Friends of Rietvlei
Newsletter November 2008

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.

Walks & Talks
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.
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!
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.
Estuary Management Plan
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.
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.
Rietvlei Visitor Facility Upgrading
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.
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.
Our Water Hyacinth Problem
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?
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
[Information for this article came from several sources – more information can be obtained from the following link to the University of the Witwatersrand website :]
Thanks go to Chevron Refinery for sponsoring envelopes for the posted newsletter.
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