Capturing baseline vegetation data, including an assessment of plant sensitivity to increased acidity, in the Waterberg
Global environmental change due to anthropogenic activity results in alterations to the Earth’s biogeochemical cycles. This study focused on nitrogen and sulphur deposition, which results in the acidification of ecosystems. Alterations to these processes will have an effect on the diversity and ecophysiology of the vegetation; moreover, little is known about the long-term impacts on the vegetation structure and composition. Increased development, mining and industrialization, within the Waterberg area, particularly with the construction of the Medupi power station, have resulted in this area coming under study. The impacts of additional air pollution to the vegetation in this area are currently unknown. The aim of this research was to determine whether increased ambient levels of atmospheric nitrogen and sulphur, resulting from the power stations, will impact the structure, functional type and the composition of the vegetation, and the resultant impacts on vegetation structure and growth as a result of the added nitrogen and sulphur to the system and increased acidity. A baseline of quantitative data was needed in order for future comparisons to be made to assess whether biodiversity is changing and at what rate. One part of the study involved the collection of baseline vegetation data along a pre-determined transect in the Waterberg area. A transect was identified which could serve as a vehicle for monitoring changes over time, with areas downwind of the Matimba and Medupi power stations assumed to be more impacted than areas upwind. The two downwind sites and the two sites closest to the power stations were found to have the highest beta diversities, with the two downwind sites having a value of 0.60 and the downwind Landelani site and upwind Withoutpan site having a value of 0.53. The high species variation between these sites may already be an indication of pollution impacts within the area. The downwind site closest to the power stations, Landelani, is particularly vulnerable as it has a high Shannon diversity index, with a value of 2.84, and high tree biomass, 46.64 tonnes/ha, with low tree density, 625 trees per hectare. iii Functional groups are assumed to react similarly under changing environmental conditions. The second part of this research focussed on photosynthetic pathways, by using two C3 woody species and two C4 grasses. The experiment was conducted in the greenhouse at the University of the Witwatersrand and showed that both tree and both grass species selected were sensitive to sulphur additions to varying degrees. Additionally Acacia sieberiana was found to be sensitive to nitrogen addition, however Combretum erythrophyllum responded to nitrogen when it was added alone. A positive response to nitrogen was seen in both grass species; however the positive response was negated by the addition of any sulphur in Eragrostis curvula. In Panicum maximum the positive response in growth to nitrogen addition exceeded any negative effects from the sulphur addition. The results of plant growth to increasing soil acidity were different between functional groups and within functional groups. A relationship between the increase in the average above and below ground mass was found to exist with a decrease in soil acidity in Acacia sieberiana (R2 = 0.45). A relationship between an increase in the average above and below ground mass with a decrease in soil acidity in Eragrostis curvula was also seen (R2 = 0.31). Changes to the structure and composition of vegetation in this area will impact land use and the management thereof, impacting land users and owners ability to generate an income and therefore their livelihoods. Changes to vegetation structure and composition will also have a greater overall effect by impacting ecosystem functioning and resilience to future disturbances.
dissertation submitted to the faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2015.