By Chris Magadza
ON August 27 I saw a large puddle just off Alps Rd, a few hundred metres from the Groombridge shops in Harare. There had been very light showers the evening before but the size of the puddle
was inconsistent with the 0,5mm I recorded at our place.
On a closer look it turned out to be a quite substantial sewer breach. This was not far from some of the very pricey properties in Harare. Indeed if one of the residents along Alps Rd looked eastwards from their upstairs patio they would have a panoramic view of the spillage. Some of the most expensive cars in Harare would be seen on that road.
The day before I had taken my students on a tour of Harare to demonstrate to them the vulnerability of the city’s residents to environmentally related diseases, and in particular the possible impacts of climate change in an urban environment like Harare.
We stopped to chat with residents on the issue of garbage dumping in drainage channels and on street “middens”. We got the usual answer that council does not collect garbage regularly.
When pressed why they did not raise the matter with their councillor the reply was telling. Even the councillor is forced to dispose of his garbage like anyone else. In any case the last they heard of him was when he was canvassing for their votes.
At the south end of Budiriro we saw a stream carrying raw sewage, with visible faecal material floating down the stream – in fact down to Lake Chivero. The municipal herd of cattle were seen drinking from this stream. Such scenes can be seen on the Marimba stream, the stream that passes by Kuwadzana extension, and on occasions on the Mukuvisi River, and several others, if one cared to search.
The Borrowdale vleis is the headwaters of the Gwebe River which flows into Lake Manyame, also a source of Harare water supply. In fact by the time the stream reaches Bargate Rd the sewerage stench is quite marked. Scenes of blocked sewers are regularly seen around Harare.
About two months ago I routinely took my students on a tour of wastewater treatment facilities and water purification works. Whereas in the past this was viewed by authorities as valuable educational exercise, this year the university had to pay $84 000 to visit the wastewater treatment facility. Upon arrival the manager, with much apology, declined to host the visit because the plant was not functioning. Needless to say we got no rebate.
Since the 70s, when I started teaching Applied Hydrobiology at the university, the Mukuvisi River has been a faithful teaching aid on pollution. I have always been able to guarantee a convincing demonstration of pollution on this river, in spite of at least two water acts, and other statutory instruments, concerning water pollution control.
Lake Chivero, one of our water supply dams, has been studied intensely over the last 30 years. A recent study by one of my students revealed that the levels of microcystin in the lake ranged between 19 µg per litre to 23 µg per litre with an average of 20 µg per litre. The World Health Organisation recommended limits are 1 µg per litre in the lake and 0,01 µg per litre in drinking water.
Microcystin is water-soluble and is normally not removed by standard water treatment procedures, which are normally designed to kill bacteria and reduce turbidity and odour.
Microcystins cause cancers, intestinal disorders and damage human male testicular chromosomes. Offspring sired by males with such microcystin-related disorders are liable to be genetically abnormal.
My student found an increasing trend in liver cancer in Harare. Further she, and other former researchers, has found an increasing trend in enteritis in Harare residents, symptoms consistent with microcystin toxicity.
Microcystin is a product of blue-green algae metabolism. Blue-green algal growth is promoted by over-fertilisation of natural waters by excessive farm fertiliser runoff or pollution by domestic and industrial wastewaters or both.
Another of my University of Zimbabwe students found out that the amount of nutrients (phosphorus and nitrogen) entering Lake Chivero, and probably other Manyame River impoundments, from sources that do not pass through the wastewater treatment works, such as the streams I have cited above, is now sufficient to keep the lake permanently polluted, even if the Harare City Council were to repair present wastewater facilities and add new ones.
An associated problem of oversupply of nutrients to lakes is the proliferation of exotic aquatic weeds, such as the water hyacinth. This weed invaded the lake in the early 60s and by the early 70s had to be controlled by use of the herbicide 2 4-D. Coincident with the application of this herbicide was an upsurge of birth defects and abortions in the then Salisbury.
The weed was successfully removed from the lake, largely by the installation of nutrient removing sewage treatment plant at the Ferle, until its re-invasion by dormant seeds in 1984. Since then the lake eutrophication has progressively worsened.
What are the underlying problems? The accumulation of garbage on streets and poor wastewater treatment are conditions I have seen in many African cities.
There are of course financial constrains. Urban population growth in Africa is such that the population doubling period is about 14 years, ranging from as little as four years in Rwanda to 28 years in Egypt.
One civil engineer estimated that the project cycle period from decision to construct such a facility as a wastewater treatment plant to its commission is in the order of a decade. Thus by the time the plant is commissioned it would have already been inadequate.
However, these are lo-gistic constrains whichcan always be over-come. Technical stra-tegies for dealing with eutrophication are now widely available. Indeed as a member of the Lake Environmental Committee I have travelled to various parts of the world with my colleagues training local scientists on eutrophication control.
This situation begs the question of exactly what are our value systems.
In the last decade-and-a-half we have seen activities that have resulted in our new Water Act and Environmental Act. In both cases the country was heavily tutored and funded by foreign donors.
The question might be asked. Whose initiative was it? Does the Environment Act reflect our environmental values?
*Professor Chris Magadza is member of the Lake Environmental Committee.