Academic Wits Research Outputs (All submissions)
Permanent URI for this collectionhttps://hdl.handle.net/10539/36827
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Item Attenuation of pollution arising from acid mine drainage by a natural wetland on the Witwatersrand(Academy of Science of South Africa (ASSAf), 2017-01) Humphries, M.S.; McCarthy, T.S.; Pillay, L.Wetlands are well known to be efficient at sequestering pollutants from contaminated water. We investigated metal accumulation in the peats of the Klip River, a natural wetland that has received contaminated water from gold mining operations in Johannesburg for over 130 years. Previous work conducted in the downstream portion identified the wetland as an important system for sequestering metals. We focused on the upstream section of the wetland, more proximal to the source of acid mine drainage, to provide a better understanding of the pollutant sources and the role of the wetland in pollutant attenuation. Geochemical and mineralogical analyses of peat cores revealed considerable metal enrichments in the peat ash, particularly in Co, Ni, Zn, Pb, Cu and U. Metal concentrations are typically between 4 to 8 times higher than those previously reported for the downstream, more distal portion of the wetland. The distribution of metal accumulation within the peat profiles suggests that contamination arises from a combination of sources and processes. Elevated concentrations in the shallow peat are attributed to the input of contaminated surface water via tributaries that drain the Central Rand Goldfield, whereas enrichments in the deeper peat suggest significant sub-surface inflow of contaminated water through the underlying dolomitic rocks. Metal immobilisation occurs through a combination of mechanisms, which include the precipitation of gypsum, metal sulfides, Fe-Mn oxyhydroxides and phosphates. Our study highlights the environmental and economic importance of natural wetland systems which have the ability to accumulate large quantities of metals and thus remediate polluted waters.Item Resilient Densification: Four Studies from Johannesburg(South African Research Chair in Spatial Analysis and City Planning; Gauteng City Region Observatory, 2015) Todes, Alison; Harrison, Philip; Weakley, DylanUnlike most cities in the world, over the last 20 years Johannesburg has become more dense and more compact. This reflects the increased rates of rural-urban migration from the late 1980s as urbanisation controls collapsed, but also the relative success of Johannesburg’s economy and democratic-era policies to contain urban sprawl (such as the urban development boundary). The ending of apartheid regulations allowed a release in a pent-up demand for access to large cities with much of the movement directed to the three large metropolitan cities in Gauteng. Densification in the city has occurred in both planned and unplanned ways. In line with directions in planning internationally, post-apartheid planning has placed strong emphasis on urban densification and compaction. At the same time, however, market forces (both formal and informal) have driven densification in the city, in ways that are often unforeseen and sometimes contrary to city policies. In order to plan for further development and to respond effectively to the densification that has happened, and is occurring, research into the processes and effects of densification is clearly needed. In this work we use an “urban resilience lens” to investigate four forms of residential densification in Johannesburg, using four illustrative case-studies. We explore the effects that densification is having in the city, showing how diverse, complex and contingent it often is.