Title Marshes a moveable feast Media name/outlet ABC Science Online Media type Web Date 10/09/02 Description A study of marshes in New South Wales has revealed that our wetlands refuse to stay put.
Researcher Tim Ralph from Macquarie University's Department of Physical Geography measured sedimentation rates in the Macquarie Marshes in the state's central west.
He found that the water channels that make up the wetlands appear and disappear as often as every 100 years, dispelling the myth of the stagnant marsh.
"What we have shown is that the channels are actually moving around quite frequently," said Mr Ralph.
The Macquarie Marshes are a 250,000-square-kilometre area of water channels and swampland fed by the Macquarie River. They lie about 250 kilometres northwest of Dubbo.
The wetlands harbour the Macquarie Marshes Nature Reserve, and have been included on the Ramsar List of Wetlands of International Importance.
Understanding the dynamic nature of the Macquarie Marshes is important from a conservation point of view, because there are only a few designated conservation areas, and they have rigid borders.
To better understand the evolution of the landscape, the researchers measured the rate of sedimentation in the water channels. They sampled the sediment at different depths and estimated its age using Lead-210 and radiocarbon dating.
Lead-210 and radiocarbon are radioisotopes that decay slowly over time. By measuring the amount of Lead-210 or Carbon-14 (radiocarbon) in a soil sample from a known depth, it is possible to infer how old the sediment is.
The researchers used Carbon-14 dating for older soil samples, and Lead-210 dating for those less than 200 years old. They found that sedimentation rates appear to have increased over time, and hypothesised that post-European agriculture may be behind the change.
After European settlement, land-clearing and grazing practices in the upper catchment may have deposited more sediment in the lower catchment, Mr Ralph explained.
However, further research is needed to confirm this hypothesis.
Information about sedimentation rates will allow researchers to predict future patterns of marsh movement, and hence better manage the marshes, he said.
"It's a possibility that a lot of the marsh areas that are held within the conservation areas might be abandoned because of this channel forming outside of the static conservation area. There's nothing to keep the water in the fence."
"Hopefully we will be able to show from the work we have done, a way of quantifying how fast things are moving around, which [conservationists] may be able to work into their conservation strategies."
URL www.abc.net.au/science/articles/2002/09/10/668318.htm?site=scie&topic=latest Persons Tim Ralph