The South African Department of Water and Sanitation (DWS) manages some 580 dams, 320 of which are considered to be major impoundments, storing more than one million cubic metres of water each. They store a combined 32 billion cubic metres of water, equivalent to 65% of South Africa’s annual rainfall runoff.
From this, irrigation uses 62%, urban and domestic use equals 27% and mining, industry and power generation absorb a further 8%. Commercial forestry utilises the remaining 3%.
Dams are, in reality, man-made or artificial lakes, necessary to sustain life and development in an arid environment that lacks natural lakes. While natural lakes form robust natural ecosystems, dams may be semi-natural at best.
Both types are prone to pollution and other pressures arising from human development of their catchment areas, with dams being generally more sensitive and less resilient to external stressors. This is because they are purposefully sited to collect water from the greatest catchment area possible.
Ensuring the healthy functioning of both natural and artificial lakes requires that deliberate lake management practices be applied. The South African National Water Resource Strategy (NWRS) recognises that “water resource management supports the provision of potable water to all people”, and that “water is central to the economy”.
Our Constitution enshrines the right to “an environment that is not harmful to life or wellbeing”, while the NWRS further observes that “the deterioration of the quality of surface water resources is one of the major threats to South Africa’s capability to provide sufficient water of appropriate quality to meet its needs and to ensure environmental sustainability”.
Reservoirs under threat
Some of the most seriously impacted reservoirs are located in the land-locked economic heartland of South Africa, which experiences an extant regional water quality crisis. This list of dams is long, and includes Bronkhorstspruit, Erfenis, Grootdraai, Klipvoor, Koppies, Laing and Roodeplaat.
All of these waters are, in the main, impacted by nutrient enrichment, known as eutrophication, arising chiefly from inadequately treated sewage and wastewater effluents (Harding 2008). More than half of the country’s total stored capacity has been shown to be affected by this anthropogenic impact (Harding 2015).
South Africa’s best-known example of excessive and sustained eutrophication is Hartbeespoort Dam, west of Pretoria, colloquially known as “Harties”. It was at this very reservoir that much of the world’s early understanding of eutrophication was developed.
Indeed, this writer’s own experience stemmed directly from “Harties” when, as an undergraduate student working vacations at the National Institute of Water Research, I was tasked with harvesting large quantities of toxic cyanobacteria (blue-green algae), from beneath the luxuriant carpet of water hyacinth, which in the Magalies River arm of the dam was almost a metre high above the water surface.
The algal biomass was used as a source of purified microcystin toxins for toxicity testing. The dominant blue-green alga, then and now, was Microcystis aeruginosa, a commonly-occurring species capable of producing a variety of hepatotoxic [liver] cyanotoxins known as microcystins.
Despite this existential threat to water security, our country lacks skills and training in the ecology and ecosystem management of such waters, termed “lentic limnology”, with a generation having passed since there was last any concerted activity in this field.
This was not always the case and, during the 1970s and 1980s, South African scientists led the world in the study of dams impacted by eutrophication originating from wastewater discharged into rivers and streams.
Getting the facts straight
Given this long and rich background of experience, it would be reasonable to assume that South Africa has remained at the forefront of eutrophication assessment and intervention. This is, however, very distant from contemporary reality.
It is, therefore, perhaps unsurprising when a press article, purportedly derived from informed expert opinion, holds a mirror to the parlous state of reservoir limnology in this country today.
First, the article announced that “recent studies have shown that increased nutrients in the [dam] water — either from excessive sewage inflows or rotting plant (hyacinth) matter — has increased the presence of microcystis blooms in the dam.” This could not be further from the truth.
This reservoir has been plagued by Microcystis and water hyacinth problems since the 1960s and, by the early 1970s, the ecological associations prevailing in this nutrient-replete waterbody had been described in detail by Professor Daan Toerien and others.
In 2001, I compiled an annotated bibliography of cyanobacteria in South Africa, rendering the history readily available to all researchers. With this history available it is thus disconcerting that a situation that has prevailed for half a century is purported to be a new and original finding.
The article describes “cyanotoxins” as being toxic bacteria, whereas this term refers to toxins produced by cyanobacteria, the latter also commonly known as blue-green algae.
n The World’s Largest Hydroelectric Dams
Secondly, the extremely invasive floating water hyacinth (Pontederia crassipes, formerly Eichhornia crassipes) has, for the past 50 years, happily cohabited with Microcystis in Hartbeespoort Dam.
In this regard, there is an established programme of biocontrol intervention in place at Harties, whereby various insect vectors are used to attack, weaken and hopefully eradicate the hyacinth. The article cites the view of an aquatic specialist who maintains that the decomposition of the weakened/dying plants increases the nutrient availability in the reservoir, i.e. solves one problem but creates another.
However, as a multitude of studies have documented, nutrient availability for plant and algal growth in Harties is to all intents and purposes non-limiting. Quite simply, the hyacinth has taken its nutrients from this luxuriant pool and returns them to the same pool during decomposition.
It is not a case of a raft of hyacinth being washed from a river into a nutrient-poor impoundment — in which case the death and decomposition of the plants could well elevate the ambient nutrient levels and trigger an algal bloom.
Thirdly, the article turns to the use of herbicides for eradicating the hyacinth, a worrying yet all-too-common practice in South Africa. Here a source claims that “herbicides contain glyphosates or Roundup; and that is a potential liver carcinogen.”
There are a number of fundamental errors with this statement which reflect a common confusion about glyphosate-based herbicides (GBHs) — but not one that presumed experts should be making. There are many types of herbicides and a subset thereof contain glyphosates — whereas the quoted source implies that all herbicides contain glyphosates.
Second, RoundUp is a trademark type of GBH, not all GBHs are RoundUp. RoundUp is, furthermore, quite different in that while indeed a GBH, its formulation contains a co-formulant, a polyethoxylated tallow amine, which is toxic to aquatic organisms and also carcinogenic.
In relation to water hyacinth, the article goes on to suggest that decomposing hyacinth results in low (dissolved) oxygen levels that “creates microcystin [sic]”. This is a garbled abstraction of the production of toxins inside cyanobacteria cells and their release when the algal cells lyse (break down). Then is submitted the non sequitur that the decomposition of the water hyacinth both contributes to algal blooms and results in “the bacteria killing each other…”.
Fourthly, the same source provides information on research to remove cyanobacteria from raw potable supplies. This is a well-established engineering ability present in many water treatment works in South Africa since the 1980s.
However, the cited work claims that the use of chlorine in treatment trials resulted in an adverse outcome. The use of chlorine or copper sulphate for this purpose was long ago found to be problematic for the very reasons mentioned in the article, and since contraindicated in potable water treatment processes. It is therefore surprising that such a lack of relevant subject awareness still pertains and that attempts to use chlorine for this purpose are still being trialled today.
Change cannot be fuelled by misinformation
Calls for an urgently needed reservoir management programme, one that embraces the remaining individual and institutional memory, integrates all available relevant knowledge and scientific findings, prioritises needs and acquires those skills and resources necessary to meet what is likely to become a crippling legacy of inaction, have been ignored by the DWS since the early 2000s. A report commissioned in 1988 and which exposed reparable failings in South Africa’s limnology skillset is as relevant today as then, but was kept secret until exposed in 2010 to an international audience.
Hartbeespoort Dam is grossly enriched with plant nutrients generated from a suite of wastewater treatment works in the reservoir’s catchment. It is but one of many similarly afflicted South African dams.
The only solution to turning this situation around is to attenuate nutrient availability at source, i.e. utilise a treatment process which can reduce nutrients to a level commensurate with the capacity of the downstream reservoir to accumulate the same.
This is not an easy task, it is not a short-term task and it will require significant funding. Hartbeespoort Dam receives nutrient loads that exceed its threshold for algal blooms by a factor of four or greater. In the absence of a fundamental reduction of nutrients at source, Harties will continue its legacy of unmanaged eutrophication and present as an increasingly unpleasant risk to human health.
What can be taken from this? In the absence of a well-funded, properly informed and cohesive strategic plan for South African reservoir limnology, misinformation will remain a problem, old findings will be “rediscovered”, and resort will be made to outdated technologies. The country will remain ill-equipped to manage its impounded water supplies.
Scientific wheels will be reinvented and a search for quick-fix “silver bullet” solutions will continue. The rapidly worsening ecological condition of South Africa’s dams will soon catapult the problems they pose to the fore, a scenario that will probably eclipse the hardships associated with electricity load shedding.
