Scientists say they have discovered large flows of pollution are reaching the Great Barrier Reef after soaking into underground water, a finding that could have implications for policymakers focused on cutting pollution from river catchments.
The new research claims almost a third of dissolved inorganic nitrogen and two-thirds of dissolved inorganic phosphorus in the reef’s waters are coming from underground sources – an amount previously undocumented.
Controlling pollution running on to the reef from farms has been a major focus for governments and agenciess, with scientists saying improving water quality will give corals a better chance of recovering from bleaching events caused by global heating.
UN science experts have repeatedly raised concerns that progress in improving water quality has been too slow and a failure to tackle the issue alongside the climate crisis could risk the reef being placed on a list of world heritage sites in danger.
Scientists at Southern Cross University, the Australian Institute of Marine Science and CSIRO collaborated on the research, which has been a decade in the making and is published in the journal Environmental Science & Technology.
Researchers took water samples and analysed them for radium isotopes that act as a marker for pollution. The study did not identify the source of the pollution but rather the route it took to the reef.
Dr Douglas Tait, an expert on the chemistry of coastal waters at Southern Cross University and lead author of the research, said the pollutants could take decades to move from farms to underground aquifers before emerging from springs at the coastline and from underwater springs – known as wonky holes – in the reef lagoon itself.
He said it was possible “this could just be the start of the front [of pollution] that is coming through” or it could be the tail-end.
“We could have a significant problem realised in the coming decades,” he said.
Prof Damien Maher, a co-author of the research also from Southern Cross University, said: “Groundwater discharge accounted for approximately one-third of new nitrogen and two-thirds of phosphorus inputs, indicating that nearly twice the amount of nitrogen enters the reef from groundwater compared to river waters.”
Tait said an excess of nutrients could cause algal blooms, promote outbreaks of coral-eating starfish and promote fish disease.
He said the study “underscores the need for a strategic shift in management approaches” to reduce the harm from pollutants.
Tait said there were a range of likely pathways that the pollution could take through groundwater, from moving through cracks and fissures in rocks below the top soil to dripping through porous rocks.
“We’re going to need to have a discussion about how these nutrients are managed. We need a much better understanding of this process so that we can manage it in the future,” he said.
State and federal governments have pledged hundreds of millions of dollars to improve water quality in the Great Barrier Reef.
Dr Stephen Lewis, a reef water quality expert at James Cook University’s TropWATER research group who was not involved in the research, said the study’s claims were surprising and he welcomed the chance to examine the results more closely.
There had been limited research into the contribution of groundwater as a route for nutrients to reach the reef, but its contribution had been considered minor. But he said the issue was a “knowledge gap” that needed to be filled.
“This study suggest [the contribution from groundwater] could be much larger,” Lewis said.
He said water sampling took place across the reef and nutrients would be detected directly and indirectly regardless of whether they arrived through rivers or groundwater.
The study’s findings would not change the need to support farmers to use fertilisers more efficiently, Lewis said, but it could help to better target reef funds in the future.
“We work with a lot of farmers and many of them are making great strides in nutrient management.”
The federal environment minister, Tanya Plibersek, said: “This is welcome research – the better we understand the threats to the Great Barrier Reef, the more we can do to protect and restore it.”
The government was investing $1.2bn to protect the reef, Plibersek said, including “over $232m in practical projects to improve the quality of water flowing to the reef”.
