River health study to aid water allocation policy

The Commonwealth Scientific and Industrial Research Organisation (CSIRO) study will look at the affect of water extraction – via surface diversion or groundwater pumping – on the relationship between nutrients and plant and animal life in river sediments.

“Water extraction reduces river flow downstream, and there is evidence that this has contributed to the degradation of our aquatic systems,” says CSIRO Land and Water scientist, Dr Andrew Herczeg.

“We aim to find out what is the most appropriate amount of groundwater needed for an environment to maintain river ecosystems, particularly during stressful dry periods. This will help water managers reduce the arbitrary nature of many water allocation policies. They will know for the first time how much water can be safely taken out of the system without affecting the river’s ecosystem and health.”

Three rivers are part of the study – the Murray River, the Wollombi Brook in NSW’s Hunter Valley and the Murrumbidgee or Macleay Rivers. Piezometers – measurement wells – have already been installed at sites on the rivers to monitor the changing depth and chemical composition of water as the river flow changes over a 12-month period.

In particular, research is examining how groundwater beneath the river surface interacts with the river’s surface water. Scientists hope to track nutrient exchange between small crustaceans, plankton, and tiny plants called macrophytes and how this affects the river’s chemical composition.

“We are spending a lot of money to restore our rivers but we need to urgently improve our knowledge about how rivers actually operate,” said Dr Herczeg. “We believe if we know more about the exchange of water, salt and nutrients, then we can make better decisions about what is an appropriate water management strategy. What happens after that is up to water managers.”