21 AUGUST 2023

Two constructed wetlands on farmland in the Cassowary Coast region are under the spotlight, with new funding announced to monitor how they can improve water flowing to the Great Barrier Reef.

The Great Barrier Reef Foundation is funding a project led by Terrain NRM at the wetland sites in Mourilyan and Tully, which were created almost four years ago as potential water treatment systems to reduce nitrogen runoff from sugarcane farms.

Terrain NRM water quality monitoring leader Alicia Buckle said monitoring over several years as part of the now completed Wet Tropics Major Integrated Project had shown the wetlands’ potential for removing dissolved inorganic nitrogen.

Removing nitrogen from the water

“We have evidence that the wetlands are removing nitrogen from the water cycle but we still have a lot to learn about how dissolved inorganic nitrogen travels through wetlands like these, and under what conditions these sites are most effective at removing nitrogen,’’ she said.

With the new funding, Terrain NRM will be working with James Cook University, Griffith University and scientists from the Queensland Government’s departments of Environment and Science and Agriculture and Fisheries to regularly monitor the wetlands, including during large rainfall events.

Terrain NRM water quality project manager Karen Lindee said results would help to determine the wider scale potential of constructed wetlands on low-lying farmland.

The one-year project is now part of the three-year Tully Johnstone Water Quality Program, funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation. This program is reducing the amount of dissolved inorganic nitrogen entering the Great Barrier Reef’s waters through a range of projects including working with farmers to improve yield and nutrient management, and building a better understanding of water quality issues using local-scale water quality monitoring.

Tully and Johnstone: Priority catchments for runoff reduction

The Tully and Johnstone River basins, on the Cassowary Coast, are priority catchments for nutrient runoff reduction. This is an area with significant sugarcane and banana land, where farmers have been working for a number of years on changing to farming practices which improve water quality.

The Wet Tropics Major Integrated Project, which included both the construction and the previous monitoring of the two wetlands, was funded by the Queensland Government’s Queensland Reef Water Quality Program. This project also focused on reducing nutrient, sediment and pesticide run-off into waterways.


Tully wetland
Tully Sugar Limited has set aside eight hectares of land to help trial ways of reducing nutrient and sediment run-off. A wetland was formed on low-lying grazing land with a design that encouraged shallow flooding and allowed natural wetland vegetation to grow back. Data has shown it is a high performing site. As vegetation has become more established, the wetland’s nitrogen removal capacity has consistently improved. It is estimated to remove over 1000kg of nitrogen a year.

Mourilyan wetland
A wet piece of marginally productive land on a cane farm was converted into a 1.2-hectare wetland, indicating that, with some remediation and construction, low-lying areas can effectively remove dissolved inorganic nitrogen from the water. Vegetation establishment has been a key factor, with a thriving ecosystem of plant life forming in a short timeframe and enabling the denitrification process to occur.


  • Wetlands are vital ecosystems. Home to 40 per cent of the world’s species, they filter polluted water, mitigate flooding and provide habitat and nursery grounds for many species.
  • They can also help to combat climate change through the abundance of plant life which releases oxygen while capturing and storing huge amounts of carbon. In this way, wetlands act as carbon sinks – areas that take in more carbon than they release.
  • Almost 50 per cent of swamps and 40 per cent of river wetlands have been cleared in the Wet Tropics region.


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