Acid Rains

Other very dangerous pollutants are sulphur and nitrogen oxides. These gases are released by factories and power plants when fossil fuels are burned and by cars. These oxides reach high into the atmosphere and mix with water and other chemicals to form rain that can be as acid as vinegar. Acid rains are responsible for the decline of many forests. Tiny droplets of acid attack plant leaves, disrupting the production of chlorophyll It also weakens the tree by altering the chemistry of the soil that surrounds its roots. Acid falls down to earth as rain and snow Black snow, as acid as vinegar, fell in Scotland in 1984.

Acid rain affects everything it falls on. Rivers, lakes and for­ests are at risk throughout Europe and North America. In Sweden more than 18000 lakes have become acidic, 4000 of them very se­riously indeed. This kills fish and drives out fish-eating wildlife.

Forests are particularly badly affected by acid rain and in many places previously green, luxuriant trees show bare branches at the top, stripped of foliage. In West Germany 50 per cent of trees are affected and, unless some curb is placed on pollution, the figure is certain to rise. In Austria, if nothing is done, scientists and environmentalists have predicted that there will be no trees left by the end of the century.

There is a possibility that damage to ecosystems from acid deposition may be more fundamental and long-lasting than was first believed. Scientists now report that acid rain leaches as much as 50 per cent of the calcium and magnesium from the forest soils. These minerals neutralise acids and are essential for plant growth. If soil chemistry is changed in this way, it may take many decades for all linked ecosystems to recover. Besides this, acid rain re­leases heavy metals and other toxic substances, providing a persis­tent source of toxicity to surrounding vegetation and aquatic life.

Comprehension check

I. Answer the following questions:

1. Is air pollution a long-life problem?

2. Why is clean air so important for a man?

3. What are the sources of air pollution?

4. What is understood by particulate pollution?

5. What are consequences of this kind of pollution?

6. What are the dangerous effects of acid rains?

7. In what way do the acid rains damage forests?

II. Match the words and the definitions given below:

Foliage	An influence which helps to control or limit some­thing
Curb	To make something less pure, less pleasant and desir­able
Shroud	A fine powder produced by flowers which is carried by the wind or by insects
Taint	Something like mist that hides or covers the object
Pollen	The leaves of a plant

III. Use the expressions in the sentences of your own:

To assume social significance, incalculable number, to be strongly linked to, the body's natural clearance mechanisms, major pollution events.

IV. Make up a summary of 10 sentences, the content of which cov­ers the plot of the text.

ECOLOGICAL STORY

Most people seem to be under the impression that a frog is just a frog the world over. Nothing could be further from the truth, for with frogs and their near relatives, toads, you find that they vary from country to country, display­ing a bewildering variety of shapes, sizes, colours, and habitats where they are to be found. The so-called flying frog of Asia, a large, tree-dwelling species, has developed very elongated fingers and toes. The skin between them is like a web and as this frog leaps from tree to tree, it spreads its fingers and toes wide so that it can glide like an aeroplane. The goliaph frogs of West Africa measure two feet in length and can eat a rat. while a pygmy species of South America is about as big as your finger­nail. In coloration, frogs are perhaps the only species that could seriously claim to rival birds, for there are frogs coloured red, green, gold and blue. When it comes to rearing their young, frogs produce some startling results. The midwife toad of Europe hands her eggs over to the male who, in order to protect them, winds them around his hind legs and carries them around until they hatch. A species of tree frog glues two leaves to­gether, and when water collects in the cup thus formed, the frog lays its eggs in this home-made pond.

Guiana has more than her fair share of frogs that possess in­genious methods of safeguarding their eggs and young, and the creek lands proved to be the best place for catching them. Bob was amusing himself by dragging one of these narrow, smelly little streams with a long-handled net, while 1 prowled hopefully around some tree roots. With the aid of a torch I succeeded in capturing three largatree frogs with huge eyes.

Bob continued doggedly with his net. I saw him haul his net out, as usual full of a pile of dirty leaves, and tip them out onto the bank. I le was just going to plunge'his net back into the water again when he stopped and peered down at the pile of leaves he had just pulled up.

Then he dropped the net and let out a delighted shout. "I've got one!' he yelled.

'What have you got?'

'A pipa toad'.

'Nonsense', I said.

'Come and have a look, then', said Bob, bursting with pride.

He opened his hand for my inspection and revealed a strange, ugly creature. It looked, to be quite frank, like a brown toad that had been run over by a heavy truck, its short, rather thin arms and legs stuck out stiffly, one at each corner of its squarish body, and it looked quite dead. It was, as Bob said, a large male pipa toad, per­haps one of the most curious amphibians in the world. Ever since we arrived in Guiana we had been trying to get specimens of this creature. Now, after Bob's success, we searched every inch of that small stream, producing a mountain of rotting leaves which we picked over as carefully as a couple of monkeys searching each other's fur. An hour later we had captured four more of these weird toads. Moreover one of them was a female with eggs, a prize that was worth anything in our eyes, for the breeding habits of the pipa toad are the most extraordinary thing about it.

At the beginning of the breeding season, the skin on the fe­male's back becomes soft and spongy. When her eggs are laid they are deposited with the help of the male along her back, where they stick like glue. After they have been fertilized they sink into her skin, forming cup-like depressions. The soft tops of the eggs then harden, forming little pockets on her back. In these pockets her young spend the whole of their early life until they have fully de­veloped when they push the little lid on the top of the pocket and make their way out into the dangerous world.

The female we captured could only just have had her eggs in­stalled, for their lids were still soft. When her young were at last young enough to leave their mother's back they chose a moment when I was looking after their mother and the other animals 1 had collected on board a ship, in the middle of the Atlantic Ocean.