Question

Which of the following statements about dissolved oxygen in lake ecosystems is correct?

1. Dissolved oxygen is generally higher in stagnant lake waters compared to flowing lotic systems.
2. The oxygen content in lakes typically decreases with depth.
3. Only the surface layer of a lake interacts with atmospheric oxygen.
4. Decomposition of organic matter does not affect dissolved oxygen levels.

• A. i, iv
• B. All
• C. ii, iii
• D. i, iii

Answer 1

Answer:

C. ii, iii

• The environment of static waters of lakes and ponds sharply contrasts with those of lotic ecosystems.

• Light penetration in lakes is usually up to a certain depth which is affected by turbidity.

• Temperature and dissolved oxygen also vary with depth.

• Dissolved oxygen in stagnant water is generally less compared to lotic systems because only a relatively small surface of the water body is indirect contact with air.

• Decomposition of organic matter usually takes place at the bottom of the lake.

• The oxygen content usually decreases with depth.

• The gradations of temperature, sunlight and oxygen are directly responsible for vertical zonation or stratification. occurring in lakes.

• They are also responsible indirectly for horizontal zonations of lakes as they profoundly influence the distribution of lake organisms which contribute to the characteristic horizontal zonations.