Changes in floristic and functional composition on a complex of gold tailings dams near Carletonville, North West Province, from 1996 to 2014

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2016

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Maguranyanga, Mike

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Abstract

A vegetation survey was carried out in July 2014 on the substrates of 5 tailings dams by selecting 10 sampling sites which were previously used as sampling plots during the 1996/97 survey of Weiersbye et al. (2006). At each sampling site a 100m transect horizontally across the substrate and covering all levels of the tailings dam from the flat top to the toe paddock was established. Each transect was surveyed for the frequency of the species occurring and these were categorized based on their mode of colonization (natural, intentionally introduced and persisting) while tailings were collected by digging approximately 20cm into the ground for soil sample collection per substrate. The recorded species were then divided using Raunkier’s classification categories into growth forms and a comparison was done between the two surveys (2014 versus 1996/7) to identify the species that were lost, those that were still persisting and the new ones that had colonized over time. A total of 51 species (over 15ha) in 36 genera within 14 families were recorded on the tailings dams, compared to 168 species (over 765ha), 98 genera and 59 families found in the previous study. Families with the most species in 2014 were similar to those of the 1996/97 survey, following the dominance order of Poaceae >Asteraceae >Fabaceae >Anacardiaceae, with the percentage frequency of grasses (Poaceae) noted to have almost doubled over this period. Compared to 6 species common across the substrates in the previous study, the later survey recorded 12 common species (6 of the species occurring on all substrates) but overall both studies found vegetation cover to be high (above 65%) on flat tops and berms with species richness being high on the toe paddock>slopes>tops and berms and substrates susceptible to low nutritional (N,P,K,C) value. Indigenous plant species (54.9%) were dominating the tailing dams and were mostly perennials (82.3%) that were naturally colonizing and persisting (72.5%) on the tailings dams (similar to the 1996/97 survey), while alien (45.1%) plant species comprised annuals/biennials (17.7%) that were intentionally introduced (27.5%) prior to the 1996/97 survey by contractors. The ceased ameliorative initiatives since the first survey are believed to have significantly contributed to a decrease in herbaceous species richness, which formed the majority of the introduced species in the former survey (58.8% compared to 29.4%) as they depended on the supplementary additions of fertilizers and lime. Approximately 117 species, 62 genera and 45 families (including Chenopodiaceae, which was dominant) were lost over the 17 years period, the majority of these were introduced prior to the 1996/97 vegetation survey, while only Ficus sp. was the only new species colonizing apart from the increase noted in alien species (some invasive in nature). The decrease in species richness has encouraged woody and semi-woody (35.3%) and grasses (35.3%) to dominate the slimes reaffirming their potential as temporal and long term rehabilitation species that have developed physiological tolerance to acidic conditions, salinity and heavy metal pollution. In conclusion, this study has identified the species that can be used for phytoremediation to provide long terms solutions for dust, air and water pollution and soil erosion suppression for rehabilitation of these contaminated lands (Appendix 8). The survey also helps to identify species that are able to naturally colonize and persist on the tailings dams without supplements, making them ideal economic species to use for rehabilitation. Results also highlight the negative impacts of the lack of ameliorative supplementations, which in turn affects the floristic composition and structure on these tailings dams over time. Keywords: Aerial cover, Macronutrients, Tailings dams, Species richness, Tailings Storage Facilities (TSFs) and Vegetation survey

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A research report submitted to the Faculty of Science, University of the Witwatersrand, in partial fulfilment of the requirements for the Degree of Master of Science by Coursework and Research Report. Johannesburg, March 2016.

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Maguranyanga, Mike (2016) Changes in floristic and functional composition on a complex of gold tailings dams near Carletonville, North West Province, from 1996 to 2014, University of Witwatersrand, Johannesburg, <http://wiredspace.wits.ac.za/handle/10539/21737>

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