How does sediment affect the Great Barrier Reef?

What is sedimentation?

Sediment has a significant impact on the health of a coral reef. It is the broken-down natural material that moves from one place to another and is caused by the erosion of soil. Erosion is the process of soil and rock being worn away and transported by natural forces like water, wind, or ice and influenced by factors such as climate, terrain, soil type and vegetation cover

When sediment particles being carried in water (suspension) eventually drop out and settle to the ground, the process is called sedimentation. Really fine sediment is made up of silt and clay.

Vegetation loss and unsustainable land use can significantly increase erosion and sedimentation rates. These activities often disturb the land, reduce vegetation cover, and expose soil to wind and water, leading to higher sediment loads in rivers and coastal areas.

How does sediment impact the Reef?

Nutrients and other pollutants attached to sediments have the potential to be released in the marine environment and cause direct and indirect impacts to the Reef including coral and seagrass.

Much of the sediment that is washed to the Reef is very fine and can stay suspended in the water for a long time, often travelling a great distance away from or along the coast. It causes turbidity, which is where the water loses its clarity and looks murky or muddy. Fine sediment can remain in inshore areas for decades, making it available for wind-driven resuspension which causes ongoing coastal turbidity. In some areas, turbidity can reduce light penetration for days, weeks or even months.

High concentrations of suspended sediment can interfere with filter feeding by organisms such as clams. Reducing the quantity and quality of light available for photosynthesis can impact coral and plant growth and potentially smother corals. Sediment can also affect the reproductive cycle and early development of coral and some species of fish, and damage gills.

How do we manage sedimentation within the Great Barrier Reef?

Without plants and trees to hold soil together, rain can easily wash large amounts of soil into creeks and rivers.

Best management practices such as excluding cattle from gullies and maintaining ground cover promote healthy soil while minimising sediment run off.

Both the Australian and Queensland governments are working with landholders on a range of pilot gully remediation projects that are delivering results. Industry and agricultural producers are also taking action to change the way they use their land, including introducing innovative management practices, to minimise the loss of sediment from their properties.

Undertaking projects such as gully remediation works also benefits producers and graziers by improving soil health for plant and fodder growth.