In November 2016, 38 sinkholes formed due to subsurface erosion above undermined ground on Donkerhoek farm near Sasolburg. The fact that the sinkholes formed more than 24 years after mining in the area ceased, emphasised the need for a method to predict the likelihood of sinkhole formation due to subsurface erosion. This is especially relevant for mining houses required to quantify their mine closure risks. The purpose of this study was to investigate the mechanisms and soil properties involved in the formation of the 38 sinkholes on Donkerhoek farm through a fieldwork and laboratory testing programme and develop a method to predict the likelihood of sinkhole formation. Three areas were selected for test pit excavation: an area with large sinkholes, one with small sinkholes and a third with no sinkholes but with a history of subsidence crack formation. The same mechanism of sinkhole formation was observed in both the large and small sinkhole areas: at the soil-rock interface, soil was being eroded into a subsidence crack in the rock, resulting in an upwards migrating cavity and the eventual formation of a sinkhole on surface when the cover over the cavity collapsed. This was the first time that this mechanism was observed in the Sasolburg area, having previously only been identified in the Secunda area. The laboratory tests, carried out on samples obtained during the fieldwork, included foundation indicator, dispersivity, XRF and XRD, soil water retention curves, consolidated undrained triaxial and permeability tests. By comparison of the results from the different study areas, it was concluded that the larger sinkholes form in areas with highly dispersive soils, higher clay content, higher swell potential and a higher capacity to retain suctions when wetted. The following soil properties and factors were identified as the main contributors to sinkhole formation: • The strength of the lid, which is highly influenced by the unsaturated behaviour of the lid material. The lid strength determines the sinkhole diameter; • The erodibility of the material which is influenced by dispersivity and the material obtaining a crumb structure due to desiccation; • The activity of the soil, which influences the volume changes during drying and thereby the width and depth of desiccation cracks; and • The thickness of the soil layer overlying the rockhead. With the critical factors identified, the Van der Merwe method to predict sinkhole size was used as basis to develop an index method to predict the likelihood of sinkhole formation due to subsurface erosion above undermined ground. The method considers combinations of the following factor groups to express a high or low likelihood of the formation of large or small sinkholes in a particular area: • The strength of the lid material, mainly influenced by the unsaturated behaviour of the soil; • The capacity for cavity formation (CCF), which combines the dispersivity, erodibility and activity of the soil; and • The influence of the thickness of the soil layer overlying the rock, evaluated by calculating the ratio between crack width in the rock and the soil layer thickness. / Dissertation (MEng)--University of Pretoria, 2019. / Civil Engineering / MEng (Geotechnical Engineering) / Unrestricted

Microorganisms exist ubiquitously on Earth, yet their functions and ecological roles remain elusive. Investigating these microbes is accomplished by using culture-dependent and culture-independent methodologies. This study employs both methodologies to characterize: 1) the genomic potential of the novel deep-subsurface bacterial isolate Thermanaerosceptrum fracticalcis strain DRI-13T by combining next-generation and nanopore sequencing technologies and 2) the microbiome of the artificial marine environment for the Hawaiian Bobtail Squid in aquaculture using next-generation sequencing of 16S rRNA gene. Microbial ecology of the deep-subsurface remains understudied in terms of microbial diversity and function. The genomic information of DRI-13T revealed a potential for syntrophic relationships, diverse metabolic potential including prophages/antiviral defenses, and novel methylation motifs. Artificial marine environments housing marine the Hawaiian Bobtail Squid (Euprymna scolopes) contain microorganisms that can directly influence animal and aquaculture health. No studies presently show if bacterial communities of the tank environment correlate with the health and productivity of E. scolopes. This study sought to address this by sampling from a year of unproductive aquaculture yield and comparing the bacterial communities from productive cohorts. Bacterial communities from unproductive samples show less bacterial diversity and abundance coupled with shifts in bacterial composition. Nitrate and pH levels between the tanks were found to be strong influences on determining the bacterial populations of productive and unproductive cohorts.

La recherche de trace de vie, passée ou présente, sur Mars est l’objectif principal de la mission martienne européenne ExoMars (ESA-Roscosmos), dont le lancement est prévu pour l’été 2020. Cette mission déposera à la surface de Mars un Rover équipé d'instruments dédiés notamment à l’étude du sous-sol de la planète dont une foreuse collectera des échantillons. Le travail de thèse présenté dans ce manuscrit porte sur la préparation du retour scientifique de l’expérience du radar WISDOM (Water Ice and Subsurface Deposits Observation on Mars) embarqué à bord du Rover d’ExoMars 2020 et dont l’objectif principal est la caractérisation, avant forage, du sous-sol proche de Mars.Les données recueillies par WISDOM permettront d’identifier les formations géologiques du sous-sol et de comprendre les processus qui en sont à l’origine. Elles guideront également les opérations de prélèvement d'échantillons en profondeur. L'objectif de cette thèse était de préparer les outils de traitements et d'interprétation de ces données. Les résultats obtenus doivent permettre d'exploiter au mieux les possibilités de l'instrument et d’atteindre les ambitieux objectifs technologiques (en termes notamment de résolution et de sensibilité) et scientifiques fixés. Plus précisément, il s’agissait de mettre en place des outils pour aboutir à une description des premiers mètres du sous-sol via l’interprétation des radargrammes de WISDOM en termes d’épaisseur de couche(s), de rugosité des interfaces, de distribution en taille d’éventuelles roches enfouies, d’orientation des strates et de constantes géo-électriques pour les unités géologiques détectées.Ce travail de thèse a permis la mise en place d’une chaîne de traitement de données ainsi que d’outils d’interprétation (traitement automatique et modélisation du radar).L’approche a été d’aborder le problème à la fois du point de vue théorique et du point de vue pratique. En conséquence, ce travail s’est appuyé sur deux aspects indissociables que sont, d’une part, la modélisation (analytique et numérique) du fonctionnement de l’instrument dans son environnement et, d’autre part, le traitement des données simulées et/ou expérimentales obtenues en milieu contrôlé ou lors de campagnes de mesures organisées dans le cadre de cette thèse. / The main objective of European ExoMars (ESA-Roscosmos) mission is to search for signs of past or present life on Mars. The mission, to be launched in summer 2020, will deliver a rover on the surface of Mars. This rover accommodates instruments designed to investigate the close subsurface and, in particular, a drill that will collect samples at depth ranging from 0.5 m to 2 m. This thesis manuscript relates the preparation of the scientific return of the WISDOM (Water Ice and Subsurface Deposits Observation on Mars) radar experiment whose main objective is to characterize, before drilling, the shallow subsurface of Mars.Data obtained by WISDOM will shed the light on geological structures in the subsurface and therefore help trace back the history of the investigated Martian sites. Furthermore, they will help to identify the most promising locations to collect samples without jeopardizing the drill. The objective of this thesis was to efficiently pave the way to data interpretation and appraise WISDOM’s potentiality.In order to reach the ambitious scientific and technologic objectives (especially in terms of resolution and sensitivity) of WISDOM, we have developed tools that rely on a deep understanding of the instrument. The ultimate goal of these tools is to provide a reliable representation of the shallow subsurface and quantitative interpretation in terms of thickness and orientation of underground layers, roughness at interfaces, distribution of buried rocks and geoelectrical constant for each geological unit detected.This thesis manuscript describes the signal processing chain and tools developed in order to prepare WISDOM’s scientific return. When possible, approaches based on automatic detection were preferred. This work relies both on theoretical and practical investigations, including an accurate (analytical and numerical) modeling of the instrument operations and test on experimental data acquired during field campaigns on potential Martian analogs.

No description available.

<p> Systematic soil sampling and analyses provided DDT, DDE and DDD, organic and mineral matter concentrations, as well as various soil physical and hydraulic properties from three study sites at Point Pelee National Park. A soil's physical properties, soil and water management practices, and DDT application history, can affect DDT degradation and change the relative amount of its metabolites. DDD is the principal product of the dechlorination of DDT in high moisture content, reducing anaerobic soil environments. The main degradation product in soils under aerobic conditions is DDE. %DDT, %DDE and %DDD abundances used in conjunction with soil environment characterization data, can be used to indicate not only whether DDT is degrading, but what environmental factors are controlling its degradation. At the Park, DDT is primarily lost from the soil by microbial degradation to DDE and DDD. %DDT, %DDE and %DDD ratios from each study site indicated that wetter more organic-rich soil environments degraded DDT to its metabolites at a faster rate than drier less organicrich soils. Moreover, historical water level data was used to illustrate that this wetter study site was flooded for part of the year when adjacent marsh water levels were high. These conditions resulted in the accumulation of organic matter over time and the creation of alternating anaerobic/aerobic conditions in the soils resulting in an increased rate of degradation of DDT in these areas. Based on the relative %DDT in the soils at each study site, relative half-life estimates for the first order decay of DDT to its metabolites DDE and DDD were calculated. Half-life estimates for DDT at the wettest and most organic-rich study site range from 6 to 8 years; significantly lower than the two other study sites, which range from 15 to 30 years and are on the high end of the range reported in the literature.</p> / Thesis / Master of Science (MSc)

The microbial origin of methane produced from sedimentary basins is a subject of great interest, with implications for the global cycling of carbon as well as natural gas exploration. Despite the growing body of research in sedimentary basin methanogenesis, few studies have sought to understand the subsurface microbial communities that produce methane, the metabolic pathways involved in the decomposition of ancient organic matter, or the components of ancient organic matter that are consumed. This research examined shale-derived dissolved organic matter (DOM) as a potential substrate to support a subsurface methanogenic community in a known microbial shale gas reserve, the Antrim Shale in the Michigan Basin, USA. Experiments were conducted that enriched fermentative and sulfate-reducing microbial communities from Antrim Shale formation waters. Additionally, 1H NMR spectroscopy was used to characterize shale-derived DOM solutions before and after they were used as growth media for fermentative and sulfate-reducing microbial communities, and to characterize the DOM of the Antrim Shale formation waters. The results of the enrichment studies demonstrate that both fermentative and sulfate-reducing microbial communities from the Antrim Shale are capable of growth using shale-derived DOM as their only source of organic carbon; further, the production of methane in a fermentative enrichment demonstrates that methanogenesis can be supported by shale-derived DOM alone. The 1H NMR characterization studies of the shale-derived DOM solutions before and after growth revealed subtle but detectable differences in DOM compositions, indicating the production and consumption of DOM components by the fermentative and sulfate-reducing microbial communities. Characterization analyses of Antrim Shale formation waters suggest that salinity and microbiological activity may influence the liberation of aliphatic and aromatic compounds from shale. The DOM characterization studies also suggest that carboxylic acids may be consumed by methanogenic communities in the Antrim Shale, and aromatic compounds may be produced by the enriched microbial communities and the communities present in the Antrim Shale.

No description available.

We are leaving traces on the surface of earth, and have been doing so, for a long time. However, for the last 300 years or so, we seem not only to be leaving traces, but objects foreign to our system on an abnormal scale. Traces that are not obvious to the eye, but hidden behind the obviousness of the present. They can be found in the air, in the water, in the rings of the trees or in the glaciers of Greenland.  What will be left after us? In a search of time and traces, to come closer to an understanding of how time passes, I have looked into man made objects. Objects, that have been constructed with time written differently into their structures. These ideas have been implemented in a geographical focal point in the area of Rosenlund sand banks, by lake Vättern, Sweden. From an architect’s point of view I have tried to understand the present that we are now dealing with, the Anthropocene, its implications and the impact of what we create as humans. This, by reconnecting a past and a future to the present through speculation, and by letting the ground play a major part as a mute, inverted infinity with all its layers bearing witness of a past that once laid super strata.

This thesis presents a three-dimensional groundwater modeling of Wekia springshed in central Florida using a numerical model, WASH123D. Springs have historically played an important role in Florida's history. The Wekiva River is a spring-fed system associated with about 19 springs connected to the Floridan aquifer. With increased urbanization and population growth in this region, there has been an increased strain on the water levels of Floridan aquifer which is a major source of potable water. Maintaining groundwater recharge to the aquifer is a key factor of the viability of the regional water supply as well as Wekiva ecosystem. Hence, the first-principle, physics-based watershed model WASH123D has been applied to conduct the study of Wekiva "springshed", which is the recharge area and watershed contributing groundwater and surface water to the spring. In this work, the hydrogeologic conditions of the Wekiva springshed are discussed followed by the modeling details such as mathematical background, domain discretization and initial and boundary conditions considered. Finally, the results from the model are discussed. The Wekiva WASH123D model was run to evaluate the average, steady state 1995 hydrological conditions. The distribution of simulated Floridan aquifer system groundwater levels using WASH123D shows very good agreement with the field observations at corresponding locations.

No description available.