Impacts of nutrient run-off

How is nutrient run-off impacting the Reef?

Declining marine water quality, through land-based run-off, is recognised as one of the most significant threats to the long-term health of the Great Barrier Reef. Nutrient run-off, along with sediment run-off and pesticides, is particularly significant.

Crown-of-thorns starfish

Crown-of-thorns starfish. David-Burdick-NOAA.

Fish cycle diagram

Reef animals need different habitats throughout their life cycle so good water quality is important everywhere as shown in the diagram above.

Nutrient run-off is associated with algal blooms, micro-organisms species shifts and coral-eating crown-of-thorns starfish (COTS) outbreaks across the Reef. The current scientific consensus is that nitrogen inputs have a higher correlation with COTS outbreaks than other nutrients such as phosphorus; however all nutrient inputs can contribute to the issue.

Pesticides also pose a risk to aquatic organisms, particularly in freshwater areas and inshore and coastal ecosystems such as seagrass habitats and estuarine wetlands.

On top of this, the cumulative pressure of additional stressors such as extreme rainfall, thermal stress, salinity stress, light stress, cyclone damage and COTS outbreaks can add to the likelihood, prevalence and impacts of coral disease. All of these pressures and stressors impact the Reef’s resilience and its recovery following extreme weather events. Good water quality is crucial to improving the Reef’s resilience and ability to recover from these pressures.

Reducing the loss of nutrients, sediment and pesticides from your farm will reduce end-of-catchment loads and agricultural chemicals which will help enhance Reef resilience in the face of continuing climate change pressures.

How are the nutrients from my farm ending up in the Reef?

Rainfall run-off and irrigation tail water can wash nutrients, into freshwater zones and coastal wetlands. Drainage through agricultural soils can cause leaching of soluble nutrients and pesticides, which infiltrate groundwater and then reach downstream waters.

While nitrogen occurs naturally, an increased amount of nitrogen through fertiliser loss is harming the Reef. The best way you can manage its long-term impacts is by better matching nitrogen inputs to the crop requirements and reducing the amount of surplus nitrogen (i.e. the difference between nitrogen inputs and nitrogen taken up by the crop).

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 nutrient run-off from my farm?

Adopting practices for effective nutrient management can improve farm productivity and profitability and reduce losses to the Reef. More information is available to help sugarcane, grazing, banana and grains and horticulture producers reduce run-off.