Abstract
M.Sc.
A comparative study was undertaken in the Olifants River catchment, to determine
the water quality at two dam sites, namely, Bronkhorstspruit Dam (control) and
Loskop Dam (polluted) in the upper Olifants River system and two river point,
namely, at Mamba and Balule in the Kruger National Park, in the lower Olifants River
system. Data was obtained during the physical and chemical analysis of water and
sediment samples, and during bioaccumulation studies using Atomic Absorption
spectrometry, testing for aluminium, chromium, copper, iron, lead, manganese,
nickel, strontium and zinc. These tests were conducted on the liver, skin, muscle and
gills of Clarias gariepinus. The information collected from Mamba and Balule, was
compared with a previous study carried out primarily in the Kruger National Park by
Marx, (1996). The study undertaken by Marx (1996) was carried out during a drought
period, which allowed for the comparison with results recorded after flooding during
the present study. This current research project therefore allowed for the comparison
between two different water sources, namely, that of dams and rivers, and under
varying environmental conditions.
The Aquatic Toxicity index (ATI) developed by Wepener et al. (1992) was employed
to facilitate the comparison between the water physical and chemical parameters that
were measured, at each sample site, with a single variable being calculated for each
sample site per survey. The water quality (ATI values) at the two control sites namely,
Bronkhorstspruit Dam and Balule deteriorated substantially after the floods. High
water levels due to the floods had a dilution effect on the concentration of pollutants
however, toxicants were washed in from upstream and due to surface runoff. The
removal of the purifying reed beds upstream of Balule and at the inflow to
Bronkhorstspruit Dam, resulted in the release of latent sludge containing metals and
organic pollutants into the water column. The ATI value's obtained for the two
control points were similar or even higher than those obtained for the two polluted
sites namely at, Loskop Dam and Mamba for the autumn and winter sampling
periods. During following surveys the water quality at all four sample sites improved,
returning to pre flood values by the last survey in summer, namely reflecting similar
values as those recorded by Marx (1996) at Balule, Mamba and Loskop Dam for the
same period. Sediment concentrations recorded a similar trend to that for water at all
four sample sites throughout the study.
The bioaccumulation study indicated that the gill concentrations recorded were
generally the highest, followed by the liver concentrations. From this one may deduce
that gills were the dominant site for metal absorption by the fish, with the excretion of
metals also taking place via this route. Liver concentrations are an indication of the
activation of protective _mechanisms in the fish sampled, the high concentrations
recorded indicate the high physiological response the fish have had to the various
levels of exposure. The low concentrations recorded in the muscle indicates the
effectiveness of the liver in the detoxification of the fish, indicating that only limited
storage of the various metals tested for took place at this site. Skin concentrations
were quite high, these concentrations represent the products of an excretory process,
which takes place via the skin. The order of concentrations recorded during the
present study, were similar to the orders recorded by Marx, (1996) and other authors,
however, the order of the skin and muscle concentrations were often reversed. This
may be due to the increased excretion of these metals via the skin, resulting from
increased exposure to these metals after the floods. Thus the increased exposure