Acid rain and its effect on wildlife
All rainfall has a natural acidity, but pollution increases it more than 1,000 times. The term acid rain can be misleading because acid can also be transported by snow, hail, fog, gas, mist, clouds, and even dust.
The cause of acid rain
Millions of years ago, vast forests spread across the earth. When the huge trees died, they decomposed and gradu-ally became coal and oil.
These fossil fuels are now burned in enormous quantities in order to generate electricity, and release vast amounts of pollutants into the air.
What is acid rain?
Gasoline-powered vehicles and coal- and oil-burning fur-naces release sulfur dioxide, nitrogen oxide, and hydrocar-bons into the air. These conta-minants are known as primary pollutants. Sunlight reacts with these pollutants to form ozone, which, in turn, reacts with sulfur and nitrogen oxide to produce sulfuric acid and nitric acid.
These sulfuric and nitric acids are stored in the droplets of water that make up clouds. In this form, the acids are carried great distances by the wind, and fall as acid rain.
Drying forests
Millions of acres of forests have suffered from the effects of acid rain. Coniferous trees (cone-bearing evergreens) seem to be the hardest hit. Sulfur dioxide kills many trees by depleting the nutrients in the soil. Even slight damage to trees can easily kill them because it reduces their resistance to frost, fungi, and deadly pests.
Studies conducted in the United States indicate that even in forests that show no external signs of acid rain damage, pollution is limiting their growth.
Poisined wildlife
Huge quantities of fish have died in Norway, Sweden, Scotland, Canada, and the eastern United States. Most have been killed by aluminum released into the water by acid rainfall. This, in turn, has affected fish-eating birds, such as the osprey, black- and red-throated divers, common tern, and goosander. These birds, along with the insect larvae on which they feed, are now absent from many streams in which they were once common.
Aluminum also causes songbirds like the blue-throat, reed bunting, and willow warbler to lay eggs with thin shells, reducing their breeding success. Dead eggs and young found in surface water indicate that many aquatic vertebrates, including several species of frog and toad, are dying as well.
The global facts
The term "acid rain" was first coined in Britain to describe conditions in Manchester 100 years ago. Today, Britain releases almost as much sul-fur dioxide into the air as does all of western Europe combined. Forests and watercourses in Britain have been adversely affected by acid rain.
The number of countries that are suffering from the effects of acid rain continues to grow. Sweden's lakes have acidified, and 4,000 of them have completely lost their fish stocks. In Norway, an estimated 60 percent of fish stocks have been lost because of acidified lakes. In Canada, an estimated 48,000 lakes are currently threatened.
In the United States, acid rain poses a severe threat to both fish and waterfowl, especially on the East Coast.
What is being done?
Acid rain and its effects have become an internationally important political issue. As a result, the following actions have been taken:
In the United States, high-er pollution standards require that all new cars are equipped with catalytic con-verters that remove 96 per-cent of carbon monoxide and hydrocarbons from the exhaust.
As a short-term solution in Sweden and Germany, lime is spread over lakes and trees to neutralize the acid.
The oil industry has spend millions of dollars adapting refineries to produce unleaded gas. One-fifth of all cars can now run on lead-free gas without modi-fication.
Japan requires that its power plants reduce nitro-gen oxide emissions by as much as 75 percent.
|
