A geochemical investigation of the sediments in Small Bay, Saldanha Bay, with special reference to the mobility of Cd, Cu, Pb and Zn

Master Thesis


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University of Cape Town

Saldanha Bay is a natural deep-water harbour situated on the Cape West Coast, approximately 100 km north of Cape Town. The bay is not an estuary, since there are no rivers or streams entering the inlet. Saldanha Bay covers a total area of approximately 9.61 x 107 m2 and consists of three interconnected water bodies: Langebaan Lagoon, Big Bay and Small Bay. The latter two are separated from each other by a causeway and a series of jetties. At present, Small Bay is the most developed of the water bodies, supporting activities such as commercial and industrial fishing, the mariculture of mussels, and the exportation of iron ore and metal concentrates. Conflicting demands are being placed on the system, and the sediments are known to be contaminated with a range of trace metals. The handling of ore and metal concentrates in particular, have been identified as a threat to the survival of the mariculture industries. The overall objective of this study was to provide a geochemical characterisation of the sediments in Small Bay. It focused on identifying the factors which have the greatest influence on the mobilities of Cd, Cu, Pb and Zn in the sediments. This was achieved through a geochemical interpretation of the results obtained from analyses of sediment solid phase samples and pore water samples. Factors affecting the metal mobilities were identified by investigating the statistical relationships between calculated partition coefficients (Kp) and the characteristics of the sediment solid and aqueous phases.

Bibliography: pages 135-145.