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Effectiveness of halophytic plants in the treatment of marine aquaculture wastewaterQuinta, Raquel Figueiredo January 2013 (has links)
This study aims to assess the overall efficiency of S. europaea and A. tripolium plants in wastewater treatment in saline aquaculture systems (IMTA), while generating a valuable secondary crop. Specifically plant N uptake and/or biomass production under different N concentration and forms, salinity, irradiance, temperature and cropping regimes are investigated. It is estimated that at a constant supply of ≥ 300 μmol NO3- l-1 S. europaea N removal of 65.3 ± 18.1 mmol N plant-1 can be achieved over one growing season. Plant growth in a non N limited hydroponic system, with or without a repeated harvest regime, showed that uncropped plants accumulated more fresh biomass than cropped (S. europaea 34 kg m-2 and 17 kg m-2, A. tripolium 21 kg m-2 and 10 kg m-2, respectively). N removal is closely related to plant biomass, and therefore the repeated harvesting can reduce N removal, however it provides a regular high value product for marketing. S. europaea showed better growth when supplied with NO3- or NH4NO3, comparing to NH4+, while A. tripolium growth was not affected by the form of N. The measured A. tripolium and S. europaea DIN uptake, as NH4+ and NO3-, when supplied separately or in an equimolar mix were in general good fits to the Michaelis-Menten model. NH4-15N uptake rates are higher than NO3-15N uptake, except in non-starved S. europaea for single N forms supplied alone. Inhibition of NO3-15N uptake by the presence of NH4+ in solution was observed in non-starved plants. S. europaea responds negatively to salinity 1 compared to 10 and 30, while A. tripolium responds negatively to salinity 30, indicating the suitability of both plant species to be used in systems with middle range salinities, but preference for S. europaea over A. tripolium at higher salinities and vice versa. DIN uptake in both plant species increased linearly with increasing irradiance, and was higher at the mid-range of temperatures tested (20-40 °C). Differences in N uptake with varying environmental conditions needs to be further investigated and taken in account when designing the treatment system. S. europaea and A. tripolium were shown to uptake organic N at comparable rates to DIN uptake, and when in solution more than 68% of organic N uptake was as intact alanine and trialanine indicating the potential of these plants to directly remove DON from the wastewater. Overall the results obtained indicate that S. europaea and A. tripolium are able to perform well in IMTA, with efficient N removal and high biomass production. The data obtained provides a sound basis for system design and scaling up.
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Tidal modulation of seabed light and its implications for benthic algaeRoberts, Emyr Martyn Tomas January 2015 (has links)
The light climate at the seabed of shallow, tidal seas is extremely variable, and light is, therefore, often the most important abiotic factor pertaining to primary production in coastal benthic ecosystems. The influence of the tide on seabed light, and thus photosynthesis, has received limited attention in the scientific literature, despite being potentially very substantial. In this thesis, three physical aspects of tidal modulation of seabed light are investigated: (1) temporal (i.e., springs-neaps) patterns induced by the tide in daily total seabed light; (2) the net effect of the tide (e.g., amplification or reduction) on seabed light integrated over a range of timescales; and (3) the potential of the tide to modify the spectrum of seabed light. The implications of these three aspects for benthic algae are explored theoretically. Observations of seabed light were made over springs-neaps cycles in winter and summer at the Menai Strait (North Wales, U.K.). At this turbid, macro-tidal site, low waters occur at about midday and midnight during neap tides, and at about 6am and 6pm during spring tides. Neap tides hosted the largest daily totals of seabed light in both seasons. A `switch' to spring tides hosting the largest daily totals in the summer months (by virtue of both morning and evening low waters occurring within the longer daylengths), as predicted by Bowers et al. (1997), did not occur. The general increase in turbidity in the strait at spring tides, and the marked increases at low waters of spring tides, were shown to be responsible. Observations at the Bay of Brest (Brittany, France), a macro-tidal site diametrically opposite to the Menai Strait in terms of the times of low waters at neaps and springs, indicated a peak at springs throughout the year. Analytical and graphical tools were developed that permit the nature of springs-neaps patterns in daily total seabed light and the occurrence (or non-occurrence) of seasonal 'switches in sense' to be predicted for sites of interest. Comparison of measured light levels with literature values for the saturation of photosynthesis in example algal species indicated that corresponding springs-neaps cycles may be induced in daily total benthic primary production. The net effect of the tide on seabed light integrated over daily intervals was described theoretically by Bowers and Brubaker (2010). Observations of the effect from the Bay of Brest (Brittany, France), made using a novel mooring configuration, showed good agreement with predictions based on the existing theoretical framework, confirming that the important parameters are the time of low water, tlw, the tidal amplitude, b, the diffuse attenuation coefficient, kPAR, and the daylength, L. The results of a simple numerical modelling study indicated that depthintegrated annual totals of irradiance and photosynthesis are amplified by the tide in the Bay of Brest, despite annual total photosynthesis being reduced by the tide at the shallowest sub-tidal positions, owing to light-saturation and photoinhibition effects. The results also suggested that differences in the areal extent, primary productivity, and vertical zonation of benthic algal communities from site to site may be partially attributable to differences in the values and temporal behaviour of tlw, b, kPAR, and L between the sites, through their influence on seabed light. Time-series observations of the spectral distribution of light at the seabed, made during winter at the Menai Strait, revealed that the most strongly attenuated wavelengths (i.e., blue and red in coastal waters) were preferentially amplified by the tide over a springs-neaps cycle. Further analysis indicated that the observed 'tidal flattening' of the spectrum of time-integrated irradiance would not significantly benefit one example species more than another (i.e., one red alga, one brown) on the basis of their different pigment compositions and photosynthetic action spectra. This was considered to be true at the mean depth of the observations, but it was predicted that at shallower depths the effect would confer a photosynthetic advantage on brown algae such as species of kelp, perhaps contributing to their dominance amongst benthic vegetation in the shallow sub-tidal zone. This study has shown that the tide has significant and predictable effects on the temporal behaviour, quantity and spectral quality of seabed light, which should be accounted for when modelling benthic marine primary productivity, interpreting the results of ecological field studies, and predicting the response of coastal benthic ecosystems to environmental change.
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The impact of large-scale sea-level changes on tides in the past, present and futureWilmes, Sophie-Bernice January 2016 (has links)
Tides propagate through the oceans as shallow water waves and are therefore sensitive to changes in water depth and areal extent of the ocean. In this thesis the impacts of climatologically driven sea-level changes and the resulting changes in ocean extent on the global tidal dynamics are investigated. The large global sea-level adjustments between the Last Glacial Maximum (LGM, 18,000-21,000 years BP) and the present are considered; the present day tidal changes are analysed and the impact of future collapses of the West Antarctic and Greenland Ice Sheets on the tides are investigated using a global tidal model. The 130 m glacio-eustatic sea-level drop during the LGM had a profound impact on the principal semi-diurnal tide, doubling global dissipation rates and resulting in 'megatides' in the North Atlantic region. It is shown that the magnitude of the Atlantic tides is sensitive to the grounding line location of the Antarctic Ice Sheet. Next, the impacts of the altered dissipation for LGM ocean mixing and the meridional overturning circulation (MOC) in the glacial ocean are explored using an intermediate complexity climate model. The importance of tidal mixing for the global ocean circulation is highlighted. Strong LGM tidal mixing could have provided a mechanism for sustaining a vigorous LGM MOC. During the deglacial period glacioeustatic sea-level rose rapidly and large adjustments of the global tides occurred into the early Holocene. In the late Holocene sea-level adjustments were small and tidal dynamics remained fairly constant over this period. Tide-gauge records covering the past decades show global changes in tidal amplitudes occurring in parallel with largescale sea-level changes which have been attributed to global warming. Using simulations forced with observed sea-level trends an attempt is made to reproduce the large-scale change patterns. For M2 the patterns agree well, but for K1 the model is unable to reproduce the trends, possibly due to the small magnitude of the K1 trends. A number of recent studies have highlighted an accelerated ice loss from the ice streams draining the West Antarctic and Greenland Ice Sheet together with widespread grounding line retreats in West Antarctica. It has been suggested that both ice sheets could undergo collapses under certain climate warming scenarios leading to increases in global mean sea-level of 5 m and 7 m, respectively. It is shown that the collapse of a polar ice sheet would lead to large changes in tidal dynamics and thus changes in sea-level variability. These changes have further reaching consequences for shelf-sea dynamics, ecosystems, and open ocean tidal mixing.
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A new proxy for constraining palaeotidal simulations for the Northwest European shelf seasWard, S. L. January 2014 (has links)
Past major changes in sea level have had significant implications for global and shelf sea tidal dynamics. Changing shelf sea tidal dynamics impact on tidal elevation amplitudes, the location of tidal mixing fronts, dissipation, shelf sea biogeochemistry and sediment transport. Some of these major changes are reflected in the geological records of shelf seas and therefore proxy data may be used to constrain tidal model outputs. This study explores a new geological proxy for northwest European shelf sea (NWESS) tidal dynamics by quantifying the relationship between modelled tidally-modulated bed shear stress (BSS) and observed seabed sediment grain size. A grain size tidal current proxy (GSTCP) has been developed by comparing tidal model output of BSS with observational data on present-day grain size data from the Irish Sea. This new proxy is shown to reproduce large-scale sediment distribution in the present-day Irish Sea, and the relationship is applied to the NWESS to predict sediment distribution across the shelf, over a range of (palaeo) time slices. A new three-dimensional palaeotidal model has been developed, which incorporates dynamic palaeotopography from the latest glacial-isostatic adjustment model for the region (Bradley, 2011). The tidal evolution of the NWESS is simulated using 1 ka time slices, from 21 ka BP (taken to be the approximate time of the Last Glacial Maximum) to present-day. Model outputs of BSS from the new palaeotidal model were compared with outputs from existing palaeotidal models, which were developed using different glacialisostatic adjustment models (Peltier, 1994; Lambeck, 1995). The new glacial-isostatic adjustment model produced significantly different relative sea level signals across the shelf, and hence there were differences in the timing of the major changes in modelled BSS between simulations. Sediment grain size evolution profiles were generated for five BGS UK shelf sediment cores, using laser particle diffractometry and radiocarbon dating techniques. Predictive grain size profiles were generated by applying the GSTCP to the modelled evolution of BSS at the sediment core locations, and were compared with the observed grain size profiles. In general, the GSTCP reproduced the observed trends in grain size variations in three of the four sediment cores, although tended to over-predict the grain size in all core locations. Despite the limitations of the GSTCP for reproducing observed sediment classifications at specific sites, the GSTCP was applied to the regional model output of BSS to generate predictive maps of seabed sediment types on the shelf, in 1 ka time slices from 21 ka BP to the present-day. Such maps of sediment distribution are useful for a number of applications, including for physical (e.g. morphodynamic) modelling and biological studies (e.g. habitat mapping). The new palaeotidal model was also used to estimate changes in the position of the shelf sea tidal mixing fronts with sea-level rise since 21 ka BP. Prior to this work, the only proxy data used to constrain palaeotidal model simulations was from one sediment core from the Celtic Deep. The timing of stratification at the core location had been used to validate a palaeotidal model; however, considerable variation in the timing of onset of stratification at the core locations considered here was predicted by different palaeotidal model simulations. Further, since the position of the tidal mixing front is very sensitive to the value used for the critical contour, it is suggested that using the timing of stratification at an isolated site is too sensitive a parameter for validating palaeotidal models. The GSTCP does not fully resolve the changes in observed grain size at the core locations, thus the proxy is considered unsuitable for constraining palaeotidal model output in this context. The main limitations are the lack of consideration of sediment availability and supply, the limited spatial extent of the geological data (i.e. few sediment cores) and the absence of wave-induced BSS. Future work should consider combined wave and current induced sediment transport, and the feedbacks between evolving morphodynamics and hydrodynamics, over a range of timescales. The new proxy can be used to approximate the large-scale sediment distribution over the NWESS for the present-day, and has been applied to palaeotidal model output to predict the evolution of large-scale patterns in sediment dynamics across the shelf over the last 21 ka. The predictive map of the large-scale distribution of seabed sediment grain size is useful for a number of applications, including for considering the marine aggregate resource, for marine habitat mapping, and for including spatially-varying bed roughnesses in hydrodynamic- and morphodynamic models.
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Operational ocean modelling : a critical evaluation of published worksSiddorn, John January 2016 (has links)
This thesis presents a subset of the author’s published works, and describes the impact his work has had on ocean forecasting systems. This impact can be broadly divided into two themes, the underpinning development of ocean forecasting models and the implementation, tuning and evaluation of those models to ensure they provide skilful products, with value to users. The systems described in this dissertation are recognised as amongst the best available, and are being used by commercial operators, military decisions makers and governmental organisations, as well as research users. They also form the basis on which future systems will be developed, meeting the challenges and addressing the priorities discussed in the thesis. The author expects to have a substantive impact on driving the research agenda in these areas over the coming years.
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Late Quaternary benthonic foraminiferal stratigraphy of the western U.K. Continental ShelfAustin, William E. N. January 1991 (has links)
Late Quaternary deposits have been investigated from three main study areas from 'western Britain in an attempt to define lithological and biostratigraphic changes. Detailed analyses of included benthonic foraminiferal assemblages are presented and a systematic section included which describes and illustrates over 200 distinct forms. Chronostratigraphic control is provided by radiocarbon dates, amino acid analysis and tephrachronology. The three study areas yield distinctive records of the depositional environments characterizing the climatic events of the Late Quaternary. From the Hebridean Shelf, B.G.S. vibrocores have been analysed within the context of a previously established seismostratigraphic sequence. Foraminiferal faunas allow the reconstruction of a regional climatostratigraphic sequence for the Lateglacial period (c. 14,000 to 10,000 BP) and this sequence is correlated, through 9 radiocarbon (AMS) dates, to the established climatostratigraphy of the Lateglacial period from N.W. Europe. Reconstructions of notional water depths during this period allow glacio-isostatic components from the shelf to be estimated and these confirm a generally accepted pattern of changing relative sea-level, from initial regression following deglaciation and subsequent transgression as the eustatic component over-takes the isostatic component. Rising sea-levels are most notable after about 10,000 BP. A cliff section at Aberdaron on the western Lleyn Peninsula provides an insight into the controversy surrounding the question of depositional origin of the "Irish Sea Drift" sequences bordering the Irish Sea. Diamicts and sorted layers from the section contain mixed boreo-arctic, temperate and pre-Quaternary species, and allochthonous/autochthonous elements are identified. While lithological changes within the section are marked, the foraminiferal assemblages maintain relatively constant faunal ratios. None of the foraminifera are considered to be in situ, but instead entrained by the Irish Sea glacier during its passage along the Basin and deposited at the site by basal melt-out processes. The third study area, the southwestern Celtic Sea, records geomorphological evidence of previously extensive glaciation in the region. Microfaunas, both foraminifera and Ostracoda, are analysed and record a transition from grounded ice lodgement facies to quiet, glacial marine facies at about 49°30 N. Amino acid analysis confirms the geomorphological evidence for glacial marine accumulation during the Late Devensian.
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Characterisation of a point-source integrating cavity absorption meter for applications in optical oceanographyLefering, Katharina January 2016 (has links)
Many biogeochemical and physical processes in the aquatic environment are driven by the spectral light absorption properties of the water body and the constituents dissolved and suspended within. Improving our knowledge on absorption processes in marine waters is of great interest to optical oceanographers as absorption influences the structure of underwater light fields. The determination of high quality absorption data are important for accurate modelling of underwater radiative transfer processes and the interpretation and derivation of ocean colour remote sensing products. Accurate measurements of spectral absorption coefficients, however, are challenging because instruments and methods are affected by scattering by marine particles and can suffer from significant systematic errors. Röttgers and co-workers (2005) introduced a point-source integrating cavity absorption meter (PSICAM) in which sample absorption is measured inside an integrating sphere using a totally diffuse light field. This set-up has been shown to be insensitive to scattering errors and therefore ideally suited for absorption determinations of marine waters. Initial characterisation and a sensitivity analysis confirmed the superior performance of the PSICAM compared to other spectrophotometric techniques but also highlighted remaining limitations in accuracy at UV/blue wavelengths. PSICAM data were subsequently used to develop and validate corrections for established absorption measurements, in particular the determination of particulate absorption coefficients with the filter pad technique and the determination of in situ absorption measurements with submersible AC-9 instruments. The latter can be used to populate radiative transfer models and simulate underwater light fields. An optical closure study demonstrated consistency between in situ measurements of radiometry and inherent optical properties coupled into radiative transfer model outputs, confirming high accuracy of input absorption data and output model parameters. The ability to model underwater and water-leaving light fields correctly is important for ecosystem modelling application and the validation of satellite remote sensing data. A preliminary analysis of the potential to simultaneously measure spectral fluorescence and absorption was carried out. This demonstrated both the magnitude of inelastic scattering effects on current PSICAM performance and potential towards further development of the system that could benefit primary production studies.
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Insight into the nitrogen cycling in the North SeaRosales Villa, Alida January 2016 (has links)
Fixed nitrogen (N) is an important element which may limit marine primary production. Nitrogen inputs to coastal waters have increased putting pressure on this ecosystem. Supply and removal of N depends on a series of N-cycling processes including canonical denitrification and anammox which remove N, while dissimilatory nitrate reduction to ammonium (DNRA) recycles N allowing it to remain available for primary producers. The sediments in the coastal zone are a key site for these processes but the environmental factors regulating them are still poor understood and the fluxes poorly quantified. This study investigated sedimentary N-cycling at 5 sites in the open North Sea in August 2013, and at one station in the Wash estuary in May, June, September and October 2013 using 15N tracer techniques, pore water studies and direct sediment flux measurements. All sites had relatively low sedimentary organic carbon content (<5%). The results of this study showed temporal variation in the Wash, and spatial variation in the North Sea and the tracer studies provided valuable new information about the sedimentary nitrogen cycle. At all sites the main process contributing to total N2 production was denitrification (>95%) with on average >80% associated with coupled denitrification. The average rates of denitrification were higher in the North Sea (7.62 mol m-2h-1) than in the Wash (4.4 mol m-2h-1). Anammox was not detected at the Wash sites and contributed only 6.6% to total N2 production at the North Sea sites. DNRA was observed during three of the months studied at the Wash sites but only at one North Sea site and, where measurable, was responsible for between. 6.5 and 30% of nitrate reduction. Temperature was identified as an important control on the overall rates of denitrification. The results indicate that denitrification is a major sink for nitrate in the North Sea.
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The production of biogenic gases in the marine environmentWilson, Sam T. January 2007 (has links)
The biogenic trace gases dimethylsulphide (DMS) and methane play a major role in the Earth’s climate and atmospheric chemistry. DMS makes a significant negative contribution to radiative forcing and methane is an important greenhouse gas. The marine environment is an important source of both DMS and methane and this thesis investigated the interactions between methylated sulphur compounds and methanogenesis within micro-environments in the upper-water column. The production of DMS is closely associated with dimethylsulphoniopropionate (DMSP) and dimethylsulfoxide (DMSO) although comparatively little is known about the dynamics of DMSO in the marine environment. This study analysed the production of DMSO by a range of marine phytoplankton species in comparison with DMSP. Algal concentrations of DMSO were taxon-dependent and an average DMSPp:DMSOp ratio of 4.85 was calculated for the phytoplankton species analysed. The consistent presence of DMSO at ~20 % of total intracellular methylated sulphur (DMSP + DMSO) suggests it is an important algal consituent. The fate of DMSP and DMSO produced by algal cells was analysed in a series of grazing experiments with the copepods Temora longicornis and Acartis clausi, and the dinoflagellate Scrippsiella trochoidea. The relative importance of assimilation, sloppy feeding, DMS production and excretion of faecal pellets as sinks for algal-DMSP was calculated. In comparison to the ambient marine environment, both algal cells and copepod faecal pellets were identified as micro-habitats of elevated DMSP and DMSO concentrations. Millimolar concentrations of DMSP were measured in algal cells and micromolar concentrations of DMSP were recorded in copepod faecal pellets. These hotspots of DMSP and DMSO may be associated with chemical processes that differ from bulk seawater characteristics, such as the transformation of DMSO as revealed in coastal pelagic particulate material. Furthermore, oxygen depletion at the micro-scale could facilitate the presence of anaerobic bacteria, or anaeorobic bacterial activity, in the predominantly aerobic pelagic environment. The occurrence of methanogenic Archaea specifically associated with copepod faecal pellets from mono-species cultures of copepods, environmental samples and total pelagic particulates was investigated using 16S rRNA gene libraries. Clusters of sequences closely related to Methanogenium, Methanobacterium and Methanolobus were recovered. This work revealed that CO2-reducing methanogens can exist in the pelagic environment where it was previously assumed methylotrophic methanogenesis dominated. This work demonstrated that the methylated sulphur compounds represent a metabolic substrate for methanogens in the upper water column. The addition of DMSP, DMSO and DMS to samples collected from the upper water column stimulated methanogenesis when incubated under anaerobic conditions. The addition of inhibitors suggest that other anaerobic bacteria e.g. sulphate-reducing bacteria, may play a key role in this process. The potential for DMSP and DMSO to serve as precursors for methane, a potent greenhouse gas, as well as DMS, has important implications when considering the emissions of these compounds from the marine environment and their role in the Earth’s climate.
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Genesis and distribution of recent sediments on the Pedro Bank South of JamaicaDolan, Peter B. January 1972 (has links)
No description available.
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