African Wildlife and Environment Issue 64

CONSERVATION

CONSERVATION

THE STATE OF OUR WATER

to South Africa another stark reality becomes evident – sewage management. Sadly South Africa has a massive and growing problem with the management of sewage works. South Africa has 824 wastewater treatment works for processing sewage effluent. This liquid waste is discharged back into rivers and then drawn by the 1085 water treatment plants and processed into drinking water. On an average day we generate a staggering 5.13 billion litres of sewage. Of this total volume only 16%, or 836m litres per day (ml/d) is treated to a standard safe for discharge back into a river or dam. The remaining sum of 4.3 billion litres daily, or 84% of the total average flow, is discharged in untreated, or at best, partially-treated form. It is this factor, coupled with our naturally low conversion of rainfall to runoff that makes us so vulnerable. Partially treated sewage is highly dangerous because it contains both nutrients and pathogens. Nutrients include phosphate and nitrate, which are now becoming a significant problem because they feed blue-green algae. Known technically as cyanobacteria, the name gives an indication of what they do. “Cyano” refers to the combination of carbon (C) and Nitrogen (N) that are both metabolised into complex molecular structures such as that shown in this figure. Carbon and nitrogen are both building blocks of cyanide (CN), which is what

plants in the country. This dam is part of the Crocodile West and Marico water management area, which is the only WMA in the country to have a surplus flow of water. That surplus flow will continue to grow as Gauteng produces more sewage. In fact the base-flow – the minimum amount of water available between natural rainfall events – consists of the Thukela, Vaal and Lesotho Highlands scheme water that has been through the kidneys and digestive systems of 45% of the national population living in Gauteng. While Hartbeespoort Dam is bad, the actual ground zero of what happens when sewage contamination is left unmanaged is found in the small town of Bethlehem in the Free State. The name suggests a biblical connotation of all that is good and wholesome, but in reality the town is the epicentre of a major problem. The sewage flows through a dysfunctional treatment plant into a stream that becomes Loch Lomond, a functional wetland and a well-known birding site. A recent fish kill has triggered an investigating and the presence of a pathogen known as Aeromonus hydropila has been identified. This is a gram-negative bacterium that can be found in both fresh and brackish waters. It can thrive under both aerobic (oxygen rich) and anaerobic (oxygen depleted) conditions. More importantly it is resistant to most common antibiotics. It is also resistant to cold temperatures, which means that once in a system, a

Anthony Turton

The important lesson to take home is that because South Africa is fundementaly water constrained, management of water resources is critical to the ability to thrive as a nation.

The Jukskei River on 17 October 2016

For the most part South Africa is naturally arid or semi-arid. What this means is that more water is lost to evapotranspiration than falls from the sky as precipitation. Abbreviated ET in hydrological models, evapotranspiration consists of two distinct components – evaporation and transpiration. Evaporation is what occurs off any open surface, most notably from intercepted water captured by leaves. A tree or bush will typically have a surface area of leaves many times greater than the surface area of the footprint. The greater the number of leaves the larger the surface area and therefore the greater the evaporative loss potential. In fact much of the natural rainfall is intercepted by leaves, captured as a thin film of water, exposing a large area to evaporative processes after the event has occurred. Transpiration refers to water that has been absorbed from the soil, by the roots, and transported through the vascular system up the trunk and through the branches where it is ventilated out of the stomata of leaves. Stomata are organs that open and close, typically on the underside of any leaf, much like a sweat pore on a human. Their opening and closing regulates the turgidity of the cells within the plant. Aridity is best understood when we compare precipitation and streamflow between countries. Precipitation includes all form of moisture coming from the atmosphere, such as snow, dew, rain or hail.

Streamflow refers to water in rivers. In our case this is the result of rainfall minus ET minus any water that infiltrates into the soil. Significantly South Africa has on average a similar level of precipitation when compared to Canada. We all think of Canada as a place of large rivers and lakes with deep snow in winter. The reason for this difference in the conversion ratio of precipitation to runoff. Canada has a very low ET rate compared to South Africa, so there is less water lost to evaporation and therefore more returned to rivers as streamflow. Our fundamental constraint is our conversion of rainfall to runoff. As a continent we convert 20% of the average rain to streamflow, but this includes the tropical rainforests of Congo. At national level we only convert slightly more than 8% of the rainfall into streamflow, but the two most important river basins from an economic perspective – the Orange and Limpopo – both have a conversion of slightly over 5%. If we take the South African component of the Orange then it is just over 3%, and if we call that 100% of the flow in the river in an annual average season, then we have built dams in the system with a combined storage capacity of almost three times that flow. This makes South Africa unique from a wildlife perspective, because all of our rivers are so profoundly impacted by dams and hydraulic infrastructure. But this is only part of the story. If we compare Canada

An example of a toxic molecule produced by Cyanobacteria. Note the complex linkage between carbon (C) and nitrogen (N) central to the building block process. Cyanide is CN so the denatured molecule remains toxic. This molecule is known as Microcystin-LR.

makes this molecule so toxic. “Bacteria” refers to the fact that these are primitive single celled organisms. So primitive in fact that they are the oldest living life forms, predating the existence of atmospheric oxygen. They produced the oxygen that sustains biological life today, but they existed under extremely harsh conditions so they are also known as “extremophiles”. NASA, the American space agency, is studying extremophiles to understand what forms of biological life might be found on distant planets. Themost extreme exampleofmicrocystin contamination is found at Hartbeespoort Dam, filled with sewage effluent from some of the largest waste water treatment

cold period will not destroy the pathogen. Aeromonus hydropila enters the bloodstream of victims where it comes into contact with vital organs. At these sites of contact it produces what is known as an aerolysin. This binds with the cell wall of the host being attacked where it forms holes in the membrane needed to sustain metabolic activities that keep the cell alive. This is also known as a Cytotoxin, with “cyto” meaning cell, because of this destruction. It is also known as an Endotoxin, with “endo” defining the fact that the toxin attaches externally to the cell wall. The most significant problem with this specific pathogen is the fact that while it is less toxic to humans than it is to amphibians,

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