Pollution's Impact On The Great Barrier Reef

The Great Barrier Reef is one of the most complex ecosystems on Earth, with thousands of species of plants, animals and microscopic organisms coexisting in a delicate balance. However, this intricate ecosystem is under threat from pollution. The main sources of pollution are land-based activities such as agriculture, deforestation, coastal development, and industrial and urban runoff. These activities increase the levels of toxicants, sediments, and nutrients in the water, which can impede coral growth and reproduction, disrupt the ecological function, and cause disease and mortality in sensitive species. Climate change is also a significant factor, with rising sea temperatures and ocean acidification exacerbating the problem. The combination of these threats is creating a perfect storm for the Great Barrier Reef and the iconic animals that depend on it.

Land-based pollution

One of the primary sources of land-based pollution is agricultural runoff. The use of fertilisers, pesticides, and herbicides in agriculture contributes to water pollution in the Great Barrier Reef. Excessive fertiliser applied to crops, such as sugarcane, can make its way into rivers and, ultimately, the Reef. Nitrogen from these fertilisers is linked to harmful algal blooms, which block sunlight, reducing coral diversity and resilience to bleaching. Similarly, pesticides and herbicides used on crops wash into the Reef, inhibiting the growth of marine plants like seagrasses, which are essential for species such as dugongs, turtles, and fish.

Deforestation and tree clearing in the catchment areas of the Reef are another major contributor to land-based pollution. Without tree roots to secure the topsoil, erosion occurs, and sediment is washed into the rivers and out onto the Reef. This sediment smothers coral and seagrass, reducing their access to sunlight and hindering their growth. The Burdekin, Fitzroy, Tully, and Daintree Rivers have been identified as posing the greatest runoff risk of inorganic nitrogen onto the coral reefs of the Great Barrier Reef.

Other land-based sources of pollution include failed septic systems, coastal development, stormwater runoff, oil and chemical spills, road construction, and urbanisation. These activities introduce pollutants such as sedimentation, toxins, pathogens, and increased nutrients into the Reef's ecosystem, disrupting ecological functions and causing disease and mortality in sensitive species.

The impact of land-based pollution on the Great Barrier Reef is far-reaching, and it is essential to address these issues through improved land management practices, targeted regulations, and a reduction in the use of harmful chemicals to protect the delicate balance of this complex and invaluable ecosystem.

Climate change

The Great Barrier Reef is the largest living structure on Earth and one of the most complex natural ecosystems in the world. It is made up of 3,000 individual reefs spread over an area the size of Italy or Japan. The reef is home to over 1,600 species of fish, 20 species of seabird, and six out of seven species of sea turtles. The reef's biodiversity attracts two million visitors a year and supports the livelihoods of around 65,000 Australians.

Rising ocean temperatures have led to an increase in marine heatwaves, which cause coral bleaching. When corals suffer heat stress, they expel the microscopic algae that live inside their tissues, revealing their white skeletons. Bleached corals are not dead, but they are at a higher risk of starvation and disease. Between 1998 and 2017, the Great Barrier Reef experienced four mass bleaching events, reducing shallow water coral reefs by as much as 50%. While coral reefs can recover from bleaching over time, temperatures must drop and conditions must return to normal for this to happen.

In addition to marine heatwaves, climate change is also increasing the frequency and intensity of severe weather events such as cyclones, flooding, and storms. Between 2004 and 2018, ten cyclones of category three or more crossed the Great Barrier Reef, causing significant damage to coral reefs. As water temperatures rise, marine species are forced to move south to cooler habitats, creating increased competition for food and shelter and threatening the entire ecosystem.

The ocean absorbs carbon dioxide from the atmosphere, leading to ocean acidification. This process makes it more difficult for corals to build skeletons and form coral reefs. Since the late 18th century, the ocean has absorbed about 30% of the carbon generated by humans, decreasing its pH level.

To protect the Great Barrier Reef from the impacts of climate change, urgent global action is needed to reduce greenhouse gas emissions. It is also important to strengthen key ecosystems like seagrass meadows, mangroves, and wetlands, which play a crucial role in absorbing carbon dioxide from the atmosphere. Additionally, interventions to help coral reefs adapt to warmer temperatures and rebuild resilient reefs are necessary.

The future of the Great Barrier Reef depends on the actions taken to address climate change. Without significant reductions in greenhouse gas emissions and efforts to increase the resilience of the reef, it is likely that the reef will continue to degrade, impacting the biodiversity, cultural heritage, and socioeconomic benefits it provides.

Water quality

The Great Barrier Reef is a natural wonder that stretches along Australia's northeastern coast, comprising 3,800 reefs and atolls in the Coral Sea. It is the largest living structure on Earth. However, the health of this majestic ecosystem is under serious threat from water pollution caused by land-based activities.

Water pollution poses one of the highest risks to the Great Barrier Reef, with decades of agricultural pollution causing the water quality of the inshore reef to remain in poor condition. This pollution comes in the form of runoff, which refers to the excess water that flows across the land surface or into groundwater after rainfall or irrigation, eventually making its way into nearby creeks and rivers. This runoff contains harmful substances such as fertilisers, pesticides, herbicides, and sediment, which wash into the reef and have detrimental effects on its delicate ecosystems.

Agricultural activities, including the use of excessive fertilisers on crops like sugarcane, are a major contributor to water pollution in the Great Barrier Reef. The nitrogen from these fertilisers is linked to harmful algal blooms, which block sunlight, reducing the resilience of corals to bleaching and decreasing coral diversity. These algal blooms also negatively impact the growth of seagrasses, which require sufficient light to grow and be healthy. Additionally, pesticides and herbicides have been detected in high concentrations in inshore areas, posing risks to marine plants and animals, including species such as dugongs, turtles, and fish.

Another consequence of agricultural practices is tree clearing, which leads to soil erosion. 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 sediment reduces the amount of sunlight available to seagrasses and corals, smothering their growth. The Burdekin, Fitzroy, Tully, and Daintree Rivers have been identified as posing the greatest runoff risk of inorganic nitrogen onto the coral reefs.

To address the issue of water pollution in the Great Barrier Reef, it is essential to focus on reducing land-based pollution. This includes implementing better land management practices, such as reducing the use of fertilisers and pesticides in agriculture, as well as restoring and protecting the land, especially along riverbanks, to prevent soil erosion. By tackling these issues at their source, we can give the Great Barrier Reef the clean water it needs to restore its health and ensure its long-term survival.

Crown-of-thorns starfish

COTS feed on coral, preying on nearly all types of coral, and can eat up to 10 square metres of coral per year. They do this by extruding their stomachs from their bodies and wrapping them around the coral, before retracting their stomachs back into their bodies. COTS prefer to eat faster-growing corals, which can help enhance the diversity of reefs by giving slower-growing species a chance to catch up. However, when COTS appear in outbreak proportions, the impact on coral reefs can be devastating.

During an outbreak, which is classified as when 15 or more COTS are found in a one-hectare area, the starfish can strip a reef of up to 90% of its living coral tissue. COTS outbreaks are a major cause of coral decline across the Great Barrier Reef and are responsible for extensive coral loss. They have been a major source of coral loss on the reef since 1962, and a fourth outbreak is currently underway.

The outbreaks are likely caused by a combination of factors, including increased larval survival due to increased nutrients from land-based runoff, which causes algal blooms, and the removal of predators. The Australian Government has implemented a Crown-of-Thorns Starfish Control Program to protect coral habitats and reduce coral mortality. The program involves targeted control measures, with trained divers injecting the starfish with bile salts or vinegar to kill them without harming the surrounding ecosystem.

Coastal development

Queensland's growing population and economy have led to increased development along the coast and on islands adjacent to the Great Barrier Reef. This development includes urban and industrial expansion, mining operations, port activities, and island resorts. While these activities bring economic and social benefits, they can also have negative consequences for the health of the reef.

One significant impact of coastal development is the modification of coastal ecosystems, which can disrupt the health of seagrass meadows. Seagrass meadows serve as important feeding and breeding grounds for dugongs and turtles, and their deterioration affects the entire food chain. Additionally, land-clearing and the construction of permanent structures such as retaining walls can alter natural water flow patterns, impacting the health of local fish species and impeding their migration.

Another consequence of coastal development is the increased runoff of pollutants into the reef. As more land is cleared for agriculture, urban areas, and industrial sites, the risk of toxicants, sediments, and nutrients flowing into the reef rises. This runoff can smother corals, disrupt ecological functions, and cause disease and mortality in sensitive species.

The Australian government has recognized the potential harm of development projects and has implemented measures to protect the Great Barrier Reef. Under the Environment Protection and Biodiversity Conservation Act 1999, the Australian Environment Minister must assess and decide on developments that may negatively impact the Great Barrier Reef World Heritage Area and Marine Park.

Despite these efforts, the Great Barrier Reef remains vulnerable to the effects of coastal development. The projected population growth in Queensland is expected to further increase development pressure, posing ongoing challenges to the conservation of this unique ecosystem.

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