Sydney, Jan 5 Conservationists led by a scientist of Indian origin has restored large tracts of acid-ravaged coastal wetlands in Australia for the first time.

Mangrove and wetlands are returning, birdlife is flocking to the area and fish abound in creeks that once ran so acid that nothing could survive in them.

The acid crisis at East Trinity near Cairns in Queensland began in the 1970s, when developers drained and cleared 800 hectares of tidal wetland to grow sugarcane.

This dried out underlying acid sulphate soils, causing them to release slugs of acid whenever they were soaked by rain, leading to fish kills and loss of wetlands, which alarmed local residents.

Today East Trinity is a world-class demonstration of large-scale restoration in action, says Ravi Naidu, managing director of the Cooperative Research Centre for Contamination Assessment and Remediation of the Environment (CRC CARE).

"There are an estimated 40 million hectares of similar acid coastal wetlands round the world and at least four million in Australia, including the lower Murray-Darling, and areas along the coasts of NSW, Queensland, SA coasts and WA," says Naidu, who was awarded a Gold Medal in environmental science in 1998 by Tamil Nadu Agricultural University.

The main restoration work is being carried out by the Queensland Department of Environment and Resource Management in partnership with CRC CARE and Southern Cross University (SCU).

"We re-introduced a partial tidal exchange through adjustable floodgates, so as to gradually re-flood the most acidic sediments and prevent them producing more acid," said CRC CARE project leader Richard Bush from SCU.

"Where the runoff was still too acid we added hydrated lime using specially designed equipment," said Bush. Gradually the mangroves began to recolonise, with a wider species diversity than the scientists had dared hope for, said a CRC CARE release.

"The birds are back too. In fact the bird life is fantastic with more than 100 wild species observable within a 10-minute boat ride of the Cairns CBD. How many cities in the world can claim that?"