Where is light penetration in a river or stream likely to be lowest?

• A. At the riverbank with overhanging vegetation
• B. In deep, turbid pools
• C. In shallow, clear riffles
• D. Near the source of a mountain stream

Answer: (B)

Verified step by step guidance

1. Understand the concept of light penetration in aquatic environments: Light penetration in water is influenced by factors such as water depth, turbidity (cloudiness caused by suspended particles), and shading from external sources like vegetation.
2. Analyze the options provided: Each option represents a different part of a river or stream with varying conditions that affect light penetration.
3. Evaluate the impact of depth and turbidity: In deep, turbid pools, the combination of greater depth and suspended particles significantly reduces light penetration compared to shallower or clearer areas.
4. Consider the role of vegetation: At the riverbank with overhanging vegetation, shading from plants can reduce light penetration, but this effect is localized and not as significant as turbidity in deep pools.
5. Compare shallow, clear riffles and mountain stream sources: Shallow, clear riffles and mountain stream sources typically have higher light penetration due to minimal turbidity and reduced depth, making them less likely to have the lowest light penetration compared to deep, turbid pools.