coaltech upper olifants river catchment wetland inventory ...

More important in the removal of metals is the role played by algae. Algae are manganese
accumulators and can accumulate other metals as well. The metal uptake ability of algae is
controlled by the specific bioaccumulation and physical-chemical factors present. Although
algae can accumulate vast amounts of metals in relation to mass, the distribution of algae in
wetlands is limited and therefore the total metal uptake by algae in the wetland. The most
important role of plants in the removal of metals from the system are therefore not in the
accumulation of metals, but in changing the environment to that more suitable for the
removal of toxicants (Palmer et al 2002, Kotze 2000, Kotze et al 2000).
Acid mine drainage has entered the Kromdraaispruit wetland (located approximately 20 km
north-west of Witbank) for 20 years, a wetland with distinct morphological zones. The
Kromdraaispruit wetland is located in the Kromdraaispruit, a tributary of the Zaalklapspruit,
flowing into the Wilge River. Vegetation in the wetland removes high percentages of influent
metals. The accumulation of iron and manganese takes place in the roots and aerial parts
(stems and leaves) of the wetland vegetation (Limpitlaw 1995). It was determined that the
biochemical water quality of acid mine drainage passing through a wetland improves with
distance moved through the wetland. It was also determined that the concentration of
sulphate-reducing bacteria increases with distance away from the pollution source (Limpitlaw
1996). The immobilisation of metals was best in the areas of optimal organic adsorption of
metals (Limpitlaw 1995, 1996).
Permanently wet seeps can function to reduce nitrate, sulphate, iron and manganese. Where
there are both nitrates and sulphates in the groundwater competition occurs for the available
carbon and reduction is therefore a slower process. Similar processes occur in the seasonal
seeps, but the leaching of immobilised substances can occur before soil saturation, thereby
affecting changes to the redox potential and pH of the site. Organic materials in the wetland
are lost when the water levels drop (Palmer et al 2002).
Wetland Database for UORC - 37 -