VOA慢速英語：研究人員表示氣候變暖會使危險(xiǎn)的藻類迅速傳播

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In early June, people in the area of Salem, the capital city of the American state of Oregon, received a warning on their cellphones.

City officials sent a message that read: “Civil emergency. Prepare for action.”

Within half an hour, the officials sent out a second message. They explained they were not warning of possible violence. The emergency was dangerous bacteria in the city’s drinking water.

Microscopic plant-life called algae had suddenly appeared and spread in the local water supply. These so-called algae blooms poison water.

Such events are increasing in lakes across the United States. Researchers say the rise in algae blooms is connected to the planet’s rising temperature, or global warming.

The researchers say this raises more questions about the effects global warming might have on human health.

Wayne Carmichael is an algae expert formerly with Wright State University in Dayton, Ohio. He worked with the World Health Organization to set the first guidelines on safe algae levels for humans.

Carmichael says as bodies of water around the world warm, there are going to be more incidents of sudden algae growth.

“That’s just logical, and it’s being borne out,” he told the Associated Press.

The kind of algae that grow in the sudden, quick way that happened in Salem, Oregon are technically called cyanobacteria, an ancient group. The bacteria are present in almost all water. But they grow best in warm, still bodies like lakes and ponds.

Cyanobacteria have long been connected to animal deaths. But, experts only partly understand the poisonous effect they have on humans.

High levels can cause liver damage and attack a person’s nervous system.

In the largest incidents, hundreds have been sickened by the algae in reservoirs and lakes. Officials in some areas now close water bodies used for recreation and post warnings during algae blooms.

But less is known about exposure to lower levels of algae, especially over the long term.

Small studies have linked the bacteria to liver cancer and others have suggested possible links to neurodegenerative diseases. But, Carmichael says, proving those links would require larger studies.

Steven Chapra is an environmental engineering professor at Tufts University in Medford, Massachusetts. He led one of the most complete studies of the relationship between global warming and the growth of the algae. Scientists from the Massachusetts Institute of Technology and the U.S. Environmental Protection Agency took part. The research was published in 2017.

It found that higher summer temperatures and more periods of extreme heat help the growth of algae. Higher numbers of rain shortages lower lake levels in the summer, warming them faster and keeping them warm longer.

The scientists also blamed more intense rainstorms brought on by climate change. They said these rains wash nutrients into lakes and reservoirs. Agricultural runoff is especially helpful to algae as famers use chemicals created to aid plant growth, Chapra says.

In 2016, an algae bloom happened in a Utah lake used for recreational activities. The bacteria sickened more than 100 people. Aislynn Tolman-Hill is a Utah County Health Department representative. She says when the story received national attention, other states contacted Utah officials about the problem.

“We started getting calls from other health departments all over the country saying, ‘Hey, we’re dealing with an algae bloom in a lake that has never ever had one before,’” said Tolman-Hill.

Officials only recently started carefully documenting the algae growths. But Ben Holcomb says the growths seem to be becoming more intense. He is a biologist for Utah’s environmental agency. And he argues that no state will go unaffected.

“They’re starting earlier, they’re lasting longer, and their peaks seem to be getting bigger,” Holcomb said.

It can happen in lakes of any size. In 2014, Lake Erie experienced an algae bloom. The U.S. lake has a surface area of more than 25,500 square kilometers. The bloom forced officials in Toledo, Ohio, to warn people against drinking from the city water supply. The restriction continued for over two days and affected more than 400,000 people.

Similar incidents have been recorded in recent years in New York, Florida and California. In Oregon, officials canceled Salem’s drinking water warning after several days and then renewed in at a later date.

Officials noted that neither state nor federal laws require testing for algae. Researchers say that needs to change.

Steven Chapra of Tufts suggests that all these incidents are the early warning signs of a much bigger problem.

“It’s going to get worse, and it’s going to get worse in a big way,” he said.

I’m Susan Shand. And I’m Pete Musto.

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Words in This Story

logical – adj. agreeing with the rules of the proper or reasonable way of thinking about or understanding something

borne out – p.v. shown the correctness of something or someone

pond(s) – n. an area of water that is surrounded by land and that is smaller than a lake

reservoir(s) – n. a usually artificial lake that is used to store a large supply of water for use in people's homes and in businesses

recreation – n. activities done for enjoyment

exposure – n. the fact or condition of being affected by something or experiencing something

neurodegenerative – adj. resulting in or characterized by the weakening of the nervous system

nutrient(s) – n. a substance that plants, animals, and people need to live and grow

runoff – n. water from rain or snow that flows over the surface of the ground into streams

peak(s) – n. the highest level or degree of excellence, quantity or activity