Headwater streams change in wet length in response to storm events and seasonal moisture conditions. These low-order channels with temporary flow are pervasive across arid and humid environments yet receive little attention in comparison to perennial waterways. This dissertation examines headwater stream length dynamics at multiple spatial and temporal scales across the Appalachians. I mapped wet stream length in four Appalachian physiographic provinces--the Appalachian Plateau, Blue Ridge, New England, and Valley and Ridge--to characterize seasonal expansion and contraction of the wet network at a broad, regional scale. Conversely, most existing field studies of stream length in headwaters are limited to a single study area or geographic setting. Field mappings showed that wet stream length varies widely within the Appalachians; network dynamics correlated with regional geology as well as local site lithology, geologic structure, and the depth, size, and spatial distribution of surficial sediment deposits. I used the field data to create logistic regression models of the wet network in each physiographic province at high and low runoffs. Topographic metrics derived from elevation data were able to explain the discontinuous pattern of headwater streams at different flow conditions with high classification accuracy. Finally, I used flow intermittency sensors in a single Valley and Ridge catchment to record channel wetting and drying at a high temporal resolution. The sensors indicated stream length hysteresis during storms with low antecedent moisture, with a higher wet network proportion on the rising limb than on the falling limb of events. As a result, maximum network extension can precede peak runoff by minutes to hours. Accurate maps of headwater streams and an understanding of wet network dynamics through time are invaluable for applications surrounding watershed management and environmental policy. These findings will contribute to the burgeoning research on temporary streams and are additionally relevant for studies of runoff generation, biogeochemical cycling, and mass fluxes of material from headwaters. / Ph. D. / During a rain storm, we may think of streams increasing in depth, width, and velocity. However, we may not necessarily envision streams also getting longer. Headwaters, which form the upstream extremities of river systems, consist of many temporary streams that expand and contract in length due to storms and changes in seasonal moisture conditions. Headwaters are spatially expansive, comprising a majority of total river length, and serve as a primary control on downstream water quality. Therefore, understanding stream length dynamics can inform policy and land use decisions to effectively conserve and manage headwater regions and protect water sources for human use and consumption. This dissertation examines changes in stream length across four study areas of the Appalachian Mountains. I mapped the wet, or active, stream network multiple times at different flow conditions in each study area. Stream length dynamics varied considerably across the Appalachians and demonstrated the same range of network expansion and contraction as other studies observed in diverse settings around the world. Wet stream length greatly depended on regional and local geology. I then sought to predict the location of wet streams at high and low flows using metrics such as slope and drainage area that I calculated from digital elevation information. Comparisons with the field maps I made showed that simple terrain metrics explained the location, length, and disconnected nature of wet networks in each province with high accuracy. I also observed stream length dynamics during storm events in one watershed using sensors that recorded the presence or absence of water. These observations demonstrated that stream length was often higher for a given flow at the beginning of a storm on the rising limb than on the falling limb when flow was decreasing, particularly if conditions were dry before the storm. The findings of this dissertation contribute to existing knowledge of temporary streams and are relevant for future studies investigating the hydrology, biology, and ecology of headwaters.

Submitted by Claudia Vanessa dos Santos Corrêa (claudiageobrax@yahoo.com.br) on 2018-06-06T02:32:25Z No. of bitstreams: 1 VERSAO FINAL COMPLETA.pdf: 29221186 bytes, checksum: e01b175cba96e8af54b4c7995ec5262a (MD5) / Approved for entry into archive by Ana Paula Santulo Custódio de Medeiros null (asantulo@rc.unesp.br) on 2018-06-06T12:02:22Z (GMT) No. of bitstreams: 1 correa_cvs_dr_rcla.pdf: 29196738 bytes, checksum: 8314696946ba060a96b1d3d2775068a3 (MD5) / Made available in DSpace on 2018-06-06T12:02:23Z (GMT). No. of bitstreams: 1 correa_cvs_dr_rcla.pdf: 29196738 bytes, checksum: 8314696946ba060a96b1d3d2775068a3 (MD5) Previous issue date: 2018-03-12 / Outra / As corridas de detritos são movimentos de massa que se desenvolvem ao longo de redes de drenagem e envolvem fluidos densos, compostos por materiais de diferentes granulometrias e composições, bem como quantidades variáveis de água, identificados como processos naturais constituintes da dinâmica e da modelagem da paisagem. Caracterizam-se pelo extenso raio de alcance, altas velocidades, altas vazões de pico e elevada capacidade de erosão e força de impacto. As áreas mais susceptíveis a ocorrência desses processos no Brasil estão situadas no sopé da Serra do Mar, da Serra da Mantiqueira e da Serra Geral, e no litoral norte do Estado de São Paulo foi registrado um grande evento de escorregamentos e corridas de detritos generalizados em 1967 que afetou a região de Caraguatatuba e São Sebastião, onde se encontra uma malha dutoviária associada a Unidades de Tratamento da Petrobras, outros empreendimentos, estruturas e uma grande área urbana em crescimento. O objetivo geral desta pesquisa é propor uma metodologia para avaliação da potencialidade de bacias hidrográficas à ocorrência de corridas de detritos, através do emprego da compartimentação fisiográfica, de estudos de retroanálise e da simulação numérica do terreno com o software RAMMS. A compartimentação fisiográfica revelou que as unidades que possuem contato direto com planícies são aquelas que possuem maior potencialidade a corridas de detritos. Na retro-análise, foi estabelecido o Fator de Desproporcionalidade, que possibilitou a análise de incoerências de incidência de cicatrizes de escorregamento em bacias hidrográficas, unidades geológicas e classes de declividade. As bacias Camburu, Pau D’Alho, Canivetal e Santo Antônio foram consideradas como as mais afetadas por escorregamentos e corridas de detritos, sendo que a classe de declividade de 350 a 500 é a mais atingida nesses locais e não houve uma unidade geológica preferencial durante a mobilização desses processos. A simulação numérica revelou que as corridas de detritos da Serra do Mar apresentam um fluxo com caráter reológico predominantemente granular e as zonas de deposição das corridas dão-se preferencialmente em regiões de baixa declividade. O emprego desta metodologia pode auxiliar na identificação de locais com potencialidade a corrida de detritos, especialmente na Serra do Mar, e contribuir com a gestão do meio físico. / The debris flows are mass movements that develop along drainage networks and involve generally dense fluids, compose of materials of different granulometries and compositions, as well as variable amounts of water, identified as natural processes that constitute the dynamics and the modeling the landscape. They are characterized by the long range, high speeds, high peak flows, high erosion capacity and impact force. The areas most susceptible to the occurrence of these processes in Brazil are in the foothills of the Serra do Mar, Serra da Mantiqueira and Serra Geral, and on the north coast of São Paulo State there was a great event of landslides and debris flows in 1967 which affected the region of Caraguatatuba and São Sebastião, where there is a pipeline network associated with Petrobras Treatment Units, other enterprises, structures and a large urban area in growth. The general aim of this research is to propose a methodology to evaluate the potential of watersheds to the occurrence of debris flows, using physiographic compartmentalization, retro-analysis studies and numerical simulation of the terrain with Ramms software. The physiographic compartmentalization revealed that the units that have direct contact with lowlands are those that have greater susceptibility to debris flows. In the retro-analysis, the Disproportionality Factor was established, which made it possible to analyze inconsistencies in the incidence of landslide scars in watersheds, geological units and declivity classes. The Camburu, Pau D’Alho, Canivetal and Santo Antônio watersheds were the most affected by landslides and debris flows, and the slope class of 350 to 500 is the most affected in these areas and there was no preferential geological unit during the mobilization of these processes. The numerical simulation revealed that the Serra do Mar debris flows have a predominantly granular rheological flow and the deposition zones of the flows are given in regions of low slope. Thus, the use of this methodology can help in the identification of areas with potential for the debris flows, especially in Serra do Mar, and contribute to the management of the physical environment.

Made available in DSpace on 2014-06-11T19:26:10Z (GMT). No. of bitstreams: 0 Previous issue date: 2010-06-30Bitstream added on 2014-06-13T18:29:36Z : No. of bitstreams: 1 pupim_fn_me_rcla.pdf: 11524545 bytes, checksum: 941e43a1eb1fa5d5255117d5f61a3e90 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Devido ao aumento da pressão antrópica sobre os ambientes naturais faz-se necessária a realização de levantamentos que contemplem diversos fatores ambientais (bióticos e abióticos) e corroborem com zoneamentos geoambientais e o planejamento territorial. O estudo da fisiografia permite a caracterização e classificação das paisagens terrestres levando em consideração os fatores formadores destas paisagens (clima atual e passado, hidrologia, geologia, geomorfologia e indiretamente aspectos bióticos) e as relações (processos) que os afetam. Desta forma, o objetivo da pesquisa foi investigar as características fisiográficas do município de Rio Claro-SP e, assim, contribuir para o melhor conhecimento dos aspectos do meio físico e suas relações. Para atingir o objetivo foram utilizados procedimentos e técnicas próprias das geociências, como interpretação de fotografias aéreas, geoprocessamento e levantamentos de campo. A sistemática de trabalho adotada se resume à quatro etapas: I) revisão bibliográfica; II) análise geomorfométrica; III) análise morfoestrutura e; IV) análise fisiográfica. Os resultados obtidos foram os mapas geomorfométricos (hipsometria, classes de declividade e curvatura do terreno), mapas morfoestruturais (lineamentos estruturais, traços de juntas, anomalias de drenagem e linhas de contorno estrutural não cotadas) e o mapa fisiográfico. A análise fisiográfica permitiu identificar e compreender os processos endógenos e exógenos que atuam e atuaram na evolução da paisagem. O município de Rio Claro-SP é caracterizado por paisagens policíclicas de origem fluvial, denudacional/paleoaluvial, denudacional e estrutural. A subdivisão das paisagens em unidades menores evidenciou a presença de subpaisagens do tipo planície de inundação e terraço para as paisagens fluviais; topos e encostas para as paisagens denudacionais/paleoaluviais,... / Due to the increase of anthropogenic pressure on natural environments it is necessary to make surveys involving several environmental factors (biotic and abiotic) and the corroborating with geoenvironmental zoning and land use planning. The study of the physiography enables the characterization and classification of landscapes, considering the factors of landscape formation (current and past climate, hydrology, geology, geomorphology and indirectly biotic aspects) and relations (processes) that affect them. Therefore, the aim of this research is to investigate the physiographic characteristics of Rio Claro-SP district and thus to contribute to a better knowledge of physical environment aspects and their relationships. To achieve the main objective specific techniques and procedures from geosciences were taken, such as aerial photo interpretation, geoprocessing and field surveys. The systematic adopted for this work followed four steps: i) reiew; II) geomorphometric analysis; III) morphostructural analysis; IV) physiographic analysis. The results gathered were the geomorphometric maps (hypsometry, slope and terrain curvature), morphostructural maps (structural lineaments, traces of joints, abnormal drainage and structural contour lines unlisted) and a physiographic map. Physiographic analysis allowed us to identify and understand the endogenous and exogenous processes that acted in landscape evolution. Rio Claro-SP is characterized by polycyclic landscapes with fluvial, denudational / paleoalluvial, denudational and structural origins. The subdivision of landscapes into smaller units showed the presence of sub-landscapes, from the type floodplain and river terrace landscapes; summit and slope to the landscapes denudational / paleoalluvial, denudational and structural; abandoned ponds in landscapes denudational / paleoalluvial

Resumo: A unidade de estudo está localizada no estado de São Paulo (Região Sudeste do Brasil) e adjacência e foi escolhida segundo critérios climatológicos, geomorfológicos, geoestruturais, ecossistêmicos e de percepção visual de um observador. Definiu-se o bloco ao qual pertencem as Serras do Japi, Ermida e Guaxinduva como uma unidade de paisagem regional específica. Tal unidade foi avaliada segundo a abordagem sistêmica da paisagem (ecologia da paisagem), considerando-se, em especial, as inter-relações entre alguns dos componentes e processos morfodinâmicos que atuam e atuaram na paisagem local. A análise integrada das características geológicas, de relevo, solo e vegetação; utilizando-se métodos de interpretação visual (fotointerpretação) e tratamento digital de imagem orbital, na aquisição dos dados e na avaliação dos processos morfodinâmicos; foi conduzida pelas análises fisiográfica, morfoestrutural e morfodinâmica. Constatouse a partir destas análises que, a neotectônica, além de exercer grande influência na alteração da rocha, no grau de dissecação do relevo e na distribuição dos depósitos sedimentares, influenciou, juntamente com a constituição litológica, nas relações entre morfogênese/pedogênese, as quais atuam na distribuição e diferenciação dos solos e cobertura vegetal. E, conseqüentemente, na distribuição dos diferentes ecossistemas, mostrando a relação direta desses com as linhas de falha e fraturas. O grau de estabilidade morfodinâmica das unidades fisiográficas está intimamente relacionado com a forma das encostas, declividade do terreno e de alguns parâmetros do solo, como profundidade, bio-estrutura, textura e umidade. O estudo dos ambientes do ponto de vista ecodinâmico, segundo avaliação das relações entre morfogênese e pedogênese, definiu 4 diferentes zonas ecodinâmicas e mostrou que...(Resumo completo, clicar acesso eletrônico abaixo) / Abstract: The studied area, located in the State of São Paulo (brasilian southeastern geographic region) was choosen by climatologic, geomorphologic, geostructural, ecosystem and visual percepion of the Author. Thus, the Serra (Highland) do Japi. Ermida and Guaxinduva geomorphological blocks and adjacencys areas were defined as units of a regional specific landscape scenery. These landscapes were evaluated following a scenery landscape system approach taking in account the interrelation among some component part and processes that had acted, and still do, in the present landscape. The integrated analysis made by photointerpretation, geologic, relief, soil and vegetation studies, the fielddata acquirement and the evaluation of the morphodynamic processes were based in physiographic, morphostructiral and morphodynamic analysis. Based on this it could be observed that neotectonic events and litologic constitution had a strong influence in the degree of rock wheatering, relief evolution, sedimentary deposits distribution and in relationship among morphogenesis and pedonesis, its carry out the final type of soil and vegetation cover. This fact leads to a consequent correlation of the several ecosystems distribution to faults and fractures lineaments of the area structural framework. The morphodynamic stability degree of the physiographic units is clearly related with the type of slope, terrain declivity and some soils factors as thickness, bio-structure, texture and humidity. The ecodynamic chacterization based on the balance of the comparison of morphogenesis and pedonesis processes had shown that the forest components have specifc actions in the geodynamic environments and are, togheter with declivity and soil parameters, limitant factors of the growing or decreasing actions in each identified zones. The 01 zone that correspond to the Japi, Ermida and Guaxinduva serras (highlands) depend...(Complete abstract click electronic access below) / Orientador: Vicente José Fulfaro / Coorientador: Jairo Roberto Jimenez Rueda / Banca: Paulina Setti Riedel / Banca: Harold Gordon Fowler / Banca: Ailton Luchiari / Banca: Mario Lincon de Carlos Etchebehere / Doutor

Radio wave signal strength and associated propagation models are rarely analyzed across individual geographic provinces. This study evaluates the effectiveness of the Radio Mobile model to predict radio wave signal strength in the Blue Ridge and Valley and Ridge physiographic provinces. A spectrum analyzer was used on 19 FM transmitters to determine model accuracy. Statistical analysis determined the significance between different terrain factors and signal strength. Field signal strength was found to be related to test site elevation, transmitter azimuth, elevation angle, transmitter elevation, path loss, and distance. Using 76 signal strength receiver sites, Ordinary Least Square regression models predicted signal strength with 60% of variability explained in the Valley and Ridge province model and 43% of variability explained in the Blue Ridge province model. Region-specific statistical models were more accurate in determining a region’s transmitter placement and level of power for broadcasting compared to generic computer models.

Waterways have been geomorphically altered or disturbed by development, mining, agriculture and other human activities for many years. Section 404 of the Clean Water Act determined that these impacts to our waterways must be mitigated for channel alterations. Stream restoration has been one method to mitigate for these impacts to our water resources. Stream restoration is considered to be a measurable improvement to the channel stability, water quality, habitat or overall function of a degraded stream system. Practices of stream restoration have changed in the last 10 to 20 years with the introduction of natural channel design methods. Natural channel design involves rebuilding a stream channel with the appropriate channel dimensions, slope, and planform to accommodate water and sediment inputs from its drainage basin without excessively aggrading or degrading. Dimensions of restored stream channels are based on a stage that is termed bankfull. The bankfull discharge is the flow that fills the channel just to the tops of its banks to the incipient point of flooding. Design dimensions used in natural channel design are based on bankfull stage and discharge because practitioners believe it is responsible for the average morphology of a stream channel. Practitioners of stream restoration use two tools to aid in the determination of these stable channel conditions: they are 1) regional channel geometry and discharge relations to drainage area (regional curves) and 2) reference reach derived dimensionless bankfull channel geometry ratios. These tools are developed for ecoregions that have similar climates, topography, geology, soils, hydrology and vegetation because these are also the features that dictate stream channel form. Regional curves and reference reach dimensionless ratios were developed for the Level III Ecoregion 67 Ridge and Valley, Tennessee. The regional power function equations of bankfull cross sectional area, width, mean depth, and discharge to drainage, and the dimensionless bankfull channel geometry ratios of reference reaches will help determine the bankfull channel dimensions used in natural channel design.

Made available in DSpace on 2014-06-11T19:32:18Z (GMT). No. of bitstreams: 0 Previous issue date: 2004-05-14Bitstream added on 2014-06-13T19:21:49Z : No. of bitstreams: 1 jesus_n_dr_rcla.pdf: 4080852 bytes, checksum: 26bd714933c57c69df93023c06fe8ef0 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / A unidade de estudo está localizada no estado de São Paulo (Região Sudeste do Brasil) e adjacência e foi escolhida segundo critérios climatológicos, geomorfológicos, geoestruturais, ecossistêmicos e de percepção visual de um observador. Definiu-se o bloco ao qual pertencem as Serras do Japi, Ermida e Guaxinduva como uma unidade de paisagem regional específica. Tal unidade foi avaliada segundo a abordagem sistêmica da paisagem (ecologia da paisagem), considerando-se, em especial, as inter-relações entre alguns dos componentes e processos morfodinâmicos que atuam e atuaram na paisagem local. A análise integrada das características geológicas, de relevo, solo e vegetação; utilizando-se métodos de interpretação visual (fotointerpretação) e tratamento digital de imagem orbital, na aquisição dos dados e na avaliação dos processos morfodinâmicos; foi conduzida pelas análises fisiográfica, morfoestrutural e morfodinâmica. Constatouse a partir destas análises que, a neotectônica, além de exercer grande influência na alteração da rocha, no grau de dissecação do relevo e na distribuição dos depósitos sedimentares, influenciou, juntamente com a constituição litológica, nas relações entre morfogênese/pedogênese, as quais atuam na distribuição e diferenciação dos solos e cobertura vegetal. E, conseqüentemente, na distribuição dos diferentes ecossistemas, mostrando a relação direta desses com as linhas de falha e fraturas. O grau de estabilidade morfodinâmica das unidades fisiográficas está intimamente relacionado com a forma das encostas, declividade do terreno e de alguns parâmetros do solo, como profundidade, bio-estrutura, textura e umidade. O estudo dos ambientes do ponto de vista ecodinâmico, segundo avaliação das relações entre morfogênese e pedogênese, definiu 4 diferentes zonas ecodinâmicas e mostrou que... / The studied area, located in the State of São Paulo (brasilian southeastern geographic region) was choosen by climatologic, geomorphologic, geostructural, ecosystem and visual percepion of the Author. Thus, the Serra (Highland) do Japi. Ermida and Guaxinduva geomorphological blocks and adjacencys areas were defined as units of a regional specific landscape scenery. These landscapes were evaluated following a scenery landscape system approach taking in account the interrelation among some component part and processes that had acted, and still do, in the present landscape. The integrated analysis made by photointerpretation, geologic, relief, soil and vegetation studies, the fielddata acquirement and the evaluation of the morphodynamic processes were based in physiographic, morphostructiral and morphodynamic analysis. Based on this it could be observed that neotectonic events and litologic constitution had a strong influence in the degree of rock wheatering, relief evolution, sedimentary deposits distribution and in relationship among morphogenesis and pedonesis, its carry out the final type of soil and vegetation cover. This fact leads to a consequent correlation of the several ecosystems distribution to faults and fractures lineaments of the area structural framework. The morphodynamic stability degree of the physiographic units is clearly related with the type of slope, terrain declivity and some soils factors as thickness, bio-structure, texture and humidity. The ecodynamic chacterization based on the balance of the comparison of morphogenesis and pedonesis processes had shown that the forest components have specifc actions in the geodynamic environments and are, togheter with declivity and soil parameters, limitant factors of the growing or decreasing actions in each identified zones. The 01 zone that correspond to the Japi, Ermida and Guaxinduva serras (highlands) depend...(Complete abstract click electronic access below)

Stand carrying capacity is the maximum size of population for a species under given environmental conditions. Site resources limit the maximum volume or biomass that can be sustained in forest stands. This study was aimed at estimating and determining the carrying capacity in loblolly pine. Maximum stand basal area (BA) that can be sustained over a long period of time can be regarded as a measure of carrying capacity. To quantify and project stand BA carrying capacity, one approach is to use the estimate from a fitted cumulative BA-age equation; another approach is to obtain BA estimates implied by maximum size-density relationships (MSDRs), denoted implied maximum stand BA. The efficacy of three diameter-based MSDR measures: Reineke's self-thinning rule, competition-density rule and Nilson's sparsity index, were evaluated. Estimates from three MSDR measures were compared with estimates from the Chapman-Richards (C-R) equation fitted to the maximum stand BA observed on plots from spacing trials. The spacing trials, established in the two physiographic regions (Piedmont and Coastal Plain), and at two different scales (operational and miniature) were examined and compared, which provides a sound empirical basis for evaluating potential carrying capacity. Results showed that the stands with high initial planting density approached the stand BA carrying capacity sooner than the stands with lower initial planting density. The maximum stand BA associated with planting density developed similarly at the two scales. The potential carrying capacity in the two physiographic regions was significantly different. The value of implied maximum stand BA converted from three diameter-based MSDR measures was similar to the maximum stand BA curve obtained from the C-R equation. Nilson's sparsity index was the most stable and reliable estimate of stand BA carrying capacity. The flexibility of Nilson's sparsity index can illustrate the effect of physiographic regions on stand BA carrying capacity. Because some uncontrollable factors on long-term operational experiments can make estimates of stand BA carrying capacity unreliable for loblolly pine, it is suggested that the stand BA carrying capacity could be estimated from high initial planting density stands in a relatively short period of time so that the risk of damages and the costs of experiments could be reduced. For estimating carrying capacity, another attractive option is to choose a miniature scale trial (microcosm) because it shortens the experiment time and reduces costs greatly. / Master of Science

Thèse numérisée par la Direction des bibliothèques de l'Université de Montréal. / Thèse de doctorat effectuée en cotutelle au Département de Géographie Université de Montréal et à l'Institut Méditerranéen d'Écologie et de Paléoécologie Université de Droit, d'Économie et de Sciences d'Aix-Marseille 111 / La tourbière de Mirabel (basses terres du St-Laurent, Québec méridional) a été étudiée dans le but de préciser l'influence exercée par les différents paramètres autogènes et allogènes sur l'accumulation postglaciaire du carbone. (l) Les dynamiques végétales régionales révèlent un contrôle climatique général, modulé localement par le contexte paléogéographique, la physiographie et les processus écologiques. (2) L'histoire postglaciaire du climat régional fut reconstituée par la méthode des analogues modernes, contrainte par les fluctuations du niveau du lac Hertel (Mont St-Hilaire). Les résultats obtenus témoignent d'un important réchauffement entre 13 000 et 11 000 cal. BP, d'un optimum thermique autour de 8000 cal. BP, et de deux périodes sèches (10 000-6500 et 5000-3000 cal. BP). (3) Les dynamiques postglaciaires internes de la tourbière furent indépendamment reconstituées en trois dimensions par l'analyse pluridisciplinaire de sept profils. Ces derniers montrent des successions végétales similaires, conformes au modèle de terrestrialisation, mais asynchrones. Ils témoignent en outre de conditions de surface très humides avant 6700 cal. BP, suivies de nombreuses fluctuations asynchrones sur l'ensemble du site. L'accumulation du carbone présente en revanche des tendances similaires dans tous les profils, caractérisées par de fortes accumulations avant 6200 cal. BP (moyennes de 7.1 à 19.1 gC.m .an'1) et de faibles accumulations depuis (moyennes de 2.7 à 6.3 gC.m'2.an ). (4) Les différentes conditions postglaciaires du développement de la tourbière sont confrontées. L'accumulation du carbone paraît avoir été essentiellement contrôlée par les interrelations entre la physiographie (alimentation minérotrophe initiale) et les processus autogènes, qui ont progressivement isolé la végétation tourbigène de la nappe phréatique. Notamment, ni le climat, ni les feux ne semblent avoir joué de rôle significatif. / Mirabel bog (St. Lawrence lowlands, southern Quebec) was studied with the aim to specify the influences exerted by the different autogenic and allogenic parameters on postglacial carbon accumulation. (1) Regional vegetation dynamics reveal a general climatic control, locally modified by the palaeogeographical context, physiography and ecological processes. (2) The postglacial history of the regional climate was reconstructed by the modem analogues method, constrained by the water level fluctuations of Lac Hertel (Mont St- Hilaire). Obtained results provide evidence for an important climate improvement between 13 000 and 11 000 cal. BP, a thermal optimum around 8000 cal. BP and two dry periods (10000-6500 and 5000-3000 cal. BP). (3) Postglacial internal dynamics were independently reconstmcted in three dimensions by the multidisciplinary analysis of seven profiles. They show similar plant successions, conforming to the terrestrialisation model but were asynchronous. They moreover attest the occurrence of very humid conditions prior to 6700 cal. BP, followed by numerous asynchronous fluctuations throughout the site. By contrast, carbon accumulation presents similar trends in all proiïles, characterised by high accumulation rates prior to 6200 cal. BP (averages from 7.1 to 19.1 gC.m .year ) and low rates since this date (averages from 2.7 to 6.3 gC.m'2.year-l). (4) The different postglacial conditions of peatland development arc coirfronted. Carbon accumulation appears to have been essentially controlled by the interplay between physiography (initial minerotrophic supply) and autogenic processes, which progressively isolated the peat-forming vegetation from groundwater. Notably, neither climate nor fire seem to have played a significant role.

The research was undertaken to investigate the impact of the Tshivhase Tea Estate on the space economy of Venda, the people and area ofMapate, and Duthuni, among whom the Tea Estate is established. The approach is based on principles. Principles of development theory are combined with appropriate spatial models. The development reality of Venda, together with many other development projects are analysed. Does the tea estate address the rural poverty problem? Findings are presented from a case study of Tshivhase and this proved the lack of growth and development impulses to alleviate the poverty of the rural people among whom it is located. Development is considered in terms of its possible simultaneous diffusion of economic activity and modernisation in all four dimensions of the spatial system : political, socio-cultural, economic and physical. / Department of Geography / M.A. (Geography)