What defines stream structure by gradient?

Stream structure by gradient is best defined by the arrangement of features such as cascades and pools. Understanding the gradient of a stream involves looking at how the stream's elevation changes over distance, which affects its flow and the physical structures within it. Cascades and pools are specific features that are created by variations in gradient.

In high-gradient streams, water flows rapidly, creating turbulence and features such as cascades where water drops over rocks, while in low-gradient streams, the water flow is slower, and deeper pools can form. These features play a crucial role in the stream's ecology, determining the habitats available for various species and influencing sediment transport processes. Therefore, the arrangement of these features directly indicates how the gradient impacts the stream's character and ecological functions.

Conversely, the other options may provide some context about the stream's environment but do not define stream structure by gradient. For instance, the color of the water, types of vegetation, and sediment presence, while relevant to stream health and conditions, do not directly relate to the physical gradient-related features that characterize how the stream flows and behaves.