Researchers study the impacts of flood events on greenhouse gas emissions

As communities across Australia’s eastern states clean up after recent heavy rain and flooding, Southern Cross University researchers are testing the waters to understand what drives the de-oxygenation of rivers and estuaries that follows in the wake of flood events.

Damien Maher, a post doctoral fellow, and Dr Isaac Santos, a senior lecturer, both with the University’s Centre for Coastal Biogeochemistry Research, are investigating the effect of the current flood event on the carbon cycle, with a particular focus on the Richmond River estuary located on the New South Wales North Coast.

“The run off from these flood events delivers a lot of nutrients from the catchment to the estuary and we know the potential for a fish kill is high. We’re wondering how these events influence greenhouse gas emissions from estuaries,” said Mr Maher said.

“We want to understand how much carbon delivered to the estuary is released to the atmosphere and how much is buried and sequestered for long term storage.”

“Like many estuaries the Richmond River catchment has significant areas of acid sulphate soils. Our preliminary findings indicate that the carbon dioxide concentrations in these waters are among the highest ever measured.”

Mr Maher said one hypothesis under investigation is that water draining from acid sulphate soils drives the de-oxygenation of estuarine water and an associated release of carbon dioxide.

“Anecdotally fish kill events occurred prior to development of the catchment but development has certainly exacerbated the problem,” he said.

“When the land was forested water on the floodplain was retained and released slowly into the main estuary, giving organic material a long time to break down. Now land clearing and the construction of extensive drain systems enable water that’s very low in oxygen to be rapidly delivered back into the river.”

Researchers from the Centre for Coastal Biogeochemistry Research expect to be conducting tests on the Richmond River for six weeks, taking water samples at a fixed station and doing surveys at 15 sites extending from the river mouth at Ballina to just beyond Broadwater.

Radon concentrations are also being measured. Radon is a naturally occurring gas that alerts researchers to groundwater.

“Radon is a good groundwater tracer because it is naturally high in groundwater while being low in surface water,” says Dr Isaac Santos, who recently brought radon technology to Australia.

“By monitoring concentrations of radon along the estuary we will be able to determine the role of groundwater in estuarine de-oxygenation and greenhouse gas emissions.”

This research is funded by grants by the Hermon Slade Foundation and the Australian Research Council.
Photo: Damien Maher testing water samples in the laboratory.