Life of a River - Biology
River Continuum Concept (pg 1 of 7)

As we have seen in earlier sections, some stream classification systems have recognized that plant and animal communities gradually change from headwaters to lower stretches of streams. The River Continuum Concept describes the evolving patterns and interactions of energy inputs, physical environment, and biological communities as one moves from the source of a stream toward its mouth (see River Continuum Concept). Generally, as one moves downstream, the physical environment and the plant and animal communities that live there increase in complexity.