Throwing around worms and dirt to make the Coorong healthier

The Coorong lagoon, at the end of the Murray River in South Australia, has faced a tough few decades as successive droughts have made the water saltier and more difficult for threatened species to live in.

But a new technique, developed by a collaboration of half a dozen different institutions, has just been shown to improve the health of the lagoon floor (its benthic health).

It involves adding more dirt – and some worms – from healthier areas, to kickstart a process called “bioturbation”.

“Bioturbation is pretty simple,” explains Dr Orlando Lam-Gordillo, a researcher at Flinders University and lead author on a paper describing the research, which is published in Science of the Total Environment.

“It’s just a movement of sediment, including all the particles of the sediment by animals.”

This movement allows dissolved oxygen and nutrients to move through the sediment, improving the health of the system.

While the central idea is simple – take sediment from a healthy part of the Coorong and add it, with worms, to a less healthy part – Lam-Gordillo says that in practice, “it was a very complicated process”.

“It was really hard in the field,” says Lam-Gordillo.

“The first steps that we did were to select two sides in the Coorong. One side with healthy conditions [Policeman Point in the south lagoon], and one side with bad conditions [Long point in the north lagoon].”

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The researchers, who were operating as part of the Healthy Coorong, Healthy Basin program, which is jointly funded by the SA and federal governments, collected sediment “cores”, in PVC pipes – about 48 per site.

“Then we freeze the sediment to try to clean out all the possible animals that it could contain,” says Lam-Gordillo.

The cores were frozen for a week, then transplanted to Long Point and placed in the sediment below the waters there.

People waist deep in the coorong lagoon, taking notes on clip boards ad moving an esky floating on the surface
Collecting sediment and macrofauna for sampling at the Coorong. Credit: Flinders University

“After the one week that the sediments were settling there, we added the worms. We added different and specific densities of worms in each of the cores, and left [them] there for one week,” says Lam-Gordillo.

“Then we start measuring, every single week, all the different parameters to understand whether distribution of these animals could improve the condition of the sediments.”

The researchers found that this technique lowered the concentrations of sulphides, ammonium, and organic carbon – all indicators of poor water health, in high amounts – within a few weeks.

Simplisetia aequisetis worms were particularly good at doing this job.

“This important collaborative work undertaken through the Healthy Coorong, Healthy Basin program has shown that improving sediment conditions can be achieved in a relatively short timeframe if the conditions are right and key organisms are present,” says Dr Kane Aldridge, director of the Goyder Institute, which manages the initiative.

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Lam-Gordillo says that the team hopes to extend the successes of this study.

“We are planning on doing more of these experiments, with little bits of changes and modifications to the design,” he says.

“We’re still waiting on the funding and the permits to get the relevant approvals to do this. But there are plans to keep going and understand better the whole system.”

He adds that the novel coring methodology they used has drawn attention from researchers in other water systems, both interstate and overseas.

“It’s very useful for knowing the possible influence of these worms or, in general, macroinvertebrates on the sediment condition,” Lam-Gordillo says.

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