What is meant by the term substrate in a river system?

The term substrate in a river system refers specifically to the material on the riverbed. This includes various types of sediment and geological formations such as gravel, sand, silt, and rocks that create the foundation upon which aquatic organisms live and interact. The substrate plays a crucial role in the river ecosystem, influencing water flow, habitat availability, and the types of organisms that can thrive in that environment.

In contrast, the water that flows through the river is not considered the substrate, as it is the medium rather than the base material. Vegetation surrounding the river contributes to the overall ecosystem but is not part of the riverbed itself. Lastly, sediment suspended in the water may affect water quality and clarity, but it does not define the static, solid material that constitutes the riverbed substrate.