3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Temporal variation in the allocation of acid mine drainage contaminants in the waters and sediments of the engineered remediation reed beds along the Varkenslaagte stream: an autum - winter study(2016-01-19) Omo-Okoro, Patricia NdidiamakaAcid Mine Drainage (AMD) refers to the seepage or runoff of acidic water from abandoned mines into the surrounding environment. Acid mine drainage is considered a serious long term environmental threat associated with mining. This study was conducted on the Varkenslaagte canal or stream which flows from north to south within the AngloGold Ashanti West Wits gold mining operation, 75 km west of Johannesburg, and receives AMD from tailings storage facilities (TSFs) located on both the northern aspect and the western aspect of the catchment. On the Varkenslaagte, 17 reed beds were planted between 1-12-2011 and 12-9-2012, in a series of shallow excavated depressions. This study was conducted in 2013 and 2014, and aimed to ascertain: (i) whether there is any temporal difference (autumn – end of the rainy season, versus winter – mid-dry season, for 2013 and 2014 combined) in selected fresh-water quality parameters and concentrations of AMD contaminants in the flowing waters in the engineered reed beds; - this was observed, as higher concentrations were recorded in winter than in autumn, for some of the selected water quality parameters, in both survey years; (ii) to determine if vertical changes exist in the elements down the sediment profile from the surface to a depth of approximately half a metre; - conspicuous vertical changes were not evident; and also; (iii) to provide a baseline for monitoring the post clean-up state of the upper Varkenslaagte, and conclude whether the reed bed system is retaining AMD contaminants (major ions, trace and major elements). Chemical variations in water and sediment samples were measured in situ in April/May 2013 and July 2014, and water samples and sediment cores collected for laboratory analyses. Water samples were collected from three points (inflow, middle and outflow) at each of 15 reed beds (RBs, numbered RB 1 -15) in receipt of AMD from two directions (downstream and laterally from TSFs on the northern and western aspects). Ion Chromatography was used to detect chloride (Cl-) and sulphate (SO42-), Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS) were used to identify major and trace elements; iron (Fe), magnesium (Mg), manganese (Mn), potassium (K), cobalt (Co), nickel (Ni), lead (Pb), copper (Cu) and zinc (Zn) in the water samples whereas X-Ray Fluorescence (XRF) analysis for elements was conducted on surface sediments (0-2cm; additional analyses of sediment core samples at depths 2-5 cm, 5-10 cm, 10-20 cm and 20 -30 cm were analyzed but were not considered further). The water in the reed beds was moderately acidic to within the target range. It ranged from pH 5.17 to 6.51 in April, 2014 (approaching the end of the wet season) (P < 0.05) (P = 0.0001) to slightly higher values of pH 5.45 to 6.82 in July, 2014 (mid-dry season) (P = 0.0053). Marginal acidity is above pH 6. A pH of 6.5 – 7.5 is within the target water quality range (TWQR) on the Highveld. High electrical conductivity (EC) values were found, ranging from 3500 – 4600 μs/cm in April and 2600 – 5500 μs/cm in July, though EC values can be higher on much of the South African gold mining Highveld. Lateral influx of AMD from the western TSFs was visually observed into two of the southernmost Varkenslaagte stream reed beds (at RBs13 and 15) during both April and July sampling. In 2014, the Varkenslaagte was still flowing from reed bed to reed bed, although very slowly, similar to 2013. Chloride, sulphate and metal concentrations were high relative to target water quality ranges in most of the reed beds in during April and July, 2014. Although higher concentrations in the sediment suggest that the reed beds are effective in capturing and retaining contaminants in sediment and root mass, the concentrations in the water in reed beds 1-15 still exceeded the target water quality ranges for aquatic ecosystems in South Africa (DWAF, 1996) and the World Health Organization (WHO) guidelines for drinking water quality (WHO, 2004). However use of the water from the Varkenslaagte by humans and livestock is prohibited by the Department of Water and Environmental Affairs, and the National Nuclear Regulator. The bar charts comparing 2013 and 2014 selected water quality data showed that during winter/drier periods with no rains, the rate of evaporation exceeded dilution; this was observed by the slightly lower pH values recorded across the reed beds in July, 2013 and 2014, in comparison with the slight higher pH values recorded across the reed beds in May, 2013 and April, 2014. The bar charts also showed that the highest EC was recorded in the winter of 2014. It was also observed from the principal component analyses (PCAs) that EC, sulphate and pH, in combination with Mg and Fe, were responsible for most of the variation in the water quality data for the two survey years, 2013 and 2014. Following the findings from this study, it is recommended that monitoring of the site should also address whether the reed beds and other control measures that have been put in place (riparian woodlands and windmill pumps) will be adequate to control the lateral seepage from the Western TSFs at some of the southernmost reed beds.Item Depositional slope surface of the western margin of the Nylsvlei, South Africa : active piedmont aggradation and sedimentation processes.(2014-03-03) Burri, Nicole M.The Nyl River and its floodplain are situated on the eastern foothills of the Waterberg mountain range in the Limpopo Province of South Africa. Tributaries flowing out of the Waterberg range display unusual downstream changes, as they approach and converge with the Nylsvlei (or Nyl floodplain). Tributary channels decrease in size downstream until, eventually, they disappear altogether forming unchannellized floodouts. On one such floodout, on the farm Driefontein, an actively aggrading piedmont has formed adjacent to the famous Wonderkrater peat mound, known for its pollen record dating back ~45,000 years. Sediments from the aggrading piedmont interlace with Wonderkrater’s peat layers, suggesting that as the piedmont aggrades so too does the peat mound. This setting presents a unique opportunity to study active aggradational processes, and their products, on hillslope deposits and floodout environments. This study aims to describe the geomorphology and nature of depositional processes along the length of the piedmont adjacent to the Wonderkrater peat mound. Cross-sections, drainage channels and vegetation indices based on topographic maps, orthophotographs and hyperspectral images, were created using ArcGIS in order to describe and determine the surface morphology and hydrology of the Driefontein piedmont in detail. Surface soil samples were collected in order to determine particle size distribution, which were in turn compared to vegetation indices and changes in slope elevation. Further grain samples were collected from depth for age dating using Optically Stimulated Luminescence (OSL), as well as to determine grain size distribution in relation to surface sediments and other fluvial environments. Hyperspectral indices were found to correlate to surface grain size distribution, demonstrating that the presence of vegetation acts as a retaining mechanism for particles along hillslopes where incline should be too steep to support fine-grained sedimentary material. Surface sediments were found to demonstrate the characteristics of an alluvial floodout system, affected greatly by the presence of vegetation and slope inclination. Sub-surface samples were characteristic of a colluvial setting, suggesting that pediment retreat and basin fill, coupled with evidential climatic changes, were dominant controls on the pediment’s morphological and aggradational mechanisms. OSL age results estimated the sediments to be between 37.33 and 58.66 ka old. As a result of its unique sedimentary characteristics, a new type of ‘slow creep fan’ class was established in order to describe the characteristics of the Driefontein piedmont.Item Geology and geochronology of the Nyl River floodplain sediments, Limpopo province, South Africa(2013-08-01) Colarossi, DebraThe Nyl River floodplain, located in the Limpopo Province, is one of the few active sedimentary basins that exist within the South African interior, providing a unique opportunity to study the effect of climate change on fluvial systems. Progradation of tributary fans into the Nyl/Mogalakwena River has raised the surface by 30 m and forced the course of the river westwards towards the Waterberg. Periods of progradation deposited thick sequences of coarse-grained sediments with sand- to gravel-sized mean grain sizes and coarsely-skewed populations in the distal reaches of the tributary fans. These periods were interspersed with periods of relative non-deposition, when active sedimentation on the fan ceased and shallow lakes (or vleis) developed in the trunk river, resulting in deposition of fine-grained, organic-rich, floodplain sediment layers with silt-sized mean grain sizes and finely-skewed distributions in the extreme outer reaches of the tributary fan. The alternating progradational sequences and non-deposition events produced interlayered floodplain and fan deposits in the furthest reaches of the tributary fans along the banks of the Nyl/Mogalakwena River. Incised river cuts within the Rooisloot tributary fan were dated using OSL and 14C techniques. For OSL samples, the SAR protocol was used to measure the equivalent dose and the burial dose was determined using the CAM and MAM. Emission counting methods, including TSAC, GM-beta counting and HRGS were used to determine the dose-rate. The OSL ages ranged from 99 years to 3884 years, constraining the sampled deposits within the late Holocene. Although the 14C ages agreed with this range, carbon contamination of the samples resulted in inverted and overestimated ages. Based on stratigraphic relationships the non-deposition events have been dated at approximately 750–800 years ago, 600 years ago, 475 years BP and 100–150 years ago and two major periods of aggradation at ~ 800–1000 years ago and ~ 500–700 years ago. The rate of aggradation (0.29 cm/year) calculated implies that the entire 30 m deposit could have been deposited in 9 000 years. However, an independent study by McCarthy et al. (2011) proved that tributary sedimentation began prior to 220 ka. Therefore, in order to deposit 30 m of sediment over 220 ka, either the mid – late Quaternary sedimentation rate was lower than the recent past (Late Holocene) or the system periodically undergoes extensive erosion in order to flush the accumulated sediment from the tributary fan system.