Environmental Science
articles by Will Kemp

Great Barrier Reef water quality


The Great Barrier Reef (GBR) stretches for more than 2000km (Bowen & Bowen, 2002). It consists of approximately 3000 individual reefs, covers an area of 345,000km2, and is the largest coral reef ecosystem in the world (De’Ath et al., 2012). The GBR was listed as a World Heritage area in 1981 because of its “outstanding universal value”, which met all four of the World Heritage natural criteria, which were:

“to contain superlative natural phenomena or areas of exceptional natural beauty and aesthetic importance;

“to be outstanding examples representing major stages of earth’s history, including the record of life, significant on-going geological processes in the development of landforms, or significant geomorphic or physiographic features;

“to be outstanding examples representing significant on-going ecological and biological processes in the evolution and development of terrestrial, fresh water, coastal and marine ecosystems and communities of plants and animals;

“to contain the most important and significant natural habitats for in-situ conservation of biological diversity, including those containing threatened species of outstanding universal value from the point of view of science or conservation.” (Douvere & Badman, 2012; UNESCO, 2013).

In the 32 years since World Heritage listing, the coral cover of the reef has dropped by approximately 50% (De’Ath et al., 2012) and, in 2012, the World Heritage Committee considered including the GBR in the List of World Heritage in Danger, but did not list it at that time. The United Nations Educational, Scientific and Cultural Organization (UNESCO) and The International Union for the Conservation of Nature (IUCN) dispatched a joint Reactive Monitoring Mission to Australia in 2012 to assess the conservation state of the GBR and the impact its condition and possible future developments may have on the “outstanding universal value” of the World Heritage Area. The mission concluded that the reef still demonstrated outstanding universal value and that previously noted threats had been effectively dealt with, but that there were serious concerns about the future management of the World Heritage area (Douvere & Badman, 2012; UNESCO, 2013).

Declining coral cover

The monitoring mission’s main concerns were the effects of future development on the reef (Douvere & Badman, 2012). However, coral cover of the reef has been declining since at least 1985. Several factors have contributed to this decline, including cyclones, crown of thorns starfish (COTS), coral bleaching, and reduced coral growth rates due to increased sea temperatures. There have been minor impacts on the reef from destructive fishing, shipping accidents, and water pollution from industrial and urban sources (De’Ath et al., 2012).

The most significant current anthropogenic contribution to reef degradation is probably poor water quality (De’Ath et al., 2012). Bowen & Bowen (2003) suggest that the entire area from the eastern side of the Great Dividing Range to the edge of the continental shelf, including the coastal strip, the lagoon of the Great Barrier Reef, and the reef itself, should be considered an effectively unified ecosystem. It is estimated that the nutrients and sediments carried into the lagoon from the rivers flowing into the central and southern parts has increased by between five and nine times since colonisation (De’Ath et al., 2012).

An increase in COTS outbreaks over the last 50 years or so, seems to be linked to this increase in nutrient levels (Brodie et al., 2005). Modeling has shown one COTS outbreak occurred on the reef every 50 to 80 years before colonization, compared with an outbreak approximately every 15 years in recent times. COTS predation accounts for 42% of the coral loss from the reef over the period since World Heritage listing, and reducing the COTS population would help stabilise the reef and possibly halt its decline (De’Ath et al., 2012).

Reef plan

A significant proportion of the excess nutrient load in rivers flowing into the GBR lagoon has been due to inefficient use of fertilisers on agricultural land – sugar cane and banana farms in particular, and this is an issue that has received a lot of attention in recent years (Bramley & Roth, 2002, Bainbridge et al., 2009). In 2003, the Reef Water Quality Protection Plan (Reef Plan), an initiative of the Commonwealth and Queensland Governments, was launched with the aim of improving agricultural management practices and reducing agricultural runoff. It has been renewed twice since then. Independent audits were carried out in 2005 and 2010 and three “report cards” have been issued (in 2009, 2010, and 2011) (Queensland Government, 2013a).

Researchers at South Jonhstone banana research center use a Parshall flume for assessing improved land management on banana farms.

Researchers at South Jonhstone banana research center use a Parshall flume for assessing improved land management on banana farms.

The Paddock to Reef Integrated Monitoring, Modelling and Reporting Program was set up to evaluate the implementation and progess of Reef Plan 2009. It is a collaboration between State and Federal governments, industry bodies, research organisations, and natural resource managers (Queensland Government, 2011). The aim of the Paddock to Reef Program is to use incentives and policies to encourage farmers to improve their land management practices in the hope that this will improve the quality of water that flows to the GBR lagoon. It will also provide models to enable accurate assessment of the outcomes. The focus of its assessment will be on the effectiveness of improved management practices, the adoption of those practices, their effects on catchment water quality, progress towards meeting targets, and the water quality and ecosystem health of the GBR (Carroll et al., 2012).

Water quality targets for 2013, which will be assessed by the Paddock to the Reef Program, are a minimum of 50% reduction in nitrogen, phosphorous, and pesticide loads in waters flowing into the GBR lagoon and a minimum of 50% ground cover on dry tropical grazing land in late dry season. A 20% reduction in sediment load is also targeted for 2020. Management targets are for 80% of agricultural landholders and 50% of graziers to have adopted improved practices, no net loss or degradation of wetlands, and an improvement in riparian areas. These targets are to be measured against 2009’s baseline state (Carroll et al., 2012).

According to the Great Barrier Reef Report Card 2011, progress towards targets was unsatisfactory – with the exception of the sediment reduction target, which appears to be on course to be met before 2020 (although it is early on in the program). Marine condition generally mainly fell into the poor to very poor categories, although this was partly due to extreme weather events in 2010-11 (Queensland Government, 2013b).

Other causes

While (water quality related) COTS outbreaks accounted for 42% of the decline in coral cover on the GBR, tropical cyclones were the cause of 48% and coral bleaching caused 10% (De’Ath et al., 2012). The severity of both of these phenomena have been related to climate change (Knutson et al., 2011; Spillman, 2011) and it seems likely that they will become more severe as the ocean warms. Although improving the water quality of the GBR lagoon and reducing the severity of COTS outbreaks will help slow the decline of coral cover on the reef, it seems unlikely that it can reverse it in the face of a changing climate.


Bainbridge, Z., Brodie, J., Faithful, J., Sydes, D., & Lewis, S. (2009). Identifying the land-based sources of suspended sediments, nutrients and pesticides discharged to the great barrier reef from the Tully-Murray basin, Queensland, Australia. Marine and Freshwater Research, 60(11), 1081-1090.

Bowen, J. & Bowen, M. J. (2002). The great barrier reef: History, science, heritage. Port Melbourne, Vic: Cambridge University Press.

Bramley, R. G. V. & Roth, C. H. (2002). Land-use effects on water quality in an intensively managed catchment in the Australian humid tropics. Marine and Freshwater Research, 53, 931–940.

Brodie, J., Fabricius, K., De’ath, G., & Okaji, K. (2005). Are increased nutrient inputs responsible for more outbreaks of crown-of-thorns starfish? an appraisal of the evidence. Marine Pollution Bulletin, 51(1), 266-278.

Carroll, C., Waters, D., Vardy, S., Silburn, D. M., Attard, S., Thorburn, P. J., Davis, A. M., Halpin, N., Schmidt, M., Wilson, B., & Clark, A. (2012). A paddock to reef monitoring and modelling framework for the great barrier reef: Paddock and catchment component. Marine Pollution Bulletin, 65(4-9), 136-149.

De’ath, G., Fabricius, K. E., Sweatman, H., & Puotinen, M. (2012). The 27-year decline of coral cover on the great barrier reef and its causes. Proceedings of the National Academy of Sciences of the United States of America, 109(44), 17995-17999.

Douvere, F. & Badman, T. (2012). Mission Report, Reactive Monitoring Mission to Great Barrier Reef, Australia, 6th to 14th March 2012. Paris, France: United Nations Educational, Scientific and Cultural organization. Retrieved from http://whc.unesco.org/en/documents/117104 on 18/9/13.

Knutson, T., Sugi, M., McBride, J., Chan, J., Emanuel, K., Holland, G., Landsea, C., Held, I., Kossin, JP, & Srivastava, A. (2010). Tropical cyclones and climate change. Nature Geoscience, 3(3), 157-163.

Queensland Government (2011). Paddock to Reef Program. Brisbane, Qld: Queensland Government. Retrieved from http://www.reefplan.qld.gov.au on 5/10/13.

Queensland Government (2013a). Reef Water Quality Protection Plan 2013. Brisbane, Qld: The State of Queensland. Retrieved from http://www.reefplan.qld.gov.au on 25/9/13.

Queensland Government (2013b). Great Barrier Reef Report Card 2011. Brisbane, Queensland: Reef Water Quality Protection Plan Secretariat. Retrieved from http://www.reefplan.qld.gov.au on 5/10/13.

Spillman, C. (2011). Advances in forecasting coral bleaching conditions for reef management. Bulletin of the American Meteorological Society, 92(12), 1586-1591.

UNESCO (2013). The Criteria for Selection. Paris, France: World Heritage Centre. Retrieved from http://whc.unesco.org/en/criteria on 19/9/13.

World Heritage Committee (1981). Convention concerning the protection of the world cultural and natural heritage – World Heritage Committee – 5th session – Report of the. Paris, France: United Nations Educational, Scientific and Cultural organization. Retrieved from http://whc.unesco.org/archive/repcom81.htm on 18/9/13.