New research reveals groundwater drives estuary water quality after floods

With floodwaters receding on the Mid North Coast, landowners and fishers are now bracing for the water quality problems that tend to follow.

But researchers at Southern Cross University’s Centre for Coastal Biogeochemistry Research say a naturally-occurring gas, known as radon, can act as an early warning system.

“Groundwater has long been suspected to be the major pathway of contamination from acid sulphate soils, but assessing groundwater discharge has been put in the too hard basket for decades,” said senior researcher Dr Isaac Santos.

“We recently brought new radon technology to Australia. Radon is a good groundwater tracer because it is naturally high in groundwater and low in surface water. Since groundwater is essentially invisible, we rely on such a chemical tracer.”

Dr Santos is the leader in the use of this technology in Australia and has previously used radon to assess submarine groundwater discharge in the US, Mexico and Brazil.

“Radon is a radioactive gas present in very low concentrations everywhere. The technology we use allows us to detect low radon concentrations with outstanding precision,” Dr Santos said.

Scientists from the University’s Centre for Coastal Biogeochemistry Research have been using radon to detect releases of groundwater contamination from acid sulphate soils into the Richmond River estuary.

“At least 80 per cent of the acid and nearly 100 per cent of trace metals released from the Tuckean Swamp into the Richmond River were related to shallow groundwater discharge into artificial drains,” said 2010 Honours student Jason de Weys from the School of Environmental Science and Management.

“This was the first time someone was able to perform continuous automated radon measurements in an estuary and capture a flood,” Jason said. “Previous work relied mostly on grab samples which are hard to sample and to analyse in the lab.”

Their research ‘Linking Groundwater Discharge to Severe Estuarine Acidification during a Flood in a Modified Wetland’, co-authored by Jason, Dr Santos and Professor Bradley Eyre, was recently published in the scientific journal Environmental Science and Technology.

“Many water management approaches such as weirs and floodgates are often designed with no information regarding the real contribution of groundwater. Our radon approach can reveal whether a system is groundwater-dominated with much less effort than previous approaches,” said Dr Santos, who was Jason’s Honours supervisor.

“This work illustrates well how new technology can be used to study complex hydrological problems. Our approach can be applied to any waterway impacted by coastal acid sulphate soils.”

Coastal acid sulphate soils are a major land and water management issue in Australia. The release of acid following rain events can result in impaired waterways and concentration of toxic metals exceeding water quality guidelines. In the Northern Rivers, fish kills have been linked to water drained from acid sulphate soil catchments.

“While groundwater is clearly a source of contamination in the Tuckean Swamp, it does not seem to play a major role in the Rocky Mouth Creek in Woodburn. The design of water management structures, such as weirs and floodgates, should account for the influence of groundwater.”

This is the first study to quantify the relative contribution of groundwater discharge to surface water acidification in coastal catchments. This research is funded by a Hermon Slade Foundation grant awarded to Dr Santos.

Geochemistry at SCU was awarded the highest possible rating of ‘well above world standard’ in the Excellence in Research for Australia 2010 National report.

Photo: Jason de Weys sampling groundwater in the Tuckean Swamp. Media opportunity: Scientists from SCU’s Centre for Coastal Biogeochemistry Research are working onsite at the Tuckean Swamp and are available for interview and photo opportunities on Thursday June 23.