Aquatic invertebrate assessment of the Seekoeivlei Nature Reserve

Abstract

The maintenance of wetlands is greatly encouraged because of their importance in the hydrological cycle and the habitat they provide for a variety of organisms. Wetlands are known for their connection between the terrestrial and aquatic environments that leads to a habitat of which certain organisms depend on for survival. The Ramsar Convention was originally adopted for the preservation of birds, their migratory routes and breeding areas that depends on wetland environments. Later the spectrum was broadened to preserve all aspects of wetlands as well as to encourage the wise use of wetlands. The Seekoeivlei Nature Reserve is one of the 23 wetlands that is designated as a Ramsar Wetland of International Importance in South Africa. The Seekoeivlei Wetland as a whole cover approximately 12 000 hectares and consists of approximately 220 oxbows formed by the meandering of the Klip River in the Frees State Province. The Seekoeivlei Wetland is considered important because of the Klip River, being an important tributary of the Vaal River. The Vaal River supplies the majority of water to the main industrial areas in Gauteng Province. However, very little is known about the aquatic biodiversity of the Seekoeivlei Wetland. Therefore, the aim of this research project was to establish the diversity, community structure and the distribution of the zooplankton and aquatic macroinvertebrates of the Seekoeivlei Nature Reserve. Water and sediment samples were collected from 21 selected sites located throughout the Seekoeivlei Nature Reserve and just outside of the reserve. Zooplankton and aquatic macroinvertebrate samples were collected from 17 of the 21 selected sites whereas the remaining sites only water and sediment samples were collected. All samples were collected during three seasonal surveys in July 2016 (winter), December 2016 (summer) and March 2017 (autumn). Water and sediment samples were collected in situ and transported back to the laboratory for further analyses. Water samples were analysed to determine nutrient and metal concentrations. Sediment analyses were conducted to determine particle size, percentage organic and metal concentrations. Water and sediment samples showed natural levels of nutrients and sediment present in the Seekoeivlei Wetland. Zooplankton and aquatic macroinvertebrates were sampled using accepted techniques followed by the identification to the lowest taxonomic level possible. Zooplankton biodiversity showed a total of 17 taxa from eight families and four orders that were identified during this study. Seasonality originally was hypothesised to have an impact on the distribution of the zooplankton, but statistical analyses showed no significant differences between the various seasons. Wetland type were also hypothesised to have an impact on the zooplankton distribution and communities, and it was found that the majority zooplankton taxa were rather present in the oxbow and pan sites than in the river. A total of 87 macroinvertebrate taxa from 51 families and 14 orders were identified during this study. The zooplankton and macroinvertebrate diversity are potentially greater as many of the invertebrates could not be identified to species level due to inadequate keys. Functional feeding groups within the macroinvertebrate communities showed that the most abundant groups were the predators and grazers. This study was successful in identifying and describing the diversity of zooplankton and aquatic macroinvertebrates present in the Seekoeivlei Nature Reserve. This project provided updated information regarding the aquatic invertebrate diversity that could potentially feed into the management plan as well as increasing the understanding of this dynamic ecosystem.