tailieunhanh - STREAM ECOLOGY & SELF PURIFICATION: An Introduction - Chapter 6

Hành tinh của chúng tôi IS bao phủ trong nước, và chưa trẻ em từ dưới năm tuổi sẽ chết trong năm nay từ Thiếu nước an toàn. Sự trớ trêu Sami sẽ xem 800 triệu người có nguy cơ hạn hán. . . . Hai-Thirds tiếp cận nghèo trên thế giới nông thôn để có Không có nước uống an toàn, và trong khi hàng triệu người vô gia cư được thực hiện từ lũ lụt, Hàng trăm triệu là đối phó với | CHAPTER 6 Stream Water Our planet is shrouded in water and yet 8 million children under the age of five will die this year from lack of safe water. The same irony will see 800 million people at riskfrom drought. .Two-thirds of the world s rural poor have no access to safe drinking water and while millions are made homeless from floods hundreds of millions are coping with WHERE IS EARTH S WATER LOCATED WATER continually moves around and above the earth as water vapor liquid water and ice. Moreover water is continually changing its form. The earth is almost a closed system like a terrarium. That means that the earth as a whole neither gains nor loses much matter including water. The water cycle see Section continually recycles water all around the globe which means that the water we drink today was once used by our predecessors in near time and very ancient Water covers three-quarters of the earth s surface. Most of this water is saltwater about 97 of the earth s water in the oceans and less than 3 is freshwater. Of the latter 77 is frozen in polar ice caps and glaciers 22 is groundwater and the remaining small fraction is in lakes rivers streams plants and animals. From Figure it is apparent that we generally only make use of a tiny portion of the available water supplies. The right-side pie shows that the vast majority of the freshwater available for our uses is stored in the ground. Look at the data provided in Table . Surface-water sources such as streams and rivers only constitute about 300 cubic miles about 1 10 000th of one percent of the world s total water supply of about 326 million cubic miles of water yet streams and rivers are the source of most of the water used. 86W to Water Shortage New York United Nations Environment Program UNEP pp. 1-5 undated. i7Wkere is Earth s Water Located USGS Water Resources http edu pp. 1-2 February 2000. 65 Copyright 2001 by Technomic Publishing Company