Water quality concerns at Loskop Dam

Wednesday, March 30, 2011

Pretoria - Although there are low levels of Escherichia coli, known as E. coli in Loskop Dam, the Council for Scientific and Industrial Research (CSIR) has warned that water quality in the dam is deteriorating fast.

A two-year study of the quality of irrigation water from Loskop Dam and its effect on crop production in the Groblersdal area has shown low levels of E. coli and no detectable levels of other disease-causing bacteria.

The dam provides water to the Loskop Irrigation Board situated downstream - one of the largest irrigation schemes in South Africa.

The main crops produced in the irrigation area and analysed by the research team include fresh produce, maize, citrus, grapes and wheat.

CSIR limnologist Dr Paul Oberholster warned that Loskop Dam's water quality is deteriorating fast, with permanent blooms of cyanobacteria visible on the surface water throughout the year since 2008.

According to a research report from the CSIR and the University of Stellenbosch, to date none of these nuisance and potentially toxic cyanobacteria had been detected in the irrigation canal water or on irrigated crops. 

A more immediate problem and cause for concern is the proliferation of nuisance filamentous algae, with strings up to 15 metres long, caused by the high levels of nutrient enrichment detected in the canals. 

According to Oberholster, the filamentous macroalgae decrease the carrying capacity of the canals.

"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 Oberholster.

Diek Engelbrecht, chairperson of the Loskop Irrigation Board (LIB) which funded the study, said while they are relieved about the results from the study in the short term, they are still concerned as the dam's water quality problems and the causes thereof have not been resolved.

"Loskop Dam is fed by the heavily contaminated Olifants River. Over the past 15 years, the dam has had a history of isolated incidents of fish mortality, which in recent years has escalated and is believed to be linked to crocodile mortalities and a decline in the crocodile population."

Since the dam's construction in 1938, it has played an important role in supplying irrigation water to the agriculture sector. 

Currently, the dam supports an export market to the European Union valued at R1 billion a year. 

The LIB provides irrigation water to 16 000 hectares of agricultural land by means of irrigation channels with a total length of more than 550 kilometres.