CSIRO scientists have achieved a major advance in the global war on toxic algae - a clay-like compound which they say can stop algal blooms in their tracks and sharply lower the risk of poisons entering the water supply and environment.

The discovery was made by a team from CSIRO Land & Water working on Perth's Swan and Canning rivers, which are beset by seasonal plagues of algae.

Dr Grant Douglas has made a discovery which promises to give water managers a weapon for arresting algal blooms before they even begin.

He has identified a naturally-occurring clay-like compound which, after special treatment, acts almost like blotting paper to soak up the nutrients, especially phosphorus, on which algae depend.

Dr Douglas's experiments indicate that if the clay is spread in a layer only fractions of a millimetre thick across the bed of a river or lake, it will lock up enough of the essential phosphorus to prevent the algae from blooming.

Furthermore, lab and field trials suggest, if the clay is sprinkled into a water body in which an algal bloom has already begun to develop, it will strip out a sustantial amount of the phosphorus in the water column, leaving the algae to starve.

This could make it the answer to a water manager's prayers, because it would enable drinking water storages to be cleansed of algae before they bloom - instead of present methods which involve killing the algae with chemicals added to the water, and can leave potent algal toxins behind in the water.

Dr Douglas says that the clay is low cost and occurs naturally in many parts of Australia and other countries. However it must first be given a special treatment, which is the subject of an international patent by CSIRO, the Water and Rivers Commission and the Swan River Trust.

Tests to establish the biological and environmental safety of the new compound are continuing, he says.

Large-scale field trials of the product began this week in Perth's Lake Monger, as part of research carried out by CSIRO for the Swan River Trust. If the trials prove successful in remediating the sediments in the lake they will be extended to the Canning River in 1998.

Meanwhile, in a second breakthrough CSIRO's Dr Jeffrey Turner has also identified what is believed to be the key to the natural mechanism which unleashes blooms of algae in the Swan river's upper reaches during the summer months.

Each summer as the fresh river flow falls away, a wedge of salt water drives upward from the estuary, reinforced twice daily by high tides, says Dr Turner. As this happens the river actually begins to flow back inland or "uphill" in terms of its normal stream.

This change in hydraulic pressure causes salty river water to flow into the groundwater aquifers that surround the river. Groundwater normally drains through the soil and sediment into the riverbed all along its valley.

But when the cycle reverses and the river again begins its run to the sea, the sudden drop in pressure allows a flush of ground water to percolate through the river mud, releasing a rich cloud of the nutrients trapped there and so triggering the algal blooms.

Dr Turner says that the new insights gained and identification of the important role played by groundwater in contributing nutrients that trigger algal blooms in the Swan, may apply to many other river and estuarine systems in Australia and overseas afflicted by algal plagues and could prove vital for managing and preventing them.

More information:
Dr Grant Douglas, CSIRO Land & Water 08 9333 6131 or
(mobile) 015 986304
Dr Jeffrey Turner, CSIRO Land & Water 08 9333 6314
Margaret Bryant, CSIRO Land & Water 08 9333 6215
email: margaret.bryant@per.clw.csiro.au