ABSTRACT
W a t e r is a necessity for all living organisms on the earth. The abun dance and availability of water resources (a function of rainfall, humid ity, and evaporation rate) determines the kinds of communities that develop. Water is also an important limiting factor for economic develop ment. Today, more and more water resources are required for industrial and agricultural production and in daily life. At the same time, water pollution is becoming increasingly serious due to human activities (Zhou, 1994).
