Study clears Coorong's muddy waters
Wednesday, 30 November 2005
The natural condition of South Australia's renowned Coorong wetland has a lot to do with flushing by tides and less to do with freshwater inputs from the River Murray, according to new research by the University of Adelaide.
Senior Lecturer in the University's Discipline of Geographical and Environmental Studies, Dr Peter Gell says initial findings of research he is conducting with PhD student Ms Deborah Haynes suggests that for almost all of the 6000 years of the Coorong's history prior to European settlement, it did not contain a certain type of phytoplankton readily found in the River Murray from the same time.
For their research, Dr Gell and Ms Haynes are examining the fossil diatom algae preserved in the sediments of cores taken from 30 sites along the length of the Coorong. They presented the first stage of their findings at the 44th Australian Society for Limnology Congress, being held in Hobart this week.
"It was something of a surprise to us that the species typical of the River Murray and lower lakes have been largely absent from the Coorong for its entire history," Dr Gell says. "The species typical of the pre-European Coorong are reflective of a strongly tidal estuary, for almost its complete length. It is now clear to us that the Coorong has been mostly an estuarine- marine system and that the exchange via the Murray Mouth was much greater than we see today"
Dr Gell says the University's findings are consistent with geomorphologists who have revealed that the lower lakes were naturally separated from the Coorong by an uplifted, old shoreline that was likely to have directed most of the Murray flow out via the northernmost Goolwa channel.
"This is not to say that River Murray flows are not important to the system. They are likely to have played the critical role in maintaining the opening, allowing for the influx of clear, oxygen-rich seawater into the system," Dr Gell says. "Sadly now, the Coorong is mostly closed at all ends and it is rapidly accumulating fine sediments that are muddying the Coorong's waters.
"We are looking at a substantially changed ecosystem. A naturally open system that is now closed; a naturally clear, brackish-marine water system that is now turbid and hypersaline."
Geographical & Environmental Studies
University of Adelaide
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