A study funded by the Council for Scientific and Industrial Research (CSIR) and the Department of Science and Technology, using innovative remote sensing techniques, recently revealed that harmful cyanobacteria are widespread in South Africa's 50 largest dams. In the study, Hartbeespoort, Darlington and Spitskop dams were found to be affected most severely by cyanobacterial surface scum, with intermediate to extensive coverage.

“Water quality in South Africa is a significant concern. Serious steps need to be taken to reduce the amount of nutrients entering our lakes,” warns University of Cape Town’s (UCT) earth observation scientist, Dr Mark Matthews whose PhD study was funded by the CSIR, under the supervision of CSIR principal scientist, Dr Stewart Bernard.

“Water that is rich in cyanobacteria poses a serious health risk and can result in death if consumed in large quantities,” warns Matthews. This warning comes after Matthews’ conclusion of a study observing 10 years of remotely sensed earth observation data (2002 to 2012) to monitor chlorophyll a, cyanobacteria, and surface scum in the 50 largest standing water bodies in South Africa.

Eutrophication and cyanobacterial blooms are widespread and extensive in South African water bodies, and poisonings of domestic and wild animals are a frequent occurrence. Eutrophication is nutrient enrichment that may lead to an increase in harmful algae in an aquatic system. These nutrients enter water bodies from agricultural and waste water sources. Cyanobacteria is a  group of blue-green algae that occur in highly visible blooms mainly in aquatic ecosystems that can be toxic to fish and other species and pose serious human health risks.

The study, entitled Eutrophication and cyanobacterial blooms in South African inland waters: 10 years of MERIS observations, relied on data from time series observations of parameters related to phytoplankton and water clarity derived from the medium resolution imaging spectrometer full resolution (MERIS FR) satellite instrument.

The study confirmed that Hartbeespoort Dam is a hypertrophic system dominated by frequent and persistent cyanobacterial blooms and surface scum conditions. The highest chlorophyll values were associated with Mthatha, Ncora, Erfenis, Krugersdrift, Ntshingwayo, and Allemanskraal Dams.

A total of 18 water bodies had between 10% and 30% average cyanobacteria area coverage. These water bodies had common and regular cyanobacterial blooms with medium coverage and include South Africa’s two largest reservoirs; Gariep and the Vaal. It must be noted that this study excluded seasonal pans, estuaries, and water bodies subject to tidal influence.

The information derived from this study can be used to prioritise management and mitigation strategies in order to reduce health risks. Matthews advises that the relevant managing authorities need to take immediate measures to reduce the risk of exposure to surface scums at Hartbeespoort, Darlington, and Spitskop. “This can be done by improving the treatment of water at sewage plants, identifying the point of entry of nutrients into the water bodies, and mitigating this,” explains Matthews. One way to do this, he says, is to build retaining dams and plant wetlands that would absorb the nutrients.

This first of its kind study, in respect to both the quantitative time series products and its application to water bodies on a national or sub-continental scale, is applying novel methods to develop operational systems for monitoring cyanobacteria and eutrophication using satellite earth observation data in near-real-time, which will be integrated into South Africa’s current water quality monitoring programmes and used to warn the public of cyanobacteria blooms.

A Water Research Commission study, set to begin in April 2015 entitled; "The integration of Earth Observation into the National Eutrophication Monitoring Programme" (EONEMP) will bring together researchers from UCT, CSIR, the Department of Water Affairs and Sanitation, and the South African National Space Agency to provide information services for cyanobacteria and eutrophication from satellite.