Masters Degrees (Earth Sciences)

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    Evaluating sources and environmental risk of pesticide pollution in Western Cape rivers
    (Stellenbosch : Stellenbosch University, 2023-12) Davies, Emma Jane; Chow, Reynold; Stamm, Christian; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: Agriculture is key to South Africa’s economy which has led to the country becoming a leading pesticide user in Sub-Saharan Africa. The Western Cape is a dominant agricultural region in South Africa, making it particularly vulnerable to pesticide pollution. After application, pesticides can be transported away from the designated site, potentially causing adverse health effects to non-target organisms. Therefore, the risk of pesticide pollution must be better understood. This research deployed passive samplers in rivers for two-week intervals every month from February 2022 - March 2023 in the agricultural catchments Grabouw, Hex River Valley, and Piketberg. This expands on a previous campaign from 2017-2019. 44 pesticides were measured using Liquid Chromatography Mass Spectrometry. The original aspects of this study include the expansion of the sampling list to include the fungicide dimethomorph and a suite of drugs. 22 (out of 44) pesticides and seven (out of 20) drugs were detected above the limit of quantification. Piketberg had high drug concentrations and detection frequencies which correlated with pesticide concentrations, whereas Grabouw and Hex River Valley did not. This suggests that pesticide pollution in Piketberg is likely sourced from both wastewater treatment plants and agriculture, whereas the absence of drugs in Grabouw and Hex River Valley suggests that pesticide contamination is more likely sourced from agriculture. This is particularly true for terbuthylazine and carbendazim because their concentrations correlated with cumulative drug concentrations (R²=0.47 and 0.77, respectively). Five pesticides were detected in control samples deployed in Jonkershoek Nature Reserve. While detections could be from neighbouring agricultural catchments via atmospheric transport, they also indicate non-agricultural sources of herbicides (e.g., atrazine and terbuthylazine from trail maintenance or invasive plant control). A few compounds typically contributed to majority of the detected concentrations, specifically, imidacloprid (54%) and dimethomorph (22%) in Hex River Valley, imidacloprid (46%) and chlorantraniliprole (38%) in Grabouw and imidacloprid (22%) and terbuthylazine (27%) in Piketberg. The newly measured fungicide, dimethomorph, had high concentrations up to 80 ng/L and detection frequencies in Hex River Valley (96%) and Piketberg (25%). Pesticides with high detection frequencies were not applied year-round but have high Groundwater Ubiquity Scores (GUS), suggesting a high leaching potential into groundwater. Environmental risk was evaluated by comparing concentrations to European Environmental Quality Standards (EQS). Four compounds exceeded EQS values, namely the insecticides imidacloprid and chlorpyrifos, the herbicide terbuthylazine, and the fungicide spiroxamine. Exceedances for chlorpyrifos, spiroxamine, and terbuthylazine coincide with application events and rainfall. All compounds that exceeded in 2022/2023 (except for spiroxamine) also exceeded during the 2017-2019 campaign, indicating high persistence and continual exposure risk to aquatic life. Assessment of pesticide mixtures suggests that certain combinations (e.g., imidacloprid and chlorantraniliprole) can have increased toxicity effects on organisms, and almost occur year-round. Hydrological and concentration patterns suggest that increased detections are mainly driven by rainfall in winter, pesticide application in summer and constant input from wastewater treatment plants or groundwater transport. Future research should prioritize sampling of groundwater, wastewater influent and effluent and soils to improve our understanding of pesticide transport pathways.
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    Plio-pleistocene palaeoenvironment of the south western continental shelf of South Africa: a foraminiferal perspective
    (Stellenbosch : Stellenbosch University, 2023-12) Walsh, Jared Tanner; Fietz, Susanne; Bergh, Eugene; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: The oceanography and ecology on the western continental shelf of South Africa (Orange Shelf) were highly influenced by the initiation and intensification of the Benguela Up- welling System (BUS) during the Plio-Pleistocene. On the Orange Shelf, literature sub- stantiating the e↵ect of the Plio-Pleistocene climate transition on foraminiferal assemblages is sparse. Foraminifera proved reliable as palaeo-proxies, and by assessing the response of foraminifera to the Plio-Pleistocene climate transition, a new perspective emerges for the changing oceanography in the BUS during this time. Furthermore, interpolations from the well-studied Namibian shelf and slope are often relied upon to interpret the palaeoceano- graphic conditions in the BUS, therefore supporting the need for new foraminifera-based palaeoceanographic studies from South Africa. Sediments and microfossil foraminifera from vibracores on the inner and outer Orange Shelf (200–400 meters below sea level) were anal- ysed using faunal analyses, foraminiferal biostratigraphy, and Strontium Isotope Stratigra- phy. The dating methods used provided conflicting results for various components. For example, in one unit, phosphorite was dated to 5.70–5.98 Ma, but Pleistocene indicator species Globorotalia truncatulinoides yielded ages approximately 2.58 Ma from its first ap- pearance. This study observed sediment reworking within Plio-Pleistocene sediment and, to a lesser extent, foraminiferal assemblages across the continental shelf. The cooling of sea surface temperatures (SST) in the BUS following the initiation of Northern Hemisphere glaciation during the Plio-Pleistocene transition was observed by the increase of temperate SST indicators Globigerina bulloides and Globoconella inflata, and the subpolar SST indi- cator Neogloboquadrina pachyderma. The influence of Agulhas leakage was prevalent on the outer shelf, and to a lesser extent on the inner shelf during the Pliocene, and was inferred from high abundances of Orbulina universa and trace abundances of Globorotalia menardii and Globigerinoides ruber. Regarding primary productivity, planktic indicators Globigerina bulloides and Neogloboquadrina pachyderma decline with the onset of the Pleistocene on both the inner and outer shelf. The inner shelf seemed to undergo less drastic changes in terms of primary productivity than the outer shelf during this time. This study suggests an external nutrient influx with increasing proximity to the coast, supporting the persistence of planktic primary productivity during the Pleistocene and the decline in upwelling intensity. Benthic primary productivity indicator Uvigerina peregrina increased during the Pleistocene. While upwelling intensity appears to decrease over the Plio-Pleistocene transition, the influx of nutrient-rich bottom water to benthic foraminifera on the outer shelf remained sufficient to support primary productivity. This study contributes to a greater understanding of the relationship between productivity, nutrient supply, and the upwelling intensification of BUS in the context of foraminifera assemblages on the Orange Shelf over the Plio-Pleistocene.
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    Controls of magma emplacement and 3d modelling of cupriferous basic bodies of the Kuperberg suite at Narrap mine, Okiep copper district, Namaqualand
    (Stellenbosch : Stellenbosch University, 2023-12) Bester, Andeon; Kisters, Alexander; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: The Okiep Copper District hosts more than 1800 copper-mineralised basic bodies that form part of the Koperberg Suite. These mafic magmas intruded the high-grade granite gneiss terrain of the Bushmanland Subprovince during a period of E-W extension (1060-1030 Ma) and peak, lower- granulite facies metamorphism. Basic bodies have different, commonly highly irregular geometries ranging from massive, steeply-plunging, carrot-shaped intrusions to thin stringers or foliation-parallel sills in the gneiss sequence. For the most part, however, basic bodies show subvertical E-W trending blade- or dyke-like geometries hosted by localised high-strain 'steep structures'. The close spatial relationship between basic bodies and steep structures highlights the importance of structural anisotropies as conduits facilitating mafic magma ascent through the stratified mid-crustal OCD. The 3D model of Narrap Mine's wall rocks and Koperberg Suite intrusions revealed three distinct structures: 1) a central cluster of vertical basic bodies cutting across various lithologies and emplacing along the vertical foliation of a prominent steep structure, 2) a subvertically orientated, laterally extensive collection of basic bodies emplaced along the upwarped lithological contact of the overlying Moddefontein Gneiss and underlying Wolfram Schist, and 3) subhorizontal penny-shaped sill-like bodies following the shallowly dipping regional gneissic layering. A commonality between all these structures is their discontinuous nature and small aspect ratios, indicative of buoyancy-driven, self- contained hydrofractures. Furthermore, these structures are congruent with mechanical anisotropies, be it lithological contacts or foliation, signifying the importance of anisotropies as magma propagation pathways. Additionally, the presence of multiple generations of Koperberg Suite magmas within a particular steep structure highlights the effectiveness of utilising steep structure fabrics as repeated pathways. This demonstrates that emplacement was independent of the regional stress field and occurred under low deviatoric stresses in the high-grade metamorphic, partially molten mid-crustal section of the OCD. In this case, structural anisotropies (foliations, lithological contacts, steep structure fabrics) determine the emplacement and orientation of basic bodies. The 3D model further indicates how the mechanically layered gneiss and interlayered metasediments impede the buoyancy-driven ascent of the Koperberg Suite magmas and modify their geometry. Basic bodies typically thicken and accumulate in schist and gneiss units as a result of the lower wall-rock rigidity. In contrast, the refractory Springbok Quartzite resists fracture dilation, yielding stringer-like geometries and the likely ponding of magmas below this unit. All these observations, including the three aforementioned structures, bear striking similarities to what is seen at the rest of the mines in the OCD, with the softer metasediment and gneisses above the Springbok Quartzite hosting the majority of the basic bodies mined historically. This stratigraphic position hosts the laterally branching structures, which have commonly emplaced along the underlying Wolfram Schist and overlying gneisses, and the subvertical clustered basic bodies that pinch and seemingly terminate against the upper contact of the Springbok Quartzite. Thus, future exploration should focus on the gneisses and schists hosting the branching structure and central cluster, in addition to following the down-plunge continuation of the central cluster below the quartzite as ponding is likely.
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    Constraints on the size and temperature of magma batches that constructed the Peninsula pluton, based on the metamorphic record of metasedimentary xenoliths
    (Stellenbosch : Stellenbosch University, 2023-03) Muller, Jared; Stevens, Gary; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: This study aimed to investigate the metamorphic histories of nine greenschist facies xenolith samples from the Malmesbury Group metasediments, which have an estimated age of deposition of approximately 575 to 550 Ma. These samples are hosted in the Peninsula Pluton granitoids (537.8 ± 1.6 Ma to 532.7 ± 1.9 Ma) of the Cape Granite Suite. The goal of the study was to put constraints on the size and temperature of the magma batches that formed the Peninsula Pluton granitoids. To achieve this, various techniques including petrography, field evidence, scanning electron microscopy, phase equilibria modelling using the freeware "Rcrust" and thermal modelling using the freeware "Energy2D" were employed to establish peak metamorphic mineral assemblages and constrain peak metamorphic conditions. The peak metamorphic assemblages for the xenoliths were determined to be quartz + biotite + plagioclase + cordierite ± K-feldspar ± ilmenite ± muscovite. The results of the bulk rock and mineral composition analyses revealed that the metasedimentary xenoliths of this study plot within a normal range of the Malmesbury group sediments and metasediments. Temperatures of formation for the magma batches that constructed the Peninsula Pluton have been noted to be between 800 and 900°C. Ti-in-biotite thermometry was used to constrain the temperature of peak metamorphism for the xenoliths of this study to be in the range of 665 to 725°C. Phase equilibria modelling revealed that the different xenoliths experienced peak temperatures between 530 and 730°C and pressures between 0 and 4.5 kbar. This has important implications for background magma temperature in the pluton and the size and temperature of the magma batches that entrained the xenoliths. Obviously if the magma arrived in the upper crust at ~ 700°C, batches could conceivably be any size. However, there is strong evidence for the Peninsula Pluton magmas having arisen by fluid absent melting involving biotite at >850°C. Two-dimensional conductive thermal modelling was used to explore the ranges of background magma temperature and magma batch sizes and temperatures that would be consistent with the xenoliths recording only amphibolite facies temperatures. The results indicate that the background magma temperature cannot be higher than the maximum temperatures recorded by the xenoliths. Additionally, if the magma batches that sampled the xenoliths and introduced them into the pluton were at 850°C, they could not have been thicker than 1m if intruded as 10m wide sills. Similarly, magma batches arriving at 750°C could not have been thicker than 2m if intruded as 10m wide sills. These size and temperature estimates contribute to the body of evidence supporting the incremental growth model of granitic plutons, as well as providing insight into the size and temperature of magma batches that were assimilated to form the Peninsula Pluton granitoids. The assimilation of these batches, as well as their frequency, can be better understood considering these data.
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    Evaluating groundwater storage changes under drought in the Western Cape using satellite and in-situ data
    (Stellenbosch : Stellenbosch University, 2023-03) Nenweli, Ritshidze; Chow, Reynold; Watson, Andrew; Stellenbosch University. Faculty of Science. Dept. of Earth Sciences.
    ENGLISH ABSTRACT: The Western Cape is a water scarce province of South Africa and has become more reliant on groundwater over the last few decades due to frequent droughts, which are anticipated to worsen in the future. While data on surface water use and storage levels in reservoirs are easily accessible throughout the year, the impact on groundwater storage at the provincial scale has not been evaluated yet. However, lack of monitoring boreholes, discontinuous measurements, unavailable monitoring data, and installation of boreholes without proper licensing has made it difficult to manage groundwater sustainably in the region. Remote sensing from National Aeronautics and Space Administration’s Gravity Recovery and Climate Experiment (GRACE) provides continuous and freely accessible datasets through which trends and variations in groundwater storage can be estimated. This research aims to understand how GRACE and Global Land Data Assimilation System (GLDAS) data can be used to monitor groundwater storage in the Western Cape. In-situ groundwater storage declined prominently in the Western Cape during droughts (2003-2006, 2009-2011, 2015-2018 and 2017-2019). While some aquifers are recovering, others (e.g., Vanhynsdorp Aquifer) are still declining, possibly from over-abstraction for irrigation. GRACE TWS (JPL-M) anomalies showed positive moderate correlation (r = 0.69) with in-situ groundwater measurements from the Adelaide Subgroup Aquifer possibly because of the unit’s large areal extent, unconfined nature, and large groundwater storage fluctuations. While the Table Mountain Group Upper Aquifer Unit (TMG UAU) and Cape Flats Aquifer both showed significant positive correlations with GLDAS CLSM (catchment land surface model) groundwater storage of 0.83 and 0.73, respectively; possibly because they are unconfined and their fast response to precipitation. GRACE TWS anomalies have the potential to monitor groundwater storage of the Adelaide Subgroup Aquifer, while GLDAS CLSM groundwater storage data has the potential to monitor groundwater storage of the unconfined TMG UAU and Cape Flats Aquifer. GRACE and GLDAS CLSM groundwater storage data have the potential to monitor groundwater in other parts of South Africa or data scarce regions of Africa to ensure that future generations have access to groundwater.