Abstract
Msc.
This study focuses on the functional evaluation of a gold Tailings Storage Facility (TSF), the
Fleurhof TSF (designated slimes dam 2L3), which is representative of gold slimes (tailings)
dams in the Witwatersrand. The aim is to evaluate the rehabilitation status (in terms of
species composition and landscape function) of TSF surfaces that were planted ~20 to ~40
years ago using the most common rehabilitation practice, namely pasture grassing. Pasture
grassing aims to obtain rapid dust control. Mine closure was not considered at the time, and
the vegetation was hence not designed with ecological processes or long-term objectives in
mind. However, over time, grassing practices became routine in the TSF vegetation industry,
and the contribution that they have made towards surface rehabilitation needs to be assessed
against the current site closure objectives.
On the selected site, evaluations of vegetation cover, species composition, and substrate
physical and chemical properties were conducted in 1975 (Thatcher, 1979). The aim of the
current mid-summer study in 2009 was addressed by assessing the same parameters of
vegetation cover, species composition, and soil physical and chemical properties, and
comparing these to the results of the previous assessment in 1975. Landscape Function
Analysis (LFA – an index-based method of evaluating the retention of resources by surfaces
and soil condition), was applied to determine the landscape function (stability, infiltration and
nutrient cycling that are derived from the eleven soil surface assessment indicators), and
compared with the landscape function of natural analogues in the same locality. Landscape
organisation (also an indicator of LFA) was used to investigate the contribution of vegetation
overall, and of discrete plant functional groups to landscape functionality.
A total of 35 plant species were observed in the quadrats (56 species on the TSF overall),
with 51% of species overall being alien. Perennial vegetation and cryptogam covers
contributed the most to stabilising the TSF slopes and flat (top) surfaces. The percentage of
vegetation basal cover on the TSF (30% – 70%) was lower than for analogue grassland sites
on a nearby hill (80% – 100%).
Lower basal vegetation cover on the TSF than on the analogue site, were associated with
lower LFA indices of stability on all TSF slope aspects (P = 8.19 x 10-13 for all aspects),
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lower nutrient cycling for the northern and southern TSF slopes (south aspect P = 4.20 x 10-6;
top aspect P = 0.03), and lower infiltration on the southern slope of the TSF (P = 2.68 x 10-6).
However, a higher infiltration on the northern TSF aspect (P = 0.02) than on the analogue
site, was attained. Perennial tussock grass patch types (which included perennial forbs) made
the largest contribution to the soil surface assessment (SSA) indicators on the TSF and
analogue sites, and therefore to the LFA indices that were derived from these SSA indicators.
The contribution of woody patches to function was not evaluated.