Action taken against Harties Dam invasive alien plant

Water and Sanitation Deputy Minister, Sello Seitlholo, and the Rhodes University Centre for Biological Control (CBC) have released weevil species to tackle the invasive alien aquatic plant at Hartbeespoort Dam in the North West. Source: SAnews.gov.za

The salvinia weevil insect is a biological control agent known as Cyrtobagous salviniae, used to manage the Salvinia minima, an invasive floating alien aquatic weed (known as the common salvinia).

The weevil species is a subaquatic herbivorous insect that feeds on the common salvinia. The species were imported from Florida State in the United Sates of America (USA), and it has proven to be effective and successful to control the aquatic plant in the USA.

Joined by Professor Julie Coetzee, the Deputy Director of the Centre for Biological Control and Principal Scientist at the National Research Foundation’s South African Institute for Aquatic Biodiversity, Seitlholo officially released the salvinia weevil insect on Monday at Mogi Adventures, located next to the Crocodile River.

The invasive alien plant was initially recorded at Hartbeespoort Dam in 2011, and has since spread through areas of the North West and Gauteng Provinces, and has reached the Limpopo River, which marks the border with the neighbouring country of Botswana, threatening South Africa’s water bodies.

According to Coetzee, the weevils multiply quickly and their impact of controlling the aquatic plant can be observed in a year.

She said the CBC, in collaboration with community partners, will rear the weevil and facilitate releases at various sites across the country where water is invaded by the common salvinia.

“This biological control programme will be monitored and the progress of the weevil and its impact on common salvinia will be noted. The weevils only feed on the salvinia minima plant and their entire life cycle depends on the plant, thus they do not have a threat of infesting other ornamental plants, crops or even the water hyacinth plants,” Coetzee said.

Seitlholo emphasised the importance of securing the country’s water resources by partnering with scientific institutes like the CBC.

“What is also important is for us to get into serious conversations with municipalities in the upper catchment that are largely responsible for causing the high nutrient load in the water due to their substandard effluent discharged from their wastewater treatment works, which is being released into the river, eventually landing in the dam.

“This results in high nutrient levels in the water, which gives rise to the spread of these alien invasive aquatic plants, compromising the ecosystem, recreation and the general local economy,” Seitlholo said.

He said the use of the weevils will run concurrently with the other remediation programme currently underway at the dam, which is being implemented by Magalies Water to eradicate alien invasion species that have negatively impacted the ecosystem in the water.

The remedial programme includes the physical removal of the water hyacinth at the dam. This also includes the pilot project of nanobubbles technology, which increases dissolved oxygen in the water, activates the decomposition of microorganisms in water and river sediment.

Given that the quality of water is affected by the discharge of effluent and raw sewage from the municipalities of Tshwane, Johannesburg and Ekurhuleni, Seitlholo said municipalities ought to play a role in the remediation programmes undertaken by the department to rehabilitate the water resource.

Despite the department’s Compliance, Enforcement and Monitoring Directorate engaging the municipalities, Seitlholo said the department has also proposed amendments to Section 19 of the National Water Act (NWA), which focuses on preventing and remedying the effects of pollution, ensuring the protection of water resources and addressing pollution.

Seitlholo said the proposed amendments to the NWA, which are currently with the State Law Advisor, enable the department to directly hold the executive mayor and the municipal manager liable for the transgressions of the municipality in terms of the pollution of the country’s water courses.

“These legislation measures are taken by the department to fundamentally deal with issues of water pollution in the country,” Seitlholo said.