Research has found that nearly twice as much nitrogen enters the Great Barrier Reef from groundwater as from river water. Scientists have used natural tracers off the coast of Queensland to discover previously unquantified sources of nitrogen and phosphorus that have a profound impact on the environment of the Great Barrier Reef.
The findings, published today in the journal Environmental Science and Technology, suggest that current efforts to protect and restore the health of the Great Barrier Reef may require a new perspective.
Dr Douglas Tait from Southern Cross University led the ground-breaking research titled "Seafloor groundwater discharge exceeds river input as nutrient source for the Great Barrier Reef".
Submarine groundwater discharge is any water released into the ocean below the waterline from a variety of sources, including aquifers and the seafloor.
Research findings and implications
The research team, which also includes Australia's Commonwealth Scientific and Industrial Research Organization (CSIRO), AIMS and the University of Gothenburg (Sweden), collected data from offshore transects, rivers and coastal holes in an area from south of Rockhampton to north of Cairns. By using radium isotopes, scientists can track how much nutrients are transferred out of land and continental shelf sediments through invisible groundwater flows.
Southern Cross University Professor Damien Maher said the team's work showed groundwater discharges were 10-15 times greater than river inputs, something that had previously been impossible to calculate.
"Groundwater discharges account for approximately one-third of new nitrogen inputs and two-thirds of phosphorus inputs, suggesting that almost twice as much nitrogen enters the Great Barrier Reef from groundwater compared to river water," Professor Maher said. He added that most efforts to mitigate the impact of nutrients on coral reefs have focused on nutrients flowing out of river systems.
Potential environmental impacts and recommendations
Lead author Dr Douglas-Tate said: "Nutrients are vital in supporting the incredible biodiversity of the Great Barrier Reef. However, excess nutrients can lead to harmful problems such as harmful algal blooms, crown-of-thorns starfish outbreaks and fish diseases, which have been on the rise in the Great Barrier Reef over the past few decades. Our study highlights the need for strategic shifts in management approaches to protect the Great Barrier Reef from the impacts of excess nutrients."
Dr Tait said that unlike river runoff, nutrients in groundwater can be stored underground for decades before being discharged into coastal waters, meaning research and strategies to protect the Great Barrier Reef need to be long-term. This study reveals the complex trophic dynamics within the Great Barrier Reef. Our understanding of nutrient sources and our ability to manage them is critical to protecting the Great Barrier Reef for future generations.