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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
411

The hydroecology of groundwater-fed streams in a glacierised catchment

Crossman, Jill Helen January 2010 (has links)
Groundwater flow typically provides stable stream habitat within glacierised floodplains. However, spatio-temporal differences within and between groundwater flow pathways can create marked variability in the physicochemical characteristics of groundwater-fed streams. Research conducted on a floodplain terrace of the Toklat River, Denali National Park, Alaska, predominantly from May to September 2008, determined the influence of groundwater flow dynamics upon benthic and hyporheic macroinvertebrate assemblages. During periods of resource depletion benthic macroinvertebrate abundance was dependent upon contributions from specific flow pathways (DFSdeep), which supplied fine particulate organic matter. Dynamics of groundwater flow pathways influenced macroinvertebrates throughout the summer, however, with higher diversity observed in perennial streams which received groundwater flow from DFSdeep. Ephemeral flow pathways of glacial seepage supported lower diversity. Within the hyporheic zone, environmental stability of surface waters was influential, as this reflected the sub-surface residence time of percolating waters; nested routes of flow within each flow pathway, of varying length or permeability, created differences in the environmental stability of each stream. Macroinvertebrate diversity in the hyporheic zone was higher at sites of lower surface environmental stability, suggesting possible migration into the hyporheic zone. Digital remote sensing used to estimate the spatial extent of groundwater upwellings within two national parks in Alaska indicated that these groundwater-fed habitats are widespread.
412

On the 3-D reconstruction of Paleozoic and Mesozoic paleobotanical problematica

Rees, Andrew Ronald January 2013 (has links)
Detailed descriptions of 3-D anatomically preserved specimens in paleobotany have been undertaken for over 100 years. Some of the most comprehensively characterised of these specimens are reproductive structures, especially cones and ovules. Throughout this time many of the ways of gaining information such specimens has remained static. In recent years new computer software and techniques have been developed that allow detailed 3- D computer reconstructions to be undertaken that allow holistic observations of the context of the whole organ. Detailed 3-D reconstructions have been undertaken of several genera of Palaeozoic and Mesozoic paleobotanical reproductive organs. These complex structures have undergone traditional preparation, such as serial sectioning, preparation specifically for reconstruction such as serial grinding and non-destructive scanning micro X-ray tomography. Reconstructions were then produced in bespoke software, Serial Paleontological Image Editing and Rendering System (SPIERS). The reconstructions produced provide a new understanding to the structure and functions of tissues within paleobotanical reproductive specimens. For the first time, specimens of extinct and extant genera have been compared using new reconstruction techniques in order to aid in the future understanding of their evolution and development, and to aid visualisation of complex structures for which illustrations in 2-D form are inadequate.
413

The geochemistry and petrogenesis of the Lower Paleozoic granitoids of North Wales

Croudace, Ian W. January 1980 (has links)
The Lower Paleozoic rocks of North Wales are penetrated by numerous bodies of dolerite and intermediate-acid material which are closely associated with pillow basalts, acid and basic tuffs and ignimbrites. Igneous activity occurred throughout the Ordovician although in Snowdonia and Lleyn it reached a climax during the Caradoc stage. The present study has considered the granitoids of Snowdonia and Lleyn which are intruded as stocks, laccoliths and high level plugs (<5 km2) into clastic and volcaniclastic sediments. A substantial body of new chemical data has been obtained for over thirty intrusions. Twenty-four major and trace elements were determined on each sample by X-ray fluorescence techniques and the rare earth abundances of forty-five selected samples were measured using a radiochemical neutron activation procedure. Three distinctly different types of granitic material are recognised and their possible evolutionary mechanisms are discussed in detail. On the basis of the geochemistries of the various sampled intrusions it is concluded that they were all ultimately derived from the mantle by partial melting. One group originated from the remobilisation of calc-alkaline plutons formed by hydrous melting of the mantle wedge above a destructive plate margin. The other two groups, it is argued, evolved from tholeiitic basaltic magma by low-pressure fractional crystallisation. The goochemical affinity between some Caradocian andesitic material from Lleyn and the tonalitic-granitic intrusions of the same area has provided good evidence against a view that the latter were emplaced late in the Caledonian cycle (Silurian-Devonian). A paleo-tectonic reconstruction of the North Wales region is presented and it is claimed that the area evolved as a volcano-tectonic rift zone, a precursor of a back-arc basin.
414

Organic matter fluorescence properties of some U.K. fresh and waste waters

Hudson, Naomi Jane January 2010 (has links)
Organic carbon is ubiquitous throughout the aquatic environment. It is an heterogeneous mixture of compounds, some of which are fluorescent, with allochthonous and autochthonous origins. The most common aquatic fluorophores are humic materials (peaks C and A) from degraded plant matter and protein-like material (peaks T1 and T2) of microbial origin. Spectral fingerprints of aquatic organic matter composition may be visualised on an excitation emission matrix (EEM) on which each fluorophore is identifiable as a characteristic peak. Protein-like fluorescence (T1 and T2) is linked to bacterial activity, sewage treatment process efficiency and therefore organic matter bioavailability but its source and fluorescence response is poorly understood. In comparison, peaks C and A are widely studied and have historically been considered to be old, degraded and stable. In this thesis I investigate the character of surface water and effluent fluorescent organic matter using EEMs. I identify the likely origins and bioavailability of common fluorophores and the applicability of fluorescence as a technique for measuring the polluting potential of organic carbon in waters. I also determine changes in sample character and organic carbon concentration, through responses of the common fluorophores, under different environmental conditions and recommend best practice for sample storage.
415

Controls and modification of large-scale climate–hydrology–ecology associations

Laize, Cedric Louis Raymond January 2015 (has links)
The study aimed to disentangle the climate–hydrology–ecology chain of processes at large spatial and temporal scales. River ecology was considered in terms of some of the main controls of physical habitat (environmental flows, hydraulics, and water temperature). The research included four complementing studies investigating associations between: (1) climate (atmospheric circulation and regional climate) and river flows; (2) river flows and river hydraulics; (3) regional climate and river water temperature; (4) regional climate and environmental flows. The first three studies focused on current conditions, had a national (mainland UK, or England and Wales) geographical scope and a seasonal temporal scale, and used only near-natural sites. In each study, the main drivers were identified, as well as the rivers or regions most/least sensitive. UK-focussed findings were then put into the wider context of future climate- and human-induced river flow change at the pan-European scale: a novel method to assess ecological risk due to flow alteration was developed and applied to flow scenarios for the 2050s. The role of basin properties in modifying those associations was also assessed. Two key aspects emerged: (i) importance of seasonal patterns; and (ii) strong basin property patterns. The study addressed the lack of studies with extensive geographical coverage, high site density, and long periods of records. Spatial patterns could only be found for studies involving climate and flow (historical or future projections); for hydraulics and temperature, spatial patterns were related to basin properties. For all studies, a small set of basin properties were found to have a significant influence: elevation, permeability (except for hydraulics), size (hydraulics and temperature only).
416

Hydroclimatic variability in northeast Turkey : identifying climate and river flow dynamics and controls

Saris, Faize January 2011 (has links)
The East Black Sea (EBS) and the Çoruh River basins (ÇRB) of northeast Turkey have a number of challenging water related issues of socio-economic and ecological importance. This PhD thesis aims to understand hydroclimatological variability across Turkey taking a large-scale perspective by defining precipitation regimes and extremes and then focussing on the climatic and basin drivers of river flow variability in northeast Turkey. At the national-scale, Turkey exhibits six precipitation regime regions of which three characterise northeast region. The northeast and southwest coastal regions of Turkey are characterised by the highest frequency of extreme precipitation events. The mountainous area of the EBS is defined by May-June Peak river flow regime, while ÇRB is characterised by April-May Peak flow regime. Intra-annual variability in the timing of river flow over northeast Turkey is controlled mainly by the regional climatic variability. Spring rainfall peak is linked to snowmelt. Important changes are detected in temperature extremes, also in precipitation and river flow for some cases. Regional precipitation and temperatures for September-May period have an important influence on river flow extremes. Temperature variability across northeast Turkey is closely linked to seasonal indices of East-North Atlantic teleconnection patterns, especially during winter.
417

Salmon population in watersheds of different complexities following ice recession in Glacier Bay as determined by the physical habitat template

Sønderland, Svein Harald January 2017 (has links)
The diets of sympatric stream dwelling juvenile coho salmon (Oncorhynchus kisutch) and Dolly Varden (Salvelinus malma) were analyzed in five streams of different age and watershed complexity since glacial retreat in Glacier Bay, southeast Alaska. Interferometric synthetic aperture radar (IFSAR) data were analyzed with geographic information systems (GRASS GIS) to understand watershed change since deglaciation. Spatiotemporal variations of watershed characteristics from GIS were then used to develop a four-dimensional physical habitat template (PHT) and a directional model of stream development. Juvenile coho salmon and Dolly Varden coexisted in all streams with a strong overlap in diet while using different foraging zones. Diet niche breadth for both species increased with the amount of terrestrial insects in the diet as a result of resource depression, as mean fork length (FL) of juvenile fish increased when aquatic insects were a greater part of the diet, but decreased with greater terrestrial input. Using the stable isotopes of δ15N and δ13C, the contribution of marine derived nutrients (MDN) to stream biota was found to be determined by salmon spawner abundance and watershed retention, and an increase in δ15N and δ13C dispersion (SD) was found with stream age, likely causing a difference in the fractioning of δ15N and δ13C. The most significant change with stream age was denudation of watersheds and the development of stream networks. Dietary overlap was linked to fish resource depression, and controlled by stream geomorphology. Juvenile salmonids were found to consume sea lice (Lepeophtheirus salmonis) in the older streams.
418

Relations between fault surface morphology and volume structure : 3-D seismic attribute analysis deepwater Niger Delta fold and thrust belt

Jibrin, Babangida January 2012 (has links)
Studies have shown that faults exhibit complex geometries that are often highly simplified and cross sections may not be sufficient to highlight the spatial variation of fault surface topography and the complex relationship with the wall rock. The main contributions of this thesis to structural geology are novel methods for investigating links between fault shape and wall rock structure. Curvature plots of sixteen faults show that thrust faults in deepwater Niger Delta exhibit corrugations on a range of wavelength and amplitude. The corrugations are characterized by large-scale anticlastic and synclastic geometries parallel to fault transport direction. The structure of the volumes in the immediate vicinity of the faults was investigated using slices of seismic attribute data sampled parallel and adjacent to thirteen faults. In half of the faults the hanging wall is more disrupted than the footwall, while in the other half the footwall is more disrupted than the hanging wall, implying that thrust zones exhibit complex geometries that existing models have yet to address. In addition, disruptions near fault surfaces may be related to discrete zones of intense fault surface maximum curvature, anomalous surface gradient and change in pattern of anticlastic and synclastic fault Gaussian surface curvature in the fault transport direction. No significant wall rock disruption was observed where fault surface curvature is planar.
419

Comparative study of methods for quantifying wood smoke in the UK atmosphere

Hu, Lihua January 2012 (has links)
The thesis investigates the inorganic aerosol concentrations and wood smoke tracer potassium and levoglucosan concentrations in Birmingham, UK. Also a multi-wavelength aethalometer was utilized as a carbonaceous aerosol detector to directly measure the local wood smoke PM mass and traffic PM mass. To achieve this, daily PM2.5 inorganic ions sodium, ammonium, potassium, magnesium, calcium, chloride, nitrate, sulphate, and organic compound levoglucosan were measured over a period of more than one and half years at four sampling locations. There were: (1) Elms road, University of Birmingham; (2) North Kilworth Mill Observatory Site; (3) Churchill Pumping Station Site; and (4) Budbrooke, Warwick Sampling Site. Correlation analysis, regression analysis, and seasonal variation were examined for those inorganic and organic elements and compounds. The results were used to provide comprehensive spatial and temporal distributions, intra-site and inter-site comparison differentiations. Wood smoke potassium and levoglucosan were used as wood smoke tracer to determine the local resident wood smoke PM mass concentrations in this thesis. Budbrooke, Warwick Sampling Site for example, a mean value of 62ng m-3 wood smoke potassium was measured at winter periods but the mean value of only 17ng m-3 was measured during summer periods. This significant difference demonstrated a frequent wood smoke activity in this area during winter periods. Also a multi-wavelength aethalometer was used as wood smoke mass detector to measure the local resident wood smoke PM mass and local traffic PM mass concentrations. These three methods have their unique processes of acquiring the wood smoke mass concentrations, thus the results from these method have considerable variations. Therefore these three methods have inter-compared with each other to achieve better wood smoke concentrations results in order to obtain the best method of measuring local wood smoke mass.
420

Urban heat and energy demand : application of an urban meteorological network

Azevedo, Juliana Antunes January 2016 (has links)
The urban heat island (UHI) effect is an inadvertent modification of climate which leads to increased temperatures in urban areas. This in turn increases localised demand for air conditioning and refrigeration which can be a significant drain on energy resources. At a time of increasing economic, political and environmental concerns with respect to energy policy, security, efficiency and climate change, there is a need to focus efforts to understand energy usage in cities for current and future climates. Using data from an Urban Meteorological Network (UMN) along with a critiqued degree days methodology, this thesis analyses the UHI and estimate current and future cooling demand in Birmingham-UK. From the results it was possible to identify that currently the main factor in energy consumption is income, however when isolating income influence through normalization process it is possible to identify the impact of the UHI. A significant finding was that the distribution of the surface UHI appears to be clearly linked to landuse, whereas for canopy UHI, advective processes appear to play an important role. Analysing Tair data available from the UMN the cooling demand for summer 2013 and future climate scenarios were calculated and demonstrated the importance of high resolution air temperature measurements in estimating electricity demand within urban areas.

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