Final answer:
In a mature river, you would primarily see features such as slow-moving water, the formation of oxbows, and the accumulation of more sediment due to the widening of the river channel and the reduced flow speed.
Step-by-step explanation:
You asked about the features you would see in a mature river. As a river matures, the characteristics of the river include a wider channel, slower water flow, and an increase in sediment deposition. The slow-moving water in a mature river is primarily due to the decreased gradient and increased volume as tributaries join together. Over time, more sediment is carried and deposited, particularly along bends and where the river's speed decreases. This can lead to features such as oxbows, which are curved lake-like formations created when a meander from the main stem of a river is cut off.
In summary, you would see features like oxbows, slower moving water, and an increase in sediment. Furthermore, in such environments, the water tends to be warmer and can carry a high load of suspended materials such as silt, leading to murkier water. Additionally, the biological community adapts to the slow-moving waters, with organisms like worms, insects, and predatory vertebrates relying less on vision and more on other senses to find food due to the decreased water clarity.