Spatio-temporal variations of the sedimentology and geochemistry of six estuaries within the eThekwini Municipality, KwaZulu-Natal, South Africa.
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Date
2014
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Abstract
Estuaries are dynamic features of a coastline whose sediments are influenced by riverine and
marine processes. Periodic events such as floods, as well as variations in mouth status,
greatly affect the energy levels within an estuary and subsequently the amount of sediment
erosion and deposition that takes place. Concurrently, pollutants are transported and
deposited into estuaries and can reside in the sediments for many years. The estuaries of the
eThekwini Municipality in KwaZulu-Natal, South Africa, are exposed to a variety of
pollutants; however with the expanding industrial sector within this region, metal
contamination is of concern.
This study investigates the sedimentology and geochemical variations of six estuaries within
the municipality namely, the uTongati, uMdloti, uMgeni, Isipingo and uMbokodweni
estuaries as well as the Durban Harbour. To determine the spatial variations in estuarine
sedimentology, sediment cores were collected longitudinal to the estuary axis. The core
samples were analysed for sediment colour, texture and organic matter content. To assess the
geochemical variations, core samples were analysed for Zn, Cu, Cr, Ni, Pb, As, Fe, Al, Ca, S,
P, Mg, Mn, Cd and V concentrations. Some samples were also carbon dated to provide a
temporal aspect to the sediment and geochemical variations. Descriptive and graphic
techniques were used to examine the sedimentology within the estuaries; and the geochemical
data was analysed with the use of multivariate statistics. Additionally, pollution indices and
sediment quality guidelines were utilized to assess the pollution levels within the sediments.
The results indicated that lower energy environments caused by protracted mouth closures in
the uMdloti and Isipingo estuaries accounted for large amassing of fines. In contrast, the
accumulation of mixed coarse and fine sediments in the uTongati and uMgeni estuaries was
an indication of high fluvial flows and open mouth conditions. All carbon dated ages for all
estuaries were greater than 700 years which may be attributed to a combination of scouring
effects from past and recent flood events and also possibly due to the deposition of re-worked
older sediments from upstream. Low metal concentrations were found within the sediments
of all estuaries, and the presence of fines and organic matter governed their concentration
variations with depth. The uMgeni and uMbokodweni estuaries which are located
immediately downstream of industrial and urban areas, were found to contain relatively
higher concentrations of elements Pb, Cu, As and Ni. These metals showed high enrichment
within the sediments; however actual concentrations were below sediment quality guideline
levels. General pollution levels within all estuaries were very low, and can be attributed to the climatic influences within this region which has a ‘cleansing’ effect on the estuarine
environments in removing contaminants.
Description
Thesis (M.Sc.)-University of KwaZulu-Natal, Durban, 2014.
Keywords
Sedimentology--KwaZulu-Natal--eThekwini Metropolitan Area, Geochemistry--KwaZulu-Natal--eThekwini Metropolitan Area, Estuaries--KwaZulu-Natal--eThekwini Metropolitan Area, Theses--Marine biology.