River pollution threatens Great Barrier Reef

Pesticide-rich plumes of sediment spewed out of Australian river mouths have been shown to reach the Great Barrier Reef, threatening to damage the coral and other sealife which make up the natural wonder.

A still from the satellite imagery. The dark brown area shows the extent of the sediment flow while the pale aqua green is the reef itself

A still from the satellite imagery. The dark brown area shows the extent of the sediment flow while the pale aqua green is the reef itself

Australia's Commonwealth Scientific and Industrial Research Organisation published satellite images this week which showed that the commonly-held belief that river waters would disperse before reaching the reef was not always true.

While under normal circumstances the force of the flow leaving estuaries is insufficient to carry sediment more than 15km out to sea, in extreme conditions the polluted waters can hit both the inner and outer reefs while sediment is still at high concentrations.

The plumes are the result of heavy rainfalls in northern Queensland in late January and early February 2007 following a long dry season.

The resulting flood waters carrying a larger sediment load than during regular rainfall and river flow.

Low rainfall preceding the increased flow means that potentially harmful pollutants such as pesticides, herbicides and fertilisers have had time to accumulate, having a significant impact on the marine ecology of the reef.

The CSIRO used images from NASA satellites to build up a picture of what was happening during these extreme events which may have gone unnoticed above the surface but could have lasting consequences for coastal waters.

According to the organisation's Arnold Dekker, extreme coastal events have been captured by remote sensing before, this is the first time they can be seen and analysed straight after the event as there are now more satellites imaging the Earth and CSIRO has invested in fast information delivery systems.

"A re-think is needed now that we know where flood plumes go and what this means as organic micropollutants may be travelling to parts of the reef scientists hadn't thought to look before."

Sam Bond

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