This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Imagine a plume of brown sediment washed off the land into Queensland rivers and carried out to sea. Here, it can settle on seagrass and inshore corals, potentially smothering them.
River water often also carries nitrogen from fertilizer residue, which can fuel algal growth and damage coral health. We have long known that poor water quality is a serious threat to areas of the Great Barrier Reef close to shore. The reef faces other major challenges, such as marine heat waves driven by climate change that trigger large-scale coral bleaching.
But unlike climate change, water quality is something Australia can directly control. Since 2014, the federal and Queensland governments have collectively spent more than A$5 billion on catchment programs for reef health. Many of these aim to improve water quality by reducing fertilizer runoff from farmland and tackling erosion to stop sediment from entering waterways.
Our new research shows water quality is improving in many rivers that flow to the reef. To find out whether water quality is changing, our research team analyzed up to 37 years of monitoring data from seven major river systems to track changes in fertilizer runoff (dissolved inorganic nitrogen) and suspended sediment. These are two of the five key pollutants scientists use to track changes in river basins.
Our research is the largest and most comprehensive analysis of catchment water quality for the reef to date. These river basins drain around two-thirds of the Great Barrier Reef water catchments, an area the size of New Zealand. Given the complexity of the data and the size of some catchments, we did not necessarily expect to detect measurable improvements in water quality.
However, the data showed small but measurable improvements in nitrogen and sediment across most monitoring sites. Rivers with improved long-term water quality include the Herbert, Burdekin and Pioneer rivers, as well as the Tully and Fitzroy. Our data show that water quality didn't follow a predictable pattern of steady improvement.
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