Macroinvertebrate biodiversity from selected ephemeral and floodplain pans of the lower Phongolo River

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, Summary vii 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 Summary viii 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.