VOA慢速英語(yǔ):藻類群體的增加污染水道

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The American city of Toledo, Ohio faced a serious problem earlier this month. Four hundred thousand people could not drink from the city’s public water supply. The water comes from Lake Erie. It was polluted with a toxin, or harmful substance, linked to the overgrowth of algae. Too many of these simple organisms can lead to harmful algal blooms, covering a large area.

The water in Toledo is now safe to drink. Yet harmful algal blooms are not going away any time soon, either in the United States or around the world.

The harmful algae entered Toledo’s water intake pipes and turned the water green. People had to depend on bottled water supplies.

“We’re happy to have this.”

“It was stressful at first. Definitely! I have a couple of dogs at home and four children, and I wanted to make sure we had enough water to brush our teeth and be able to drink it.”

Lake Erie supplies water to 11 million people in the north central United States. Algal overload is common in waterways worldwide. It results from chemical fertilizers polluting water supplies and poor waste treatment systems.

Laura Johnson is a researcher with the National Center for Water Quality at Heidelberg University in Tiffin, Ohio. She says overgrowth of algae can reduce oxygen levels in water and kill fish.

“It also becomes a problem when the type of algae that are growing is acyanobacteria that can produce toxins. And when that happens, then we have issues, because then those toxins can be in places like our drinking water, or we can get in contact with it if we’re trying to swim there.”

It can also damage the human nervous system and liver. Climate change is making the problem worse. Changing weather systems produce stronger, more intense winds and storms. These can take minerals and other important nutrients away from the land.

The U.S. National Oceanic and Atmospheric Administration studies Algal blooms from space. Richard Stumpf is an oceanographer.

“So we can use the satellite data to actually find the bloom, (and) estimate the concentration. We can’t tell you if it’s toxic. But we can tell you if it’s there and how much there is.”

This information helps scientists and government officials to take action. Richard Stumpf says the U.S. National Oceanic and Atmospheric Administration is also gathering information on phosphorous, a chemical that fuels the reproduction of algae.

“It’s only the spring phosphorous -- the phosphorus in the spring time -- that creates the bloom in the summer. Knowing that means that you can now create a strategy for how do you modify fertilizing practices, how do you modify cultivating practices so that the phosphorous stays on the fields, which is what the farmers, they don’t want this to go somewhere else, and so it stays there and doesn’t run into the rivers and then into the lake?”

Laura Johnson says the long-term goal must be to keep nutrients on the land.

Activists for clean water want the government to enact stronger controls. They also want to persuade farmers to cut back on fertilizers by paying them. Farmers often resist additional rules and recently faced a reduction in federal assistance.

As the debate continues, one thing is clear. The algal problem is not goingaway any time soon. I’m Jonathan Evans.