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Please send us your
feedback on what you, our members, enjoy and
would like in the form of Friends of
Rietvlei activities. What walks would you
prefer; what kind of talks do you like.
»»» Send us an email or a note with your
ideas.««« |
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Walks & Talks |
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The wet weather we have experienced through most of
August and September has curtailed our outdoor
activities. We did manage a pleasant walk on Sunday
24 August on the old Kynoch site, unfortunately only
a few people turned up – but we had a pleasant walk
to the old canal and then down along the new
rehabilitated Duikersvlei stream on the southern and
western boundaries of the property. The old part of
the stream is an unsightly concrete channel, but the
banks of the new part is well planted and looks very
natural, if it hadn’t been for the visible gabions
in places one would not know that this is a
realignment of the original stream. |
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Our end-of-year function and the students’
report-back on their projects will be a joint event
between Friends of Rietvlei and Friends of BCA on
Thursday 20 November; this will be at the Rietvlei
Education Centre at 19h30 for 20h00. As we are
celebrating the end of 2008 together we would ask
you to bring a plate of snacks to share. All are
welcome so bring friends and neighbours. There will
also be a power-point presentation on Milnerton
Conservation Area, so don’t miss this evening! |
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Our next walk will be in the Milnerton Conservation
Area on Sunday 23 November at 15h00; Jeremy Keyser,
the Environmental Conservation Manager, will be
accompanying us and showing us this gem of a
conservation area. Meet at the third circle in Grand
National Boulevard at the entrance to the northern
part of the conservation area. From Racecourse Rd at
the Paddocks Shopping Centre, turn into Grand
National Boulevard at the traffic lights – carry
straight on past two traffic circles to the third
one. Parking space is limited, so share vehicles if
possible. Wear sturdy walking shoes. |
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FOR QUERIES ON THE TALK AND WALK CONTACT PAULINE 083
2552537 OR 021 5576920 (A/H) |
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Estuary Management Plan |
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The public meeting on 15 September in the Blaauwberg
Subcouncil Chamber was quite well attended, although
it appears that the majority of the public were
members of Friends of Rietvlei. There were a few
representatives from some of the ratepayers
associations, but many missed out on the opportunity
to provide inputs into the process. |
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At the meeting Dr Lynne Jackson of the consultants
Peak Consulting gave a presentation outlining most
of the problems that the Diep River is experiencing.
The immediate outcome of the meeting was that three
technical working groups were established to look at
water dynamics, water quality and biodiversity in
the system respectively. These technical working
groups met during October, with further work
continuing during November. The Friends of Rietvlei
has been represented on these working groups. The
findings of the study and a draft Estuary Management
Plan will be presented to the public shortly. Please
contact Niel Van Wyk on 021 5528305 should you want
to discuss this feedback. |
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Rietvlei Visitor Facility Upgrading |
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In our previous newsletter we reported on the
reserve management’s plans to upgrade visitor
facilities in the Rietvlei Wetland reserve. A
working group was formed to assist reserve manager
Koos Retief, the working group had a very fruitful
meeting and the various parties involved have agreed
on the way forward. The priority is to improve the
braai facilities in the “Point” area, i.e. the
picnic sites along the north shore of North Lake
between MAC clubhouse and the slipway, and the
fishing areas just east of the slipway. There will
be funds left over to improve some of the braai
facilities on the peninsula on the southern shore of
North Lake, MAC has also indicated that they will do
some fund-raising to provide more funds for the
upgrading of the facilities on the peninsula – this
area is mainly used by their members. |
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Koos Retief did indicate to the working group that
he hoped to have the work completed by end of
October, but ordering procedures, the weather and
other factors have delayed the work. We are
confident that Rietvlei Wetland Reserve will receive
a “new look” during the summer. Koos knows that he
has both the Friends and MAC’s full support with
this important project. |
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Our Water Hyacinth Problem |
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During our recent floods residents would have seen
the rafts of water hyacinth being carried down the
estuary – several times the City had workers at the
estuary mouth clearing away the plants washed up on
the beach. Like many other rivers in South Africa,
the Diep River is also infested with water hyacinth;
but where does this plant come from and how can it
be controlled? |
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Water hyacinth, Eichhornia crassipes, is
widely recognized as one of the world’s worst weeds.
The plant is a native of the Amazon, but tolerates a
wide range of climatic and aquatic conditions,
allowing world-wide infestation across a range of
latitudes and climates. In South Africa the weed was
first recorded on the Cape Flats in 1908, and was
introduced into KwaZulu Natal at about the same
time; since then it has spread throughout the
country. |
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Impacts |
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This most damaging water weed blocks waterways,
affecting both navigation and drainage, and
increases siltation and flooding. Water hyacinth has
a high rate of evapotranspiration leading to water
loss from dams; and it displaces indigenous flora
and fauna by modifying the habitat. It is also a
health hazard as it provides suitable breeding sites
for vectors of animal and human diseases – this
leads to an increase in cases of encephalitis,
schistosomiasis (bilharzia), filariasis (caused by a
parasitic nematode worm), river blindness and
possibly cholera. |
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Fortunately for us in the Cape, most of these are
tropical diseases and would not occur here. However
the ecological effects of water hyacinth in our
waters are severe and in some areas have led to the
localised extinction of indigenous fish and
invertebrate species. |
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Control |
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Water hyacinth is a declared weed that must be
controlled in terms of legislation. Complete
eradication is nearly impossible as the cost will be
prohibitive; the aim of control is thus to reduce
infestations to acceptable levels of about 10% cover
rather than trying to eradicate it completely.
Re-infestation occurs easily from seed banks or from
vegetative growth, which means that control is a
continuous exercise. |
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Controlling techniques include physical removal,
application of herbicides, releasing biological
control agents, and harvesting for commercial or
subsistence purposes. Water hyacinth can be used for
fodder, as a fertilizer, as a fibre source and for
making paper, or for removing mineral nutrients from
polluted water. However the potential benefits of
these uses is far outweighed by the negative costs
of water hyacinth to communities – thus far none of
these commercial uses have proved sustainable over
the medium to longer term. |
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Physical removal has been widely used all over the
world, but it is ineffective for large infestations,
and seems to work only in small confined areas like
ponds. Mechanical harvesters were developed in some
parts of the world, but with dubious success and
most have been abandoned as being too expensive and
ineffective. Chemical control has been practiced
since the early 1900’s; formulations of 2,4-D and
Glyphosate are aerially sprayed, and are often used
because of the immediate impact it has on the weed.
However, both physical and chemical methods are
costly and unsustainable in the long term, and
biological control is now accepted to be the most
cost-effective and environmentally friendly
technique for the control of water hyacinth. |
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Biological control uses natural enemies (insects,
spiders and pathogens) from the region of origin;
use of these agents has resulted in dramatic
successes in many parts of Africa and the world. In
South Africa a biological control programme was
initiated in 1973, but terminated in 1975, and then
resumed in 1985. Presently control of water hyacinth
in South Africa relies on six established agents. |
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The agents presently used include two weevil
species, a pyralid moth, a galumnid mite, the water
hyacinth bug and a fungal pathogen. An additional
three insect species are presently under
investigation. |
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Although biological control has been effective in
certain areas in South Africa, it has not been as
successful as in some other parts of the world. The
main problem is that in waters enriched with
nitrates and phosphates water hyacinth tends to
outgrow the biological control agents. In areas
where additional mechanical or chemical clearing
takes place, the regular removal of water hyacinth
also results in the removal of the biological
agents. Low winter temperatures have a further
negative impact as this kills off large numbers of
the insect species used as control agents. In fact
low water temperatures and frost are the major
limiting factors in the successful use of biological
agents. In most parts of the world biological
control is successful only in areas with tropical or
subtropical climatic conditions. |
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In our coastal regions where frost and low
temperatures is not a major factor, biological
control could be much more successful, but this will
only be the case if the levels of nitrates and
phosphates entering our river systems are reduced.
This means that sources of pollution and enrichment
of the water has to be managed and eliminated where
possible. |
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In the Diep River the levels of nitrogen and
phosphate are quite high, and these levels will have
to be reduced if we want to tackle the water
hyacinth level successfully. While biological agents
provide us with the best option to deal with the
problem, and also has much less impact on the
environment, successful control will most probably
have to rely on a combination of biological agents
together with mechanical and chemical clearing of
the weed. |
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[Information for this article came from several
sources – more information can be obtained from the
following link to the University of the
Witwatersrand website :
http://web.wits.ac.za/Academic/Science/APES/Research/Water/WaterHyacinth.htm] |
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| Thanks go to Chevron Refinery for
sponsoring envelopes for the posted newsletter. |
