Biological Communities of Rivers and Streams

The interacting communities of microbes, plants, and animals are highly variable across space and dynamic through time. Layers of slime on stones, wood, sand grains, and other surfaces comprise rich communities of bacteria, fungi, diatoms, and algae (aufwuchs). Generally, high-gradient streams of the mountains support less plant community diversity than low-gradient streams, lakes, and reservoirs. Shade and high current velocities may limit this flora. In contrast, Appalachian streams contain a diverse fauna of invertebrates, salamanders, and fish. Animal communities vary according to elevation and stream size. The variations are related to changes in temperature, stream chemistry, flow, and local geomorphology (Scott 2001).