They transport fine materials, or sediment throughout their watersheds. In fast flowing streams, sediment adds erosional force to the water, cutting through valleys and scouring stream bottoms. In slow flowing streams, sediment is deposited, settling out to form sandbars, levees, and fertile flood plains. Like water, sediment is crucial to life. Sediment and organic matter comprise soils , the skin of a watershed and interface between the living and nonliving parts.
Soils have different textures, mineral content and water holding and transmitting properties.
They play a key role in watersheds by determining which plants grow, how much water runs off the land and how susceptible the land is to erosion. Vegetation is another key watershed component. Plant roots slow and absorb runoff, releasing the water slowly to groundwater and streams and back into the atmosphere. Vegetation also plays many other important roles, including providing nutrients and habitat for fish and wildlife. Each watershed, with a distinctive combination of soils and plant communities, supports a diversity of habitats that support a diversity of life.