Water pollution

Ever since man progressed from a hunting to an agricultural society, with the corresponding development of stable communities, as agricultural methods improved a smaller percentage of the population produced all food needed, larger communities and diverse secondary industries developed and grew into the present modern society. Concurrent with this growth, however, was the increasing percentage of waste materials and the problems of disposal. When the total volume of waste from a community was relatively small, the easiest method of disposal was to “throw it away”, usually into the nearest receptacle. Since man cannot exist without water, community development and city growth centered in areas where the water supplies were adequate and continuous. Initially this meant development in river valleys, and thus the nearest receptacle for wastes was the river.

The term “pollution” has been variously defined by many people, but if it may be described here as “the detrimental effects on a localized ecological structure by the addition of the waste products of a society “, then it is apparent that the first noticeable pollution problems should have involved the supply of drinking water.

It is in this particular area that the question of pollution takes on a new meaning. Is a body of water polluted when it directly affects man, or should it be classified as polluted when the ecological structure is first upset? The hydrosphere is a dynamic system containing physiochemical and biological equilibria, and there is no doubt that a normally active waterway has a large capacity to assimilate wastes. However, in many areas this capacity is now being reached or exceeded so that many waterways are becoming increasingly contaminated. Before this contamination becomes readily noticeable however, equilibria are changed and the ecological structure may be seriously affected. Some examples of water systems where the effects of pollution have become or are becoming increasingly apparent are the Adriatic, Baltic and Mediterranean seas; the Thames, Rhine and Seine rivers; and the Great Lakes in America and Canada. But dynamic systems have a remarkable capacity for regeneration, and with careful planning even the most seriously polluted waterways may be brought back into full use. An example of river regeneration on a large scale is the successful attempt to restore the Thames estuary.

I. Закончите следующие предложения соответствующими фразами из текста:

1. As agricultural methods improved, ………..

2. Concurrent with this growth, however, was the increasing percentage of …………...

3. Since man cannot exist without water, ………….

4.It is in this particular area that the question of ……..

5. The hydrosphere is a dynamic system containing ……...

6. But dynamic systems have a remarkable capacity for ………..