Thesis (M.S.)--University of West Florida, 2006. / Title from title page of source document. Document formatted into pages; contains 104 pages. Includes bibliographical references.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 55-68). Also available via the Internet.

Due to sorption processes, sediments can retain a wide range of toxic substances, which are transported together with the sediment over long distances from the place of their origin. Dam reservoirs are significant sinks of such sediments and they can be indicative of the overall burden level in surface water of the basin. This thesis works with the assumption that sediments of a valley reservoir can help to estimate the sources and extent of water pollution in the area of interest. The aim of this thesis was to assess i) the level of contamination of bottom sediments in the Orlík reservoir with organic and inorganic pollutants, and ii) the potential impact of individual tributaries on the overall level of contamination of the sediments. In the literature review, the current level of knowledge in the topic of the total contents and speciation of toxic elements and specificities of the behavior of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in water, sediments and aquatic organisms was evaluated. The biological activity and eutrophication potential of sediments were discussed, as well. A total of 34 composite samples of bottom sediment collected in different parts of the Orlík reservoir and its major tributaries were evaluated. Bioavailability of major pollutants was also observed in individual tributaries based on their content in the tissues of mollusks. Atomic spectrometry revealed increased concentrations of As, Cd and Zn in sediments of the Orlík reservoir. Arsenic concentration limits were significantly exceeded at the bottom part of the reservoir from the confluence of the Otava and Vltava rivers toward the body of the dam. Higher level of cadmium and zinc were detected in sediments of the Otava River. The analysis of tissues of bivalves in tributary areas confirmed significant bioaccumulation ability of cadmium. Among others, significant dependence of phosphorus level on the total content of iron and aluminum in sediments was detected.

Determining accurate exposure estimates and subsequent risk of hydrophobic organic contaminants (HOCs) in aquatic sediments requires measuring the bioavailable and/or bioaccessible concentration in sediment; as total extractable concentrations have not been found to produce accurate results. Organic carbon normalization was originally proposed as a means of accounting for the bioavailable concentration by estimating the chemical activity of the contaminant expressed as the freely dissolved chemical concentration in the interstitial water, thus correcting exhaustive extractable concentrations for the sorbing phase of sediments. Organic carbon normalization often fails, however, to accurately reflect exposure as other environmental variables (i.e. organic carbon composition, aging time of contaminants in the environment) alter desorption, such that changes in chemical activity as represented by the interstitial water concentrations are not controlled by organic carbon alone. Desorption-based samplers, such as single-point Tenax extractions (SPTE), provide a clearer estimate of bioaccessibility than organic carbon normalization by serving as a sink for desorbing compound for the length of the extraction. In this way, SPTEs account for all the factors affecting desorption and the resulting interstitial water concentrations, providing estimates of the chemical concentration that will become available for exposure in a given time frame. The utility of SPTEs as an exposure metric has been demonstrated many times in the literature through estimates of bioaccumulation and development of toxicity benchmarks. The simplicity, accuracy, and robust nature of this technique suggests this tool could serve as an ideal means of evaluating exposure and risk of HOCs, and more specifically acutely toxic compounds, such as pyrethroids, during environmental sampling and risk assessments of aquatic sediments. However, the use of this method is limited within the scientific literature and absent from most risk assessment protocols. The reasons for its limited use are linked to poor methodological standardization, an absence of understanding of environmental and methodological variation on estimates of bioaccessibility provided by SPTEs, and only a vague idea of how Tenax extractions relate to other exposure metrics, such as passive samplers. Therefore, the dissertation goals were to: evaluate the effects of variation in the SPTE, specifically the Tenax mass to organic carbon mass (Tenax:OC) ratio, on exposure estimates of pyrethroids (Chapter Two); understand how methodological and environmental variation affect the relation of SPTEs to bioaccessibility represented by desorption of pyrethroids from the labile desorbing fraction (Frap) (Chapter Three); and, determine how bioavailability and bioaccessibility are linked through evaluation of chemical activity expressed as the freely dissolved chemical concentrations provided by SPTEs, passive sampler concentrations, and Frap (Chapter Four). The most variable aspect of the SPTE within the Tenax literature is the Tenax:OC ratio used during 24 h SPTEs. Yet, no study has evaluated how altering this ratio may affect 24 h SPTE concentrations and thus, biological exposure estimates provided by Tenax extractions. Manipulating the Tenax:OC ratio used during 24 h SPTEs of pyrethroids from laboratory-spiked and field-contaminated sediments revealed the effect of this variation was such that Tenax extractable pyrethroid concentrations varied between 0.85 to 3.91-fold between the highest and lowest ratios examined. The results of this experiment suggest most of the variation in toxicological endpoints derived using Tenax extractable concentrations is due to toxicokinetic and toxicodynamic variation in biological responses across sediments and not due to methodological variation of the Tenax extraction (Chapter Two). The utility of the SPTEs as an estimate of exposure is linked to the ability of SPTEs to reflect the chemical concentration that desorbs from sediment. As many factors, such as the organic carbon content, aging time of sediments, and hydrophobicity of the compounds, can impact desorption, understanding how these factors affect the relationship of SPTEs to biological exposure is needed to evaluate the consistency of the Tenax extraction. The relation of SPTE concentrations to Frap was proportional despite changes in organic carbon content of the sediment being extracted, the hydrophobicity of the pyrethroids, or the Tenax mass used during the extraction, such that the SPTE concentration was equal to 1.46 ± 0.03 times the pyrethroid concentration in Frap (Chapter Three). Only the aging time of the pyrethroids in the sediment significantly affected this relationship, as desorption from longer aged sediments slowed, reducing the 24 h SPTE concentration to Frap ratio by -0.0027/d (Chapter Three). The results of Chapters Two and Three demonstrate the consistency of the Tenax extraction as a representation of biological exposure of pyrethroids in sediment. However, other aspects limit the widespread use of the Tenax method, particularly the relation of this technique to more widely accepted bioavailability-based metrics, such as passives samplers. Tenax extractions are often disregarded in favor of passive samplers as the link between bioavailability-based metrics, chemical activity, and exposure is well understood. However, as SPTEs and passive samplers both demonstrate a clear relation to bioaccessibility through estimates of Frap, it was hypothesized that both exposure metrics represent the same chemical fraction of sediment, and as such could be considered complementary tools for evaluating biological exposure through estimates of the freely dissolved interstitial water concentration. This was confirmed when comparisons of the chemical activity expressed as the interstitial water concentration at equilibrium were done using the chemical concentration estimated by Frap, a passive sampler, and SPTEs. Strong linear relationships (p<0.0001) were found among all three metrics, such that Frap, passive sampler, or 24 h SPTE concentrations of pyrethroids from sediment provide comparable estimates of the freely dissolved interstitial water concentration in sediment. Thus, Tenax extractions and passive samplers, which describe the bioaccessible and bioavailable concentrations, respectively, describe the same chemical fraction in sediment; the labile desorbing fraction. This dissertation provides further concrete evidence that the SPTE offers a robust, rapid, and cost-effective means of evaluating exposure of acutely toxic compounds in sediment. With data that link this exposure metric to more widely accepted methods, such as passive samplers, and demonstrate the robust character of the SPTE, the research presented here should further the use of the SPTE within the scientific and risk assessment communities.

No description available.

This thesis work was directed at aspects of two related problems: (1) sediment compaction and fluid expulsion processes in a subduction margin accretionary prism, and (2) the nature and concentration of gas hydrates that form bottom-simulating reflectors (BSRs) observed in the accretionary prism sediments of the northern Cascadia margin. The formation of the gas hydrate and the occurrence of BSRs in the study area are believed to be mainly a consequence of upward fluid expulsion in the accretionary prism. Therefore, the two study objectives are closely correlated. Most of this thesis work was carried out analyzing multichannel seismic data and incorporating available information including downhole and other geophysical measurements. Seismic techniques, such as velocity analysis, forward modelling, and waveform velocity inversion, were used in analyzing the data to advance our understanding of the tectonic and geophysical processes in a dynamic accretionary prism environment. The velocity structure and the inferred porosity variations across the frontal region of the accretionary prism have been quantitatively assessed by a detailed seismic velocity analysis. Within the Cascadia basin sediments approaching the deformation front, and within the frontal thrust zone of the accretionary prism, seismic velocities increase landward as a result of sediment consolidation. An important conclusion is that more than one third of the pore fluid content of the incoming sediment is lost by the time they are incorporated into the accretionary prism. In the lower slope region of the deformation front, a pronounced velocity decrease is evident. This low-velocity zone is explained by underconsolidation resulting from rapid horizontal shortening and vertical thickening of the sediment column, accommodated by displacements along thrust faults or by distributed deformation. A prominent BSR becomes visible immediately landward of the deformation front in the accreted sediment, and is developed over much of the low-to-mid continental slope. The upward pore-fluid migration is believed to play an important role in the formation of a gas hydrate BSR. From the estimated fluid loss of 35% over the 3-km-thick Cascadia Basin sediments with an average sediment porosity of 30%, the quantity of the expelled fluid reaches 315 m3/m2 over a distance of 12 km before the basin sediments are incorporated into the accretionary prism. Assuming that 100 mmol/L of methane is removed from the expelled fluid as it moves into the hydrate stability field, a 90-m-thick layer with an average hydrate saturation of 10% of the pore space can be formed by the rising fluids. A velocity-depth function in the lower slope region, representing a no-hydrate/no-gas reference profile, has been established from the detailed semblance velocity analyses and the ODP log data. The observed and measured sediment velocities near the ODP drill sites increase downward more rapidly than the reference profile above the BSR. Based on the reference profile, the velocity inversion results imply that the velocity increase due to hydrate above the BSR accounts for ~2/3 of the impedance contrast required to produce the BSR reflection amplitudes. The remainder of the impedance contrast appears to come from the velocity decrease associated with small concentrations of free gas below the BSR. The integrated analysis of the multichannel seismic and ODP downhole velocity data has allowed the velocity enhancement associated with the formation and concentration of gas hydrate to be estimated. If the BSR is overlain by a 100 m zone of sediment with a mean porosity of 50% in which the hydrate saturation increases linearly from zero at the top of the zone to 20% at the BSR, the estimated hydrate concentration-depth profiles indicate a total hydrate amount of about 5 m3/m2 of ocean floor or methane amount of 820 m3/m2 at STP. Throughout the Vancouver Island continental margin, where the clear BSR have been observed in an area of 30x200 km, the total methane gas estimated can amount to about 175 Tcf (trillion cubic feet) or 2.6 Gt of carbon. / Graduate

Conventional morphodynamic models are typically based on a coupled system of hydrodynamic equations, a bed-update equation, and a sediment-transport equation. However, the sediment-transport equation is almost invariably empirical, with numerous options available in the literature. Bed morphological evolution predicted by a conventional model can be very sensitive to the choice of sediment-transport formula. This thesis presents a physics-based model, where the shallow water-sediment-mixture flow is idealised as being divided into two layers of variable (in time and space) densities: the lower layer concerned with bedload transport, and the upper layer representing sediment in suspension. The model is referred to as a Quasi-2-Layer (Q2L) model in order to distinguish it from typical 2-Layer models representing stratified flow by two layers of different but constant and uniform densities. The present model, which does not require the selection of a particular empirical formula for sediment transport rates, is satisfactorily validated against widely used empirical expressions for bedload and total transport rates. Analytical solutions to the model are derived for steady uniform flow over an erodible bed. Case studies show that the Q2L model, in contrast to conventional morphodynamic approaches, yields more realistic results by inherently including the influence of the bed slope on the sediment transport. This conclusion is validated against experimental data from a steep sloping duct. An analytical study using the Q2L model investigates the influence of bed-slope on bedload transport; the resulting expressions are in turn used to modify empirical sediment transport formulae (derived for horizontal beds) in order to render them applicable to arbitrary stream-wise slopes. The Q2L model provides an alternative approach to studying sediment-transport phenomena, whose adequate analysis cannot be undertaken following coniv ventional approaches without further increasing their degree of empiricism. The Q2L model can also lead to the enhancement of conventional morphodynamic models. For coarse sediments and/or relatively low flow velocities, bedload transport is usually responsible for most sediment transport. Bedload transport consists of a combination of particles rolling, sliding and saltating (hopping) along the bed. Hence, saltation models provide considerable insight into near-bed sediment transport. This thesis also presents an analysis of the statistics and mechanics of a saltating particle model. For this purpose, a mathematically simple, computationally efficient, stochastic Lagrangian model has been derived. This model is validated satisfactorily against previously published experimental data on saltation. The model is then employed to derive two criteria aimed at ensuring that statistically convergent results are achieved when similar saltation models are employed. According to the first criterion, 103 hops should be simulated, whilst 104 hops ought to be considered according to the second criterion. This finding is relevant given that previous studies report results after only a few hundred, or less, particle hops have been simulated. The model also investigates sensitivity to the lift force formula, the friction coefficient, and the collision line level. A method is proposed by which to estimate the bedload sediment concentration and transport rate from particle saltation characteristics. This method yields very satisfactory results when compared against widely used empirical expressions for bedload transport, especially when contrasted against previously published saltation-based expressions.

No description available.

No description available.

The quality of water within an estuary is inseparable from the component parts; suspended particulate matter (SPM) and the balance of macro-nutrients. Long-term temporal variations and the horizontal advection of both SPM and macro-nutrient concentrations are well-constrained, but the vertical fluxes associated with micro-scale processes, such as turbulence and flocculation, are poorly constrained. The importance of three micro-scale processes on the interactions between SPM and inorganic macro-nutrients, nitrate (NO–3 ), ammonium (NH+4) and phosphate (PO3 –4 ), are examined in four field campaigns and five laboratory experiments. Field campaigns were conducted in two turbid estuaries. One field campaign was conducted in the Seine estuary, France, and three campaigns in the Tamar estuary, U.K., in order to consider the effects of seasonal variations (spring, summer and autumn). Physical conditions measured included current velocity, turbidity, turbulence and particle size, were recorded using a suite of oceanographic instrumentation. Five different laboratory studies were conducted using the same mini annular flume, with different background conditions. Inorganic macro-nutrients were measured spectrophotometrically on a continuous flow analyser (for NO – 3 and PO3 –4) and fluorimetry (NH +4). Three hypotheses are presented as potential mechanisms controlling the release and uptake of macro-nutrients from sediments. Mechanism One (M1) described an exchange process between inorganic macro-nutrients and flocculation/disaggregating particles. It was hypothesised that flocculating particles would decrease water column macro-nutrient concentrations, and vice versa. In this study, flocculation was observed in both field sites, but there was no significant relationship between flocculation and macro-nutrient concentration. Similarly, the five laboratory studies demonstrated no statistically significant relationships between flocculation and macro-nutrient concentrations. Mechanism Two (M2) hypothesised that turbulence would enhance the release portion of the exchange processes described in M1. Furthermore, it was proposed that increased turbulence would break bonds between macro-nutrients and the surface of particle faces. Turbulence was observed to limit the floc size in all experiments (both field and laboratory), but this study determined that it did not promote a significant release mechanism for inorganic macro-nutrients. However, this study observed that turbulence played a key role in the vertical distribution of PO 3 – 4 and NH +4. In both the Seine and Tamar estuaries, surface and near-bed concentrations were observed to be statistically significantly different (p = < 0.05). Finally, Mechanism Three (M3) hypothesised that increased salinity provides additional salt water cations that would enhance flocculation and M1. This study measured an increase in floc size with increasing salinity in but did not enhance the proposed M1. Instead, as with turbulence, differences in water density as a result of the salinity affected the vertical distribution of NO –3. This research concluded that micro-scale processes have no significant impact on the water-column concentration of inorganic macronutrients. Instead, it was observed that two of the three micro-scale processes, turbulence and salinity, play a key role in the vertical distribution of inorganic macro-nutrients in the Tamar and Seine estuaries.