Professor Anja du Plessis
Professor Anja du Plessis
Parts of the Vaal River system, 40km of the river spanning from the Taaibosch Spruit to the Vaal Barrage, have become carpeted by water lettuce and water hyacinth due to decades of inaction and mismanagement. The two weeds are South American plants, with the water hyacinth first documented in South Africa in the early 1900s in the Cape Flats.
It spread from there to various parts of the country, through our river systems or by people who took alien invasive plants and planted them or put them into rivers. Both are classified in our environmental legislation as invasive plant species which require removal due to the associated problems.
The plants spread naturally by producing flowers and seeds. They also reproduce by branching and thrive on high nutrient levels in water. The growth rates have consequently increased exponentially and become largely out of control, due to high nutrient levels, caused primarily by the discharge of raw sewage into water sources, as well as other sources of nutrients, who all contribute to eutrophication, a severe problem affecting our water resources across the country at different levels and/or magnitudes.
The dense mats formed by the invasive plants, cover the water surface and can consequently lead to many negative environmental impacts such as the large-scale death of fish, many human health risks as well as economic losses. These can also be a breeding ground for mosquitoes and bilharzia-carrying snails. Uncontrolled growth and hyper-nutrient water can also be a perfect breeding ground for bacteria that can, in some cases, react with treatment agents at waterworks facilities.
The crisis in the Vaal is attributed to continuous and increasing pollution of our scarce water resources, by fertilisers, herbicides, pesticides, effluent rich in nutrients as well as raw sewage and other rubbish that is dumped or thrown into our water resources.
The numerous dysfunctional/non-functional wastewater treatment works and other pollution sources such as a multitude of industries, throwing their untreated wastewater into water resources, has created a rich soup of nutrients, creating perfect conditions for the growth of water lettuce and hyacinth.
The key is to address the occurrence of the weeds immediately before it becomes a problem and to address major pollution sources, that is, the continued pumping of raw sewage into rivers, due to non-maintained dysfunctional/non-functioning wastewater treatment works. Unfortunately, this has not been the case despite the weed being discovered by relevant authorities in 2021, with inaction ultimately leading to this ever-expanding crisis which now includes the questionable application of glyphosate.
The spraying of glyphosate on infested parts of the Vaal raised various concerns related to its immense negative effects on the environment, possible human health effects, economic costs as well as the heavily criticised reactive and questionable decision-making by relevant authorities.
Glyphosate-based pesticides are of concern as it has been linked to certain types of cancer as well as adverse effects on human development and hormonal systems.
A precautionary principle is therefore recommended – avoid until we know more about how the chemical impacts affect human health of current and future human generations.
Glyphosate will eventually kill the invasive plants however, it will be accompanied by more nutrients being available, increasing sunlight into the water body – stimulating eutrophication and the growth of cyanobacteria.
Additionally, the dead water lettuce and hyacinth will sink to the bottom, plants will decompose and release more nutrients into the system. The factors will consequently be attributed to increased eutrophication, possible algal blooms, and growth of cyanobacteria, all associated with major negative effects on the environment, human health and economic activities and growth. All while the primary underlying cause of the crisis, the continuous inflow of raw sewage and nutrient rich effluent, has yet to be addressed.
The crisis, affecting millions of people and economic activities dependent on the Vaal River system, could have been minimised and r possibly averted if the sources of water pollution were systematically addressed and if measures were put in place, in 2021, when water lettuce was first observed.
The overall response was done in haste and has been heavily criticised and questioned.
Years of inaction, reactive management as well as questionable implemented decisions have led to additional known and unknown implications on the environment, human health and socio-economic development.
If the continued decay, that is, dysfunctional and/or non-functioning wastewater treatment works, is not suitably addressed, we will continue to escalate water problems to major crises. The water lettuce and hyacinth crisis in the Vaal will not be solved and disappear overnight as each flower can produce thousands of seeds that can survive in the sediment for up to 25 years. There is therefore no quick fix. Upstream interventions need to be included in our intervention plan since the system is the symptom of upstream catchment activities. If there is no suitable intervention/s upstream or in the system, the invasive plants will continue to spread and worsen.
We have the necessary minds and skills as well as the willingness to work together in confronting the avoidable crisis. We, however, also need to hold those accountable, ensure transparency in the review of decisions made, and ensure that we do better for the current and future generations. Let’s not create another Hartbeespoort Dam and, most importantly, review how we got here to ultimately make informed decisions on the way forward.
Du Plessis is a water resource management specialist in the Department of Geography at Unisa.
Pretoria News
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