Abstract
M.Sc.
The water quality in the Vaal River system has deteriorated due to increasing industrial, mining and
agricultural activities in the Vaal Dam and Vaal River Barrage catchment areas. This study was
undertaken to determine the water quality in the Vaal Dam, and three localities within the Vaal
River Barrage reservoir (i.e. the Riviera Aquatic Club, Abrahamsrust Pleasure Resort and at the
Barrage structure). The objectives of this study, was to determine the fish population species
composition, evaluate the general health of the selected fish species and obtain site specific metal
bioaccumulation data for each locality. Suggestions and proposals for future monitoring and
management of these waterbodies were also made.
Metereological information on the Vaal River Barrage area was supplied by Rand Water, as well as
physical and chemical data of fixed localities, sampled fortnightly (January 1997 to September
1998). In addition, water samples were collected at the Vaal Dam and the three Vaal River
Barrage localities mentioned above, during February, May, August and November 1997. These
samples were analysed by the Chemistry Department of the Rand Afrikaans University in
accordance with standard methods. The chemical and physical characteristics and metal
concentrations (aluminium, cadmium, calcium, copper, iron, magnesium, manganese, nickel,
strontium and zinc) of these separate sets of data were then compared with Rand Water's Raw
Water Quality Criteria. The aluminium, ammonia, chromium, copper, dissolved organic carbon,
fluoride, iron, lead, manganese, nitrate, sulphate, total hardness and turbidity variables did not
comply with the recommended guideline values. No guideline levels for strontium are available,
however.
Sedimentation, turbidity, salination and eutrophication within the Vaal River system play an
important role in the bioaccumulation of metals by benthic organisms. Metals that adsorb to
sediment particles, through various processes, are generally more persistent and less mobile than
those in the overlying water and pose a severe long-lasting threat to the aquatic environment.
Generally, the highest metal concentrations (AI, Cd, Cu, Fe, Mn, Ni, Pb, Sr and Zn) in the sediment
samples collected at the four localities and seasons, were found in the finer sediment classes
(class D). The Riviera Aquatic Club locality had the highest overall concentrations of the metals
analysed.
The adult fish communities within the Vaal Dam and Vaal River Barrage were assessed, as it is
believed that the fish community structure is indicative of environmental conditions. Adult Labeo
capensis, Labeo umbratus, Cyprinus carpio, Clarias gariepinus, Barbus aeneus and Micropterus
sa/moides, were collected (using gill nets) to determine the adult fish community composition and
age. When compared with a study conducted by Mulder (1971), it is clear that Labeo capensis has
remained the most abundant species within the system, but that Barbus aeneus has now been
replaced by Labeo umbratus as the second most abundant species. Furthermore, age
determination tables (Mulder, 1971) were used to classify the fish population between the ages of 2
and 7 years. This indicates a healthy, dynamic community structure where recruitment is taking
place.
The Health Assessment Index (HAl) was used to determine the general health of the two fish
species selected for metal analysis (i.e. Labeo capensis and Labeo umbratus). Except for
moderate to severe gill damage recorded, no damage to external variables, were of concern.
However, both Labeo capensis and Labeo umbratus had high percentages (89% and 93%, respecii
tively) of abnormal livers. Using the Plascon Colour Chart (Watson, personal communication),
these livers were classified as ranging from tan to "coffee with cream" in colour. High haematocrit
and plasma protein levels were observed and could be due to environmental stress, while the
White Blood Cell Counts were within normal ranges. Generally speaking, only mild to moderate
parasite infections were observed and probably do not pose a serious health threat to the fish host.
Total HAl values for Labeo capensis indicate that this this fish population was in relatively good
health, but too few Labeo umbratus individuals were collected to make accurate assumptions
about this population.
Metal analysis (AI, Cd, Cu, Fe, Mn, Ni, Pb, Sr and Zn) was carried out on the tissues and organs
(skin, muscle, gill filaments, gill arches, liver, hindgut content, gonads and vertebrae) of Labeo
capensis and Labeo umbratus, collected during the study period. Only aluminium, iron and
strontium are discussed. Aluminium concentrations were relatively high at all of the localities, but
as pH values were mostly alkaline, aluminium is rendered biologically unavailable and as for iron,
was mostly accumulated in the non-edible portion and viscera of the fish. Strontium accumulates
in bony tissues due to its similarity with calcium, but is not essential for bone formation. The
human health risks of these metals in the edible portion of the fish still have to be refined and
communicated to the general public of South Africa.
In conclusion, this baseline study has determined the metal concentrations in the aquatic
environment (due to anthropogenic activities) that may be accumulated by fish and may affect the
adult fish community structures and their general health.