Abstract
M.Sc. (Aquatic Health)
Urban impoundments play both a recreational and functional role in the urban areas.
From the recreational point of view these impoundments offer aesthetically pleasing
environs as well as habitat for aquatic organisms in a built environment. The
functional role of impoundments is related to attenuation of storm water run-off that is
released into urban water courses. Storm water run-off can have adverse effects on the
ecological integrity of aquatic ecosystems. Water quality will influence other physical
and biological components of these systems. It is for this reason that the ecological
health of impoundments is assessed from an ecotoxicological perspective, focusing on
Westdene and Emmarentia dams in Johannesburg.
It has become common practice to use aquatic biota to assess the impacts of human
activities on aquatic ecosystems. This is because animals and plants can provide a
long-term integrated reflection of water quality, quantity, habitat quality and other
environmental conditions. Water and sediment quality were assessed by applying
standard techniques and protocols. Fish were utilized as bioindicator organisms in
order to quantify the concentrations of metals available in the dam. Abundance of the
macro invertebrate community was also measured. Physico-chemical water analyses
were done during each sampling period to assess the water quality against the South
African Water Quality Guidelines.
Ammonia, which can be toxic to aquatic life, remained high in both dams. High
phosphate concentration during the low rainfall season in Westdene Dam could result
in eutrophication related problems. The microbiological analysis of the water suggests
that the main cause of faecal and total coliforms contamination of the impoundments
possibly originates from dominant birds, African Sacred Ibis (Threskiornis
v
aethiopicus) and Egyptian Goose (Alopochen aegyptiaca ) in the dam and others water
birds frequenting the dams.
Abnormally high concentrations of the heavy metals Nickel and Chromium were
found in the water body and fish (Clarias gariepinus and Tilapia sparmanii ) thus
indicating bioavailabity of these metals resulting in bioaccumulation in fish. High
concentration of Lead in sediment was recorded and may greatly impact benthic
macroinvertebrates population and their habitat.