to contractile-protein-driven motility, to crystalline immobilization. At least four physical states of matter exist in the cell: aqueous, non-aqueous, immiscible-aqueous, and solid. Levels of order vary from crystalline to free solution. The relative volumes of these states profoundly influence the cell's response to inertial acceleration. Such subcellular phenomena as stretch-receptor activation, microtubule re-assembly, synaptic junction formation, chemotactic receptor activation, and statolith sedimentation were studied recently with respect to both their basic mechanisms and their responsiveness to inertial acceleration. From such studies a widespread role of cytoskeletal organization is becoming apparent.

Bathymetry and Sediment-Storage Capacity Change in Three Reservoirs on the Lower Susquehanna River, 1996-2008

USGS Publications Warehouse

Langland, Michael J.

2009-01-01

The Susquehanna River transports a substantial amount of the sediment and nutrient load to the Chesapeake Bay. Upstream of the bay, three large dams and their associated reservoirs trap a large amount of the transported sediment and associated nutrients. During the fall of 2008, the U.S. Geological Survey in cooperation with the Pennsylvania Department of Environmental Protection completed bathymetric surveys of three reservoirs on the lower Susquehanna River to provide an estimate of the remaining sediment-storage capacity. Previous studies indicated the upper two reservoirs were in equilibrium with long-term sediment storage; only the most downstream reservoir retained capacity to trap sediments. A differential global positioning system (DGPS) instrument was used to provide the corresponding coordinate position. Bathymetry data were collected using a single beam 210 kHz (kilohertz) echo sounder at pre-defined transects that matched previous surveys. Final horizontal (X and Y) and vertical (Z) coordinates of the geographic positions and depth to bottom were used to create bathymetric maps of the reservoirs. Results indicated that from 1996 to 2008 about 14,700,000 tons of sediment were deposited in the three reservoirs with the majority (12,000,000 tons) being deposited in Conowingo Reservoir. Approximately 20,000 acre-feet or 30,000,000 tons of remaining storage capacity is available in Conowingo Reservoir. At current transport (3,000,000 tons per year) and deposition (2,000,000 tons per year) rates and with no occurrence of major scour events due to floods, the remaining capacity may be filled in 15 to 20 years. Once the remaining sediment-storage capacity in the reservoirs is filled, sediment and associated phosphorus loads entering the Chesapeake Bay are expected to increase.

Heavy metals relationship with water and size-fractionated sediments in rivers using canonical correlation analysis (CCA) case study, rivers of south western Caspian Sea.

PubMed

Vosoogh, Ali; Saeedi, Mohsen; Lak, Raziyeh

2016-11-01

Some pollutants can qualitatively affect aquatic freshwater such as rivers, and heavy metals are one of the most important pollutants in aquatic fresh waters. Heavy metals can be found in the form of components dissolved in these waters or in compounds with suspended particles and surface sediments. It can be said that heavy metals are in equilibrium between water and sediment. In this study, the amount of heavy metals is determined in water and different sizes of sediment. To obtain the relationship between heavy metals in water and size-fractionated sediments, a canonical correlation analysis (CCA) was utilized in rivers of the southwestern Caspian Sea. In this research, a case study was carried out on 18 sampling stations in nine rivers. In the first step, the concentrations of heavy metals (Cu, Zn, Cr, Fe, Mn, Pb, Ni, and Cd) were determined in water and size-fractionated sediment samples. Water sampling sites were classified by hierarchical cluster analysis (HCA) utilizing squared Euclidean distance with Ward's method. In addition, for interpreting the obtained results and the relationships between the concentration of heavy metals in the tested river water and sample sediments, canonical correlation analysis (CCA) was utilized. The rivers were grouped into two classes (those having no pollution and those having low pollution) based on the HCA results obtained for river water samples. CCA results found numerous relationships between rivers in Iran's Guilan province and their size-fractionated sediments samples. The heavy metals of sediments with 0.038 to 0.125 mm size in diameter are slightly correlated with those of water samples.

Colloid formation in Hanford sediments reacted with simulated tank waste.

PubMed

Mashal, Kholoud; Harsh, James B; Flury, Markus; Felmy, Andrew R; Zhao, Hongting

2004-11-01

Solutions of high pH, ionic strength, and aluminum concentration have leaked into the subsurface from underground waste storage tanks atthe Hanford Reservation in Washington State. Here, we test the hypothesis that these waste solutions alter and dissolve the native minerals present in the sediments and that colloidal (diameter < 2 microm) feldspathoids form. We reacted Hanford sediments with simulated solutions representative of Hanford waste tanks. The solutions consisted of 1.4 or 2.8 mol/kg NaOH, 0.125 or 0.25 mol/kg NaAlO4, and 3.7 mol/kg NaNO3 and were contacted with the sediments for a period of 25 or 40 days at 50 degrees C. The colloidal size fraction was separated from the sediments and characterized in terms of mineralogy, morphology, chemical composition, and electrophoretic mobility. Upon reaction with tank waste solutions, native minerals released Si and other elements into the solution phase. This Si precipitated with the Al present in the waste solutions to form secondary minerals, identified as the feldspathoids cancrinite and sodalite. The solution phase was modeled with the chemical equilibrium model GMIN for solution speciation and saturation indices with respect to sodalite and cancrinite. The amount of colloidal material in the sediments increased upon reaction with waste solutions. At the natural pH found in Hanford sediments (pH 8) the newly formed minerals are negatively charged, similar to the unreacted colloidal material present in the sediments. The formation of colloidal material in Hanford sediments upon reaction with tank waste solutions is an important aspect to consider in the characterization of Hanford tank leaks and may affect the fate of hazardous radionuclides present in the tank waste.

CO2 solubility and speciation in rhyolitic sediment partial melts at 1.5-3.0 GPa - Implications for carbon flux in subduction zones

NASA Astrophysics Data System (ADS)

Duncan, Megan S.; Dasgupta, Rajdeep

2014-01-01

Partial melts of subducting sediments are thought to be critical agents in carrying trace elements and water to arc basalt source regions. Sediment partial melts may also act as a carrier of CO2. However, the CO2 carrying capacity of natural rhyolitic melts that derive from partial fusion of downgoing sediment at sub-arc depths remains unconstrained. We conducted CO2-solubility experiments on a rhyolitic composition similar to average, low-degree experimental partial melt of pelitic sediments between 1.5 and 3.0 GPa at 1300 °C and containing variable water content. Concentrations of water and carbon dioxide were measured using FTIR. Molecular CO2(CO2mol.) and carbonate anions (CO32-) both appear as equilibrium species in our experimental melts. Estimated total CO2 concentrations (CO2mol.+CO32-) increased with increasing pressure and water content. At 3.0 GPa, the bulk CO2 solubility are in the range of ∼1-2.5 wt.%, for melts with H2O contents between 0.5 and 3.5 wt.%. For melts with low H2O content (∼0.5 wt.%), CO2mol. is the dominant carbon species, while in more H2O-rich melts CO32- becomes dominant. The experimentally determined, speciation-specific CO2 solubilities yielded thermodynamic parameters that control dissolution of CO2 vapor both as CO2mol. and as CO32- in silicate melt for each of our compositions with different water content; CO2vapor ↔CO2melt :lnK0=-15 to -18, ΔV0 = 29 to 14 cm3 mol-1 and CO2vapor +Omelt →CO32-melt :lnK0=-20 to -14, ΔV0 = 9 to 27 cm3 mol-1, with ΔV0 of reaction being larger for formation of CO2mol. in water-poor melts and for formation of CO32- in water-rich melts. Our bulk CO2 solubility data, [CO2] (in wt.%) can be fitted as a function of pressure, P (in GPa) and melt water content, [H2O] (in wt.%) with the following function: [CO2](wt.%)=(-0.01108[H2O]+0.03969)P2+(0.10328[H2O]+0.41165)P. This parameterization suggests that over the range of sub-arc depths of 72-173 km, water-rich sediment partial melt may carry as much as 2.6-5.5 wt.% CO2 to the sub-arc mantle source regions. At saturation, 1.6-3.3 wt.% sediment partial melt relative to the mantle wedge is therefore sufficient to bring up the carbon budget of the mantle wedge to produce primary arc basalts with 0.3 wt.% CO2. Sediment plumes in mantle wedge: Sediment plumes or diapirs may form from the downgoing slab because the sediment layer atop the slab is buoyant relative to the overlying, hanging wall mantle (Currie et al., 2007; Behn et al., 2011). Via this process, sediment layers with carbonates would carry CO2 to the arc source region. Owing to the higher temperature in the mantle wedge, carbonate can breakdown. Behn et al. (2011) suggested that sediment layers as thin as 100 m, appropriate for modern arcs, could form sediment diapirs. They predicted that diapirs would form from the slab in the sub-arc region for most subduction zones today without requiring hydrous melting. H2O-rich fluid driven carbonate breakdown: Hydrous fluid flushing of the slab owing to the breakdown of hydrous minerals could drive carbonate breakdown (Kerrick and Connolly, 2001b; Grove et al., 2002; Gorman et al., 2006). The addition of water would cause decarbonation creating an H2O-CO2-rich fluid that would then flux through the overlying sediment layer, lower the solidus temperature, and trigger melting. Recent geochemical (Cooper et al., 2012) and geodynamic (van Keken, 2003; Syracuse et al., 2010) constraints suggest that the sub-arc slab top temperatures are above the hydrous fluid-present sediment solidus, thus in the presence of excess fluid, both infiltration induced decarbonation and sediment melting may occur. Hot subduction: This is relevant for subduction zones such as Cascadia and Mexico, where slab-surface temperatures are estimated to be higher (Syracuse et al., 2010). A higher temperature could cause carbonate breakdown and sediment partial melting without requiring a hydrous fluid flux. In this case a relatively dry silicate sediment melt will have the opportunity to dissolve and carry CO2. For hot subduction zones, even if sedimentary layer itself does not carry carbonate, CO2 released from basalt-hosted carbonates may be dissolved in sediment partial melt. Experiments conducted on subducted sediment compositions show that the partial melt compositions are generally rhyolitic (Johnson and Plank, 1999; Hermann and Green, 2001; Schmidt et al., 2004; Auzanneau et al., 2006; Hermann and Spandler, 2008; Spandler et al., 2010; Tsuno and Dasgupta, 2011). Therefore, solubility of CO2 in rhyolitic sediment partial melts needs to be known. Previous studies on rhyolitic melts experimentally determined CO2 solubility from 0.05 to 0.66 GPa (Fig. 1; Fogel and Rutherford, 1990; Blank et al., 1993; Tamic et al., 2001). This pressure range is not appropriate for global sub-arc depth range of 72-173 km (Syracuse and Abers, 2006) settings (P = 2-5 GPa). Carbon dioxide solubility experiments at pressures from 1.5 to 3.5 GPa are available but only on simple compositions - i.e., albite, which does not have the chemical complexity of natural sediment partial melts (Fig. 1; Brey, 1976; Mysen, 1976; Mysen et al., 1976; Mysen and Virgo, 1980; Stolper et al., 1987; Brooker et al., 1999). For example, natural rhyolitic melt derived from partial fusion of pelitic sediments contain non-negligible concentrations of Ca2+, Mg2+, Fe2+. Many of these studies were also conducted under mixed-volatile conditions (CO2 + H2O) with H2O contents from 0.06 to 3.3 wt.%. These studies were used in calculating various solubility models: Volatile-Calc (Newman and Lowenstern, 2002), that of Liu et al. (2005), and that of Papale et al. (2006). Volatile-Calc can be used to calculate CO2 solubility only on a generic rhyolite composition up to 0.5 GPa. The model of Liu et al. (2005) is also on a generic rhyolite up to 0.5 GPa, but can calculate mixed volatile concentrations provided the vapor composition is known. The model of Papale et al. (2006) can be used to calculate mixed volatile concentrations for a melt composition of interest, but only up to 1.0 GPa.The literature data show that CO2 solubility increases with increasing pressure and decreases with increasing melt silica content (decreasing NBO/T; e.g., Brooker et al., 2001). The effect of temperature remains somewhat ambiguous, but is thought to be relatively smaller than the pressure or compositional effects, with Mysen (1976) measuring increasing CO2 solubility with temperature for albite melt, Brooker et al. (2001) and Fogel and Rutherford (1990) noticing decreasing CO2 solubility with increasing temperature, and Stolper et al. (1987) concluding that temperature has essentially no effect on total melt CO2 concentration at saturation. The presence of water in the melt also is known to affect CO2 solution (e.g., Mysen, 1976; Eggler and Rosenhauer, 1978), yet quantitative effect of water on CO2 solution in natural rhyolitic melt has only been investigated up to 0.5 GPa (Tamic et al., 2001). In order to determine the CO2 carrying capacity of sediment partial melts, experiments must be conducted at conditions (pressure, temperature, major element compositions, and XH2O) relevant to sub-arc settings.In this study we measured the solubility and speciation of CO2 in rhyolitic sediment partial melts. Experiments were conducted from 1.5 to 3.0 GPa at 1300 °C with variable water contents and synthesized glasses were analyzed for water and carbon speciation using Fourier-transformed infrared spectroscopy. Our measured solubility data allowed us to constrain volume change and equilibrium constant of the CO2 dissolution reactions. Moreover, we parameterize CO2 solubility in sediment partial melt as a function of pressure and melt water content. Our data and empirical model suggest that the CO2 carrying capacity of sediment partial melts is sufficiently high at sub-arc depths and hydrous sediment melt can potentially carry the necessary dose of CO2 to arc mantle source regions.

Geomorphology and sediment transport on a submerged back-reef sand apron: One Tree Reef, Great Barrier Reef

NASA Astrophysics Data System (ADS)

Harris, Daniel L.; Vila-Concejo, Ana; Webster, Jody M.

2014-10-01

Back-reef sand aprons are conspicuous and dynamic sedimentary features in coral reef systems. The development of these features influences the evolution and defines the maturity of coral reefs. However, the hydrodynamic processes that drive changes on sand aprons are poorly understood with only a few studies directly assessing sediment entrainment and transport. Current and wave conditions on a back-reef sand apron were measured during this study and a digital elevation model was developed through topographic and bathymetric surveying of the sand apron, reef flats and lagoon. The current and wave processes that may entrain and transport sediment were assessed using second order small amplitude (Stokes) wave theory and Shields equations. The morphodynamic interactions between current flow and geomorphology were also examined. The results showed that sediment transport occurs under modal hydrodynamic conditions with waves the main force entraining sediment rather than average currents. A morphodynamic relationship between current flow and geomorphology was also observed with current flow primarily towards the lagoon in shallow areas of the sand apron and deeper channel-like areas directing current off the sand apron towards the lagoon or the reef crest. These results show that the short-term mutual interaction of hydrodynamics and geomorphology in coral reefs can result in morphodynamic equilibrium.

Hypolyminetic Oxygen Depletion And Dynamics of P Binding Forms: Insights From Modeling Sediment Early Diagenesis Coupled With Automatic Parameter Estimation

NASA Astrophysics Data System (ADS)

Shafei, Babak; Schmid, Martin; Müller, Beat; Chwalek, Thomas

2014-05-01

Sediment diagenesis can significantly impact on lake water quality through depleting hypolimnion oxygen and acting as a sink or source of nutrients and contaminants. In this study, we apply MATsedLAB, a sediment diagenesis module developed in MATLAB [1, 2] to quantify benthic oxygen consumption and biogeochemical cycling of phosphate (P) in lacustrine sediments of Lake Baldegg, located in central Switzerland. MATsedLAB provides an access to the advanced computational and visualization capabilities of the interactive programming environment of MATLAB. It allows for a flexible definition of non steady-state boundary conditions at the sediment-water interface (SWI), the model parameters as well as transport and biogeochemical reactions. The model has been extended to facilitate the model-independent parameter estimation and uncertainty analysis using the software package, PEST. Lake Baldegg represents an interesting case where sediment-water interactions control P loading in an eutrophic lake. It is of 5.2 km2 surface area and has been artificially aerated since 1982. Between 1960 and 1980, low oxygen concentrations and meromictic condition were established as a result of high productivity. Here, we use the cores for the measurements of anions and cations which were collected in April and June 2012 respectively from the deepest location (66 m), by Torres et al. (2013) to calibrate the developed model [3]. Depth profiles of thirty three species were simulated by including thirty mixed kinetic-equilibrium biogeochemical processes as well as imposing the fluxes of organic and inorganic matters along with solute concentrations at the SWI as dynamic boundary conditions. The diffusive transport in the boundary layer (DBL) above the SWI was included as the supply of O2 to the sediment surface can be diffusion-limited, and applying a constant O2 concentration at the sediment surface may overestimate O2 consumption. Benthic oxygen consumption was calculated as a function of the present and past deposited OM. The results revealed the transient nature of sediment oxygen uptake and existence of temporal lag associated with benthic oxygen consumption for the aerated versus non-aerated scenarios. The model closely reproduced phosphate partitioning among OM and various redox-sensitive inorganic minerals. The results showed that P associated with OM is the dominant pool as inorganic binding P such as apatite, vivinite and adsorbed P contain a minor fraction of solid phase P. The calculated flux of dissolved P through the SWI under seasonal and decadal variations suggest that oxygen concentration at the SWI and the flux of settling OM along with its composition expressed as the ratio of degradable to inert OM are the major factors that control P release to the overlying water under dynamic forcing. References [1] Couture, R., et al. (2009). "Non steady-stae modeling of arsenic diagenesis in lake sediments." Environmental Science and Technology 44 (1): 197-203. [2] Shafei, B., et al. (2010). "Arsenic sorption in aquatic sediments: equilibrium, kinetic and mixed modeling approaches." Geochimica et cosmochimica acta 74 (12): A938-A938. [3] Torres, N. T., et al. (2013). "Sediment porewater extraction and analysis combining filter tube samplers and capillary electrophoresis." Environmental Science-Processes & Impacts 15(4): 715-720.

Vegetation modulated landscape evolution: Effects of vegetation on landscape processes, drainage density and topography

NASA Astrophysics Data System (ADS)

Bras, R. L.; Istanbulluoglu, E.

2004-12-01

Topography acts as a template for numerous landscape processes that includes hydrologic, ecologic and biologic phenomena. These processes not only interact with each other but also contribute to shaping the landscape as they influence geomorphic processes. We have investigated the effects of vegetation on known geomorphic relations, thresholds for channel initiation and landform evolution, using both analytical and numerical approaches. Vegetation is assumed to form a uniform ground cover. Runoff erosion is modeled based on power function of excess shear stress, in which shear stress efficiency is inversely proportional to vegetation cover. Plant effect on slope stability is represented by additional cohesion provided by plant roots. Vegetation cover is assumed to reduce sediment transport rates due to physical creep processes (rainsplash, dry ravel, and expansion and contraction of sediments) according to a negative exponential relationship. Vegetation grows as a function of both available cover and unoccupied space by plants, and is killed by geomorphic disturbances (runoff erosion and landsliding), and wildfires. Analytical results suggest that, in an equilibrium basin with a fixed vegetation cover, plants may cause a transition in the dominant erosion process at the channel head. A runoff erosion dominated landscape, under none or loose vegetation cover, may become landslide dominated under a denser vegetation cover. The sign of the predicted relationship between drainage density and vegetation cover depends on the relative influence of vegetation on different erosion phenomena. With model parameter values representative of the Oregon Coast Range (OCR), numerical experiments conducted using the CHILD model. Numerical experiments reveal the importance of vegetation disturbances on the landscape structure. Simulated landscapes resemble real-world catchments in the OCR when vegetation disturbances are considered.

Maximum Flow Efficiency in an Anabranching River, Magela Creek, Northern Australia

NASA Astrophysics Data System (ADS)

Jansen, J. D.; Nanson, G. C.

2002-12-01

In this field- and laboratory-based study, we demonstrate that the development of anabranching channels in some rivers increases the conveyance of sediment and water, compared with a single channel at the same flow discharge. That is, under certain conditions, anabranching channels exhibit greater sediment transporting capacity per unit available stream power. Anabranching is a globally widespread river pattern noted in diverse physiographic, hydrologic and sedimentologic environments, and recent efforts have sought to unravel controls on their origin and maintenance. It is widely held that most rivers form a single-channel in order to minimise boundary roughness while conveying water and sediment, but do all rivers show a tendency to develop a single channel? And if so, what factors lead to long-term anabranching? The observation that anabranching commonly develops in environments where water and sediment conveyance is maintained with little or no recourse to increasing energy slope prompted the hypothesis that rivers may adopt a multiple channel pattern in order to optimise their efficiency where they cannot otherwise increase slope. It is reasoned that development of a system of multiple channels reduces total flow width and raises mean flow depth, thereby maximising sediment transport per unit area of the channel bed and maintaining or enhancing water and sediment throughput. In testing the hypothesis we present: (1) results of a field experiment in which hydraulic variables and bedload discharge are measured and compared for single-channel versus multichannel reaches of the same river (Magela Creek, northern Australia); (2) comparison of these field results with bedload transport modelling via well known bedload equations; and (3) results of an experimental flume study comparing hydraulic variables and sediment flux in single-channel versus divided flow. Magela Creek is representative of several anabranching systems draining the Alligators Rivers Region of monsoonal northern Australia. We investigate the dynamics of flows up to four-times bankfull discharge and find that at high flowstage hydraulic variables interact in a complicated manner that precludes conventional hydraulic geometry analytical methods. The complex trends among hydraulic variables reflect the differential and stage-dependent interactions between bank vegetation and channel roughness. Abrupt decline in overbank velocity promotes proximal sedimentation in the form of vertically-accreting islands, levees and sand splays - mechanisms of sediment sequestration that may eventually lead to channel avulsion and creation of new channels. Given that river pattern reveals much about river dynamics, the prevalence of anabranching - particularly among the world's largest rivers - invites the speculation that a fundamental physical principle may underpin the widespread adoption of anabranching; it may be the most efficient means of transmitting large water and sediment discharges in alluvial rivers. However, just as different equilibrium states are expected to exist in braiding, meandering and straight rivers, we anticipate that other anabranching rivers may differ in their efficiency. Moreover, the development of sediment and water flux imbalances between anabranches is a highly likely outcome of their independent functioning. Channel atrophy coupled with in-channel sedimentation lies at the heart of channel avulsion and abandonment processes and therefore is central to the anabranching pattern.

Use of column experiments to investigate the fate of organic micropollutants - a review

NASA Astrophysics Data System (ADS)

Banzhaf, Stefan; Hebig, Klaus H.

2016-09-01

Although column experiments are frequently used to investigate the transport of organic micropollutants, little guidance is available on what they can be used for, how they should be set up, and how the experiments should be carried out. This review covers the use of column experiments to investigate the fate of organic micropollutants. Alternative setups are discussed together with their respective advantages and limitations. An overview is presented of published column experiments investigating the transport of organic micropollutants, and suggestions are offered on how to improve the comparability of future results from different experiments. The main purpose of column experiments is to investigate the transport and attenuation of a specific compound within a specific sediment or substrate. The transport of (organic) solutes in groundwater is influenced by the chemical and physical properties of the compounds, the solvent (i.e., the groundwater, including all solutes), and the substrate (the aquifer material). By adjusting these boundary conditions a multitude of different processes and related research questions can be investigated using a variety of experimental setups. Apart from the ability to effectively control the individual boundary conditions, the main advantage of column experiments compared to other experimental setups (such as those used in field experiments, or in batch microcosm experiments) is that conservative and reactive solute breakthrough curves can be derived, which represent the sum of the transport processes. There are well-established methods for analyzing these curves. The effects observed in column studies are often a result of dynamic, non-equilibrium processes. Time (or flow velocity) is an important factor, in contrast to batch experiments where all processes are observed until equilibrium is reached in the substrate-solution system. Slight variations in the boundary conditions of different experiments can have a marked influence on the transport and degradation of organic micropollutants. This is of critical importance when comparing general results from different column experiments investigating the transport behavior of a specific organic compound. Such variations unfortunately mean that the results from most column experiments are not transferable to other hydrogeochemical environments but are only valid for the specific experimental setup used. Column experiments are fast, flexible, and easy to manage; their boundary conditions can be controlled and they are cheap compared to extensive field experiments. They can provide good estimates of all relevant transport parameters. However, the obtained results will almost always be limited to the scale of the experiment and are not directly transferrable to field scales as too many parameters are exclusive to the column setup. The challenge for the future is to develop standardized column experiments on organic micropollutants in order to overcome these issues.

ORGANIC CONTAMINANT DISTRIBUTION IN SEDIMENTS, POLYCHAETES (NEREIS VIRENS) AND THE AMERICAN LOBSTER, HOMARUS AMERICANUS IN A LABORATORY FOOD CHAIN EXPERIMENT

EPA Science Inventory

A laboratory experiment was conducted to investigate the transfer of organic contaminants from an environmentally contaminated marine sediment through a simple marine food chain. The infaunal polychaete, Nereis virens, was exposed to contaminated sediment collected from the Passa...

The use of sequential extraction to evaluate the remediation potential of heavy metals from contaminated harbour sediment

NASA Astrophysics Data System (ADS)

Nystrøm, G. M.; Ottosen, L. M.; Villumsen, A.

2003-05-01

In this work sequential extraction is performed with harbour sediment in order to evaluate the electrodialytic remediation potential for harbour sediments. Sequential extraction was performed on a sample of Norwegian harbour sediment; with the original sediment and after the sediment was treated with acid. The results from the sequential extraction show that 75% Zn and Pb and about 50% Cu are found in the most mobile phases in the original sediment and more than 90% Zn and Pb and 75% Cu are found in the most mobile phase in the sediment treated with acid. Electrodialytic remediation experiments were made. The method uses a low direct current as cleaning agent, removing the heavy metals towards the anode and cathode according to the charge of the heavy metals in the electric field. The electrodialytic experiments show that up to 50% Cu, 85% Zn and 60% Pb can be removed after 20 days. Thus, there is still a potential for a higher removal, with some changes in the experimental set-up and longer remediation time. The experiments show that thc use of sequential extraction can be used to predict the electrodialytic remediation potential for harbour sediments.

Sediment dynamics in the Adriatic Sea investigated with coupled models

USGS Publications Warehouse

Sherwood, Christopher R.; Book, Jeffrey W.; Carniel, Sandro; Cavaleri, Luigi; Chiggiato, Jacopo; Das, Himangshu; Doyle, James D.; Harris, Courtney K.; Niedoroda, Alan W.; Perkins, Henry; Poulain, Pierre-Marie; Pullen, Julie; Reed, Christopher W.; Russo, Aniello; Sclavo, Mauro; Signell, Richard P.; Traykovski, Peter A.; Warner, John C.

2004-01-01

Several large research programs focused on the Adriatic Sea in winter 2002-2003, making it an exciting place for sediment dynamics modelers (Figure 1). Investigations of atmospheric forcing and oceanic response (including wave generation and propagation, water-mass formation, stratification, and circulation), suspended material, bottom boundary layer dynamics, bottom sediment, and small-scale stratigraphy were performed by European and North American researchers participating in several projects. The goal of EuroSTRATAFORM researchers is to improve our ability to understand and simulate the physical processes that deliver sediment to the marine environment and generate stratigraphic signatures. Scientists involved in the Po and Apennine Sediment Transport and Accumulation (PASTA) experiment benefited from other major research programs including ACE (Adriatic Circulation Experiment), DOLCE VITA (Dynamics of Localized Currents and Eddy Variability in the Adriatic), EACE (the Croatian East Adriatic Circulation Experiment project), WISE (West Istria Experiment), and ADRICOSM (Italian nowcasting and forecasting) studies.

Non-equilibrium thermodynamical description of rhythmic motion patterns of active systems: a canonical-dissipative approach.

PubMed

Dotov, D G; Kim, S; Frank, T D

2015-02-01

We derive explicit expressions for the non-equilibrium thermodynamical variables of a canonical-dissipative limit cycle oscillator describing rhythmic motion patterns of active systems. These variables are statistical entropy, non-equilibrium internal energy, and non-equilibrium free energy. In particular, the expression for the non-equilibrium free energy is derived as a function of a suitable control parameter. The control parameter determines the Hopf bifurcation point of the deterministic active system and describes the effective pumping of the oscillator. In analogy to the equilibrium free energy of the Landau theory, it is shown that the non-equilibrium free energy decays as a function of the control parameter. In doing so, a similarity between certain equilibrium and non-equilibrium phase transitions is pointed out. Data from an experiment on human rhythmic movements is presented. Estimates for pumping intensity as well as the thermodynamical variables are reported. It is shown that in the experiment the non-equilibrium free energy decayed when pumping intensity was increased, which is consistent with the theory. Moreover, pumping intensities close to zero could be observed at relatively slow intended rhythmic movements. In view of the Hopf bifurcation underlying the limit cycle oscillator model, this observation suggests that the intended limit cycle movements were actually more similar to trajectories of a randomly perturbed stable focus. Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.

Mobilization of natural colloids from an iron oxide-coated sand aquifer--Effect of pH and ionic strength

USGS Publications Warehouse

Bunn, Rebecca A.; Magelky, Robin D.; Ryan, Joseph N.; Elimelech, Menachem

2002-01-01

Field and laboratory column experiments were performed to assess the effect of elevated pH and reduced ionic strength on the mobilization of natural colloids in a ferric oxyhydroxide-coated aquifer sediment. The field experiments were conducted as natural gradient injections of groundwater amended by sodium hydroxide additions. The laboratory experiments were conducted in columns of undisturbed, oriented sediments and disturbed, disoriented sediments. In the field, the breakthrough of released colloids coincided with the pH pulse breakthrough and lagged the bromide tracer breakthrough. The breakthrough behavior suggested that the progress of the elevated pH front controlled the transport of the mobilized colloids. In the laboratory, about twice as much colloid release occurred in the disturbed sediments as in the undisturbed sediments. The field and laboratory experiments both showed that the total mass of colloid release increased with increasing pH until the concurrent increase in ionic strength limited release. A decrease in ionic strength did not mobilize significant amounts of colloids in the field. The amount of colloids released normalized to the mass of the sediments was similar for the field and the undisturbed laboratory experiments.

Importance of Dissolved Neutral Hg-Sulfides, Energy Rich Organic Matter and total Hg Concentrations for Methyl Mercury Production in Sediments

NASA Astrophysics Data System (ADS)

Drott, A.; Skyllberg, U.

2007-12-01

Methyl mercury (MeHg) is the mercury form that biomagnifies to the greatest extent in aquatic food webs. Therefore information about factors determining MeHg concentrations is critical for accurate risk assessment of contaminated environments. The concentration of MeHg in wetlands and sediments is the net result of: 1) methylation rates, 2) demethylation rates, and 3) input/output processes. In this study, the main controls on Hg methylation rates and total concentrations of MeHg, were investigated at eight sites in Sweden with sediments that had been subjected to local Hg contamination either as Hg(0), or as phenyl-Hg. Sediments were selected to represent a gradient in total Hg concentration, temperature climate, salinity, primary productivity, and organic C content and quality. Most sediments were high in organic matter content due to wood fibre efflux from pulp and paper industry. The pore water was analysed for total Hg, MeHg, DOC, H2S(aq), pH, DOC, Cl and Br. The chemical speciation of Hg(II) and MeHg in pore water was calculated using equilibrium models. Potential methylation and demethylation rates in sediments were determined in incubation experiments at 23° C under N2(g) for 48 h, after addition of isotopically enriched 201Hg(II) and Me204Hg. In all surface (0-20 cm) sediments there was a significant (p<0.001) positive relationship between the experimentally determined specific potential methylation rate constant (Km, day-1) and % MeHg (concentrations of MeHg normalized to total Hg) in the sediment. This indicates that MeHg production overruled degradation and input/output processes of MeHg in surface sediments, and that % MeHg in surface sediments may be used as a proxy for net production of MeHg. To our knowledge, these are the first data showing significant positive relationships between short term (48 h) MeHg production and longer term accumulation of MeHg, across a range of sites with different properties (1). If MeHg was not normalized to total Hg, the relationship was not significant. For sub-sets of brackish waters (p<0.001, n=23), southern, high-productivity freshwaters (p<0.001, n=20) as well as northern, low-productivity freshwater (p=0.048, n=6), the sum of neutral Hg-sulfides [Hg(SH)20 (aq)] and [HgS0 (aq)] in the sediment pore water was significantly, positively correlated with both the potential methylation rate constant (Km) and total MeHg concentrations (2). This indicates that methylating sulphate reducing bacteria passively take up neutral Hg-sulfides, which are transformed to MeHg. Differences in slopes of the relationships were explained by differences in primary productivity and availability of energy-rich organic matter to methylating bacteria. High primary productivity at southern freshwater sites, reflected by a low C/N ratio (large contribution from free living algae and bacteria) in the sediment and a high annual temperature sum, resulted in high methylation rates. In conclusion, concentrations of neutral Hg-sulfides and availability of energy rich organic matter, but also total Hg concentrations in sediments are important factors behind net production and accumulation of MeHg . References: (1) Drott et. al. submitted, (2) Drott, A.; Lambertsson, L.; Björn, E.; Skyllberg, U. Importance of dissolved neutral mercury sulfides for methyl mercury production in contaminated sediments. Environmental Science & Technology 2007, 41, 2270-2276.

Selenite sorption by carbonate substituted apatite

DOE PAGES

Moore, Robert C.; Rigali, Mark J.; Brady, Patrick

2016-08-31

The sorption of selenite, SeO 3 2–, by carbonate substituted hydroxylapatite was investigated using batch kinetic and equilibrium experiments. The carbonate substituted hydroxylapatite was prepared by a precipitation method and characterized by SEM, XRD, FT-IR, TGA, BET and solubility measurements. The material is poorly crystalline, contains approximately 9.4% carbonate by weight and has a surface area of 210.2 m 2/g. Uptake of selenite by the carbonated hydroxylapatite was approximately an order of magnitude higher than the uptake by uncarbonated hydroxylapatite reported in the literature. Distribution coefficients, K d, determined for the carbonated apatite in this work ranged from approximately 4200more » to over 14,000 L/kg. A comparison of the results from kinetic experiments performed in this work and literature kinetic data indicates the carbonated apatite synthesized in this study sorbed selenite 23 times faster than uncarbonated hydroxylapatite based on values normalized to the surface area of each material. Furthermore, the results indicate carbonated apatite is a potential candidate for use as a sorbent for pump-and-treat technologies, soil amendments or for use in permeable reactive barriers for the remediation of selenium contaminated sediments and groundwaters.« less

Methodology for predicting maximum velocity and shear stress in a sinuous channel with bendway weirs using 1-D HEC-RAS modeling results

Treesearch

Paul Sclafani; Christopher I. Thornton; Amanda L. Cox; Steven R. Abt

2012-01-01

As with every natural process, river morphology incorporates a complex and nuanced set of processes that combine to produce an infinite set of possible outcomes. Natural laws that govern natural systems cause rivers to react to changes in the environment in order to maintain equilibrium. Changes in hydraulics, sediment transport, and habitat help keep natural systems...

Research and Development of Methods for Estimating Physicochemical Properties of Organic Compounds of Environmental Concern

DTIC Science & Technology

1979-02-01

coefficient (at equilibrium) when hysteresis is apparent. 6. Coefficient n in Freundlich equation for 1/n soil or sediment adsorption isotherms ýX - KC . 7...Biodegradation Chemical structures cal clasaes (e.g., Diffusion Correlations phenols). General Diffusion coefficients Equations terms for organic...OF THE FATE AND TRANSPORT OF ORGANIC CHEMICALS Adsorption coefficients: K, n* from Freundlich equation + Desorption coefficients: K’*, n’* from

Availability of polycyclic aromatic hydrocarbons to earthworms (Eisenia andrei, Oligochaeta) in field-polluted soils and soil-sediment mixtures.

PubMed

Jager, Tjalling; Baerselman, Rob; Dijkman, Ellen; de Groot, Arthur C; Hogendoorn, Elbert A; de Jong, Ad; Kruitbosch, Jantien A W; Peijnenburg, Willie J G M

2003-04-01

The bioavailability of polycyclic aromatic hydrocarbons (PAHs) for earthworms (Eisenia andrei) was experimentally determined in seven field-polluted soils and 15 soil-sediment mixtures. The pore-water concentration of most PAHs was higher than predicted. However, most of the compound was associated with dissolved organic carbon (DOC) and not directly available for uptake by earthworms. The apparent sorption could be reasonably predicted on the basis of interactions with DOC; however, the biota-soil accumulation factors (BSAFs) for earthworms were up to two orders of magnitude lower than predicted by equilibrium partitioning. The large variability between sites was not fully explained by differences in sorption. Experimental results indicate that the pool of freely dissolved PAHs in the pore water became partially depleted because of uptake by the earthworms and that bioaccumulation is thus also influenced by the kinetics of PAH desorption and mass transport. A pilot study with Lumbricus rubellus showed that steady-state body residues were well correlated to E. andrei. Current results show that depositing dredge spoil on land may lead to increased bioavailability of the lower-molecular-weight PAHs. However, risk assessment can conservatively rely on equilibrium partitioning, but accurate prediction requires quantification of the kinetics of bioavailability.

A 20,000-year record of environmental change from Laguna Kollpa Kkota, Bolivia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Seltzer, G.O.; Abbott, M.B.

Most records of paleoclimate in the Bolivian Andes date from the last glacial-to-interglacial transition. However, Laguna Kollpa Kkota and other lakes like it, formed more than 20,000 yr BP when glaciers retreated and moraines dammed the drainage of the valleys they are located in. These lakes were protected from subsequent periods of glaciation because the headwalls of these valleys are below the level of the late-Pleistocene glacial equilibrium-line altitude. The chemical, mineral, and microfossil stratigraphies of these glacial lakes provide continuous records of environmental change for the last 20,000 years that can be used to address several problems in paleoclimatemore » specific to tropical-subtropical latitudes. Preliminary results from Laguna Kollpa Kkota indicate that glacial equilibrium-line altitudes were never depressed more than 600 m during the last 20,000 years, suggesting that temperatures were reduced only a few-degrees celsius over this time period. Sedimentation rates and the organic carbon stratigraphy of cores reflect an increase in moisture in the late Pleistocene just prior to the transition to a warmer and drier Holocene. The pollen and diatom concentrations in the sediments are sufficient to permit the high resolution analyses needed to address whether or not there were climatic reversals during the glacial-to-interglacial transition.« less

Factors controlling dimethylsulfide emission from salt marshes

NASA Technical Reports Server (NTRS)

Dacey, John W. H.; Wakeham, S. G.; Howes, B. L.

1985-01-01

The factors that control the emission of methylated gases from salt marshes are being studied. Research focusses on dimethylsulfide (DMS) formation and the mechanism of DMS and CH4 emission to the atmosphere. The approach is to consider the plants as valves regulating the emission of methylated gases to the atmosphere with the goal of developing appropriate methods for emission measurement. In the case of CH4, the sediment is the source and transport to the atmosphere occurs primarily through the internal gas spaces in the plants. The source of DMS appears to be dimethyl sulfoniopropionate (DMSP) which may play a role in osmoregulation in plant tissues. Concentrations of DMSP in leaves are typically several-fold higher than in roots and rhizomes. Even so, the large below ground biomass of this plant means that 2/3 of the DMSP in the ecosystem is below ground on the aerial basis. Upon introduction to sediment water, DMSP rapidly decomposes to DMS and acrylic acid. The solubility of a gas (its equilibrium vapor pressure) is a fundamental aspect of gas exchange kinetics. The first comprehensive study was conducted of DMS solubility in freshwater and seawater. Data suggest that the Setchenow relation holds for H at intermediate salinities collected. These data support the concept that the concentration of DMS in the atmosphere is far from equilibrium with seawater.

U-Th and 10Be constraints on sediment recycling in proglacial settings, Lago Buenos Aires, Patagonia

NASA Astrophysics Data System (ADS)

Cogez, Antoine; Herman, Frédéric; Pelt, Éric; Reuschlé, Thierry; Morvan, Gilles; Darvill, Christopher M.; Norton, Kevin P.; Christl, Marcus; Märki, Lena; Chabaux, François

2018-03-01

The estimation of sediment transfer times remains a challenge to our understanding of sediment budgets and the relationships between erosion and climate. Uranium (U) and thorium (Th) isotope disequilibria offer a means of more robustly constraining sediment transfer times. Here, we present new uranium and thorium disequilibrium data for a series of nested moraines around Lago Buenos Aires in Argentine Patagonia. The glacial chronology for the area is constrained using in situ cosmogenic 10Be analysis of glacial outwash. Sediment transfer times within the periglacial domain were estimated by comparing the deposition ages of moraines to the theoretical age of sediment production, i.e., the comminution age inferred from U disequilibrium data and recoil loss factor estimates. Our data show first that the classical comminution age approach must include weathering processes accounted for by measuring Th disequilibrium. Second, our combined data suggest that the pre-deposition history of the moraine sediments is not negligible, as evidenced by the large disequilibrium of the youngest moraines despite the equilibrium of the corresponding glacial flour. Monte Carlo simulations suggest that weathering was more intense before the deposition of the moraines and that the transfer time of the fine sediments to the moraines was on the order of 100-200 kyr. Long transfer times could result from a combination of long sediment residence times in the proglacial lake (recurrence time of a glacial cycle) and the remobilization of sediments from moraines deposited during previous glacial cycles. 10Be data suggest that some glacial cycles are absent from the preserved moraine record (seemingly every second cycle), supporting a model of reworking moraines and/or fluctuations in the extent of glacial advances. The chronological pattern is consistent with the U-Th disequilibrium data and the 100-200 kyr transfer time. This long transfer time raises the question of the proportion of freshly eroded sediments that escape (or not) the proglacial environments during glacial periods.

The Separatory Cylinder: A Novel Solvent Extraction System for the Study of Chemical Equilibrium in Solution.

ERIC Educational Resources Information Center

Cwikel, Dori; And Others

1986-01-01

Dicusses the use of the separatory cylinder in student laboratory experiments for investigating equilibrium distribution of a solute between immiscible phases. Describes the procedures for four sets of experiments of this nature. Lists of materials needed and quantities of reagents are provided. (TW)

Analyzing Ligand Depletion in a Saturation Equilibrium Binding Experiment

ERIC Educational Resources Information Center

Claro, Enrique

2006-01-01

I present a proposal for a laboratory practice to generate and analyze data from a saturation equilibrium binding experiment addressed to advanced undergraduate students. [[superscript 3]H]Quinuclidinyl benzilate is a nonselective muscarinic ligand with very high affinity and very low nonspecific binding to brain membranes, which contain a high…

A New Application for Radioimmunoassay: Measurement of Thermodynamic Constants.

ERIC Educational Resources Information Center

Angstadt, Carol N.; And Others

1983-01-01

Describes a laboratory experiment in which an equilibrium radioimmunoassay (RIA) is used to estimate thermodynamic parameters such as equilibrium constants. The experiment is simple and inexpensive, and it introduces a technique that is important in the clinical chemistry and research laboratory. Background information, procedures, and results are…

Dissociation of Laboratory-Synthesized Methane Hydrate in Coarse-Grained Sediments by Slow Depressurization

NASA Astrophysics Data System (ADS)

Phillips, S. C.; You, K.; Borgfeldt, T.; Meyer, D.; Dong, T.; Flemings, P. B.

2016-12-01

We performed four dissociation experiments in which experimentally-formed methane hydrate was dissociated via slow, stepwise depressurization, revealing in situ salinity conditions. Overall, these results suggest the occurrence of local pore water freshening around dissociating hydrate in which bulk equilibrium behavior is limited by salt diffusion. Depressurization was performed at a constant confining temperature over 1 to 3 weeks by releasing small volumes of methane gas from the top of a vertically-oriented sample into an inverted graduated cylinder. We identify three distinct regimes of depressurization based on pressure drop behavior: (1) release of free gas down to initial hydrate dissociation at 3.3 MPa in NaBr or 4.64 MPa in NaCl, (2) dissociation of methane hydrate characterized by a slow, logarithmic increase in pressure after each gas release and (3) residual free gas release. Initial hydrate dissociation in NaCl brine at 4.64 MPa corresponds to the phase boundary for hydrate in 9.6 wt% NaCl. In the NaCl experiment, pressure increases of 0.16 MPa while the sample was shut in over 3 days likely correspond to a recovery in salinity of 0.7 wt. %. Salt ions likely diffuse from brine ahead of the hydrate front, based on a length scale for diffusion of NaCl of 6.3 cm for 3 days. In this experiment dissociation at bulk equilibrium is expected to decline from 4.54 to 4.04 MPa; however actual dissociation during 73 gas releases over 15 days, results in a pressure drop from 4.64 to 3.25 MPa. Hydrate samples were formed by injection of methane gas at 1 ºC and 12.24 MPa within a cylinder packed with medium-grained quartz sand and initially saturated in a 7 wt% NaBr or NaCl solution. In two experiments in which the system was thoroughly leak tested, total methane consumed during formation and recovered during depressurization match within 7% indicating this approach to be relatively accurate for determining total methane in experimental or pressure core samples.

Modelling of hyperconcentrated flood and channel evolution in a braided reach using a dynamically coupled one-dimensional approach

NASA Astrophysics Data System (ADS)

Xia, Junqiang; Zhang, Xiaolei; Wang, Zenghui; Li, Jie; Zhou, Meirong

2018-06-01

Hyperconcentrated sediment-laden floods often occur in a braided reach of the Lower Yellow River, usually leading to significant channel evolution. A one-dimensional (1D) morphodynamic model using a dynamically coupled solution approach is developed to simulate hyperconcentrated flood and channel evolution in the braided reach with an extremely irregular cross-sectional geometry. In the model, the improved equations for hydrodynamics account for the effects of sediment concentration and bed evolution, which are coupled with the equations of non-equilibrium sediment transport and bed evolution. The model was validated using measurements from the 1977 and 2004 hyperconcentrated floods. Furthermore, the effects were investigated of different cross-sectional spacings and allocation modes of channel deformation area on the model results. It was found that a suitable cross-sectional distance of less than 3 km should be adopted when simulating hyperconcentrated floods, and the results using the uniform allocation mode can agree better with measurements than other two allocation modes.

Amending soils with sediment material from constructed wetlands increases phosphorus sorption

NASA Astrophysics Data System (ADS)

Laakso, Johanna; Uusitalo, Risto; Leppänen, Janette; Yli-Halla, Markku

2017-04-01

Sediment of agricultural constructed wetlands (CWs) is comprised of matter eroded from surrounding fields. This material is rich in aluminium (Al) and iron (Fe) (hydr)oxides that have a high affinity for phosphorus (P). Sediment material returned to fields could therefore affect soil P retention characteristics. We incubated a clay soil with a high soil test P (STP, 24 mg PAc l-1; extracted with pH 4.65 ammonium acetate buffer) and a sandy loam with excessive STP (210 mg PAc l-1) for three weeks with increasing amounts of CW sediment: 0, 2, 5, 10 and 50% of the sample volume. After incubation, the soil-sediment mixtures were studied with the quantity/intensity (Q/I) technique, using chemical extractions and by exposing the mixtures to simulated rainfall. Sorption affinity for P regularly increased with increasing the sediment share of the mixtures, the 0% sediment content having the lowest and 50% sediment content the highest P sorption. With 0% sediment application, the value of equilibrium P concentration (EPC0) determined by Q/I technique, was 0.69 and 44.3 mg l-1 for clay soil and sandy loam, respectively. With 2-5% sediment amendment, the EPC0 decreased 13-36% for clay soil and 13-54% for sandy loam. The 50% sediment mixtures had EPC0 of 0.05 mg l-1 for both soils. At a practically feasible sediment addition rate of 5%, dissolved reactive P (DRP) in percolating water from simulated rainfall decreased by 55% in the clay soil and 54% in sandy loam (p<0.001 in both cases). Particulate-P (PP) also showed a decreasing trend with increasing sediment addition rate. Upon prolonged simulated rainfall, the decreasing effect of sediment on DRP and PP declined somewhat. The effects of sediment addition can be attributed partly to increased salt concentrations in the sediment, which have a short-term effect on P mobilisation, but mostly to increased concentrations of Al and Fe (hydr)oxides, increasing long-term P sorption capacity. Amending the soils with sediment material would decrease P solubility and might at large application rates hamper P uptake by plants or, on the other hand, the sediment amendment in the soil might reduce P losses by runoff.

[Influence of Vallisneria spiralis on the physicochemical properties of black-odor sediment in urban sluggish river].

PubMed

Xu, Kuan; Liu, Bo; Wang, Guo-Xiang; Ma, Jiu-Yuan; Cao, Xun; Zhou, Feng

2013-07-01

Using Indoor simulation method, the effect of Vallisneria spiralis on the physicochemical propertise of black and stink sediment was investigated. The surface sediment of urban sluggish river which had been heavily polluted was used as material in the study. The results showed that the redox environment of the sediment was significantly improved by Vallisneria spiralis. During the experiment, the Eh of surface sediment rose from -70 mV to 90 mV. The ferrous content was reduced by 25% in the experiment group while increased by 38% in the control group; the organic matter was decomposed effectively, prevented from natural decomposition to the smelly substances. There was a 3 mm thick greyish yellow oxide layer after 7 days in the experimental group, and the oxide layer gradually thickened over time. The thickness of the oxide layer reached 11 mm at the end of the experiment, and no significant odor was detected. On the contrary, the oxide layer in the control group was only 1 mm thick and the thickness remained unchanged. Meanwhile, an obnoxious odor existed during the whole experiment. The roots of Vallisneria spiralis had significant influence on the porosity of sediment. On one hand, the densification of sediment could be improved by Vallisneria spiralis. On the other hand, Vallisneria spiralis was able to change the state of the surface sediment flows, reduce the erosion of river sediment and inhibit the transfer of black-odor substances, which has a positive ecological meaning.

11. MOVABLE BED SEDIMENTATION MODELS. AUTOMATIC SEDIMENT FEEDER DESIGNED AND ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

11. MOVABLE BED SEDIMENTATION MODELS. AUTOMATIC SEDIMENT FEEDER DESIGNED AND BUILT BY WES. - Waterways Experiment Station, Hydraulics Laboratory, Halls Ferry Road, 2 miles south of I-20, Vicksburg, Warren County, MS

Reactive solute transport in an acidic stream: Experimental pH increase and simulation of controls on pH, aluminum, and iron

USGS Publications Warehouse

Broshears, R.E.; Runkel, R.L.; Kimball, B.A.; McKnight, Diane M.; Bencala, K.E.

1996-01-01

Solute transport simulations quantitatively constrained hydrologic and geochemical hypotheses about field observations of a pH modification in an acid mine drainage stream. Carbonate chemistry, the formation of solid phases, and buffering interactions with the stream bed were important factors in explaining the behavior of pH, aluminum, and iron. The precipitation of microcrystalline gibbsite accounted for the behavior of aluminum; precipitation of Fe(OH)3 explained the general pattern of iron solubility. The dynamic experiment revealed limitations on assumptions that reactions were controlled only by equilibrium chemistry. Temporal variation in relative rates of photoreduction and oxidation influenced iron behavior. Kinetic limitations on ferrous iron oxidation and hydrous oxide precipitation and the effects of these limitations on field filtration were evident. Kinetic restraints also characterized interaction between the water column and the stream bed, including sorption and desorption of protons from iron oxides at the sediment-water interface and post-injection dissolution of the precipitated aluminum solid phase.

Effects of the Razor Clam Tagelus plebeius on the Fate of Petroleum Hydrocarbons: A Mesocosm Experiment.

PubMed

Klerks, P L; Kascak, A; Cazan, A M; Deb Adhikary, N; Chistoserdov, A; Shaik, A; Osman, S; Louka, F R

2018-02-22

The relationship between organisms and contaminants may be a two-way interaction: contaminants affecting the biota and the biota affecting the environmental fate and distribution of the contaminants. This may be especially so for sediment-dwelling organisms, because their burrowing and feeding can drastically influence sediment characteristics. The present study looked at the influence of the suspension-feeding stout razor clam Tagelus plebeius on the distribution of crude oil and pyrene in greenhouse mesocosm experiments. Water column turbidity and sediment redox also were monitored during the 15- to 30-day exposures to provide information on the influence of hydrocarbons and the razor clams on environmental conditions. For the experiment with crude oil, sediment was taken from the mesocosms at the end of the experiment, and the hydrocarbon-degradation potential was assessed in incubations with 14 C-naphthalene. The experiments used four treatments: hydrocarbons present/absent and razor clams present/absent. Hydrocarbon dosing levels were relatively low (1 mL of oil or 30 mg of pyrene per mesocosm with 22 L of natural sediment and 11 L of seawater). The presence of the razor clams resulted in hydrocarbon concentrations at the sediment surface being 25% lower than in mesocosms without clams. No consistent effects were noted for polycyclic aromatic hydrocarbon (PAH) concentrations in the water column or in subsurface sediment. The naphthalene-degradation potential was elevated for sediment from mesocosms dosed with oil, but the presence of the clams did not affect this potential. The presence of the razor clams resulted in a lowering of water column turbidity, but no effect on sediment redox. The hydrocarbon addition had no effect on turbidity, but sediment redox was lowered. While results show that the presence of the razor clams resulted in a loss of hydrocarbons from the surface sediment, the other results do not provide a clear picture of the underlying mechanisms and the fate of the PAHs lost from the sediment surface. We hypothesize that the loss of surface sediment PAHs was due to burial of surface sediment and possibly bioaccumulation by the clams. While additional research is needed for further insights into underlying mechanisms, the present work demonstrates that the presence of sediment-burrowing suspension feeders decreases hydrocarbon levels in surface sediment. This means that assessments of the impact of an oil spill should pay attention to effects on these organisms and to their influence on the fate and distribution of the spilled oil.

Detrital magnetization of laboratory-redeposited sediments

NASA Astrophysics Data System (ADS)

Valet, Jean-Pierre; Tanty, Cyrielle; Carlut, Julie

2017-07-01

We conducted several redeposition experiments in laboratory using natural and artificial sediments in order to investigate the role of grain size and lithology on sedimentary remanence acquisition. The role of grain size was investigated by using sorted sediment from natural turbidites. Taking advantage of the magnetic grain size distribution within turbidites, we compared redeposition experiments performed with coarse magnetic grains taken from the bottom layers of a turbidite with fine grains from the upper layers of the same turbidite. In order to document the magnetization acquired for increasing sediment concentrations that is analogous to increasing depth in the sediment column, the samples were frozen at temperatures between -5 and -10 °C. Magnetization acquisition behaved similarly in both situations, so that little smearing of the palaeomagnetic signal should be linked to grain size variability within this context. Other series of experiments were aimed at investigating the influence of lithology. We used clay or carbonated sediments that were combined with magnetic separates from basaltic rocks or with single-domain biogenic magnetite. The experiments revealed that the magnetization responded differently with clay and carbonates. Clay rapidly inhibited alignment of magnetic grains at low concentrations and, therefore, significant magnetization lock-in occurred despite large water contents, perhaps even within the bioturbated layer. Extension of the process over a deeper interval contributes to smear the geomagnetic signal and therefore to alter the palaeomagnetic record. In carbonates, the magnetization was acquired within a narrow window of 45-50 per cent sediment concentration, therefore, little smearing of the geomagnetic signal can be expected. Finally, experiments on carbonate sediments and biogenic magnetite with increasing field intensities indicate that magnetization acquisition is linear with respect to field intensity. Altogether, the results suggest that sediments with dominant carbonate content should be favoured for records of geomagnetic field changes provided that the minor clay fraction does not vary excessively. They confirm the advantage of using cultures of magnetotactic bacteria for redeposition experiments.

The Role of Grain Dynamics in the Onset of Sediment Transport

NASA Astrophysics Data System (ADS)

Clark, A., IV; Shattuck, M. D.; Ouellette, N. T.; O'Hern, C.

2016-12-01

Despite decades of research, the grain-scale mechanisms that control the onset of sediment transport are still not well understood. A large collection of data, known as the Shields curve, shows that Θ c, which is the minimum dimensionless shear stress at the bed for grains to move, is primarily a function of the shear Reynolds number Re*. To understand this collapse, it is typically assumed that the onset of grain motion is determined by the conditions at which fluid forces violate static equilibrium for surface grains. Re* compares the grain size to the size of the viscous sublayer in the fluid flow, so the relevant fluid lift and drag forces vary with Re*. A complimentary approach, which remains relatively unexplored, is to ask instead when mobilized grains can stop. In this case, Re* is the ratio of two important time scales related to grain motion: (1) the time for a grain to equilibrate to the fluid flow and (2) the time for the shear stress to accelerate a grain over the characteristic bed roughness. Thus, Re* controls whether grains are accelerated significantly between collisions with the bed. To test how this effect relates to the Shields curve, we perform simulations of granular beds sheared by a model fluid flow, where Re* is varied only through the fluid-grain coupling, which alters the grain dynamics. We find good qualitative agreement with the Shields curve, and the quantitative discrepancies are consistent with lift forces calculations at varying Re*. Our results suggest that the onset of sediment transport may be better described as when mobile grains are able to stop, which varies significantly with Re*, and theoretical descriptions that account for this effect may be more successful than those that consider only static equilibrium.

Tidal controls on river delta morphology

NASA Astrophysics Data System (ADS)

Hoitink, A. J. F.; Wang, Z. B.; Vermeulen, B.; Huismans, Y.; Kästner, K.

2017-09-01

River delta degradation has been caused by extraction of natural resources, sediment retention by reservoirs, and sea-level rise. Despite global concerns about these issues, human activity in the world’s largest deltas intensifies. Harbour development, construction of flood defences, sand mining and land reclamation emerge as key contemporary factors that exert an impact on delta morphology. Tides interacting with river discharge can play a crucial role in the morphodynamic development of deltas under pressure. Emerging insights into tidal controls on river delta morphology suggest that--despite the active morphodynamics in tidal channels and mouth bar regions--tidal motion acts to stabilize delta morphology at the landscape scale under the condition that sediment import during low flows largely balances sediment export during high flows. Distributary channels subject to tides show lower migration rates and are less easily flooded by the river because of opposing non-linear interactions between river discharge and the tide. These interactions lead to flow changes within channels, and a more uniform distribution of discharge across channels. Sediment depletion and rigorous human interventions in deltas, including storm surge defence works, disrupt the dynamic morphological equilibrium and can lead to erosion and severe scour at the channel bed, even decades after an intervention.

Passive sampling methods for contaminated sediments: Practical guidance for selection, calibration, and implementation

PubMed Central

Ghosh, Upal; Driscoll, Susan Kane; Burgess, Robert M; Jonker, Michiel To; Reible, Danny; Gobas, Frank; Choi, Yongju; Apitz, Sabine E; Maruya, Keith A; Gala, William R; Mortimer, Munro; Beegan, Chris

2014-01-01

This article provides practical guidance on the use of passive sampling methods (PSMs) that target the freely dissolved concentration (Cfree) for improved exposure assessment of hydrophobic organic chemicals in sediments. Primary considerations for selecting a PSM for a specific application include clear delineation of measurement goals for Cfree, whether laboratory-based “ex situ” and/or field-based “in situ” application is desired, and ultimately which PSM is best-suited to fulfill the measurement objectives. Guidelines for proper calibration and validation of PSMs, including use of provisional values for polymer–water partition coefficients, determination of equilibrium status, and confirmation of nondepletive measurement conditions are defined. A hypothetical example is described to illustrate how the measurement of Cfree afforded by PSMs reduces uncertainty in assessing narcotic toxicity for sediments contaminated with polycyclic aromatic hydrocarbons. The article concludes with a discussion of future research that will improve the quality and robustness of Cfree measurements using PSMs, providing a sound scientific basis to support risk assessment and contaminated sediment management decisions. Integr Environ Assess Manag 2014;10:210–223. © 2014 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals, Inc. on behalf of SETAC. PMID:24288273

Consensus sediment quality guidelines for polycyclic aromatic hydrocarbon mixtures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Swartz, R.C.

1999-04-01

Sediment quality guidelines (SQGs) for polycyclic aromatic hydrocarbons (PAHs) have been derived from a variety of laboratory, field, and theoretical foundations. They include the screening level concentration, effects ranges-low and -median, equilibrium partitioning concentrations, apparent effects threshold, {Sigma}PAH model, and threshold and probable effects levels. The resolution of controversial differences among the PAH SQGs lies in an understanding of the effects of mixtures. Polycyclic aromatic hydrocarbons virtually always occur in field-collected sediment as a complex mixture of covarying compounds. When expressed as a mixture concentration, that is, total PAH (TPAH), the guidelines form three clusters that were intended in theirmore » original derivations to represent threshold (TEC = 290 {micro}g/g organic carbon [OC]), median (MEC = 1,800 {micro}g/g OC), and extreme (EEC = 10,000 {micro}g/g OC) effects concentrations. The TEC/MEC/EEC consensus guidelines provide a unifying synthesis of other SQGs, reflect causal rather than correlative effects, account for mixtures, and predict sediment toxicity and benthic community perturbations at sites of PAH contamination. The TEC offers the most useful SQG because PAH mixtures are unlikely to cause adverse effects on benthic ecosystems below the TEC.« less

Effects of triclosan on marine benthic and epibenthic organisms.

PubMed

Perron, Monique M; Ho, Kay T; Cantwell, Mark G; Burgess, Robert M; Pelletier, Marguerite C

2012-08-01

Triclosan is an antimicrobial compound that has been widely used in consumer products such as toothpaste, deodorant, and shampoo. Because of its widespread use, triclosan has been detected in various environmental media, including wastewater, sewage sludge, surface waters, and sediments. Triclosan is acutely toxic to numerous aquatic organisms, but very few studies have been performed on estuarine and marine benthic organisms. For whole sediment toxicity tests, the sediment-dwelling estuarine amphipod, Ampelisca abdita, and the epibenthic mysid shrimp, Americamysis bahia, are commonly used organisms. In the present study, median lethal concentration values (LC50) were obtained for both of these organisms using water-only and whole sediment exposures. Acute 96-h water-only toxicity tests resulted in LC50 values of 73.4 and 74.3 µg/L for the amphipod and mysid, respectively. For the 7-d whole sediment toxicity test, LC50 values were 303 and 257 mg/kg (dry wt) for the amphipod and mysid, respectively. Using equilibrium partitioning theory, these whole sediment values are equivalent to interstitial water LC50 values of 230 and 190 µg/L for the amphipod and mysid, respectively, which are within a threefold difference of the observed 96-h LC50 water-only values. Triclosan was found to accumulate in polychaete tissue in a 28-d bioaccumulation study with a biota-sediment accumulation factor of 0.23 kg organic carbon/kg lipid. These data provide some of the first toxicity data for triclosan with marine benthic and epibenthic species while also indicating a need to better understand the effects of other forms of sediment carbon, triclosan ionization, and organism metabolism of triclosan on the chemical's behavior and toxicity in the aquatic environment. Copyright © 2012 SETAC.

Ammonia Gas Transport and Reactions in Unsaturated Sediments: Implications for Use as an Amendment to Immobilize Inorganic Contaminants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Lirong; Szecsody, James E.; Truex, Michael J.

Use of gas-phase amendments for in situ remediation of inorganic contaminants in unsaturated sediments of the vadose zone may be advantageous, but there has been limited development and testing of gas remediation technologies. Treatment with ammonia gas has been studied and has a potential for use in treating inorganic contaminants such as uranium because it induces a high pore-water pH causing mineral dissolution and subsequent formation of stable precipitates that decrease the mobility of some contaminants. For field application, knowledge of ammonia transport and the geochemical reactions induced by ammonia is needed. Laboratory studies were conducted to support calculations neededmore » for field treatment design, to quantify advective and diffusive ammonia transport in unsaturated sediments, to evaluate reactions among gas, sediment, and water, and to study reaction-induced pore-water chemistry changes as a function of ammonia delivery conditions. Ammonia gas quickly partitions into sediment pore water and increases pH up to 13.2. Injected ammonia gas front movement can be reasonably predicted by gas flow rate and equilibrium partitioning. The ammonia gas diffusion rate is a function of the water content in the sediment. Measured diffusion front movement was 0.05, 0.03, and 0.02 cm/hr. in sediments with 2.0%, 8.7%, and 13.0% water content, respectively. Sodium, aluminum, and silica pore-water concentrations increase on exposure to ammonia and then decline as aluminosilicates precipitate with declining pH. When uranium is present in the sediment and pore water, up to 85% of the water-leachable uranium was immobilized by ammonia treatment.« less

Sediment quality criteria: A review with recommendations for developing criteria for the Hanford Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Driver, C.J.

1994-05-01

Criteria for determining the quality of liver sediment are necessary to ensure that concentrations of contaminants in aquatic systems are within acceptable limits for the protection of aquatic and human life. Such criteria should facilitate decision-making about remediation, handling, and disposal of contaminants. Several approaches to the development of sediment quality criteria (SQC) have been described and include both descriptive and numerical methods. However, no single method measures all impacts at all times to all organisms (U.S. EPA 1992b). The U.S. EPA`s interest is primarily in establishing chemically based, numerical SQC that are applicable nation-wide (Shea 1988). Of the approachesmore » proposed for SQC development, only three are being considered for numerical SQC on a national level. These approaches include an Equilibrium Partitioning Approach, a site-specific method using bioassays (the Apparent Effects Threshold Approach), and an approach similar to EPA`s water quality criteria (Pavlou and Weston 1984). Although national (or even regional) criteria address a number of political, litigative, and engineering needs, some researchers feel that protection of benthic communities require site-specific, biologically based criteria (Baudo et al. 1990). This is particularly true for areas where complex mixtures of contaminants are present in sediments. Other scientifically valid and accepted procedures for freshwater SQC include a background concentration approach, methods using field or spiked bioassays, a screening level concentration approach, the Apparent Effects Threshold Approach, the Sediment Quality Triad, the International Joint Commission Sediment Assessment Strategy, and the National Status and Trends Program Approach. The various sediment assessment approaches are evaluated for application to the Hanford Reach and recommendations for Hanford Site sediment quality criteria are discussed.« less

Uranium series isotopes concentration in sediments at San Marcos and Luis L. Leon reservoirs, Chihuahua, Mexico

NASA Astrophysics Data System (ADS)

Méndez-García, C.; Renteria-Villalobos, M.; García-Tenorio, R.; Montero-Cabrera, M. E.

2014-07-01

Spatial and temporal distribution of the radioisotopes concentrations were determined in sediments near the surface and core samples extracted from two reservoirs located in an arid region close to Chihuahua City, Mexico. At San Marcos reservoir one core was studied, while from Luis L. Leon reservoir one core from the entrance and another one close to the wall were investigated. 232Th-series, 238U-series, 40K and 137Cs activity concentrations (AC, Bq kg-1) were determined by gamma spectrometry with a high purity Ge detector. 238U and 234U ACs were obtained by liquid scintillation and alpha spectrometry with a surface barrier detector. Dating of core sediments was performed applying CRS method to 210Pb activities. Results were verified by 137Cs AC. Resulting activity concentrations were compared among corresponding surface and core sediments. High 238U-series AC values were found in sediments from San Marcos reservoir, because this site is located close to the Victorino uranium deposit. Low AC values found in Luis L. Leon reservoir suggest that the uranium present in the source of the Sacramento - Chuviscar Rivers is not transported up to the Conchos River. Activity ratios (AR) 234U/overflow="scroll">238U and 238U/overflow="scroll">226Ra in sediments have values between 0.9-1.2, showing a behavior close to radioactive equilibrium in the entire basin. 232Th/overflow="scroll">238U, 228Ra/overflow="scroll">226Ra ARs are witnesses of the different geological origin of sediments from San Marcos and Luis L. Leon reservoirs.

Estimates of Sediment Load Prior to Dam Removal in the Elwha River, Clallam County, Washington

USGS Publications Warehouse

Curran, Christopher A.; Konrad, Christopher P.; Higgins, Johnna L.; Bryant, Mark K.

2009-01-01

Years after the removal of the two dams on the Elwha River, the geomorphology and habitat of the lower river will be substantially influenced by the sediment load of the free-flowing river. To estimate the suspended-sediment load prior to removal of the dams, the U.S. Geological Survey collected suspended-sediment samples during water years 2006 and 2007 at streamflow-gaging stations on the Elwha River upstream of Lake Mills and downstream of Glines Canyon Dam at McDonald Bridge. At the gaging station upstream of Lake Mills, discrete samples of suspended sediment were collected over a range of streamflows including a large peak in November 2006 when suspended-sediment concentrations exceeded 7,000 milligrams per liter, the highest concentrations recorded on the river. Based on field measurements in this study and from previous years, regression equations were developed for estimating suspended-sediment and bedload discharge as a function of streamflow. Using a flow duration approach, the average total annual sediment load at the gaging station upstream of Lake Mills was estimated at 327,000 megagrams with a range of uncertainty of +57 to -34 percent (217,000-513,000 megagrams) at the 95 percent confidence level; 77 percent of the total was suspended-sediment load and 23 percent was bedload. At the McDonald Bridge gaging station, daily suspended-sediment samples were obtained using an automated pump sampler, and concentrations were combined with the record of streamflow to calculate daily, monthly, and annual suspended-sediment loads. In water year 2006, an annual suspended-sediment load of 49,300 megagrams was determined at the gaging station at McDonald Bridge, and a load of 186,000 megagrams was determined upstream at the gaging station upstream of Lake Mills. In water year 2007, the suspended-sediment load was 75,200 megagrams at McDonald Bridge and 233,000 megagrams upstream of Lake Mills. The large difference between suspended-sediment loads at both gaging stations shows the extent of sediment trapping by Lake Mills, and a trap efficiency of 0.86 was determined for the reservoir. Pre-dam-removal estimates of suspended-sediment load and sediment-discharge relations will help planners monitor geomorphic and habitat changes in the river as it reaches a dynamic equilibrium following the removal of dams.

A sandpile model of grain blocking and consequences for sediment dynamics in step-pool streams

NASA Astrophysics Data System (ADS)

Molnar, P.

2012-04-01

Coarse grains (cobbles to boulders) are set in motion in steep mountain streams by floods with sufficient energy to erode the particles locally and transport them downstream. During transport, grains are often blocked and form width-spannings structures called steps, separated by pools. The step-pool system is a transient, self-organizing and self-sustaining structure. The temporary storage of sediment in steps and the release of that sediment in avalanche-like pulses when steps collapse, leads to a complex nonlinear threshold-driven dynamics in sediment transport which has been observed in laboratory experiments (e.g., Zimmermann et al., 2010) and in the field (e.g., Turowski et al., 2011). The basic question in this paper is if the emergent statistical properties of sediment transport in step-pool systems may be linked to the transient state of the bed, i.e. sediment storage and morphology, and to the dynamics in sediment input. The hypothesis is that this state, in which sediment transporting events due to the collapse and rebuilding of steps of all sizes occur, is analogous to a critical state in self-organized open dissipative dynamical systems (Bak et al., 1988). To exlore the process of self-organization, a cellular automaton sandpile model is used to simulate the processes of grain blocking and hydraulically-driven step collapse in a 1-d channel. Particles are injected at the top of the channel and are allowed to travel downstream based on various local threshold rules, with the travel distance drawn from a chosen probability distribution. In sandpile modelling this is a simple 1-d limited non-local model, however it has been shown to have nontrivial dynamical behaviour (Kadanoff et al., 1989), and it captures the essence of stochastic sediment transport in step-pool systems. The numerical simulations are used to illustrate the differences between input and output sediment transport rates, mainly focussing on the magnification of intermittency and variability in the system response by the processes of grain blocking and step collapse. The temporal correlation in input and output rates and the number of grains stored in the system at any given time are quantified by spectral analysis and statistics of long-range dependence. Although the model is only conceptually conceived to represent the real processes of step formation and collapse, connections will be made between the modelling results and some field and laboratory data on step-pool systems. The main focus in the discussion will be to demonstrate how even in such a simple model the processes of grain blocking and step collapse may impact the sediment transport rates to the point that certain changes in input are not visible anymore, along the lines of "shredding the signals" proposed by Jerolmack and Paola (2010). The consequences are that the notions of stability and equilibrium, the attribution of cause and effect, and the timescales of process and form in step-pool systems, and perhaps in many other fluvial systems, may have very limited applicability.

Towards Non-Equilibrium Dynamics with Trapped Ions

NASA Astrophysics Data System (ADS)

Silbert, Ariel; Jubin, Sierra; Doret, Charlie

2016-05-01

Atomic systems are superbly suited to the study of non-equilibrium dynamics. These systems' exquisite isolation from environmental perturbations leads to long relaxation times that enable exploration of far-from-equilibrium phenomena. One example of particular relevance to experiments in trapped ion quantum information processing, metrology, and precision spectroscopy is the approach to thermal equilibrium of sympathetically cooled linear ion chains. Suitable manipulation of experimental parameters permits exploration of the quantum-to-classical crossover between ballistic transport and diffusive, Fourier's Law conduction, a topic of interest not only to the trapped ion community but also for the development of microelectronic devices and other nanoscale structures. We present progress towards trapping chains of multiple co-trapped calcium isotopes geared towards measuring thermal equilibration and discuss plans for future experiments in non-equilibrium statistical mechanics. This work is supported by Cottrell College Science Award from the Research Corporation for Science Advancement and by Williams College.

Thermal Equilibrium in Plastic and Glass Microscale Containers

ERIC Educational Resources Information Center

Curbelo, Estela; Cerda, Maria F.; Mendez, Eduardo

2007-01-01

The study describes the various thermal equilibrium conditions, which should be taken care for while designing or selecting the plastic and glass microscale containers for physical chemistry experiments. The results show that the thermal equilibrium completely depends on the material of the container for the same volume and thickness.

Phosphate-Induced Immobilization of Uranium in Hanford Sediments.

PubMed

Pan, Zezhen; Giammar, Daniel E; Mehta, Vrajesh; Troyer, Lyndsay D; Catalano, Jeffrey G; Wang, Zheming

2016-12-20

Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred only at high initial U(VI) (>25 μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.

Phosphate-Induced Immobilization of Uranium in Hanford Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Zezhen; Giammar, Daniel E.; Mehta, Vrajesh

2016-12-20

Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred onlymore » at high initial U(VI) (>25 μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.« less

Phosphate-Induced Immobilization of Uranium in Hanford Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pan, Zezhen; Giammar, Daniel E.; Mehta, Vrajesh

2016-12-20

Phosphate can be added to subsurface environments to immobilize U(VI) contamination. The efficacy of immobilization depends on the site-specific groundwater chemistry and aquifer sediment properties. Batch and column experiments were performed with sediments from the Hanford 300 Area in Washington State and artificial groundwater prepared to emulate the conditions at the site. Batch experiments revealed enhanced U(VI) sorption with increasing phosphate addition. X-ray absorption spectroscopy measurements of samples from the batch experiments found that U(VI) was predominantly adsorbed at conditions relevant to the column experiments and most field sites (low U(VI) loadings, <25 μM), and U(VI) phosphate precipitation occurred onlymore » at high initial U(VI) (>25μM) and phosphate loadings. While batch experiments showed the transition of U(VI) uptake from adsorption to precipitation, the column study was more directly relevant to the subsurface environment because of the high solid:water ratio in the column and the advective flow of water. In column experiments, nearly six times more U(VI) was retained in sediments when phosphate-containing groundwater was introduced to U(VI)-loaded sediments than when the groundwater did not contain phosphate. This enhanced retention persisted for at least one month after cessation of phosphate addition to the influent fluid. Sequential extractions and laser-induced fluorescence spectroscopy of sediments from the columns suggested that the retained U(VI) was primarily in adsorbed forms. These results indicate that in situ remediation of groundwater by phosphate addition provides lasting benefit beyond the treatment period via enhanced U(VI) adsorption to sediments.« less

Entrainment of bed sediment by debris flows: results from large-scale experiments

USGS Publications Warehouse

Reid, Mark E.; Iverson, Richard M.; Logan, Matthew; LaHusen, Richard G.; Godt, Jonathan W.; Griswold, Julie P.

2011-01-01

When debris flows grow by entraining sediment, they can become especially hazardous owing to increased volume, speed, and runout. To investigate the entrainment process, we conducted eight largescale experiments in the USGS debris-flow flume. In each experiment, we released a 6 m3 water-saturated debris flow across a 47-m long, ~12-cm thick bed of partially saturated sediment lining the 31º flume. Prior to release, we used low-intensity overhead sprinkling and real-time monitoring to control the bed-sediment wetness. As each debris flow descended the flume, we measured the evolution of flow thickness, basal total normal stress, basal pore-fluid pressure, and sediment scour depth. When debris flows traveled over relatively dry sediment, net scour was minimal, but when debris flows traveled over wetter sediment (volumetric water content > 0.22), debris-flow volume grew rapidly and flow speed and runout were enhanced. Data from scour sensors showed that entrainment occurred by rapid (5-10 cm/s), progressive scour rather than by mass failure at depth. Overriding debris flows rapidly generated high basal pore-fluid pressures when they loaded and deformed bed sediment, and in wetter beds these pressures approached lithostatic levels. Reduction of intergranular friction within the bed sediment thereby enhanced scour efficiency, entrainment, and runout.

Bottom currents and sediment waves on a shallow carbonate shelf, Northern Carnarvon Basin, Australia

NASA Astrophysics Data System (ADS)

Belde, Johannes; Reuning, Lars; Back, Stefan

2017-04-01

The modern seafloor of the Australian Northwest Shelf between Exmouth and Dampier was analyzed for large scale sedimentary bedforms on 3D seismic reflection data. The Carnarvon MegaSurvey of Petroleum Geo-Services (PGS), a merged dataset of multiple industrial 3D seismic reflection surveys with a total size of 49,717 km2, offers an extensive view of the continental shelf, slope and rise of the Northern Carnarvon Basin. Over the shelf two fields of large scale sediment waves were observed in water depths between 55-130 m, where the seafloor may be influenced by different processes including internal waves, tides and storms. Based on the dimensions and orientations of the sediment waves the dominant direction and approximate strength of local bottom currents could be estimated. Information on local sediment grain-size distribution was provided by the auSEABED database allowing a classification of the observed sediment waves into sand- or mudwaves. The first sediment wave field is positioned northwest of the Montebello Islands where the shelf is comparatively narrow and local sediment is mainly sand-sized. It most likely formed by increased bottom currents induced by the diversion of tidal flows around the islands. The second sediment wave field is located north of the Serrurier and Bessieres Islands within a local seafloor depression. Local sediments are poorly sorted, containing significant amounts of mud and gravel in addition to the mainly sand-sized grains. The coarser sediment fraction could have been reworked to sandwaves by cyclone-induced bottom currents. Alternatively, the finer sediment fraction could form mudwaves shaped by less energetic along-slope oriented currents in the topographic depression. The sediment waves consist partially of carbonate grains such as ooids and peloids that formed in shallow water during initial stages of the post glacial sea-level rise. These stranded carbonate grains thus formed in a different environment than the sediment waves in which they were redeposited. In fossil examples of similar high-energy ramp systems this possible out-of-equilibrium relationship between grains and bedforms has to be taken into account for the interpretation of the depositional environment.

Isotopic exchange of carbon-bound hydrogen over geologic timescales

NASA Astrophysics Data System (ADS)

Sessions, Alex L.; Sylva, Sean P.; Summons, Roger E.; Hayes, John M.

2004-04-01

The increasing popularity of compound-specific hydrogen isotope (D/H) analyses for investigating sedimentary organic matter raises numerous questions about the exchange of carbon-bound hydrogen over geologic timescales. Important questions include the rates of isotopic exchange, methods for diagnosing exchange in ancient samples, and the isotopic consequences of that exchange. This article provides a review of relevant literature data along with new data from several pilot studies to investigate such issues. Published experimental estimates of exchange rates between organic hydrogen and water indicate that at warm temperatures (50-100°C) exchange likely occurs on timescales of 104 to 108 yr. Incubation experiments using organic compounds and D-enriched water, combined with compound-specific D/H analyses, provide a new and highly sensitive method for measuring exchange at low temperatures. Comparison of δD values for isoprenoid and n-alkyl carbon skeletons in sedimentary organic matter provides no evidence for exchange in young (<1 Ma), cool sediments, but strong evidence for exchange in ancient (>350 Ma) rocks. Specific rates of exchange are probably influenced by the nature and abundance of organic matter, pore-water chemistry, the presence of catalytic mineral surfaces, and perhaps even enzymatic activity. Estimates of equilibrium fractionation factors between organic H and water indicate that typical lipids will be depleted in D relative to water by ∼75 to 140‰ at equilibrium (30°C). Thus large differences in δD between organic molecules and water cannot be unambiguously interpreted as evidence against hydrogen exchange. A better approach may be to use changes in stereochemistry as a proxy for hydrogen exchange. For example, estimated rates of H exchange in pristane are similar to predicted rates for stereochemical inversion in steranes and hopanes. The isotopic consequences of this exchange remain in question. Incubations of cholestene with D2O indicate that the number of D atoms incorporated during structural rearrangements can be far less than the number of C-H bonds that are broken. Sample calculations indicate that, for steranes in immature sediments, the D/H ratio imparted by biosynthesis may be largely preserved in spite of significant structural changes.

Uptake, metabolism and sub-lethal effects of BDE-47 in two estuarine invertebrates with different trophic positions.

PubMed

Díaz-Jaramillo, M; Miglioranza, K S B; Gonzalez, M; Barón, E; Monserrat, J M; Eljarrat, E; Barceló, D

2016-06-01

Two microcosm types -sediment-biota and biota-biota- were constructed to simulate different pathways of BDE-47 uptake, metabolism and oxidative stress effects in two key estuarine invertebrates (polychaete Laeonereis acuta and crab Cyrtograpsus angulatus). In the sediment-biota experiment, both species were exposed to spiked sediments; an environmentally reported and a high concentration of BDE-47 for 2 weeks. In the biota-biota experiment, crabs were fed with polychaetes pre-exposed to BDE-47 in the sediment-biota experiment. The sediment-biota experiment first revealed that polychaetes significantly accumulated BDE-47 (biota-sediment accumulation factor >2; p < 0.05) to a much greater extent than the crab organs (muscle, hepatopancreas, gills) at both sediment concentrations. For oxidative stress responses, polychaete and crab tissues exposed to spiked sediment showed a significant increase (p < 0.05) of only glutathione S-transferase (GST) activity with respect to controls in both BDE-47 concentrations. No lipid peroxidation (TBARS) or total antioxidant capacity (ACAP) changes were evident in the species or organs exposed to either BDE-47 sediment concentration. The biota-biota experiment showed that feeding crabs with pre-exposed polychaetes caused BDE-47 accumulation in organs as well as significant amounts of BDE-47 eliminated through feces (p < 0.05). Unlike the sediment-biota exposure, crabs fed with pre-exposed BDE-47 polychaetes showed the most conspicuous oxidative stress responses. Significant changes in GST and ACAP in both hepatopancreas and gills, in addition to enhanced TBARS levels in the hepatopancreas with respect to controls (p < 0.05), revealed that BDE-47 assimilated by invertebrates represents a potential source of toxicity to their predators. No methoxylated metabolites (MeO-PBDEs) were detected during BDE-47 metabolism in the invertebrates in either of the two different exposure types. In contrast, hydroxylated metabolites (OH-PBDEs) were detected in polychaetes and crab organs/feces in both experiments. Our results demonstrate that PBDE hydroxylation is one of the main biotransformation routes of BDE-47 in estuarine animals, which could be associated with the oxidative stress responses found. Copyright © 2016 Elsevier Ltd. All rights reserved.

Effects of organic carbon supply rates on uranium mobility in a previously bioreduced contaminated sediment.

PubMed

Wan, Jiamin; Tokunaga, Tetsu K; Kim, Yongman; Brodie, Eoin; Daly, Rebecca; Hazen, Terry C; Firestone, Mary K

2008-10-15

Bioreduction-based strategies for remediating uranium (U)-contaminated sediments face the challenge of maintaining the reduced status of U for long times. Because groundwater influxes continuously bring in oxidizing terminal electron acceptors (O2, NO3(-)), it is necessary to continue supplying organic carbon (OC) to maintain the reducing environment after U bioreduction is achieved. We tested the influence of OC supply rates on mobility of previously microbial reduced uranium U(IV) in contaminated sediments. We found that high degrees of U mobilization occurred when OC supply rates were high, and when the sediment still contained abundant Fe(III). Although 900 days with low levels of OC supply minimized U mobilization, the sediment redox potential increased with time as did extractable U(VI) fractions. Molecular analyses of total microbial activity demonstrated a positive correlation with OC supply and analyses of Geobacteraceae activity (RT-qPCR of 16S rRNA) indicated continued activity even when the effluent Fe(II) became undetectable. These data support our hypothesis on the mechanisms responsible for remobilization of U under reducing conditions; that microbial respiration caused increased (bi)carbonate concentration and formation of stable uranyl carbonate complexes, thereby shifted U(IV)/U(VI) equilibrium to more reducing potentials. The data also suggested that low OC concentrations could not sustain the reducing condition of the sediment for much longer time. Bioreduced U(IV) is not sustainable in an oxidizing environment for a very long time.

Drop-tower experiments for capillary surfaces in an exotic container

NASA Technical Reports Server (NTRS)

Concus, Paul; Finn, Robert; Weislogel, Mark

1991-01-01

Low-gravity drop-tower experiments are carried out for an 'exotic' rotationally-symmetric container, which admits an entire continuum of distinct equilibrium symmetric capillary free surfaces. It is found that an initial equilibrium planer interface, a member of the continuum, will reorient toward a non-symmetric interface, as predicted by recent mathematical theory.

High-Frequency Sound Interaction in Ocean Sediments

DTIC Science & Technology

2003-09-30

results, combined with measured sediment properties, to test the validity of sediment acoustic models , and in particular the poroelastic (Biot...understanding of the dominant scatterers versus frequency near the sediment surface, the potential need for poroelastic sediment models , the...work are described under a separate ONR project titled “ Acoustic propagation and scattering within sand sediments: Laboratory experiments, modeling

Barrier Island Sensitivity to Sea-Level Rise: Insights from Numerical Model Experiments, North Carolina Outer Banks and Chandeleur Islands, LA U.S.A

NASA Astrophysics Data System (ADS)

Moore, L. J.; List, J. H.; Williams, S.; Patsch, K.

2009-12-01

As dynamic and low-lying coastal landforms, barrier islands are especially vulnerable to sea level rise, changes in sediment supply and coastal storms. Changes in these factors may ultimately result in new conditions that are sufficiently different from present to cause a shift in equilibrium state from landward-migrating to submerging, i.e., a threshold crossing. Because the loss of barrier islands would be extremely disruptive of human activities, an understanding of how barrier islands evolve under conditions of rising sea level is vital to the development of wise coastal management practices. To advance understanding of barrier island response to changing conditions, we apply the morphological-behavior model GEOMBEST (GEOmorphic Model of Barrier and EStuarine Translations; Stolper et al., 2005, Moore et al., 2007 and Moore et al., accepted pending minor revisions) to field sites in the North Carolina Outer Banks and the Chandeleur Islands of southeastern Louisiana. Sensitivity analyses reveal that, in general, substrate sand proportion, substrate slope, sea-level rise rate and sediment-supply rate are the most important factors in determining barrier island response to sea-level rise while shoreface erosion rates, substrate erodibility, and shoreface depth are often less important. More specifically, substrate composition appears to be the most important factor in muddy coastal environments, such as the Chandeleur Islands, where model results suggest that a threshold crossing may occur on the order of decades to a century from present, while the other three factors appear to be most important in North Carolina and other similar environments. When substrate sand proportions are low and/or sediment-loss rates are high, shoreface erosion rate and substrate erodibility may become important in limiting the rate at which sand can be liberated from the substrate, thereby increasing barrier island vulnerability to threshold crossing. Barrier system history (e.g., previous sediment supply rates, substrate slope) determines barrier island volume and the degree to which the shoreface extends into the substrate, and is therefore of critical importance in determining whether or not a barrier will persist as sea-level rises. Surprisingly, larger barriers, which are associated with little incision into the substrate, are more vulnerable to sea-level rise than smaller barriers that have been losing sand in the past, or that have encountered rapidly changing substrate slopes. Overall, our results indicate that barrier islands with muddy substrates, and barriers which are in near-equilibrium with substrate slope, will be most vulnerable to geomorphic threshold crossing as sea level rises. Plans to merge GEOMBEST with a marsh progradation model will allow a more detailed assessment of barrier island response where co-evolution of back-barrier marsh and barrier environments is critical in determining the conditions under which threshold crossings are most likely.

Saltmarsh pool and tidal creek morphodynamics: Dynamic equilibrium of northern latitude saltmarshes?

NASA Astrophysics Data System (ADS)

Wilson, Carol A.; Hughes, Zoe J.; FitzGerald, Duncan M.; Hopkinson, Charles S.; Valentine, Vinton; Kolker, Alexander S.

2014-05-01

Many saltmarsh platforms in New England and other northern climates (e.g. Canada, northern Europe) exhibit poor drainage, creating waterlogged regions where short-form Spartina alterniflora dominates and stagnant pools that experience tidal exchange only during spring tides and storm-induced flooding events. The processes related to pool formation and tidal creek incision (via headward erosion) that may eventually drain these features are poorly understood, however it has been suggested that an increase in pool occurrence in recent decades is due to waterlogging stress from sea-level rise. We present evidence here that saltmarshes in Plum Island Estuary of Massachusetts are keeping pace with sea-level rise, and that the recent increase in saltmarsh pool area coincides with changes in drainage density from a legacy of anthropogenic ditching (reversion to natural drainage conditions). Gradients, in addition to elevation and hydroperiod, are critical for saltmarsh pool formation. Additionally, elevation and vegetative changes associated with pool formation, creek incision, subsequent drainage of pools, and recolonization by S. alterniflora are quantified. Pool and creek dynamics were found to be cyclic in nature, and represent platform elevation in dynamic equilibrium with sea level whereby saltmarsh elevation may be lowered (due to degradation of organic matter and formation of a pool), however may be regained on short timescales (101-2 yr) with creek incision into pools and restoration of tidal exchange. Rapid vertical accretion is associated with sedimentation and S. alterniflora plant recolonization.

Benthic phosphorus regeneration in the Potomac River Estuary

USGS Publications Warehouse

Callender, E.

1982-01-01

The flux of dissolved reactive phosphate from Potomac riverine and estuarine sediments is controlled by processes occurring at the water-sediment interface and within surficial sediment. In situ benthic fluxes (0.1 to 2.0 mmoles m-2 day-1) are generally five to ten times higher than calculated diffusive fluxes (0.020 to 0.30 mmoles m-2 day-1). The discrepancy between the two flux estimates is greatest in the transition zone (river mile 50 to 70) and is attributd to macrofaunal irrigation. Both in situ and diffusive fluxes of dissolved reactive phosphate from Potomac tidal river sediments are low while those from anoxic lower estuarine sediments are high. The net accumulation rate of phosphorus in benthic sediment exhibits an inverse pattern. Thus a large fraction of phosphorus is retained by Potomac tidal river sediments, which contain a surficial oxidized layer and oligochaete worms tolerant of low oxygen conditions, and a large fraction of phosphorus is released from anoxic lower estuary sediments. Tidal river sediment pore waters are in equilibrium with amorphous Fe (OH)3 while lower estuary pore waters are significantly undersaturated with respect to this phase. Benthic regeneration of dissolved reactive phosphorus is sufficient to supply all the phosphorus requirements for net primary production in the lower tidal river and transition-zone waters of the Potomac River Estuary. Benthic regeneration supplies approximately 25% as much phosphorus as inputs from sewage treatment plants and 10% of all phosphorus inputs to the tidal Potomac River. When all available point source phosphorus data are put into a steady-state conservation of mass model and reasonable coefficients for uptake of dissolved phosphorus, remineralization of particulate phosphorus, and sedimentation of particulate phosphorus are used in the model, a reasonably accurate simulation of dissolved and particulate phosphorus in the water column is obtained for the summer of 1980. ?? 1982 Dr W. Junk Publishers.

Simulation of acid water movement in canals

NASA Astrophysics Data System (ADS)

Van Truong, To; Tat Dac, Nguyen; Ngoc Phienc, Huynh

1996-05-01

An attempt to tackle the problem of the propagation of acid water in canals is described, and a mathematical model to simulate the acid water movement is developed, in which the jurbanite equilibrium is found to prevail. The processes of settling owing to sedimentation, precipitation and redissolution have been considered in the modelling. Data available from Tan Thanh, in the Plain of Reeds of the Mekong Delta in Viet Nam, are used as a case study.

Characterization of Long-term Stability of Sodium Dithionite for Evaluation of its Potential Utility for Cr(VI) Remediation at Los Alamos National Laboratory

NASA Astrophysics Data System (ADS)

Telfeyan, K.; Migdissov, A. A.; Reimus, P. W.

2017-12-01

Sodium dithionite (Na2S2O4) has proven to be an effective remediation agent in aquifers contaminated with Cr(VI). S2O42- rapidly reduces the Fe(III) in aquifer sediments to Fe(II), which then reduces aqueous Cr(VI) to insoluble Cr(III). Previous work demonstrated that the reaction products from this treatment have no long-lasting undesirable effects. However, current literature regarding the stability of dithionite in aqueous solution and its decomposition products, which are important for developing a practical treatment approach, is sparse and inconsistent. Furthermore, S2O42- treatment effectiveness depends on site-specific geochemical and hydrological conditions, so experiments using site-specific materials are necessary to develop an optimal treatment strategy. In this study, we conducted (1) batch aqueous-phase-only experiments aimed at elucidating dithionite lifetimes and decomposition products as a function of dithionite concentration and pH, (2) batch experiments at the most practical pH for a field deployment, with use of four different representations of site aquifer sediments to evaluate dithionite reaction rates in the presence of the sediments and to determine the reduction capacity of the treated sediments, and (3) column experiments to represent a field-scale deployment of dithionite and determine the Cr(VI) reduction capacity of the reduced sediments. The aqueous-phase-only batch experiments verified the presence of S2O42- in aqueous anoxic solution beyond 100 days at alkaline pH. Each sampling interval also recorded the concentration of decomposition products, which enabled the derivation of a possible hydrolysis/decomposition reaction. In the batch experiments with sediments, dithionite reacted more rapidly than in blank solutions, but measurable concentrations remained for over a month. Cr was then added to the reactors to determine the efficacy of treatment. Depending on the sediment type and concentration of dithionite, the treated sediments were able to remove between 100 and 1000 µg Cr per gram of sediment. Column experiments then determined that the dithionite treatment of aquifer sediments could treat over 30 pore volumes of contaminated water (900 ppb Cr) prior to any breakthrough of Cr, suggesting that S2O42- should be an effective treatment agent at this site.

The role of varying flow on channel morphology: a flume experiment

NASA Astrophysics Data System (ADS)

Hempel, L. A.; Grant, G.; Eaton, B. C.; Hassan, M. A.; Lewis, S.

2017-12-01

Numerous studies have explored how alluvial channels develop under different sediment and flow conditions, yet we still know very little about how channels adjust and respond to changing flow conditions. One reason for this oversight is the long-held idea that channels with complex flow regimes are adjusted to a single, channel-forming discharge. But growing evidence shows that channel form reflects time-dependent processes occuring over multiple flows. To better understand how stream channels adjust to a range of flows, and identify the timescales associated with those adjustments, we conducted a series of hydrograph experiments in a freely-adjustable flume that developed a self-formed, meander pattern with pool-riffle morphology. Hydrographs had different shapes, magnitudes, and durations, but the total sediment volume fed under equilibrium conditions was kept constant among experiments. We found that hydrograph shape controlled channel morphology, the rate of channel development, and degree of regularity in the pool-riffle pattern. Hydrographs with slowly rising rates of rise and fall produced channels that were equivalent in size to channels generated from constant flow experiments, and had regularly spaced pool-riffle and meander patterns, while hydrographs with fast rates of rise and fall produced undersized channels with a chaotic bed structure and pool-riffle pattern. The latter suggests that during quickly rising hydrographs, the flow rate increases faster than the channel capacity and planform pattern adjusts. We confirmed these observations by comparing the timescales associated with pool-riffle and planform curvature development, which were identified under simple, constant flow conditions, to the total duration of the hydrograph. Hydrographs with step durations equal to or longer than the channel adjustment time produced channels with a more regular pool-riffle patterns compared to channels with step durations shorter than the adjustment time. This work points to the importance of the hydrograph as a fundamental control on channel adjustment and offers the prospect of better understanding of how changes in the flow regime, either through climate, land use, or dams, translate into morphodynamic changes.

Accelerated relative sea-level rise and rapid coastal erosion: Testing a causal relationship for the Louisiana barrier islands

USGS Publications Warehouse

List, J.H.; Sallenger, A.H.; Hansen, M.E.; Jaffe, B.E.

1997-01-01

The role of relative sea-level rise as a cause for the rapid erosion of Louisiana's barrier island coast is investigated through a numerical implementation of a modified Bruun rule that accounts for the low percentage of sand-sized sediment in the eroding Louisiana shoreface. Shore-normal profiles from 150 km of coastline west of the Mississippi delta are derived from bathymetric surveys conducted during the 1880s. 1930s and 1980s. An RMS difference criterion is employed to test whether an equilibrium profile form is maintained between survey years. Only about half the studied profiles meet the equilibrium Criterion this represents a significant limitation on the potential applicability of the Bruun rule. The profiles meeting the equilibrium criterion, along with measured rates of relative sea-level rise, are used to hindcast shoreline retreat rates at 37 locations within the study area. Modeled and observed shoreline retreat rates show no significant correlation. Thus in terms of the Bruun approach relative sea-level rise has no power for hindcasting (and presumably forecasting) rates of coastal erosion for the Louisiana barrier islands.

MODELING FINE SEDIMENT TRANSPORT IN ESTUARIES

EPA Science Inventory

A sediment transport model (SEDIMENT IIIA) was developed to assist in predicting the fate of chemical pollutants sorbed to cohesive sediments in rivers and estuaries. Laboratory experiments were conducted to upgrade an existing two-dimensional, depth-averaged, finite element, coh...

Floating liquid phase in sedimenting colloid-polymer mixtures.

PubMed

Schmidt, Matthias; Dijkstra, Marjolein; Hansen, Jean-Pierre

2004-08-20

Density functional theory and computer simulation are used to investigate sedimentation equilibria of colloid-polymer mixtures within the Asakura-Oosawa-Vrij model of hard sphere colloids and ideal polymers. When the ratio of buoyant masses of the two species is comparable to the ratio of differences in density of the coexisting bulk (colloid) gas and liquid phases, a stable "floating liquid" phase is found, i.e., a thin layer of liquid sandwiched between upper and lower gas phases. The full phase diagram of the mixture under gravity shows coexistence of this floating liquid phase with a single gas phase or a phase involving liquid-gas equilibrium; the phase coexistence lines meet at a triple point. This scenario remains valid for general asymmetric binary mixtures undergoing bulk phase separation.

Numerical modeling of sorption kinetics of organic compounds to soil and sediment particles

NASA Astrophysics Data System (ADS)

Wu, Shian-chee; Gschwend, Phillip M.

1988-08-01

A numerical model is developed to simulate hydrophobic organic compound sorption kinetics, based on a retarded intraaggregate diffusion conceptualization of this solid-water exchange process. This model was used to ascertain the sensitivity of the sorption process for various sorbates to nonsteady solution concentrations and to polydisperse soil or sediment aggregate particle size distributions. Common approaches to modeling sorption kinetics amount to simplifications of our model and appear justified only when (1) the concentration fluctuations occur on a time scale which matches the sorption timescale of interest and (2) the particle size distribution is relatively narrow. Finally, a means is provided to estimate the extent of approach of a sorbing system to equilibrium as a function of aggregate size, chemical diffusivity and hydrophobicity, and system solids concentration.

Different erosion characteristics of sediment deposits in combined and storm sewers.

PubMed

Xu, Zuxin; Wu, Jun; Li, Huaizheng; Liu, Zhenghua; Chen, Keli; Chen, Hao; Xiong, Lijun

2017-04-01

To investigate the different erosion patterns of sediments in combined and storm sewers, sediments from three separate sewer systems and two combined sewer systems in urban Shanghai were collected for the flushing experiments. These experiments were conducted with different consolidation periods and shear velocities. As the consolidation period increases, dissolved oxygen exhibits a positive effect on the microbial transformations of organic substrates. Potential structural changes and separations of the surface and bottom layers of sediments are observed. The results also reveal that the organic matter, particle size and moisture have different effects on the erosion resistance of sediments. Furthermore, illicit connections behaved as an important factor affecting the viscosity and static friction force of particles, which directly alter the erosion resistance of sewer sediments.

Characteristics of the near-bottom suspended sediment field over the continental shelf off northern California based on optical attenuation measurements during STRESS and SMILE

NASA Astrophysics Data System (ADS)

Trowbridge, J. H.; Butman, B.; Limeburner, R.

1994-08-01

Time-series measurements of current velocity, optical attenuation and surface wave intensity obtained during the Sediment Transport Events on Shelves and Slopes (STRESS) experiments, combined with shipboard measurements of conductivity, temperature and optical attenuation obtained during the Shelf Mixed Layer Experiment (SMILE), provide a description of the sediment concentration field over the central and outer shelf off northern California. The questions addressed are: (1) existence and characteristics of bottom nepheloid layers and their relationship to bottom mixed layers; (2) characteristics of temporal fluctuations in sediment concentration and their relationship to waves and currents; (3) spatial scales over which suspended sediment concentrations vary horizontally; and (4) vertical distribution of suspended sediment.

Testing the Validity of Local Flux Laws in an Experimental Eroding Landscape

NASA Astrophysics Data System (ADS)

Sweeney, K. E.; Roering, J. J.; Ellis, C.

2015-12-01

Linking sediment transport to landscape evolution is fundamental to interpreting climate and tectonic signals from topography and sedimentary deposits. Most geomorphic process laws consist of simple continuum relationships between sediment flux and local topography. However, recent work has shown that nonlocal formulations, whereby sediment flux depends on upslope conditions, are more accurate descriptions of sediment motion, particularly in steep topography. Discriminating between local and nonlocal processes in natural landscapes is complicated by the scarcity of high-resolution topographic data and by the difficulty of measuring sediment flux. To test the validity of local formulations of sediment transport, we use an experimental erosive landscape that combines disturbance-driven, diffusive sediment transport and surface runoff. We conducted our experiments in the eXperimental Landscape Model at St. Anthony Falls Laboratory a 0.5 x 0.5 m test flume filled with crystalline silica (D50 = 30μ) mixed with water to increase cohesion and preclude surface infiltration. Topography is measured with a sheet laser scanner; total sediment flux is tracked with a series of load cells. We simulate uplift (relative baselevel fall) by dropping two parallel weirs at the edges of the experiment. Diffusive sediment transport in our experiments is driven by rainsplash from a constant head drip tank fitted with 625 blunt needles of fixed diameter; sediment is mobilized both through drop impact and the subsequent runoff of the drops. To drive advective transport, we produce surface runoff via a ring of misters that produce droplets that are too small to disturb the sediment surface on impact. Using the results from five experiments that systematically vary the time of drip box rainfall relative to misting rainfall, we calculate local erosion in our experiments by differencing successive time-slices of topography and test whether these patterns are related to local topographic metrics. By examining these patterns over different timescales, we are able to assess whether there is a signature of nonlocal transport in long-term topographic evolution or if, instead, local formulations are appropriate over timescales much greater than individual transport events.

Column experiments on organic micropollutants - applications and limitations

NASA Astrophysics Data System (ADS)

Banzhaf, Stefan; Hebig, Klaus

2016-04-01

As organic micropollutants become more and more ubiquitous in the aquatic environment, a sound understanding of their fate and transport behaviour is needed. This is to assure both safe and clean drinking water supply for mankind in the future and to protect the aquatic environment from pollution and negative consequences caused by manmade contamination. Apart from countless field studies, column experiments were and are frequently used to study transport of organic micropollutants. As the transport of (organic) solutes in groundwater is controlled by the chemical and physical properties of the compounds, the solvent (the groundwater including all solutes), and the substrate (the aquifer material), the adjustment and control of these boundary conditions allow to study a multitude of different experimental setups and to address specific research questions. The main purpose, however, remains to study the transport of a specific compound and its sorption and degradation behaviour in a specific sediment or substrate. Apart from the effective control of the individual boundary conditions, the main advantage of columns studies compared to other experimental setups (such as field studies, batch/microcosm studies), is that conservative and reactive solute breakthrough curves are obtained, which represent the sum of the transport processes. The analysis of these curves is well-developed and established. Additionally, limitations of this experimental method are presented here: the effects observed in column studies are often a result of dynamic, non-equilibrium processes. Time (or flow velocity) plays a major role in contrast to batch experiments, in which all processes will be observed until equilibrium is reached in the substrate-solution-system. Slightly modifying boundary conditions in different experiments have a strong influence on transport and degradation behaviour of organic micropollutants. This is a significant severe issue when it comes to general findings on the transport behaviour of a specific organic compound that are transferable to any given hydrogeochemical environment. Unfortunately, results of most column experiments therefore remain restricted to their specific setup. Column experiments can provide good estimates of all relevant transport parameters. However, the obtained results will almost always be limited to the scale they were obtained from. This means that direct application to field scale studies is infeasible as too many parameters are exclusive for the laboratory column setup. The remaining future challenge is to develop standard column experiments on organic micropollutants that overcome this issue. Here, we present a review of column experiments on organic micropollutants. We present different setups and discuss weaknesses, problems and advantages and provide ideas how to obtain more comparable results on the transport of organic micropollutants in the future.

Measurement of the equilibrium relative humidity for common precipitant concentrations: facilitating controlled dehydration experiments.

PubMed

Wheeler, Matthew J; Russi, Silvia; Bowler, Michael G; Bowler, Matthew W

2012-01-01

The dehydration of crystals of macromolecules has long been known to have the potential to increase their diffraction quality. A number of methods exist to change the relative humidity that surrounds crystals, but for reproducible results, with complete characterization of the changes induced, a precise humidity-control device coupled with an X-ray source is required. The first step in these experiments is to define the relative humidity in equilibrium with the mother liquor of the system under study; this can often be quite time-consuming. In order to reduce the time spent on this stage of the experiment, the equilibrium relative humidity for a range of concentrations of the most commonly used precipitants has been measured. The relationship between the precipitant solution and equilibrium relative humidity is explained by Raoult's law for the equilibrium vapour pressure of water above a solution. The results also have implications for the choice of cryoprotectant and solutions used to dehydrate crystals. For the most commonly used precipitants (10-30% PEG 2000-8000), the starting point will be a relative humidity of 99.5%. © 2012 International Union of Crystallography. All rights reserved.

METHODS FOR THE DETERMINATION OF TOTAL ORGANIC ...

EPA Pesticide Factsheets

Organic matter in soils and sediments is widely distributed over the earth's surface occurring in almost all terrestrial and aquatic environments (Schnitzer, 1978). Soils and sediments contain a large variety of organic materials ranging from simple sugars and carbohydrates to the more complex proteins, fats, waxes, and organic acids. Important characteristics of the organic matter include their ability to: form water-soluble and water- insoluble complexes with metal ions and hydrous oxides; interact with clay minerals and bind particles together; sorb and desorb both naturally-occurring and anthropogenically-introduced organic compounds; absorb and release plant nutrients; and hold water in the soil environment. As a result of these characteristics, the determination of total organic carbon (a measure of one of the chemical components of organic matter that is often used as an indicator of its presence in a soil or sediment) is an essential part of any site characterization since its presence or absence can markedly influence how chemicals will react in the soil or sediment. Soil and sediment total organic carbon (TOC) determinations are typically requested with contaminant analyses as part of an ecological risk assessment data package. TOC contents may be used qualitatively to assess the nature of the sampling location (e.g., was it a depositional area) or may be used to normalize portions of the analytical chemistry data set (e.g., equilibrium partitioning).

The oceanic budgets of nickel and zinc isotopes: the importance of sulfidic environments as illustrated by the Black Sea

PubMed Central

Little, Susan H.; Archer, Corey; Cameron, Vyllinniskii; Andersen, Morten B.; Rijkenberg, Micha J. A.; Lyons, Timothy W.

2016-01-01

Isotopic data collected to date as part of the GEOTRACES and other programmes show that the oceanic dissolved pool is isotopically heavy relative to the inputs for zinc (Zn) and nickel (Ni). All Zn sinks measured until recently, and the only output yet measured for Ni, are isotopically heavier than the dissolved pool. This would require either a non-steady-state ocean or other unidentified sinks. Recently, isotopically light Zn has been measured in organic carbon-rich sediments from productive upwelling margins, providing a potential resolution of this issue, at least for Zn. However, the origin of the isotopically light sedimentary Zn signal is uncertain. Cellular uptake of isotopically light Zn followed by transfer to sediment does not appear to be a quantitatively important process. Here, we present Zn and Ni isotope data for the water column and sediments of the Black Sea. These data demonstrate that isotopically light Zn and Ni are extracted from the water column, probably through an equilibrium fractionation between different dissolved species followed by sequestration of light Zn and Ni in sulfide species to particulates and the sediment. We suggest that a similar, non-quantitative, process, operating in porewaters, explains the Zn data from organic carbon-rich sediments. This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’. PMID:29035259

A Colorful Demonstration to Visualize and Inquire into Essential Elements of Chemical Equilibrium

ERIC Educational Resources Information Center

Eilks, Ingo; Gulacar, Ozcan

2016-01-01

One of the topics that chemistry teachers have a great challenge introducing is chemical equilibrium. When being introduced to chemical equilibrium, many students have difficulties in understanding that some reactions do not go to completion, as this contrasts most of their supposed prior experiences in chemistry lessons. Students may also…

Dynamic Processes of Conceptual Change: Analysis of Constructing Mental Models of Chemical Equilibrium.

ERIC Educational Resources Information Center

Chiu, Mei-Hung; Chou, Chin-Cheng; Liu, Chia-Ju

2002-01-01

Investigates students' mental models of chemical equilibrium using dynamic science assessments. Reports that students at various levels have misconceptions about chemical equilibrium. Involves 10th grade students (n=30) in the study doing a series of hands-on chemical experiments. Focuses on the process of constructing mental models, dynamic…

A Graphical Simulation of Vapor-Liquid Equilibrium for Use as an Undergraduate Laboratory Experiment and to Demonstrate the Concept of Mathematical Modeling.

ERIC Educational Resources Information Center

Whitman, David L.; Terry, Ronald E.

1985-01-01

Demonstrating petroleum engineering concepts in undergraduate laboratories often requires expensive and time-consuming experiments. To eliminate these problems, a graphical simulation technique was developed for junior-level laboratories which illustrate vapor-liquid equilibrium and the use of mathematical modeling. A description of this…

Equilibrium between Different Coordination Geometries in Oxidovanadium(IV) Complexes

ERIC Educational Resources Information Center

Ugone, Valeria; Garribba, Eugenio; Micera, Giovanni; Sanna, Daniele

2015-01-01

In this laboratory activity, the equilibrium between square pyramidal and octahedral V(IV)O[superscript 2+] complexes is described. We propose a set of experiments to synthesize and characterize two types of V(IV)O[superscript 2+] complexes. The experiment allows great flexibility and may be effectively used at a variety of levels and the activity…

Utilization of a Microcomputer for the Study of an Iodine Oxidation and Equilibrium Reaction: A Physical Chemistry Experiment.

ERIC Educational Resources Information Center

Julien, L. M.

1984-01-01

Describes a physical chemistry experiment which incorporates the use of a microcomputer to enhance understanding of combined kinetic and equilibrium phenomena, to increase experimental capabilities when working with large numbers of students and limited equipment, and for the student to develop a better understanding of experimental design. (JN)

Mechanisms of sediment transport to shoreline salients onshore of fringing coral reefs

NASA Astrophysics Data System (ADS)

Hansen, J.; Cuttler, M.; Traykovski, P.; Lowe, R.; Buckley, M. L.; Storlazzi, C. D.; Rosenberger, K. J.

2016-12-01

Shoreline salients, often extending several hundred metres seaward relative to the adjacent shoreline, are a common morphological feature found in the lee of many fringing coral reefs globally. However, the physical mechanisms that govern the formation and equilibrium dynamics of these salients remains poorly understood. A recent field experiment in NW Australia at Ningaloo Reef examined the mechanism of sediment delivery to a salient that extends 700 m seaward onshore of a 4 km long fringing reef that sits 2 km offshore. The experimental array consisted of wave, water level, and velocity measurements at >20 sites from 20 m depth offshore of the reef, the reef crest, and numerous sites throughout the 3 m depth lagoon shoreward of the reef. Two sites within the lagoon, one each side of the salient, also measured the migration of 0.5 m wavelength, 0.1 m high sand ripples using horizontal and vertically mounted echo sounders. Consistent with existing theory, mean (wave-averaged) flows in the lagoon shoreward of the reef and along the shoreline were divergent up to 0.2 m/s, corresponding to the circulation pattern resulting from wave breaking induced setup on the reef and associated mass flux into the lagoon, and seaward return flow through two lateral channels. These divergent alongshore mean flows are inconsistent the accreted shoreline morphology. However, the two sites that measured ripple properties and migration showed consistent migration in the local (salient following) onshore direction up to 2 m/day (mean 0.14 m/day across the two sites) resulting in onshore sediment fluxes as large as 200 kg/m/day (mean 10.1 kg/m/day) assuming ripple migration equates to net bedload transport. Despite the considerable infragravity energy within the lagoon ( 50% of the energy spectrum) the 0.5 m wavelength ripples were suborbital based on the orbital diameter of the 0.2-0.5 m high short waves which enter the lagoon via refraction through the lateral channels and incomplete dissipation over the reef. These preliminary results indicate that onshore ripple migration of biogenic sediment generated by the coral reef from short waves within the lagoon is the primary source of sediment to the salient. Additional analyses will focus on the hydrodynamic mechanisms responsible for the variable rate of migration.

Numerical and experimental analysis of the sedimentation of spherical colloidal suspensions under centrifugal force

NASA Astrophysics Data System (ADS)

Antonopoulou, Evangelia; Rohmann-Shaw, Connor F.; Sykes, Thomas C.; Cayre, Olivier J.; Hunter, Timothy N.; Jimack, Peter K.

2018-03-01

Understanding the sedimentation behaviour of colloidal suspensions is crucial in determining their stability. Since sedimentation rates are often very slow, centrifugation is used to expedite sedimentation experiments. The effect of centrifugal acceleration on sedimentation behaviour is not fully understood. Furthermore, in sedimentation models, interparticle interactions are usually omitted by using the hard-sphere assumption. This work proposes a one-dimensional model for sedimentation using an effective maximum volume fraction, with an extension for sedimentation under centrifugal force. A numerical implementation of the model using an adaptive finite difference solver is described. Experiments with silica suspensions are carried out using an analytical centrifuge. The model is shown to be a good fit with experimental data for 480 nm spherical silica, with the effects of centrifugation at 705 rpm studied. A conversion of data to Earth gravity conditions is proposed, which is shown to recover Earth gravity sedimentation rates well. This work suggests that the effective maximum volume fraction accurately captures interparticle interactions and provides insights into the effect of centrifugation on sedimentation.

Dispersal of river sediment in the Southern California Bight

USGS Publications Warehouse

Warrick, J.A.; Farnsworth, K.L.

2009-01-01

The rivers of Southern California deliver episodic pulses of water, sediment, nutrients, and pollutants to the region's coastal waters. Although river-sediment dispersal is observed in positively buoyant (hypopycnal) turbid plumes extending tens of kilometers from river mouths, very little of the river sediment is found in these plumes. Rather, river sediment settles quickly from hypopycnal plumes to the seabed, where transport is controlled by bottom-boundary layer processes, presumably including fluid-mud (hyperpycnal) gravity currents. Here we investigate the geographical patterns of river-sediment dispersal processes by examining suspended-sediment concentrations and loads and the continental shelf morphology offshore river mouths. Throughout Southern California, river sediment is discharged at concentrations adequately high to induce enhanced sediment settling, including negative buoyancy. The rivers draining the Western Transverse Range produce suspended-sediment concentrations that are orders of magnitude greater than those in the urbanized region and Peninsular Range to the south, largely due to differences in sediment yield. The majority of sediment discharge from the Santa Clara River and Calleguas Creek occurs above the theoretical negative buoyancy concentration (>40 g/l). These rivers also produce event sediment loading as great as the Eel River, where fluid-mud gravity currents are observed. The continental shelf of Southern California has variable morphology, which influences the ability to transport via gravity currents. Over half of the rivers examined are adjacent to shelf slopes greater than 0.01, which are adequately steep to sustain auto-suspending gravity currents across the shelf, and have little (<10 m) Holocene sediment accumulation. Shelf settings of the Ventura, Santa Clara, and Tijuana Rivers are very broad and low sloped (less than 0.004), which suggests that fluid-mud gravity currents could transport across these shelves, albeit slowly (??10 cm/s) and only with adequate wave-generated shear stress and sediment loading. Calleguas Creek is unique in that it discharges directly into a steepsloped canyon (greater than 0.1) that should allow for violent auto-suspending gravity currents. In light of this, only one shelf setting-the Santa Clara and Ventura-has considerable Holocene sediment accumulation (exceeding 60 m), and here we show that the morphology of this shelf is very similar to an equilibrium shape predicted by gravity-current sediment transport. Thus, we conclude that a wide distribution of river-shelf settings occur in the Southern California Bight, which will directly influence sediment dispersal processes-both dilute suspended and gravity-current transport-and sediment-accumulation patterns. ?? 2009 The Geological Society of America.

Flow structure at low momentum ratio river confluences

NASA Astrophysics Data System (ADS)

Moradi, Gelare; Rennie, Colin. D.; Cardot, Romain; Mettra, François; Lane, Stuart. N.

2017-04-01

The flow structure at river confluences is a complex pattern of fluid motion and can be characterized by the formation of secondary circulation. As river confluences play an essential role on flow hydrodynamics and control the movement of sediment through river networks, there has been substantial attention given to this subject in recent decades. However, there is still much debate over how momentum ratio and sediment transport can control secondary circulation and mixing processes. In particular, studies have tended to assume that there is some equilibrium between the bed morphology present and the flow structures that form in the junction region. However, this overlooks the fact that tributaries may be associated with highly varying sediment supply regimes, especially for shorter and steeper tributaries, with temporal changes in sediment delivery ratios (between the main stem and the tributary) that do not follow exactly changes in momentum ratio. This may lead to bed morphologies that are a function of rates of historical sediment supply during sediment transporting events and not the momentum ratio associated with the junction during its measurement. It is quite possible that tributaries with low flow momentum ratio have a relatively higher sediment delivery ratio, such that the tributary is still able to influence significantly secondary circulation in the main channel, long after the sediment transport event, and despite its low flow momentum during measurement. The focus of this paper is low momentum ratio junctions where it is possible that the tributary can deliver large amounts of sediment. Secondary circulation at junctions is thought to be dominated by streamwise-oriented vortical cells. These cells are produced by the convergence of surface flow towards the centre of the main channel, with descending motion in the zone of maximum flow convergence. Once flow arrives at the bed, it diverges and completes its rotation by an upwelling motion through the surface at the channels margins. Numerical models, laboratory experiments and field studies have confirmed the presence of this motion. However, such studies have focused on situations where the momentum ratio is close to one and there have been fewer investigations of confluences where the momentum ratio is much less than one. This study presents field investigations in two upper Rhône river confluences in Switzerland, using an acoustic Doppler current profiler (aDcp). These two confluences are characterized by low momentum ratios but potentially higher sediment delivery ratios during extreme events. Results show that sediment delivery from the tributary during extreme events leads to the formation of a tributary mouth bar and associated bed discordance as well as a bank attached bar downstream of the tributary. In both cases, this discordant bed forms a two-layer flow and the water from the tributary penetrates into the upper part of the main river water column. This results in a mixing interface that is shifted toward the outer bank. When this mixing layer detaches from the tributary outer bank, it forms a large recirculation region in the upper part of the water column and a pronounced scour hole at this bank. The bank attached bar that forms downstream during sediment supply events leads to substantial curvature of the main channel flow, even when the flow momentum of the tributary is low and helps to shift the zone of deepest main river flow towards the outer bank.

Multiple C-terminal tail Ca2+/CaMs regulate CaV1.2 function but do not mediate channel dimerization

PubMed Central

Kim, Eun Young; Rumpf, Christine H; Van Petegem, Filip; Arant, Ryan J; Findeisen, Felix; Cooley, Elizabeth S; Isacoff, Ehud Y; Minor, Daniel L

2010-01-01

Interactions between voltage-gated calcium channels (CaVs) and calmodulin (CaM) modulate CaV function. In this study, we report the structure of a Ca2+/CaM CaV1.2 C-terminal tail complex that contains two PreIQ helices bridged by two Ca2+/CaMs and two Ca2+/CaM–IQ domain complexes. Sedimentation equilibrium experiments establish that the complex has a 2:1 Ca2+/CaM:C-terminal tail stoichiometry and does not form higher order assemblies. Moreover, subunit-counting experiments demonstrate that in live cell membranes CaV1.2s are monomers. Thus, contrary to previous proposals, the crystallographic dimer lacks physiological relevance. Isothermal titration calorimetry and biochemical experiments show that the two Ca2+/CaMs in the complex have different properties. Ca2+/CaM bound to the PreIQ C-region is labile, whereas Ca2+/CaM bound to the IQ domain is not. Furthermore, neither of lobes of apo-CaM interacts strongly with the PreIQ domain. Electrophysiological studies indicate that the PreIQ C-region has a role in calcium-dependent facilitation. Together, the data show that two Ca2+/CaMs can bind the CaV1.2 tail simultaneously and indicate a functional role for Ca2+/CaM at the C-region site. PMID:20953164

Multiple C-terminal tail Ca(2+)/CaMs regulate Ca(V)1.2 function but do not mediate channel dimerization.

PubMed

Kim, Eun Young; Rumpf, Christine H; Van Petegem, Filip; Arant, Ryan J; Findeisen, Felix; Cooley, Elizabeth S; Isacoff, Ehud Y; Minor, Daniel L

2010-12-01

Interactions between voltage-gated calcium channels (Ca(V)s) and calmodulin (CaM) modulate Ca(V) function. In this study, we report the structure of a Ca(2+)/CaM Ca(V)1.2 C-terminal tail complex that contains two PreIQ helices bridged by two Ca(2+)/CaMs and two Ca(2+)/CaM-IQ domain complexes. Sedimentation equilibrium experiments establish that the complex has a 2:1 Ca(2+)/CaM:C-terminal tail stoichiometry and does not form higher order assemblies. Moreover, subunit-counting experiments demonstrate that in live cell membranes Ca(V)1.2s are monomers. Thus, contrary to previous proposals, the crystallographic dimer lacks physiological relevance. Isothermal titration calorimetry and biochemical experiments show that the two Ca(2+)/CaMs in the complex have different properties. Ca(2+)/CaM bound to the PreIQ C-region is labile, whereas Ca(2+)/CaM bound to the IQ domain is not. Furthermore, neither of lobes of apo-CaM interacts strongly with the PreIQ domain. Electrophysiological studies indicate that the PreIQ C-region has a role in calcium-dependent facilitation. Together, the data show that two Ca(2+)/CaMs can bind the Ca(V)1.2 tail simultaneously and indicate a functional role for Ca(2+)/CaM at the C-region site.

Geochemical Effects of Millimolar Hydrogen Concentrations in Groundwater: An Experimental Study in the Context of Subsurface Hydrogen Storage.

PubMed

Berta, Marton; Dethlefsen, Frank; Ebert, Markus; Schäfer, Dirk; Dahmke, Andreas

2018-04-17

Hydrogen storage in geological formations is one of the most promising technologies for balancing major fluctuations between energy supply from renewable energy plants and energy demand of customers. If hydrogen gas is stored in a porous medium or if it leaks into a shallow aquifer, redox reactions can oxidize hydrogen and reduce electron acceptors such as nitrate, Fe III and Mn IV (hydro)oxides, sulfate, and carbonate. These reactions are of key significance, because they can cause unintentional losses in hydrogen stored in porous media and they also can cause unwanted changes in the composition of protected potable groundwater. To represent an aquifer environment enclosing a hydrogen plume, laboratory experiments using sediment-filled columns were constructed and percolated by groundwater in equilibrium with high (2-15 bar) hydrogen partial pressures. Here, we show that hydrogen is consumed rapidly in these experiments via sulfate reduction (18 ± 5 μM h -1 ) and acetate production (0.030 ± 0.006 h -1 ), while no methanogenesis took place. The observed reaction rates were independent from the partial pressure of hydrogen and hydrogen consumption only stopped in supplemental microcosm experiments where salinity was increased above 35 g L -1 . The outcomes presented here are implemented for planning the sustainable use of the subsurface space within the ANGUS+ project.

Diverse origins of Arctic and Subarctic methane point source emissions identified with multiply-substituted isotopologues

NASA Astrophysics Data System (ADS)

Douglas, P. M. J.; Stolper, D. A.; Smith, D. A.; Walter Anthony, K. M.; Paull, C. K.; Dallimore, S.; Wik, M.; Crill, P. M.; Winterdahl, M.; Eiler, J. M.; Sessions, A. L.

2016-09-01

Methane is a potent greenhouse gas, and there are concerns that its natural emissions from the Arctic could act as a substantial positive feedback to anthropogenic global warming. Determining the sources of methane emissions and the biogeochemical processes controlling them is important for understanding present and future Arctic contributions to atmospheric methane budgets. Here we apply measurements of multiply-substituted isotopologues, or clumped isotopes, of methane as a new tool to identify the origins of ebullitive fluxes in Alaska, Sweden and the Arctic Ocean. When methane forms in isotopic equilibrium, clumped isotope measurements indicate the formation temperature. In some microbial methane, however, non-equilibrium isotope effects, probably related to the kinetics of methanogenesis, lead to low clumped isotope values. We identify four categories of emissions in the studied samples: thermogenic methane, deep subsurface or marine microbial methane formed in isotopic equilibrium, freshwater microbial methane with non-equilibrium clumped isotope values, and mixtures of deep and shallow methane (i.e., combinations of the first three end members). Mixing between deep and shallow methane sources produces a non-linear variation in clumped isotope values with mixing proportion that provides new constraints for the formation environment of the mixing end-members. Analyses of microbial methane emitted from lakes, as well as a methanol-consuming methanogen pure culture, support the hypothesis that non-equilibrium clumped isotope values are controlled, in part, by kinetic isotope effects induced during enzymatic reactions involved in methanogenesis. Our results indicate that these kinetic isotope effects vary widely in microbial methane produced in Arctic lake sediments, with non-equilibrium Δ18 values spanning a range of more than 5‰.

Use of Sodium Dithionite as Part of a More Efficient Groundwater Restoration Method Following In-situ Recovery of Uranium at the Smith-Ranch Highland Site in Wyoming

NASA Astrophysics Data System (ADS)

Harris, R.; Reimus, P. W.; Ware, D.; Williams, K.; Chu, D.; Perkins, G.; Migdissov, A. A.; Bonwell, C.

2017-12-01

Uranium is primarily mined for nuclear power production using an aqueous extraction technique called in-situ recovery (ISR). ISR can pollute groundwater with residual uranium and other heavy metals. Reverse osmosis and groundwater sweep are currently used to restore groundwater after ISR mining, but are not permanent solutions. Sodium dithionite is being tested as part of a method to more permanently restore groundwater after ISR mining at the Smith-Ranch Highland site in Wyoming. Sodium dithionite is a chemical reductant that can reduce sediments that were oxidized during ISR. The reduced sediments can reduce soluble uranium (VI) in the groundwater to insoluble uranium (IV). Laboratory studies that use sodium dithionite to treat sediments and waters from the site may help predict how it will behave during a field deployment. An aqueous batch experiment showed that sodium dithionite reduced uranium in post-mined untreated groundwater from 38 ppm to less than 1 ppm after 1 day. A sediment reduction batch experiment showed that sodium dithionite-treated sediments were capable of reducing uranium in post-mined untreated groundwater from 38 ppm to 2 ppm after 7 days. One column experiment is showing post-mined sodium dithionite-treated sediments are capable of reducing uranium in post-mined groundwater for over 30 pore volumes past the initial injection. While these results are promising for field deployments of sodium dithionite, another column experiment with sodium dithionite-treated sediments containing uranium rich organic matter is showing net production of uranium instead of uranium uptake. Sodium dithionite appears to liberate uranium from the organic matter. Another sediment reduction experiment is being conducted to further investigate this hypothesis. These experiments are helping guide plans for field deployments of sodium dithionite at uranium ISR mining sites.

Nonequilibrium Thermodynamics of Hydrate Growth on a Gas-Liquid Interface

NASA Astrophysics Data System (ADS)

Fu, Xiaojing; Cueto-Felgueroso, Luis; Juanes, Ruben

2018-04-01

We develop a continuum-scale phase-field model to study gas-liquid-hydrate systems far from thermodynamic equilibrium. We design a Gibbs free energy functional for methane-water mixtures that recovers the isobaric temperature-composition phase diagram under thermodynamic equilibrium conditions. The proposed free energy is incorporated into a phase-field model to study the dynamics of hydrate formation on a gas-liquid interface. We elucidate the role of initial aqueous concentration in determining the direction of hydrate growth at the interface, in agreement with experimental observations. Our model also reveals two stages of hydrate growth at an interface—controlled by a crossover in how methane is supplied from the gas and liquid phases—which could explain the persistence of gas conduits in hydrate-bearing sediments and other nonequilibrium phenomena commonly observed in natural methane hydrate systems.

Experimental study on local scouring at pile-supported piers

NASA Astrophysics Data System (ADS)

Moreno, Mario; Birjukova, Olga; Grimaldi, Carmelo; Gaudio, Roberto; Cardoso, António H.

2017-06-01

In spite of the increasing importance of complex piers for bridges, the number of studies on these piers is comparatively small and the predictors of scour depth at complex piers are only a few, derived from limited experimental evidence. The main purpose of this paper is to share with the hydraulics community the results of 67 tests on scouring at pile-supported piers (including complex piers) aligned with the flow, under clear-water conditions close to the threshold of beginning of sediment motion, while contributing to shade some more light on the influence of the pile-cap thickness on the equilibrium scour depth, the reliability of the superposition approach, the contribution of each one of the complex pier components to the equilibrium scour depth of the ensemble, and the performance of existing predictors of local scour at complex piers.

Nonequilibrium Thermodynamics of Hydrate Growth on a Gas-Liquid Interface.

PubMed

Fu, Xiaojing; Cueto-Felgueroso, Luis; Juanes, Ruben

2018-04-06

We develop a continuum-scale phase-field model to study gas-liquid-hydrate systems far from thermodynamic equilibrium. We design a Gibbs free energy functional for methane-water mixtures that recovers the isobaric temperature-composition phase diagram under thermodynamic equilibrium conditions. The proposed free energy is incorporated into a phase-field model to study the dynamics of hydrate formation on a gas-liquid interface. We elucidate the role of initial aqueous concentration in determining the direction of hydrate growth at the interface, in agreement with experimental observations. Our model also reveals two stages of hydrate growth at an interface-controlled by a crossover in how methane is supplied from the gas and liquid phases-which could explain the persistence of gas conduits in hydrate-bearing sediments and other nonequilibrium phenomena commonly observed in natural methane hydrate systems.

Numerical simulation of the three-dimensional river antidunes

NASA Astrophysics Data System (ADS)

Iwasaki, T.; Inoue, T.; Onda, S.; Yabe, H.

2017-12-01

This study presents numerical simulations of the formation and development of the three-dimensional river antidunes. We use a Boussinesq type depth-integrated hydrodynamic model to account for the non-hydrostatic pressure effects on the flow field, dissipative feature of the free surface and the bed shear stress distribution. In addition, a non-equilibrium bedload transport model is incorporated into the model to consider the lag effect of the bedload transport on the bedform dynamics. The model is applied to idealized laboratory-scale conditions, i.e., steady water and sediment supplies, uniform sediment and a straight channel with constant slope and channel width, to understand the model performance and applicability. The results show that the model is able to reproduce an upstream-migrating antidunes and associated free surface dynamics. The model also captures the formation of the two dimensional and the three-dimensional antidunes. The antidunes reproduced by the model are somewhat unstable, i.e., the repeated cycle of dissipation and regeneration of antidunes is observed. In addition, as the calculation progresses, the modelled three-dimensional antidunes generally tend to lose their three-dimensionality, i.e., the reduction of the spanwise wavenumber. In the early stage of the calculation, the antidune mode is dominant, whereas, the free bars also develop when the formative condition of bars is satisfied. The numerical results show the coexisting of free bars and antidunes, which are a common evident in flume experiments and field observations.

Effects of benthos, temperature, and dose on the fate of hexabromocyclododecane in experimental coastal ecosystems.

PubMed

Bradshaw, Clare; Strid, Anna; von Stedingk, Hans; Gustafsson, Kerstin

2015-06-01

The authors studied the fate of the brominated flame retardant hexabromocyclododecane (HBCDD) added in a particulate suspension to experimental ecosystems assembled from brackish (Baltic Sea) coastal bays. Two experiments examined how benthic macrofauna (over 21 d) and increased temperature (14 d) affected HBCDD concentrations and fractionation of α, β, and γ diastereomers in the water, sediment, and biota. A third experiment run over 3 seasons (231 d), studied the effect of HBCDD dose on the same endpoints. In all treatments of the 3 experiments, HBCDD partitioned mainly to the sediment, and this proportion increased with time. Presence of macrofauna tended to increase the HBCDD concentration in the sediment and decreased its concentration in the water. Increased temperature (+ 5°C) decreased the amount of HBCDD in sediment and water but not in the filter- and deposit-feeding infaunal bivalves (Macoma balthica). The partitioning between water, sediment, and biota was not concentration dependent. In all treatments, sediment became enriched in γ-HBCDD, M. balthica in α-HBCDD, and water in α- and β-HBCDD. Bioaccumulation of HBCDD in M. balthica was high in all experiments (log biota-sediment accumulation factor [BSAF] > 1.25), the α diastereomer contributing the most (log BSAF 2.1-5.2). There is a risk of trophic transfer of HBCDD from benthic to pelagic food webs, as well as secondary poisoning of marine consumers. © 2015 SETAC.

Performance of ultrafiltration membrane process combined with coagulation/sedimentation.

PubMed

Jang, N Y; Watanabe, Y; Minegishi, S

2005-01-01

Effects of coagulation/sedimentation as a pre-treatment on the dead-end ultrafiltration (UF) membrane process were studied in terms of membrane fouling and removal efficiency of natural dissolved organic matter, using Chitose River water. Two types of experiment were carried out. One was a bench scale membrane filtration with jar-test and the other was membrane filtration pilot plant combined with the Jet Mixed Separator (JMS) as a pre-coagulation/sedimentation unit. In the bench scale experiment, the effects of coagulant dosage, pH and membrane operating pressure on the membrane fouling and removal efficiency of natural dissolved organic matter were investigated. In the pilot plant experiment, we also investigated the effect of pre-coagulation/sedimentation on the membrane fouling and the removal efficiency of natural dissolved organic matter. Coagulation/sedimentation prior to membrane filtration process controlled the membrane fouling and increased the removal efficiency of natural dissolved organic matter.

Quantification of Fine-grained Sediment Concentration in the Aquatic Environment Using Optical and Acoustic Sensors: Insight from Lab Experiments

NASA Astrophysics Data System (ADS)

Xu, K.; Champagne, B. N.

2017-12-01

The transport of sediment in the coastal zone and continental shelf is highly impacted by fluvial and oceanographic dynamics. In Louisiana, the Mississippi River delivers a bulk of water, sediment, and nutrients to the coast. However, coastal land loss highlights the importance of the sediment deposited at the mouth of the river. Sediment is the foundation to build land and suspended sediment concentration (SSC) tracks the delivery, deposition, and erosion of sediment. On a more applicable scale, variables such as SSC can be used to calculate sediment transport flux, an important parameter for projects such as sediment diversions and barrier island restoration. In order to rely on suspended sediment concentration (SSC) as continuous data, lab experiments are needed to establish the relationship between turbidity and SSC. Factors such as sensor type (optical or acoustic) and grain size (coarse or fine) can greatly impact the estimated SSC. In this study, fine-grained sediment was collected from multiple sites in coastal Louisiana and used to calibrate both optical backscatter (OBS) and acoustic backscatter (ABS) sensors to establish the relationship between sensor type and accuracy of the SSC estimation. Multiple grain-size analyses using a Laser Diffraction Particle Size Analyzer helped determine the effects of sensor accuracy regarding grain size. The results of these experiments were combined in order to establish the calibration curves of SSC. Our results indicated that the OBS-3A sensor's turbidity data were more correlated with the SSC than the OBS-5+'s data. Possible explanations for this could be due to differences between the instruments' measuring ranges and their sensitivity to various grain sizes. This technology development has a broad impact to the studies of sediment delivery, transport, and deposition in multiple types of coastal protection and restoration projects.

Enhanced picture of protein-folding intermediates using organic solvents in H/D exchange and quench-flow experiments

PubMed Central

Nishimura, Chiaki; Dyson, H. Jane; Wright, Peter E.

2005-01-01

Hydrogen/deuterium exchange followed by trapping of the labeled species in the aprotic solvent DMSO has been used to elucidate structure in both the burst-phase molten globule-folding intermediate of apomyoglobin and in an equilibrium intermediate that models the kinetic intermediate. Precise estimates can be made of exchange times in an interrupted exchange-out experiment at pH 4 followed by analysis in DMSO solution, giving extensive sequence-specific information about the structure of the equilibrium intermediate. In addition, the use of DMSO as a solvent for NMR measurements after quench-flow pH-pulse labeling experiments gives a greatly increased data set for the elucidation of the kinetic folding pathway. Interestingly, differences are observed in some regions of apomyoglobin between the equilibrium and kinetic intermediates. These differences are quantitative rather than qualitative; that is, the overall patterns of labeling and secondary structure formation remain similar between the two species. However, local differences are observed, which probably reflect the difference in the solution conditions for the equilibrium experiment (pH 4) vs. the kinetic experiment (pH 6) and the change in the status of the stabilizing hydrogen bond between the side chains of His-24 and His-119. PMID:15769860

Recent and historic sediment dynamics along Difficult Run, a suburban Virginia Piedmont stream

NASA Astrophysics Data System (ADS)

Hupp, Cliff R.; Noe, Gregory B.; Schenk, Edward R.; Benthem, Adam J.

2013-01-01

Suspended sediment is one of the major concerns regarding the quality of water entering the Chesapeake Bay. Some of the highest suspended-sediment concentrations occur on Piedmont streams, including Difficult Run, a tributary of the Potomac River draining urban and suburban parts of northern Virginia. Accurate information on catchment level sediment budgets is rare and difficult to determine. Further, the sediment trapping portion of sediment budget represents an important ecosystem service that profoundly affects downstream water quality. Our objectives, with special reference to human alterations to the landscape, include the documentation and estimation of floodplain sediment trapping (present and historic) and bank erosion along an urbanized Piedmont stream, the construction of a preliminary sediment balance, and the estimation of legacy sediment and recent development impacts. We used white feldspar markers to measure floodplain sedimentation rates and steel pins to measure erosion rates on floodplains and banks, respectively. Additional data were collected for/from legacy sediment thickness and characteristics, mill pond impacts, stream gaging station records, topographic surveying, and sediment density, texture, and organic content. Data were analyzed using GIS and various statistical programs. Results are interpreted relative to stream equilibrium affected by both post-colonial bottomland sedimentation (legacy) and modern watershed hardening associated with urbanization. Six floodplain/channel sites, from high to low in the watershed, were selected for intensive study. Bank erosion ranges from 0 to 470 kg/m/y and floodplain sedimentation ranges from 18 to 1369 kg/m/y (m refers to meters of stream reach). Upstream reaches are net erosional, while downstream reaches have a distinctly net depositional flux providing a watershed sediment balance of 2184 kg/m/y trapped within the system. The amounts of both deposition and erosion are large and suggest nonequilibrium channel conditions. Both peak discharge and number of peaks above base have substantially increased since the mid-1960s when urbanization of the watershed began. Deposition patterns are most closely correlated with channel gradient, sinuosity, and channel width/floodplain width for recent and historic periods. The substantial amounts of fine grained sediment deposited on the floodplain over the past two centuries or so do not appear to be closely related to historic mill pond presence or location. The floodplain continues to provide the critical ecosystem service of sediment trapping in the face of multiple human alterations. Trends in sediment deposition/erosion may react rapidly to land use practices within the watershed and offer a valuable barometer of the effects of management actions.

Recent and historic sediment dynamics along Difficult Run, a suburban Virginia Piedmont stream

USGS Publications Warehouse

Hupp, Cliff R.; Noe, Gregory B.; Schenk, Edward R.; Bentham, Adam J.

2012-01-01

Suspended sediment is one of the major concerns regarding the quality of water entering the Chesapeake Bay. Some of the highest suspended-sediment concentrations occur on Piedmont streams, including Difficult Run, a tributary of the Potomac River draining urban and suburban parts of northern Virginia. Accurate information on catchment level sediment budgets is rare and difficult to determine. Further, the sediment trapping portion of sediment budget represents an important ecosystem service that profoundly affects downstream water quality. Our objectives, with special reference to human alterations to the landscape, include the documentation and estimation of floodplain sediment trapping (present and historic) and bank erosion along an urbanized Piedmont stream, the construction of a preliminary sediment balance, and the estimation of legacy sediment and recent development impacts. We used white feldspar markers to measure floodplain sedimentation rates and steel pins to measure erosion rates on floodplains and banks, respectively. Additional data were collected for/from legacy sediment thickness and characteristics, mill pond impacts, stream gaging station records, topographic surveying, and sediment density, texture, and organic content. Data were analyzed using GIS and various statistical programs. Results are interpreted relative to stream equilibrium affected by both post-colonial bottomland sedimentation (legacy) and modern watershed hardening associated with urbanization. Six floodplain/channel sites, from high to low in the watershed, were selected for intensive study. Bank erosion ranges from 0 to 470 kg/m/y and floodplain sedimentation ranges from 18 to 1369 kg/m/y (m refers to meters of stream reach). Upstream reaches are net erosional, while downstream reaches have a distinctly net depositional flux providing a watershed sediment balance of 2184 kg/m/y trapped within the system. The amounts of both deposition and erosion are large and suggest nonequilibrium channel conditions. Both peak discharge and number of peaks above base have substantially increased since the mid-1960s when urbanization of the watershed began. Deposition patterns are most closely correlated with channel gradient, sinuosity, and channel width/floodplain width for recent and historic periods. The substantial amounts of fine grained sediment deposited on the floodplain over the past two centuries or so do not appear to be closely related to historic mill pond presence or location. The floodplain continues to provide the critical ecosystem service of sediment trapping in the face of multiple human alterations. Trends in sediment deposition/erosion may react rapidly to land use practices within the watershed and offer a valuable barometer of the effects of management actions.

Hydro-bio-geomechanical properties of hydrate-bearing sediments from Nankai Trough

USGS Publications Warehouse

Santamarina, J.C.; Dai, Shifeng; Terzariol, M.; Jang, Jeonghwan; Waite, William F.; Winters, William J.; Nagao, J.; Yoneda, J.; Konno, Y.; Fujii, T.; Suzuki, K.

2015-01-01

Natural hydrate-bearing sediments from the Nankai Trough, offshore Japan, were studied using the Pressure Core Characterization Tools (PCCTs) to obtain geomechanical, hydrological, electrical, and biological properties under in situ pressure, temperature, and restored effective stress conditions. Measurement results, combined with index-property data and analytical physics-based models, provide unique insight into hydrate-bearing sediments in situ. Tested cores contain some silty-sands, but are predominantly sandy- and clayey-silts. Hydrate saturations Sh range from 0.15 to 0.74, with significant concentrations in the silty-sands. Wave velocity and flexible-wall permeameter measurements on never-depressurized pressure-core sediments suggest hydrates in the coarser-grained zones, the silty-sands where Sh exceeds 0.4, contribute to soil-skeletal stability and are load-bearing. In the sandy- and clayey-silts, where Sh < 0.4, the state of effective stress and stress history are significant factors determining sediment stiffness. Controlled depressurization tests show that hydrate dissociation occurs too quickly to maintain thermodynamic equilibrium, and pressure–temperature conditions track the hydrate stability boundary in pure-water, rather than that in seawater, in spite of both the in situ pore water and the water used to maintain specimen pore pressure prior to dissociation being saline. Hydrate dissociation accompanied with fines migration caused up to 2.4% vertical strain contraction. The first-ever direct shear measurements on never-depressurized pressure-core specimens show hydrate-bearing sediments have higher sediment strength and peak friction angle than post-dissociation sediments, but the residual friction angle remains the same in both cases. Permeability measurements made before and after hydrate dissociation demonstrate that water permeability increases after dissociation, but the gain is limited by the transition from hydrate saturation before dissociation to gas saturation after dissociation. In a proof-of-concept study, sediment microbial communities were successfully extracted and stored under high-pressure, anoxic conditions. Depressurized samples of these extractions were incubated in air, where microbes exhibited temperature-dependent growth rates.

Modelling of sediment transport pattern in the mouth of the Rhone delta: Role of storm and flood events

NASA Astrophysics Data System (ADS)

Boudet, L.; Sabatier, F.; Radakovitch, O.

2017-11-01

The delta of the Rhone River is one of the most important in the Mediterranean Sea. Beach erosion problems along its coasts have developed in recent decades, raising the need for a better understanding of the sediment transport processes at the Rhone mouth and the adjacent beaches. Because field data are very difficult to obtain in such an energetic environment, a high-resolution numerical model (Delft3D) is applied to this area. This model is calibrated by taking into account hydrodynamical and morphological observations. Special attention is given to storm and flood events, which are the major morphological drivers. Therefore, scenarios with different wave and flow conditions are run to estimate the influence of these events on the sediment transport. The analysis of historical hydrological data shows that storms from the southeast represent 70% of the events between 1979 to 2010 and that 20% of them were followed by a flood within a few days. Consequently, specific simulations for such conditions are performed using Delft3D. The model simulates trends in the bedload sediment transport that are consistent with the bedforms observed in the bathymetry data. The total sediment transport at the outlet is only influenced by the river flow, but sediment transport at the mouth-bar depends on an equilibrium between the influence of floods and storms and the succession of these events. A period of 2 or 3 days separating the storm and flood peaks is sufficient to differentiate wave and river flow-induced sediment transport. The waves constrain the total transport on the mouth-bar and shallow mouth-lobe and induce a longshore transfer towards the adjacent beaches. The riverine sediments can be exported seaward only if a flood is energetic enough compared to the storm intensity. Regardless, when a flood is greater than the decadal return period (7800 m3 s-1), the sediment is transported from the outlet across the mouth-bar and is directed offshore.

Formation of natural gas hydrates in marine sediments 1. Conceptual model of gas hydrate growth conditioned by host sediment properties

USGS Publications Warehouse

Clennell, M.B.; Hovland, M.; Booth, J.S.; Henry, P.; Winters, W.J.

1999-01-01

The stability of submarine gas hydrates is largely dictated by pressure and temperature, gas composition, and pore water salinity. However, the physical properties and surface chemistry of deep marine sediments may also affect the thermodynamic state, growth kinetics, spatial distributions, and growth forms of clathrates. Our conceptual model presumes that gas hydrate behaves in a way analogous to ice in a freezing soil. Hydrate growth is inhibited within fine-grained sediments by a combination of reduced pore water activity in the vicinity of hydrophilic mineral surfaces, and the excess internal energy of small crystals confined in pores. The excess energy can be thought of as a "capillary pressure" in the hydrate crystal, related to the pore size distribution and the state of stress in the sediment framework. The base of gas hydrate stability in a sequence of fine sediments is predicted by our model to occur at a lower temperature (nearer to the seabed) than would be calculated from bulk thermodynamic equilibrium. Capillary effects or a build up of salt in the system can expand the phase boundary between hydrate and free gas into a divariant field extending over a finite depth range dictated by total methane content and pore-size distribution. Hysteresis between the temperatures of crystallization and dissociation of the clathrate is also predicted. Growth forms commonly observed in hydrate samples recovered from marine sediments (nodules, and lenses in muds; cements in sands) can largely be explained by capillary effects, but kinetics of nucleation and growth are also important. The formation of concentrated gas hydrates in a partially closed system with respect to material transport, or where gas can flush through the system, may lead to water depletion in the host sediment. This "freeze-drying" may be detectable through physical changes to the sediment (low water content and overconsolidation) and/or chemical anomalies in the pore waters and metastable presence of free gas within the normal zone of hydrate stability. 

Mars Sample Return: The Next Step Required to Revolutionize Knowledge of Martian Geological and Climatological History

NASA Technical Reports Server (NTRS)

Mittlefehldt, D. W.

2012-01-01

The capability of scientific instrumentation flown on planetary orbiters and landers has made great advances since the signature Viking mission of the seventies. At some point, however, the science return from orbital remote sensing, and even in situ measurements, becomes incremental, rather than revolutionary. This is primarily caused by the low spatial resolution of such measurements, even for landed instrumentation, the incomplete mineralogical record derived from such measurements, the inability to do the detailed textural, mineralogical and compositional characterization needed to demonstrate equilibrium or reaction paths, and the lack of chronological characterization. For the foreseeable future, flight instruments will suffer from this limitation. In order to make the next revolutionary breakthrough in understanding the early geological and climatological history of Mars, samples must be available for interrogation using the full panoply of laboratory-housed analytical instrumentation. Laboratory studies of samples allow for determination of parageneses of rocks through microscopic identification of mineral assemblages, evaluation of equilibrium through electron microbeam analyses of mineral compositions and structures, determination of formation temperatures through secondary ion or thermal ionization mass spectrometry (SIMS or TIMS) analyses of stable isotope compositions. Such details are poorly constrained by orbital data (e.g. phyllosilicate formation at Mawrth Vallis), and incompletely described by in situ measurements (e.g. genesis of Burns formation sediments at Meridiani Planum). Laboratory studies can determine formation, metamorphism and/or alteration ages of samples through SIMS or TIMS of radiogenic isotope systems; a capability well-beyond flight instrumentation. Ideally, sample return should be from a location first scouted by landers such that fairly mature hypotheses have been formulated that can be tested. However, samples from clastic sediments derived from an extensive region of Mars can provide important, detailed understanding of early martian geological and climatological history. Interrogating clastic "sediments" from the Earth, Moon and asteroids has allowed discovery of new crustal units, identification of now-vanished crust, and determination of the geological history of extensive, remote regions. Returned sample of martian fluvial and/or aeolian sediments, for example from Gale crater, could be "read like a book" in terrestrial laboratories to provide truly revolutionary new insights into early martian geological and climatological evolution.

Oxygen microprofiles within the sediment-water interface studied by optode and its implication for aeration of polluted urban rivers.

PubMed

Liu, Bo; Han, Rui-Ming; Wang, Wen-Lin; Yao, Hong; Zhou, Feng

2017-04-01

To reveal the detailed vertical oxygen distribution at the sediment-water interface (SWI) and its relation with the oxygen consumption processes during and after aeration of polluted urban rivers, experimental systems constructed with collected sediment and in situ overlying water from a polluted urban river were aerated above or beneath the sediment-water interface 12 h a day for 15 days and left nonaerated for the following 10 days. The results showed that aeration of water or sediment both increased dissolved oxygen (DO) concentrations in the SWI, characterized by shifts in a "decrease-increase-decrease" manner during around 3 h for the aeration of water treatment (AW) and 6 h for the aeration of sediment treatment (AS). The oxygen penetration depth for AS experiments was between 0.66 and 4.16 mm with an average of 1.79 mm, significantly higher than that for AW experiments; however, the oxygen dissipation constant (mm -1 ) measuring the decay rate of DO near the SWI was greater for the AW experiments than the AS experiments. During the 10-day nonaeration period, the accumulation of nitrate in both the overlying water and sediment was greatly increased concomitantly with the higher oxygenation in AS experiments. From the nitrogen removal viewpoint, these results suggest that the SWI needs moderate oxygenation which enables nitrate and nitrite to be removed by denitrification rather than to be totally nitrified and accumulate as would result from the conventional practice by singly elevating DO concentrations.

Verifying Food Web Bioaccumulation Models by Tracking Fish Exposure and Contaminant Uptake

DTIC Science & Technology

2012-03-01

Arnot, J. A. and F. A. P. C. Gobas (2004). "A Food Web Bioaccumulation Model for Organic Chemicals in Aquatic Ecosystems." Environmental Toxicology...site in Eagle Harbor, Washington." Aquatic Toxicology 88: 277-288. Myers, M. S., L. L. Johnson, et al. (2003). "Establishing the Causal Relationship...P. Connolly, et al. (1992). "An Equilibrium Model of Organic Chemical Accumulation in Aquatic Food Webs with Sediment Interaction." Environmental

Lack of Evidence for Onshore Sediment Transport from Deep Water at Decadal Time Scales: Fire Island, New York

DTIC Science & Technology

2011-01-01

the net volume change within the cell.  Qsource includes net longshore transport, net onshore transport, and contributions from bluff or dune erosion...in restoration of the downcoast beach at Westhampton Dunes (Daley et al., 2000; Terchunian and Merkert, 1994) and after the Westhampton groin...nourishment, backshore dune erosion added to the control volume, and overwash losses out of the control volume or losses due to equilibrium profile

Problem-based test: replication of mitochondrial DNA during the cell cycle.

PubMed

Sétáló, György

2013-01-01

Terms to be familiar with before you start to solve the test: cell cycle, generation time, S-phase, cell culture synchronization, isotopic pulse-chase labeling, density labeling, equilibrium density-gradient centrifugation, buoyant density, rate-zonal centrifugation, nucleoside, nucleotide, kinase enzymes, polymerization of nucleic acids, re-replication block, cell fractionation, Svedberg (sedimentation constant = [ S]), nuclear DNA, mitochondrial DNA, heavy and light mitochondrial DNA chains, heteroplasmy, mitochondrial diseases Copyright © 2013 Wiley Periodicals, Inc.

Non-Equilibrium Sediment Transport Modeling - Extensions and Applications

DTIC Science & Technology

2013-01-01

which considers the bed slope effect but can be lumped in the Manning’s n coefficient.      2 2 2 1/3 1 2 s b t t Uh U h UVh t x y z n m UUU U...n m UUU U h h gh gh g x x y y x x h C C C UhC m q U h h x x y y p L

Study on the stability control strategy of Triphala solution based on the balance of physical stability and chemical stabilities.

PubMed

Huang, Hao-Zhou; Zhao, Sheng-Yu; Ke, Xiu-Mei; Lin, Jun-Zhi; Huang, Shu-Sen; Xu, Run-Chun; Ma, Hong-Yan; Zhang, Yi; Han, Li; Zhang, Ding-Kun

2018-06-04

Triphala is a well-known prescription in Indian Ayurveda and TCM medicine for its great effect on gingivitis and hyperlipidemia. However, its solution is unstable for the containing of excessive polyphenol, leading to the production of sediment in the short term and the decrease of efficacy. Based on the analysis of sediment formation, a novel control strategy is proposed. To conduct the analysis, the sediment formation was recorded for a consecutive five days. The changes in the composition of the supernatant and the sediment were studied by the HPLC profile analysis. The main components of the sediment were identified as corilagin, ellagic acid and gallic acid, and the amount of ellagic acid sediment increased with the storage time. Then, with a series of pH status adjustments of the Triphala solution, the physical and chemical stabilities were acquired by Turbiscan and HPLC respectively. The results showed that as the pH value increased, so did the physical stability, but the particle size and TSI of the association decreased. While the fingerprint of chemical profile similarity decreased, so did the chemical stability. Combining physical and chemical stability parameters, an equilibrium point was found out. When the pH value was adjusted to 5.0, both the physical and chemical stabilities were better: the verification test showed that the sedimentation inhibition rates on the 3rd, 5th,10th and15th days were 41%, 55%, 41%, and 23%, respectively. This manuscript provided a new control strategy that will pique pharmaceutical and food development engineers' interest and trigger research ideas controlling the quality of decoction. Copyright © 2018 Elsevier B.V. All rights reserved.

Advective removal of intraparticle uranium from contaminated vadose zone sediments, Hanford, U.S.

PubMed

Ilton, Eugene S; Qafoku, Nikolla P; Liu, Chongxuan; Moore, Dean A; Zachara, John M

2008-03-01

A column study on U(VI)-contaminated vadose zone sediments from the Hanford Site, WA, was performed to investigate U(VI) release kinetics with water advection and variable geochemical conditions. The sediments were collected from an area adjacent to and below tank BX-102 that was contaminated as a result of a radioactive tank waste overfill event. The primary reservoir for U(VI) in the sediments are micrometer-size precipitates composed of nanocrystallite aggregates of a Na-U-Silicate phase, most likely Na-boltwoodite, that nucleated and grew within microfractures of the plagioclase component of sand-sized granitic clasts. Two sediment samples, with different U(VI) concentrations and intraparticle mass transfer properties, were leached with advective flows of three different solutions. The influent solutions were all calcite-saturated and in equilibrium with atmospheric CO2. One solution was prepared from DI water, the second was a synthetic groundwater (SGW) with elevated Na that mimicked groundwater at the Hanford site, and the third was the same SGW but with both elevated Na and Si. The latter two solutions were employed, in part, to test the effect of saturation state on U(VI) release. For both sediments, and all three electrolytes, there was an initial rapid release of U(VI) to the advecting solution followed by slower near steady-state release. U(VI)aq concentrations increased during subsequent stop-flow events. The electrolytes with elevated Na and Si depressed U(VL)aq concentrations in effluent solutions. Effluent U(VI)aq concentrations for both sediments and all three electrolytes were simulated reasonably well by a three domain model (the advecting fluid, fractures, and matrix) that coupled U(VI) dissolution, intraparticle U(VI)aq diffusion, and interparticle advection, where diffusion and dissolution properties were parameterized in a previous batch study.

Uranium series isotopes concentration in sediments at San Marcos and Luis L. Leon reservoirs, Chihuahua, Mexico

DOE Office of Scientific and Technical Information (OSTI.GOV)

Méndez-García, C.; Montero-Cabrera, M. E., E-mail: elena.montero@cimav.edu.mx; Renteria-Villalobos, M.

2008-01-01

Spatial and temporal distribution of the radioisotopes concentrations were determined in sediments near the surface and core samples extracted from two reservoirs located in an arid region close to Chihuahua City, Mexico. At San Marcos reservoir one core was studied, while from Luis L. Leon reservoir one core from the entrance and another one close to the wall were investigated. ²³²Th-series, ²³⁸U-series, ⁴⁰K and ¹³⁷Cs activity concentrations (AC, Bq kg⁻¹) were determined by gamma spectrometry with a high purity Ge detector. ²³⁸U and ²³⁴U ACs were obtained by liquid scintillation and alpha spectrometry with a surface barrier detector. Dating ofmore » core sediments was performed applying CRS method to ²¹⁰Pb activities. Results were verified by ¹³⁷Cs AC. Resulting activity concentrations were compared among corresponding surface and core sediments. High ²³⁸U-series AC values were found in sediments from San Marcos reservoir, because this site is located close to the Victorino uranium deposit. Low AC values found in Luis L. Leon reservoir suggest that the uranium present in the source of the Sacramento – Chuviscar Rivers is not transported up to the Conchos River. Activity ratios (AR) ²³⁴U/²³⁸U and ²³⁸U/²²⁶Ra in sediments have values between 0.9–1.2, showing a behavior close to radioactive equilibrium in the entire basin. ²³²Th/²³⁸U, ²²⁸Ra/²²⁶Ra ARs are witnesses of the different geological origin of sediments from San Marcos and Luis L. Leon reservoirs.« less

Sensitivity analysis of non-cohesive sediment transport formulae

NASA Astrophysics Data System (ADS)

Pinto, Lígia; Fortunato, André B.; Freire, Paula

2006-10-01

Sand transport models are often based on semi-empirical equilibrium transport formulae that relate sediment fluxes to physical properties such as velocity, depth and characteristic sediment grain sizes. In engineering applications, errors in these physical properties affect the accuracy of the sediment fluxes. The present analysis quantifies error propagation from the input physical properties to the sediment fluxes, determines which ones control the final errors, and provides insight into the relative strengths, weaknesses and limitations of four total load formulae (Ackers and White, Engelund and Hansen, van Rijn, and Karim and Kennedy) and one bed load formulation (van Rijn). The various sources of uncertainty are first investigated individually, in order to pinpoint the key physical properties that control the errors. Since the strong non-linearity of most sand transport formulae precludes analytical approaches, a Monte Carlo method is validated and used in the analysis. Results show that the accuracy in total sediment transport evaluations is mainly determined by errors in the current velocity and in the sediment median grain size. For the bed load transport using the van Rijn formula, errors in the current velocity alone control the final accuracy. In a final set of tests, all physical properties are allowed to vary simultaneously in order to analyze the combined effect of errors. The combined effect of errors in all the physical properties is then compared to an estimate of the errors due to the intrinsic limitations of the formulae. Results show that errors in the physical properties can be dominant for typical uncertainties associated with these properties, particularly for small depths. A comparison between the various formulae reveals that the van Rijn formula is more sensitive to basic physical properties. Hence, it should only be used when physical properties are known with precision.

Evaluation of lead concentration by one-box type multimedia model in Lake Biwa-Yodo River basin of Japan.

PubMed

Kondo, Akira; Yamamoto, Megumi; Inoue, Yoshio; Ariyadasa, B H A K T

2013-07-01

A one box type multimedia model was developed and applied for Lake Biwa-Yodo River basin in Japan to assess the distribution of lead in the environment. This model is based on mass balance and includes four environmental media; the atmosphere, the soil, the water body, and the sediment. The mass balance of lead is represented by the summation of mass transfer flux at equilibrium, emission flux, advection flux, and deposition flux or sedimentation flux. In the case of metallic compounds, dissolution rate and exchange equilibrium have also been taken into consideration. Pollutant Release and Transfer Registry (PRTR) in Japan was used as one of the major data source for this study. The emission of lead in Lake Biwa-Yodo River basin is calculated based on five sources of registered emission in PRTR, unregistered emission in PRTR, incinerators, leaded gasoline, and landfills. In this study, we estimated lead emission from 1957 to 2007 to observe the temporal accumulation of lead. Calculated lead concentrations were compared with the measured/observed concentrations. It was found out that the model could closely predict lead concentration in the soil and the water body. The concentration in the atmosphere was underestimated by the calculated concentrations. The reason was attributed to the underestimation of the amount of lead emission from incinerators. Copyright © 2013 Elsevier Ltd. All rights reserved.

Structural instability, multiple stable states, and hysteresis in periphyton driven by phosphorus enrichment in the Everglades

USGS Publications Warehouse

Dong, Quan; McCormick, Paul V.; Sklar, Fred H.; DeAngelis, Donald L.

2002-01-01

Periphyton is a key component of the Everglades ecosystems. It is a major primary producer, providing food and habitat for a variety of organisms, contributing material to the surface soil, and regulating water chemistry. Periphyton is sensitive to the phosphorus (P) supply and P enrichment has caused dramatic changes in the native Everglades periphyton assemblages. Periphyton also affects P availability by removing P from the water column and depositing a refractory portion into sediment. A quantitative understanding of the response of periphyton assemblages to P supply and its effects on P cycling could provide critical supports to decision making in the conservation and restoration of the Everglades. We constructed a model to examine the interaction between periphyton and P dynamics. The model contains two differential equations: P uptake and periphyton growth are assumed to follow the Monod equation and are limited by a modified logistic equation. Equilibrium and stability analyses suggest that P loading is the driving force and determines the system behavior. The position and number of steady states and the stability also depend upon the rate of sloughing, through which periphyton deposits refractory P into sediment. Multiple equilibria may exist, with two stable equilibria separated by an unstable equilibrium. Due to nonlinear interplay of periphyton and P in this model, catastrophe and hysteresis are likely to occur.

ISTA 14-in-situ accumulation of PAHs in low-density polyethylene membranes in sediment.

PubMed

Devault, Damien A; Combe, Matthieu; Gourlay-Francé, Catherine

2010-10-01

The use of passive samplers for the assessment of organic contaminants has been extended to solid matrixes for the past decade. Passive sampling is usually applied to sediment in laboratory experiments involving significant upheaval, whereas in-situ experiments remain rare. In this study, low-density polyethylene (LDPE) strips were deployed within the sediments of a small river contaminated with polycyclic aromatic hydrocarbons (PAHs). LDPE strips were deployed in the 3-cm depth sediment layer. Over a period of 36 days, LDPE strips were regularly retrieved and accumulated PAHs in LDPE were extracted and analyzed. Accumulations of hydrophobic contaminants in LDPE directly exposed in the sediment were observed. Accumulations in LDPE were observed for moderately hydrophobic PAHs with the highest concentrations in the sediment. Low accumulations were observed for more hydrophobic compounds, despite their presence in high concentrations in the sediment. This was explained by very low exchange rates and competitive interactions with particles in the sediment. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2010.

Evaporation in equilibrium, in vacuum, and in hydrogen gas

NASA Technical Reports Server (NTRS)

Nagahara, Hiroko

1993-01-01

Evaporation experiments were conducted for SiO2 in three different conditions: in equilibrium, in vacuum, and in hydrogen gas. Evaporation rate in vacuum is about two orders of magnitude smaller than that in equilibrium, which is consistent with previous works. The rate in hydrogen gas changes depending on hydrogen pressure. The rate at 10 exp -7 bar of hydrogen pressure is as small as that of free evaporation, but at 10 exp -5 bar of hydrogen pressure it is larger than that in equilibrium. In equilibrium and in vacuum, the evaporation rate is limited by decomposition of SiO2 on the crystal surface, but it is limited by a diffusion process for evaporation in hydrogen gas. Therefore, evaporation rate of minerals in the solar nebula can be shown neither by that in equilibrium nor by that in vacuum. The maximum temperature of the solar nebula at the midplane at 2-3 AU where chondrites are believed to have originated is calculated to be as low as 150 K, 1500 K, or in between them. The temperature is, in any case, not high enough for total evaporation of the interstellar materials. Therefore, evaporation of interstellar materials is one of the most important processes for the origin and fractionation of solid materials. The fundamental process of evaporation of minerals has been intensively studied for these several years. Those experiments were carried out either in equilibrium or in vacuum; however, evaporation in the solar nebula is in hydrogen (and much smaller amount of helium) gas. In order to investigate evaporation rate and compositional (including isotopic) fractionation during evaporation, vaporization experiments for various minerals in various conditions are conducted. At first, SiO2 was adopted for a starting material, because thermochemical data and its nature of congruent vaporization are well known. Experiments were carried out in a vacuum furnace system.

Simulations in support of the T4B experiment

NASA Astrophysics Data System (ADS)

Qerushi, Artan; Ross, Patrick; Lohff, Chriss; Raymond, Anthony; Montecalvo, Niccolo

2017-10-01

Simulations in support of the T4B experiment are presented. These include a Grad-Shafranov equilibrium solver and equilibrium reconstruction from flux-loop measurements, collision radiative models for plasma spectroscopy (determination of electron density and temperature from line ratios) and fast ion test particle codes for neutral beam - plasma coupling. ©2017 Lockheed Martin Corporation. All Rights Reserved.

Instantaneous charge state of uranium projectiles in fully ionized plasmas from energy loss experiments

NASA Astrophysics Data System (ADS)

Morales, Roberto; Barriga-Carrasco, Manuel D.; Casas, David

2017-04-01

The instantaneous charge state of uranium ions traveling through a fully ionized hydrogen plasma has been theoretically studied and compared with one of the first energy loss experiments in plasmas, carried out at GSI-Darmstadt by Hoffmann et al. in the 1990s. For this purpose, two different methods to estimate the instantaneous charge state of the projectile have been employed: (1) rate equations using ionization and recombination cross sections and (2) equilibrium charge state formulas for plasmas. Also, the equilibrium charge state has been obtained using these ionization and recombination cross sections and compared with the former equilibrium formulas. The equilibrium charge state of projectiles in plasmas is not always reached, and it depends mainly on the projectile velocity and the plasma density. Therefore, a non-equilibrium or an instantaneous description of the projectile charge is necessary. The charge state of projectile ions cannot be measured, except after exiting the target, and experimental data remain very scarce. Thus, the validity of our charge state model is checked by comparing the theoretical predictions with an energy loss experiment, as the energy loss has a generally quadratic dependence on the projectile charge state. The dielectric formalism has been used to calculate the plasma stopping power including the Brandt-Kitagawa (BK) model to describe the charge distribution of the projectile. In this charge distribution, the instantaneous number of bound electrons instead of the equilibrium number has been taken into account. Comparing our theoretical predictions with experiments, it is shown the necessity of including the instantaneous charge state and the BK charge distribution for a correct energy loss estimation. The results also show that the initial charge state has a strong influence in order to estimate the energy loss of the uranium ions.

Metal/silicate partitioning of Pt and the origin of the "late veneer"

NASA Astrophysics Data System (ADS)

Ertel, W.; Walter, M. J.; Drake, M. J.; Sylvester, P. J.

2002-12-01

Highly siderophile elements (HSEs) are perfect tools for investigating core forming processes in planetary bodies due to their Fe-loving (siderophile) geochemical behavior. Tremendous scientific effort was invested into this field during the past 10 years - mostly in 1 atm experiments. However, little is known about their high-pressure geochemistry and partitioning behavior between core and mantle forming phases. This knowledge is essential to distinguish between equilibrium (Magma Ocean) and non-equilibrium (heterogeneous accretion, late veneer) models for the accretion history for the early Earth. We therefore chose to investigate the partitioning behavior of Pt up to pressures of 140 kbar (14 GPa) and temperatures of 1950°C. The used melt composition - identical to melt systems used in 1 atm experiments - is the eutectic composition of Anorthite-Diopside (AnDi), a pseudo-basalt. A series of runs were performed which were internaly buffered by the piston cylinder apparatus, and were followed by duplicate experiments buffered in the AnDi-C-CO2 system. These experiments constitute reversals since they approach equilibrium from an initially higher and lower Pt solubility (8 ppm in the non-buffered runs, and essentially Pt free in the buffered runs). Experimental charges were encapsulated in Pt capsules which served as source for Pt. Experiments up to 20 kbar were performed in a Quickpress piston cylinder apparatus, while experiments at higher pressures were performed in a Walker-type (Tucson, AZ) and a Kawai-type (Misasa, Japan) multi anvil apparatus. Time series experiments were performed in piston-cylinder runs to determine minimum run durations for the achievement of equilibrium, and to guarantee high-quality partitioning data. 6 hours was found to be sufficient to obtain equilibrium. In practice, all experiments exceeded 12 hours to assure equilibrium. In a second set of runs the temperature dependence of the partitioning behavior of Pt was investigated between the melting point of the 1 atm, AnDi system and the melting point of the Pt capsule material. Over 150 piston cylinder and 12 multi anvil experiments have been performed. Pt solubility is only slightly dependent on temperature, decreasing between 1800 and 1400°C by less than an order of magnitude. In consequence, the partitioning behavior of Pt is mostly determined by its oxygen fugacity dependence, which has only been determined in 1 atm experiments. At 10 kbar, metal/silicate partition coefficients (D's) decrease by about 3 orders of magnitude. The reason for this is not understood, but might be attributed to a first order phase transition as found for, e.g., SiO2 or H2O. Above 10 kbar any increase in pressure does not lead to any further significant decrease in partition coefficients. Solubilities stay roughly constant up to 140 kbar. Abundances of moderately siderophile elements were possibly established by metal/silicate equilibrium in a magma ocean. These results for Pt suggest that the abundances of HSEs were most probably established by the accretion of a chondritic veneer following core formation, as metal/silicate partition coefficients are too high to be consistent with metal/silicate equilibrium in a magma ocean.

Adsorption laboratory experiment for undergraduate chemical engineering: Introducing kinetic, equilibrium and thermodynamic concepts

NASA Astrophysics Data System (ADS)

Muryanto, S.; Djatmiko Hadi, S.

2016-11-01

Adsorption laboratory experiment for undergraduate chemical engineering program is discussed. The experiment demonstrated adsorption of copper ions commonly found in wastewater using bio-sorbent, i.e. agricultural wastes. The adsorption was performed in a batch mode under various parameters: adsorption time (up to 120 min), initial pH (2 to 6), adsorbent dose (2.0 to 12.0 g L-1), adsorbent size (50 to 170 mesh), initial Cu2+ concentration (25 to 100 ppm) and temperatures (room temp to 40°C). The equilibrium and kinetic data of the experiments were calculated using the two commonly used isotherms: Langmuir and Lagergren pseudo-first-order kinetics. The maximum adsorption capacity for Cu2+ was found as 94.34 mg g-1. Thermodynamically, the adsorption process was spontaneous and endothermic. The calculated activation energy for the adsorption was observed as high as 127.94 kJ mol-1. Pedagogically, the experiment was assumed to be important in increasing student understanding of kinetic, equilibrium and thermodynamic concepts.

Toxicity of lead-contaminated sediment to mallards

USGS Publications Warehouse

Heinz, G.H.; Hoffman, D.J.; Sileo, L.; Audet, D.J.; LeCaptain, L.J.

1999-01-01

Because consumption of lead-contaminated sediment has been suspected as the cause of waterfowl mortality in the Coeur d?Alene River basin in Idaho, we studied the bioavailability and toxicity of this sediment to mallards (Anas platyrhynchos). In experiment 1, one of 10 adult male mallards died when fed a pelleted commercial duck diet that contained 24% lead-contaminated sediment (with 3,400 μg/g lead in the sediment). Protoporphyrin levels in the blood increased as the percentage of lead-contaminated sediment in the diet increased. Birds fed 24% lead-contaminated sediment exhibited atrophy of the breast muscles, green staining of the feathers around the vent, viscous bile, green staining of the gizzard lining, and renal tubular intranuclear inclusion bodies. Mallards fed 24% lead-contaminated sediment had means of 6.1 μg/g of lead in the blood and 28 μg/g in the liver (wet-weight basis) and 1,660 μg/g in the feces (dry-weight basis). In experiment 2, we raised the dietary concentration of the lead-contaminated sediment to 48%, but only about 20% sediment was actually ingested due to food washing by the birds. Protoporphyrin levels were elevated in the lead-exposed birds, and all of the mallards fed 48% lead-contaminated sediment had renal tubular intranuclear inclusion bodies. The concentrations of lead in the liver were 9.1 μg/g for mallards fed 24% lead-contaminated sediment and 16 μg/g for mallards fed 48% lead-contaminated sediment. In experiment 3, four of five mallards died when fed a ground corn diet containing 24% lead-contaminated sediment (with 4,000 μg/g lead in this sample of sediment), but none died when the 24% lead-contaminated sediment was mixed into a nutritionally balanced commercial duck diet; estimated actual ingestion rates for sediment were 14% and 17% for the corn and commercial diets. Lead exposure caused elevations in protoporphyrin, and four of the five mallards fed 24% lead-contaminated sediment in a commercial diet and all five fed the contaminated sediment in a corn diet had renal intranuclear inclusion bodies. Lead was higher in the livers of mallards fed 24% lead-contaminated sediment in the corn diet (38 μg/g) than in the commercial diet (13 μg/g).

Direct sampling during multiple sediment density flows reveals dynamic sediment transport and depositional environment in Monterey submarine canyon

NASA Astrophysics Data System (ADS)

Maier, K. L.; Gales, J. A.; Paull, C. K.; Gwiazda, R.; Rosenberger, K. J.; McGann, M.; Lundsten, E. M.; Anderson, K.; Talling, P.; Xu, J.; Parsons, D. R.; Barry, J.; Simmons, S.; Clare, M. A.; Carvajal, C.; Wolfson-Schwehr, M.; Sumner, E.; Cartigny, M.

2017-12-01

Sediment density flows were directly sampled with a coupled sediment trap-ADCP-instrument mooring array to evaluate the character and frequency of turbidity current events through Monterey Canyon, offshore California. This novel experiment aimed to provide links between globally significant sediment density flow processes and their resulting deposits. Eight to ten Anderson sediment traps were repeatedly deployed at 10 to 300 meters above the seafloor on six moorings anchored at 290 to 1850 meters water depth in the Monterey Canyon axial channel during 6-month deployments (October 2015 - April 2017). Anderson sediment traps include a funnel and intervalometer (discs released at set time intervals) above a meter-long tube, which preserves fine-scale stratigraphy and chronology. Photographs, multi-sensor logs, CT scans, and grain size analyses reveal layers from multiple sediment density flow events that carried sediment ranging from fine sand to granules. More sediment accumulation from sediment density flows, and from between flows, occurred in the upper canyon ( 300 - 800 m water depth) compared to the lower canyon ( 1300 - 1850 m water depth). Sediment accumulated in the traps during sediment density flows is sandy and becomes finer down-canyon. In the lower canyon where sediment directly sampled from density flows are clearly distinguished within the trap tubes, sands have sharp basal contacts, normal grading, and muddy tops that exhibit late-stage pulses. In at least two of the sediment density flows, the simultaneous low velocity and high backscatter measured by the ADCPs suggest that the trap only captured the collapsing end of a sediment density flow event. In the upper canyon, accumulation between sediment density flow events is twice as fast compared to the lower canyon; it is characterized by sub-cm-scale layers in muddy sediment that appear to have accumulated with daily to sub-daily frequency, likely related to known internal tidal dynamics also measured in the experiment. The comprehensive scale of the Monterey Coordinated Canyon Experiment allows us to integrate sediment traps with ADCP instrument data and seafloor core samples, which provides important new data to constrain how, when, and what sediment is transported through submarine canyons and how this is archived in seafloor deposits.

Laboratory experiments on dam-break flow of water-sediment mixtures

USDA-ARS?s Scientific Manuscript database

Dams induce sedimentation and store significant amounts of sediment as they age; therefore, dam failures often involve the release of sediment-laden water to the downstream floodplain. In particular, tailings dams, which are constructed to impound mining wastes, can cause devastating damage when the...

The distribution of triclosan and methyl-triclosan in marine sediments of Barker Inlet, South Australia.

PubMed

Fernandes, Milena; Shareef, Ali; Kookana, Rai; Gaylard, Sam; Hoare, Sonja; Kildea, Tim

2011-04-01

In this work, we investigated the transport and burial of triclosan and its methylated derivative, in surface sediments near the mouth of Barker Inlet in South Australia. The most likely source of this commonly used bactericide to the area is a wastewater outfall discharging at the confluence of the inlet with marine waters. Triclosan was detected in all samples, at concentrations (5-27 μg kg(-1)) comparable to values found in other surface sediments under the influence of marine wastewater outfalls. Its dispersal was closely associated with fine and organic-rich fractions of the sediments. Methyl-triclosan was detected in approximately half of the samples at concentrations <11 μg kg(-1). The occurrence of this compound was linked to both wastewater discharges and biological methylation of the parent compound. Wastewater-borne methyl-triclosan had a smaller spatial footprint than triclosan and was mostly deposited in close proximity to the outfall. In situ methylation of triclosan likely occurs at deeper depositional sites, whereas the absence of methyl-triclosan from shallower sediments was potentially explained by photodegradation of the parent compound. Based on partition equilibrium, a concentration of triclosan in the order of 1 μg L(-1) was estimated in sediment porewaters, a value lower than the threshold reported for harmful effects to occur in the couple of species of marine phytoplankton investigated to date. Methyl-triclosan presents a greater potential for bioaccumulation than triclosan, but the implications of its occurrence to aquatic ecosystem health are difficult to predict given the lack of ecotoxicological data in the current literature.

Sediment supply controls equilibrium channel geometry in gravel rivers

PubMed Central

Finnegan, Noah J.; Willenbring, Jane K.

2017-01-01

In many gravel-bedded rivers, floods that fill the channel banks create just enough shear stress to move the median-sized gravel particles on the bed surface (D50). Because this observation is common and is supported by theory, the coincidence of bankfull flow and the incipient motion of D50 has become a commonly used assumption. However, not all natural gravel channels actually conform to this simple relationship; some channels maintain bankfull stresses far in excess of the critical stress required to initiate sediment transport. We use a database of >300 gravel-bedded rivers and >600 10Be-derived erosion rates from across North America to explore the hypothesis that sediment supply drives the magnitude of bankfull shear stress relative to the critical stress required to mobilize the median bed surface grain size (τbf*/τc*). We find that τbf*/τc* is significantly higher in West Coast river reaches (2.35, n = 96) than in river reaches elsewhere on the continent (1.03, n = 245). This pattern parallels patterns in erosion rates (and hence sediment supplies). Supporting our hypothesis, we find a significant correlation between upstream erosion rate and local τbf*/τc* at sites where this comparison is possible. Our analysis reveals a decrease in bed surface armoring with increasing τbf*/τc*, suggesting channels accommodate changes in sediment supply through adjustments in bed surface grain size, as also shown through numerical modeling. Our findings demonstrate that sediment supply is encoded in the bankfull hydraulic geometry of gravel bedded channels through its control on bed surface grain size. PMID:28289212

The influence of environmental conditions on lead transfer from spent gunshot to sediments and water: Other routes for Pb poisoning.

PubMed

Binkowski, Łukasz J

2017-11-01

Lead (Pb) from spent gunshot and fishing sinkers is recognized as the main source of Pb poisoning among waterfowl. It is also suspected to directly pollute water and sediments, but no appropriate, comprehensive evaluation of this issue has so far been carried out. An experiment on Pb pellets in microcosms (n = 160) with two sediment types (mud and gravel), three water pH values (4, 7 and 9) and two wind levels (wind and windless simulation) was therefore run. Substantial differences in Pb transfer (measured with ICP-OES) between sediment types and pH levels of water were observed. Simulated wind conditions were a significant factor only for some variables and circumstances. The strongest Pb deposit to water and sediments occurred in mud microcosms with water of pH value of 4. Median pellet erosion during the experiment differed little between sediment types. The experiment revealed that Pb transfer from spent gunshot to the environment occurs only in specific environmental conditions. Copyright © 2017 Elsevier Ltd. All rights reserved.

Response of crayfish to hyporheic water availability and excess sedimentation

USGS Publications Warehouse

Dyer, Joseph J.; Worthington, Thomas A.; Brewer, Shannon K.

2015-01-01

Crayfish in many headwater streams regularly cope with seasonal drought. However, it is unclear how landscape changes affect the long-term persistence of crayfish populations. We designed two laboratory experiments to investigate the acute effects of common landscape stressors on crayfish: water withdrawal and sedimentation. The first experiment tested the interaction among water withdrawals (four 24-h water reductions of 0, 15, 30, or 45 cm) and two substrate treatments (pebble and cobble) on the burrowing depth of crayfish. The second experiment evaluated the effects of excess fine sediment (three treatments of 0, 45, and 90% sediment) and substrate type (cobble and pebble) on crayfish burrowing depth. Crayfish were able to burrow deeper into the simulated hyporheic zone in cobble substrate when compared to pebble. Crayfish subjected to greater water withdrawals in the pebble treatment were not able to reach the simulated hyporheic zone. Excess fine sediment reduced the depth that crayfish burrowed, regardless of substrate type. Results from this study suggest excess fine sediment may reduce crayfish persistence, particularly when seeking refuge during prolonged dry conditions.

Chemical and biological availability of hydrocarbons in urban harbor sediments

USGS Publications Warehouse

LeBlanc, L.A.; Brownawell, Bruce J.

2002-01-01

The degradation of saturated and aromatic hydrocarbons was studied in batch slurry experiments conducted with field-aged sediments, highly impacted by hydrocarbon pollution. Experiments focused on examining the effects of desorption limitations to hydrocarbon mineralization and degradation. Degradation of PAH (e.g., naphthalene, fluorene, acenaphthene) and saturated hydrocarbons was examined in field-aged sediments collected from four sites in greater NY Harbor and western Long Island Sound. The sites were Rikers Island in far western Long Island Sound, Williamsburg Bridge in the East River, Shooters Island in the Arthur Kill, and the Kill Van Kull off Bayonne, New Jersey. Patterns of hydrocarbon desorption and degradation in weathered sediments were complicated by the mixed combustion and oil-derived hydrocarbon sources, and differed markedly from patterns seen in sediments following an oil spill. Rates of degradation in experiments with spiked sediments, especially over short timescales, did not appear to be limited by rates of desorption. This is an abstract of a paper presented at the 224th ACS National Meeting (Boston, MA 8/18-22/2002).

Vertical Transport of Sediment from Muddy Buoyant River Plumes in the Presence of Different Modes of Interfacial Instabilities

NASA Astrophysics Data System (ADS)

Strom, K.; Rouhnia, M.

2016-12-01

Previous studies have suggested that sedimentation from buoyant, muddy plumes lofting over clear saltwater can take place at rates higher than that expected from individual particle settling (i.e., CWs). Two potential drivers of enhanced sedimentation are flocculation and interfacial instabilities. We experimentally measured the sediment fluxes from each of these processes using two sets of laboratory experiments that investigate two different modes of instability, one driven by sediment settling and one driven by fluid shear. The settling-driven and shear-driven instability experiments were carried out in a stagnant stratification tank and a stratification flume respectively. In both sets, continuous interface monitoring and concentration measurements were made to observe developments of instabilities and their effects on the removal of sediment. Floc size was measured during the experiments using a floc camera and image analysis routines. This presentation will provide an overview of the stagnant tank experiments, but will focus on results from the stratified flume experiments and an analysis that attempts to synthesizes the results from the entirety of the study. The results from the stratified flume experiments show that under shear instabilities, the effective settling velocity is greater than the floc settling velocity, and that the rate increases with plume velocity and interface mixing. The difference between effective and floc settling velocity was denoted as the shear-induced settling velocity. This rate was found to be a strong function of the Richardson number, and was attributed to mixing processes at the interface. Conceptual and empirical analysis shows that the shear-induced settling velocity is proportional to URi-2. The resulting effective settling velocity models developed from these experiments are then used to examine the rates and potential locations of operations of these mechanism over the length of a river mouth plume.

Biofilms' contribution to organic carbon in salt marsh sediments

NASA Astrophysics Data System (ADS)

Valentine, K.; Quirk, T. E.; Mariotti, G.; Hotard, A.

2017-12-01

Coastal salt marshes are productive environments with high potential for carbon (C) accumulation. Organic C in salt marsh sediment is typically attributed to plant biomass. Recent field measurements, however, suggest that biofilms - mainly composed of benthic diatoms and their secretion - also contribute to basal C in these environments and can be important contributors to marsh productivity, C cycling, and potentially, C sequestration. The potential for biofilms to soil organic C and the influence of mineral sedimentation of biofilm-based C accumulation is unknown. We conducted controlled laboratory experiments to test (1) whether biofilms add measurable amounts of organic C to the sediment and (2) the effect of mineral sedimentation rate on the amount of biofilm-based C accumulation. Settled beds of pure bentonite mud were created in 10-cm-wide cylinders. Each cylinder was inoculated with biofilms collected from a marsh in Louisiana. A small amount of mud was added weekly for 11 weeks. Control experiments without biofilms were also performed. Biofilms were grown with a 12/12 hours cycle, with a gentle mixing of the water column that did not cause sediment resuspension, with a nutrient-rich medium that was exchanged weekly, and in the absence of metazoan grazing. At the end of the experiment, the sediment columns were analyzed for depth-integrated chl-a, loss on ignition (LOI), and total organic carbon (TOC). Chl-a values ranged from 26-113 mg/cm2, LOI values ranged from 86-456 g/m2/yr, and TOC values ranged from 31-211 g/m2/yr. All three of these metrics (chl-a, LOI, and TOC) increased with the rate of mineral sedimentation. These results show that biofilms, in the absence of erosion and grazing, can significantly contribute to C accumulation in salt marshes, especially with high rates of mineral sedimentation. Given the short time scale of the experiment, the increase in organic C accumulation with the rate of sedimentation is attributed to stimulated biofilm production rather than increased C preservation.

Sediment data for computations of deposition rates in the tidal Potomac system, Maryland and Virginia

DOE Office of Scientific and Technical Information (OSTI.GOV)

Glenn, J.L.; Martin, E.A.; Rice, C.A.

1986-01-01

Sixty-two cores ranging in length from 33 to 1,002 cm were collected from the tidal Potomac system and from selected tributaries downstream from the local head-of-tides between June 1978 and July 1981. Segments from selected depths below the sediment surface have been analyzed for a variety of constituents, including lead-210, trace metals, nutrients, and particle size. The core sites were positioned throughout the hydrologic divisions and geomorphic units of the tidal Potomac system and in water depths ranging from 1 to 30 cm. Alpha counting methods were used to determine the polonium-210 radioactivity and secular equilibrium was assumed between lead-210more » and polonium-210. The alpha decay of polonium-210 provides a measure of the lead-210 radioactivity of the lead-210 produced by in-situ decay of radium-226 in the sediment column and the lead-210 from external sources. Only the unsupported lead-210 was used in computations of the deposition rate. The background level of lead-210 in tidal Potomac system sediment cores usually is based on in-situ measurements of total lead-210 at depths below which no unsupported lead-210 is believed to be present, and the lead-210 concentrations are relatively constant. 6 refs., 3 figs., 1 tab.« less

The use of analytical sedimentation velocity to extract thermodynamic linkage.

PubMed

Cole, James L; Correia, John J; Stafford, Walter F

2011-11-01

For 25 years, the Gibbs Conference on Biothermodynamics has focused on the use of thermodynamics to extract information about the mechanism and regulation of biological processes. This includes the determination of equilibrium constants for macromolecular interactions by high precision physical measurements. These approaches further reveal thermodynamic linkages to ligand binding events. Analytical ultracentrifugation has been a fundamental technique in the determination of macromolecular reaction stoichiometry and energetics for 85 years. This approach is highly amenable to the extraction of thermodynamic couplings to small molecule binding in the overall reaction pathway. In the 1980s this approach was extended to the use of sedimentation velocity techniques, primarily by the analysis of tubulin-drug interactions by Na and Timasheff. This transport method necessarily incorporates the complexity of both hydrodynamic and thermodynamic nonideality. The advent of modern computational methods in the last 20 years has subsequently made the analysis of sedimentation velocity data for interacting systems more robust and rigorous. Here we review three examples where sedimentation velocity has been useful at extracting thermodynamic information about reaction stoichiometry and energetics. Approaches to extract linkage to small molecule binding and the influence of hydrodynamic nonideality are emphasized. These methods are shown to also apply to the collection of fluorescence data with the new Aviv FDS. Copyright © 2011 Elsevier B.V. All rights reserved.

The use of analytical sedimentation velocity to extract thermodynamic linkage

PubMed Central

Cole, James L.; Correia, John J.; Stafford, Walter F.

2011-01-01

For 25 years, the Gibbs Conference on Biothermodynamics has focused on the use of thermodynamics to extract information about the mechanism and regulation of biological processes. This includes the determination of equilibrium constants for macromolecular interactions by high precision physical measurements. These approaches further reveal thermodynamic linkages to ligand binding events. Analytical ultracentrifugation has been a fundamental technique in the determination of macromolecular reaction stoichiometry and energetics for 85 years. This approach is highly amenable to the extraction of thermodynamic couplings to small molecule binding in the overall reaction pathway. In the 1980’s this approach was extended to the use of sedimentation velocity techniques, primarily by the analysis of tubulin-drug interactions by Na and Timasheff. This transport method necessarily incorporates the complexity of both hydrodynamic and thermodynamic nonideality. The advent of modern computational methods in the last 20 years has subsequently made the analysis of sedimentation velocity data for interacting systems more robust and rigorous. Here we review three examples where sedimentation velocity has been useful at extracting thermodynamic information about reaction stoichiometry and energetics. Approaches to extract linkage to small molecule binding and the influence of hydrodynamic nonideality are emphasized. These methods are shown to also apply to the collection of fluorescence data with the new Aviv FDS. PMID:21703752

Assessment of the environmental fate and effects of azilsartan, a selective antagonist of angiotensin II type 1.

PubMed

Weltman, R; Brands, C M J; Corral, E; Desmares-Koopmans, M J E; Migchielsen, M H J; Oudhoff, K A; de Roode, D F

2012-06-01

In this paper the results of a thorough evaluation of the environmental fate and effects of azilsartan are presented. Azilsartan medoxomil is administered as a pro-drug for the treatment of patients with essential hypertension. The pro-drug is converted by hydrolysis to the active pharmaceutical ingredient azilsartan. Laboratory tests to evaluate the environmental fate and effects of azilsartan medoxomil were conducted with azilsartan and performed in accordance with OECD test guidelines. The predicted environmental concentration (PEC) in surface water was estimated at 0.32 μg L(-1) (above the action limit of 0.01 μg L(-1)), triggering a Phase II assessment. Azilsartan is not readily biodegradable. Results of the water sediment study demonstrated significant shifting of azilsartan metabolites to sediment. Based on the equilibrium partitioning method, metabolites are unlikely to pose a risk to sediment-dwelling organisms. Ratios of the predicted environmental concentrations (PECs) to the predicted-no-effect concentrations (PNECs) did not exceed the relevant triggers, and the risk to aquatic, sewage treatment plant (STP), groundwater and sediment compartments was concluded acceptable. A terrestrial assessment was not triggered. Azilsartan poses an acceptable risk to the environment. Copyright © 2012 Elsevier Ltd. All rights reserved.