Abstract
M.Sc.
The Department of Water Affairs (DWA) through the National Water Act 36 of 1998 (NWA) recognises that river management in South Africa is extremely important and consequently the ecological integrity of our river systems must be upheld. The conservation of our aquatic resources and aquatic ecosystems can only be achieved by the holistic management of the resources itself, and in turn the aquatic biodiversity. As such, the National River Health Programme (RHP) through the DWA has been formulated to identify and monitor the current ecological state of South African rivers (Balance et al., 2001). The Luvuvhu and Olifants Rivers in the Kruger National Park (KNP) have been monitored in terms of the River Health Programme, but little published literature is available on their biological communities as determined by the use of accepted indices such as the SASS5 protocol (Dickens and Graham, 2002) and the Fish Response Assessment Index (FRAI) (Kleynhans, 2007a). This project therefore studied the two rivers on an individual basis, as well as comparing them to each other.
The working hypotheses for this project are that:
(1) In comparison to the Luvuvhu River, the biological communities of the Olifants River in the KNP have been negatively affected by anthropogenic impacts; and
(2) The ecological integrity of the biological communities improves as the Luvuvhu and Olifants Rivers flow though the KNP.
To test these hypotheses the aims and objectives of this project were to:
(1) Determine the fish and macroinvertebrate biological community structure in the Olifants and Luvuvhu Rivers in the KNP;
(2) Determine the in situ water quality of the two rivers; and
(3) Determine whether the changes in the biological communities along the two rivers can be related to anthropogenic stressors on the rivers from sources outside the KNP.
The research methodology for this study was based on the implementation of the various indices used by the RHP for the biological communities sampled. Four sites in the Luvuvhu River and five sites in the Olifants River were selected based on data availability and site accessibility. The SASS5 protocol was used to assess the macroinvertebrates, and the Fish Response Assessment Index (FRAI) was used to assess the fish communities. In situ water quality parameters were assessed against South African Water Quality Guidelines for Freshwater Ecosystems (DWA, 1996) and the Kruger National Park’s thresholds of potential concern. This was done to determine the health of the biological communities in terms of
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anthropogenic stressors, and then to assess the trends seen between the individual sites, and between the two rivers. Various univariate diversity indices were used to assess community structure. Multivariate statistical analyses were performed on the water quality as well as the macroinvertebrate and fish communities to establish any temporal and spatial trends. PRIMER and CANOCO computer software were used to construct hierarchical clusters and NMDS plots for the biotic communities, while PCA bi-plots were used to represent the water quality variables and their effects on the biotic community structure.
The ecological integrity of the biological communities of the Olifants River has deteriorated. The fish and macroinvertebrate communities have declined in terms of species richness and abundance, as well as community structure. However, macroinvertebrates were not found to have diminished as drastically. This is due mainly to the fact that they respond rapidly to changes in conditions, and the 2010 season was a good one regarding habitat and water quality. As such they increased in diversity and number, but on the whole, this will change as the trend of decreasing species richness and abundance will continue. The decrease in water quality can be said to be a driver of these results, as the in situ variables revealed that the EC for the Olifants is extremely high. The abstraction of water upstream has led to an overall reduction in flow, and as such habitat availability is reduced, and fish and macroinvertebrate communities relying on these habitats have been negatively affected. There has been no increase in biological community integrity from the point where the Olifants River entered the park, to where it left the park. In fact, there has been a decrease in the integrity along the length of the river. The loss in biological community structure can therefore be attributed to habitat loss through water abstraction and the adverse water quality from the numerous anthropogenic influences upstream.