“A large proportion of our dams are what is known as eutrophic – that means that there’s too much algae that is starting to live in the water because of nutrient like phosphate,” hydrogeologist Christine Colvin, senior manager of fresh water programmes at the WWF SA told News24.
She warned that the release of toxins into drinking water in dams presented a risk to all water consumers.
“Those algae bloom and then they die, and when they die, they release toxins – cytotoxins – into the water.”
According to her research, the most common pollutant in South African river systems was phosphate.
“The most widespread pollutant in our rivers is phosphate and that’s something that comes off agricultural land. It’s released from the soil and it’s used in fertilizers.
“Work that I saw published about two years ago said that 80% of our rivers were exceeding the phosphate levels,” said Colvin.
Phosphate also occurs naturally and could end up river systems by natural means.
Colvin conceded that natural phosphate could naturally enter river systems, but said that the amounts of natural phosphate were usually very low and larger amounts could directly attributed to pollution.
“The natural phosphate levels are incredibly low so you can just have one poorly managed farm or one faulty wastewater treatment plant way up in river system and it’s going to end up polluting that entire ecosystem,” she said.
As a nutrient, the phosphate has a measurable impact on the river ecosystem which feeds the dams.
“Phosphate is a nutrient that then shifts the whole ecosystem of that river system, so you can start getting algal blooms; the indigenous and natural fish and vegetation that should be living in the river system are ‘out-competed’ and you have a whole new ecosystem that develops in that river,” Colvin explained.
According to the Water Research Commission (WRC), about a third of South African dams face eutrofication which occurs when high levels of pollutant in water bodies result in excessive plant growth.
The Water Wheel report of 2008 found that 35% of SA dams are impaired by the process of eutrofication, higher than the continental average of 28%.
Dams in Europe have a rate of 53% while those in North America are at 48%.
The WRC report said that SA had fallen from its status as a leader in the field of eutrophication study. This was due, in part, to a termination of funding for the research, the organisation found.
“Many of the researchers involved in early eutrophication research have since moved into better research fields, into consultation or have emigrated. As a result, appropriate management strategies directed against eutrophication have been seriously constrained by a widespread lack of understanding of the problem, particularly at the decision-making level.”
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