Predicting the long-term behaviour of present-day ice sheets is hampered by the short timescales of our observations and restricted knowledge of the subglacial environment. Studying palaeoice sheets can help by revealing the nature and amplitude of past centennial- to millennial-scale ice sheet change. This thesis uses glacial sediments and landforms to examine the evolution of the partly marine-based British-Irish Ice Sheet (BIIS) and its bed, in western Scotland. Three zones of the former BIIS are considered: ranging from a mountain ice cap, to a core area of the ice sheet, to a peripheral marine-terminating sector. The topography of the subglacial landscape was an important in uence on the location of dynamic and stable components of the ice sheet. At an ice cap scale, zones of glacier inception and retreat were linked to catchment elevation and size. At the ice sheet scale, the migration of ice divides and thermal boundaries were focused through corridors of low relief subglacial topography. The main west-east ice divide of the BIIS in central Scotland migrated by 60 km, 10% of the ice sheet's width, through one such corridor during the glacial cycle. A major change in the ow regime of the BIIS in western Scotland accompanied the development of a marine-based sector on the Malin Shelf. As the BIIS advanced to the shelf edge, ice ow was drawn westwards { orthogonal to the earlier, geologically controlled, ow pattern. Retreat of the BIIS from the shelf edge occurred at an average rate of 10 m a-1, but was punctuated by at least one episode of accelerated retreat at 100 m a-1. In each zone of the BIIS examined, a rich palimpsest landscape is preserved and the role of earlier glaciations in conditioning or priming the landscape is highlighted. Western Scotland in particular is dominated by features relating to a 'restricted' mountain ice sheet, suggested to have been the prevailing ice sheet mode during the Early and Middle Quaternary. Where the last BIIS was underlain by soft sediments, glacier movement at the bed was facilitated by a combination of basal sliding and a localised mosaic of shallow deforming spots, allowing landform and sediment preservation. In places, till deposition was focused over permeable substrates acting to seal the bed, promote lower e ective pressures, and enhance motion by basal sliding. The modern land surface in western Scotland provides an approximation for the relief of the former glacier bed, and can be used for conceptual palaeoglaciological reconstructions. Areas of focused postglacial deposition have, however, obscured parts of the ice sheet bed, with demonstrable implications for quantitative palaeoglaciological analyses. Methods to improve the representation of former ice sheet bed in these areas are discussed and may be pertinent to future palaeo-ice sheet modelling exercises.

Understanding how deltas build and maintain themselves is critical to predicting how they will respond to perturbations such as sea level rise. This is especially an issue of interest in coastal Louisiana, where land loss is exacerbated due to subsidence and decreased sediment supply. Feedbacks between ecology and geomorphology have been well documented in tidal environments, but the role of vegetation in delta morphodynamics is not well understood. This study investigates spatial and temporal correlations between vegetation succession and sediment accumulation at the Wax Lake Delta in Louisiana. I established a 2500 m long transect along the western levee of Pintail Island, capturing the full range of island elevations and the transition from bare sediment to herbaceous plants and trees. Shallow (50-100 cm deep) sediment cores taken along this transect were analyzed for particle size, organic matter content, and bulk density, and dated using ²¹⁰Pb. The resulting sedimentation rates and composition trends over time were compared to remote sensing-based analyses of temporal changes in island topography and flooding frequency derived from historical Landsat images. We found that the topography of Pintail Island has developed from a non-systematic arrangement of elevations to a discrete set of levees and intra-island platforms with distinct vegetation types, designated as high marsh, low marsh, and mudflat habitat. This elevation zonation is consistent with alternative stable state theory as so far applied to tidal salt marsh systems. At all but the youngest sampling site, sediment cores showed a significant decrease in organic matter content and a significant increase in grain size with depth. The total organic matter contribution to vertical growth was not sufficient to account for all the elevation change required to achieve the differentiation from low marsh to high marsh deduced from the time-lapse Landsat imagery analysis. Mineral sediment accumulation rates suggested that elevation growth was accelerating or holding steady over time, in contrast to theory suggesting rates should slow as elevation increases. These results provide an empirical foundation for future mechanistic models linking mineral sedimentation, organic sedimentation, vegetation succession, elevation change, and flood frequency in the delta. / text

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No description available.

A study of downstream suspended sediment transport dynamics in the West River at Cape Bounty, Melville Island, Nunavut, was undertaken in 2012. The first component of the research quantified the sediment mobilized in the West River during the 2012 season. A nival bed-contact survey was undertaken to identify areas of the river in which stream flow was isolated from the bed, and was combined with a reach-based sediment budget approach to assess sediment entrainment and downstream movement. This analysis revealed the propensity of the West River to store suspended sediment through much of the season. Permafrost disturbances in 2007 inundated the West River with fine sediments, the majority of which are progressing from the headwaters as a sediment slug that is subject to substantial downstream storage. Diurnal and event hysteresis analysis from 2004-2012 demonstrate the change in sediment delivery inter-annually, transitioning from a system characterized by clockwise hysteresis prior to the 2007 disturbances, to counter-clockwise hysteresis post 2007. The latter is reflective of the important contribution of the headwater sediment slug from disturbance to downstream sediment transport and common net sediment storage in the lower reaches of the river. The second project studied the delivery of suspended sediment following late season major rainfall events (MRE) and the control antecedent catchment conditions prior to rainfall exert on the magnitude of stream runoff and suspended sediment transport. Two MREs on July 9 and July 23, totalling 35.4 and 10.6 mm, respectively, resulted in exceptionally low discharge response and sediment mobilization. Analysis of synoptic level pressure patterns and catchment soil moisture revealed low volumetric water content preceding both MREs, a result of sustained exceptional early summer warmth under stable regional high pressure. Compared to similar MREs in 2007-2009, the soil in 2012 did not become saturated, and substantial runoff did not occur. These studies contribute to an understanding of the processes of sediment transport in response to disturbances, rainfall, and antecedent catchment conditions, all of which are becoming important components of the Arctic fluvial systems but have had limited study due to the emphasis on snow melt processes and hydrological fluxes. / Thesis (Master, Geography) -- Queen's University, 2013-09-25 11:36:58.882

The concept of talus slopes co-evolving with vegetation cover is investigated on the Trotternish Ridge, Isle of Skye, Scotland.  This uses several lines of contemporary and palaeoenvironmental evidence.  Through a replicated set of grazing enclosures, the composition and structure of present-day vegetation is linked to contemporary grazing regimes and slope erosion processes.  Vegetation history is reconstructed from the fossil pollen content of organic palaeosols intercalated within the talus deposits.  A new method using Long Chain Alcohols is used to support the interpretation of the fossil pollen records.  Geomorphological development is revealed through analysis of talus stratigraphy and the sedimentary deposits immediately below the slopes.  These lines of evidence are combined to construct a conceptual model for talus co-evolution on the Trotternish Ridge.  Talus development began as the climate warmed from around 17.5k cal yrs BP, and the glaciers of the last Ice Age retreated.  Slopes initially comprised rockfall debris, with a sparse cover of vegetation having little or no effect on slope processes.  Heathland and grassland vegetation, evidenced by the organic palaeosols, was intermittently present on the talus slope surfaces from 7.7-7.6k cal yr BP until approximately 0.6-0.5k cal yr BP.  This vegetation cover limited physical and hydrological surface processes, enabling the upper part of the talus slopes to over-steepen.  Evidence of increased frequency of organic palaeosol burial, and increased rates of sediment deposition after around 2.0k cal yr BP, both indicate greater debris flow and other erosional activity in the late Holocene.  This is attributed to both increased incidence of intense rainfall events and much higher levels of grazing associated with the introduction of cattle, sheep and rabbits.  Contemporary evidence shows that heavy grazing changes the vegetation composition and structure, and increases susceptibility to erosion.  Talus co-evolution on the Trotternish Ridge may be similar to that at other British and Faroese sites which share the same basaltic geology.

Traditionally, the interactions between geomorphic character and aquatic biodiversity have been widely acknowledged, but poorly quantified. However, the coupling of these disciplines is currently rising up legislative and political agendas, such as the European Union Water Framework Directive (EU WFD). The Directive requires Member States to classify rivers into types based on their natural morphology and geomorphic processes, and to link the biota to river types existing under natural conditions. Typing now forms the basis for evaluating environmental sensitivity to river engineering and determining reference conditions for river restoration. The Scottish Environment Protection Agency (SEPA) has adapted the Montgomery and Buffington (1997) channel typology developed in the Pacific Northwest of the USA for use in Scotland. The modified typology identifies eleven distinct channel types (e.g. bedrock, plane-bed, wandering and meandering). In this study, 43 reference condition sites in the upper River Dee catchment in the Cairngorms, Scotland were chosen to determine the geomorphic validity of the proposed typology, and assess whether channel types support a distinct macroinvertebrate community. Agglomerative Hierarchical Cluster Analysis failed to clearly identify eleven channel types based on catchment controls or on physical habitat characteristics. Four clusters were observed based on catchment drivers and six on physical habitat. Boundaries appear to be fuzzy, relating to a collective number of interacting environmental variables, geological discontinuities, and the geographic complexity of a river system. Multivariate ordinations and Analysis of Similarity indicated that macroinvertebrate communities only differed significantly between bedrock and step-pool reaches. A redundancy analysis showed differences in macroinvertebrate abundances among channel types were related to hydraulic, catchment drivers, physical habitat and physico-chemical variables. The results of the study have important implications for the use of geomorphic typologies in predicting aquatic biota.

<p> This study investigated the effects of riparian vegetation on sediment transport rates and flow dynamics in the South Platte River just downstream of Fort Lupton, Colorado. FaSTMECH, a two-dimensional coupled fluvial and hydraulic model, was used to compute flow characteristics (velocity and depth) in addition to sediment mobility characteristics (shear stress and sediment flux) for four discharge levels ranging from 5% of bankfull flow to bankfull flow (Qbf). Estimates of a dimensionless drag coefficient (Cd) representative of the middle-aged bushy willows found on the river banks at the study site were used to create a spatially variable roughness in the model throughout the river reach. Model results show that during average annual flood events, vegetation on the river banks causes increased drag forces on the flow, leading to an increased proportion of flow being diverted into the main channel and resulting in higher velocities. The spatial distribution of shear stresses collapse under these conditions with an order of magnitude decreases over river banks and significant increases throughout the main channel. Sediment fluxes in the reach increase by nearly an order of magnitude with the presence of bank vegetation, however, the greatest differences occur during Qbf when the highest fraction of the sediment is mobile. Further analysis of vegetation effects was conducted by performing a sensitivity analysis by altering the representative non-dimensional vegetation drag coefficient by as much as +/- 400%. These alterations represent differences in vegetation density, height, orientation, leafy/leafless structure, age, rigidity, and vegetation type. Although there is a relationship between sediment fluxes and changes in Cd, there only exists a 14% increase in transport at Qbf between the two exterior limits of Cd.</p>

Orientador: José Marques Junior / Coorientador: Livia Arantes Camargo / Banca: Antonio Carlos de Azevedo / Banca: Marcílio Vieira Martins Filho / Resumo: A agricultura atual necessita de metodologias para determinação de atributos do solo que sejam menos agressivas ao meio ambiente. A espectroscopia de fluorescência de raios X (EFRX) tem sido uma técnica promissora no fornecimento simultâneo de análise quantitativa e elementar da composição do solo. Sobre este aspecto, o presente trabalho foi realizado com o objetivo de caracterizar as classes, geologia e geomorfologia dos solos do Planalto Ocidental Paulista, utilizando EFRX e a técnica multivariada. Foram coletadas 262 amostras de solo na profundidade de 0,0 - 0,2 m, para caracterização química, mineralógica e espectral. As intensidades dos picos dos elementos Si, Al, Fe e Ti dos espectros obtidos pela EFRX relacionaram-se com as classes de solos, formações geológicas e graus de dissecação da paisagem presentes no Planalto Ocidental Paulista. A análise de componentes principais, utilizando os dados obtidos pela EFRX, aliados aos atributos argila, areia, teores de Fe extraídos por ditionito-citrato-bicarbonato de sódio e por oxalato ácido de amônio, permitiu a caracterização das classes de solos, formações geológicas e graus de dissecação da paisagem presentes na região de estudo. A intensidade do pico do Fe apresentou o segundo maior autovetor na caracterização do eixo da componente principal 1, e as intensidade dos picos do Ti e Si apresentaram, respectivamente, o quarto e o quinto maiores autovetores neste eixo. / Abstract:Current agriculture needs methodologies to determine soil attributes that are less aggressive to the environment. X-ray fluorescence spectroscopy (EFRX) has been a promising technique in providing simultaneous quantitative and elemental analysis of soil composition. The objective of this work was to characterize the classes, geology and geomorphology of the soils of the Western Plateau, using EFRX and the multivariate technique. A total of 262 soil samples were collected at 0.0 - 0.2 m depth for chemical, mineralogical and spectral characterization. The intensities of the peaks of the Si, Al, Fe and Ti elements of the spectra obtained by the EFRX were related to the classes of soils, geological formations and degrees of dissection of the landscape present in the Western Plateau. The main components analysis, using the data obtained by EFRX, allied to the attributes clay, sand, Fe content extracted by dithionite-citrate-bicarbonate sodium and ammonium oxalate, allowed the characterization of the soil classes, geological formations and degrees of dissection of the landscape present in the study region. The intensity of the peak of Fe presented the second largest eigenvector in the characterization of the axis of the main component 1, and the intensity of the peaks of Ti and Si presented, respectively, the fourth and fifth largest eigenvectors on this axis. / Mestre

<p> The midcontinent of the U.S. is heavily karstified containing well developed subsurface drainage systems that are covered by beds of coarse-grained, poorly sorted fluvial sediments, resembling those found in upland surface streams. The movement of coarse sediment as bed load within karst streams has been considered negligible in the past as it was assumed that all karst is developed through dissolution rather than mechanical abrasion. The frequency and magnitude of sediment transporting events in karst streams has implications for models of fluviokarst landscape development and the stability of aquatic ecosystems. </p><p> Within Tumbling Creek Cave (TCC) in the Ozark Plateau of south-central Missouri, and Bear Cave Hollow (BCH), one of TCC&#129;es surface drainage streams, bed load entrainment and transport dynamics of coarse-grained (16-180 mm), mainly siliciclastic material, was evaluated using hydrological measurements and 670 painted tracer particles. Tracers are used in this research for the first time in a karst stream. Tracers are well suited for studying the stochastic and spatially variable nature of bed load transport because they reflect the movement of individual particles of known characteristics, and they are also inexpensive and simple to employ.</p><p> Median surficial sediment grain size in the study reaches ranged from 39 to 71 mm in TCC, and from 24 to 37 mm in BCH with bed and/or water slopes ranging from 0.006 to 0.077 in TCC and from 0.002 to 0.009 in BCH. TCC is classified as a pool-riffle channel morphology type and BCH is classified as a plane-bed channel. Preliminary data from surveys of the longitudinal (downstream) movement of tracers over a 10-month period indicate that minor amounts (0-13.2%) of coarse bed material in TCC are mobilized by relatively low flows (5-28% of bankfull) that recur somewhat frequently (less than 3.1 years). BCH transports a higher percentage of material (0-59.1%) during similar flows (2-29% of bankfull) and frequencies (less than 3.59 years). Bed load transport was observed to be in a state of partial transport for any one grain size class in TCC during the study, while the complete mobilization of tracer size classes was observed in BCH at the highest observed flow, indicating &ldquo;phase 2&rdquo; transport and the break-up of the armor layer. The differences are attributed to the wider observed range of grain sizes covering the bed in TCC compared to BCH.</p><p> The use of the Shields (1936) criteria tends to over predict the critical shear stress required for entrainment of the largest mobilized grain size of individual tracers, while the empirical equation of Bagnold (1980) performs much better. Thus, the Shields equation may be better suited as a gage for complete mobilization of a grain size class across a reach, while the Bagnold (1980) equation may be better suited for estimating entrainment of grains from patches of the bed.</p><p>