Air Pollution's Impact On The Great Barrier Reef

The Great Barrier Reef, the largest living structure on Earth, is under threat from air pollution. Stretching along Australia's northeastern coast, the reef is formed of 3,800 reefs and atolls. While climate change is the greatest threat to the reef, air pollution is a significant contributor to its poor health. Land-based activities, such as agriculture, coastal development, and deforestation, release pollutants into the air, which then enter the water and harm the reef. These pollutants include pesticides, herbicides, insecticides, fungicides, and other toxins, which reduce the resilience of the reef and negatively impact its biodiversity. With the reef already suffering from rising sea temperatures and ocean acidification, the added stress of air pollution is creating a perfect storm of threats to this delicate ecosystem and the iconic animals that depend on it.

Land-based pollution

Agricultural activities, such as the use of fertilisers and pesticides, are a major contributor to the problem. Excessive fertiliser applied to crops like sugarcane can wash into rivers and, ultimately, out to the Great Barrier Reef. Nitrogen from these fertilisers is linked to harmful algal blooms, which block sunlight and reduce the resilience of corals to bleaching. Additionally, increased nutrients in the water stimulate excessive growth of algae, which compete with corals for space and light.

Deforestation and tree clearing in the catchment areas of the Great Barrier Reef are also causing significant harm. Without tree roots to secure the topsoil, erosion occurs, and an estimated 17 million tonnes of sediment are washed into the rivers and eventually out onto the Great Barrier Reef each year. This sedimentation reduces water clarity, restricting the growth of light-dependent plants and animals, including corals. It also smothers coral and seagrass growth, hindering their ability to photosynthesise.

Other land-based sources of pollution include coastal development, oil and chemical spills, failed septic systems, stormwater runoff, road construction, and grazing of feral animals. These activities introduce toxicants, sediments, and nutrients into the reef ecosystem, impeding coral growth and reproduction and disrupting ecological functions.

The impact of land-based pollution on the Great Barrier Reef is far-reaching. It affects not only the health of the reef but also the industries that depend on it, such as tourism, fishing, and recreation. It is crucial to address these preventable sources of pollution to restore and protect the Great Barrier Reef for future generations.

Climate change

The rise in ocean temperatures has already triggered four mass coral bleaching events in just seven years, reducing shallow water coral reefs by up to 50%. When corals experience heat stress, they expel the microscopic algae living in their tissues, exposing their white skeletons. While bleached corals are not dead, they are more susceptible to starvation and disease. Coral reefs can recover from bleaching, but only if temperatures decrease and conditions return to normal.

The ocean absorbs about 30% of the carbon dioxide humans have generated, which has led to ocean acidification. This process decreases the ocean's pH level, making it more acidic. As a result, corals find it more difficult to build skeletons and form coral reefs, which are essential for providing habitats for marine life and protecting coastlines from storms.

To protect the Great Barrier Reef from climate change, it is imperative to reduce emissions and strengthen key ecosystems like seagrass meadows, mangroves, and wetlands, which play a crucial role in absorbing carbon dioxide from the atmosphere. The Reef Blueprint 2030 aims to drive adaptation and innovation in managing the Reef's resilience, setting a gold standard for Marine Park management.

Water quality

The Great Barrier Reef is one of the most complex ecosystems on the planet. It is the largest living structure on Earth, stretching along Australia's northeastern coast. The health of the reef is under constant threat from poor water quality, which is influenced by land-based runoff.

The main water quality issues are increasing sediment, nutrients, and contaminants entering coastal waters from agricultural, industrial, and urban activities. The Burdekin, Burnett, and Fitzroy Rivers are the largest of the 35 major waterways, or catchments, that run out to the reef. Most of the sediment entering the Great Barrier Reef comes from catchments in major pastoral areas, such as these rivers.

Sedimentation, or soil, is a natural part of reef ecosystems, but excessive amounts put significant pressure on the health of inshore reefs and seagrass meadows. When farm animals overgraze, the land becomes susceptible to erosion. A lack of vegetation can cause the land to become unstable, and heavy rainfall can cause high levels of soil to wash into waterways. This sediment smothers corals and seagrasses, blocking the light they need to grow and thrive.

Nutrients in the form of dissolved inorganic nitrogen (DIN) from fertilisers increase the growth of single-celled plants called phytoplankton, causing algal blooms that block sunlight and reduce coral diversity. Excess DIN can also make corals more susceptible to bleaching and disease. Herbicides inhibit the growth of non-target plants such as seagrasses, on which dugongs, turtles, and fish depend. Pesticides inhibit photosynthesis in marine plant species and are likely to impact coral fertility and reproduction. These chemicals may take years to break down, having long-term effects on the marine environment.

Climate change, which is predicted to increase the frequency and intensity of rainfall, is likely to cause higher levels of sediment, nutrients, and pesticides to enter the reef unless targeted preventative action is taken.

Coastal development

The Great Barrier Reef's ecosystem is vulnerable to the effects of past, current, and future coastal development. The catchment area of the Great Barrier Reef is home to over a million people, with Queensland's continued growth driving development along the coast and islands adjacent to the reef. This development is largely driven by economic and social benefits, but it has had, and will continue to have, a negative impact on the health of the reef.

The Great Barrier Reef catchment is used for agriculture, urban and industrial development, mining, port activities, and island development. Agriculture is the primary land use, with cattle grazing being the most extensive, and over 70% of the catchment supporting some form of agriculture. The impact of agriculture on the reef is twofold. Firstly, it contributes to water pollution through land-based runoff, and secondly, it requires the clearing of habitats, which disrupts the ecosystem.

Urban and industrial development occupies less than 0.7% of the catchment area, with minimal expansion since 2014. However, urban runoff still contributes to water pollution, and the development of permanent structures can alter water flow and impede fish migration. The development of ports has been a major driver of coastal reclamation, infilling areas of the ocean, wetlands, and other water bodies. Port development can also create artificial barriers to freshwater flow, further altering the natural ecosystem.

The Curtis Island gas precinct, located off the coast of Queensland, is one of the biggest developments along the Great Barrier Reef coast. It is the site of the world's first project to convert coal seam gas to liquefied natural gas. This development, along with others, has contributed to the decline of the reef's ecosystems. The direct result of coastal development is the degradation of the reef's beauty, biological richness, and cultural values.

To protect the Great Barrier Reef, there is a need for a stronger commitment to reversing its decline. This includes placing the burden of proof on developers to demonstrate that their projects will not cause harm, improving the environmental impact assessment process, and setting specific targets for ecosystem health and biodiversity recovery. With enough commitment and action, it is possible to improve the condition of the Great Barrier Reef and safeguard its future.

Crown-of-thorns starfish

COTS feed on coral, with a preference for fast-growing, hard, reef-building corals such as branching and plate corals. They consume coral by extruding their stomachs from their bodies, covering the coral with digestive enzymes, and converting coral tissue into a soup before retracting their stomachs back into their bodies. A single adult COTS can consume up to 10 square metres of coral per year, and during an outbreak, they can strip a reef of 90% of its living coral tissue. COTS breed by spawning over the summer months, with females releasing up to 200 million eggs in a year. The resulting larvae feed on phytoplankton before metamorphosing into juvenile starfish, which initially feed on crustose coralline algae before transitioning to coral as adults.

COTS outbreaks are a significant threat to the Great Barrier Reef and have been a major source of coral loss since 1962. The outbreaks generally start offshore from Cairns and can take about a decade to spread south along the Reef. The fourth outbreak, currently underway, has already caused extensive damage to reef-building corals. The outbreaks are likely caused by a combination of factors, including increased larval survival due to higher nutrient levels from land-based runoff, and the removal of natural predators such as the giant triton snail, humphead Maori wrasse, and various species of fish and invertebrates.

To control COTS outbreaks, targeted control programs have been implemented, with trained divers injecting the starfish with bile salts or vinegar to kill them without harming the surrounding ecosystem. Additionally, baits are being developed to lure COTS into aggregations for easy removal. These efforts are crucial to protecting the Great Barrier Reef and preserving its biodiversity and resilience.

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