Impacts of sediment run-off

How is sediment run-off impacting the Reef?

Sediment discharged from rivers reduces sunlight available to sea grasses and corals and can smother coral growth. The resulting decline in water quality also increases the risk of serious long-term effects on Reef health and decreases its resilience to pressures caused by climate change, ocean acidification and tropical cyclones.

How is the sediment from my property ending up in the Reef?

Over time, unsustainable practices reduce pasture and ground cover, which increases the risk of valuable top soil being lost when it rains. Reduced ground cover also increases overland flow, exacerbating gully and streambank erosion and increasing sediment and nutrient delivery to waterways draining to the Reef lagoon.

Fine sediments (e.g. silt and clay) travel further in the Reef lagoon and can form flocs, which stress coral in the following ways:

  • block light
  • smother corals
  • reduce oxygen and pH levels.

Watch the sediment journey to see how sediment travels to the Great Barrier Reef

Duration 1:32

The ocean and the paddock are more connected than you might think.

When erosion occurs on hill slopes, gullies and stream banks, soil and nutrients run-off the paddock and into local waterways.

Though most soil particles and nutrients drop out at the river mouth - some fine particles or ‘sediment’ continues its journey to the ocean and the Great Barrier Reef.

Nutrients on the sediment feed bacteria, fungi and plankton. These attach to fine particles and form flocs that act as murky ‘clouds’ - blocking essential sunlight from seagrass and coral.

After a few weeks, flocs smother the coral and the bacteria that feed off flocs bloom, which the coral cannot remove.

Eventually, the coral becomes stressed and can die.

High winds and tides can resuspend and move flocs. They will continue to block out light to coral and seagrass.

Some flocs break down and disperse over a year and are carried into deeper areas where they are no longer resuspended. Other flocs, carried into coastal areas by onshore winds and tidal currents, end up as mud in mangroves and estuaries.

By improving land condition, maintaining ground cover and reducing erosion you can help to improve the quality of water in local waterways and help restore the Great Barrier Reef lagoon.

How do we know this?

Extensive research has taken place to determine what is contributing to the decline in Reef health. The overarching scientific consensus is that key Great Barrier Reef ecosystems continue to be in poor condition largely due to the collective impact of land run-off associated with past and ongoing catchment development, coastal development activities, extreme weather events and climate change impacts.

The 2017 Scientific Consensus Statement is a document prepared by a multidisciplinary group of scientists with expertise in Great Barrier Reef water quality science and management, with oversight from the Reef Water Quality Independent Science Panel. It states the main source of the primary pollutants (nutrients, fine sediments and pesticides) from Great Barrier Reef catchments is diffuse source pollution from agriculture. These pollutants pose a risk to Great Barrier Reef coastal and marine ecosystems.

What can I do to reduce sediment run-off from my farm?

When farmers adopt improved management practices, this minimises soil loss and reduces the risk of sediment run-off to the Reef. More information is available to help grazing, banana, sugarcane and grains and horticulture producers reduce run-off.