CRC Care

CRC Care

Clever science leads to stunning reversal of acid-sulfate soil contamination at East Trinity, Queensland


Source: CRC Care

Scientists involved in an 18-year project to remediate acid sulphate soils at a north Queensland site have pulled off a major accomplishment, turning the once badly acidified land into a place where mangroves, native birds and other wildlife have now returned.

The 774-hectare site at East Trinity, located directly across Trinity Inlet, Cairns, was originally a natural estuarine floodplain, covered by mangroves and salt-marsh, but became an environmental disaster in the 1970s after being drained to create a sugarcane farm.

CRC CARE, with Queensland’s Department of Environment and Science (DES) and Southern Cross University (SCU), developed a highly effective remediation approach – known as Lime Assisted Tidal Exchange, or LATE– after the Queensland Government purchased the property in 2000 with the intention of protecting Trinity Inlet and the Great Barrier Reef.

Queensland Minister for Environment Leeanne Enoch said the processes used at East Trinity are now seen as a benchmark for rehabilitating acid sulphate soils.

“During the site’s transition to a sugarcane farm, a large 7km bund wall was constructed to prevent the natural flow of tide. Because of this, previously waterlogged soils were exposed to air, resulting in a chemical reaction where sulfuric acid was released at a level of acidity equivalent to battery acid,” Ms Enoch said.

“Acid water leaked from the soil into the waterways – along with large quantities of iron, aluminium and other metals – resulting in fish kills and the death of the mangrove forests. The sugarcane production also failed, and the soils and waters became severely degraded.

Ms Enoch said the remediation processes used at East Trinity are now seen as a benchmark for rehabilitating acid sulfate soils.

“The standard treatment for acid sulfate soils was to mix lime into the soil to help neutralise the acidity. But in 2000 when the Government bought the property, the cost of doing this was estimated to cost about $78 million in lime alone, which was far from cost-effective. So scientists were charged with coming up with a low-cost solution,” Ms Enoch said.

“That’s exactly what they did. They reintroduced tide to the site by re-engineering the floodgates that had been originally used to stop the tide from entering. This stopped the soil from drying further and assisted in the process of neutralising acid. Then they added a type of lime to the tidal waters to help further neutralise the soil acidity.

According to Professor Richard Bush, Project Leader for the East Trinity Remediation Project, the bulk of the original remediation cost estimate was for the lime required using a conventional approach. The LATE method reduced lime use to less than 5% of the original requirements.

“The program worked,' said Ms Enoch. 'When the mangrove forests first died, acid-tolerant paperbark trees took over large areas of the site. These invading paperbarks have now being recolonised by the original mangroves. The return of mangroves has brought back many species of fish and birds.”

Ms Enoch said the success of the remediation work at East Trinity had also generated a lot of international scientific interest and led it to becoming a CRC CARE national demonstration site for innovative acid sulfate soil remediation.

“Now, the research and field program being used at East Trinity is being exported to other parts of the world.”

Part of the East Trinity site before (above, in 2003) and after (below, in 2012) LATE remediation. Photos: Richard Bush.

Additionally, the East Trinity acid sulfate soil restoration project was one of the few landscape-scale case studies to be included in the National Standards for Ecological Restoration, which are now being adopted internationally

'The project outcomes go well beyond the considerable scientific advancements,' said Professor Bush. 'This initiative empowered the local community, brought all stakeholders together, nurtured a cohort of emerging international leaders in land management, and opened new opportunities for the traditional owners. This is one of the most exciting projects that I have been involved with”.