4 . When John Todd was a child, he loved to explore the woods around his house, observing how nature solved problems. A dirty stream, for example, often became clear after flowing through plants and along rocks where tiny creatures lived. When he got older, John started to wonder if this process could be used to clean up the messes people were making.

After studying agriculture, medicine, and fisheries in college, John went back to observing nature and asking questions. Why can certain plants trap harmful bacteria (细菌)? Which kinds of fish can eat cancer-causing chemicals? With the right combination of animals and plants, he figured, maybe he could clean up waste the way nature did. He decided to build what he would later call an eco-machine.

The task John set for himself was to remove harmful substances from some sludge (污泥). First he constructed a series of clear fiberglass tanks connected to each other. Then he went around to local ponds and streams and brought back some plants and animals. He placed them in the tanks and waited. Little by little, these different kinds of life got used to one another and formed their own ecosystem. After a few weeks, John added the sludge.

He was amazed at the results. The plants and animals in the eco-machine took the sludge as food and began to eat it! Within weeks, it had all been digested, and all that was left was pure water.

Over the years, John has taken on many big jobs. He developed a greenhouse — like facility that treated sewage (污水) from 1,600 homes in South Burlington. He also designed an eco-machine to clean canal water in Fuzhou, a city in southeast China.

“Ecological design” is the name John gives to what he does. “Life on Earth is kind of a box of spare parts for the inventor,” he says. “You put organisms in new relationships and observe what’s happening. Then you let these new systems develop their own ways to self-repair.”

6 . Some scientists say that animals in the oceans are increasingly threatened by noise pollution caused by human beings.

The noise that affects sea creatures comes from a number of human activities. It is caused mainly by industrial underwater explosions, ocean drilling,and ship engines. Such noises are added to natural sounds. These sounds include the breaking of ice fields, underwater earthquakes, and sounds made by animals themselves.

Decibels(分贝) measured in water are different from those measured on land. A noise of one hundred and twenty decibels on land causes pain to human ears. In water, a decibel level of one hundred and ninety-five would have the same effect.

Some scientists have proposed setting a noise limit of one hundred and twenty decibels in oceans. They have observed that noises at that level can frighten and confuse whales.

A team of American and Canadian scientists discovered that louder noises can seriously injure some animals. The research team found that powerful underwater explosions were causing whales in the area to lose their hearing. This seriously affected the whales’ ability to exchange information and find their way. Some of the whales even died. The explosions had caused their ears to bleed and become infected.

Many researchers whose work depends on ocean sounds object to a limit of one hundred and twenty decibels. They say such a limit would mean an end to important industrial and scientific research.

Scientists do not know how much and what kinds of noises are harmful to ocean animals. However, many scientists suspect that noise is a greater danger than they believed. They want to prevent noises from harming creatures in the ocean.