Assessing the effectiveness of South African savanna biosphere reserves in maintaining aquatic ecosystem structure and function
Chilo, Refilwe Pauline
Biosphere reserves are sites established by UNESCO (United Nations Educational, Scientific and Cultural Organization) as scientifically significant. They are not formally protected areas; however, the label promotes a landscape management structure that encompasses sustainable development. The principle of sustainable development recognises the interconnectedness that exists between land use and freshwater resources which results in the interconnectedness of challenges experienced by both aspects. Therefore, land management has an impact on freshwater resources such as headwater streams which play a vital role in riverine processes and have a significant influence on the health of downstream ecosystems. This study investigated the structure and function of headwater streams in the context of Biosphere Reserve (BR) land management. The ecosystem health status and community structure of headwater streams in these reserves was compared to that of headwater streams in adjacent, unprotected sites. Land cover, physico-chemical and macroinvertebrate community data were collected from each stream (6 sites in the Magaliesberg biosphere reserve, 5 in the Marico biosphere reserve, 4 in the Waterberg biosphere reserve and 6 unprotected sites), with macroinvertebrates assessed using a combination of rapid bio-assessment (SASS5) and trophic group classifications. Unprotected sites did not have a single A/B category site, indicating all unprotected headwater streams were modified to some degree. Marico BR, Magaliesberg BR and Waterberg BR all had A/B categorised sites. Category C and D/E/F sites were present in all the BRs but the proportion was highest in the unprotected sites. A total of 6 of the sampling points were in core (conservation priority) areas, however not a single one was unmodified and natural (A category). There was no statistically significant difference between the SASS5 assessment indices of biosphere and unprotected sites. Relative abundances of two Functional Feeding Groups (FFGs), namely filter feeders and predators, were analysed to assess changes in trophic processes and structuring; neither one was significantly different across these management contexts. Although pH had significant correlations with some aquatic macroinvertebrate data, including family-level richness in the macroinvertebrates, there was no statistically significant difference in pH across the range of geology types or ecoregions sampled in the study. This suggests variation in stream pH may be due other processes like acid deposition from urban and mining areas. The overall lack of significant difference in land-cover between BRs and unprotected sites meant that the effects of differing land-cover management practices on the structure of macroinvertebrates assemblages could not be fully explored. Nonetheless, both rapid bio-assessment of river health and comparative analysis of FFGs suggest that the ecological health of headwater streams inside biosphere reserves is improved in comparison to that of adjacent unprotected streams, apart from a few outliers. Therefore, South African savanna biosphere reserves are effective in maintaining aquatic ecosystem structure and function.
A thesis submitted in fulfillment of the requirements for the Degree of Master of Science at School of Animal, Plant and Environmental Sciences Faculty of Science University of the Witwatersrand, Johannesburg