Abstract
The escalating population growth and increased forestry, mining, agricultural and
industrial development in the catchment areas over past years has had a profound
effect upon water quality and quantity, resulting in increased pollution levels and a
reduction in flow rates. This is cause for concern not only to water users in the upper
catchments but also to the down stream user, the Kruger National Park, which is
exceedingly dependent on good quality waters in order to maintain and sustain a large
variety of ecosystems. This study was therefore aimed at investigating the physicochemical,
nutrient and metal concentrations of four major river systems that transect
the park, namely the Luvuvhu, Shingwedzi, Letaba and Sabie Rivers.
By virtue of its position along South Africa’s eastern border the Kruger National Park
(KNP) receives waters from seven major river systems each of which enter via the
western boundary, flow eastwards through the park and on into Mozambique. The
majority of the catchment areas of these river systems are situated upstream of the
park itself making water quality and quantity management an important yet
challenging task.
Water quality is a significant and powerful determinant of health of aquatic
ecosystems. Full assessment of chemical and physical attributes upon the river
systems was supported by biological monitoring thus integrating changes in the
system over time. Water and sediment samples were collected seasonally between
September 2005 to March 2006 at sites outside and inside the borders of the Kruger
National Park. Sites outside were located of sufficient distance from the border so as
to be regarded as representative of water quality conditions before entering the Park.
At each site physico-chemical variables were measured in the water. Two metal
bioaccumulation indicator species (Labeobarbus marequensis and Barbus radiatus)
were also sampled during this time period. These samples as well as water and
sediment samples were analysed for Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn.
Physico-chemical analyses of water and sediment allowed for the separation of the
rivers into two distinct groups. The Luvuvhu and Sabie Rivers grouped together
showing little deviations from normal water quality guidelines. On the other hand the
Shingwedzi and Letaba Rivers deviated from normal values sometimes by large
degrees. This was particularly true for the Letaba 1a site for all physico-chemical
variables barring temperature. Nutrient concentrations correlated with these findings.
Nitrates and Sulphates can be identified as possible problem nutrients; however
historic data suggest levels to be acceptable for these river systems. Multivariate
analysis of sites with regards to physico-chemical and nutrient concentrations
produced three major clusters. Determining factors were conductivity, nitrates,
organic content and grain size of 53 μm.
Fish were utilised as bioindicator organisms in order to quantify the levels of metals
available within each river system. These organisms accumulate metals in their tissues
and thus provide not only instantaneous data but rather a time integrate of measure of
the bioavailability of metals. Although metal concentrations within water, sediment
and fish were not consistently high within one system, three distinct trends were
observed. Firstly metal levels were generally found to occur in slightly higher
concentrations during the high flow periods when waters were turbid; this could be
attributed to increased run off from the surrounding lands as well as increased
exposure to sediment bound chemicals released back into the systems. Secondly a
trend of high concentrations of Cr, Cu, Fe, Pb, Mn, Ni and Zn was found occurring at
the Luvuvhu 1, Luvuvhu 2 and Shingwedzi 1 sites during the high flow sampling.
Metal levels at these sites were consistently higher than those recorded at other
sampling sites. The last trend noted was that the Sabie River on a whole showed lower
metal readings with regard to water, sediment as well as fish samples.
In order to integrate bioaccumulation data and metal concentrations in the different
phases of the water and sediments an equilibrium partitioning (EP) technique was
implemented. Toxic effect-derived quality data is the lowest for Al, Cr, Cu, Pb and
Zn, whilst product standard-based criteria produce the lowest values for Fe, Mn and
Ni. Cadmium values were found to be similar for both criteria. Results indicate that
current water quality guidelines are over protective for Al and Fe, whilst those for Ni
and Mn are too lenient. The EP method has not been utilised extensively in South
Africa and was carried out for the first time upon these river systems, it is thus
essential that further research be carried out.
Recommendations are made as to the continued monitoring of these diverse systems.
It is suggested that each river be looked at in greater detail and that the development
of a field biomonitoring programme should be implemented in order to determine the
impacts upon the biological components and the aquatic ecosystem as a whole. Future
studies should also look at incorporating the use of aquatic macroinvertebrates (SASS
5) as well as other available techniques in order to supply a more detailed assessment.
Prof. V. Wepener
Dr. T. Gyedu-Ababio
Prof. J.H.J. Van Vuren