Segui questo link per vedere altri tipi di pubblicazioni sul tema: Water column.
Tesi sul tema "Water column"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "Water column".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Verspecht, Florence. "Temporal dynamics of the coastal water column". University of Western Australia. School of Environmental Systems Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0097.
Testo completoAbstract (sommario):
Field measurements and numerical modelling of the shallow coastal waters offshore in south-western Australia were used to describe changes in the water column's vertical structure and the biological response on temporal scales of the order of hours and days. A cycle of chlorophyll a concentration, primary production, and photosystem II function on a diel timescale, which was related to changes in the solar irradiance and thermal structure, was identified. The diel cycle included (1) vertically well-mixed (or weakly linear) conditions in density and chlorophyll a early in the morning, resulting from vertical mixing through penetrative overnight convection; (2) depleted chlorophyll a concentration in the surface layer during the middle of the day due to photoinhibition; (3) an increased chlorophyll a concentration in the bottom layer by late afternoon due to optimum light conditions; and (4) the formation of a chlorophyll a break point (CBP) at the thermocline, which migrated downwards with the deepening surface mixed layer. On a longer timescale (days), moored acoustic instruments were used to derive echo level (EL), which approximated suspended particulate matter (SPM). Wind events ultimately controlled SPM, a conclusion based on (1) elevated EL during high windgenerated turbulence and bed shear stress, (2) positive time-lagged correlations between wind speed and EL at three field sites with different exposures to wave action, and (3) significant negative correlations between wind speed and depth-differentiated echo level (d(EL)/dz) at all sites. Sea breezes produced a similar response in EL through the water column to a small storm event, and wind-driven SPM resuspension resulted in a reduction in the sub-surface light climate (kd). Near-bed dissolved oxygen concentrations varied in accord with elevated wind speeds, EL and kd, highlighting a possible suppression of photosynthesis. One-dimensional modelling revealed that wind stirring was most often the dominant process in these waters. It was found that for a brief period during thermal stratification there was shear production of turbulent instabilities that migrated from the thermocline to the surface and the seabed. Convective cooling was not able to mix the water column entirely overnight without the addition of wind, and minimum wind speeds were determined for this complete vertical mixing. Bottom-generated turbulence was limited to a small region above the bed, and was deemed insignificant compared with mixing generated at the surface. Minimum wind speeds required for de-stratification and prevention of stratification were determined for summer, autumn and winter. A hypothetical desalination outfall was simulated for all seasons and it was concluded that positioning of the discharge at middepth was preferable compared to at the seabed. The results of this thesis advance the current knowledge of coastal biophysical oceanography and provide new insights into the temporal dynamics of the coastal water column of south-western Australia.
2
Coltman, Kenna Maria. "Water table management effects on water quality: a soil column study". The Ohio State University, 1992. http://rave.ohiolink.edu/etdc/view?acc_num=osu1195165287.
Testo completo
3
Coltman, Kenna Marie. "Water table management effects on water quality : a soil column study /". Connect to resource, 1992. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1195165287.
Testo completo
4
Diedrich, Hannes [Verfasser]. "Observation of Total Column Water Vapour / Hannes Diedrich". Berlin : Freie Universität Berlin, 2016. http://d-nb.info/1109790406/34.
Testo completo
5
Munson, Kathleen M. (Kathleen May). "Transformations of mercury in the marine water column". Thesis, Massachusetts Institute of Technology, 2014. http://hdl.handle.net/1721.1/87513.
Testo completoAbstract (sommario):
Thesis: Ph. D., Joint Program in Oceanography (Massachusetts Institute of Technology, Department of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2014.Cataloged from PDF version of thesis.
Includes bibliographical references.
Methylation of mercury (Hg) in the marine water column has been hypothesized to serve as the primary source of the bioaccumulating chemical species monomethylmercury (MMHg) to marine food webs. Despite decades of research describing mercury methylation in anoxic sediments by anaerobic bacteria, mechanistic studies of water column methylation are severely limited. These essential studies have faced analytical challenges associated with quantifying femtomolar concentrations of the methylated Hg species dimethylmercury (DMHg) and MMHg in marine systems. In addition, the complex biogeochemical cycling of Hg in natural systems require consideration of gaseous, dissolved, and particulate species of Hg in order to probe potential controls on its ultimate transfer into marine food webs. The presented work provides a comprehensive study of Hg chemical speciation and transformations in Tropical Pacific waters. We developed an analytical method for MMHg determination from seawater that has the potential to ease measurements of MMHg distributions, as well as mechanistic studies of Hg species transformations. We used this method, in addition to previously established methods, to measure dissolved and particulate Hg species distributions and fluxes along a transect of the Pacific Ocean. Over significant gradients in oxygen utilization and primary productivity, we observed a region of methylated Hg species focused in the Equatorial Pacific that appeared spatially separated from higher concentrations in North Pacific Intermediate Waters. From the first full water column depth profiles of this region, we also observed the intrusion of elevated Hg into deep waters of the Equatorial and South Pacific Ocean. In addition we observed substantial potential rates of mercury methylation in subsurface and low oxygen waters along the Pacific transect as well as the Sargasso Sea using Hg isotope tracers. We observed dynamic production and decomposition of methylated Hg in low productivity waters, despite low ambient methylated Hg concentrations. From the addition of bulk organic matter as well as individual compounds important for methylation in anaerobic bacteria, we observe no simple limitation of Hg methylation in marine waters but highly dynamic conversion of Hg between methylated and inorganic species.
by Kathleen M. Munson.
Ph. D.
6
Magagna, Davide. "Oscillating water column wave pump : a wave energy converter for water delivery". Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/349009/.
Testo completoAbstract (sommario):
The research presented in this dissertation investigates the development and the performances of a new type of Wave Energy Converter (WEC) aimed to provide water delivery and energy storage in the form of potential energy. The Oscillating Water Column Wave Pump (OWCP) concept was proposed and tested through a series of experimental investigations supported by scientific theory. The OWCP was developed after an extensive study of the existing wave energy technology available, from which it emerged that the Oscillating Water Column (OWC) device could be further implemented for water delivery purposes. The existing theory of the OWC was employed to develop a mathematical theory able to describe the system wave response and water removal of the OWCP. In order to understand and validate the mathematical models of the OWCP, experimental investigations were carried out under the influence of incident linear waves in a two-dimensional (2D) and three-dimensional (3D) wave flume. The experimental equipment and methodology are outlined, including the description of wave flumes, models and data acquisition equipment. Experimental tests were used to verify the concept of the OWCP and assess its performances, investigating both the response of the device to the waves with and without water removal. In order to increase the efficiencies of delivery, array configurations of multiple OWCPs were adopted. The research demonstrated that up to 14% of the energy carried by the incoming waves can be converted into useful potential energy for a single device. Moreover a further increase of the efficiencies can be obtained with the array configuration improving the overall capability of the OWCP, for optimal separation distance between the array components. Further model tests are required to extended this research to validate the developed mathematical models as an effective prediction tool of the performances of the OWCP and further increase the efficiency of water removal that can be achieved.
7
Wheeler, Jeanette Danielle. "Behavioral responses of invertebrate larvae to water column cues". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103337.
Testo completoAbstract (sommario):
Thesis: Ph. D., Joint Program in Biological Oceanography (Massachusetts Institute of Technology, Department of Biology; and the Woods Hole Oceanographic Institution), 2016.Cataloged from PDF version of thesis.
Includes bibliographical references (pages 139-150).
Many benthic marine invertebrates have two-phase life histories, relying on planktonic larval stages for dispersal and exchange of individuals between adult populations. Historically, larvae were considered passive drifters in prevailing ocean currents. More recently, however, the paradigm has shifted toward active larval behavior mediating transport in the water column. Larvae in the plankton encounter a variety of physical, chemical, and biological cues, and their behavioral responses to these cues may directly impact transport, survival, settlement, and successful recruitment. In this thesis, I investigated the effects of turbulence, light, and conspecific adult exudates on larval swimming behavior. I focused on two invertebrate species of distinct morphologies: the purple urchin Arbacia punctulata, which was studied in pre-settlement planktonic stages, and the Eastern oyster Crassostrea virginica, which was studied in the competent-to-settle larval stage. From this work, I developed a conceptual framework within which larval behavior is understood as being driven simultaneously by external environmental cues and by larval age. As no a priori theory for larval behavior is derivable from first principles, it is only through experimental work that we are able to access behaviors and tie them back to specific environmental triggers. In this work, I studied the behavioral responses of larvae at the individual level, but those dynamics are likely playing out at larger scales in the ocean, impacting population connectivity, community structure, and resilience. In this way, my work represents progress in understanding how the ocean environment and larval behavior couple to influence marine ecological processes.
by Jeanette Danielle Wheeler.
Ph. D.
8
Kooverji, Bavesh. "Pneumatic power measurement of an oscillating water column converter". Thesis, Stellenbosch : Stellenbosch University, 2014. http://hdl.handle.net/10019.1/86662.
Testo completoAbstract (sommario):
Thesis (MScEng)--Stellenbosch University, 2014.ENGLISH ABSTRACT: A measurement device was developed to accurately determine the pneumatic power performance of an Oscillating Water Column (OWC) model in a wave flume. The analysis of the pneumatic power is significant due to the wave-topneumatic energy being the primary energy conversion process and where the most energy losses can be expected. The aim of the research study is to address the accurate pneumatic power measurement of unsteady and bidirectional airflow in OWC model experiments. The two fundamental measurements required for the pneumatic power measurement are the pressure difference over an orifice on the OWC model and the volumetric flow rate of air through the outlet. The designed, constructed and assembled measurement device comprised of a venturi flow meter, containing a hot-film anemometer, which could measure the pressure drop and the volumetric flow rate in one device. The assembled pneumatic power measurement device was calibrated in a vertical wind tunnel at steady state. The results from the calibration tests showed that the volumetric flow rate measurements from the pneumatic power measurement device was accurate to within 3 % of the wind tunnel’s readings. The pneumatic power measurement device was incorporated onto a constructed Perspex physical model of a simple OWC device. This assembled system was used as the test unit in the wave flume at Stellenbosch University (SUN). The results from the experimental tests underwent comparative analysis with three analytical OWC air-flow models which were simulated as three scenarios using Matlab Simulink. These results showed that the measurement device has the ability to measure the pneumatic power but there is difficulty in modelling the complex air-flow system of the OWC device. This results in varying levels of agreement between the experimental and simulated pneumatic power results. The research study has revealed that there is difficulty in designing an accurate device for a wide range of test parameters due to the variance in output values. The unsteady and bidirectional nature of the air flow is also difficult to accurately simulate using a one-dimensional analytical model. Recommendations for further investigation are for CFD systems to be used for the analysis of the air-flow in an OWC system and to be used to validate future pneumatic power measurement devices.
AFRIKAANSE OPSOMMING: ‘n Meetinstrument was ontwikkel om die pneumatiese kraglewering van ‘n model van die Ossillerende Water Kolom (OWK) golfenergie omsetter in ‘n golf tenk akkuraat te meet. Dit is belangrik om die omskakeling van golf na pneumatiese energie te analiseer siende dat die grootste energieverlies in dié proses plaasvind. Die doel van hierdie navorsingsprojek was om die akkurate pneumatiese kragmeting van variërende en twee-rigting vloei van lug in ‘n OWK model na te vors. Die twee fundamentele metings wat benodig word vir die pneumatiese kragbepaling is die drukverskil oor die vloei vernouing en die volumetriese vloeitempo van lug deur die uitlaat van die toetstoestel. Die spesiaal ontwerpte meettoestel wat gebruik is in die eksperiment het bestaan uit ‘n venturi vloeimeter wat ‘n verhitte-film anemometer bevat het wat die drukverandering en die volumetriese vloeitempo kan meet in ‘n enkele instrument. Die pneumatiese kragmeting was gekalibreer in ‘n vertikale windtonnel waarin ‘n konstante vloei tempo geïnduseer was. Die kalibrasieproses het bevestig dat die meettoestel metings lewer met ‘n fout van minder as 3 % wanneer dit vergelyk word met die bekende konstante vloei tempo soos bepaal in die windtonnel. ‘n Fisiese model van ‘n vereenvoudigde OWK golfenergie omsetter was ontwerp en gebou uit Perspex om as toetstoestel te gebruik vir die evaluering van die ontwerpte pneumatiese kraglewering meettoestel. Die toetse was uitgevoer in ‘n golftenk by die Universiteit Stellenbosch (SUN). The toetsresultate was vergelyk met drie ander OWK lugvloei modelle wat gesimuleer was deur om die analitiese modelle op te stel en te simuleer in Matlab Simulink. Die vergelyking van modellering resultate het gewys dat die meettoestel die vermoë het om pneumatiese krag te meet. Daar was wel komplikasies met die modellering van die komplekse lugvloei in die OWK toestel, die resultate het geen definitiewe ooreenstemming gewys tussen die eksperimentele en gesimuleerde pneumatiese krag resultate nie. Die navorsingsprojek het gewys dat daar komplikasies is om ‘n enkel toestel te ontwerp wat oor ‘n wye bereik kan meet weens die variasie van die verskillende parameters. Die variërende en twee-rigting lugvloei is ook moeilik om akkuraat te simuleer met ‘n een-dimensionele analitiese simulasie model. Aanbevelings vir verdere navorsing sluit in om die lugvloei in die OWK stelsel te modelleer en te analiseer in ‘n drie-dimensionele model om die lesings van ‘n pneumatiese krag meettoestel te bevestig.
9
Perdigão, José Nuno Bebiano Mesquita de Azeredo. "Reactive-control strategies for an oscillating-water-column device". Phd thesis, Instituições portuguesas -- UTL-Universidade Técnica de Lisboa -- IST-Instituto Superior Técnico -- -Departamento de Engenharia Mecânica, 1998. http://dited.bn.pt:80/29667.
Testo completo
10
Falconer, Haley Ryanne Watson. "Column filter studies phosphorus removal using biogenic iron oxides /". Pullman, Wash. : Washington State University, 2009. http://www.dissertations.wsu.edu/Thesis/Fall2009/H_Falconer_100709.pdf.
Testo completoAbstract (sommario):
Thesis (M.S. in environmental engineering)--Washington State University, December 2009.Title from PDF title page (viewed on Jan. 12, 2010). "Department of Civil and Environmental Engineering." Includes bibliographical references (p. 52-53).
11
Horko, Michael. "CFD optimisation of an oscillating water column wave energy converter". University of Western Australia. School of Mechanical Engineering, 2008. http://theses.library.uwa.edu.au/adt-WU2008.0089.
Testo completoAbstract (sommario):
Although oscillating water column type wave energy devices are nearing the stage of commercial exploitation, there is still much to be learnt about many facets of their hydrodynamic performance. This research uses the commercially available FLUENT computational fluid dynamics flow solver to model a complete OWC system in a two dimensional numerical wave tank. A key feature of the numerical modelling is the focus on the influence of the front wall geometry and in particular the effect of the front wall aperture shape on the hydrodynamic conversion efficiency. In order to validate the numerical modelling, a 1:12.5 scale experimental model has been tested in a wave tank under regular wave conditions. The effects of the front lip shape on the hydrodynamic efficiency are investigated both numerically and experimentally and the results compared. The results obtained show that with careful consideration of key modelling parameters as well as ensuring sufficient data resolution, there is good agreement between the two methods. The results of the testing have also illustrated that simple changes to the front wall aperture shape can provide marked improvements in the efficiency of energy capture for OWC type devices.
12
Harikrishanan, M. "Flow and water column structure at the Herbridean shelf-edge". Thesis, Bangor University, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.265238.
Testo completo
13
Martins-rivas, Hervé. "Power extraction from an oscillating water column along a coast". Thesis, Massachusetts Institute of Technology, 2008. http://hdl.handle.net/1721.1/45257.
Testo completoAbstract (sommario):
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2008.Includes bibliographical references (p. 121-123).
For reasons of wave climate, geography, construction, maintenance, energy storage and transmission, some devices for extracting energy from sea waves will likely be installed on the coast. We study here the specific case where an Oscillating Water Column (OWC) is attached to the tip of a long breakwater. A three-dimensional numerical model of a skeletal geometry of the the Foz do Douro breakwater is developed in order to determine the response inside the OWC pneumatic chamber to incident waves and assess the possible effects of the breakwater geometry. The model uses the hybrid element method and linear water wave theory. Then, a more analytical approach for a simplified geometry is presented. Making use of an exact solution for the scattering by a solid cylinder connected to a wedge, we solve for the linearized problems of radiation and scattering for a hollow cylinder with an open bottom. Power-takeoff by Wells turbines above an air chamber is modeled by including the compressibility of air. It is shown for the case of a circular OWC attached to a thin breakwater, that the incidence angle affects only the waves in and outside the column but not the power extraction which depends only on the averaged water-surface displacement inside. Optimization by controlling the turbine characteristics is examined for a wide range of wavelengths. Finally, the same approach is used to solve the case of an OWC positioned along a straight coast line. It is found that in this configuration, the extracted power does depend on the incidence angle. It is also shown that the average efficiency is doubled compared to the thin breakwater geometry.
by Hervé Martins-rivas.
S.M.
14
Hick, Peter T. "Determination of water column characteristics in coastal environments using remote sensing". Thesis, Curtin University, 1997. http://hdl.handle.net/20.500.11937/2515.
Testo completoAbstract (sommario):
This thesis illustrates the specific aspects that influence or limit the application of remotely-sensed data for information retrieval from coastal marine, estuarine and riverine environments. The thesis is drawn principally from ten separate studies and is divided into discrete sections, or experiments, that provide an understanding of the fundamental aspects of the effects of the atmosphere, water surface, water column and bottom on sensor-received reflected signal.The results show the importance of precise calculation of acquisition parameters and the absolute importance of relevant reference data. Most instrumentation for remote sensing at visible wavelengths has been developed for terrestrial applications where signal is rarely limiting and target features are relatively static. For in-water applications, where signal is small and noise can be large, the features to be sensed may be temporally dynamic and obscured.However, the work presented also shows the great benefit and spatial cost-effectiveness that can be obtained if the spectral and temporal specification is adequately considered. The prime motivation for such applications usually comes from the requirement to detect and quantify water column characteristics, such as phytoplankton forming as algal blooms, and bottom stratigraphic condition, such as benthic habitat mapping for fishery or conservation purposes.
15
Morrison, Iain George. "The hydrodynamic performance of an oscillating water column wave energy converter". Thesis, University of Edinburgh, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.493723.
Testo completo
16
Close, Hilary Gwyneth. "Size-related Isotopic Heterogeneity in Lipids from the Marine Water Column". Thesis, Harvard University, 2012. http://dissertations.umi.com/gsas.harvard:10487.
Testo completoAbstract (sommario):
Microbes, including Bacteria, are globally important mediators of elemental transformations in the marine water column, but not until recently has their biomass been suggested to contribute significantly to carbon export flux. Here I characterize lipid and carbon isotopic signatures in marine particulate organic matter (POM) explicitly at microbial size scales, and I quantitatively explore how these signatures are transferred down the water column. In the North Pacific Subtropical Gyre (NPSG) an isotopically-enriched pool of submicron POM appears to dominate export to mesopelagic depths, supporting recent observations that bacterioplankton communities contribute to export flux in proportion to their biological abundance. In the Eastern Tropical North Pacific (ETNP) complex pathways emerge for the flux of POM to the deep ocean. I use the largest data set to date for natural \(^{13}C\) signatures of individual water column lipids to reveal that submicron and larger-size suspended POM size classes are isotopically distinct. Results point to de novo production of lipids above and within the oxygen minimum zone. I develop quantitative models to deconvolve the signatures of sinking and in situ sources of these lipids. Results converge on a best-fit model for downward flux in the ETNP that includes both surface-derived and sub-photic zone lipids. Overall results from the modern ocean suggest that approximately half of total suspended POM is submicron in size, much of it is bacterial in origin, and despite the small size of this material, it participates dynamically in water column export flux. These results also suggest some revised interpretations of organic matter signatures in the geologic record. I formulate a quantitative model of marine microbial production and degradation, and reproduce "inverse" isotopic signatures found in lipids and organic matter preserved in Proterozoic sedimentary rocks. Results suggest that the disappearance of this inverse \(^{13}C\) pattern was a consequence of the shift from Bacteria to Eukarya as dominant producers of marine autotrophic biomass. Together, results of this thesis reveal that heterogeneity in the isotopic signatures of marine suspended POM is associated with particle size, and by extension, must be a function of the composition of the total planktonic community.Earth and Planetary Sciences
17
Leitch, John Gaston. "Productivity analysis and optimization of oscillating water column wave power devices". Thesis, Queen's University Belfast, 1985. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329360.
Testo completo
18
Uys, Ehbenezer Chris. "Entrainment in an air/water system inside a sieve tray column". Thesis, Stellenbosch : University of Stellenbosch, 2010. http://hdl.handle.net/10019.1/4237.
Testo completoAbstract (sommario):
Thesis (MScEng (Process Engineering))--University of Stellenbosch, 2010.ENGLISH ABSTRACT: Mass transfer efficiency in distillation, absorption and stripping depends on both thermodynamic efficiency and hydrodynamic behaviour. Thermodynamic efficiency is dependent on the system kinetics while hydrodynamics is the study of fluid flow behaviour. The focus of this thesis is the hydrodynamic behaviour in tray columns, which affects entrainment. In order to isolate hydrodynamic behaviour from the thermodynamic behaviour that occurs inside sieve tray columns, investigations are conducted under conditions of zero mass transfer. When the gas velocity is sufficiently high to transport liquid droplets to the tray above, entrainment occurs. The onset of entrainment is one of the operating limits that determines the design of the column and thus impacts on the capital cost. By improving the understanding of the parameters that affect entrainment, the design of the tray and column can be improved which will ultimately increase the operability and capacity while reducing capital costs. Existing correlations predicting entrainment in sieve tray columns are based on data generated mainly from an air/water system. Previous publications recommend that more testing should be performed over larger ranges of gas and liquid physical properties. An experimental setup was therefore designed and constructed to test the influence of the following parameters on entrainment: 1. gas and liquid physical properties 2. gas and liquid flow rates 3. tray spacing The experimental setup can also measure weeping rates for a continuation of this project. The hydrodynamic performance of a sieve tray was tested with air and water over a wide range of gas and liquid flow rates and at different downcomer escape areas. It was found that the downcomer escape area should be sized so that the liquid escaping the downcomer always exceeds a velocity of approximately 0.23 m/s in order to create a sufficient liquid seal in the downcomer. For liquid velocities between 0.23 and 0.6 m/s the area of escape did not have an effect on the percentage of liquid entrained. It was also established that entrainment increases with increasing gas velocity. The rate at which entrainment increases as the gas velocity increase depends on the liquid flow rate. As soon as the liquid flow rate exceeded 74 m3/(h.m) a significant increase in entrainment was noted and the gas velocity had to be reduced to maintain a constant entrainment rate. This is because the increased liquid load requires a longer flow path length for the froth to fully develop. The undeveloped froth, caused by the short (455 mm) flow path, then creates a non-uniform froth that is pushed up against the column wall above the downcomer. Consequently, the froth layer is closer to the tray above resulting in most of the droplets ejected from the froth reaching the tray above and increasing entrainment. By reducing the gas velocity, the froth height and ejecting droplet velocity is reduced, resulting in a decrease in entrainment. The results from the experiments followed similar trends to most of the entrainment prediction correlations found in literature, except for the change noted in liquid flow rates above 74 m3/(h.m). There was, however, a significant difference between the experimental results and the correlations developed by Hunt et al. (1955) and Kister and Haas (1988). Although the gas velocities used during the air/water experiments were beyond the suggested range of application developed by Bennett et al. (1995) their air/water correlation followed the results very well. The entrainment prediction correlation developed by Bennett et al. (1995) for non-air/water systems was compared with the experimental air/water results to test for system uniformity. A significant difference was noted between their non-air/water prediction correlation and the air/water results, which motivates the need for a general entrainment prediction correlation over a wider range of gas and liquid physical properties. Based on the shortcomings found in the literature and the observations made during the experiments it is suggested that the influence of liquid flow path length should be investigated so that the effect on entrainment can be quantified. No single correlation was found in the literature, which accurately predicts entrainment for a large range of liquid loads (17 – 112 m3/(h.m)), high superficial gas velocities (3 – 4.6 m/s) and different gas and liquid physical properties. It is therefore recommended that more work be done, as an extension of this project, to investigate the influence of gas and liquid physical properties on entrainment (under zero mass transfer conditions) for a large range of liquid (5 – 74 m3/(h.m)) and gas (2 – 4.6 m/s) flow rates. In order to understand the effect of droplet drag on entrainment, tray spacing should be varied and increased to the extent where droplet ejection velocity is no longer the mechanism for entrainment and droplet drag is responsible for droplet transport to the tray above. Since it is difficult and in most cases impossible to measure exact gas and liquid loads in commercial columns, another method is required to measure or determine entrainment. Since liquid hold-up was found to be directly related to the entrainment rate (Hunt et al. (1955), Payne and Prince (1977) and Van Sinderen et al. (2003) to name but a few), it is suggested that a correlation should be developed between the dynamic pressure drop (liquid hold-up) and entrainment. This will contribute significantly to commercial column operation from a hydrodynamic point of view.
19
Minns, Julian. "Comparative performance of a novel oscillating water column wave energy converter". Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10042.
Testo completoAbstract (sommario):
This thesis presents research which shows that a helically configured Oscillating Water Column (OWC) could deliver improved performance compared to a conventional tube OWC, whilst saving a significant amount of draft. It is anticipated that savings in the deployment costs for this compact machine will outweigh any additional manufacturing costs. In order to prove the benefits of the helical concept, its performance relative to a conventional plain tube OWC was investigated in detail using scaled physical models. These models evolved during the course of the study, and refined models were developed. A variable impedance turbine simulator was also developed to test the models at their optimum conditions. The tests themselves were also refined leading to a high degree of confidence in the final result. A mathematical model was also adapted to model the performance of the physical models, and to help understand the physical processes involved in the system. With this series of improving physical models and tests, it has been shown that it is possible to achieve a 27% reduction in draft, with a 24% increase in power output.
20
Williams, N. L., L. W. Juranek, K. S. Johnson, R. A. Feely, S. C. Riser, L. D. Talley, J. L. Russell, J. L. Sarmiento e R. Wanninkhof. "Empirical algorithms to estimate water column pH in the Southern Ocean". AMER GEOPHYSICAL UNION, 2016. http://hdl.handle.net/10150/614732.
Testo completoAbstract (sommario):
Empirical algorithms are developed using high-quality GO-SHIP hydrographic measurements of commonly measured parameters (temperature, salinity, pressure, nitrate, and oxygen) that estimate pH in the Pacific sector of the Southern Ocean. The coefficients of determination, R-2, are 0.98 for pH from nitrate (pH(N)) and 0.97 for pH from oxygen (pH(Ox)) with RMS errors of 0.010 and 0.008, respectively. These algorithms are applied to Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) biogeochemical profiling floats, which include novel sensors (pH, nitrate, oxygen, fluorescence, and backscatter). These algorithms are used to estimate pH on floats with no pH sensors and to validate and adjust pH sensor data from floats with pH sensors. The adjusted float data provide, for the first time, seasonal cycles in surface pH on weekly resolution that range from 0.05 to 0.08 on weekly resolution for the Pacific sector of the Southern Ocean.
21
Liptak, Michael A. "Water Column Productivity, Calcite Precipitation, and Phosphorus Dynamics in Freshwater Marshes". The Ohio State University, 2000. http://rave.ohiolink.edu/etdc/view?acc_num=osu1364288585.
Testo completo
22
Williams, Joshua Bruce. "Algorithm Development for Column Water Vapor Retrieval Using the SAM Sensor". DigitalCommons@USU, 2008. https://digitalcommons.usu.edu/etd/59.
Testo completoAbstract (sommario):
To understand and model the energetics of the Sun-Earth connection, measurements of specific atmospheric molecules are beneficial. The objective is to formulate an algorithm to derive temporally varying atmospheric water vapor concentrations as functions of altitude, latitude, and longitude from solar irradiance absorption measurements. The Visidyne SAM (Sun and Aureole Measurement) instrument, which studies the size and distribution of cloud particles, was used to obtain the experimental data. By introducing a spectrometer to the SAM instrument, column water vapor is produced as part of the data product. A new model optimized algorithm is developed and tested versus existing algorithms. Through a least-squares analysis, the new algorithm showed an improvement of a factor of 23 over the industry standard. A test was also conducted to determine which water absorption bandpass produces the smallest error. Through these tests a model optimized algorithm has been produced.
23
Hick, Peter T. "Determination of water column characteristics in coastal environments using remote sensing". Curtin University of Technology, School of Surveying and Land Information, 1997. http://espace.library.curtin.edu.au:80/R/?func=dbin-jump-full&object_id=10817.
Testo completoAbstract (sommario):
This thesis illustrates the specific aspects that influence or limit the application of remotely-sensed data for information retrieval from coastal marine, estuarine and riverine environments. The thesis is drawn principally from ten separate studies and is divided into discrete sections, or experiments, that provide an understanding of the fundamental aspects of the effects of the atmosphere, water surface, water column and bottom on sensor-received reflected signal.The results show the importance of precise calculation of acquisition parameters and the absolute importance of relevant reference data. Most instrumentation for remote sensing at visible wavelengths has been developed for terrestrial applications where signal is rarely limiting and target features are relatively static. For in-water applications, where signal is small and noise can be large, the features to be sensed may be temporally dynamic and obscured.However, the work presented also shows the great benefit and spatial cost-effectiveness that can be obtained if the spectral and temporal specification is adequately considered. The prime motivation for such applications usually comes from the requirement to detect and quantify water column characteristics, such as phytoplankton forming as algal blooms, and bottom stratigraphic condition, such as benthic habitat mapping for fishery or conservation purposes.
24
Chan, Philip Chi Ho. "Column study of the effects of operational and water quality factors on bromate reduction by zerovalent iron /". View abstract or full-text, 2005. http://library.ust.hk/cgi/db/thesis.pl?CIVL%202005%20CHAN.
Testo completo
25
Actkinson, John Ira. "Minesweeping for pressure actuated mines by air injection into a water column". Thesis, Monterey, California. Naval Postgraduate School, 2011. http://hdl.handle.net/10945/5493.
Testo completoAbstract (sommario):
Approved for public release; distribution is unlimited.The U.S. Navy historically has not had an adequate means to remotely pressure-sweep for mines at reasonable speeds and cost, and this is still the case. The Navy has addressed such threats, but countermeasures are time consuming and considered to be very resource intensive. During this thesis two sets of data were collected in tow tank experiments using two different sizes of Bubble Squid apparatus. This thesis is a continuation of work already completed by Lieutenant Jeffery Murawski from December 2009. This continuation was able to extend the proof-of-concept with larger scale tow-tank testing at NPS. Further testing with the much larger three-meter Bubble Squid apparatus culminated in experiments conducted in March 2010 at the David Taylor Research Basin in Carderock, MD. The data that was collected and analyzed in this thesis will show that the Bubble Squid apparatus is a viable concept for solving the pressure influence minesweeping capability gap.
26
Mackinnon, Pauline Anna. "The influence of geometry on turbulent losses in an oscillating water column". Thesis, Queen's University Belfast, 1987. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.357453.
Testo completo
27
King, Linda L. 1964. "Chlorophyll diagenesis in the water column and sediments of the Black Sea". Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/12565.
Testo completo
28
Freeman, Kate. "Numerical modelling and control of an oscillating water column wave energy converter". Thesis, University of Plymouth, 2015. http://hdl.handle.net/10026.1/3290.
Testo completoAbstract (sommario):
An oscillating water column (OWC) wave energy converter (WEC) is a device designed to extract energy from waves at sea by using the water to move trapped air and thus drive an air turbine. Because the incident waves and the force caused by the power take-off (PTO) interact, control of the power take off (PTO) system can increase the total energy converted. A numerical model was developed to study the interaction of an OWC with the water and other structures around it. ANSYS AQWA is used here to find the effects on the water surface in and around the central column of a five-column, breakwater-mounted OWC. For open OWC structures, coupled modes were seen which lead to sensitivity to incident wave period and direction. The frequency-domain displacements of the internal water surface of the central column were turned into a force-displacement, time-domain model in MATLAB Simulink using a state space approximation. The model of the hydrodynamics was then combined with the thermodynamic and turbine equations for a Wells turbine. A baseline situation was tested for fixed turbine speed operation using a wave climate for a region off the north coast of Devon. A linear feedforward controller and a controller based on maximising turbine efficiency were tested for the system. The linear controller was optimised to find the combination of turbine speed offset and proportional constant that gave maximum energy in the most energy abundant sea state. This increased the converted energy by 31% in comparison to the fixed speed case. For the turbine efficiency control method, the increase was 36%. Energy conversion increases are therefore clearly possible using simple controllers. If increased converted energy is the only criterion for controller choice, then the turbine efficiency control is the best method, however the control action involves using very slow turbine speeds which may not be physically desirable.
29
Ibrahim, Sallehuddin. "Measurement of gas bubbles in a vertical water column using optical tomography". Thesis, Sheffield Hallam University, 2000. http://shura.shu.ac.uk/19852/.
Testo completoAbstract (sommario):
This thesis presents an investigation into the application of optical fibre sensors to a tomographic imaging system for use with gas/water mixtures. Several sensing techniques for measurement of two component flow using non-intrusive techniques are discussed and their relevance to tomographic applications considered. Optical systems are shown to be worthy of investigation. The interaction between a collimated beam of light and a spherical bubble is described. Modelling of different arrangements of projections of optical sensing arrays is carried out to predict the expected sensor output voltage profiles due to different flow regimes represented by four models. The four flow models investigated are: a single pixel flow, two pixels flow, half flow and full flow models. The response of the sensors is based on three models: optical path length, optical attenuation and a combination of optical attenuation model and signal conditioning. In the optical path length model, opaque solids or small bubbles, which are conveyed, may totally or partially interrupt the optical beams within the sensing volume. In the optical attenuation model, the Lambert-Beer's Law is applied to model optical attenuation due to the different optical densities of the fluids being conveyed. The combination of optical attenuation model and signal conditioning is designed to improve the visual contrast of the tomograms compared with those based on the optical attenuation model. Layergram back-projection (LYGBP) is used to reconstruct the image. A hybrid reconstruction algorithm combining knowledge of sensors reading zero flow with LYGBP is tested and shown to improve the image reconstruction. The combination of a two orthogonal and two rectilinear projections system based on optical fibres is used to obtain the concentration profiles and velocity of gas bubbles in a vertical column. The optical fibre lens is modelled to determine the relationships between fibre parameters and collimation of light into the receiver circuit. Modelling of the flow pipe is also carried out to investigate which method of mounting the fibres minimises refraction of the collimated light entering the pipe and the measurement cross-section. The preparation of the ends of the optical fibre and design of the electronics, which process the tomographic data, are described. Concentration profiles obtained from experiments on small bubbles and large bubbles flowing in a hydraulic conveyor are presented. Concentration profiles are generated using the hybrid reconstruction algorithm. The optical tomographic system is shown to be sensitive to small bubbles in water of diameter 1-10 mm and volumetric flow rates up to 1 1/min, and large bubbles in water of diameter 15-20 mm and volumetric flow rates up to 3 1/min. Velocity measurements are obtained directly from cross correlation of upstream and downstream sensors' signals as well as from upstream and downstream pixel concentration values. Suggestions for further work on optical tomographic measurements are made.
30
Dai, Saishuai. "Assessing the performance of an oscillating water column type wave energy device". Thesis, University of Strathclyde, 2016. http://digitool.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=27860.
Testo completoAbstract (sommario):
To meet the need of clean energy, a variety of renewable energy technologies have been developed. Among those, wave energy stands out for its outstanding merits. For instance, wave energy is clean, renewable, has high energy intensity and long resource available time. However, due to the short development history of wave energy technologies, the cost of wave energy is too high compared with the other renewable energy technologies. As well as lack of cost effective Wave Energy Converters (WECs) scenarios, another reason that keeps the cost of wave energy high is that the performance of a WECs may not be accurately assessed during its design and development stage. This leads to error in estimating the cost of energy produced by the full scale device. Therefore, this study aims to drive the cost of WECs down by investigating several major aspects that will bias the assessing of the performance of a WEC during the design and development stage. Literature review suggested the uncertainty in the measurement, the tank width effect (in tank testing), the performance of the simulated simple Power Take Off (PTO) and the scale effect are major aspects that bias the assessment. By tank testing and Computational Fluid Dynamic (CFD) simulation, the above three aspects were investigated. It is found that the uncertainty in the measurement leads to an uncertainty in the power captured at model scale about 5% around the peak output. The appearance of the tank wall will over estimate the performance of a single unit depending on the width of the tank. A 1 : 150th scaled (of the full scale.) device may under estimate the performance of the device by about 34% compared with a 1 : 16.67th scaled device, while a 1 : 50th scaled device under estimate the performance of a 1 : 16.67th scaled device by 6.6%. The CFD simulation demonstrated its advantage over the tank testing when scaling and tank width effect is concerned. Therefore, to better estimate the performance, the assessment shall be carried out by both experiment and numerical simulation. Based on the study carried out, recommendation and guide line for tank testing of a FSCOWC device was given at the end of the thesis.
31
Chienthavorn, Orapin. "Detection in superheated water chromatography". Thesis, Loughborough University, 1999. https://dspace.lboro.ac.uk/2134/32394.
Testo completoAbstract (sommario):
Superheated water has been used successfully as an eluent in liquid chromatography and has been coupled to various modes of detection, ultraviolet (UV), fluorescence, and nuclear magnetic resonance spectroscopy (NMR) and mass spectrometry (MS). A number of compounds were examined on poly(styrene-divinylbenzene) (PS-OVB), polybutadiene (PBO), and octadecylsilyl bonded silica (OOS) column with isothermal and temperature programmes.
32
Guidi, Lionel. "Particle flux transformation in the mesopelagic water column: process analysis and global balance". Diss., Texas A&M University, 2008. http://hdl.handle.net/1969.1/85946.
Testo completoAbstract (sommario):
Marine aggregates are an important means of carbon transfers downwards to the deep ocean as well as an important nutritional source for benthic organism communities that are the ultimate recipients of the flux. During these last 10 years, data on size distribution of particulate matter have been collected in different oceanic provinces using an Underwater Video Profiler. The cruise data include simultaneous analyses of particle size distributions as well as additional physical and biological measurements of water properties through the water column. First, size distributions of large aggregates have been compared to simultaneous measurements of particle flux observed in sediment traps. We related sediment trap compositional data to particle size (d) distributions to estimate their vertical fluxes (F) using simple power relationships (F=Ad^b). The spatial resolution of sedimentation processes allowed by the use of in situ particle sizing instruments lead to a more detailed study of the role of physical processes in vertical flux. Second, evolution of the aggregate size distributions with depth was related to overlying primary production and phytoplankton size-distributions on a global scale. A new clustering technique was developed to partition the profiles of aggregate size distributions. Six clusters were isolated. Profiles with a high proportion of large aggregates were found in high-productivity waters while profiles with a high proportion of small aggregates were located in low-productivity waters. The aggregate size and mass flux in the mesopelagic layer were correlated to the nature of primary producers (micro-, nano-, picophytoplankton fractions) and to the amount of integrated chlorophyll a in the euphotic layer using a multiple regression technique on principal components. Finally, a mesoscale area in the North Atlantic Ocean was studied to emphasize the importance of the physical structure of the water column on the horizontal and vertical distribution of particulate matter. The seasonal change in the abundance of aggregates in the upper 1000 m was consistent with changes in the composition and intensity of the particulate flux recorded in sediment traps. In an area dominated by eddies, surface accumulation of aggregates and export down to 1000 m occured at mesoscale distances (<100 km).
33
Holzhauer, Eva. "Assessment of the power available in a fixed offshore oscillating water column plant". Thesis, Cranfield University, 2012. http://dspace.lib.cranfield.ac.uk/handle/1826/8053.
Testo completoAbstract (sommario):
The early effects of the global warming can be observed and people around the world are beginning to realize the seriousness of the situation. Reducing the CO2 emissions produced by fossil energy seems to be one of the main worldwide technological challenges at the time of writing. Hence, since the oil crisis in the 70s, a growing interest in renewable energies has been noticed. In Europe, the European Commission fixed a target: to produce 20% of the EU energy from renewable sources by 2020. Similar initiatives, in varying degrees, are being considered around the globe.
Among all the renewable energy technologies currently on the market, the ocean energy industry is still at an early stage, despite investigations that have been carried out on both tidal and wave energy devices over the past 40 years. The subject of this thesis focuses on one of the wave energy devices: the Oscillating Water Column.
The information found in the literature about this type of plants is mainly about onshore and floating offshore OWCs. Very little information about fixed offshore OWC is available. Besides, the availability of large numbers of fixed offshore structures installed in the world oceans suggests that many of these could possibly host an OWC plant. Hence, the present study investigated a fixed offshore OWC.
The aim of this thesis is to assess the power available in a fixed offshore OWC plant. To illustrate the procedure of power assessment, the fictional scenario of a platform located in the Santa Maria sea region, off the coast of Californian, is introduced. This work intends to develop a methodology to study the feasibility of such installation and estimate the power extractable through various complementary approaches. From a theoretical approach based on the wave climate of Santa Maria to wave tank experiments with various geometries and shapes of chamber (cylinder and bent duct buoy in frontward and backward position), the viability of a fixed offshore OWC plant is demonstrated for the chosen location. Results highlight the performance of the Backward Bent Duct Buoy (BBDB) for the Santa Maria characteristic sea conditions. With the intention of completing the study with a Computational Fluid Dynamics (CFD) analysis, numerical investigations about the implementation of an alternative method to generate regular waves demonstrates better results of wave propagation than the common wave generation method based on Linear Wave Theory previously used at Cranfield University. In the conclusion, the work achievements and recommendations for future CFD investigations to reproduce the wave tank experiments are discussed.
34
Niewinski, Desi. "Water column oxygen respiration dynamics and quantification of nitrogen cycling genes insediment of Lake Erie". Wright State University / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=wright1547330489488682.
Testo completo
35
Jana, Partha. "REMOVAL OF ARSENIC(III) FROM WATER WITH A NEW SOLID-SUPPORTED THIOL". UKnowledge, 2012. http://uknowledge.uky.edu/chemistry_etds/11.
Testo completoAbstract (sommario):
Arsenic is a highly toxic, easily transportable and widespread contaminant in groundwater throughout the world. Arsenic causes acute toxicity by disrupting biological functions. In groundwater arsenic concentrations can reach up to a few milligrams per liter. Current regulations on arsenic content in drinking water are becoming more stringent and require the standard to be reduced to a few parts per billion. Arsenic exists as oxyanions in aqueous solution in either trivalent or pentavalent oxidation states depending on the oxidation-reduction potential and pH of the medium. Several treatment methods are available for removing arsenic from water. However, cost, operational complexity of the technology, skill required to operate the technology and disposal of arsenic bearing residual are factors that should be considered before the selection of any treatment method. Most of these techniques are also effective only in removing As(V) and not As(III). N,N’-bis(2-mercaptoethyl)isophthalamide), abbreviated BDTH2, is known to effectively precipitate soft heavy metals from water. A solid-supported reagent with the metal capture ability of BDTH2 would be ideal to use as a filtration column packing material for removal of aqueous As(III). In order to attain this objective, a new dithiol compound, 2,2'-(isophthaloylbis(azanediyl))bis(3-mercaptopropanoic acid) (abbreviated ABDTH2) has been synthesized and immobilized on silica beads. Silica-supported reagent ABDTH2 (SiABDTH2) thus prepared, completely removed As(III) from water by forming As-S bonds. In batch study, SiABDTH2 reduced the concentration of As(III) in aqueous solutions from 200 ppb to below 5 ppb at pH 5, 7 and 9. XAFS study of ABDT-As(III) and SiABDT-As(III) indicated that arsenic was present in +3 oxidation state as well as As(III) was only bonded to sulfur atom of ABDT unit. When SiABDTH2 was used as filtration column material, only 3% of ABDTH2 was leached out from the column. However, 100% As(III) was removed from 20 L of 200 ppb As(III) aqueous solution at a flow rate of 20 mL/min.
36
Bartleson, Richard Dixon. "Interactions of seagrass beds and the water column effects of bed size and hydrodynamics /". College Park, Md. : University of Maryland, 2004. http://hdl.handle.net/1903/2106.
Testo completoAbstract (sommario):
Thesis (Ph. D.) -- University of Maryland, College Park, 2004.Thesis research directed by: Marine-Estuarine-Environmental Sciences. Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.
37
Brendmo, Arne. "An investigation of wave-energy absorption by single and double oscillating water-column converters". Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for fysikk, 1995. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-14721.
Testo completo
38
Bugden, John B. C. "Spatial and temporal variation of microbial properties in the water column of Florida Bay". FIU Digital Commons, 1992. http://digitalcommons.fiu.edu/etd/1947.
Testo completoAbstract (sommario):
Physical and biological properties of the water column of Florida Bay were examined at seven study sites over an eighteen month period. The results indicated seasonality in some parameters, but was not evident in others. The data displayed statistically significant (P < 0.05) differences between study sites indicating spatial variation. The presence of seagrass affected the overlying water column, especially with respect to the biological parameters: those areas overlying seagrass beds displayed statistically significantly higher values than those over sparsely covered or barren areas. During the period of the study, Florida Bay experienced a seagrass die-off event: microbial activity and numbers were statistically significantly higher over areas of dying seagrass than over healthy or dead areas. The results of this study pointed to phosphorus being the controlling, or limiting factor, for microbial activity in the water column of Florida Bay.
39
Cohen, Ashley B. "The Degradation of Pigments in the Water Column and Sediments of the Bermuda Rise". Thesis, State University of New York at Stony Brook, 2015. http://pqdtopen.proquest.com/#viewpdf?dispub=1586743.
Testo completoAbstract (sommario):
The export of particulate carbon from the surface ocean into deeper water and to the seabed is a critical component of the carbon cycle. The concentrations and compositions of particulate pigments collected at different depths and sinking at different settling velocities can be used as a proxy for biologically mediated processes important to the early degradation of OM. By knowing what processes the compositional and quantitative changes in the particulate pigments represent, the POM cycle of the BaRFlux area can be better understood. It is important to understand the POM cycle because deposition of OM to the seabed is the only way that OM is sequestered. The removal of POM from the marine POM cycle is especially important to understand in subtropical gyre areas like the BaRFlux site because: 1. subtropical gyres are areas of downwelling, and therefore POM transport to the deep ocean and may increase as global warming continues. 2.the flux of CO2 to the ocean is increasing from rising levels of atmospheric CO2, and CO2 removed by the biological pump will lessen processes like ocean acidification.
This thesis examines the early degradation of chloropigments in the sediment and water column in the Bermuda Rise area of the Sargasso Sea. Water column particulate samples were collected with in-situ pumps, Niskin bottles, and Indented Rotating Sphere (IRS) sediment traps, and sediment was collected by box cores during 2011-2013 to record seasonal patterns in quantity and quality of particulate pigments as a function of water column depth and particle size. Chl-a, Chl-b, and pheopigments were separated and quantified using reverse-phase High Performance Liquid Chromatography (HPLC).
The comparison of data from in-situ pumps and Niskin bottles indicates that collection method significantly affects particulate pigment data concentrations. Niskin bottle data showed total pigment concentrations 10 times greater than in-situ pump pigment concentrations at shallow depths. At depths below the euphotic zone, Niskin bottle and in-situ pump concentrations both appear similar because the particulate pigment concentrations were below the detection limit. For the BaRFlux study area, the differences in Niskin bottle and pump data are most likely from: 1. the biased particle distribution due to sampling a small volume of seawater with Niskin bottles in an area of dilute particle concentration; 2. the greater retention efficiency of picophytoplankton on Niskin GF/F filters than 1-µm in-situ pump microquartz filters.
The compositional changes seen in small suspended particulate pigments over depth is consist with small suspended particles being consumed by shallow water zooplankton and then increasingly altered by microbial activity with increasing depth. The composition of small and large particulate pigments were compared to determine if aggregation-disaggregation was an important process. Larger suspended particulate pigments were nearly 100% Chl-a over depth and distinct from smaller suspended particulate pigments other than samples from May or June, during which particle exchange may be more important. The comparison of particulate pigment data to CTD beam transmissivity profiles suggests that the nepheloid layer consists of small suspended particulate matter rather than large particles.
Sediment trap samples were compositionally enriched in pheopigments relative to smaller bottle and pump samples, indicative of enrichment with more rapidly sinking larger zooplankton fecal pellets. The mole% of chlorophyll-a labile pigment increased with increasing settling velocity, suggesting aggregation may increase the settling velocity of particles enough to escape zooplankton feeding. The particulate pigment composition of seafloor sediment collected in August was compositionally distinct from that of suspended and sinking particulate pigments and was nearly 100% pheophorbide-a, indicating POM degradation by feeding macrobenthos.
40
Bayoumi, Ahmed Seif-Eldine Mohamed. "Development of numerical wave power prediction tool offshore oscillating water column wave energy converter". Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=18992.
Testo completoAbstract (sommario):
Marine renewable energy sources are crucial alternatives for a sustainable development. The idea of generating electrical power from water waves has been realized for many years. In fact, waves are now considered as an ideal renewable energy source since a Wave Energy Converter (WEC) has no fuel cost and provides cleanly a high power density that is available most of the time. The third generation of WECs is intended to be installed offshore. This allows the device to harvest the great energy content of waves found in deep water and minimise the environmental impacts of the device. On the other hand, moving WECs to offshore locations will increase the initial and maintenance costs. So many types of device may be suggested for wave power extraction that the task of selecting a particular one is made complicated. Therefore modelling of different WECs allows the comparison between them and the selection of the optimum choice. Recent studies showed that the SparBuoy Oscillat ing Water Column (OWC) has the advantage of being simple, axi-symmetrical, and equally efficient at capturing energy from all directions, but its efficiency (capture factor) is affected significantly by the incident wave periods variation due to the dynamic coupling of the water column and the floating structure. The proper modelling of the device allows the optimization of the geometries and the Power Take-Off (PTO) mechanism in order to maximise the power absorbed. The main objective of this research is to develop experimentally validated numerical wave power prediction tool for offshore SparBuoy OWC WEC. The numerical tool should be able to predict the spar motions and the water column oscillations inside the structure, in addition to the estimation of the pneumatic power absorber and the evaluation of the device performance. Three uncoupled linear second order differential equations have been used to predict the spar surge, heave and pitch motions, where wave forces have been calculated. Three uncoupled linear second order differential equations have been used to predict the spar surge, heave and pitch motions, where wave forces ha ve been calculatedanalytically in frequency domain in inertia and diffraction regimes. Mooring system has been involved in surge motion only using static and quasi-static modelling approaches. Finite element multi-static model have been developed using OrcaFlex to validate the analytical results. Single Degree of Freedom (DOF) mechanical oscillation model has been presented to simulate the water column oscillations inside captive cylindrical OWC where PTO damping and stiffness due to air compressibility inside the pneumatic chamber have been taken into account linearly. Later on, nonlinearity due to large waves has been investigated. Linearized frequency domain model based on classical perturbation theory and nonlinear model where wave forces are calculated in time domain have been proposed. Furthermore, nonlinearity due to damping forces has been considered. First, iterative procedure has been used to optimise the linear and quadratic damping coefficients in frequency domain. Then, another model has been provided where equivalent viscous damping coefficients are calculated in time domain by taking into consideration the instant oscillation amplitude. Finally the nonlinear effects due to air compressibility inside the OWC chamber has been considered in a time domain model which include the water column oscillations amplitudes. Two different dynamic models have been implemented to describe floating OWC and will be referred to in the text as simplified 2DOF model and Szumko model. Both models considered two translational modes of motions in heave direction. Simplified 2DOF model has been solved analytically in frequency domain due to its simplicity, while numerical solutions in time domain have been provided for both models using Matlab. Different approaches have been adopted to modify both models in order to obtain a satisfactory agreement between the predicted and measured results. A floating platform consists of four similar SparBuoy OWC WECs rigidly attached together by trusses where spars are located at the corners have been tested experimentally. Numerical model has been developed to predict the platform motions. Finally the experimentalresults have been compared to those obtained from the modelling of single SparBuoy OWC.
41
Kashada, Mohamed Abdulsalam. "Modelling of unsteady pipe flow with "liquid column separation" (water hammer induced transient cavitation)". Thesis, University of Newcastle upon Tyne, 2017. http://hdl.handle.net/10443/4012.
Testo completoAbstract (sommario):
Understanding of waterhammer pressure transients in liquid-filled pipelines and their computational (numerical) modelling as unsteady one-dimensional flow is well established in the literature and engineering practice. However, for the particular issue of the potential for low transient pressure to initiate a change of phase or release of dissolved gases, leading to the phenomenon of localised transient cavitation known as liquid column separation, there is not yet a consensus on the reliability of the various numerical models that have been proposed in the literature. To contribute to further progress on this, therefore, this present work builds primarily on two previous studies, by Bergant & Simpson (1999) at Adelaide University and Arfaie (1989) at Newcastle University. The aim of this work is to repeat and extend the Bergant & Simpson (1999) comparison of the Discrete Vapour Cavity Method (DVCM) and Discrete Gas Cavity Method (DGCM) while also taking into account the contribution of Arfaie (1989) in respect of: - his suggestion for an improved transient internal boundary condition at the moving liquid column separation interface; - his recommendation that the greater damping associated with unsteady pipe friction models (as opposed to conventional quasi-steady friction) may improve overall model performance; and - his observation that the mode of column separation behaviour (particularly when column separation causes a pressure spike that may exceed the widely regarded Joukowsky pressure maximum) may influence the choice of best model. The basic DVCM and DGCM models tested (with the gas release physical parameters for the latter) are those established in the literature. In these the transient internal boundary condition at the moving column separation interface can be either the conventional Wylie & Streeter (1993) formulation as in Bergant & Simpson (1999) or the Arfaie (1989) improvement. There are many models available for unsteady friction, but previous work by Bughazem (1997) at Newcastle University had established that a Brunone-type Instantaneous Acceleration Based model is not only simple to implement but also works well on the specific experimental apparatus used ii in this study. Bughazem & Anderson (1996) had outlined (but not implemented or tested) a possible alternative integration of this into a fully Method of Characteristics approach. This is developed and applied, but its additional implementation complexity for no obvious gain in performance led to its being set aside. The very simple Arfaie (1989) experimental apparatus used is intended to eliminate any modelling issues (especially for external boundary conditions) not associated with column separation as well as to attempt to restrict column separation to a single location (to support its visualisation). Flow visualisation on this apparatus did not show the conventional full-bore vapour cavity suggested by the term “column separation”. Rather scattered vapour or released gas bubbles appeared along the pipe soffit during the transient column separation event. To support clarification of Arfaie’s views on the different modes of column separation behaviour, an extensive series of experimental runs were recorded to facilitate development of a map for the occurrence of these, with the intention of helping analysts and designers to determine if pressure higher than Joukowsky might occur. It was determined that these may occur for PM =~1.2~2 where PM is the Martin ratio: PM = ρ.a.VoPR−Pv Initially the comparison of computed against experimental results followed the conventional qualitative approach as in Arfaie (1989) and others. However, this proves problematic where a large number of experimental runs (with scatter due to uncertainties) have been taken, as well as when there are more than one factor for comparison. This process, though, did highlight an issue with predicting the data value for vapour pressure, where the actual value on the experimental traces is different from the Steam Tables value used for prediction and thus appearing on the computed traces. This introduced a further factor to the investigation. Following Arfaie (1989) and others, initially qualitative comparison taken over a period including up to five pressure peaks were made (overall shape of peaks and ability to maintain phase of solution features). However, for consistent comparison across a number of experimental runs, two specific quantifiable criteria are defined: - the time duration of the first column separation event; and iii - the maximum pressure peak amplitude occurring as a result of that. Graphs can be compiled to attempt to explore the behaviour of different model options, but with a large amount of data showing scatter due to uncertainty these do not lead to clear outcomes. Consequently, following previous work on CFD modelling at Newcastle University by Ahmeid (1997), a statistical approach using Design of Experiments (DOE) with Analysis of Variance (ANOVA) was adopted which demanded quantified criteria. ANOVA indicates whether significant differences can be detected from the data and the DOE approach (as compared with “one factor at a time” testing) can indicate if there are interactions present between the factors. With this recourse to statistical methodology, Normal Probability plots indicated that the data for first cavity duration are better than data for maximum pressure peak amplitude, giving more significant ANOVA outcomes for the former than the latter. Though this first attempt at using these techniques has not produced clear or comprehensive outcomes, the methodology is promising for future studies. The present outcomes are that: - For basic method, DGCM, as suggested by Bergant & Simpson (1999), performs best for cavity duration, but it is not yet possible to say this for maximum pressure amplitude. - Similarly, with quasi-steady friction at least, the Arfaie (1989) internal boundary condition is a small improvement over the conventional Wylie & Streeter (1993), certainly for cavity duration. - Unsteady friction does reduce error magnitude and scatter, but the greater damping may lead to non-conservative (under-estimation) prediction of maximum pressure amplitude. - There is evidence that the mode of column separation behaviour does interact with the other factors, but it is not yet clear exactly what, if any, real effect it has. - Finally, though the data value for vapour pressure is significant (certainly for cavity duration), in practice small variations in its value seem to make little difference to computed predictions. There is sufficient evidence that with better quality data and further consideration of quantifiable criteria for comparison that the statistical methodology demonstrated can be an effective tool for computational model testing. iv Unfortunately for this present study, it exposed the limitation of the apparatus used in producing repeatable results with controlled uncertainties, especially for peak pressure. A clear conclusion is that better experimental data from an improved experimental apparatus are required.
42
Carolus, Thomas, e Christoph Moisel. "Bidirectional air turbines for oscillating water column systems: Fast selection applying turbomachinery scaling laws". Elsevier, 2017. https://publish.fid-move.qucosa.de/id/qucosa%3A36340.
Testo completoAbstract (sommario):
The collector of an oscillating water column system (OWC) for wave energy utilization requires a bidirectional turbine that copes with pneumatic power while providing specified impedance or, in terms of an OWC designer, “damping”. Damping is realized by keeping to a specific flow rate through the turbine at a given pressure head due to the individual performance characteristic of the turbine. With the number of turbine designs increasing designers of OWC systems are facing more options to select and dimension a bidirectional turbine. Energy yield, size and hence cost of the turbine and electric generator, operational behaviour, envisaged control strategy and noise emitted by the turbine are possible criteria for selection.
The primary objective of this paper is to describe a simple procedure for making a first choice of a turbine for a particular OWC application. Here we confine ourselves to a family of reaction type of turbines (axial-flow Wells and mixed-flow turbines by Moisel) with their approximately linear pressure head/volume flow rate characteristics. Starting point is the set of non-dimensional steady-state characteristics of each turbine in the family. Utilizing standard scaling laws and a very simple time domain model for the cyclic turbine operation (i.e. based one single sea state and turbine operation assumed to be fixed rotational speed), first estimates of turbine size and rotor speed, number for stages or flows, and performance curves can be determined. The resulting turbine may also serve as a starting configuration for a refined analysis, e.g. the optimization of the turbine and the complete OWC system, utilizing more complex stochastic models. Three case studies illustrate the application of the method: selection and scaling of turbines, effect of collector parameters, turbines in series and parallel.
43
Studley, Allison F. "Numerical Modeling of Air-Water Flows in Bubble Columns and Airlift Reactors". Thesis, Virginia Tech, 2010. http://hdl.handle.net/10919/36380.
Testo completoAbstract (sommario):
Bubble columns and airlift reactors were modeled numerically to better understand the hydrodynamics and analyze the mixing characteristics for each configuration. An Eulerian-Eulerian approach was used to model air as the dispersed phase within a continuous phase of water using the commercial software FLUENT. The Schiller-Naumann drag model was employed along with virtual mass and the standard k-e turbulence model. The equations were discretized using the QUICK scheme and solved with the SIMPLE coupling algorithm. The flow regimes of a bubble column were investigated by varying the column diameter and the inlet gas velocity using two-dimensional simulations. The typical characteristics of a homogeneous, slug, and heterogeneous flow were shown by examining gas holdup. The flow field predicted using two-dimensional simulations of the airlift reactor showed a regular oscillation of the gas flow due to recirculation from the downcomer and connectors, whereas the bubble column oscillations were random and resulted in gas flow through the center of the column. The profiles of gas holdup, gas velocity, and liquid velocity showed that the airlift reactor flow was asymmetric and the bubble column flow was symmetric about the vertical axis of the column. The average gas holdup in a 10.2 cm diameter bubble column was calculated and the results for the two-dimensional simulation of varying inlet gas velocities were similar to published experimental results. The average gas holdup in the airlift reactor for the three-dimensional simulations compared well with the experiments, and the two-dimensional simulations underpredicted the average gas holdup.Master of Science
44
Staudinger, Jeff. "Evaluation of mass transfer correlations for packed column air stripping of volatile organic contaminants from water supplies". Thesis, Virginia Polytechnic Institute and State University, 1986. http://hdl.handle.net/10919/101153.
Testo completoAbstract (sommario):
The application of packed column air stripping systems to the removal of volatile organic contaminants (VOCs) from drinking water sources was investigated. The crucial element for the design of such systems exists in obtaining accurate predictions of mass transfer rates. The first phase of this study evaluated three semi-empirical correlations available for predicting packed column mass transfer rates. From this initial screening, the Onda model was selected for further investigation. A test data base was established from water treatment pilot study results reported in the literature. Ten separate studies were selected for evaluation, encompassing approximately 450 data points. Eleven different VOCs were encountered in these investigations, and the basic packing types tested included rings, saddles, Tri-Packs, and Tellerettes. Comparison of measured mass transfer rates with the corresponding rates predicted by the Onda correlation yielded a relative standard deviation of 17%. A ± 30% accuracy value was therefore assigned to the model based on 90% confidence limits. This assessment agrees with the observed accuracy of the correlation for the chemical engineering-based system results utilized in the model's original derivation. From the overall evaluation, no severe deficiencies and/or limitations with the Onda correlation were noted. In particular, gas-phase resistance predictions appeared reasonably accurate. However, further investigative studies involving observed column performance with larger packing materials (≥2 inches in nominal size) is encouraged to verify the accuracy of the correlation for such situations.
Within the context of the evaluation procedure, several related areas were investigated. First, Henry's constant temperature relations reported in the literature were established within approximately 20% for common VOCs at low concentration levels. Secondly, the transfer unit performance model for calculating observed mass transfer rates was found sensitive to experimental measurement errors below a stripping factor of 1.5. Therefore, measured results obtained under such operating conditions must be viewed with appropriate caution. Finally, economic design boundaries for column operational parameters were established based upon optimization study results reported in the literature.M.S.
45
Roca, Martí Montserrat. "Carbon export from the upper water column of the polar oceans by using natural radionuclides". Doctoral thesis, Universitat Autònoma de Barcelona, 2017. http://hdl.handle.net/10803/457190.
Testo completoAbstract (sommario):
Els oceans Àrtic i Austral representen el 20-35% de l’absorció oceànica global de diòxid de carboni (CO2) atmosfèric. Aquesta absorció és en part causada per la bomba biològica a través de la fixació de CO2 a la superfície de l’oceà i la transferència d’una fracció de la matèria orgànica a aigües profundes. Un dels majors reptes de la investigació polar és pronosticar els efectes del canvi climàtic sobre el funcionament de l’ecosistema marí i la captació de carboni a altes latituds. La poca informació existent sobre la dinàmica dels ecosistemes àrtic i antàrtic, la rapidesa dels efectes del canvi climàtic en els sistemes marins polars, a més de la seva rellevància en el cicle global del carboni han motivat aquesta tesi. L’objectiu d’aquest treball és contribuir al coneixement dels fluxos d’exportació de partícules i de carboni associats a la bomba biològica i dels processos que controlen aquests fluxos a la capa superficial de la columna d’aigua dels oceans polars. Els dos parells de radionúclids 234Th/238U i 210Po/210Pb s’han utilitzat en tres estudis en combinació amb altres tècniques que ofereixen informació complementària sobre paràmetres d’interès ecològic i exportació de partícules. En primer lloc, l’exportació de carboni orgànic particulat (COP) es va quantificar durant el declivi d’una floració massiva de diatomees al sector Atlàntic de l’oceà Austral a l’estiu de 2012. Els fluxos de COP mesurats a 100 m van ser elevats: 26 ± 15 mmol C m-2 d-1, de mitjana. Aquests resultats són comparables a altres estudis de floracions fitoplanctòniques en etapes tardanes a l’oceà Austral. Tot i així, l’eficiència d’exportació va ser generalment baixa: només <20% de la producció primària neta (PPN) diària va arribar als 100 m, presumiblement degut a un reciclatge actiu de carboni i nutrients a la superfície. Per contra, l’eficiència de transferència de COP mesurada entre 100 i 300 m va ser elevada (~60%), probablement com a conseqüència de l’enfonsament de diatomees. En segon lloc, els fluxos d’exportació de carboni al centre de l’Àrtic es van avaluar per primera vegada mitjançant l’aplicació conjunta dels parells 234Th/238U i 210Po/210Pb, coincidint amb el rècord mínim de gel marí del 2012. D’acord al parell 234Th/238U, els fluxos de COP a la base de la zona eufòtica van ser molt baixos (2 ± 2 mmol C m-2 d-1) durant l’agost i el setembre, quan algues de la classe de les prasinofícies haurien contribuït significativament als fluxos. Segons el parell 210Po/210Pb, els fluxos de partícules van ser majors abans del juliol/agost que a finals d’estiu, amb els màxims observats sota condicions extremes de gel associats a una exportació massiva d’agregats d’algues del gel formats per diatomees. Més del 30% de la PPN anual va ser exportada des de la zona eufòtica, indicant una elevada eficiència d’exportació de la bomba biològica al centre de l’Àrtic. Finalment, la dinàmica i l’exportació de partícules a la columna d’aigua de l’Àrtic es van estudiar mitjançant l’anàlisi de la distribució de 210Pb i 210Po a diverses plataformes continentals i conques oceàniques a l’estiu de 2007. Es van detectar dèficits de 210Po substancials (>50% respecte el 210Pb) des de la superfície als 200 m a les plataformes, però també sorprenentment a les conques. Els dèficits de 210Po van ser especialment pronunciats a la conca de Makarov, on la PPN anual va ser tres vegades superior que a la conca eurasiàtica i va estar dominada per diatomees. Aquesta observació, paral·lelament als resultats del 2012, indica que les diatomees podrien tenir un paper més important en la producció i exportació de carboni orgànic al centre de l’Àrtic del que ens pensàvem fins ara.The Arctic and Southern Oceans account together for about 20 to 35% of the global oceanic uptake of carbon dioxide (CO2) from the atmosphere. This is partly caused by the biological pump, which transforms CO2 into organic matter in surface waters and pumps a fraction of it to the deep ocean. A major challenge to polar research is to predict how climate change will affect the marine ecosystem functioning and the carbon uptake at high latitudes. The limited baseline data on ecosystem dynamics in the Arctic and Southern Oceans, the rapid impacts of climate change on polar marine systems, together with their relevance within the global carbon cycle, have motivated this thesis. This work represents an attempt to contribute to the knowledge of the particle and carbon export fluxes driven by the biological pump and the processes that control these fluxes in the upper water column of the polar oceans. The two pairs of radionuclides 234Th/238U and 210Po/210Pb have been used in three studies in combination with other techniques that provide complementary information on ecologically relevant parameters and particle export. First, the export of particulate organic carbon (POC) was quantified during the decline of a vast diatom bloom in the Atlantic sector of the Southern Ocean in summer 2012. The POC fluxes at 100 m were high, averaging 26 ± 15 mmol C m-2 d-1, which are comparable to other studies of the later stages of blooms in the Southern Ocean. However, the export efficiency of the bloom was generally low: only <20% of the daily net primary production (NPP) reached 100 m, presumably due to an active recycling of carbon and nutrients in surface waters. In contrast, the transfer efficiency of POC measured between 100 and 300 m was high (~60%), likely as a consequence of the direct sinking of diatoms. Second, carbon export fluxes in the central Arctic were assessed for the first time by the joint application of the 234Th/238U and 210Po/210Pb pairs during the record sea-ice minimum in 2012. The 234Th/238U proxy revealed that POC fluxes at the base of the euphotic zone were very low (2 ± 2 mmol C m-2 d-1) during August and September, when prasinophytes would have contributed significantly to the fluxes. On the other hand, the 210Po/210Pb proxy indicated that particle fluxes were higher before July/August than in the late summer, with maximum fluxes under heavy sea-ice conditions associated with a massive export of sea-ice algal aggregates composed of diatoms. More than 30% of the annual NPP was exported from the euphotic zone, showing a high export efficiency of the biological pump in the central Arctic. Last, particle dynamics and particle export in the water column of the Arctic Ocean were studied by analysing the distribution of 210Pb and 210Po on a pan-Arctic scale in summer 2007. Substantial deficits of 210Po (>50% with respect to 210Pb) were detected from surface waters to 200 m on the shelves, but also, and more surprisingly, in the basins. The 210Po deficits were particularly pronounced in the Makarov Basin, where the annual NPP was higher than in the Eurasian Basin by a factor of 3 and was dominated by diatoms. This observation, together with the results from 2012, indicates that diatoms could have a more important role in production and export of organic carbon in the central Arctic than is currently thought.
46
Romigh, Melissa Marie. "Organic carbon flux at the mangrove soil-water column interface in the Florida Coastal Everglades". Texas A&M University, 2005. http://hdl.handle.net/1969.1/3751.
Testo completoAbstract (sommario):
Coastal outwelling of organic carbon from mangrove wetlands contributes to
near-shore productivity and influences biogeochemical cycling of elements. I used a
flume to measure fluxes of dissolved organic carbon (DOC) between a mangrove forest
and adjacent tidal creek along Shark River, Florida. Shark RiverÂs hydrology is
influenced by diurnal tides and seasonal rainfall and wind patterns. Samplings were
made over multiple tidal cycles in 2003 to include dry, wet, and transitional seasons.
Surface water [DOC], temperature, salinity, conductivity and pH were significantly
different among all sampling periods. [DOC] was highest during the dry season (May),
followed by the wet (October) and transitional (December) seasons. Net DOC export
was measured in October and December, inferring the mangrove forest is a source of
DOC to the adjacent tidal creek during these periods. This trend may be explained by
high rates of rainfall, freshwater inflow and subsequent flushing of wetland soils during
this period of the year.
47
Stewart, Terence Patrick. "The influence of harbour geometry on the performance of oscillating water column wave power converters". Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.359126.
Testo completo
48
Baker, Beverly Eloise. "Effect of Water Column pH and NO3 on Ortho-Phosphate Release Rates from Freshwater Sediments". W&M ScholarWorks, 1989. https://scholarworks.wm.edu/etd/1539617604.
Testo completo
49
LEBRE, DANIEL T. "Desenvolvimento de metodologia para a determinacao de herbicidas e inseticidas em aguas superficiais utilizando extracao liquido-solido e cromatografia liquida de alta eficiencia". reponame:Repositório Institucional do IPEN, 2000. http://repositorio.ipen.br:8080/xmlui/handle/123456789/10809.
Testo completoAbstract (sommario):
Made available in DSpace on 2014-10-09T12:44:14Z (GMT). No. of bitstreams: 0Made available in DSpace on 2014-10-09T13:57:09Z (GMT). No. of bitstreams: 1 06866.pdf: 7359127 bytes, checksum: 1cbe4a8ebc4462e23ff8a89a820eddab (MD5)
Dissertacao (Mestrado)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN/CNEN-SP
50
Montgomery, Shelagh. "Total dissolved mercury in the water column and interstitial waters of natural aquatic systems and hydroelectric reservoirs of Northern Québec (Canada)". Thesis, McGill University, 1994. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=22778.
Testo completoAbstract (sommario):
For the purpose of evaluating the importance of the water column as a vector of mercury (Hg) to the biota of hydroelectric reservoirs, a comprehensive study was undertaken to provide continuous profiles of total dissolved Hg concentrations, (Hg$ sb{ tau} rbrack rm sb{D},$ in the water column and interstitial waters of natural and artificial environments. Water column samples were collected during the ice-free season (June to October), at various locations and depths within the La Grande-2 and Laforge-1 hydroelectric reservoirs, as well as in several neighbouring lakes. Close-interval sampling of porewaters in lake sediments, peat bogs, and flooded soils was accomplished via in situ dialysis. All Hg analyses were conducted in the field laboratory within 12 hours of sample collection, using cold vapour atomic fluorescence spectrometry. Water column (Hg$ sb{ tau} rbrack rm sb{D}$ are nearly constant, with an average value of 2.3 ng L$ sp{-1}.$ No significant concentration difference was noted regardless of: (1) the type of aquatic system, (2) the composition of the underlying soil, (3) the impoundment history, (4) the depth of the water column, or (5) seasonal changes. Preliminary results for porewater (Hg$ sb{ tau} rbrack rm sb{D}$ show them to be 2 to 3 times greater than those of the overlying water. In most profiles (Hg$ sb{ tau} rbrack rm sb{D}$ values do not show much variation with depth, away from the sediment-water interface. Despite the concentration differences near the interface, diffusion of Hg from the sediments to the water column is not apparent from this study, as satisfactory determinations of (Hg$ sb{ tau} rbrack rm sb{D}$ right at the interface were not possible. Biogeochemical processes acting near the interface (e.g. assimilation by periphyton, chelation by organic matter, methylation-demethylation, absorption on metal oxides) may be responsible for attenuating the release of dissolved Hg to the water column.