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 postdoctoral fellow, and Dr Isaac Santos, a senior lecturer, both with the University’s Centre for Coastal Biogeochemistry Research, are investigating the effect of the latest flood event on the carbon cycle, with a particular focus on the Richmond River estuary.
‘The runoff 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,’ 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 sulfate 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 sulfate 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. 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.’
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.’
Their research is funded by grants by the Hermon Slade Foundation and the Australian Research Council.
Damien Maher testing water samples in the laboratory.