LIVERMORE, Calif. - The question of whether European settlement in Australia has affected the Great Barrier Reef may finally have been answered.
The answer is "yes," according to a team of scientists, writing in this week's science journal Nature.
By studying the geochemistry of coral in the Great Barrier Reef, the scientists, including Stewart Fallon of the Center for Accelerator Mass Spectrometry, at Lawrence Livermore National Laboratory, found evidence that sediment from runoffs has increased sharply in the 150 years since the first Europeans settled along the Australian coast.
The findings were published in the Feb. 13, 2003 issue of Nature.
The article's authors conclude that land-use practices, such as cleaning and overstocking, have led to a major degradation of the semi-arid region, resulting in substantially increased sediment loads entering the inner Great Barrier Reef.
However, they reached no conclusions regarding the resulting impact on the offshore marine environment.
Using a new approach to study the coral, the researchers measured the barium content within the coral skeleton, using a relatively new technique called "laser ablation inductively coupled plasma mass spectrometry." They analyzed a 5.3-meter core from the Havannah Porites coral dating back to approximately 1750, as well as shorter cores collected five years ago for Havannah and the nearby Pandora reef.
The corals are affected by episodic discharges of freshwater flood plumes from the Burdekin River, the largest single contributor of suspended sediment to the inner Great Barrier Reef lagoon. Although the buoyant, low-salinity flood plumes generally flow more northward along the Great Barrier Reef coastline, they occasionally reach the mid-shelf region, and thus directly impact the more 'pristine' regions.
Barium deposits in the coral samples can provide high fidelity records of suspended sediment loads entering the reef. According to the researchers:
Barium is desorbed from fine grained suspended particles (clays) in the low salinity region (0-5ppt) of the estuarine mixing zone. Thereafter barium behaves as an essentially conservatively dissolved tracer, being advected with the flood plume and partitioned into the coral carbonate skeleton in proportion to the ambient seawater concentration.
The Havannah coral shows a significant increase in barium beginning around 1870, about two decades after the arrival in northern Queensland of European settlers, who began clearing land for their sheep and cattle. The researchers used historical weather records to disregard spikes in the barium/calcium content of the coral during drought-breaking floods, which produced increased suspended sediment loads.
According to the barium records in the coral, the Burdekin River shows a five to tenfold increase in suspended sediment load following European settlement.
The Nature report concludes with a warning that reducing sediment discharges must become a high priority, if coral reefs are to survive the lethal combination of direct human impacts and rapid climate change.
Stewart Fallon is a principle scientist for the Center for Accelerator Mass Spectrometry at Lawrence Livermore National Laboratory.
Founded in 1952, Lawrence Livermore National Laboratory is a national security laboratory, with a mission to ensure national security and apply science and technology to the important issues of our time. Lawrence Livermore National Laboratory is managed by the University of California for the U.S. Department of Energy's National Nuclear Security Administration.
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