NSW estuaries are warming at twice the rate of the ocean

New South Wales rivers, lakes and lagoons are warming more rapidly than the ocean.
By Angela Heathcote April 15, 2020 Reading Time: 2 Minutes

THE ANALYSIS OF 166 New South Wales rivers, lakes and lagoons over a 12-year period has revealed that the state’s estuaries are warming at twice the rate of the ocean and the atmosphere. 

Scientists say the changes will severely impact economic activity and those that rely on the estuaries for their livelihoods, and ecological biodiversity. 

By closely monitoring estuaries along the NSW coast, scientists found that they have warmed by more than 2°C compared to 1°C of warming in the ocean and atmosphere, while the water has also become more acidic, growing by 0.09 pH units annually.

According to Elliot Scanes, a marine biologist at the University of Sydney and the lead author of the study, the reason estuaries are warming at a faster rate is that they tend to be shallow and can therefore absorb more heat per volume of water, as well as the length of time water stays within an estuary. 

Traits such as depth, size and vegetation also contributed to the way an individual estuary is coping.

“Each estuary is unique,” Elliot says. “A lake and a lagoon may experience the same degree of atmospheric warming, however the traits of that estuary will determine the amount of warming that takes place in the water.”

If Australia has a business-as-usual mindset towards carbon emissions, the leading cause of global heating, Elliot says we are likely to see a continuation in the warming of estuaries in NSW, and around Australia. 

“Climate change is likely to decrease rainfall in eastern Australia, which will further affect the salinity, pH and temperature of estuaries.”

The breakdown of estuaries due to global heating will also impact the ability of coastal communities to cope with increasing severe weather events.

“The rates of change observed in this study may also jeopardise the viability of coastal vegetation such as mangroves and saltmarsh in the coming decades and reduce their capacity to mitigate storm damage and sea-level rise,” says Pauline Ross, who leads the research group at the University of Sydney and worked with Elliot on the study.

As for marine life, Elliot says research in other countries such as the USA indicate that estuarine vegetation such as mangroves are moving into new areas that were once too cold, and we could see the same process happen in Australia, but more research is needed.

“We don’t have many measurements of how animals have been affected by these changes in estuaries because this change is recent,” Elliot says. But as an example, “Some research has shown that oysters may be producing weaker shells as a result of lower pH in Wallace Lake, Forster.

“We do, however, have laboratory studies replicating these conditions that have shown a range of effects indicating that some species will be winners and others will be losers.”