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U.S. slows flow of red soil runoff on Okinawa

Scientist: Bases cut environmental hazard in half over four years

CAMP HANSEN, Okinawa — Four years after coming to Okinawa to combat one of its most visible environmental problems, Larry Soenen still is seeing red.

Red soil, that is. With each rain shower, the light, muddy soil runs downhill to the island’s once-pristine shores, smothering coral and endangering fragile marine life.

The red soil is a fine clay “like talcum powder,” said Soenen, a U.S. Forest Service soil scientist. “It stays suspended in water because it’s so light, not settling until it’s out to sea.”

But there’s far less of it these days, Soenen says. When he came to Okinawa in 2002, the U.S. military was thought responsible for 12 percent of the red soil running to the sea and killing the island’s coral reefs. Now the bases are thought responsible for just 5 to 6 percent.

“I’d like to believe my efforts have reduced the amount of red soil runoff from Marine bases on Okinawa by half, but I think our efforts are only part of the story,” Soenen said recently in his office on Camp Hansen. “I think the decrease is also down because we now have a better handle on where the problems really are.”

Robert F. Bolland, a marine biology professor for the University of Maryland on Okinawa, said the red soil sediment, plus a gradual warming of waters around Okinawa, are killing the coral reefs.

“Runoff … can easily be seen after every rainfall,” he said. “It smothers the coral. … It’s a result of extensive deforestation for dams, the leveling of vast tracts of land for pineapple and sugar cane fields and construction.

“And all this is speeded up,” he said, “ by the widespread practice in Japan of straightening rivers and lining them with cement.”

Japan built 23 erosion dams since 1978 in northern Okinawa. But the fine red clay particles still managed to reach the ocean.

“I still get a bit upset when I drive down the road and it’s raining real hard and see a lot of red soil coming down the road,” Soenen said. “But at least we know that with the preventative measures we’ve taken on the base lands we’re making a difference.”

Soenen said the Marine Corps spends about $1.5 million annually on the red soil erosion problem, funding some 30 different projects a year.

He said that his approach is to be “systematically preventative.”

“We follow the problem from the ocean to the source and then do something about it — whether it’s with hydroseeding, building settling ponds or rebuilding roads,” he said. “There’s still room for improvement, but we’ve made some pretty significant progress.”

Soenen works mostly in the 17,000-acre Central Training Area, which includes Camp Hansen, and in the 19,000 acres of the Jungle Warfare Training Center north of Camp Schwab.

Several measures have been taken to control erosion on the base land, Soenen said. Roads were rebuilt and hard-hit areas were hydroseeded from the air with a soupy mix of straw, grass seeds and fertilizer.

“We work closely with the University of the Ryukyus and the Okinawa Prefecture Red Soil Institute,” Soenen said.

He said he also taught local farmers who had small plots on base property to till the soil so that water — and the red soil particles suspended in the water — do not drain downhill.


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