OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

• Decreased light penetration to the bottom sediments, leading to a dramatic loss of benthic photosynthetic
organisms. Examples are to be found in the lower reaches of the Olifants River following sediment scouring
of the Phalaborwa Barrage.
• Clogging of fish gills, preventing them from breathing and leading rapidly to death. This can cause a
dramatic change in the composition of fish populations, with only those species able to breathe air being
able to survive (e.g. Barbel, Clarias gariepinus). Examples of this feature are to be seen downstream of
some clay pits near Pretoria, where large volumes of fine sediments are occasionally released during
rainfalls.
• Coating the surface of aquatic plant leaves with a layer of fine sediments that prevent photosynthesis and
lead to the death of the plants. Examples can be seen in the middle reaches of the Olifants River where
accelerated erosion of mine waste rock piles leads to increased levels of suspended sediments.
• Deposition of (previously suspended sediments onto the bottom of river beds when water flow rates decline
leads to the smothering of both micro- and macro-habitats for aquatic invertebrates. This loss or alteration
of habitat results in a rapid loss of these organisms and interruptions in the food webs of the affected area.
Again, specific examples of this can be seen in the middle and lower reaches of the Olifants River in South
Africa. An additional example is provided by the lower reaches of the Mazowe River in Zimbabwe and
Mozambique where artisan alluvial gold mining has caused a dramatic increase in suspended sediment
levels. A similar situation has been recorded from the artisan alluvial gold mining on the Luenha River in
Mozambique.
• Suspended sediments occur in a variety of different particle sizes and often “carry” considerable quantities
of adsorbed ions, especially metal ions; these present a potential toxicity problem to both aquatic and
terrestrial organisms. Occasional examples of this have been recorded from the Mwambashi River on the
Zambian Copperbelt, where cattle died after drinking river water containing particles of suspended /
adsorbed copper.
6.1.6 Changes to patterns of water supply and demand
All mining activities require water for a wide variety of processes, from dust suppression after blasting and
during ore conveying, to dissolution of the commodity of interest and to transportation of waste sludge and
tailings to disposal sites. In addition, water is also needed for domestic purposes for mine workers and their
families. Impacts associated with changes to patterns of water supply and demand are normally greatest in arid
and semi-arid areas. Specific concerns relate to:
• In arid areas, the quantity of water required by a specific mining operation can have a dramatic influence on
the regional water balance. Inevitably, the promise of economic returns from mining will have an influence
on decision-making by water supply authorities as to whether or not the required water should be supplied.
In turn, the provision of water to a mining operation will mean that less water is available for other users,
including the aquatic environment.
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