The geochemistry and phosphorus sorption characteristics of Mgeni catchment sediments

Hounsome, Robin Simon

The geochemistry and phosphorus sorption characteristics of Mgeni catchment sediments

Master Thesis

1995

Publisher

University of Cape Town

Department

Department of Geological Sciences

Faculty

Faculty of Science

Abstract

The Mgeni River is vital for the continued industrial and social development of Durban and Pietermaritzburg and the river has been impounded in four places to provide a crucial water resource to these areas. The river is highly susceptible to anthropogenic pollution, particularly phosphorus, which may be derived from unsanitised peri-urban areas or run-off from fertilised agricultural lands. Sediments may be sources or sinks of pollution in aquatic systems. Grab samples of the uppermost sediment layer were taken from sites at each of the impoundments and analysed for salient geochemical characteristics, such as major and trace element concentrations, clay mineralogy, organic carbon, P fractionation, and particle size distribution. Batch experiments were also carried out to determine the P sorption desorption characteristics of the sediments under different pH and redox conditions. The sediments are dominated by clay sized material (< 2mm) which is composed of kaolinite, gibbsite, goethite, mica and other undifferentiated· 2: 1 layer silicates and quartz. Kaolinite, gibbsite and goethite are found extensively throughout the catchment area and are the result of intense weathering. These minerals readily sorb cations onto their surfaces. The significant correlations which were found between the clay content and the concentration of trace metals, particularly Mo, Pb, and Zn, most likely result from accumulations of cations on the mineral surfaces. It was suggested, therefore, that the Mgeni sediments are potential sinks for polluting elements.

Description

Includes bibliographical references.

Keywords

Geological Sciences

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