Recent efforts to eliminate an alien invader between Pietermaritzburg and Durban have left residents and environmentalists in a froth.
In the last two weeks of February the KwaZulu-Natal Department of Water and Forestry Affairs sprayed a broad-spectrum glysophate herbicide on Hammarsdale dam, Sterkspruit river, parts of the Umlazi river and Shongweni dam to eliminate the prolific water hyacinth, which poses a threat to the biodiversity of many South African waterways.
The water hyacinth had spread alarmingly in the Hammarsdale dam. Though everyone agrees the South American weed had to be contained, residents and members of the Shongweni and Summerveld Conservancies are angered that they were not consulted before the aerial spraying.
They fear the herbicide affected surrounding flora and fauna. One resident, whose garden lies about 100m from the river bank, says his vegetables died several days after the spraying.
Vincent Knott of the Shongweni Conservancy says environmental damage has also been noted along the Sterkspruit river in the Shongweni Valley. Reeds are dying along the riverbank and the herbicide “burnt” leaves on trees near the river.
Though the extent of the environmental damage has not yet been assessed, Peter Wragg of the Summerveld Conservancy says: “If that section of river is representative of the entire area sprayed, it suggests that all the reed beds around Shongweni dam, its feeder rivers, as well as some herbaceous vegetation on the banks — up to 100m or more away from the water — may have been killed.”
The department says that minimal damage was caused compared with the ecological effects of the weed.
“The Hammarsdale dam belongs to the government. It is the government’s responsibility to take action to eradicate the source of the infestation and prevent it from washing downstream and causing even more damage in the Sterkspruit river and Shongweni dam,” says Debbie Muir, a biocontrol and aquatic weeds officer with the Working for Water Project.
She says the spraying was conducted in consultation with the provincial government’s aquatic weeds advisory committee and that it complied with all regulations.
Nicola van Zyl, of the Endangered Wildlife Trust Poison Working Group, says that broad-spectrum glysophate herbicides are fairly safe for birds and fauna, and are “soft on the environment”, if used according to instructions.
But research conducted by a European Community task group suggests the herbicide poses a risk to predatory mites, insects and spiders that consume or parasitise insects. Eliminating them could cause insect populations to spiral out of control.
Dave Allen, an ornithologist at the Durban Museum, says the spraying should not directly affect bird life, but it will affect their habitat and food sources. Massive amounts of rotting vegetation could change the oxygen levels in the water, affecting fish, invertebrates and underwater vegetation — the primary food for water birds.
Conservationists are also concerned that the aerial spraying could have affected rare plant species growing along the Sterkspruit river and at Hammarsdale dam.
About 60% of the water hyacinth on Shongweni dam is reported to have been killed, but Wragg believes that biological control, application of the herbicide by boat, or mechanical removal could have been employed.
When Knott of the Shongweni Conservancy objected that the department had failed to consult concerned parties, he says officials told him that someone at Shongweni dam had been notified, as had a member of the Hammarsdale Industrial Conservancy.
“What I found strange is that the Hammarsdale Industrial Conservancy has been dormant for a number of months, so one can’t help but wonder who they contacted,” says Knott.
Muir has agreed to meet members of the Shongweni Conservancy, but a second spraying is planned for March 8 and another thereafter.