22. Material ﬂow accounts: the USA and the world Donald G. Rogich and Grecia R. Matos Movements and transformations, material ﬂows, in the environment are continuous. These can be driven by solar energy and geologic processes, or by living organisms which are part of the natural environment. They can also be the result of human activity. All movements and transformations cause change, and these changes may or may not be compatible with sustaining the environmental conditions that exist. Where changes in one part of an ecosystem are useful to, or reversed by, another component of the same system, the system will remain in balance because the cycle of change is closed. With the exception of energy from the sun, natural systems have closed cycles, things that die and decay, the outputs from one part of the system, produce the nutrients for other living things, which in turn provide the basis for new growth. In contrast, the majority of the outputs from industrial activities have no utility to any other part of the environment, they are wastes, and the cycle of change is open: ‘the industrial system is an open one in which nutrients are transformed into “wastes”, but not signiﬁcantly recycled. The industrial system, as it exists today, is therefore ipso facto unsustainable’ (Ayres and Ayres 1998). When humans lived as hunter-gatherers they were part of the closed natural system. With the rise of agriculture and the creation of concentrated settlements (cities), they began to live in more open...
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