Vaal a victim of bad management

Raw sewage leads to high nutrient levels plants thrive on. TAKING OVER AFTER DECADES OF INACTION

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.

These two weeds are both South American plants, with the hyacinth first documented in SA 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 as invasive plant species.

These 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. They all contribute to eutrophication, a severe problem affecting our water resources across the country.

The current crisis in the Vaal is attributed to continuous and increasing pollution of our already scarce water resources by fertilisers, herbicides, pesticides, effluent rich in nutrients, as well as raw sewage and other rubbish that is dumped into our water resources. Dysfunctional wastewater treatment works (WWTWs) and other pollution sources, such as a multitude of industries throwing their untreated wastewater directly 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 these weeds immediately before it becomes a problem and to address major pollution sources, such as the continued pumping of raw sewage into rivers, due to unmaintained, dysfunctional, or nonfunctioning WWTWs.

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 reactive and questionable decision-making by authorities.

Glyphosate-based pesticides 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 human health.

Glyphosate will eventually kill these 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.

These 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 – all while the underlying cause of this crisis, the inflow of raw sewage and nutrient rich effluent, has yet to be addressed.

We have the necessary skills to confront this 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.

Let’s not create another Hartbeespoort Dam

▶ Du Plessis is associate professor and research specialist in integrated water resource management, University of South Africa