Coastal land clearing has led to poor water quality in the Great Barrier Reef lagoon and threats to reef animals, according to the first data providing evidence of the damage.

The Water Quality and Ecosystem Health research team at the Australian Institute of Marine Science has collected 20 years of data, which shows the connection between high rates of land clearing and reduced reef water quality in the late 1990s and early 2000s.

“Our analyses show that water quality in the lagoon dropped significantly during the late 1990s and early 2000s, a period that coincided with very high rates of vegetation clearing on land adjacent to rivers,” says research team leader, Britta Schaffelke.

“It also included three major river floods. This is the first direct evidence that catchment activity affects marine water quality,” she says.

According to Britta, reef water quality is critically important for a healthy ecosystem.

“When water quality deteriorates, we see deterioration of important habitats such as coral reefs and seagrass beds, and these are home to many species of reef fish, crustaceans and marine mammals,” she says.

The research shows that seasonal processes, such as strong winds and river floods, drive water quality in the lagoon, particularly turbidity, or cloudiness due to suspended particles. Land use in the catchment also affects the sediment and nutrient content of river floodwater that empties into the lagoon.

Water quality typically declines rapidly over the wet season, as rivers bring in sediment and nutrients, but improves again after floods as sediment settles or is carried out of the lagoon.

Reducing the load carried by coastal rivers would improve the reef’s water clarity, says Britta.

Photo: Land clearing and acidification threaten the Great Barrier Reef.

Australian Institute of Marine Science, Britta Schaffelke, Tel: +61 7 4753 4382, b.schaffelke@aims.gov.au, www.aims.gov.au/docs/research/water-quality/position-paper.html