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The geomorphological behaviour of steep jointed rock slopes has been studied using distinct element method computer models. In order to model steep slopes effectively, methodologies need to be combined from the studies of environmental modellers, geomorphologists and engineers. The distinct element method is ideal for the study of the development of jointed rock masses as the discontinuum approach can model the progressive failure of rock blocks along discontinuities. Initial, theoretical modelling identified the limiting boundary conditions between the multiple block failure mechanisms of toppling, sliding and toppling-and-sliding, based upon the discontinuity geometry for a theoretically modelled limestone rock mass. It is demonstrated that joint dip, friction angle and spacing exert the greatest control upon rock mass failure mechanisms. Two field locations, the Colorado Plateau and the Isle of Purbeck, have been chosen to provide a link between theoretical modelling and classic rock mass landforms which are controlled by variation in discontinuity geometry. In the Portland Limestone of the Isle of Purbeck, it is the joint geometry variation which influences development. Bedding steepens and average block size decreases in the coastal rock cliffs from east to west. Comparison between the model outputs highlighted that there is an increase in the rate of simulated cliff retreat from Winspit in the east to Durdle Door in the west. The Colorado Plateau rock cliffs form large, embayed plan-form escarpments and detached monoliths. It is the variation of joint set spacing in the cap-rock of cuesta-form composite scarps that controls development. Model results suggest there is a continuum of rock mass landforms, with buttes becoming detached at plan-form necks in the escarpment as determined by the joint geometry. The results show excellent similarity with the landforms observed in the field. This thesis introduces a research tool that can provide an understanding of slope behaviour.

<p> Northwestern Indiana has land surfaces and soils that are around 15,000 years old, resulting from sediments deposited from the Wisconsinan Glaciation during the late Pleistocene period. These geologically young soils exhibit depletion of base cations and low pH's (near 4.0) which are chemically similar to much older and more intensely weathered soils. We hypothesize that FeS2 (iron pyrite) within the shale fragments of the glacial deposits was oxidized upon exposure of oxygen near the earth's surface and resulted in naturally occurring acid sulfate weathering. To test our hypothesis, we isolated the area with ArcGIS, collected clast samples from gravel pits, utilized historic soils databases, and analyzed samples with X-ray diffraction to determine if associated properties and soil minerals would support acid sulfate weathering as the cause of the current soil chemical properties. Soil samples and glacial outwash cobble-sized clasts were collected and X-ray diffraction was used to determine the presence of pyrite or of pyrite weathering products jarosite and gypsum. Existing soil databases and lab data were examined to obtain further details of the occurrence of the potential acid sulfate weathering. A review of the geologic literature was also conducted to put the acid sulfate weathering processes into a landscape perspective and geologic context. The clast samples and some soil samples indicated the presence of jarosite and gypsum which are commonly associated with acid sulfate weathering. This research also found that ultic soil properties and low pH soils were associated with sandy glacial outwash and this information was displayed spatially. The sandy outwash has a lower CEC and lower buffering capacity when compared to nearby higher clayey glacial till. There was inferential evidence of acid sulfate weathering in calcareous glacial which is illustrated by iron oxide pseudomorphs. The lack of initial pyritic shale combined with the neutralizing potential for the calcareous till prevented these soils from developing ultic properties and low pH's. Additionally, this research assessed the potential for naturally occurring arsenic in the soils. Elevated arsenic levels were found in soils that occurred in the lowest part of the landscape. Understanding the process of naturally occurring acid sulfate weathering and associated elevated arsenic within this landscape will provide more information on use and management of these areas.</p>

Biodiversity is widely thought to enhance resilience in ecosystems by providing ‘insurance’ which buffers the effects of disturbances on ecosystem functioning. However, little empirical evidence is available to support this assumption. Biodiversity and resilience are both complex, multifaceted concepts, and the mechanisms underlying the relationship between them are far from clear. However, understanding this relationship is important because resilience underpins the ability of ecosystems to continue to provide essential ‘goods and services’ in the face of increasing human pressure and an uncertain future. In this thesis I address two properties thought to be important in determining the resilience of ecological assemblages, namely functional redundancy (similarities in ecological functioning between species) and response disparity (differences in species’ responses to disturbance). Both are related to biodiversity, being determined by the degree of similarity or difference among the species in an assemblage. After developing a conceptual framework for understanding the relationship between biodiversity and resilience, I provide a critical evaluation of existing methods for measuring redundancy and response disparity, and develop measures of these two properties that better reflect the continuous, multidimensional nature of differences between species. A key element of my approach is the use of different sets of functional traits to describe individual species’ contributions to different ecological functions. This is valuable because it explicitly recognises that species have multiple functional roles, an obvious fact that is often overlooked and a source of much misunderstanding about redundancy and disparity. I then use these methods to measure redundancy and response disparity in riparian plant assemblages from different–sized streams and under different land management regimes, providing some of the first empirical evidence for these aspects of resilience in real, species–rich assemblages. In particular, I provide the first empirical confirmation of two hypotheses about the roles of redundancy and response disparity in the resilience of plant assemblages, namely (1) that minor species in the tail of the abundance distribution provide redundancy for functions performed by the dominant species, and (2) that groups of species that provide redundancy for each others’ functioning differ in their response traits, thus providing response disparity (Walker et al., 1999, Ecosyst. 2:95–113). This thesis also contributes to our understanding of the effects of land management practices on the resilience of riparian systems, something which is poorly understood but of critical interest to conservation and land managers. Ecosystem–based approaches to management place emphasis on maintaining desirable functioning in ecosystems. However, often it is very difficult for managers to assess whether this is being achieved (the ‘manager’s dilemma’). The resilience measures developed here are valuable because they provide a measure of the long–term sustainability of the various functions performed by species assemblages. Both redundancy and response disparity were present in the riparian assemblages studied. Species in the tail of the abundance distribution were particularly important providers of redundancy. These tail species, often inadequately sampled or left out of functional diversity analyses, provided 53–100% (mean 82%) of the redundancy for the functioning of the more abundant species. For most functions performed by a particular species, between 5 and 20 other species were potentially able to perform that function in a similar way, thus providing redundancy. However, all assemblages also had species (1–40%) with low redundancy for one or more functions, suggesting that certain particular aspects of functioning may lack resilience, even in assemblages with high overall resilience. iii iv Species providing redundancy for a particular function were seldom very similar in their contributions to other functions. Functional ‘analogues’ (species identical or very similar in all functions) were relatively uncommon (42–71% of species across different management regimes and stream sizes had no analogues for the small number of functions studied, and this number was shown to increase with the number of functions considered). Redundancy was usually provided by a large number of partially similar species rather than by a few identical species. Redundancy and disparity were therefore simultaneously present in each assemblage, because each species contributed both to redundancy (for some functions) and disparity (for others). This suggests that the commonly held view of redundancy provided by ‘identical copies’ is far too one–dimensional, and successfully lays to rest the debates about its existence and the concerns that promoting redundancy will somehow be detrimental to diversity. I therefore propose that it is time to put redundancy back on the research agenda as an important aspect of functional organisation which leads to resilience. The highly distributed nature of redundancy, involving many partially similar species, also has important implications for our understanding of change in ecosystems. It means that functional compensation will seldom be a simple matter of species replacing each other as ‘drop–in replacements’. Rather, compensatory changes in species composition or abundance will have knock–on effects that affect many other species and lead to many ‘readjustments’ in species’ functioning, responses to disturbance, interactions and abundances. The results of this study have shown that the way changes in species composition or diversity affect resilience are often idiosyncratic, depending on which particular species are involved. It is therefore not appropriate to try to model the impacts of changes in biodiversity on ecosystem resilience deterministically. However, ecosystem managers require information about resilience to implement ecosystem– based management. This information needs to be simple enough to be useful, but flexible anough to account for the fact that idiosyncratic species effects frequently make considering the details of a particular situation unavoidable. In this thesis I outline an approach that involves the judicious use of generalisations together with a flexible means of combining compositional, functional and resilience perspectives on species assemblages, allowing exploration of the relationship between diversity and resilience in a particular system. This approach is more flexible, and allows a wider range of questions to be addressed, than commonly used approaches using indices of diversity or ecosystem health. Rather than summarising a large amount of detailed information in the form of an index, my approach retains the detail but concentrates on making it easier to interpret. This provides a flexible way of using the detail to answer specific management questions, thus increasing its usefulness to managers. The finding of a generally positive relationship between redundancy and species richness in this study is a useful generalisation for managers trying to implement an ecosystem–based approach to conservation and land management. It suggests that, in general, maintaining species–rich assemblages will tend to maintain redundancy. However, this relationship varied with growth form (woody vs herbaceous), stream order (small streams vs main river) and the function being considered. The amount of redundancy and response disparity associated with each species for each function were also highly variable, pointing to the need to use generalisations with care. Comparison of assemblages under the different land management regimes (Kruger National Park, privately–owned reserves and communal rangeland) suggested that management practices in river catchments do affect the resilience of riparian vegetation, but not always in the manner expected. Management practices in the conservation areas did not necessarily promote higher diversity or resilience than management practices in the communal area, which may come as a surprise to many conservationists. While assemblages from the main river were less resilient in the communal area than in the reserves, assemblages from the small streams were more diverse and resilient than those in the reserves, even though communal rangeland areas are not managed specifically for biodiversity conservation. Far from being ‘degraded’ as is usually assumed, small streams within these communally managed areas are in fact valuable as biodiversity hotspots, and this should be reflected in conservation planning and ecosystem service assessments in the region.

A região central da Amazônia encontra-se no interior da maior bacia de drenagem do planeta. Nas bacias dos rios Uatumã e Urubu, localizadas nesta região, o relevo apresenta drenagens com longos trechos retilíneos, inflexões abruptas, mudanças de curso evidenciadas por meandros abandonados, assimetrias de bacias, além de variações suavesdos padrões de dissecção e rugosidade, que são feições morfológicas sugestivas da ação de atividade tectônica moderna no seu modelado. Geologicamente, a área de estudo é coberta por sedimentos terciários seccionados por falhas normais e juntas. De modo a se identificar a influência de estruturas geológicas em superfície e subsuperfície sobre o relevo, aplicou-se no modelo digital de elevação da SRTM técnicas geomorfométricas que foram separadas em dois grupos: 1) assimetria de bacia, isobase e sinuosidade de canais usadas para revelar a gênesede formas do relevo, e 2) rugosidade (geometria fractal), densidade da rede drenagem e semivariograma utilizadas para verificar a distribuição espacial da rugosidade, dissecção e elevação. Além disso, as tendências direcionais do relevo também foram examinadas pela anisotropia da elevação (semivariograma), rugosidade (geometria fractal de autoafinidade) e densidade da rede de drenagem (geometria fractal de autosimilaridade). Os resultados do primeiro grupo permitiram delinear 9 domínios geomorfológicos que mostram rumos preferenciais de migração e, possivelmente, relação com basculamento de blocos. A comparação dos limites desses domínios com dadosgeológicos e geofísicos sugere que esses limites provavelmente se relacionam com falhas em subsuperfície, as quais teriam controlado a geração de falhas mais novas e o modelado do relevo da região. Tal fato é corroborado pela correspondência entre falhas em subsuperfície e superfície com os limites e as formas dos domínios, a mudança de sinuosidade de rios ao cruzar os limites e a relação da região com alta concentração de atividade sísmica ao longo de um dos limites. Outros dados geomorfológicos também apontam o controle estrutural do relevo. É o caso da relaçãoentre a orientação e aproximação das linhas no mapa de isobase com as falhas normais de alto ângulo mapeadas nas várzeas dos principais rios. Para o grupo 2, os resultados mostram a coincidência espacial entre domínios, definidos pela análise da rugosidade (dimensão fractal) e da elevação (semivariograma), e estruturas geológicas em subsuperfície. Este é o caso da área de Silves, onde a topografia colinosa apresenta diversos rios anelares e radiais, denotando condicionamento por falhas e dobras mapeadas por levantamentos sísmicos. Outro exemplo de tal influência é a associação de altos magnéticos com baixos padrões de dissecção mapeados pela análise da densidade da rede de drenagem. Além da distribuição espacial, as tendências direcionais dessas variáveis geomorfométricas foram analisadas e comparadas entre si e também com informações geológicas. Os resultados indicam que as direções predominantes para o maior eixo da anisotropia de elevação são NNE-SSW e NE-SW para as regiões de interflúvio, além de NW-SE para as planícies aluvionares. A direção de maior aglomeração da rede de drenagem, mostrada por sua anisotropia, coincide com atual campo de esforços da região investigada, exceto nas planícies de inundação. A direção com maior rugosidade, NNE-SSW, está presente na região de Presidente Figueiredo e é coincidente com a direção de cachoeiras e corredeiras. / The central region of the Amazon is located within the largest drainage basin in the world. In the basins of the Uatumã and Urubu rivers in this region, the landscape have drainages with long straight stretches, abrupt inflections, course changes evidenced by abandoned meanders, and basin asymmetries, and smooth variations of the landscape dissection and roughness patterns, which are morphological features suggestive of the action of modern tectonic activity. Geologically, the study area is covered by Tertiary sediments that are cut by normal faults and joints. To identify the influence of surface and subsurface geological structures on relief, we applied geomorphometric techniques on the digital elevation model from SRTM. These techniques have been separated into two groups: 1) basin asymmetry, isobase and river sinuosity were used for reveal the genesis of relief forms, and 2) fractal geometry, drainage density and semivariogram were used to verify the spatial distribution of the roughness, dissection and elevation. Furthermore, the trend-surfaces were also observed by elevation (semivariograma), roughness (self-affine fractal geometry) and drainage density anisotropy (self-similarity fractal geometry). The results of the first group permited the delineation of nine geomorphological domains that exhibit preferential migration paths and a potential relationship to block tilting. The comparison of the boundaries of these domains with geological and geophysical data suggests that these boundaries are likely related to subsurface faults that would have controlled the generation of younger faults and the relief modelling of the region. This interpretation is confirmed by the correspondence between subsurface and surface faults and the boundaries and shapes of the domains, the change in the sinuosity of rivers when crossing boundaries, and the effects of a high concentration of seismic activity along one of the limits on the region. Other geomorphological data also indicate structural control of the relief. There is a relationship between the orientation and approximation of the isobase map lines and the high-angle normal faults mapped in the floodplains of the main rivers. For the second group of variables, the results reveal the spatial coincidence between domains, defined by the analysis of roughness (fractal dimension) and elevation (semivariogram), and subsurface geological structures. This is the case in the area of Silves, where the undulating relief exhibits drainage with annular and radial patterns, coinciding with faults and folds previously mapped by seismic surveys. Another example of such influence is the combination of high magnetic with low dissection pattern mapped by drainage density. In addition to the spatial distribution, trends of these geomorphometric variables were compared among themselves and also with geological information. The results indicate that the predominant directions of the major anisotropy axis is NNE-SSW and NE-SW for the interfluve regions, and NW-SE to the alluvial plains. The direction of higher clustering of the drainage network, shown by its anisotropy, coincides with the modern stress field in the region investigated, except in flood plains. The direction with higher roughness, NNE-SSW, is present in the region of Presidente Figueiredo and is coincident with the direction of waterfalls and rapids.