Page 25 - Dainfern Precinct Living Issue 4 May 2024

NATURE

nvasive alien plants introduced developing countries like South Africa. HOW CAN IAPS BE
and/or spread outside their This damage is aggravated by climate
natural habitats have affected change, pollution, habitat loss and CONTROLLED?
native biodiversity in almost human-induced disturbance. There are four methods that can be used
every ecosystem type on earth to control and/or avert infestations of
and are one of the greatest IAPs are not static and can be IAPs. These are mechanical, chemical,
threats to biodiversity. Such introduced to a new water source from biological and an integrated control.
Iinvasions are among the top one that is impacted by birds, humans,
drivers of biodiversity loss and species boats, jet skis or any moveable object, MECHANICAL
extinction around the world, with via the transfer of IAP seeds, seedlings Mechanical control refers to the use
invasive species having contributed to or plants. These can regrow asexually of machinery to physically remove
nearly 40% of all animal extinctions, as (i.e. vegetatively) and sexually (i.e. IAPs from a system. For example, in an
suggested in a study done by Bellard, seeds), allowing for exponential growth aquatic environment, IAPs such as Pistia
Casey & Blackburn (2016). The problem in the new water source. Environmental stratiotes and Eichhornia crassipes are
continues to increase greatly from an factors such as wind and poor water controlled by raking, mowing or hauling.
ecological, socio-economic and health quality (i.e. high organic nutrients) can Disturbance stemming from the physical
point of view, worldwide. Invasive alien exacerbate the spread of IAPs such removal can cause the seed bank to
plants exacerbate poverty and threaten as Pistia stratiotes (water lettuce) and proliferate, and it is therefore essential to
development through their impact on Pondeteria crassipes (water hyacinth) by have continuous follow-up action in order
agriculture, forestry, fisheries and natural promoting seeding and seed dispersal, to improve efficiency. The disadvantages
systems – which are an important basis as seen in the Vaal River Barrage of this method, when used solely, is that
of peoples’ livelihoods – particularly in Reservoir (VRBR).

Impact of water lettuce on water quality

Quick Facts

1. The area under management for invasive alien plants is
approximately 930 hectares in extent, with numerous reed
beds and other smaller channels on the Vaal.
2. Poor water quality from numerous upstream pollutants
and overflows from sewers have contributed to the reduced
water quality, acting as a feeder for these plants.
3. Rand Water, in collaboration with industry-leading
scientists from the Centre for Biological Control (CBC), uses
host-specific biocontrol agents that have been approved
by the Department of Forestry, Fisheries and Environment;
these will not alter or disturb the natural/indigenous
ecosystems at the VRBR.

4. Rand Water’s water supply will not be impacted by
the integrated control being implemented at the VRBR
because:

• Rand Water does not extract water for purification and
subsequent dispersion from the VRBR.
• The water that is purified and dispersed by Rand Water
undergoes a stringent testing process that is ascribed
to SANS 241; it cannot cause cancer as a result of the
herbicides used at the VRBR.

• Scientists and studies from credible institutions
reiterate that following an integrated control method
is best to reduce IAP populations and limit future
infestations in the long-term.
Water hyacinth and water lettuce in
the Vaal River Barrage System
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