Native Plant Choking Murray Waterways

[mrmoshe]

Native plant choking Murray waterways

The Murray River may have a reasonable flow after summer rain but some of the wetlands in the basin are struggling after years of drought.

Scientists are facing a new challenge as a native plant takes over one of the major waterways, upstream of Echuca on the Victoria-New South Wales border.

Not only is it strangling the system, but it is spreading to adjoining wetlands and is now threatening to play havoc with the river flow.

It is called Barmah Lake and not only is it surrounded by the biggest area of river red gums in Australia, it is also a major wetland in the Murray-Darling Basin and a crucial breeding site for thousands of native water birds.

But after years of drought the most common native here is what's called the giant rush - it is a reed-like plant that is taking over.

Keith Ward, an ecologist working with the Goulburn Broken Catchment Management Authority, says it has taken over at least 70 per cent of the lake system and some adjoining wetlands over the last number of years.

"It's actually starting to dominate a lot of the wetlands," he said.

"Now these systems are very rich in flora and also a number of waterbirds that feed amongst it.

"The threat is once it's dominated by giant rush, it dominates to the exclusion of just about all other plants and there is a lot of waterbirds that can no longer feed in those type of areas."

Fast growing

Wading through the lake, the water is still shallow - about knee deep - but that is exactly the conditions this weed-like native loves.

The rushes now surround the outskirts of the wetlands and have spread right across the system.

Even on the flood plains where there is no water, they are about two metres in height and scientists are having trouble keeping up.

Mr Ward said the problem is that it grows very quickly.

"We've been monitoring growth rates of 11 millimetres per day," he said.

Scientists are also trying to establish which fish have survived the drought conditions here in the lake.

They are using what is called electro fishing, sending a charge into the water, temporarily stunning the fish, and bringing them to the surface.

Big job ahead

Zeb Tonkin, a member of the team from Arthur Rylah Institute based in Melbourne, says a majority of these habitats have dried up.

"It's come down to a few key refuge pools where these species are hanging out and waiting for some water to come down. We've been able to identify these," he said.

The challenge now is to try and create a balance and find a way of slowing its spread.

They have trialled a system of burning the clumps of rushes on the flood plains.

But Mr Ward, who has been working in this wetland for almost 20 years, acknowledges they have a big job ahead.

"It can attain a height of three metres in its adult form so you need very deep floods to get rid of it when it's an adult," he said.

"Already it's half adult size so if we don't get flooding this winter, it's going to be there for good."