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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.

Modelling evolution of genome size in prokaryotes in response to changes in their abiotic environment

Bentkowski, Piotr January 2014 (has links)
The size of the genomes of known free-living prokaryotes varies from � 1:3 Mbp to � 13 Mbp. This thesis proposes a possible explanation of this variation due to variability of the physical conditions of the environment. In a stable environment, competition for the resource becomes the main force of selection and smaller (thus cheaper) genomes are favoured. In more variable conditions larger genomes will be preferred, as they have a wider range of response to a less predictable environment. An agent-based model (ABM) of genome evolution in an free-living prokaryotic population has been proposed. Using the classic Hutchinson niche space model, a gene was defined as a Gaussian function over a corresponding niche dimension. The cell can have more than one gene along a given dimension, and the envelope of all the corresponding responses is considered a full description of a cell’s phenotype over that dimension. Gene deletion, gene duplication, and modifying mutations are permitted during reproduction, so the number of genes and their phenotypic effect (height and position of the Gaussian envelope) are free to evolve. The surface under the curve is fixed to prevent ‘supergenes’ from occurring. Change of the environmental conditions is simulated as a bounded random walk with a varying length of the step (a parameter representing variability of the environment). Using this approach, the model is able to reproduce the phenomenon of genome streamlining in more stable environments (analogical to e.g. oligotrophic gyre regions of the ocean) and genome complexification in variable environments. Horizontal gene transfer (HGT) was also introduced, but was found to act in a similar manner as gene duplication and shown no important contribution to the speed of evolution and the adaptive potential of the population.

Climate change and global crop yield : impacts, uncertainties and adaptation

Deryng, Delphine January 2014 (has links)
As global mean temperature continues to rise steadily, agricultural systems are projected to face unprecedented challenges to cope with climate change. However, understanding of climate change impacts on global crop yield, and of farmers' adaptive capacity, remains incomplete as previous global assessments: (1) inadequately evaluated the role of extreme weather events; (2) focused on a small subset of the full range of climate change predictions; (3) overlooked uncertainties related to the choice of crop modelling approach and; (4) simpli�ed the representation of farming adaptation strategies. This research aimed to assess climate change impacts on global crop yield that accounts for the knowledge gaps listed above, based on the further development and application of the global crop model PEGASUS. Four main research topics are presented. First, I investigated the roles of extreme heat stress at anthesis on crop yield and uncertainties related to the use of seventy-two climate change scenarios. I showed large disparities in impacts across regions as extreme temperatures adversely a�ects major areas of crop production and lower income countries, the latter appear likely to face larger reduction in crop yields. Second, I coordinated the �rst global gridded crop model intercomparison study, comparing simulations of crop yield and water use under climate change. I found modelled global average crop water productivity increases by up to 17�20.3% when including carbon fertilisation e�ects, but decreases to {28�13.9% when excluding them; and identi�ed fundamental uncertainties and gaps in our understanding of crop response to elevated carbon dioxide. Third, to link climate impacts with adaptation, I introduced the recently developed concept of representative agricultural pathways and examined their potential use in models to explore farming adaptation options within biophysical and socio-economic constraints. Finally, I explored tradeo�s between increasing nitrogen fertiliser use to close the global maize yield gap and the resulting nitrous oxide emissions. I found global maize production increases by 62% based on current harvested area using intensive rates of nitrogen fertiliser. This raises the share of nitrous oxide emissions associated with maize production from 20 to 32% of global cereal related emissions. Finally, these results demonstrated that in some regions increasing nitrogen fertiliser application, without addressing other limiting factors such as soil nutrient imbalance and water scarcity, could raise nitrous oxide emissions without enhancing crop yield.

Quantifying the well-being benefits of urban green space

Andrews, Barnaby January 2014 (has links)
Rapid urbanisation compounded by underlying population growth has placed increasing pressures upon green space areas within cities. Anecdotal evidence suggests that such areas are major sources of wellbeing yet the complex nature of the services provided by such areas and the non-market, unpriced characteristics of the benefits they yield raise concerns that they are inadequately incorporated within decision making and planning systems. This thesis seeks to address the problem of quantifying the well-being benefits of urban green space through the extension of two complementary strands of research. The first seeks to contribute to the incorporation of urban green space benefits within conventional decision making systems. Within this strand of the research the authors report two studies designed to address various challenges associated with the estimation of economic values for the non-market benefits generated by urban green space. The first of these studies contributes to the literature on the estimation and transferral of valuation functions across locations to allocate available resources at an inter-city, national level. The second valuation study operates at an intra-city level through an experimental study the dimensions of which are designed to reveal optimal locations in the presence of potential local dis-amenities (a potentiality which is confirmed through the application of advanced statistical analysis techniques). The second strand of research addresses the complexities of relationships between urban green space and individual well-being. Here recent methodological advances in the field of applied social-psychology are extended to yield a richer picture of the diverse impact of both direct experience and passive viewing of green space upon wellbeing. An experiment is designed to permit enhanced controls for the potential correlation between environment and activity in determining experiential perceptions of well-being effects. A common theme of all applications is the explicit incorporation of spatial complexity and variation in the environment within each study and across the various methodologies employed. From a practical perspective it is argued that these results provide inputs to both the decision making and planning fields. More fundamentally, the work presented within this thesis represents a useful methodological contribution to both the applied economic valuation and social-psychology research literatures.

Predicting biodiversity loss in insular neotropical forest habitat patches

De Souza, Maira January 2014 (has links)
Neotropical forests have experienced high rates of biodiversity loss as a result of burgeoning land-use changes. Habitat conversion into cropland, pastures, and more recently hydroelectric lakes, are leading drivers of forest loss and fragmentation of pristine forests in the world’s most biodiverse region. This thesis aims to improve our understanding of the impacts of habitat fragmentation on biodiversity loss in Neotropical forests by evaluating the patterns of floristic changes and vertebrate extinctions in forest patches. Two approaches at different scales were conducted. First, a systematic literature review was carried out on the effects of fragmentation on Neotropical primates at a continental-scale. Second, biodiversity inventories were conducted on medium and large bodied vertebrates (including mammals, birds and tortoises) and trees ≥10 cm diameter at breast height at 37 islands and three continuous forest sites within the Balbina Hydroelectric Reservoir in Brazilian Amazonia. Patch area was a key driver of species persistence for all study taxa, yet other factors were also important. Hunting pressure exerted a strong influence on patterns of primate persistence within 760 fragments, and edge effects, including edge-related ground-fires, were the main predictors of floristic transitions using data from 87 quarter hectare forest-plots at Balbina. Additionally, matrix composition and species life-history traits played a key role in explaining patterns of species persistence. This study therefore highlights the importance of considering anthropogenic stressors in assessing the effects of land-use change to explain patterns of species persistence in forest patches, aside from including parameters related to the matrix and ecological life history traits of focal species. As conservation recommendations, prioritising large (>100 ha) patches, increasing their protection, and enhancing connectivity of surrounding habitats becomes clearly important. For future Amazonian dams, it is recommended that engineers should consider the overall topography of planned reservoirs to maximise landscape connectivity and/or reject plans targeting unfavourable river basins.

Modelling spatial variation and environmental impacts of land use change in the exploitation of land-based renewable bioenergy crops

Thomas, Amy R. C. January 2014 (has links)
Spatial factors are of particular importance to the sustainability of land based energy crops, due both to the need to minimise feedstock transport, and to the importance of cultivation site attributes in determining key environmental impacts. This study uses geographical information system (GIS) mapping to identify sites suitable for the cultivation of Miscanthus or short rotation coppiced (SRC) SRC willow for co-firing with coal or generation of combined heat and power (CHP). Modelling using an adapted version of DayCent was performed for typical sites to assess variation in yield, nitrous oxide (N2O) emissions, evapotranspiration (ET) and change in soil organic carbon (SOC) according to soil properties, hydrologic regime and previous land use. Development of the DayCent model as part of this research gave improved simulation of the impacts of tillage on soil porosity, and resultant N2O emissions from soil, and improved simulation of growth of SRC willow following coppicing management, leading to improved yield predictions. For land use change from arable to perennial cultivation, increased SOC was simulated, along with reduced N2O emissions, particularly on soils prone to anoxia. However, in general, benefits of cultivation of Miscanthus and SRC willow for energy are maximised when the crops are grown at sites where high yields are achieved, and used to generate CHP, since this minimises the land area required per unit energy generated. Further model development work and additional field data for model verification are necessary for firmer conclusions on the change in net greenhouse gas (GHG) emissions following land use change. Additionally, indirect land use change may negate perceived benefits, and locations are difficult to predict or identify in a complex global system. Given the magnitude of identified variations in yields and changes in N2O emissions, spatial variation in benefits of bioenergy cultivation should be a factor in decisions to provide economic support for cultivation. However, calculations suggest that emissions offset by replacing energy generation from fossil fuels may have greater impact on GHG savings per gigajoule (GJ) than cultivation site attributes. Since total energy conversion efficiency may be in the region of 30% for electricity-only generation and up to 90% for CHP generation, planning feedstock supply chains to maximise efficiency of feedstock end use is therefore beneficial.

Environmental and biochemical controls on the molecular distribution and stable isotope composition of leaf wax biomarkers

Eley, Yvette January 2014 (has links)
Leaf wax n-alkyl lipids are increasingly used as proxies in palaeoclimate studies. Palaeovegetation assemblages are reconstructed from their molecular distribution patterns, while their δ13C and δ2H signals are thought to reflect plant-environment interactions and palaeohydrological shifts, respectively. Such applications depend, however, upon these compounds faithfully recording environmental conditions. To explore the influence of environmental, physical and biochemical controls on n-alkane composition, leaf waxes from seven UK saltmarsh plants were analysed over two growing seasons. Linked analysis of sedimentary n-alkanes enabled further investigation of leaf wax biomarker integration into saltmarsh sediments. The molecular distribution and concentration of n-alkanes from the saltmarsh plants varied significantly. Bulk and n-alkane δ13C recorded different seasonal shifts, with a range of up to 13‰ in the offset between bulk and n-alkane 13C/12C values. This indicated that post-photosynthetic 13C/12C fractionation may be an important additional control on n-alkane δ13C signals. n-Alkane δ2H also varied among the sampled species by >100‰, and could not be explained by physical processes controlling the movement of water inside/outside and within leaves. Comparison with the 2H/1H of chloroplast-synthesised compounds (fatty acids, phytol) suggested these differences instead reflected the varied biochemical mechanisms operating in the chloroplast and cytosol. Sedimentary biomarker analysis further highlighted that small/moderate vegetation change could drive shifts of ~40‰ in sedimentary nalkane 2H/1H, while using globally averaged “typical” values to correct for fractionation between source water and n-alkane 2H/1H may not be representative of a specific geographical location. Results demonstrate: (i) the importance of biochemical mechanisms in controlling the molecular and isotopic composition of n-alkyl lipids; and (ii) the need to further constrain the influence of vegetation change on the isotope composition of sedimentary n-alkanes. Future research should address these areas in other biomes and depositional environments, to ensure accurate interpretation of modern and ancient leaf wax lipid data.

A study of diapycnal mixing in the Southern Ocean using a tracer release experiment and numerical models

Mackay, Neill January 2014 (has links)
The Diapycnal and Isopycnal Mixing Experiment in the Southern Ocean (DIMES) includes a tracer release experiment and microstructure programme with the aims of diagnosing the strength and variability of mixing in the Southern Ocean. Here numerical models are used to advect and diffuse a tracer in the Antarctic Circumpolar Current, beginning in the Southeast Pacific and progressing through Drake Passage, and model outputs are then compared with observations from the DIMES tracer. The prescribed diapycnal diffusivity fields within the models are varied between different model runs, and the model parameters are optimised using a cost function to give the best fit to the observations. A simple 2D model with dimensions of along-stream distance and depth yields estimates for diapycnal diffusivity neutral density surface onto which the tracer was released. A more complex 3D model using an offline version of the MITgcm with time-evolving observation-based velocities from the SatGEM product yields similar estimates for the Pacific and Drake Passage, respectively. Point microstructure dissipation measurements collected as part of DIMES are used to construct three-dimensional diffusivity fields which are then used in conjunction with the 3D model to test whether the mixing rates inferred from microstructure and the tracer measurements are consistent with one another. Good agreement is found in the Southeast Pacific, but in Drake Passage, where both topography and current field becomes more heterogeneous, the microstructure estimates are 5 times too low to account for the time and spatially averaged mixing implied by the tracer. By contrast, model diffusivities constructed using predicted rates of lee wave generation from modified linear theory predict the along-stream variation in tracer vertical profile widths reasonably well throughout the model domain, but do not capture the across-stream variation.

Fingerprints and drivers of recent changes in oceanic oxygen : from regional to global scales

Andrews, Oliver D. January 2014 (has links)
Observations and Earth System Model (ESM) projections indicate that a reduction in the oxygen inventory of the global ocean, termed ocean deoxygenation, is a likely consequence of on-going anthropogenic warming. The contribution of external forcing factors to observed changes in dissolved oxygen concentration ([O2]) relative to natural internal variability is examined using statistical methods which synthesise historical measurements and ocean biogeochemistry model output. Using a formal optimal fingerprinting method, an externally forced signal, derived from ESM response patterns, is detected within the observational record of [O2] between �1970 and �1992 at the 90% confidence level. Positive detection results in response to external forcing are robust for depth-averaged (100–3000 m) and depth-resolving zonal mean patterns globally and for the Pacific basin, however [O2] changes in the Atlantic basin are indistinguishable from internal variability as characterised by unforced ESM integrations. Current ESMs are also shown, using optimal detection techniques, to consistently underestimate the magnitude of observed [O2] change by a factor of �2 – 4. Accordingly, targeted hindcast experiments are conducted using the PlankTOM10-NEMO3.1 model, quantifying the impact of physical and biogeochemical processes on the spatiotemporal distribution of O2. The largest magnitude of uncertainty is shown to be entrained into [O2] response patterns due to model parameterisation of pCO2-sensitive C:N ratios in carbon fixation and imposed atmospheric forcing data. Historical trends and variability in Bottom Mixed Layer (BML) [O2] for the North Sea region are also investigated.

Assessing the multifunctional role of anaerobic digestion in England

Tickner, Robert C. D. January 2014 (has links)
No description available.

Transforming sustainabilities : grassroots narratives in an age of transition : an ethnography of the Dark Mountain Project

Graugaard, Jeppe D. January 2014 (has links)
The framing of sustainability as a goal of aligning human needs with protection of the environment has been pursued through various definitions and frameworks in policies and programmes across a wide range of contexts. And yet, unsustainable modes of production and consumption are accelerating the global destruction of natural habitats, depletion of resources, release of greenhouse gasses and other forms of pollution. Thus, the nature and scale of the changes that the earth is undergoing is bringing conventional approaches to, and understandings of, the sustainability challenge into question. This thesis re-examines the framing of the sustainability challenge instead as one of understanding the relations between humans and nature implied by dominant cultural narratives. Through building a theoretical understanding of how human-nature relationships can be understood and studied, and devising a methodology for examining individual and collective ontologies and epistemologies, it investigates how alternative worldviews are imagined and embodied in grassroots innovations. Specifically, it provides an indepth ethnographic study of the Dark Mountain Project – a network of writers, artists and thinkers who explore cultural narratives that move beyond the meta-narrative of progress. It shows how engaging with the beliefs and assumptions entailed by the dominant Western meta-narrative can open up for new knowledges and actions to address the sustainability challenge. The thesis suggests that creating sustainable ways of living involves active participation in the way ‘sustainability’ is imagined, storied and enacted. Findings indicate that creating spaces for active experimentation with alternate ways of seeing, co-creation of new vocabularies and development of creative practices, is a direct way to enable re-narration and re-experiencing of human-nature relations. It concludes that engaging with transitions in worldviews as a transformation in the experience of social life provides a promising starting point for future work on the sustainability challenge.

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