The River Continuum

In 1980, ecologists published the River Continuum Concept, showing that river ecosystems change predictably from source to mouth. Headwater streams are shaded by trees, so their food web depends on leaf litter falling in from the surrounding forest canopy.

As the river widens, algae and aquatic plants become the primary energy source. In the lower reaches, the river grows too deep for light, running on fine organic particles from upstream. Each section supports different species adapted to its conditions.