- The Washington Times - Wednesday, February 12, 2003

Skeletal analyses of the Great Barrier Reef off northeastern Australia show a five- to 10-fold surge in river sediment sweeping over the world's largest coral system — a fragile refuge to thousands of species and a sturdy contributor to the local treasury — since European settlers arrived on the continent more than 200 years ago.

The results, compiled from readings of the reef record from about 1750 to 1998, raise concerns about the ecological and economic impact of the potentially damaging dirt, scientists told United Press International.

Investigators from the Australian National University in Canberra and the Australian Institute of Marine Science in Townsville uncovered evidence of the dramatic rise in river runoff since the 1860s, when the newcomers introduced grazing, agriculture, mining and land clearing to the pristine area.

The clues came from measures of the metallic element barium, a signature of sediment, in a 250-year-old coral. Spit into the ocean as freshwater sweeps into the sea, barium is deposited in the corals' carbonate skeleton that is as telling in its precise layering as the age-revealing tree rings of an ancient redwood.

Malcolm McCulloch of the Research School of Earth Sciences at ANU and his colleagues found only an occasional dollop of dirt from river floods reached the inner reef area in the early part of the record. But after about 1870 — as the Europeans began to settle and farm the land — they noted a spike in sediment amounts dumped on the coral.

The terrestrial matter, eroded by modern agricultural practices and transported to the oceans in river water, might pose a hazard to reef-building corals by decreasing the availability of light and interfering with feeding, scientists pointed out.

"Sediment is bad news for coral reefs," noted Julia Cole of the Department of Geosciences at the University of Arizona in Tucson, who analyzed the findings. "In Australia, large increases in sedimentation were a byproduct of introducing intensive agricultural practices, and that may also apply to other parts of the world."

The exact impact of the sedimentary influx remains uncertain, primarily because the way in which corals reefs respond to such a change in their environment is a complex and poorly understood process, study co-author Timothy Wyndham of the earth sciences school told UPI.

Nevertheless, the findings feed fears of serious environmental damage to the Great Barrier Reef — a picture-perfect haven for more than 1,500 species of fish, 4,000 types of clams, sea slugs and other mollusks, 215 kinds of birds and 400 varieties of coral and a local gold mine that brings in more than $1 billion from the 2 million tourists who visit each year.

Sensitive to changes in climate and patterns of water movement, the vulnerable reefs keenly feel the effects of global warming, water-heating El Nio, the building of moorings or breakwaters and other accidental and deliberate intrusions. Conservationists have voiced concern any additional nutrients running off land from human habitation might disrupt the delicate balance of the reef system, and the sea and land animals that depend upon it for survival.

Evidence from other parts of the world suggests there is significant cause for concern, Wyndham said. Scientists suspect increased terrestrial runoff is behind the decline in coral reefs around the world, including in southeast Asia and the Caribbean.

"Land-use intensification is widespread so that many reefs close to continents or large islands are likely to have experienced increased delivery of sediment over the past century," Cole stated. "As coastal populations increase, this phenomenon is likely to expand."

If scientists have a way to evaluate and measure the sediments reaching the coral reefs, they will be better able to assess and manage the effects, she said.

"McCulloch and (colleagues) have cleverly developed a history of sedimentation on Australia's Great Barrier Reef by quizzing the corals themselves," Cole said.

Corals keep a meticulous record of their sedimentary exposure. As they build their skeletons from calcium and carbonate, they incorporate trace amounts of other elements.

The scientists pored over the diary etched in the skeleton of Porites coral, a species that grows in large, boulder-like formations, adding an element-laden layer a year.

"By measuring the amount of barium … in the skeleton, (the researchers) have developed an effective proxy record of terrestrial sedimentation on the reef that extends from 1750 to 1985," Cole noted.

The investigators found sediment flow from the Burdekin River catchment has increased by a factor of five to 10 since the European settlement, Wyndham told UPI.

They also discerned the influence of drought on rates of erosion, noting floods that follow a prolonged dry spell carry larger loads of sediment to the reef.

The results provide a yardstick for measuring the much-debated effects of sedimentation, McCulloch said.

"The influence of sediment supply on the water quality in the Great Barrier Reef is a long-standing and controversial issue," Wyndham said. "This study provides a basis for comparing the past and present environment in terms of sediment supply. We believe that our study provides a basis for a more informed decision-making process with regard to the management of the GBR."

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