During high rainfall or river flow events, gully erosion causes sediment and nutrients to wash out to the Great Barrier Reef. Excess sediment and nutrients means poor water quality, impacting the health of the Reef (read our explainer here).
Fixing these eroding gullies and stopping sediment and nutrient run-off at the source is therefore a priority for our community and government.
Gully remediation projects in the Reef catchments – like those Greening Australia undertakes – reshape massive eroding gullies and stabilise the soil with techniques such as revegetation to reduce sediment. But do these projects also reduce nutrient export? The aim of this project was to understand nutrient export from different remediated gullies to identify the best remediation techniques for overall improvements to water quality.
The impact of excess nutrients on the health of the Reef has been well researched. Nutrients impact the Reef along with sediment run-off. Particulate and dissolved nutrients (e.g. dissolved inorganic nitrogen) are transported with fine sediment during rainfall events, from gullies to Reef ecosystems where they become bioavailable (i.e. the nutrients are in a form that can be consumed and utilised by marine organisms directly).
Most gully remediation methods include the use of erosion stabilisation materials that will initially alter nutrient run-off from the gully system. However, we do not fully understand the impact or longevity of these alterations and what implications they may have on downstream ecosystems (e.g. the Reef).
Previous collaborative research with Griffith University and the Queensland Department of Environment and Science, for example, showed that some gully treatments reduced nutrients in proportion with sediment reductions, while there was no clear trend with other treatments.
In this project, a team of experts from Griffith University, Queensland Department of Environment and Science, TropWATER at James Cook University, and Greening Australia aimed to better understand nutrient export from remediated gullies in order to identify which remediation methods are successful for reducing both sediment and nutrient export.
We measured sediment and nutrient run-off from different remediated gully treatments located at Strathalbyn Station in the Burdekin catchment, across four wet seasons. Sediment tracing studies and laboratory experiments were also conducted to evaluate how different remediation materials may alter nutrients over time.
This project’s findings will help inform best practice guidelines for future gully remediation interventions.
The project team from Griffith University, Queensland Department of Environment and Science, TropWATER at James Cook University, and Greening Australia collected samples across four wet seasons and found that using certain remediation materials when fixing eroding gullies can reduce nutrient run-off.
Materials that have high Carbon to Nitrogen (C/N) ratios, such as bagasse or rock capping, can reduce nutrient run-off from fixed gullies. By contrast materials with low C/N ratios, such as Rhodes grass and sorghum hay mulch, can increase nutrient run-off as they decompose.
Locally sourced soils (cracking clay) can be used; however, it is critical to maintain groundcover and reduce grazing pressure to prevent the imported soil and associated nutrients from being mobilised during high rainfall.
Lessons learned and next steps:
For more detailed information on findings and next steps, please refer to the technical report.
This project was part of the $10 million Innovation and Systems Change Program funded by the Great Barrier Reef Foundation’s partnership with the Australian Government’s Reef Trust.
The project built on previous water quality research and gully remediation projects including Strathalbyn Phase Three (funded by the Great Barrier Reef Foundation) and the Innovative Gully Remediation Project (funded through the Queensland Government’s Reef Water Quality Program).
Martha is Greening Australia’s Technical Lead in Science and Planning for the Reef Aid program, working on the monitoring, evaluation and reporting for our projects to improve water quality on the Great Barrier Reef. She is a highly skilled and passionate environmental scientist and marine biologist, with a MSc from James Cook University and over 10 years of experience working in coastal ecology and environmental research. Martha also brings experience in project management and innovative technology to the team. She is passionate about improving the long-term wellbeing of the Reef and coastal habitats for their inhabitants and our community.