Declining marine water quality from land-based run-off is one of the most significant threats to the long-term health and resilience of the Great Barrier Reef.
Land-based run-off can include sediments, nutrients such as nitrogen and phosphorus, and pesticides.
This run-off and declining water quality are contributing to declines in many of the attributes that make up the outstanding universal value of the world heritage property, particularly those related to coral reefs and seagrass meadows.
The Reef receives run-off from 35 major catchments that drain 424,000 square kilometres of coastal Queensland. Most sediment entering the Great Barrier Reef comes from catchments in major pastoral areas such as the Burdekin, Herbert and Fitzroy rivers.
There are two types of catchments that deliver water into the Great Barrier Reef:
- Coastal catchments provide a continuous flow of freshwater to the Reef from small catchments supporting intensive farming, for example Tully River and Pioneer River.
- Large catchments drain large inland grazing areas and tend to be seasonal and influenced by flooding.
Impacts on natural resources
Increased sediments, nutrients and pesticides flowing into inshore areas, can cause a range of impacts including higher algal growth, a build-up of pollutants in sediments and marine species, reduced light and smothered corals. The coastal zones, especially areas close to river mouths, are particularly exposed to this run-off.
Phytoplankton, bacteria and benthic organisms quickly remove dissolved inorganic nutrients from seawater. However, high levels over a long time can create ecological changes across large areas, as well as metabolic changes in most marine plants and animals.
Changes in water quality affect the biodiversity and resilience of Reef systems. Higher levels of chlorophyll and lower water clarity indicate higher concentration levels of pollutants, such as suspended sediments, nitrogen and phosphorus, which lead to more algae and less coral diversity. In these conditions, algae take over and reduce the chances for new hard corals to establish and grow.
Some pollutants have been known to stay in the marine environment for decades, and can build up in animals that have high fat contents (e.g. whales and dolphins), are higher on the food web or are long-lived. Pollutants, such as heavy metals, can disrupt reproduction, impact the immune system, and cause neurological disorders and cancers.
Cumulative effect and the timing of exposure to pollutants can magnify the impacts of catchment run-off.
Impacts on communities
Declining water quality and changes to the Great Barrier Reef ecosystem have serious economic implications for Reef-dependent industries, such as tourism and fishing, and for adjacent communities. Declining ecosystem health can affect the Reef’s attractiveness for tourism and recreation.
Examples of Reef-dependent activities are traditional use of marine resources, commercial marine tourism, fishing, and recreational, research and educational activities. Reef-dependent activities are likely to be more sensitive to changes in the condition of the Region's values.
The Great Barrier Reef Marine Park Authority (GBRMPA) is a partner in the Australian and Queensland Governments' joint commitment to a Reef 2050 Water Quality Improvement Plan. It is an action plan to halt and reverse the decline in the quality of water flowing into the Great Barrier Reef from the catchment.
Water quality guidelines
GBRMPA has developed water quality guidelines for describing the concentrations of sediment, nutrients and pesticides that are needed for the protection and maintenance of marine species and the Reef's ecosystem health.
Land-based facilities discharging sewage effluent directly into the Marine Park are managed under the Sewage Discharge Policy 2005 and the Great Barrier Reef Marine Park Regulations 1983.
Vessel-based sewage discharges must comply with regulations administered by the GBRMPA and with those for Queensland coastal waters requirements.
Various regulations, conventions and Reef policies cover the potential effects of ship-sourced pollutants, including discharge and disposal of waste, exchanges of ballast water, oil spills and anti-foulant paint.
Aquaculture facilities located within and next to the Great Barrier Reef Marine Park produce a range of marine and freshwater species, including pearl and edible oysters, prawns and barramundi. GBRMPA must approve these facilities as per the Aquaculture Position Statement.
Traditionally, land-based aquaculture farms have often discharged high concentrations of suspended solids and nutrients into nearby waterways. However, this situation is improving with the use of new techniques, such as settlement and bio-filtration ponds that contain algae, bivalves or fish in new and existing aquaculture farms.
Discharges from aquaculture farms are now regulated to make sure they protect the water quality of local waterways and the Great Barrier Reef.
On 2 March 2005, the Commonwealth Minister for Environment and Heritage accredited Queensland law under the Great Barrier Reef Marine Park (Aquaculture) Regulations 2000.
A statement of reasons is available for this decision. Based on this agreement, no GBRMPA permission is required for a land-based aquaculture facility to operate (that is any land-based aquaculture facility that discharges aquaculture waste to a waterway leading to the Great Barrier Reef Marine Park).