Posted by: Saving Water SA (Cape Town, South Africa) – partnered with Water Rhapsody conservation systems – 31 March 2011
By: Tamir Kahn
Farmers who depend on the Loskop Dam to irrigate their crops can breathe a sigh of relief after scientists found the water poses no immediate threat to human health, which means exports of fruit and vegetables are safe — at least for now.
“It’s a great relief,” said the Loskop Irrigation Board’s Diek Engelbrecht yesterday.
Farmers have been so worried about the declining water quality in the heavily polluted Olifants River, which flows into the dam, that the irrigation board commissioned a study from the Council for Scientific and Industrial Research (CSIR) and the University of Stellenbosch. Farmers were concerned that if their crops became contaminated with heavy metals or pathogens, their produce would no longer make export grade.
The dam provides water to 16000ha of agricultural land, and supports a European export market worth about R1bn a year.
The Transvaal Agricultural Union (TAU) last year said its members were worried that polluted water would jeopardise their livelihood. If they lost their export markets, they would have to dump produce locally and prices would fall, with knock-on effects for farmers who rely on domestic customers, it said.
Fortunately for the farmers, the study found very low levels of E.coli and no detectable levels of other disease-causing bacteria in the irrigation water or on the crops. The scientists analysed fresh produce, maize, citrus, grapes and wheat — the main crops in the region. E.coli levels are an important gauge of the amount of untreated sewage in the water, and can survive for weeks on the surface of crops, with the concentration rising after each successive watering. The issue is of particular concern as a 2009 Green Drop report found 55% of SA’s 900 water treatment plants attained a score of less than 50%.
Despite the good news on the pathogen front, CSIR scientist Paul Oberholster warned that the quality of water in the Loskop Dam, which feeds the Loskop Irrigation Board’s water supplies to the Groblersda l area, is deteriorating rapidly.
The researchers found there had been permanent blooms of pollution- loving cyanobacteria on the surface of the dam since 2008. The cyanobacteria are a concern because they release toxins, which though not fully understood, pose health risks to humans and animals. The government does not systematically monitor cyanobacterial blooms.
Mr Engelbrecht said farmers remained concerned about the high levels of filamentous algae in the water, which clogged waterways and irrigation channels. The algae, which grow filaments up to 15m long, thrive in water that is rich in nutrients that arise from pollution. “Detached algae continuously drift down the canals, clogging the control gates and crop sprayers, causing economical losses. The irrigation board then has to bear the costs of removing these nuisance algae,” said Dr Oberholster.
Another CSIR study, investigating chemical pollution in the upper Olifants River catchment area, found it was contaminated with high levels of microbial pollutants, disease-causing organisms and endocrine disruptors. The Olifants catchment area rises in the grasslands of the Highveld and provides water to more than 200 dams, including Loskop Dam.
The scientists found evidence of acid rain and acid water, which they attributed to abandoned industrial activity. They recommended several measures to reduce pollution, including the use of phosphate free detergents, upgrading sewage treatment plants and implementing shoreline zoning, so that water users were at least 20m from watercourses.
Source: Business Day