水草的水质净化作用.docVIP

水草的水质净化作用 X. WATER PURIFICATION This is probably the most important chapter in this handbook. The subject was only briefly mentioned in the first edition. Several papers did refer to the capacity of water plants to extract plant nutrients from the water in which they grew. But the interest in this rather obvious fact was related to the ability which this property conferred to farmers in South-East Asia to establish a nutrient cycle. This double cycle, plants-pigs-humans-fish-humans-plants, enabled a limited set of nutrients to be continually reutilized in ponds in a system powered by the sun. Other papers, which described the fertilizing potential of water plants, recognized that the nutrient content of water plants had been salvaged from water and might otherwise have been lost to the sea. The reason which has prompted the spate of papers within the last ten years on the nutrient extraction possibilities of aquatic plants is the increasing awareness of the problems of water pollution - both fresh and salt water - as a consequence of population growth and industrial development, and the disposal of human, animal and industrial wastes into inland waters and into the sea. In the past industrial wastes scarcely existed and human and animal wastes were carefully returned to the land to conserve the fertility which it was recognized that they contained. Now it is often cheaper to buy fresh supplies of fertilizer in concentrated, easily applied forms and flush away wastes into sewers or streams. Many examples of the devastating consequences of this waste on formerly clean and useful rivers and lakes have aroused public and scientific awareness of the need not only to arrest this practice but to try and reverse it by extracting the pollutants. The remarkable ability of aquatic plants, particularly the water hyacinth, to extract compounds and elements from water efficiently has become well recognized. It is particularly interesting that among the scientists who have d