A water monitoring program at wetlands on farms is helping scientists and landholders to learn more about how wetlands work as treatment systems for nutrient and sediment runoff.

Water samples have been collected from two constructed wetlands in the Innisfail and Tully region of Far North Queensland over the past five years, both on a regular basis and during large rainfall events.

Terrain NRM’s project officer Maria Ribbeck said the data was providing valuable insights into the way wetlands function and their extensive capacity to filter pollutants and improve water quality.

Learning the best wetland conditions for nitrogen removal

“It is also helping us to learn the best conditions for wetlands to optimise removal of nitrogen from the water cycle,’’ she said.

“One of the two constructed wetlands is on eight hectares of low-lying land on a farm managed by Tully Sugar Limited. The data has shown us it’s a high-performing site, with capacity to remove an over 1000 kg of nitrogen a year from the water passing through the wetland.”

Greg Shannon, Cane Productivity and Development Manager at Tully Sugar Limited, said the project was raising awareness of wetlands and their usefulness in the farming landscape.

“The last year’s findings were recently presented to us,’’ he said. “This project has helped us understand how wetlands work and how we can optimise their ability to treat water. The longer this wetland is monitored, the more data we can get, and this will make the findings more and more useful for our decision-making in terms of wetland maintenance and management as time goes by.

“It probably should be noted that not everyone can have a wetland like this on their farm, but we had a piece of cattle grazing land with a natural depression in it already, so it was possible to develop it into a wetland with help from Terrain NRM and the Wet Tropics Major Integrated Project.”

Monitoring at two constructed wetlands

The two constructed wetlands have been monitored for the last year through the Tully Johnstone Wetlands Monitoring Project, funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.  Terrain NRM has worked with James Cook University, Griffith University and the Queensland Government’s departments of Environment and Science and Agriculture and Fisheries on the project.

Flood-damaged riverbank upstream from the Daintree River ferry crossing will be repaired and nearby wetlands restored in a new $1.98 million project.

Terrain NRM has received funding from the Australian Government through its Reef Coastal Restoration Program to rehabilitate areas close to the ferry crossing in the Lower Daintree wetlands precinct, working with Douglas Shire Council, landholders and Jabalbina Yalanji Aboriginal Corporation.

Repairing flood-damged riverbank

“We’ll be repairing around 100 metres of eroding riverbank and restoring mangrove habitat,” Terrain NRM’s Charles Hammond said. “The erosion here, on the Daintree River, has been steadily getting worse, especially with floods like the one after Cyclone Jasper.

“Remediation work will include a mix of hard and soft engineering, and replanting mangroves and other vegetation.

“Within the Lower Daintree area, we will also be working with landholders and traditional owners to improve the condition of nearby wetlands. This is an important wetland area for the health of the Daintree River because it’s a settling area for sediment, nutrients and other loads in runoff. It’s also a fish nursery and home to more than 70 species of birds as well as flying foxes, estuarine crocodiles and other animals.”

Improving wetland connectivity

The project aims to improve wetland connectivity and the coastal ecosystem including the fish nursery habitat.

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.

A new reef water quality program has been announced to reduce the runoff of dissolved inorganic nitrogen (DIN) from farms in the Tully and Johnstone catchments. The $10.7 million program will deliver a range of projects – from helping farmers with nutrient management planning, installing constructed wetlands and expanding local scale water quality monitoring.

The program is being managed by Terrain NRM and funded by the partnership between the Great Barrier Reef Foundation and the Australian Government’s Reef Trust.

Charles Hammond, Waterway Health Leader at Terrain NRM, said the Tully and Johnstone catchments are priorities for DIN runoff due to high rainfall, intensive agriculture on the coastal plain and short sharp rivers.

“There has been significant investment in these catchments previously and farmers have been working hard to improve water quality,’’ he said. “This program will continue to support farmers to make changes to land management and farm practices.

Mr Hammond said four organisations would be delivering on-ground projects.

A partnership led by Canegrowers Innisfail is addressing nitrogen losses by providing extension support to farmers to develop nutrient management plans, identify crop constraints, improve nutrient use efficiency and refine nitrogen inputs.

A boggy spot on a Mourilyan cane farm has been converted into a high-performing “constructed” wetland, removing more than 90 per cent of nitrate from water in the system. 

The Wet Tropics Major Integrated Project team has worked closely with wetlands experts and a third-generation cane farmer to transform the low-lying and unusable strip of land into a water treatment system on his 101-hectare property. 

The 1.2 hectare wetland is proving that, with some remediation and construction, low-lying wet areas can effectively remove high levels of dissolved inorganic nitrogen from the water. 

Acting Project Manager Fiona George said this wetland shows the potential of wet areas on farms to improve the quality of farm run-off water. 

“This constructed wetland is evidence that a wet piece of marginally productive land can yield excellent water quality outcomes with the help of a tailored design and relatively minimal earthworks,” Ms George said. 

“We enhanced existing features that helped it to perform as a denitrifying wetland.” 

Vegetation uptake has been a key factor, with a thriving ecosystem of plant life establishing itself in a short timeframe and enabling the denitrification process to occur. 

The Wet Tropics Major Integrated Project has trialled a range of catchment repair systems in the Tully-Innisfail area, including seven different bioreactor designs, a landscape wetland, three in-drain wetlands, a high-efficiency sediment basin, three constructed wetlands and a riparian revegetation site. 

The constructed wetlands are yielding the best results, proving that, with improved hydrology and the appropriate amount of vegetation, they have high potential to reduce nitrate levels.