Impact of runoff

Increased runoff of sediment, nutrients and chemicals from the land is the greatest immediate challenge to the state of water quality in the GBR, and the coastal marine ecosystems that fringe the northern half of Australia.

Well documented by research carried out over almost 30 years, the increased sediment and nutrient loads now carried by runoff have multiple impacts which range from smothering inshore corals under layers of silt, cutting the light which is essential for the growth of corals and seagrass and favouring the growth of reef algae which can displace corals.

AIMS is developing bioindicators that can detect sub-lethal stress in organisms that is due to reduced water quality.

Added to this is a slow trickle of toxic chemicals from agricultural, industrial and domestic activity which can weaken the health and resilience of corals and other organisms, making them more susceptible to disease outbreaks or climate impacts.

AIMS scientists estimate that average yearly inputs of nitrogen from the land have nearly doubled from 23,000 to 43,000 tonnes over the last past 150 years, while phosphorus inputs have tripled from 2,400 tonnes to 7,100 tonnes. In wet years, these inputs can be many times higher. (For more information, go to Catchments and Corals by Miles Furnas.)

AIMS scientists consider that most of this material is eventually flushed out of the GBR lagoon, transferred to the atmosphere or buried in coastal sediments, but net levels in reef waters may be increasing slowly. The nutrient cycles which hold the key to the health of the reef remain a “black box” about which there are many unanswered questions. If the Reef is to survive the threats of runoff and climate change, .to be there for future generations to enjoy, improved understanding of the sources and fates of nutrients is required.

The Great Barrier Reef lagoon is so large and complex that processes within it that control the fate of nutrients – how long they remain there, what lifeforms exploit them and where they go – is only partly understood. One of AIMS’ most vital missions is to understand and interpret the nutrient cycle in the Reef and in Australia’s tropical northern waters.

The scientific insights and data gathered by AIMS researchers are critical inputs to Australia’s Reef Water Quality Protection Plan, acknowledged as setting a world-best standard for minimizing minimising human water quality impacts in reef waters.

Related links:
Floods muddy waters of the Great Barrier Reef

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March 6, 2008