Browsing by Author "Roychoudhury, Alakendra N"

Now showing 1 - 9 of 9
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    The formation and origin of carbonate minerals in the Darling and Yzerfontein hypersaline pans, Western Cape, South Africa
    (2009) Mauger, Carla; Compton, John; Roychoudhury, Alakendra N
    The Darling and Yzerfontein hypersaline pans are located on the western coastal plain of South Africa. The area has an arid, Mediterranean type climate. The carbonate minerals calcite and dolomite have precipitated in the pans through the evaporation and concentration of ions derived from weathering of bedrock, marine aerosols and coastal rainfall. Five pans were studied, the brine-type pans Rooipan South, Zwartwater North and Zwartwater South, the brackish saline pan Rooipan North, and the coastal Yzerfontein pan. Directly below the surficial halite crust of the three brine-type pans is a black organic-matter rich layer in which bacterial sulphate reduction is occurring (hydrogen-sulphide smell). All of the pans contain disseminated calcite, with only the Zwartwater North and Zwartwater South pans containing a mixture of dolomite and calcite. Yzerfontein and Zwartwater North pans contain small aragonitic gastropod shells (Tomichia ventricosa) which are no longer active in the pans due to the high present-day salinities of the pan waters. Low-magnesian calcite is likely the first evaporite mineral to precipitate in the pans because of its low solubility.
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    A geochemical investigation of ground water and soils affected by evaporation pond seepage, at the Namakwa Sands Mineral Seperation Plant(MSP)
    (2004) Petersen, Jacques R; Roychoudhury, Alakendra N
    Evaporation ponds are used for treating wastewaters in arid regions worldwide. Namakwa Sands an Anglo American plc operation, mines heavy minerals along the semi arid West Coast of South Africa. An acid effluent is generated during treatment of these heavy minerals. The effluent is neutralized and disposed of into unlined evaporation ponds. Seepage from the ponds affects the surrounding environment as well as the subsurface waters. The main objective of this study was to investigate the effects of the seepage on the groundwater resources and potential implications for contaminant migration in the subsurface environment.
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    Groundwater redox conditions at a petroleum contaminated site, Kuils River, South Africa : pathways for BTEX biodegradation
    (2003) Merrett, Greg Lee; Roychoudhury, Alakendra N
    A shallow sandy aquifer, contaminated by petrol from an underground storage tank, was studied to determine if intrinsic bioremediation of the hydrocarbons is taking place. Groundwater samples taken from 32 monitoring wells were analysed for NO₃-,NH₄+, Mn²+, Fe²+, SO₄²-, and ΣH₂S. Portable electrodes were used to make field measurements of electrical conductivity, redox potential, and pH. The variation and distribution of these redox-sensitive groundwater constituents show that bioremediation via NO₃- reduction, Fe³+ reduction, and SO₄²- reduction (and possibly methanogenesis in the most reduced part of the plume) is occurring. In some cases redox processes are taking place simultaneously resulting in redox zones that overlap. Iron and sulphate reduction are the dominant processes taking place.
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    Seasonal variability of sediment oxygen demand and biogeochemistry on the Namibian inner shelf
    (2006) Joubert, Warren R; Roychoudhury, Alakendra N; Monteiro, Pedro M S
    The Central Benguela inner shelf is characterised by hypoxic to anoxic sub-thermocline water conditions on a semi-permanent basis. Historical understanding of the incidence of hypoxia is that the inner shelf area off Namibia is one of the main areas of formation of low oxygen water (LOW) in the Benguela upwelling system. Local biogeochemical remineralization of organic matter mostly related to the primary production in surface waters (Chapman and Shannon, 1985) is thought to drive seasonal variability in sediment oxygen demand. New understanding of the system suggests that shelf hypoxia is driven by a remotely forced equatorial hypoxic boundary condition thought to trigger anaerobic remineralization and increased sediment fluxes of reduced metabolites (Monteiro et al., in press). The study focused on seasonal variability of sediment oxygen demand on the Namibian inner shelf and its relation to particulate organic carbon and reduced metabolite fluxes.
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    Sorption of the platinum-group elements in selected solid matrices
    (2003) Lopes, Lidia Velazquez; Roychoudhury, Alakendra N
    Recent research on the platinum-group elements (PGE) has shown increased concentrations in environmental samples, probably as a result of the widespread use of PGE (Pt, Pd and Rh in particular) as catalysts in the chemical and car industry. Most of the recent research on PGE focuses on the analysis of concentrations in environmental samples exposed to anthropogenic sources of PGE, but there are very few studies that have investigated sorption behaviour of PGE in soils.
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    South African research in the Southern Ocean: New opportunities but serious challenges
    (2013) Treasure, Anne M; Moloney, Coleen L; Bester, Marthán N; McQuaid, Christopher D; Findlay, Ken P; Best, Peter B; Cowan, Don A; de Bruyn, P J Nico; Dorrington, Rosemary A; Fagereng, Åke; Froneman, P William; Grantham, Geoff H; Hunt, Brian P V; Meiklejohn, K Ian; Pakhomov, Evgeny A; Roychoudhury, Alakendra N; Ryan, Peter G; Smith, Valdon R; Chown, Steven L; Ansorge, Isabelle J
    South Africa has a long track record in Southern Ocean and Antarctic research and has recently invested considerable funds in acquiring new infrastructure for ongoing support of this research. This infrastructure includes a new base at Marion Island and a purpose-built ice capable research vessel, which greatly expand research opportunities. Despite this investment, South Africa's standing as a participant in this critical field is threatened by confusion, lack of funding, lack of consultation and lack of transparency. The research endeavour is presently bedevilled by political manoeuvring among groups with divergent interests that too often have little to do with science, while past and present contributors of research are excluded from discussions that aim to formulate research strategy. This state of affairs is detrimental to the country's aims of developing a leadership role in climate change and Antarctic research and squanders both financial and human capital.
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    A trace element study of sediments from the Olifants River estuary, the Berg River estuary, and the off-shore Mud Belt
    (2004) Taylor, Arthur; Compton, John; Roychoudhury, Alakendra N
    Trace elements have received increased attention since the mid-1900's. Although some studies have investigated trace element accumulation as a result of urban expansion in the Western Cape, South Africa, few have catalogued the accumulation and behavior of trace elements resulting from agricultural practices. This study investigates the distribution and behavior of trace elements for the Olifants and Berg river catchments by focusing on the sediments of the estuaries. The dominant industry in both catchments is agriculture and there exists relatively little urban sprawl. Two sediment samples taken from the offshore mud belt in the vicinity of the two river mouths were also analyzed. The sediments were analyzed for trace elements using inductively coupled plasma mass spectrometry (ICP-MS), major elements using X-ray fluorescent spectroscopy (XRF), total sulfur using XRF, total and organic carbon using a C:H:N analyzer, and grain size analysis was performed (>62 μm, 38-63 μm, 2-38 μm, <2μm). The mud belt cores were dated using 14C dating. Estuarine surface waters were analyzed for trace elements, pH, dissolved oxygen (DO), electrical conductivity (EC), and temperature. The trace elements arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn) were focused on. The trace element concentrations in the sediments were compared with those of soils that occur in the study area, as well as their parent materials, to determine background concentrations. The concentration profiles of elements with respect to depth are compared with natural deposition rates to recognize signs of recent enrichment of individual trace elements. Inter-element comparisons are made in an attempt to determine speciation. Comparison between the estuarine and mud belt sediments were made to assess the estuaries ability to filter fluvial trace elements, as well as to determine the sediment contributions of the Olifants and Berg rivers to the mud belt. Statistical analysis was performed to"group sediment populations Trace element and organic matter concentrations showed strong positive correlations with fine-sized particles. The mud belt sediments displayed considerably more OC than the estuarine sediments. The trace elements appear to associate predominantly with clay minerals (alumino-silicates), Fe/Mn oxides, and organic matter. Trace element correlations with S and carbonate carbon were also observed. Comparison with estimates of natural deposition rates and compositions of soils occurring in the catchments did not suggest an anthropogenic pollution input. From the data available the estuarine and Mud Belt sediments appear enriched in Cd, Cu and Zn in comparison to the background soils. The estuaries seem to effectively trap Zn and Pb, but do not capture As well. Statistical analysis suggest that, of the rock types considered, the sediments of the Olifants and Berg river estuaries and those of the off shore mud belt are most similar to sediments derived from the Malmesbury and Ecca Groups. The Olifants and Berg rivers are important sources of water for the farming community, as well as for municipal use in the Western Cape. Based on this investigation of the estuarine waters and sediments the rivers appear to be in good health in regards to trace element concentrations.
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    Trace metal accumulation in urban sediments, Black River, Western Cape, South Africa
    (2003) Haniff, Naadira; Roychoudhury, Alakendra N; Compton, John
    The increase in urbanisation and the use of metal compounds and products domestically and in industry has resulted in the production of by-products and wastes, which needs to be evaluated in the urban environment. The discharge of some of these wastes into urban rivers should be evaluated to determine the potential effects, for example, toxicity and mobility. The effects may, in part, be determined by the chemical states in which these wastes manifest themselves, and by the chemical associations they have.