Seawater could reduce wetland weeds

Laine Clark
(Australian Associated Press)


Scientists have discovered weeds choking Australia’s freshwater coastal wetlands can be reduced by reconnecting the area with the sea.

A Queensland research team has found freshwater weeds which dramatically impact water quality and the ecosystem can be controlled by tidal flows after studying a wetlands area in the state’s far north.

Nathan Waltham – who led the James Cook University research team – says rehabilitating a wetlands area with seawater is a more favourable long-term alternative to controlling weeds with chemicals.

“It’s almost like having Mother Nature assist us,” Dr Waltham told AAP.

“The tide should get in there more often in the future. That would save the need for pesticides and herbicides.”

The research was held at Mungalla wetlands, north of Townsville, where hydrodynamic modelling was used to asses the impact of removing an embankment and reconnecting the area with the sea.

After encouraging results the embankment was removed and scientists found seawater had controlled weed growth and improved water quality.

“The weeds are a problem because they entirely cover the surface area of the wetlands and that has major problems on water quality,” said Dr Waltham, who heads JCU’s Centre for Tropical Water and Aquatic Ecosystem Research.

“By clearing the weeds we see an improvement in water quality and with the tides coming back we are seeing more fish coming back as well.”

Dr Waltham said their research focused on Great Barrier Reef catchments but was relevant for wetlands “all around Australia”.

He said the restriction of tidal flushing onto coastal wetlands and creeks by roads, pipelines, floodgates and culverts in the country had “negatively impacted” on not only the water but also birds, fish and plants.

He said their research provided simulations that would determine the potential impact of other coastal wetlands being reconnected to the sea.

“For example, the removal or height adjustment of tidal barriers, the dredging of silted streams, the removal of weeds from choked streams and the reintroduction of tidal flows can now all be modelled beforehand,” Dr Waltham said.

“Now we might look at similar earth walls that have been built a number of decades ago along our coastline and there are lots.

“We now have some good science and modelling capabilities to look at that and inform future restoration of precious coastal wetlands.”

The research – released on Tuesday – was funded by the federal government’s National Environment Science Program Tropical Water Quality Hub.

It was led by the JCU’s Centre for Tropical Water and Aquatic Ecosystem Research in collaboration with the CSIRO.


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