Groundwater is carrying a significant portion of the pollutants coming into the Great Barrier Reef, a recent study has found. According to the study, previously unquantified nitrogen and phosphorus have been discharging into and impacting the reef system, and researchers have now found that groundwater is responsible for about one-third of new nitrogen and two-thirds of new phosphorus coming into the Great Barrier Reef.

These findings, published in the journal Environmental Science & Technology, show that about twice as much nitrogen is coming into the world’s largest reef system from groundwater compared to rivers.

Researchers from Southern Cross University in Australia, Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO), the Australian Institute of Marine Science (AIMS) and Gothenburg University in Sweden, collaborated on the study. Researchers used radium isotopes to test reef water samples and collected data from an area stretching from south of Rockhampton to north of Cairns in northeastern Queensland, Australia.

The study shows that groundwater was discharging into the reef about 10 to 15 times more than rivers were. Groundwater as a significant carrier of pollution to the Great Barrier Reef hasn’t been accounted for in previous studies. Instead, efforts to minimize pollution have primarily focused on rivers rather than groundwater.

“Nutrients are essential to support the incredible biodiversity of the Great Barrier Reef. However, an excess of nutrients can lead to detrimental issues such as harmful algal blooms, crown-of-thorns starfish outbreaks, and fish diseases, which have been on the rise in the Reef over the past few decades,” said Douglas Tait, lead author of the study. “Our study underscores the need for a strategic shift in management approaches aimed at safeguarding the Great Barrier Reef from the effects of excess nutrients.”

Although the research team didn’t follow the pollution to identify the original sources, they did note that groundwater pollution can spend many years underground before it discharges into the ocean. 

“This could just be the start of the front [of pollution] that is coming through,” Tait told The Guardian. “We could have a significant problem realized in the coming decades.”

Because of this factor of groundwater pollution, it will be important for policymakers to consider long-term strategies to mitigate groundwater pollution into the reef. Further, this research reveals more studies are needed to examine exactly how the pollutants are moving through groundwater to the reef system.

“This study sheds new light on the complex nutrient dynamics within the Great Barrier Reef,” Tait said in a statement. “Our understanding and ability to manage the sources of nutrients is pivotal in preserving the Reef for generations to come.”

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