Stretching north to south along Australia’s northeast coast for 2,600 km with an area of approximately 344,400 square kilometres, the Great Barrier Reef is the biggest single structure on Earth made by living creatures and one of the few things that can be seen from outer space. This beautiful and delicate formation is seriously threatened by increasing land-based pollution along with bleaching due to global warming.

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Fertilizers and Pesticides

Pollution has a significant impact on the fragile coral reef ecosystems in the Great Barrier Reef. It has been estimated that 22% of the world’s coral reefs are threatened by land-based pollutants. Humans have added harmful pollutants into our oceans in numerous different ways.

A major pollutant is the runoff from mining and farming as fertilizers, herbicides, pesticides and human derived sewage get into rivers that flow into the ocean. Fertilizers add nitrogen and phosphorous into the ocean. These nutrients increase the growth of algae, which leads to oxygen depletion so there is less for other creatures, decreasing the biodiversity in the affected areas. Algae blooms also take over sections of coral, blocking out sunlight and diminishing its ability to survive. The blue-green algae and nitrate fertilizers cause reproduction problems fro coral larvae.

80% of the land adjacent to the Great Barrier Reef is farmland. The agricultural activity here is intensive cropping of sugar cane, banana and cotton farms, and beef cattle grazing. Farmers use large quantities of nitrogen fertilizers as they provide an essential nutrient for both crop and animal production. Excess nitrogen is lost to ground and surface water and runs off into the rivers and then the ocean.

Thousands of tons of nitrogen and phosphorous from fertilisers are washed into the sea poisoning marine life.

Farmers use pesticides to kill off specific types of insects and weeds that maybe harmful to their crops. Pesticides are made of heavy metals such as lead, mercury, arsenic and other toxins which are not only dangerous to humans but to other aquatic and plant species. When the soil on the farm erodes, it runs off the land taking the chemicals downstream into the coral ecosystems off the coast.

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Petroleum and Chemicals

Petroleum leaks and other chemicals get dumped into the oceans causing toxicity and making it difficult for the coral reefs to survive. Frequent oil spills can cause damage to the reproductive system of corals; decreased viability of coral larvae; and changes to the physical properties of the reef flat which can interfere with the normal settlement of coral larvae. Of course, oil is toxic to many animal, fish and bird species.

Sedimentation

Sedimentation is another major problem with a large impact on the fragile ecosystem of the Great Barrier Reef. The sediment that flows out of rivers due to erosion carries with it the pollutants and fertilizers from the inland farms. Sedimentation build-up also occurs at the mouth of the rivers that lead to the oceans.

28 million tons of sediment flow into the waters of the Great Barrier Reef each year, according to the World Wildlife Fund. That is equivalent to 3.5 million dump trucks emptying soil onto the reef. Farms with 4.9 million cattle are depositing 18 million tons of sediment a year and the sugar cane farms cause another 1.3 million tons. This leaves the water thick and brown along many parts of the coast line. Reefs and seagrass need sunlight to survive.

Effects

Pollution from farmlands near the coast is destroying the biodiversity of the Great Barrier Reef. For example, there has been a major increase in the population of the crown-of-thorns starfish. These starfish eat coral across the Reef. There is evidence that this is due to water pollution rather than over-fishing or natural causes.

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Human pollution is a major problem for the Great Barrier Reef and its survival in today’s difficult environmental conditions. If something is not done to halt pollution, the Great Barrier Reef and its 400 species of coral, 5,000 species of molluscs, 1,500 species of fish, 200 species of birds, 30 species of whales, dolphins and porpoises and other living creatures that make up its amazing biodiversity are under serious threat of destruction and extinction.

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