coaltech upper olifants river catchment wetland inventory ...

3.5.2.4 Water quality
Floodplain wetlands are connected systems with the water in different zones
(compartments). These zones include the permanent, seasonal and temporary wet zones. It
is therefore possible that salts previously deposited during a drying out cycle will be
dissolved and leached from the soil during rewetting. This can contribute to a mineral
exchange between floodwater and sediment. Flooding changes the redox potential in the
wetland that will in turn increase the solubility of metals such as manganese and iron, and
triggers the release of phosphates. The opposite applies when the wetland dries out. The
concentration of nutrients in this wetland type is normally low, due to the dilution effect of
water passing through the wetland. The wet and dry cycles in a wetland, therefore contribute
to the water quality leaving the system. Water leaving the system during a drying out cycle
will have less dissolved salts and will therefore be of a better quality (Palmer et al 2002,
Kotze 2000, Kotze et al 2000).
3.5.2.5 Storage and evaporation of mine water
Wetlands can be used for the storage and evaporation of water, thereby contributing to
potential storage facilities at mine sites. The use of natural wetlands in stead of man made
dams is highly detrimental to the wetland (Palmer et al 2002, Kotze 2000, Kotze et al 2000,
Limpitlaw 1995, 1996).
3.5.3 Sediment trapping
Wetlands play an important role in the sediment balance of streams and rivers. Wetlands
generally slow the water flow in a channel, thereby allowing the precipitation of sediments to
take place. However, should the flow velocity increase, the sediment load in the water will
increase as well (Palmer et al 2002, Kotze 2000, Kotze et al 2000, Kitheka 2003, Zierholtz
2001).
The soil losses in the portion of the UORC investigated by Palmer et al (2002) are moderate
to high, at an average of 44 - 47 tons/km 2 /year. The extent to which wetlands contribute to
sediment trapping in the catchment has not yet been determined. The presence of this
function in wetlands depends on the type of wetland (Palmer et al 2002, Midgley et al 1994).
Wetland Database for UORC - 38 -