We need to go beyond farm-based changes. And that means scaling up broad landscape repair work, including restoring wetlands and installing engineered water treatment systems to intercept runoff before it reaches waterways.

Wetlands as pollutant removers

Researchers have been monitoring several wetlands, including three constructed wetlands in the Wet Tropics – on cane, banana and cattle farms. The concentrations of nitrogen and sediment going into and out of the wetlands show they are working effectively to clean pollutants from runoff and further data has been collected to estimate the quantities removed.

Tony Weber from Alluvium Consulting says the data collected from these wetlands is being used to test a model that predicts how wetlands will perform under different weather and landscape conditions. The model can calculate the overall water quality improvement if wetlands were repeated across the landscape, making it useful for planning and managing future wetlands to improve the quality of water flowing to the Reef.

“It takes time and a lot of data to understand how wetlands function,” he says. “But what we’ve learned is clear—vegetation is everything. With the right amount of vegetation and proper maintenance, wetlands can effectively remove a lot of nutrients.”

Water flow also matters. Tony says wetlands need to hold water long enough for pollutants to be removed and if water flows through too quickly, they don’t work as effectively.

The Road Ahead

Wetlands are an important part of the broader Reef ecosystem. Evidence shows that the negative impacts of pollutants running off the land to the Reef can be reduced by installing treatment wetlands in addition to expanding the restoration of natural wetlands, particularly on land with low agricultural value.

James Donaldson, former Executive Officer at Wet Tropics Waterways, says the goal is to reduce pollutants at the source through good farm practices, and then to use treatment wetlands as interceptors that clean up any runoff before it enters waterways. Natural wetlands can provide the final ‘polish’.

“Wetlands are important to our aquatic landscapes—they protect our rivers, lakes and the Reef lagoon from pollutants and provide vital habitat for birds, fish, reptiles and amphibians. They also provide a buffer against storms and floods.

“We need to protect the wetlands we have and bring degraded ones back to life.”

Fast Facts

• Historic loss of wetlands from clearing and draining land has stabilised.
• Treatment wetlands are man-made systems designed to mimic the natural processes of wetlands in treating water.

The wetland monitoring is a collaboration between Terrain NRM, James Cook University, Griffith University and Queensland Government agencies. It is funded by the partnership between the Australian Government’s Reef Trust and the Great Barrier Reef Foundation.