Abstract:
Due to the severe regulation, diversion, introduction of exotic species, and pollution of
freshwater systems there has been a significant decline in the overall condition of these
freshwater habitats globally. Of the approximate 79 large river-floodplain ecosystems found
across the world, most are affected by human activities in one way or another. Several
floodplain systems in southern Africa have been identified as floodplains of concern, of which
the Phongolo River Floodplain is one. This is one of South Africa’s largest natural floodplain
systems and the only one in South Africa that sustains permanent pans of water throughout
the dry season. Endorheic wetland systems such as pans are widespread, not only across
South Africa but globally, but are not well studied. This is mainly due to the belief that they
have no important functions in the ecosystem or have very few functions similar to other
wetland types.
Scientific research in South Africa has largely neglected endorheic aquatic ecosystems,
particularly in terms of biodiversity. This has led to a general state of degradation and a distinct
lack of information about biodiversity of most of these habitats. Study of these habitats is key
to maintaining high biological diversity in the overall ecosystem and because South Africa is
a water scarce country, there is a limited extent of freshwater ecosystems, meaning loss and
degradation of such habitats has a greater effect on the natural ecosystem than in tropical
countries. Research has also shown that small aquatic ecosystems contribute a great deal to
regional diversity and are important ecosystems as they support a large and diverse number
of invertebrate species. Under international obligation by the Convention on Biological
Diversity (CBD), South Africa must work towards conserving its biodiversity and this can only
be done if there is a proper assessment of biodiversity of all habitats.
The Lower Phongolo River and floodplain is of considerable interest and value as it is utilised
by both resident human populations from Ndumo and Phongolo and a very diverse range of
biota. This places a great deal of pressure on the system, as both subsistence and small scale
commercial agriculture occur in the region and large scale agriculture irrigation schemes also
operate to the south, within the Phongolo River catchment. The Ndumo Game Reserve (NGR),
located on the Lower Phongolo River Floodplain, was chosen as the study region. The reason
for this is that the NGR was proclaimed in 1924 with the primary objective to establish a
protected area that would conserve the floodplain’s natural biodiversity. The NGR would then
also protect the ecological integrity of the ephemeral and floodplain pans as well as the
Phongolo and Usuthu River systems that flow through it. The NGR was also placed on the list
of Wetlands of International Importance in terms of the Ramsar convention in 1997. It has,
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however, never been determined whether or not the NGR does indeed protect the biodiversity
of the floodplain or the ecological integrity of the aquatic systems.
Macroinvertebrates are important species for assessments of the ecological integrity of
wetland systems. These biota are good indicators of disturbance and are particularly sensitive
to organic compounds and human-induced disturbances. Disturbances in wetlands are thus
reflected in the macroinvertebrate abundance and type of species present. For these reasons,
aquatic macroinvertebrates have become one of the most commonly used organisms for
biomonitoring and is why they were the chosen study organisms of this dissertation. This study
specifically addressed biodiversity of macroinvertebrates found in ephemeral and floodplain
pans located within a protected area (NGR) and outside this protected area. This main aim
was to provide baseline information on the biodiversity of macroinvertebrates, determine
which abiotic factors possibly affect macroinvertebrate distribution, and determine whether the
NGR is in fact protecting biodiversity.
Three surveys were undertaken and a total of 51 pans were selected for sampling. A single
macroinvertebrate and water sample was collected at each possible site during every survey.
The first survey took place in February (wet season), the second survey in September (dry
season) and the third survey in December (controlled flood season). Macroinvertebrates were
identified to lowest possible taxonomic level and water quality analysed for various nutrients.
Analysis of macroinvertebrate biodiversity indicated that the Phongolo River Floodplain is
indeed a biodiversity hotspot as termed by previous studies since 155 taxa from 68 families
and 21 orders were identified during the study. Diversity may have been even greater as many
macroinvertebrates could not be identified to species level. Specific adaptations and
evolutionary traits affected distribution of macroinvertebrate taxa between ephemeral and
floodplain pans. Macroinvertebrates commonly found in temporary systems, such as
zooplankton, were more prominent in the ephemeral pans while taxa more adapted to
permanent water and not able to withstand desiccation were found in floodplain pans. Water
nutrient analysis indicated the water was generally of good quality although nitrates were high
in floodplain pans within the NGR during the wet season due to increased animal faeces
entering the pans. Macroinvertebrate abundance was greater in floodplain pans outside the
NGR while general biodiversity was higher within the NGR. Results indicated that the
controlled flooding from the Pongolapoort Dam increases biodiversity and water nutrient
quality of the floodplain pans. Ephemeral pans within the NGR had a much greater biodiversity
and higher abundance of macroinvertebrates than ephemeral pans located outside the NGR.
This was attributed to anthropogenic activities outside the NGR such as habitat fragmentation,
whereas ephemeral pans within the NGR are protected from such activities. Ephemeral pans
had greater biodiversity and abundance of macroinvertebrates than floodplain pans possibly
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because floodplain pans contained vertebrate predators such as fish which fed on
macroinvertebrates.
This study was successful in identifying and describing the biodiversity of macroinvertebrates
from ephemeral and floodplain pans of the Lower Phongolo River Floodplain. It was found that
anthropogenic activities, though present, are not affecting pans outside the NGR as much as
expected as many similar macroinvertebrate taxa were found both within and outside the
NGR. Results from this study will be used in order to create an ecological risk assessment of
the Lower Phongolo River and provides important baseline information to the lack of available
macroinvertebrate data.