Question

Regarding the factors influencing zonation in lake ecosystems, which statement is correct?

1. Horizontal zonation in lakes is solely determined by the direct influence of sunlight and temperature.
2. Vertical zonation is a direct result of temperature, sunlight, and oxygen gradients.
3. The distribution of lake organisms does not play a role in horizontal zonation.
4. Dissolved oxygen levels are uniform at all depths in a lake.

• A. All
• B. ii only
• C. ii, iii
• D. None of these

Answer 1

Answer:

B. ii only

• 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.