M.Sc Thesis / Northern peatlands are able to persist on the landscape and continue to accumulate carbon in the long-term thanks to a suite of ecohydrological feedbacks that confer resilience to disturbance such as the drier and warmer conditions associated with climate change. One feedback of particular interest operates between peat pore-water residence time and chemistry, whereby changes in hydraulic structure with depth restrict turnover in deeper layers, allowing decay end-products to accumulate and thermodynamically suppress decomposition. In this way, the burial of peat facilitates its continued recalcitrance. While this feedback has been observed in more extensive northern peatlands, at least on the side of carbon dynamics and geochemistry, there has been no observational study of profiles of pore-water residence time nor has it been assessed in smaller peat-forming systems. The peat-filled bedrock depressions of the Canadian Shield offered a unique opportunity to study this feedback in systems where primary peat formation occurs under geological constraints on growth in the form of the largely impermeable bedrock. These systems play important hydrological, biogeochemical and ecological roles on the landscape. Understanding their resilience on the landscape may reveal key insights into their evolution and their response to disturbance, which is increasing in the eastern Georgian Bay region. These systems have previously exhibited a hydrological feedback between water table depth and specific yield that varies with depression size. To assess the hydraulic structure that constrains pore-water transport to support continued recalcitrance, profiles of hydrophysical properties and pore-water residence time in four deep (>0.4 m mean depth) and five intermediate (<0.4 m) depressions. Hydraulic structure varied by depression size and depth in the profile, with very low hydraulic conductivities measured in the catotelms of deep sites. The two classes of depressions exhibited distinct hydrology, in the form of dampened water table fluctuations and hydraulic gradients in the deeper sites. Stable isotope analysis of δ2H and δ18O was used to estimate relative pore-water residence times using the simplified inverse transit time proxy (ITTP) for samples collected from May-August 2017. These estimates were observed to have similar controls to hydraulic structure and a close relationship with depth-averaged conductivity on a whole-site basis. While it was hypothesized that the catotelms of deeper depressions would have less pore-water turnover than that of shallower depressions, the ITTP was only able to differentiate between catotelm-acrotelm and deep-intermediate individually. The relative residence time of pore-water in deep catotelms based on δ2H was longer than in intermediate catotelms, but not significantly. These results broadly supported previous pore-water residence time work despite the likely ubiquitous promotion of turnover in the wetter-than-average study period. Carbon accumulation was quantified from extracted peat cores and pore-water chemistry was assessed as dissolved organic matter (DOM) quality using fluorescence spectrometry of monthly pore-water samples. Fluorescence and absorption indices varied by the same depression characteristics as hydraulic structure of site size and depth, but only the humification index exhibited significant temporal variation. Characterization of pore-water DOM was somewhat unclear across the seven indices calculated, although the DOM of intermediate sites appeared to be less humified, more recently produced and autochthonous in nature compared to deep sites Carbon accumulation was predominantly driven by the waterlogged, relatively stable carbon stored deep in the catotelm. Total carbon accumulated in the profile, and even more so the amount stored in the catotelm, were strongly related to depression depth. The thickness and carbon storage of the acrotelm was insensitive to depression morphology, with some intermediate sites being considered all acrotelm based on their water table behaviour. Overall, deeper peat-filled depressions showed stronger signs of the pore-water residence time-chemistry feedback, suggesting the carbon stored in their deep peat layers is more resilient to decay, by way of less conductive deep peat, longer relative pore-water residence times and more humified, less biologically active DOM. In order to comprehensively assess this feedback, longer stable isotope records are essential to ensure robust residence time estimates through differing moisture conditions, and a greater variety of depression sizes may allow for elucidation of threshold depression sizes where hydrological behaviours diverge. This study, at least on a categorical basis, can be used to inform conservation strategies of the relative vulnerability of these important reptile habitats and carbon stores, as well as guide restoration efforts to construct sufficiently deep, resilient systems. / Thesis / Master of Science (MSc)

Submitted by Fernando Souza (fernandoafsou@gmail.com) on 2017-08-11T16:27:01Z No. of bitstreams: 1 arquivototal.pdf: 6707446 bytes, checksum: 70b00f769ff8670c847cb8cacf2f2eb6 (MD5) / Made available in DSpace on 2017-08-11T16:27:01Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 6707446 bytes, checksum: 70b00f769ff8670c847cb8cacf2f2eb6 (MD5) Previous issue date: 2016-08-31 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / Each individual has a different profile that influences the way he organizes and processes information. This profile can be described as the learning style with which every person learns a particular subject or content according to his individual differences, thus contributing to the construction of the teaching and learning process. Learning styles have been used and recognized as an important human factor, that directly affect the learning performance of each student. In addition, educational games are seen as powerfull tools to aid the teaching and learning process, since students can learn while playing. Consequently, joining game adaptation with the student's profile can enhance learning. Research in education area suggest the use of games in the teaching and learning process, because games can improve students engagement, reinforce concepts through practice, favor the development of logic, analysis, strategy, and even memory. However, the pontential of these games are not always exploited in the way it would be as, for example, by providing feedback to support the learning and motivation process. Moreover, feedback is an important feature for educational games and aims to increase the students’ effort, performance and motivation, by providing to them useful and immediate information about their performance. This work presents results of a research whose focus was to describe a model based on learning styles to be used in educational games, aiming at providing adaptive feedback according to the learning style of each user. This model was implemented in a questions and answers educational game called MyQuímica, whose purpose is to support the teaching and learning process of Chemistry. More precisely, the game aims to assist the learning of chemical nomenclatures and helps students to familiarize with the periodic table. Tests were conducted with a total of forty nine students from the 1st and 2nd years of public high schools at João Pessoa. According to these students, the game with adaptive feedback was more effective in the teaching and learning process than the game without adaptation. Moreover, the variation of the feedback displayed, according to each identified learning style, indicates that the students were more motivated in solving the game challenges as well as the results in terms of score have improved. / Cada indivíduo possui um perfil diferente que influencia na forma como ele organiza e processa informação. Esse perfil pode ser descrito como o estilo de aprendizagem com o qual cada pessoa aprende um determinado assunto ou conteúdo de acordo com suas diferenças individuais, contribuindo para a construção do processo de ensino e aprendizagem. Os estilos de aprendizagem têm sido utilizados e reconhecidos como sendo um fator humano importante, que afeta diretamente o desempenho de aprendizagem de cada aluno. Somado a isso, os jogos educativos são vistos como poderosas ferramentas para auxiliar o processo de ensino e aprendizagem, uma vez que os alunos podem aprender brincando. Consequentemente, unir adaptação do jogo com o perfil do aluno pode potencializar a aprendizagem. Pesquisas na área da educação sugerem o uso de jogos no processo de ensino/aprendizagem, pois os jogos podem engajar o estudante, reforçar conceitos através da prática, favorecer o desenvolvimento da lógica, da análise, da estratégia e até da memória. Contudo, o potencial desses jogos nem sempre é aproveitado da melhor maneira, como seria, por exemplo, a partir da disponibilização de feedbacks que fornecem suporte no processo de educação e de motivação. Além disso, feedback é uma característica importante para jogos educativos e tem como objetivo aumentar o esforço, o desempenho e a motivação do aluno, fornecendo a ele informação útil e imediata sobre seu desempenho. Este trabalho apresenta resultados de uma pesquisa cuja finalidade foi descrever um modelo baseado em estilos de aprendizagem para ser utilizado em jogos educativos, visando promover feedback adaptativo ao estilo de aprendizagem de cada usuário. Este modelo foi implementado em um jogo educativo no estilo perguntas e respostas, denominado MyQuímica, que visa apoiar o processo de ensino e aprendizagem de Química. Mais precisamente, o jogo procura auxiliar no aprendizado das nomenclaturas químicas e ajudar na familiarização dos alunos com a tabela periódica. Testes foram realizados com um total de quarenta e nove alunos de escolas públicas de João Pessoa, do 1º ano e do 2º ano do Ensino Médio. De acordo com os alunos, o jogo com feedbacks adaptativos foi mais eficaz no processo ensino e aprendizagem do que o jogo sem adaptação. Além disso, a variação dos feedbacks apresentados, de acordo com cada estilo de aprendizagem identificado, mostrou indícios de que os alunos se motivaram mais na resolução dos desafios, bem como houve um aumento nos resultados em termos de pontuação.

Biodiversity is important to ecosystem function at many scales, and variation functional traits within a species can potentially influence ecosystem functioning by altering nutrient cycling dynamics. High population extinction rates are resulting in a rapid loss of within-species biodiversity, so there is a need to better understand the importance of intraspecific variation to ecosystem-level processes. Tidal salt marshes are ideal ecosystems for investigating intraspecific variation in plant-nutrient relationships because they are dominated by a monoculture of the foundation species Spartina alterniflora, with distinct phenotypes that correspond to environmental gradients across the marsh. We conducted a field survey of existing phenotypic variation and biogeochemical characteristics in three salt marshes in South Carolina, USA, and used path analysis to model relationships among plant traits and nutrient dynamics. Leaf %N and C:N were important predictors of nitrogen and carbon cycling dynamics respectively. There were strong effects of site on soil variables, but plant traits responded most to tidal position within the marsh, indicating a potential decoupling of plant-soil feedbacks which are often tightly linked. Overall, variation in plant tissue chemistry does play a role in nutrient cycling, but other feedbacks may be broken down or obscured by hydrologic drivers in this highly dynamic ecosystem.

This study investigates modes of atmospheric variability in response to changes in Earth's orbit and changes in 20th century sea surface temperatures (SST). The orbital forcing is manifested by a change in obliquity and precession, and changes the distribution of the top-of-atmosphere insolation. A smaller obliquity reduces the the annual insolation that the poles receive and increases the annual insolation in the tropics. As the meridional insolation gradient increases, the zonal mean atmospheric-ocean circulation increases. The resulting climate also has a reduced global mean temperature due to the effect of climate feedbacks. This cooling can be attributed to a reduced lapse rate, increased cloud fraction. reduced water vapor in the atmosphere, and an increase in the surface albedo. A change in the precession, as the perihelion shifts from the winter to the summer solstice, causes a strengthening as well as an expansion of the N. Pacific summer subtropical anticyclone. This anticyclonic anomaly can be attributed to the weakening of the baroclinic activity, but also represents the circulation response to remote and local diabatic heating. The remote diabatic heating is associated with monsoonal activity in the SE Asia and North Africa. Regarding the 20th century SST forcing, it is represented by a multidecadal variability in the inter-hemispheric SST difference. This change in the SST causes a latitudinal shift in the ascending branch of the Hadley cell and precipitation in the tropics, as well as an increase in the atmospheric meridional heat transport from the warmer to the colder hemisphere.

No description available.

Canadian High Arctic terrestrial ice masses and the polar atmosphere evolve co-dependently, and interactions between the two systems can lead to feedbacks, positive and negative. The two primary positive cryosphere-atmosphere feedbacks are: 1) The snow/ice-albedo feedback (where area changes in snow and/or ice cause changes in surface albedo and surface air temperatures, leading to further area changes in snow/ice); and 2) The elevation - mass balance feedback (where thickness changes in terrestrial ice masses cause changes to atmospheric circulation and precipitation patterns, leading to further ice thickness changes). In this thesis, numerical experiments are performed to: 1) quantify the magnitudes of the two feedbacks for chosen Canadian High Arctic terrestrial ice masses; and 2) to examine the direct and indirect consequences of surface air temperature changes upon englacial temperatures with implications for ice flow, mass flux divergence, and topographic evolution. Model results show that: a) for John Evans Glacier, Ellesmere Island, the magnitude of the terrestrial snow/ice-albedo feedback can locally exceed that of sea ice on less than decadal timescales, with implications for glacier response times to climate perturbations; b) although historical air temperature changes might be the direct cause of measured englacial temperature anomalies in various glacier and ice cap accumulation zones, they can also be the indirect cause of their enhanced diffusive loss; c) while the direct result of past air temperature changes has been to cool the interior of John Evans Glacier, and its bed, the indirect result has been to create and maintain warm (pressure melting point) basal temperatures in the ablation zone; and d) for Devon Ice Cap, observed mass gains in the northwest sector of the ice cap would be smaller without orographic precipitation and the mass balance – elevation feedback, supporting the hypothesis that this feedback is playing a role in the evolution of the ice cap.

The biochemistry of leaves merges the fates of trees and the atmosphere. Leaf primary metabolism cycles carbon and indirectly drives atmospheric circulation via the latent heat of transpiration. Tropical forests contain half of global forest carbon, and actively cycle carbon and energy year round, making them critical components of the coupled biosphere-climate system. Climate change threatens tropical forests with rising temperatures and increasing variability of precipitation. Their response will influence future biodiversity as well as the fate of the climate. Understanding the physiological attributes that define tropical tree responses and feedbacks to climate is a current research priority. The emission of isoprene gas from plant leaves has been demonstrated to enhance leaf tolerance to high temperatures and drought. Isoprene is a volatile secondary metabolite produced in the chloroplast by approximately one-third of plant species. While the benefits of isoprene are supported by extensive laboratory and greenhouse-based research, work has only begun to explore how the trait is integrated in plant functional strategies. Whether isoprene influences differential species performance and survival across environments has yet to be tested. An impediment to filling this clear ecological research gap has been a lack of instrumentation capable of quantifying isoprene emissions from leaves in remote field settings. The first study presented here tests the hypothesis that isoprene emission influences plant community assembly shifts across environmental gradients and through time in tropical forests. The capacity for a species to produce isoprene was associated with increased relative abundance at higher temperatures and following drought anomalies. A negative relationship with the length of seasonal drought suggests a trade-off between isoprene emission and other plant traits, such as deciduous leaf habit. The second study presents the development of a new instrument that is uniquely optimized for field-based ecological research on leaf volatiles. The new system, named PORCO (Photoionization of Organic Compounds), utilizes custom leaf cuvettes, precision light control, and an optimized commercial photoionization detector to achieve real-time detection of leaf emissions with detection limits better than 0.5 nmol m⁻² leaf s⁻¹. The third study utilizes PORCO to test hypotheses about the structuring of isoprene within plant functional strategies and across forest microenvironments in an eastern Amazonian evergreen tropical forest. The results support the role of isoprene—and potentially other volatile isoprenoids—in mitigating effects of intermittent sun exposure in the sub-canopy. Emissions are structured in a complex, multivariate manner that depends on taxonomy, leaf and wood characteristics, tree height, and light environment. The results from this dissertation work demonstrate that isoprene emission from leaves affects plant responses to climate at ecologically relevant scales. Isoprene influences climate not only by its effect on primary leaf functions, but also by directly altering atmospheric chemistry, and contributing to aerosol and cloud properties. Understanding isoprene's role in forest responses to increasing temperatures and drought will help to predict the feedbacks between forest ecosystems and climatic change.

Abstract Exotic plant species may facilitate their invasion into native communities through the modification of ecosystem disturbances such as fire regimes. Where frequent fires are common, invasive plants that suppress fire may induce a positive feedback which further suppresses fire and promotes their continued invasion. In the pine rockland savanna ecosystem of south Florida, the frequent understory fire regime may be altered by the fire-resistant invasive shrub Brazilian pepper (Schinus terebinthifolius). In this thesis, I document the interaction of Brazilian pepper and fire in these savannas. I show that fire causes significant (30%-50%) mortality among low-density populations of Brazilian pepper. However, Brazilian pepper exhibits rapid growth and reproduces quickly following fire, and in the absence of fire it has a low mortality rate. Furthermore, Brazilian pepper can cause a reduction in fire temperature from 47° C at low densities, to almost 200° C at high densities, where it can completely impede fire spread. This creates the potential for Brazilian pepper to initiate a fire-suppressing feedback if it can reach a density threshold during extended fire-free intervals. At a landscape scale, I analyzed digital aerial photographs to show that fire frequency correlates with the extent of Brazilian pepper invasion into pine savanna fragments in southern Florida. In savannas where fire is frequent, Brazilian pepper does not heavily invade, but savannas that are heavily invaded tend to be unburned for more than 20 years. This supports both the regulation of low-density Brazilian pepper populations by fire, and the potential for high-density Brazilian pepper populations to suppress fire and facilitate further invasion.

Fire is a natural process that has existed on our planet for more than ~350 million years, and is a process that continues to influence our everyday lives. On Earth, a relationship exists between the process of combustion and the natural functioning of the Earth system. Here, the process of combustion has been implicated in playing an essential role for life on Earth, where natural Earth system processes have been shown to influence ignition probability, fire spread and fire behaviour, and where fire can provide a variety of feedbacks, to the Earth system over different timescales. Over medium timescales of decades to hundreds of thousands of years, the likelihood and behaviour of fires are controlled by regional climate changes and vegetation type, whilst the occurrence of fire can play a crucial role in influencing biome persistence and development. Over long timescales (hundreds of thousands to multi-million year), the components influencing the probability of fire and fire behaviour not only involve processes occurring over local and regional spatial scales, and over short and medium timescales, but also long term processes occurring globally, such as changes in atmospheric oxygen concentration and the evolution of vegetation. Across these timescales in Earth’s past, combustion has been shown to impact global ecosystems, climate and the carbon cycle by generating feedbacks that influence Earth’s biogeochemical cycles. However, it is clear that our understanding of the role that fire plays in the Earth system, although improving is still developing. This thesis provides an analysis of these Earth system - fire relationships and feedbacks across medium and long timescales in deep time, in order to understand the role that fire may have played and what the record of fire can tell us about the functioning and re-equilibrating of the Earth system during and after significant carbon-cycle perturbation events occurring in Earth’s deep past. The results presented in this thesis contribute what is believed to be the first fossil evidence that rising atmospheric oxygen and fire feedbacks may have aided in the termination of a significant carbon-cycle perturbation event, termed the ‘Toarcian oceanic anoxic event’ that occurred ~183 million years ago during the Jurassic period, and the return of the Earth system towards ‘background functioning’. This thesis also provides an analysis of the record of wildfire in the form of fossil charcoal across the initiation of an anoxic event that occurred ~93 million years ago, during the Cretaceous period. The results illustrate that CO2 - climate driven changes in wildfire activity can be observed across medium timescales even during times of significant carbon-cycle perturbations, and modelled high atmospheric oxygen concentrations. These results illustrate how hypothesized changes in the hydrological cycle, and likely moisture content of fuel, appear to be the dominant control on wildfire activity during this period. Finally, this thesis provides an analysis of charcoal abundance variations occurring across natural, orbitally forced cycles, termed the Milankovitch cycles. The results presented illustrate that natural variations in charcoal abundance are possible over intermediate timescales within the geological record. This thesis therefore illustrates a need to take into consideration and incorporate ‘natural background’ fluctuations in fire activity occurring over medium timescales, when analysing and predicting past and future climate change patterns.

A presente pesquisa teve como objetivo investigar os efeitos da privação das retroalimentações sensoriais (aural, cinestésica e visual) na abordagem inicial de peças para piano por estudantes de diferentes níveis acadêmicos. A metodologia seguiu um delineamento experimental tipo hierárquico no qual 12 pianistas (alunos de início, meio e fim de curso da graduação, e alunos da pós-graduação em Música) foram submetidos a quatro condições de estudo com privação singular e/ou pareada das retroalimentações: (i) Condição A: Decodificação Visual com retroalimentação cinestésica e privação da retroalimentação aural; (ii) Condição B: Decodificação Visual com privação das retroalimentações aural e cinestésica (prática mental); (iii) Condição C: Decodificação Aural com retroalimentação cinestésica e privação da retroalimentação visual da partitura (“tocar a música de ouvido”); (iv) Condição D: Decodificação Aural com privação das retroalimentações cinestésica e visual da partitura. Para a coleta de dados, quatro encontros foram realizados individualmente com os pianistas. Cada encontro foi destinado ao estudo de uma peça em uma das condições de privação, seguidos de uma performance e entrevista semiestruturada. Os dados obtidos foram analisados qualitativamente e quantitativamente acerca do tempo de prática despendido em cada condição de estudo, das estratégias desenvolvidas pelos participantes e do produto das performances. Os resultados apontam que em todas as quatro condições, os participantes demonstraram a necessidade de estratégias de manipulação do conhecimento declarativo/semântico para a leitura e entendimento da linguagem musical, notada ou estimulada de forma aural. Em três das quatro condições (A, B e C), os participantes recorreram à manipulação de estratégias visando: (i) acessar o conhecimento procedimental no instrumento e fora dele a fim de estabelecer e/ou coordenar os movimentos para as situações de performance, (ii) capacitar meios de acesso e/ou de criação de uma representação mental para orientar suas performances e/ou fornecer subsídios básicos para a execução musical e capacidade de retenção das informações sensoriais. Na amostra investigada os pós-graduandos demonstraram níveis de expertise mais desenvolvidos através de produtos qualitativamente superiores aos demais estudantes no que concerne à comunicação expressiva e fluência na execução, nas condições A e B. / The present research aimed at investigating the effects of sensory feedbacks privation (auditory, kinesthetic and visual) during the initial approach to piano pieces by students belonging to different academic levels. The methodology was based on an experimental nested-design in which 12 pianists (freshman, sophomore and senior undergraduate students, and graduate students of Music) were submitted to four different studying conditions with single and/or paired privation of feedbacks: (i) Condition A: Visual Decoding with kinesthetic feedback and auditory feedback privation; (ii) Condition B: Visual Decoding with privation of auditory and kinesthetic feedbacks (mental practice); (iii) Condition C: Auditory Decoding with kinesthetic feedback and privation of visual feedback from the score (‘playing by ear’); (iv) Condition D: Auditory Decoding with privation of kinesthetic and visual (score) feedbacks. Data collection took place in four sections, individually with each pianist. In each section, the participant studied one piece under one condition of feedback privation, followed by performance and semi-structured interview. Data were analyzed qualitatively and quantitatively in terms of the practice time spent in each condition of study, of strategies developed by participants and of performance products. Results have shown that in all four conditions, the participants have shown the necessity of strategies for the manipulation of declarative/semantic knowledge for reading and musical language understanding, notated or auditory stimulated. In three out of four conditions (A, B and C), the participants have manipulated strategies aiming: (i) accessing the procedimental knowledge in and out of the instrument to establish and/or coordinate the movements for the performance; (ii) enabling means of access and/or creation of a mental representation to guide their performances and/or providing basic subsidies for musical execution and the capacity for holding the sensorial information. Within the investigated sample, the graduate students have shown more developed expertise levels through their qualitatively higher products in comparison to the other students in terms of expressive communication and fluency in conditions A and B.