Water quality scrutinised on the Great Barrier Reef

While climate change remains the biggest threat, poor water quality continues to exacerbate its impact on the Great Barrier Reef, according to a new report.

A body of 200 experts, using 4,000 publications’ worth of evidence, has collated the review on the water quality of the Great Barrier Reef.

The review, called the 2022 Scientific Consensus Statement, finds varying levels of health across the entire reef.

The statement, which is the fifth of its kind, rests on data compiled from 1990 to 2022. This means it hasn’t taken the most recent mass bleaching event into account.

“It was challenging yet rewarding to synthesise decades of peer-reviewed scientific literature, paying tribute to the numerous researchers who have studied the Great Barrier Reef and documenting the history of my field,” says report co-author Dr Steve Lewis, a research scientist in James Cook University’s TropWATER division.

“The review shows a substantial rise in sediment, nutrient, and pesticide concentrations since European settlement in most river basins of the Great Barrier Reef catchment.

“This evidence was gained through multiple sources from monitoring data, model simulations, coral cores and sediment cores.”

Thirty-five experts involved in the study have agreed on 8 conclusions, including that pollutant loads flowing into the Great Barrier Reef have increased, land management is impairing the reef’s water quality, and that meeting water quality targets in the next decade is “imperative” to improve climate resilience.

“The review confirms that excess dissolved inorganic nutrients (such as nitrogen and phosphorus) affects a variety of organisms and ecosystems in the Great Barrier Reef, from phytoplankton, seagrasses, macroalgae, corals, mangroves to freshwater habitats,” says co-author Professor Guillermo Diaz-Pulido, a marine ecologist at Griffith University.

“However, the effects are very variable and difficult to generalise, which is not surprising given the high diversity of species in the Great Barrier Reef.”

Some areas, particularly closer to the shore, recorded declines in their ecosystem. Conversely, midshelf and outer shelf regions of the reef saw increases in coral cover, and some places saw fast coral recovery after bleaching events and crown-of-thorns starfish attacks.

“The review shows how important good water quality is to help the Great Barrier Reef recover from climate change impacts,” says co-author Dr Katharina Fabricius, a senior principal research scientist at the Australian Institute of Marine Science.

“This is particularly important in areas close to the coast, which are more susceptible to runoff and not recovering as well as reefs further offshore.

“Climate change is increasing the intensity of floods and droughts, making it even more challenging to minimise the runoff of pollutants.”

Another major finding of the report was that ways to improve water quality will be adopted faster when they are locally effective, involving engagement with landholders, Indigenous communities, and broader communities.

“Most of the changes in land management for water quality improvement have been in the sugarcane and grazing industries,” says report co-author Dr Anthea Coggan, a senior environmental economist at CSIRO.

“Often the first step to achieving a water quality benefit is improving the knowledge, aspirations, skills and attitudes of land managers towards the land management change and many programs have been very successful at this.

“A consistent way of measuring factors such as the extent and longevity of change will further improve our understanding of the impact on water quality outcomes into the future.”