Browsing by Author "Roychoudhury, Alakendra"

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    An integrated geochemical and microbiological investigation of sulphate reduction in hypersaline pans
    (2007) Porter, Donovan; Roychoudhury, Alakendra; Cowan, Don
    Geochemical and microbiological methods were used to derive a holistic picture of sulphate reduction in five hypersaline pans in South Africa. Sulphate reduction rates were determined using a radioactive tracer (35 So/-) technique. This was applied to determination of in situ sulphate reduction rates, the effect of increased salinity on the activity of sulphate-reducers, the determination of kinetic parameters for sulphate uptake, the effect of temperature on sulphate reduction and the determination of favoured organic substrates. Such measurements were supported by the collection of pertinent geochemical data from pan sediments. The sulphate-reducing microbial community was quantified by competitive polymerase chain reaction. The structure of the microbial community was studied by denaturing gradient gel electrophoresis, from which bands were excised for DNA sequencing. Denaturing gradient gel electrophoresis patterns were analysed statistically by cluster analysis and principal components analysis. High in situ rates of sulphate reduction (up to 3684 nmol.cm-3 .daf1 ) were measured, showing strong correlations to salinity and sulphate concentrations. Rather than inhibiting sulphate reduction, slurry experiments showed increased sulphate reduction rates with increased salinity. Optimum salinities were 272-311 at hypersaline pans and 134-244 at highly saline pans. The use of compatible solutes, not K+, for osmoprotection, was inferred. Half-saturation constants measured here ( 64-780mM) are the first reported for hypersaline sites and were much higher than previously measured in other environments, implying greater regulation of sulphte transport. Values for apparent activation energy were within a narrow range (28-62 kJ.mor1 ) and similar to those measured in other environments. Sulphate reduction rates rarely increased significantly after addition of organic substrate solutions and there were no narrow substrate preferences. It was inferred that sulphate-reducers generally had sufficient organic carbon in situ. However, the use of acetate and n-butyrate suggests that complete oxidation of organic matter was more widespread than predicted on bio-energetic grounds. This was supported by DNA sequence data suggesting the presence of members of the completely-oxidising Desulfobacteraceae. Changes in bacterial numbers paralleled changes in sulphate reduction rates. Significant correlations between geochemical and microbiological data inferred from statistical analysis of denaturing gradient gel electrophoresis data revealed the importance of salinity, sulphate concentration and organic matter reactivity as determinants of SRB community structure.
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    A geochemical investigation into the occurrence and fate of nitrogen and phosphorus in the lower Oliphants River, Western Cape
    (2004) Germs, Wijnand J; Compton, John; Roychoudhury, Alakendra
    Knowledge of nutrient dynamics within aquatic ecosystems are of fundamental importance for water quality management, especially in cultivated areas where irrigation farming pose a salinization and eutrophication risk to water bodies. A range of water quality problems is associated with eutrophication, which is generally controlled by the nutrients nitrogen and phosphorus. The lower Olifants River is situated in an arid region with intensive irrigation agriculture. This study set out to investigate the loading and fate of nitrogen and phosphorus in the lower Olifants River.
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    Geochemistry of a pristine fynbos ecosystem in the Harold Porter National Botanical Gardens and Kogelberg Biosphere Reserve
    (2002) Smit, A K; Compton, John; Roychoudhury, Alakendra
    Water, soil and rock samples were taken from the Harold Porter National Botanical Gardens and the Kogelberg Biosphere Reserve in order to investigate interactions between the various nutrient pools in a pristine fynbos ecosystem. Physical variables (pH, EC, temperature, DO, alkalinity) were measured in the field, and water samples were collected and analysed for chemical composition. Chemical composition and mineralogy of soil and rock samples from the Peninsula, Cedarberg and Goudini formations were determined to assess the influence of parent geology on soil chemistry. The surface water chemistry in the study area was remarkably homogeneous, with only major ions Na, CI, Mg, Ca, Si and S04 exceeding concentrations of 1 ppm at any of the sample sites. Concentrations of other major ions AI, K, NH4, N03 and Fe ranged between 0.1 and 0.7 ppm. The minor and trace elements B, Sb, Sr, Zn and Mn were present in concentrations greater than 1 ppb. Compared to the seawater chloride ratio, Na, Mg, K and S04 were depleted in the streams relative to CI, showing that these elements are preferentially accumulated and are conserved within the fynbos ecosystem. In contrast, CalCI ratio is elevated in streams, indicating an external source of Ca other than the seawater. This source may be windblown dust. The Fe content of soils appears to be lower than that of the parent bedrock, especially in the case of the iron-rich Goudini Formation. This indicates an as yet undetermined pathway for iron to leave the system, which may be through deeper anoxic groundwaters in the area. Only one site from the Oudebosch River headwaters showed significant deviation from other sites in several of the elemental trends, and also had no measurable DOC content, compared to the other sites which ranged from 10 to 16 mg/L DOC. These differences are probably the result of the different vegetation (afromontane forest as opposed to fynbos) and geological setting (clay rich, Cedarberg Formation soils). Soils contained higher concentrations of water-soluble ions than the streams, and organic carbon content ranges from 6 to 34 wt%. Organic 0 horizons and Melanic/Humic A horizons constituted the major soil types. Cation exchange capacities of the soil samples ranges between 31.3-93 mmolJkg, and about half of the soil samples were determined to be acid saturated and fairly leached of ions, probably due to the high rainfall. The soil composition and mineralogy correlate well with that of the underlying bedrock, and was dominated by quartz, with some clays, micas, feldspars and hematite. The study was similar to one in the Cedarberg, which has the same geological setting and equal fynbos species richness. This is the first integrated geochemical study to characterise the pristine fynbos biome of the Harold Porter National Botanical Gardens and the Leopards Gorge River Catchment, and will allow rapid assessment of any future changes.
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    The partitioning and mobility of metals in the Blesbokspruit
    (2004) Starke, Michael; Roychoudhury, Alakendra
    The Blesbokspruit is situated south-east of Johannesburg on South Africa's East Rand, famous for its prolific gold and uranium deposits. With the onset of mining in the region around 1930, the Blesbokspruit was altered from a non-perennial to a perennial stream and a wetland due to the construction of roads and embankments as well as the discharge of mine effluent. Various studies have highlighted the detrimental impact South African gold mines and their slimes dams have on the environment especially the release of metals into aquatic ecosystems. Unable to degrade naturally, metal pollution accumulates within aquatic ecosystems with the potential to move up the biologic chain. Water and sediment samples were taken from throughout the Blesbokspruit in an attempt to characterise the aqueous and sediment geochemistry of the stream. Filtered and acidified water samples were analysed for major cations and anions using Atomic Absorption Spectrophotometry and Ion Chroma topography respectively. The waters were found to have elevated levels of Cl⁻, SO₄²⁻, Na⁺ and Ca²⁺. These elevated salt concentrations are derived from the discharge of saline effluent into the Blesbokspruit by the Grootvlei Proprie ary Mines Ltd and are responsible for the increase in electrical conductivity downstream of the mine. The generally mildly alkaline nature of the Blesbokspruit is the result of the underlying dolomites of the Chuniespoort Group . ICP-MS was used to quantify aqueous and sediment metal enrichment relative to natural concentrations reported in the literature. The results of the ICP-MS indicate aqueous and sediment enrichment in chalcophile metals derived from the oxidation of sulphide minerals. U is also enrichment within the water and is derived from the ore minerals mined from the underlying Witwatersrand Supergroup. However, total metal concentrations are not indicative of bioavailable metal concentrations. For this reason it is important to determine how metals are partitioned within the sediment. A sequential extraction was performed on sediment samples from the Blesbokspruit as a method of determining metal partitioning and mobility under various possible environmental conditions. The sequential extraction extracted metals from the following five operationally defined fractions: the exchangeable fraction, sensitive to changes in ionic concentration; the pH- sensitive bound to carbonates fraction; the redox-sensitive bound to Fe and Mn oxides and bound to organic matter fractions and essentially inert and unavailable residual fraction. Metal extracts from the five fractions were analysed by ICP-MS. The results of the sequential extraction indicate that only minor proportions of metals are exchangeable, while a significant proportion of many of the metals analysed for were hosted in the residual phase and are therefore not bioavailable under most natural conditions. Varying amounts of the meta ls analysed were partitioned within the carbonates, Fe and Mn oxides and organic matter.