A trace element study of sediments from the Olifants River estuary, the Berg River estuary, and the off-shore Mud Belt
Master Thesis
2004
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University of Cape Town
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Abstract
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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Includes bibliographical references (leaves 99-105).
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Reference:
Taylor, A. 2004. A trace element study of sediments from the Olifants River estuary, the Berg River estuary, and the off-shore Mud Belt. University of Cape Town.