ANU's Dr Jennie Mallela takes a coral core skeleton sample.
ANU's Dr Jennie Mallela takes a coral core skeleton sample. ANU

Research shows impact of fertiliser run-off on reef health

RESEARCH into coral on the Great Barrier Reef has shown the long-term effects of fertiliser run-off on the health of the reef.

Research by Dr Jennie Mallela, from Australian National University's Research School of Earth Sciences and the Research School of Biology, has shown that the levels of phosphorous in coral located close to shore have increased over recent decades. 

This increase is related to the increased discharge of phosphorous coming from nearby land.

Phosphorous, a chemical element that is present in fertilisers, has been linked with deteriorating water quality and can have detrimental impacts on coral reefs, including reduced growth and in some instances, death of entire coral colonies.

"One of the things that has been highly controversial about the Great Barrier Reef is the causes of deteriorating of water quality, and the associated deterioration of coral reefs, but there is a lack of water quality information," Dr Mallela said.

"There are water quality programs that run for five-10 years, but we are missing long term data that encompass decades of information.

"I wanted to see is if we could get that information using coral skeletons. The great thing about corals is that they are a bit like trees in the sense that they have annual growth bands and we can date them easily.

"They are also very long-lived." 

Dr Mallela studied massive Porites coral, a long-lived coral family that is abundant across the Great Barrier Reef.

She specifically looked at Porites found off Dunk Island, a near shore reef in the central Great Barrier Reef.

"One of the great things about ANU is that there are brilliant geochemical analytic tools that allow us to look at what the coral skeleton actually captures," she said.

"My colleagues and I were also able to tie in data we were getting from the coral skeleton with data from the land, which is actually quite rare.

"Steve Lewis, a co-author on this research, and colleagues, were able to get river quality records and annual records of fertiliser-phosphorous application for our study region all the way back from 1925 to 2005."

Dr Mallela stressed the fact that Australians needed to be aware that what they did on land affected water quality.

"Nothing is isolated," she said. "What we do on land does affect water quality in rivers, and it also has impacts on the marine environment. 

What we do on land does affect water quality in rivers, and it also has impacts on the marine environment. 

"And these impacts have a lag effect - they can happen down the line. The impacts can vary depending on the season, what kind of weather is happening, whether there is rain, and so on."

The good news, she said, is that there was the potential to manage the amount of phosphorous entering the water.

"Whether people are putting too much fertiliser on their land in general, or whether they are putting it on during periods of rain which then washes it into the water can be investigated," Dr Mallela said.

"We can then help with the management of fertiliser application and whether they are using too much."

Dr Mallela's research, Coral Skeletons Provide Historical Evidence of Phosphorus Runoff on the Great Barrier Reef, can be found here