• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • No language data
  • Tagged with
  • 38
  • 38
  • 38
  • 38
  • 29
  • 29
  • 15
  • 7
  • 7
  • 6
  • 6
  • 4
  • 3
  • 3
  • 2
  • 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.
1

GPR investigations of the sedimentary architecture of jökulhlaup eskers : Skeidarájökull, Iceland and Bering glacier, Alaska

Burke, Matthew John January 2008 (has links)
Eskers are ridges of stratified glaciofluvial material deposited in englacial, subglacial or supraglacial channels and ice-walled canyons. Eskers have been used to infer the dynamics and palaeo-hydrology of large ice sheets, despite observations of palaeo-esker sedimentary architecture lacking rigorous constraints on depositional timescale. This research aims to identify the hydrological, glaciological and sedimentary controls on the sedimentary architecture of single event outburst flood (jokulhlaup) eskers at SkeiOarârjOkull and Bering Glacier. These eskers formed during monitored outbursts, providing time constraints on the depositional events, thereby making the eskers ideal analogues for palaeo-eskers. GPR data was collected using a pulseEKKO Pro 1100 system at SkeiOarârjOkull and Bering Glacier during field seasons in 2006 and 2007. At SkeiOarãrjOkull grids of 100 MHz GPR lines were collected on the glacier surface and 200 MHz GPR grids were collected on all workable sections of an esker and ice-walled canyon fill generated by a jokulhlaup in November 1996. At Bering Glacier 200 MHz GPR grids were collected on workable sections of an ice-walled canyon fill and esker generated during outbursts in July-August and October 1994, respectively. Examination of the GPR data has allowed development of site-specific models for esker and ice-walled canyon fill deposition, providing the first detailed insight into the sedimentary architecture of single event jokulhlaup eskers. These models show that single high-magnitude jOkulhlaups can generate eskers with complexities previously unexpected for single events. The englacial position of an esker is controlled by the presence of structural weaknesses within the ice and the jokulhlaup release mechanism. Esker sedimentary architecture, on the other hand, is controlled by a complex interaction between hydrological, glaciological and sedimentary factors. The most fundamental control on jokulhlaup esker sedimentary architecture is conduit geometry, which determines the type of macroform from which the esker is composed. Thus, eskers deposited during jOkulhlaups should be made up of both wide ridges as composite macroforms in areas of conduit expansion and narrow ridges composed of upper-stage plane beds in constricted conduits. The smaller scale sedimentary features, which include antidunes and boulder clusters, as well as the frequency of erosional structures, are controlled by interactions between the flow conditions and sediment supply. The eskers generated during the 1996 SkeiOarãrhlaup and 1994 Bering Glacier outburst flood demonstrate sedimentary architectures that are similar to those identified in many palaeo-eskers described from previous studies. The research suggests that jOkulhlaups may have had a greater role in palaeo-esker sedimentary architecture than previously hypothesised.
2

The vulnerability of broad vegetation community types to climate and land use change within Northumberland National Park

Ovens, Christopher January 2015 (has links)
Future climate and land use change are predicted to have a concomitant impact on ecological communities. Some sources have proposed that at global scales, and for particular regions, land use change will have a greater impact than changes in climate. This research aimed to test this assertion for the semi-natural landscape of Northumberland National Park (NNP) in the north east of England. The methodology applied a simple habitat suitability model to simulate changes in the distribution of relevant vegetation communities through changes in land use occurring under two future land use scenarios formulated for the study area. Appropriate landscape metrics were then applied to the results to gauge how the associated changes in patch characteristics impacted on the sensitivity and adaptive capacity of the communities. A relatively simple bioclimatic envelope model was also applied to the results of the land use modelling to estimate the sensitivity of vegetation communities to changes in climate predicted under the UKCP09 Medium emissions scenario. Together the applied measures offer a simple and accessible method for estimating the current and future vulnerability of Broad Vegetation Communities (BVCs) within the study area. Results were analysed at the landscape level for NNP, as well as the five National Character Areas (NCAs), which wholly or partially coincide with its area. Class level results were analysed for nine Priority Broad Vegetation Communities (PBVCs) for NNP and each of the NCAs. Overall the results strongly suggest that the climate changes predicted to affect the park in the future are likely to have a notably greater impact on the vulnerability of the PBVCs than the simulated changes in land use. Landscape level results suggest that vulnerability is likely to be notably reduced in the future under both land use scenarios. This is due the majority of PBVCs exhibiting significant reductions in overall vulnerability in the future, largely due to significant reductions in their levels of climate stress. However, two PBVCs (Blanket Bog and Raised Bog) exhibited considerable increases in vulnerability, due to the increases in the climate stress that they experience. These PBVCs may be regarded as a potential focus for future conservation efforts. The approach adopted within this research has allowed a number of relevant management recommendations to be made for NNP and for individual PBVCs and NCAs. PBVCs most at risk have been identified and relevant causes investigated. The characteristics of the methodology (simplicity, accessibility, robustness) mean that it provides a useful framework for providing meaningful vulnerability assessments for whole ecological communities across entire landscapes with comparative ease and speed.
3

Disaster management, climate change and variability and social resilience

O'Brien, Geoff January 2008 (has links)
Accelerated climate change and increasing climate variability caused by increasing anthropogenic greenhouse gas emissions is the single largest threat to the international goals of sustainable development, the Millennium Development Goals (MDGs) and disaster risk reduction. Global discourses recognise the need for effective and sustainable responses to produced climate risks. The risk types likely to occur are known, but only in broad terms. That they are produced by human action is accepted; but their scale, severity, longevity and frequency are not known. The challenge for policymakers is developing an effective framework within which sustainable responses can be formulated. Addressing the problems of produced risks requires a comprehensive approach to risk management to be effective. The mechanisms within the climate change, sustainable development and disaster risk reduction discourses are not sufficiently effective or integrated to respond to this challenge. Fundamental reform to current modes of risk reduction is needed, but this can only be achieved by a shift in the dominant perspective on formulating sustainable responses. This requires a shift to an enabling policy framework that encourages bottom-up resilient responses. Resilience is argued as a tool for policy development that can enhance adaptive capacity to current climate risks and shape energy policy to respond to mitigate future climate risks.
4

Getting down to local level : exploring vulnerability to improve disaster management systems in Nepal

Aryal, Komal January 2012 (has links)
This research explores disaster vulnerability in Nepal. Disaster vulnerability is increasing due to the following reasons: weak governance; demographic growth; rapid urban expansion; relatively weak land use planning; the growth of informal settlements; poor construction methods; steep land farming practices; the encroachment of river plains and forest areas; and environmental degradation. This research is divided into three parts; problem overview, mapping past disaster events and community vulnerability. Often disaster management practice at the national level has tended to focus on large-scale events. In Nepal, there is a history of government responses to large-scale disasters; however, evidence increasingly shows that small-scale disasters have a more significant impact on people’s livelihoods. This is the case in Nepal and it is unclear whether small-scale disasters have prompted policy change. The purpose of this research is to evaluate the impact of small-scale disasters and to ascertain if there is any evidence of a shift in government disaster management policy. Local disasters seem to dominate the lived risk experience, but there is little understanding of how small-scale disasters can contribute to disaster risk reduction knowledge. Urban and rural communities differ in their understanding of small-scale disaster knowledge base, not least because both populations have little experience of the risks they take as a result of migration to new environments. This study captures 10 years of field experience in Nepal. This research has found that:- Small-scale disasters have a greater impact than larger disasters. Without an integrated policy and legislative framework approach from government and a focus on small-scale disasters, it is unlikely that effective disaster risk reduction measures will be integrated into sector development planning. People’s knowledge of, relationship to, and interactions with small-scale hazards in a changing climate produce new risks and vulnerabilities at the local level. This thesis concludes with recommendations for improving disaster risk reduction at the local level in Nepal.
5

Pliocene vegetation and climate of Arctic Norway and the variability of the Norwegian Atlantic current

Panitz, Sina January 2016 (has links)
The Pliocene Epoch (5.33–2.59 Ma) is characterised by climatic conditions similar to those predicted for 2100, with enhanced warming in the (sub-)Arctic. The climate evolution at high latitudes is not well understood due to the sparsity of time-continuous palaeoenvironmental records. This study provides new records of Pliocene vegetation changes in Arctic Norway and the variability of the Norwegian Atlantic Current based on analyses of terrestrial and marine palynomorphs from ODP Site 642 (Norwegian Sea, 67°N) to assess climate variability and identify different scale forcing mechanisms. The Piacenzian pollen record (3.60–3.14 Ma) shows vegetation changes between cool temperate and boreal forests during warmer-than-present and similar-to-present climate phases, respectively, implying shifts of the northern deciduous/mixed forest limit of 4–8° latitude. During warm phases, warmest month temperatures were 8–14°C higher than present. The development of peatlands during cooler phases may have amplified the cooling through CO2-drawdown and positive vegetation-snow feedbacks. The high regional and hemispheric-wide climate variability highlights the importance of well-dated, high-resolution records for regional to global palaeoenvironmental reconstructions and data-model comparisons. Long-term Pliocene vegetation changes (5.03–3.14 Ma) reveal a continuous decline of thermophilic elements over successive warm phases, supporting the notion of long-term climate cooling caused by decreasing CO2 concentrations. This cooling is superimposed on shifts between cool temperate and boreal climate phases on multi-millennial timescales. Minima in eccentricity (400-ka), together with low-amplitude obliquity/precession cycles are associated with the development of boreal conditions. At 4.56 Ma, a marked decline in pollen influx suggests atmospheric circulation changes in response to the shoaling of the Central American Seaway, a hypothesis supported by model results. Subsequently, changes in northward heat transport via the North Atlantic Current strongly affected vegetation changes. The Pliocene climate evolution represents the later part of late Neogene cooling instead of a reversal of that trend. Dinoflagellate cyst assemblage changes (3.320–3.137 Ma) indicate variations in Atlantic and Arctic water influence, corresponding to cool temperate and boreal terrestrial climatic conditions in Arctic Norway, respectively. These records emphasise a high climate variability on glacial-interglacial timescales and linkage of both marine and terrestrial environmental changes.
6

Measurement and modelling of sub-canopy radiation to seasonal snow in Alpine forests

Webster, Clare January 2017 (has links)
The overlap of seasonal snow and forests contributes significantly to global snowmelt, largely driven by net radiation, the combination of shortwave and longwave radiation. In sub-canopy longwave radiation models, unavailability of forest canopy temperature measurements often results in locally measured air temperatures being used to represent the temperature of the emitting canopy. The validity of this assumption was tested using extensive field measurements in three sub-canopy mid-latitude alpine environments, and resulted in improvements to model simulations of sub-canopy incoming longwave radiation. Three different radiometer configurations (stationary distributed, stationary linear, and moving linear) were simultaneously compared in a spruce forest in the eastern Swiss Alps, capturing the annual range of sun angles and sky conditions. The two linear configurations showed the greatest similarity in shortwave transmissivity, and the measurements of longwave enhancement were largely similar between all three configurations. Simulation of incoming longwave radiation at a point commonly partitions the up-looking hemispherical view between radiation coming from the sky (the sky-view fraction, Vf) and the forest canopy (1 - Vf). In this two-part model, using air temperature as a proxy for tree temperature at three forested sites with Vf < 0.3 resulted in model underestimations, representing canopy temperatures elevated above air temperature. Importantly, these errors were largest during sunny, clear-sky conditions, particularly along sun-lit canopy discontinuities. However, in denser canopies, measured tree trunk temperatures were cooler than local air temperature. Model estimations were improved by applying a bulk offset to air temperature (+3�C), reducing error from 11 Wm-2 to 4 Wm-2. Within sun-lit discontinuous forests, measured canopy temperatures varied between 5-25�C above air temperature and errors of the two-part model were as high as 40 Wm-2. Point-scale simulations of longwave radiation were improved by explicitly accounting for tree trunk temperatures within the canopy-view fraction, creating a three-part model (sky, trunk and canopy). Modelled estimates of incoming longwave radiation beyond the point-scale were improved through extensive canopy temperature measurements using infrared thermal imagery around forest gaps. A parametrisation to estimate canopy temperature using sub-canopy shortwave radiation and air temperature was developed for modelling sub-canopy incoming longwave radiation using the two-part model along canopy discontinuities. These findings provide a framework for incorporating sub-canopy longwave radiation within larger scale snowmelt models. Particularly, it is important to represent both canopy discontinuities, as well as canopy temperatures at sub-daily time steps. Exclusion of these factors could lead to inaccurate estimations of snowmelt initiation and runoff rates.
7

Exploring factors driving organic carbon burial and storage in small constructed ponds : an experimental approach

Taylor, Scott January 2017 (has links)
The significance of ponds in the terrestrial carbon cycle has received increasing attention in recent years. Evidence suggests that ponds exhibit rates of biogeochemical cycling orders of magnitude greater than larger water bodies and, cumulatively, the storage of organic carbon (OC) in small ponds may equal or possibly surpass that of large water bodies. This project furthers our understanding of OC storage within ponds, combining survey and experimental approaches to accurately quantify sediment carbon stocks and accumulation rates. It incorporates four distinct, yet complimentary components aiming to: i) Evaluate the accuracy of estimating OC storage in entire ponds from sediment cores; ii) Monitor physicochemical dynamics and quantify OC storage across newly constructed ponds; iii) Quantify OC storage across a suite of mature ponds and assess the impact of vegetation community development; iv) Identify variations in microbial communities between different ponds in relation to sediment physicochemistry and vegetation coverage, exploring the implications for OC storage and burial. Carbon stocks were surveyed in 12 mature ponds across an experimental field site at Druridge Bay, Northumberland. Comprehensive historical ecological data was used to separate these ponds into three distinct groups based on hydrology and vegetation. One pond was selected from each of the resulting three groups and exhumed in its entirety to accurately quantify OC storage. Three sediment cores were taken beforehand in a novel attempt to evaluate the percentage difference between sediment core estimates and whole pond sediment OC storage. Whole pond exhumation suggests that the three ponds stored between 1565 – 2288 g OC m2, whilst results from the cores alone gave estimates within a 10-15% range. A further three ponds from each group were selected to quantify burial rates using sediment cores. Results suggest the ponds have stored between 1413 – 4459 g OC m2 over 20 yrs, equating to around 67 – 212 g OC m2 yr-1. OC storage was greater in ponds that had undergone the fastest establishment of vascular plant communities. Three new ponds were constructed at the Druridge site. Physicochemical parameters were monitored at approximately fortnightly intervals across a period of three years. All three ponds were hyper-eutrophic, dominated by algae. However, OC storage was negligible, further suggesting that OC burial is only significant upon the establishment of vascular plant communities. Sediment samples were subject to 16s rRNA analysis to identify microbial communities involved in carbon cycling. Variations in microbial community composition between ponds were observed and showed complex relationships with sediment physicochemistry and vegetation coverage. Microbial diversity was significantly higher in ponds storing more OC. Ponds dominated by Juncus vegetation, had lower diversity and a greater abundance of facultative anaerobic bacteria, and stored less OC. The intense rates of OC burial observed in this study demonstrate the functional capacity of constructed ponds to operate as significant sinks of OC. High rates of OC accumulation compared to the surrounding terrestrial landscape highlights the potential for their construction across landscapes to act as versatile, yet effective carbon mitigation features.
8

The importance of small water bodies for carbon capture in Northumberland

Inegbedion, Otaigbe January 2017 (has links)
Small water bodies (SWBs) are an important biogeochemical sub-compartment of the global carbon cycle that has been given little or no attention. They have similar capabilities to oceans, large lakes and river systems to exist in flux and could store more carbon in their sediments than the above systems. This research is aimed at determining the number and surface area of inland water bodies in Northumberland, the carbon stocks in the sediments of those water bodies and the microbial influence on the carbon stocks. These further define the Northumberland regional carbon stocks, the level of allochthonous and autochthonous carbon influence in the regional carbon stocks and the effects of surrounding vegetation, sediment wetness, dry bulk density, microbes, anoxia, pond permanence and temporariness on carbon stock variations. The importance of SWBs is in their abundance and the ability to estimate this will aid the understanding of their actual contributions to the global carbon cycle as a net source or sink. Using Landsat-8 and World Imagery data, number and surface area of water bodies in Northumberland were identified by manual digitising of water bodies on ArcGIS 10.0. This showed variation in number and surface area of water body abundance with respect to imagery types, time and scale of analysis. The correctness of estimating water body abundance is subject to the continuous temporal change of small water body abundance. The continuous changes are associated with the nature of water bodies, regional/sub-regional landscape (hypsometry), precipitation and land use. Carbon stock in Northumberland was determined by Total Elemental Analyser (TEA) combustion of sediment from various types and sizes of ponds collected from Druridge Bay, Northumberland. Carbon stocks varied in each ponds type and size range. These variations were influenced by the prevailing environmental/physical, biological and chemical/biochemical factors in pond sediments. The microbial community drives carbon stock by altering the microbial community structure, allochthonous and autochthonous carbon processes and the oxygenation in the ponds. PCR pyrosequencing targeted at the 16s rRNA gene showed diversity in the microbial composition of the Northumberland pond sediments and the results showed a varying level of anoxia triggered by factors such as anoxic Proteobacteria, Bacteroidetes, Chloroflexi, Cyanobacteria and Chlorobi dominance. These dominant phyla also influenced other phyla to develop anoxic ecological relationships and produce predominantly anoxia based processes like methanogenesis and fermentation. Anoxic pond bottoms were also triggered by high terrestrial inputs amongst other factors. This research shows for the first time that carbon stock in a region’s SWBs varied because of numerous physical/environmental, chemical and biological factors. Also, SWBs stock carbon from the terrestrial environment and in-situ aquatic processes. Northumberland water body distribution has shown that more carbon is stocked in the small sized water body systems than larger water body system and their global abundance places them as an important carbon capture mechanism.
9

Bioaccessibility of potentially harmful elements (PHEs) from environmental matrices and implications for human health

Boisa, Ndokiari January 2013 (has links)
Internationally publicized impacts upon human health associated with exposure to potentially harmful elements (PHE) have been reported globally. Particular concern has surrounded the exposure to Pb indicated by the presence of highly elevated concentrations of Pb in blood and hair samples amongst internally displaced populations (IDPs) in Mitrovica, Kosovo, following the Kosovan War (Runow, 2005). The exposure risk to humans depends in part on the potential of the PHE to mobilise from its matrices in the human digestive and respiratory systems (bioaccessibility) and enter the blood stream (bioavailability). This study utilizes physiologically based in-vitro extraction methods to assess the bioaccessibility of PHEs in surface soils and metallurgical waste in Mitrovica and assesses the potential daily ingestion of soil-bound PHEs (As, Cd, Cu, Mn, Pb, and Zn) and inhalation (Pb) of particulate matter < 10 μm (PM10). A total of 63 samples (52 surface soils and 11 mine/smelter waste) were selected based on PHE loadings and their spatial distribution. For the in-vitro oral bioaccessibility 0.3 g subsamples were analysed using the UBM method (adopted by BARGE, Wragg et al., 2009). The mean bioaccessibility of Cd, Pb and Zn in the gastric phase is 51 %, 57 % and 41 %, respectively, compared to 18 %, 16% and 14%, respectively, in the gastric-intestinal phase. The trend with As and Cu data is less consistent across the sample locations, with a mean of 20 % and 22 % in the gastric phase and 22 % and 26 % bioaccessibility in the gastric-intestinal phase, respectively. To investigate the role of mineralogy in understanding the bioaccessibility data subsamples (< 250 μm) were submitted to the British Geological Survey, Nottingham, for X-ray diffraction (XRD) analyses. Samples associated with lower bioaccessibilities typically contain a number of XRD-identifiable primary and secondary mineral phases, particularly As- and Pb-bearing arseninian pyrite, beudantite, galena and cerrusite. For the inhalation bioaccessibility, PM10 subsamples were extracted from 33 samples using a locally developed laboratory based wet method. The 0.3 g PM10 subsamples were analysed using a new tracheobronchial fluid and protocol developed as part of this study. The bioaccessibility of Pb for all the 33 samples tested ranged from 0.02 to 11 % and it is consistent with a range (0.17 to 11 %) previously reported by Harris and Silberman (1988) for Pb bioaccessibility in inhalable particulates (< 22 μm) using canine serum. Quantification of the potential human exposure risk associated with the inhalation and ingestion of soil-associated PHEs indicates the likely possibility of local populations exceeding the recommended tolerable daily intake of Pb. IEUBK model (USEPA, 2007) predicted mean blood Pb concentrations for children based on bioaccessible (ingestion) data are above the CDC level of concern (10 μg/dL).
10

The power of ponds? : quantifying sediment carbon stocks within, and fluxes from, small ponds

Gilbert, Peter January 2016 (has links)
The role of ponds within the terrestrial carbon cycle has been receiving increasing interest. Existing evidence suggests that they have substantial global coverage, with ecosystem function rates disproportionately intense for their size making them significant cyclers of atmospheric carbon. This project aims to: (1) provide a comprehensive survey and quantification of carbon stocks within lowland ponds from a diverse range of ecological pond types; (2) provide a comparison of carbon stocks from pond sediments across significantly different biogeographical regions across England; and (3) monitor the temporal and spatial variability of carbon fluxes from ponds. Carbon stocks were surveyed in 40 ponds across Druridge Bay, Northumberland. These ponds were selected for their distinct plant communities and hydrological patterns that form four broad pond types: dune-slack ponds; arable field ponds; pasture field; and classically vegetated ponds. High measures of percentage carbon were found within the sediments, however, when quantified in terms of carbon (C) stock, (kg-1 C m-2 < upper 10 cm), little difference was observed among classically vegetated, arable, and pasture pond types (means = 3.14, 3.17, 4.94 kg-1 C m-2 < upper 10 cm respectively); only sediment C stocks of dune-slack ponds (6.18 kg-1 C m-2 < upper 10 cm) were significantly different from other pond types. Equally, the heterogeneity of C stocks among dune-slack ponds varied markedly, with ponds in arable fields being fairly consistent. No significant difference was observed between C stocks in the pond sediments compared to those in surrounding soil. This does not mean that they play a similar role in the carbon cycle, but highlights the importance of acquiring sediment burial rates within these systems in order to quantify their role as C stores. To test if the patterns of C storage could be generalised beyond the Northumberland ponds to other regions in the England, 15 ponds were surveyed, 5 each from 3 separate regions of England with differing climatic influences and biogeographical characteristics: temporary ponds on the Lizard Peninsula, Cornwall, with Mediterranean climate; pingo ponds of Thomspon Common, Norfolk; and peat excavation ponds at Askham Bog, Yorkshire. Sediment C stocks of ponds sampled in Cornwall (mean = 2.6 kg-1 C m-2 < upper 10 cm), were > 43 % lower compared to those in Yorkshire (6.0 kg-1 C m-2 < upper 10 cm) and Norfolk (7.7 kg-1 C m-2 < upper 10 cm). However, cumulatively, the variation observed among all sites was comparable to the high level of variation observed in the comprehensive survey of ponds at Druridge. The absence of detailed C flux rates from small water bodies, especially from desiccated sediments during summer dry phases, is a key factor constraining their inclusion in terrestrial carbon budgets. Thus, CO2 fluxes were monitored from 26 neighbouring experimental ponds of known age, history and ecology, focusing on short-term hydrological changes over two, two-week periods, comprising a drying phase and re-wetting phase. During the drying phase flux rates exhibited a 9-fold increase resulting in a shift from a net intake of CO2 to a net site emission whilst the reverse was observed during the rewetting phase. Moreover, significant variability in fluxes of CO2 were observed among ponds on individual sampling days; the highest range observed was -2154 to 10658 mg m-2 d-1. The result is marked spatial variability in CO2 processing. The large degree of temporal and spatial heterogeneity repeatedly observed throughout this study, both in sediment carbon stocks and CO2 fluxes, highlights the complexity of carbon processing within small aquatic systems such as ponds. This study specifically highlights the need for accurate measures of burial rates within pond systems in order to fully assess their carbon capture capability.

Page generated in 0.0713 seconds