An analytical investigation of the biophysical factors that inhibit successful ecological restoration of gold tailings dams
Van Wyk, Stephanus Johannes.
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The sphere of influence of gold tailings dams has a considerable detrimental impact on the environmental quality of numerous aquatic and terrestrial ecosystems and directly or indirectly affects human living standards. It is therefore of utmost importance to find a persistent modus operandi to restore this wasteland and to mitigate the negative results associated with these tailings dams, which mainly include air, soil and water pollution. The inherent nature of gold tailings material though, does not submit to the expectations of ecological principles derived from natural systems after ecological restoration is applied. It is therefore necessary to investigate and describe this unnatural medium with its associated characteristics, and the responses of vegetation as reflected by ecosystem development. Through this ecological assessment, restoration techniques could be refined, which could lead to sustainably viable solutions. This study investigates various integrated facets of gold tailings revegetation, focusing on the soil-vegetation interaction, and the proposal of numerous variables to describe and evaluate ecological performance within the framework of sustainability. Through the assimilation of basic quantitative data and monitoring of restoration performance at different time intervals, the stability and long-term effectiveness of ecological restoration of gold tailings media at various stages of the remediation curve is assessed. An overview of restoration indicates that only a more holistic approach in the form of ecological reconstruction should drive ecological remediative processes, and using existing scientific criteria, which are based on basic ecological principles, self-sustaining ecosystem development could be achieved. Results from soil analysis, vegetation abundance and species performance data of pot trials and field surveys, were multivariately and statistically analysed to establish significant limiting and interacting variables, which determine the performance of revegetated systems. The influence of these topoedaphic variables, which included macro-and microclimatological factors, soil physical and chemical parameters and eventually plant species resemblance, was established through the assessment of experimental growth models, and soil and vegetation dynamics on established revegetated gold tailings dams. The manipulation of these variables through soil profile reconstruction, which implies physical fraction reshuffling and either chemical dilution or enhancement, as well as aspect (microclimatological) and soil chemical changes, showed major responses to seedling abundance, species composition and secondary successional associated characteristics. The major existing need for ecological standards criteria were also addressed through the assessment of a statistically sound method, which was based on scientifically derived floristic information. Several ecological indicators of functional return were identified and the method used was further extended not only to indicate the re-occurrence of ecological sensitivity indicators, but also to give clarity on the functional performance and ecological blending of the revegetated areas. The question surrounding the characterisation of these ecologically dissimilar areas as separate systems with different (new) ecological principles was, however, highlighted through this study and future research should focus on defining these principles as well as short-and long-term modelling of revegetated areas. The contribution of this research to restoration ecology is significant with regards to the intensive investigation and explanation of characteristics and processes that will drive ecological succession and determine restoration success.