Queensland trials new method to fight invasive species in wetlands

Posted 1 February 2017

Dry wetlandsLet the wetlands dry out – that could be the simple solution to the problem of invasive flora and fauna in one of north Queensland's coastal ecosystems. 

After all, seasonal water flows were what nature intended for the Lower Burdekin all along, said Scott Fry, who manages NQ Dry Tropics’ Systems Repair project. 

“We wanted to move away from the traditional means of weed control, which are spraying with a helicopter, burning, getting excavators in or even boat-based spraying,” he said. 

“But if we can dry these areas out, they seem to get control of themselves.”

Fry said weeds – including typha grass, water hyacinth, salvinia and hymenachne – had proliferated since the area's deepwater creek systems and lagoons had been used to store surface water and pumped groundwater for agricultural use. 

“The soil stays permanently wet, so it's perfect conditions for those weeds. It's choked all the shallow coastal wetlands,” Fry said. 

And that has had consequences not only for the ecosystem itself, but for the adjacent Great Barrier Reef and far beyond.

“Fish that should migrate from the ocean up into deepwater wetlands no longer have the habitat,” Fry said. 

“The habitat has also gone for birds from the East Asian-Australasian flyway zone that come down from as far away as Siberia periodically.”

In conjunction with Lower Burdekin Water and Burdekin Shire Council, NQ Dry Tropics has been trialling the reinstatement of dry periods since mid-2013, as part of a $2 million project funded through the Australian Government Reef Programme Biodiversity Fund. 

“We've found we need a minimum of about four months to dry out all the rhizomes under the ground,” Fry said. “The soil is a good clay soil, which will dry out and crack. This means runoff is held in them and it doesn't enter the Great Barrier Reef lagoon.”

Marked improvements in biodiversity had also been noted.

“We've seen fish go from one native species and two exotic species up to 18 species in some of the wetlands. Ultimately we should have about 26 fish species,” Fry said. 

“It's too early to say if bird numbers are coming back, but surveys conducted by Bird Life Australia have spotted a few individual species they hadn't seen for a couple of years.”