Great Barrier Reef catchment water quality targets and relative priorities for water quality improvement

Science shows five main pollutants impact the reef – sediments (especially fine sediments), dissolved inorganic nitrogen, particulate nitrogen, particulate phosphorus and pesticides. Water quality targets have been developed for these pollutants for catchments that flow to the Great Barrier Reef. The targets are included in the Reef 2050 Water Quality Improvement Plan 2017–2022 (PDF, 3.6MB) .

Other pollutants such as heavy metals, pharmaceuticals, plastics and micro plastics also affect the Reef but occur at a much lower scale and have more localised impacts. At this time, there is insufficient information available to set targets for these pollutants.

The pesticide target is based on the concentrations required to protect 99 percent of species at the river mouth, applying across all catchments. This reflects the fact that high concentrations of pesticides have a worse effect on Reef aquatic species.

The targets for sediments, particulate nutrients and dissolved inorganic nitrogen are based on the quality of water that corals and seagrass need to be healthy. They are calculated as reductions in anthropogenic loads – the pollutant load from human activities.

The targets are set as percentages with the required reduction also shown in tonnes or kilotonnes. The percentage figure reflects the change required from the 2013 modelled pollutant loads baseline – the last time a scientific baseline was set. This means that progress recorded between 2009 and 2013 has already been accounted for when setting the targets, and progress since 2013 will contribute to achieving the new targets. The tonnes/kilotonnes figure reflects the reduction needed to meet the target by 2025. The percentages show the scale of the challenge for an individual catchment. The tonnes/kilotonnes demonstrate the scale of the challenge between catchments.

The catchment targets have been added together to give indicative targets for each region and the whole of the Great Barrier Reef. They have been incorporated in the revised Reef 2050 Long-Term Sustainability Plan (Reef 2050 Plan). The new targets replace the previous commitments to achieving reductions of up to 80% in dissolved inorganic nitrogen and up to 50% in sediment in priority areas by 2025. They are more specific, eliminating the need to say ‘up to’. They will help track overall progress. This comparison also demonstrates the target reduction required for some individual catchments is higher than that calculated for a whole region. For example, the dissolved inorganic nitrogen reduction required from the Haughton basin (639 tonnes by 2025) is similar to the total reduction required from all of four of the Mackay Whitsunday catchments (631 tonnes by 2025).

Some catchments have a target of maintain current load for some or all pollutants. This means the catchment has a minimal anthropogenic load for the relevant pollutant/s. The aim in these catchments is to maintain current water quality so there is no increase in pollutant loads.

Targets have not been determined for the Black catchment, and some targets were not determined for the Ross catchment, due to a lack of information. Targets could be set in the future if new information becomes available.

The Reef 2050 Water Quality Improvement Plan also includes catchment management priorities from the risk assessment in the 2017 Scientific Consensus Statement. The targets are based on the water quality needs of seagrass and coral across the whole Great Barrier Reef. The risk assessment takes account of the particular environment that is exposed to pollutants from each river. For example, rivers in the Wet Tropics flow to the zone where crown-of-thorns starfish initiate and are, therefore, a higher priority for reducing dissolved inorganic nitrogen which leads to increased outbreaks of crown-of-thorns starfish. The Mary River flows out onto the important seagrass beds in Hervey Bay and is, therefore, a higher priority for reducing sediment which that the light available to seagrass and restricts its growth.

Read more about the targets, land uses and pollutant sources for each catchment.

For more information, read the Development of basin-specific ecologically relevant water quality targets for the Great Barrier Reef (PDF, 3.2MB) technical report.