TOXIC blooms of blue-green algae could be wiped out by spraying rivers and lakes with a fine layer of special clay, say researchers in Australia.
Blue-green algal blooms鈥攄ense, floating mats of cyanobacteria鈥� have increased dramatically over recent years. They form when nutrients in rivers and lakes are particularly abundant, something often blamed on discharges from sewage works and the use of fertilisers. More than half of these blooms produce toxins, which can claim the lives of humans and animals (快猫短视频, 18 May 1996, p 5).
But last week, a team from Australia鈥檚 research organisation CSIRO, the Water and Rivers Commission and the Swan River Trust tested a new technique that could stop algal blooms in their tracks. The researchers sprayed a section of the Canning river in Perth with a slurry of a chemically modified, absorbent clay called Phoslock.
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鈥淭he Canning river has a long history of algal blooms,鈥� says Grant Douglas of CSIRO. The clay is good at binding phosphorus, one of the major nutrients algal blooms need to survive. 鈥淲e sprayed the slurry from the back of a boat onto the water surface,鈥� Douglas says. 鈥淭he clay then strips out phosphorus as it sinks down through the water.鈥�
When the clay settles on the riverbed, it forms a barrier 1 millimetre thick, separating the algae from phosphorus-rich sediments. Because the clay does not remove all of the phosphorus in the water, Douglas says it will not endanger other organisms in the area dependent on normal levels of phosphorus. The team is now measuring phosphorus levels and looking for signs of algal blooms.
鈥淭he clever thing about this mineral clay is that it has a high mutual affinity鈥攊t sticks to itself as it settles, so it forms this cap on the riverbed,鈥� says Colin Reynolds, an expert in blue-green algal blooms at Britain鈥檚 Institute of Freshwater Ecology. 鈥淚t鈥檚 unusual to praise one鈥檚 competitors, but I think they鈥檙e onto something extremely valuable.鈥�