Galina Churkina
In this chapter, urban and natural ecosystems are compared and contrasted. The chapter starts with definitions of both ecosystems and presents the case of the urban ecosystem as a striking example of environmental engineering typical for various living organisms. It proceeds by describing differences in overground and underground structures of natural and urban ecosystems. Energy, water, and nutrient inputs required for the functioning of both ecosystems are discussed thereafter. An overview of gaseous, liquid, and solid outputs from urban and natural ecosystems concludes this chapter. The consequences of these differences for the environment and humans are discussed in Chapters 4 , 5 , and 6 in detail.