Growing water problems
Poor water quality is the greatest threat to South Africa’s water security
“R IPPING off hapless citizens” (letter in The Witness, October 16) mentioned my knowledge of tax misuse. Exposed here, it relates to more than R500 million spent by the Department of Water and Sanitation (DWS) to improve water quality in Gauteng’s Hartbeespoort Dam (Harties).
I consider it tax “misuse” as it knowingly applied a method previously discredited as regionally inapplicable. Harties’ major water quality problem results from nutrient pollution, which is the greatest threat to water security nationwide. To increase public awareness and comprehension of this problem, it seems appropriately informative to examine sources and consequences of nutrient pollution in a broad context, although coverage is necessarily simplified and incomplete.
DECLINING WATER QUALITY A GREATER THREAT
Water is South Africa’s most limiting natural resource, as recent water restrictions in KZN and Cape Town’s narrow avoidance of day zero surely reminded us. Despite over 5 000 dams across the country potentially able to capture and store nearly 70% of mean annual run-off, water supply remains insecure. However, water security involves not only water quantity, but also water quality.
Water quality relates to the types and amounts of dissolved chemicals and suspended particles (living and inanimate) it contains — attributes that are often insidiously intangible and sometimes even sinister. Ominously, water quality is progressively declining in SA — in line with population growth and its litany of associated consequences: more development, more waste, more habitat disturbance and environmental degradation, etc.
It is important to recognise that declines in water quality often pose a greater threat than direct water shortages: they are often cryptic and cumulative, and not necessarily directly improved or reversed immediately by drought-breaking rain.
Pollution by nutrients — notably nitrogen (N) and particularly phosphorus (P) — is the most widespread of many threats to water quality in SA. Termed “eutrophication” (literally food enrichment), it is the greatest threat to inland and coastal waters globally — a bizarre irony given the natural scarcity of these essential life elements that justifies great expenditure to fertilise crops. The shortage of P is especially acute in natural freshwaters, which receive only residual amounts left to leach into watercourses. Conversely, sewage is nutrient-rich as humans excrete more P per unit time than leaches from scores of hectares of natural land. With increasing and more urbanised populations, ageing wastewater (sewage) treatment plants are literally drowning in sh**, many unable to meet even the liberal effluent discharge limits legislated for P. Alongside nutrient-rich run-off from agricultural lands, nutrient inputs to dams are unsurprisingly high and rising. Disconcertingly, up to 70% by volume of all water stored in dams is already highly or extremely nutrient enriched.
BROKEN LINK IN THE FOOD CHAIN
Eutrophication has many consequences, mostly negative. Excessive plant growth is the most obvious symptom. Prolific plant production with no fertiliser cost — lots of fodder for livestock, or plentiful food for fish aquaculture — may sound ideal for any agricultural enterprise, however,
the reality is far from ideal — blooms of unsightly, smelly and sometimes toxic algae and cyanobacteria (aka blue-green algae: Photo 1) and/or floating water plants (Photo 2). Particularly as this bountiful production does not feed fish, but instead fuels underwater microbial decomposers that deplete oxygen levels in water — the result of a “broken link” in the food chain explained by my PhD student’s research into zooplankton feeding biology in the highly eutrophic Harties ecosystem in the mideighties.
Zooplankton are small invertebrates, mostly less than one millimetre, that act as the principal herbivores in pelagic zones — broadly equivalent to antelope grazers in savannah ecosystems.
He showed that the blue-green alga Microcystis — the “plant” then dominant in Harties, simply grew too large to be eaten by filter-feeding zooplankton, particularly the water flea Daphnia. Excluded from the “direct” food chain by “immunity” to grazer reduction, Microcystis proliferated freely to form expansive surface scums (Photo 1) before dying and decomposing.
Eutrophication is a global problem. In natural lakes, specialised pelagic fish can deplete zooplankton sufficiently for algae to proliferate unchecked by zooplankton grazing, leading to the concept of “biomanipulation” — purposeful food web alteration to control algae.
In essence, increase the number of fisheating “large fish” to reduce the number of zooplankton-eating “small fish”, thereby allowing algal-eating zooplankton to increase and consequently reduce algae. This seemingly obvious and simple solution hinges on two criteria: zooplankton Roodeplaat Dam: raft of water hyacinth (photo 2). must eat and reduce the problem algae, and zooplankton must be too few to reduce algae because of their depletion by small fish predation. Neither criteria pertain in Harties.
Microcystis is immune to grazing and “small fish” are lacking (fishes in dams derive from riverine species which lack specialised zooplankton-eating “small fish”). So biomanipulation is a non-starter from the outset.
BIOMANIPULATION NOT A CREDIBLE TOOL TO TREAT SYMPTOMS OF EUTROPHICATION
How does all this relate to wasteful tax use? In 2004, two articles on Harties in Water Wheel (“New hope for troubled waters” and “An action plan”) announced DWS proposals for future eutrophication management. Namely, to replace control measures that prevent nutrient pollution with restorative biomanipulation to treat symptoms of eutrophication.
Hoping to avoid a misguided failure (knowing that biomanipulation is scientifically unfounded), I prepared a detailed commentary and position paper (published in 2006) that evaluated its prospective suitability in Harties and SA reservoir ecosystems. This negated biomanipulation as a viable management option, exposing it as an “illusory pipe dream” in every respect. The “Harties Metsi a me” (HMaM) restoration programme went ahead regardless in February 2008, steered by a DWS regional executive and a fish-centred ecological consultancy in Gauteng whose frugal knowledge of basic lake ecology, and almost total ignorance of dam(ned) zooplankton (regarded as an inconvenient truth) was evident from the pronouncements in 2004.
Was HMaM successful and what did it cost? Overall, it cost “more than R500 million to 2015” (DWS 2017). DWS principals unsurprisingly hailed it a great success, with a dedicated public website detailing its operational structure and accomplishments (e.g. removal of 350 tons of fish in total, etc.), and subsequent calls for its expansion and extension.
However, analyses of a very detailed record of satellite images provided no objective support for this purported success. Algal abundance during six years before and four years after HMaM began in 2008 did not differ on average. A very slight negative trend (decline in algae) evident in Harties after 2008 cannot be attributed directly and exclusively to HMaM, since parallel trends occurred in neighbouring and distant dams. All coincided broadly with a surprising, and presently inexplicable nation-wide decline of P in river water.
Research continued since I retired in 2007 has filled previous knowledge gaps, leaving biomanipulation with no credibility as a tool to manage eutrophication in our dams — a bland statement based on considerable substantive evidence outside the scope of this article, but published in several research articles.
SCURRILOUS ATTEMPT TO HIDE THE DEBACLE
Having spent half a billion rand, DWS surreptitiously “plugged the plug” on HMaM in 2017. A regional press report attributed its termination to “allegations of corruption, nepotism and infighting”.
The DWS website detailing HMaM activities and achievements suddenly disappeared, suggesting a scurrilous attempt to hide the debacle and avoid accountability by the DWS section involved — nefarious circumstances, given its funding from the national fiscus. While Hartbeespoort Dam itself cannot be renamed Hartbeesgate Dam, at least its Nkandla-gate scale financial haemorrhage has been plugged. Other tax wastages must await calling out. Readers can decide for themselves whether my charge of tax “misuse” or “waste” is justified.
Closer to home: what effect has the Khayelitsha housing scheme on Midmar’s shores had on water quality in the Mgeni system? Despite predictable negative consequences (“Howick to Hollywood”, The Witness, October 16, 2002), and legislated environmental restrictions, it was driven ahead by a subsequently disgraced former mayor of Howick with vested interests in its development.
UNTESTED NEW TECHNOLOGIES COULD PROVIDE THE ANSWER Elsewhere, near-coastal arid nations like Israel rely on seawater desalinisation to ensure an adequate water supply. Although trialled as an emergency measure for Wilderness, the process (able also to mitigate water quality problems) remains unaffordable in SA. Recycling of domestic wastewater is economically more feasible, but unjustifiably remains widely perceived as abhorrent — a public mind-set that circumstances may force to change.
New and emerging technologies (reverse osmosis and membrane filtration) remain largely untested, but may prove cost-effective in time. A more immediate glimmer of hope to combat eutrophication is offered by the growing global shortage of natural P, providing a potential economic incentive to improve P recovery from wastewater, to fertilise crops more conservatively, and even to retrieve P accumulated in lake sediment deposits (2 000 tons in Harties alone), but it cannot directly increase water supply.
POTABLE WATER UNDER THREAT
In the interim, it is crucial to increase citizen awareness of the threat posed by the accelerating water quality decline in our reservoirs — the source of potable water for most citizens. Three decades ago, South Africa was globally at the cuttingedge of reservoir limnology (the discipline of human-made lake studies), with highly competent, scientifically skilled expertise available to address the prominent concerns. The practitioners remaining today are fewer than fingers on a hand, and like me, all are in their twilight years. The HMaM saga indicates the present level of scientific (in)competency in reservoir limnology. Given our reliance on reservoirs, this is a parlous situation for which the National Research Foundation and Water Research Commission are largely, if inadvertently, responsible.
• Rob Hart, professor emeritus, School of Life Sciences, UKZN; but written in a personal capacity. Hart is an alumnus of the University of Natal, and a Fellow of UKZN, who holds a PhD (Rhodes) and a DSc (Natal). Author of some 125 major publications, he has held continuous NRF accreditation since 1987 and was honoured with the Gold Medal award of the African Society of Aquatic Sciences in 2017.
Hartbeespoort Dam: surface scum of Microcystis alga at wall (photo 1).