river continuum

The river continuum concept describes how biological communities in rivers change along their length, from source to mouth. This is due to a longitudinal gradation in physical and chemical factors like temperature, dissolved materials, and turbidity.1

Inland aquatic ecosystems, including rivers, generally have three main trophic levels: primary producers (like algae), consumers (animals), and decomposers (bacteria and fungi). Energy flows through these levels, while essential elements cycle between biotic and abiotic components.2

In streams, unlike lakes, plankton populations are absent, and much of the energy comes from outside the stream (allochthonous). The processing of elements follows a downstream sequence. Hypotheses like the river continuum concept help explain these differences in lotic communities based on changing ecological factors along the river system.2