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Interaction between rigid and flexible track-grouser systems with a clay soil is examined in order to obtain a better understanding of the manner in which energy is transferred and dissipated in the bearing soil substrate. Analytical framework is developed for the establishment of the kind of mechanisms involved in this interaction with a view to obtaining a rational prediction of track-soil performance. / The method of visioplasticity is used to determine the specific participants contributing to the expenditure of energy at different soil levels beneath a simple representative multiple grouser element. Subsoil reponse behaviour and dissipated energy components are investigated for different grouser shapes, spacings, displacements, and flexibility boundary conditions. / A predictive model is established for the off-road track performance prediction based on the principle of energy conservation for the entire track/grouser-soil system. This energetic model provides successful predictions which are in good agreement with the experimentally measured performance of a full track model at various degrees of slip.

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Soil water erosion is recognized as the principal mechanisms behind soil organic carbon (SOC) losses from soils, a soil constituent essential for ecosystem functions. SOC erosion can thus be far-reaching, affecting the future human welfare and the sustainability of ecosystems. Little research has yet been done to investigate the main mechanisms involved in the lateral translocation of SOC on the landscape. Understanding the effects of the different water erosion mechanisms, which control SOC losses (SOCL) at the hillslope level, creates scope for further scientific studies. Empirical data from 357 plots, with a range in slope length from 1 (n=117) to 22.1m (n=240) were analysed to estimate the global variations of particulate organic carbon content (POCC), POC losses (POCL) and sediment POC enrichment ratio (ER). The global average POCL rate was calculated to be 12.1 g C m-2 y-1. Tropical clayey soil environments revealed the highest POCL (POCL=18.0 g C m-2 y-1), followed by semi-arid sandy (POCL=16.2 g C m-2 y-1) and temperate clayey soil environments (POCL=2.9 g C m-2 y-1). The global net amount of SOC displaced from its original bulk soil on an annual basis was calculated to be 0.59±0.09 Gt C, making up an approximated 6.5% of the net annual fossil fuel induced C emissions (9 Gt C). POCL data for different spatial scales revealed that up to 83% of the eroded POC re-deposits near its origin in hillslopes, and is not exported out of the catchment. The low organic carbon sediment ER obtained from the data of clayey soils (ER of 1.1) suggests that most of the eroded POC remains protected within soil aggregates. Consequently, erosion-induced carbon dioxide (CO2) emissions in tropical areas with clayey soils are likely to be limited (less than 10%), as the process of POC re-burial in hillslopes is likely to decrease the rate of organic matter (OM) decomposition and thus serve as a potential carbon sink. Water erosion in sandy and silty soils revealed organic carbon sediment ER as high as 3.0 and 5.0, suggesting that in these soils the eroded POC is not re-buried, but is made vulnerable to micro-decomposers, thus adding to the atmospheric CO2 influx. The results obtained in the review study only reaffirm that large variations of POCL are evident across the different pedo-climatic regions of the world, making it a scientific imperative to conduct further studies investigating the link between SOC erosion by water and the global carbon cycle. A field study was designed to quantify the POC exported in the eroded sediments from 1x1m2 and 2x5m2 erosion plots, installed at different hillslope aspects, and to further identify the main erosion mechanisms involved in SOC erosion and the pertaining factors of control. The erosion plots were installed on five topographic positions under different soil types, varying vegetation cover, and geology in the foothills of the Drakensberg mountain range of South Africa. Soil loss (SL), sediment concentration (SC), runoff water (R) and POCL data were obtained for every rainfall event from November 2010 up to February 2013. Scale ratios were calculated to determine which erosion mechanism, rain-impacted flow versus raindrop erosion, dominates R, SL and POCL. Averaged out across the 32 rainfall events, there were no significant differences in R and POCL between the two plot sizes but SL were markedly higher on the 5m compared to the 1m erosion plots (174.5 vs 27g m-1). This demonstrates that the sheet erosion mechanism has a greater efficiency on longer as opposed to shorter slopes. Rain-impacted flow was least effective where soils displayed high vegetation coverage (P < 0.05) and most efficient on steep slopes with a high prevalence of soil surface crusting. By investigating the role of scale in erosion, it was possible to single out the controlling in situ (soil surface related conditions) and ex situ (rainfall characteristics) involved in the export of SOC from soils. This information will in future contribute toward generating SOC specific models and thus further inform erosion mitigation. / M. Sc. University of KwaZulu-Natal, Durban 2013.

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Two BSC based indicators for rangeland condition assessment are species composition and cover. While there is strong agreement that BSC composition is a good indicator, there is less agreement that BSC cover alone is a good indicator. Although BSC have been included in previous remotely- sensed studies, their spectral characteristics, and hence their contributions to remotely-sensed spectral signatures, are not well known. / Data collection methods were refined for suitable method selection, stratification and site characterization, and morphological/functional group classification. Cover data of BSC were collected using a 100m line-intercept method on the stratified land units and statistical analyses were based on the cover variance analyses. Spectra of BSC groups were collected and characterized for different remote sensing indices. Five grazing gradient models based on collected spectra were developed for the evaluation of BSC effect on remotely-sensed data. Both existing and newly developed remote sensing indices were examined for BSC detection. / Sampling for cover of BSC in the field showed that there is indeed a detectable change with distance from water, suggesting that BSC cover can be used as an indicator of rangeland condition, provided that appropriate stratification of the study sites is carried out prior to sampling, and spectral differences in morphological and functional groups are taken into account. / Spectral analysis of BSC components showed that different classes of organisms in the crusts have different spectral characteristics, an din particular, that the (commonly-used) perpendicular vegetation index (PD54) is not suitable for detecting BSC. On the other hand, ground-level spectral modelling showed that the Normalized Difference Vegetation Index (NDVI) and Soil Stability Index (SSI) did show a distinguishable contribution from BSC. / A procedure for detecting cover of BSC was developed for image taken during the period after an effective rain, in contrast to the normal practice of selecting images of dry surfaces for interpretation. / The most suitable interval appears to be 2-4 days after rain in late autumn, winter and early spring. Of the existing indices, the SSI is the best for estimating cover of BSC from Landsat images. However, eight new indices, specifically designed for detection of BSC were developed during the course of this work. The best results were obtained for indices using the middle-infrared bands. / These results are promising for application to rangeland monitoring and suggest that BSC cover is an important indicator of rangeland condition if appropriate stratification, classification and data-collection methods are used. The effects of BSC cover on a remotely-sensed method are considerable, and thus they can not be neglected during image interpretation. There are different phenological patterns for BSC, annual and perennial elements, thus there is the possibility for the selection of imagery based on each phenological stage to detect these elements. Application of certain indices such as the PD54 may create mis-estimation of land covers. Although some of the existing and newly developed indices had significant results for BSC cover estimation, there is a requirement for a standalone remotely-sensed method to conclude the best index. / This thesis considers various aspects of the use of ground-based methods and remote sensing of Biological Soil Crusts (BSC). They are mostly distributed in winter rainfall dominated areas such as those at Middleback Field Centre (MFC) in South Australia. They can be used potentially as an indicator of rangeland condition by estimating grazing pressure (trampling). / Thesis (PhDEnvironmentalManagement)--University of South Australia, 2007.

Two BSC based indicators for rangeland condition assessment are species composition and cover. While there is strong agreement that BSC composition is a good indicator, there is less agreement that BSC cover alone is a good indicator. Although BSC have been included in previous remotely- sensed studies, their spectral characteristics, and hence their contributions to remotely-sensed spectral signatures, are not well known. / Data collection methods were refined for suitable method selection, stratification and site characterization, and morphological/functional group classification. Cover data of BSC were collected using a 100m line-intercept method on the stratified land units and statistical analyses were based on the cover variance analyses. Spectra of BSC groups were collected and characterized for different remote sensing indices. Five grazing gradient models based on collected spectra were developed for the evaluation of BSC effect on remotely-sensed data. Both existing and newly developed remote sensing indices were examined for BSC detection. / Sampling for cover of BSC in the field showed that there is indeed a detectable change with distance from water, suggesting that BSC cover can be used as an indicator of rangeland condition, provided that appropriate stratification of the study sites is carried out prior to sampling, and spectral differences in morphological and functional groups are taken into account. / Spectral analysis of BSC components showed that different classes of organisms in the crusts have different spectral characteristics, an din particular, that the (commonly-used) perpendicular vegetation index (PD54) is not suitable for detecting BSC. On the other hand, ground-level spectral modelling showed that the Normalized Difference Vegetation Index (NDVI) and Soil Stability Index (SSI) did show a distinguishable contribution from BSC. / A procedure for detecting cover of BSC was developed for image taken during the period after an effective rain, in contrast to the normal practice of selecting images of dry surfaces for interpretation. / The most suitable interval appears to be 2-4 days after rain in late autumn, winter and early spring. Of the existing indices, the SSI is the best for estimating cover of BSC from Landsat images. However, eight new indices, specifically designed for detection of BSC were developed during the course of this work. The best results were obtained for indices using the middle-infrared bands. / These results are promising for application to rangeland monitoring and suggest that BSC cover is an important indicator of rangeland condition if appropriate stratification, classification and data-collection methods are used. The effects of BSC cover on a remotely-sensed method are considerable, and thus they can not be neglected during image interpretation. There are different phenological patterns for BSC, annual and perennial elements, thus there is the possibility for the selection of imagery based on each phenological stage to detect these elements. Application of certain indices such as the PD54 may create mis-estimation of land covers. Although some of the existing and newly developed indices had significant results for BSC cover estimation, there is a requirement for a standalone remotely-sensed method to conclude the best index. / This thesis considers various aspects of the use of ground-based methods and remote sensing of Biological Soil Crusts (BSC). They are mostly distributed in winter rainfall dominated areas such as those at Middleback Field Centre (MFC) in South Australia. They can be used potentially as an indicator of rangeland condition by estimating grazing pressure (trampling). / Thesis (PhDEnvironmentalManagement)--University of South Australia, 2007.